Technical Proposal-v8

Technical Proposal

1.Introduction The adaptive control of electromagnetic (EM) properties across the surface of an aerospace structure can greatly enhance its operational capabilities and survivability. The ability to change (reconfigure) boundary conditions can be used to control the radar cross section (RCS) of a given aerospace platform. This particularly applies to so-called ‘scattering centers’. Scattering centers on the surface can occur where there are discontinuities, regions of high curvature, or specialized devices. Typically, the desire is to reduce RCS so as to decrease the detection range. Methods to do this include surface shaping, radar absorbing materials (RAM), and specialized shaping of orifices such as antenna apertures. RAM is a dense material and, thus, introduces serious weight issues when engineering the overall systems capabilities. These methods are particularly effective when the radar source is within a limited range of directions relative to the platform. Biological models serve as inspiration for developing new materials and engineering systems that possess novel properties and functionality. Analogous to the circulatory system, an ERS spatially controls the flow of electrons by adjusting impedance characteristics both locally and globally. In this manner, the radio frequency character of a surface can be manipulated to yield the desired EM response. Some direct comparisons can be made between these two types of systems. Adjusting peripheral blood flow resistance by controlling vessel diameter is analogous to having variable resistors or switches in electrical circuits to spatially control the currents. Local control of circuit properties in a reconfigurable antenna achieves the desired RF characteristics, just as local control in a vascular network enables the efficient and necessary distribution of blood. Two and three dimensional microfluidic networks with pervasive, interconnected channels (1-1000 microns in diameter) are finding widespread application in microfluidic devices , including those used in biotechnology ), sensors , chemical reactors , and fluidic-based computers . In addition, embedded microfluidic networks have been able to emulate many of the key responses of biological vascular systems). Numerous literature studies have investigated the interactions of electrical fields with colloidal dispersions to control electrorheological fluids (Yethiraj and Blaaderen, 2003), separate carbon nanotubes (Krupke et al, 2003), control display devices, and assemble irreversible nanowires (Hermanson at al, 2001). Others have also shown the feasibility of using particle-field and particle-particle interactions induced by electric field for manipulation and assembly of colloidal particles into structures such as conductive microwires and switchable 2-D photonic crystals ). Our previous work included a number of experimental and modeling strategies that are summarized here because of their relevance to the present proposal. Experimental strategies involved directly probing and interpreting nanoparticle interactions, dynamics, and structures in response to varying AC electric fields and confined microfluidic/electrode geometries. Direct measurements involved the use of advanced microscopy techniques (total internal reflection (Wu et al, 2006), video, confocal (Dinsmore at al 2001) to monitor in situ steady-state and transient nanoparticle three dimensional structures (e.g. fluid dispersions, inhomogeneous fluids, percolating nanowires, crystals) with nanometer resolution. Simultaneous impedance

measurements characterized AC electrical properties associated with nanoparticle structures and their dynamic response over a broad range of electric field amplitude (0-10V) and frequency (010GHz) phase space. Models were implemented to capture relevant steady-state and transient nanoparticle structures and electrical property responses on appropriate length, time, and energy scales. Experimental and modeling tasks together revealed the design rules and control parameters involved with using AC electric fields to tune concentrated nanoparticle microstructure within electrode gaps as a new approach to tune device impedance properties. In the absence of any applied fields, the gold colloids are randomly distributed above the glass substrate and electrode surfaces and remain confined within a quasi-2D layer (~100nm) due to gravity and particle-surface electrostatic repulsion. In the presence of AC electric fields, Fig 1 shows a matrix of steady-state microstructures assembled in between and above a single electrode pair gap as a function of AC voltage (0.5-2.5V) and frequency (10Hz-1MHz). All colloidal microstructures in Fig 1 were assembled in a completely reversible fashion as the result of ~100nm electrostatic repulsion (the Debye length is κ-1=30nm) preventing intimate contact and irreversible adhesion between colloids and surfaces via van der Waals and dipolar attraction . This reversibility allows dynamic reconfigurability between all of the steady-state microstructures in Fig 1 by tuning the AC field amplitude and frequency, although the rate of dynamic transition depends on the initial and final configurations (e.g. wires form more quickly from random configuration than empty gap).

Increasing Amplitude

2.5 V

2.0 V

1.5 V

0.5 V 10 Hz

1 kHz

100 kHz

1 MHz

Figure 1: Optical microscopy images of steady-state configurations of 800-nm gold colloids within a 30µm gap between interdigitated coplanar gold film electrodes as a function of applied AC electric filed frequency and voltage. By exploiting the reversible nature of such colloidal based devices, we can demonstrate control, tunability, and scalability of impedance characteristics not easily achieved with solid-state

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materials or microelectromechnical devices. Figure 2 compares the real and imaginary impedances of the random colloidal structure (inset, top) and assembled structure (inset, bottom; wire formation as in structure d in Fig 1). By using the equivalent circuits fit to the measured impedance spectra, we eliminate the extraneous contributions of the measurement circuit and device components including the substrate, electrodes, and electrolyte solution. As a result, we demonstrate a four order of magnitude change in resistance when the gold colloids assemble at 2.5V and 1 MHz as compared to the random case (Bahukudumbi et al, 2007).

Z on /kΩ

Z off /kΩ

20

0

0.5

0.0 100

101

102

103

ω/kHz Figure 2. Measured real (circles) and imaginary (triangles) impedance spectra for (top) no applied field and (bottom) an applied field of 2.5V and 1MHz corresponding to the assembled colloidal configuration shown in the upper right corner (d) of Fig 1. Equivalent circuits used to fit the measured impedance spectra are shown as insets. To summarize, we have demonstrated the ability to reversibly manipulate nanoparticle structures within 2D coplanar microelectrode gaps to produce multi-functional materials and devices with unique electrical properties (see Fig 2). This work has gained a fundamental understanding of how interactions between nanoparticles, patterned electrodes, AC electric fields, and confined microfluidic geometries can be intelligently designed to control reconfigurable surfaces that interact with electromagnetic fields. It has shown how directed assembly of nanoparticle microstructures can be integrated into novel material and device architectures to tune multi-scale electrical, thermal, magnetic, and optical properties. Our vision for this proposed work is to investigate electromagnetically tunable colloidal-based materials (ETCMs) for reconfigurable, multifunctional antennas. Building on our demonstration of order of magnitude impedance change through guided colloidal assembly, we will focus on developing integrated networks capable of manipulating colloidal microstructures and their associated electromagnetic properties for antenna applications.

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2. Proposed Research: 2. 1 Colloidal assembly In this work, our goal is to exploit transport properties at colloidal and microfluidic dimensions to controllably alter permeability, permittivity, and conductivity at the macro level. In this concept, multifunctionality will arise from a combination of structural colloidal components and functional microfluidic components, where the microfluidic system will be used to reversibly control physical properties through fluidic transport and directed colloidal assembly. TAMU investigators have achieved orders of magnitude change in impedance through guided colloidal assembly in a Toyon-led project funded by DARPA. Our focus is to alter the electromagnetic, thermal, and mechanical properties of the system through circulation of colloidal particles within microfluidic networks (i.e. circulatory system) and then locally direct colloidal microstructure and properties via electrical signals (i.e. nervous system). Our approach will involve first investigating microfluidic pressure driven flow within quasi-2D and 3D microfluidic networks, which will provide a foundation to then explore integration of electrical and microfluidic networks to tune local material EM properties through electric field directed colloidal assembly. In the case employing only pressure driven flow, the local concentration of particles will be tuned by pumping particles from local reservoirs to different positions in a quasi-2D microfluidic network as a means to alter the 2D surface configuration of material permeability and permittivity on the length scales of the microfluidic network. With the ability to spatially reconfigure such properties on surfaces, this approach will be used to dynamically adapt the boundary conditions on macroscopic surfaces to interact in a controllable fashion with incoming EM fields. Implementation of such an approach will require proper placement of various colloidal fluids with specific electrical and magnetic properties within a vascular network. In addition, geometric constraints may be imposed on the static vascular network and its associated reservoir system to optimize responses achieved by altering local particle concentrations within such a structure. One example of an EM reconfigurable device based only on pressure driven flow could include a microfluidic inductor consisting of conductive coils wrapped around microfluidic channels. Such a device could be realized with robocasting by creating conducting coil network geometries through which magnetic colloidal dispersions can be pumped at different concentrations and hence different permittivities. Conducting structures could be generated with the robocasting technique by mixing metal nanoparticles with ceramic inks at a sufficient concentration so that percolating metal nanoparticle networks within ceramic network structures could transport current with low resistance. Design of such a microfluidic system will require careful consideration of several fluid mechanical issues associated with changing local particle concentrations within the network. The dynamic response in such systems will be related to the range of flow rates that can be achieved with pressure driven flow as well as convective and diffusive mixing of concentrated colloidal streams with dilute or pure solvent streams. For example, flow rates and operating pressures scale with the radius of microfluidic channels to the fourth power, which becomes increasingly significant at small length scales. In another example, diffusive mixing of particles depends on the particle radius to the first power in bulk media, but depends on the particle radius

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squared in confined geometries due to lubrication interactions. Other important fluid mechanical variables include the continuous fluid viscosity, dielectric properties, and density (in terms of how it affects the buoyancy of entrained colloidal particles). Another key issue is how to handle the transport of incompressible fluids within closed volume networks. To address these issues in the proposed research, an integrated suite of advanced microscopy techniques including total internal reflection, video, and confocal methods will be used to directly measure 3D particle transport within vascular networks for a range of flow conditions. For example, measurements for stagnant conditions will be used to understand diffusive transport of colloidal particles within such microfluidic networks and their dependence on particle shape, size, concentration, and particle-particle and particle-surface interactions. Measuring colloidal distributions throughout the network in the absence of flow will also demonstrate the importance of gravitational forces on particles in terms of their buoyancy or sedimentation, which will be used to optimize particle size as well as the particle and fluid densities. Measurements of particle transport within the network in the presence of pressure driven flow will characterize the competition between convective and diffusive transport as a function of shear rate (Peclet number). The experiments will also explore the possibility of employing flexible diaphragms upstream, downstream, and within microfluidic networks to accommodate incompressible fluid flows within closed systems. To both interpret these experiments and to gain predictive control over these systems, a number of colloidal scale modeling tools will be employed to accurately connect colloidal interactions, dynamics, and structure to transport properties within confined geometries associated with the microfluidic networks. Specifically, theories for colloidal and surface forces will be used to understand how control colloidal stability in such systems so that aggregation or deposition on mirovascular walls does not clog the system (in the circulatory analogy, this would be a clot these are undesirable when they cause strokes or heart attacks, but are important when they stop bleeding; particle interactions could be made attractive in the presence of air as a self-healing scheme for the microfluidic network). Multi-body hydrodynamic interactions will be modeled using Stokesian Dynamics methods to understand all mechanisms of particle transport within the microfluidic networks. In particular, these simulations will describe the concentration dependent colloidal dispersion viscosity within channels to maintain some threshold pressure for pumping (if blood gets too thick it stops flowing) and will also describe the diffusive and convective transport of particles when mixing of high and low concentration streams occurs within the network. After understanding pressure driven transport of colloidal particles with varying electrical and magnetic properties within microfluidic networks, the second task will involve incorporating conducting pathways into such networks to control local electric fields that direct the assembly of particle configurations with electrical properties useful for tuning reconfigurable antennas. As mentioned above, by incorporating metal nanoparticles into ceramic inks in the robocasting technique, conducting inks could be used in conjunction with standard insulating inks to generate 3D microelectronic networks integrated into 3D microfluidic networks (i.e. integrated circulatory and nervous systems). With such a structure, the purely 2D approaches described in the preliminary results (see section 1) can be applied within 3D networks to achieve amplified responses and possibly to minimize device footprints, which would both occur as the result of

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exploiting volumetric effects over purely surface phenomena. The same capacitive, resistive/conductive, and inductive properties achieved in preliminary work on 2D systems will now be exploited in 3D networks integrated into 3D structural materials. Although the second design is more complex than the pressure driven flow case in terms of its fabrication, it is expected to have a number of advantages in terms of device response times. Because electrical signals can be transmitted rapidly through conducting pathways to locally tune colloidal configurations into conducting wire and parallel plate capacitors, the response of the integrated micro- vascular/electrical device could be many orders of magnitude faster. The inspiration for this approach follows directly its analogy with the human body; pressure driven transport of chemicals through the circulatory system is much slower than the response time associated with electrical signals transmitted through the nervous system. However, just as in the body where these two systems are intimately integrated and rely on one another, this second device will rely on pressure driven flow to control local particle concentration within the microfluidic network on slower timescales, but will manipulate local particle configurations on millisecond timescales or less using by tuning local AC electric fields. A multi-scale modeling effort will also be included as part of developing this second device configuration. In particular, equivalent circuits of particle scale structures will be developed based on molecular scale properties (particle material composition, surface chemistry and modifications, medium properties, etc.). These particle scale equivalent circuits will be integrated as components into larger scale equivalent circuit models that capture the AC impedance properties of the integrated micro- vascular/fluidic network that will ultimately be introduced as components into circuit models of reconfigurable antennas at the device level (Fig 3). This part of the work will focus on using molecular scale modeling techniques to understand how control of particle and solution electrical properties (e.g. surface modifications, adsorbed polyelectrolytes/conducting macromolecules, bulk electrolyte, continuous media dielectric properties, etc.) can be tuned to control the equivalent circuit at the particle scale to be introduced into models at continuum and macroscopic length scales. Here we describe in more detail order of magnitude estimates of the length, time, energy, and force scales important to the performance characteristics of colloidal microfluidic impedance control devices. Preliminary scaling arguments provided here are intended to provide some intuition and predictive capabilities for the frequency and amplitude dependent behavior of colloidal microstructures and their associated electromagnetic properties. These scaling arguments suggest opportunities (and limits) for tuning device characteristics over a broad range based on available colloidal fluid characteristics (e.g. particle size, shape, dielectric properties; fluid viscosity, dielectric properties; other parameters - temperature, micro-channel dimensions, etc.). One of the most fundamental length scales in colloidal based fluids is the particle size (radius, a). Conservative surface and body forces and dissipative hydrodynamic forces have different functional dependencies on particle size. Basic forces relevant to this work include gravity (a3), hydrodynamic (a1), interparticle (a1), electrophoretic (a1), and dielectrophoretic (a3) forces. The average distance between colloids is another important length scale in colloidal fluids that together with interparticle forces strongly determines the formation of different microstructures

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as well as their dynamic relaxation. Another force relevant to colloids is the random Brownian force, which is characterized by the thermal energy, kT, which depends only on the temperature.

Figure 3. Microscopic and macroscopic interpretation of colloidal assembly on resulting electromagnetic properties. The interplay of these forces and their relative contributions determine dominant forces for different conditions and the resulting behavior and properties of colloidal fluids. For example, colloidal diffusion is determined by the balance of Brownian and hydrodynamic drag forces as characterized by the Stokes-Einstein diffusion coefficient (D=kT/6πµa). However, when a colloidal particle is near a wall, in a microfluidic channel for instance, the diffusion coefficient is proportional to a-2 due to hydrodynamic interactions between the two surfaces. For electrophoretic responses of colloidal fluids in the proposed work, the a1 dependence of both the electrophoretic force and opposing hydrodynamic forces result in no net particle size dependence in the bulk (a1/a1=1), although hydrodynamic interactions for particles near the wall produce an a-1 dependence (a1/a2). For dielectrophoretic responses of colloidal fluids, the a3 dependence of the dielectrophoretic force produces an a2 dependent response in bulk media and a1 response near a wall surface. For anisotropic colloids having more than one length scale (e.g. major and minor axis of rod shaped particles), there will also be more than one distinct force and time scale associated with each relevant length scale. The magnitude of each force also depends on the material properties and operating conditions. Electrophoretic forces are proportional to the colloid surface charge, and hence the zeta potential ζ, whereas dielectrophoretic forces are proportional to the colloidal polarizability (i.e. dielectric properties). Colloidal diffusion is directly proportional to temperature, T, and inversely proportional to the continuous medium viscosity, η. Gravitational forces on colloidal particles are proportional to the density difference, ∆ρ, between the surrounding fluid medium and the particles, to promote either sedimentation or buoyancy. All dynamic colloidal fluid processes involving hydrodynamic interactions depend on the average interparticle and surface spacing

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which depend directly on the range, magnitude, and sign of relevant colloidal and surface forces (i.e. electrostatic, van der Waals, forces due to adsorbed and unadsorbed macromolecules). Considering all of these factors together, we will perform dimensional analysis and obtain the relevant dimensionless parameters that determine the colloidal system behavior. Further experimental investigations will be based on this information, so that the material and system parameters are understood at a fundamental level to intelligently design and optimize the performance of the colloidal microfluidic impedance device. Our preliminary investigations have focused on dominant single-particle transport mechanisms as a function of AC field amplitude and frequency to understand the relative roles of transport mechanisms in producing the microstructures in Fig 1. The observed structures in Fig 1 and their transient assembly can be explained in terms of a competition between sedimentation, selfdiffusion, and several AC electric field mediated transport mechanisms including electrophoresis (EP), AC electro-osmosis (EO), and dielectrophoresis (DP). In all cases, sedimentation concentrates particles onto the interdigitated electrode surface, and Brownian motion tends to produce laterally homogeneous, random configurations. To assemble the microstructures in Fig 1, AC electric field mediated colloidal transport must be comparable to, or exceed, the characteristic transport rates associated with sedimentation and self-diffusion (Peclet numbers greater than one). To understand the relative roles of these transport mechanisms in producing the microstructures in Fig 1, the dominant single-particle transport mechanisms as a function of AC field amplitude and frequency are reported in Fig 2. The maximum velocity associated with dynamic EP, uEP, for colloids with thin electrical double layers (κa>>1) is given by, uEP     mr     m    2    2

0.5

V

where the quantity (/)(V/r) is the Smoluchowski EP rate, is the medium permittivity,  is the zeta potential, r is the electrode gap, V is the applied voltage (approximately related to the electric field, E, for the coplanar geometry as E=V/r), =6a is the Stokes resistance coefficient,  is field frequency, m=C(4/3)a3 is colloid mass, and C is colloid density. AC EO flows due to tangential electric fields determine the transport of entrained particles as, uEO    8 r   2  1   2  V 2 2

where =CS/(CS+CD), CS is the Stern layer capacitance, CD is the diffuse layer capacitance, =( r/2), and  is the medium conductivity (0.2 for gold film electrodes with CD = and CS=0.007F/m2 as discussed in Ref. ). Colloidal transport and assembly into wires via DP in nonuniform electric fields can be collectively characterized using, 2 uDP    a 2  r 2  f f CM 2  1  2  V 2 2

where fCM=Re[(p-)/(p+2)] is the real part of the Clausius-Mossotti factor (fCM=1 for gold colloids),  is the complex permittivity given as =-i/ (subscript "p" refers to particle), and fφ is a correction factor accounting for interparticle spacing, chain orientation, and effective medium dielectric properties at finite colloid concentrations (fφ≈5 from Ref. ). Our preliminary results using these predictions are reported in Fig 4. The three dominant transport regimes that 8

emerge in Fig 4 obviously correlate with the three microstructural regimes observed in Fig 1, which allows for direct connections to be made between assembly mechanisms and structures.

V/volts

10

1

0.1 10-3

EP

10-2

EO

10-1

100

DP

101

102

103

104

/kHz

Figure 4. Voltage vs. frequency phase diagram indicating magnitude of dominant transport mechanism for single colloids in coplanar electrode device shown in Fig 1. Transport rates are computed using Eqs 1-3 and abbreviated as electrophoresis (EP), AC electroosmosis (EO), and dielectrophoresis (DP). Rates contours are defined by the linear spectrum scale shown in the inset with red=2000m/s and violet=0.01m/s 2. 2 Measurement and Characterization of Electromagnetic Properties at High Frequencies The use of Electromagnetically Tunable Colloidal-based Materials (ETCMs) – the term used to describe the dynamic properties of dielectric, ferrous, and conductive colloidal particles suspended in a fluid media – represents a very novel concept in the design paradigm of antennas, filters, and couplers (along with many other types of electromagnetic devices) operating at RF, microwave, and millimeter-wave frequencies (from 3 MHz up to 30 GHz). In a general context, fluids have traditionally been considered in and around these devices only in the capacity as a cooling mechanism (much like the radiator in a combustion engine) – such that their sole purpose lies in the mitigation of heat that accumulates from resistive power dissipation in these devices and their local packaging. In most cases this heat is a result of conductor and material losses, and the fluidic components are electromagnetically shielded – or isolated – from the operation of the device. Under the framework proposed in this work, microfluidic elements transport particle laden suspensions of ETCMs that interact directly with the electromagnetic fields and perform an operational role in the functionality of the component.

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In addition to the intrinsic electromagnetic properties, the characterization and understanding of the transient electromagnetic properties of the ETCMs represents a key objective of this research. This behavior is coupled to the kinetic properties of the colloidal particles in an AC field (also covered in this proposal) so the overall behavior of the ETCMs and system must be considered. The knowledge of these properties is essential in the successful application of these materials in UAV, MUAV, and other applications. Both communication and radar applications – each of which use spread spectrum technologies & each of which are vital to the successful mission of UAVs – rely on a high degree of linearity within the receiver/transceiver architectures and/or a well understood system that can be properly compensated for thru signal processing techniques. This is essential for the transmitted and received electromagnetic fields to maintain their information content (voice data, or real time video streaming, and accurate radar signatures for target detection and identification). 2.2.1 Electromagnetic Characterization of Materials One of the fundamental milestones in the development and application of ETCMs for RF applications resides in the characterization of their intrinsic electromagnetic properties – specifically the relative permeability µr , permittivity ε r , and conductivity σ . However, within the context of the microfluidic system these materials are not in bulk quantities so the effective constitutive material parameters ( µ eff and ε eff ) will be quantities of interest in determining the relative material parameters. These properties hold the key to the vast range of capabilities they can provide in a device and must therefore be well understood as they relate to: •

The use of non-aqueous suspension media, concentration and material types

•

The size, shape, and other geometrical properties of the colloidal particles

•

The microstructure and orientation in the electromagnetic fields

The characterization process begins by first examining the local and distributed wave impedance (specifically defined as the ratio of the electric and magnetic fields in a given media) within these material systems. These measurements will provide a means to develop a knowledge base and accumulate experience with the ETCMs that can be used to turn around and implement these technologies into to highly functional devices with novel reconfiguration and agility capabilities. In addition to exploring the basic science of these materials it will also lay the groundwork for the rapid transition of these technologies into AFOSR applications where they are both suitable and practical – such as reconfigurable antennas and other adaptable electromagnetic devices. A multi-disciplinary team is crucial for the success of these measurements, and the expertise of the Texas A&M University researchers in this proposal has significant synergy to achieve this. 2.2.2 Measurement Techniques and Test Fixtures The intrinsic and transient electromagnetic properties of the ETCMs and the microfluidic systems will have dynamic behavior derived from pressure driven components, mixing of colloidal materials, and kinetic effects from AC biasing fields. Accurate characterization of these 10

properties will require a methodical and systematic approach towards the development of test fixtures and measurement techniques. This work will address these issues with great care, and apply several established methods as the groundwork for the measurement techniques and test fixtures. A principal component for this will be the coaxial measurement cell. This geometry (similar in structure to cable TVs and modems) has very well understood field configurations and has long been a very accurate measurement tool used to determine the electromagnetic properties of materials (Lewis, 1967). To accommodate the dynamic properties of the particle-laden fluids we propose to use a coaxial fixture with inlet and outlet ports that can be used as a material delivery system. Figure 5 shows a cross-section of this device, and indicates the direction of electromagnetic wave propagation. This device is structurally similar to one used in (Vincent, et al., 1996), however the inlet/outlet for our device have been specifically designed (size, orientation, etc.) to avoid coupling electromagnetic energy into the material delivery systems and reservoirs.

Figure 5. Coaxial measurement cell with inlet and outlet for the delivery of materials into the device. The wide-reaching applicability of this device comes from the coaxial geometry, which supports TEM (Transverse Electromagnetic) wave propagation (electric and magnetic fields are well known and each are transverse to the direction of wave propagation) over an extremely broad frequency range. This provides an ideal environment for very accurate measurements of material properties to be taken. Figure 6 shows the electric and magnetic fields of the coaxial geometry. The isotropic material properties are derived form this device anisotropy ur u(although u r ur ur can be measured) through the electric ( D   E ) and magnetic flux ( B   H ) – or equivalently

(

through the wave impedance and propagation velocity v p = c ε r µ r

)

−1/ 2

(proportional to the

inverse square of the product of relative properties) and wave impedance η = 120π µr / ε r (proportional to the square of the quotient of relative material properties). This device will allow a continuous flow of ETCMs of varying concentration and composition and the measurement of the dynamic properties.

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Figure 6. Vector and scalar plots of the electric and magnetic fields within the coaxial measurement cell. For continuous wave (CW) measurements – in which the vector network analyzer (VNA) measures the complex characteristic impedance and propagation velocity after proper calibration – the coaxial measurement cell can be used to extract the intrinsic material properties 50 MHz to 50 GHz using the current facilities at Texas A&M University. These measurements will be performed using two-port S-Parameters (two-port network parameter based on reflected and transmitted power at the input and output terminals of the coaxial cell). Figure 7 demonstrates this measurement. The ETCMs will be pumped though the coaxial measurement cell to measure the dynamic properties of these materials. Three sets of measurements will be performed with this device once the calibration has been performed – providing a characterization of the individual material properties as well as a mix of the two. First, solutions with varying concentrations (by weight or volume fraction) of magnetic particles will be incrementally injected into the measurement cell through the inlet valve and the two-port S-parameters will be measured. The coaxial measurement cell will then be flushed with the particle-free media. Next, solutions with varying concentrations (by weight or volume fraction) of dielectric particles will be incrementally injected into the measurement cell through the inlet valve and the two-port Sparameters will be measured. The cell will again be flushed with the particle-free media. Lastly, homogeneous mixtures of materials will be injected into the measurement cell through the inlet valve and the two-port S-parameters will be measured. This work will be performed in the first year of the contract.

Figure 7. Basic set-up for coaxial measurements.

2.2.3 Electromagnetic Properties of Colloidal-Based Microstructures Another major component to this research is investigating the high frequency (> 50 MHz) electromagnetic properties of colloidal-based microstructures formed using low frequency (<1 MHz) fields. The multi-scale modeling and experimentation of these materials and their properties are especially important for this work as there are numerous mechanisms which couple the mechanical, chemical, and electromagnetic properties – inevitably affecting the performance of devices relying on this technology. As this work enters the second and third year – once the base material properties are well understood – we will examine the diverse possibilities presented by the ability to alter the size, shape, and suspension media. We have

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used scaling analysis (see section 2.1) to predict assembly mechanism for various particle size at different electrode spacing (Fig 8). 10

DEP

1

a/µm

X

0.1

EP

AC-EO 0.01

1

10

100

1000

r/µm

Figure 8. Effect of electrode spacing (r) and particle radius (a) on assembly mechanism. Analysis done for an assembly frequency of 1 MHz. Yellow star indicates are experimental data points, where this analysis accurately predicts observed dielectrophoresis (DEP). AC-EO is ac electroosmosis and EP is electrophoresis. Using these properties we will be able to determine the appropriate electrode geometry, material composition, and applied fields which can maximize the capabilities of devices using these technologies. This behavior is crucial for operation at higher frequencies where the skin effect and other electromagnetic phenomena are more exaggerated. Figure 9 shows a pictorial representation of the skin effect (for a material with conductivity σ , magnetic permeability µ , and radial operating frequency ω ) in conductors – a forward and return current path is required for the flux linkage in the EM field. This effect results in resistive power loss PResistive to heat as current begins to crowd a finite-thickness, or “skin,” on the surface of the conductor (directly related to the penetration of the magnetic field into a conductor). This basic transmission line representation demonstrates the need for maximal conductivity and minimal permeability in conducting materials used for microstructure switches and capacitors at GHz frequencies. Devices used in previous experiments to test the microstructured systems encountered significant losses due to these effects (when the conductor thickness is less than the skin depth the device behaves as a thin-film resistor). This will be minimized in new devices that are under development for this work through the use of thicker conductors and different electrode geometries.

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Figure 9. Skin effect in conductors at GHz frequencies. 2.2.4 Multi-Scale Electromagnetic Properties of Colloidal-Based Microstructures By combining all of the aforementioned techniques that capture phenomena on several different length scales, these systems can be translated down to the particle length scale and used to capture the device properties resulting from the microstructured colloidal systems. Figure 10 illustrates the multi-scale modeling strategy developed by the investigators for the microstructures shown in Figure 1 – making full use of equivalent circuit representations. Using this representation we will be able to engineer systems that can mitigate many of the effects which may hinder the performance of the overall device. For example, the skin effect that was discussed in the previous section will be a major concern at RF frequencies due to the very small microstructure size. This will present opportunities to investigate exotic materials, non-linear effects (frequency dependence, superconductivity, etc.). and optimal uses of these systems in an application. The ability to link the performance of the device back through system and down to the interactions between colloidal particles will provide significant scientific knowledge with regards to the fundamental material properties and their roles in high frequency applications.

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Figure 10. Multi-scale modeling and impact on device performance. The ETCMs are examined first for their microstructure materials and kinetic properties, which are then subjected to the electromagnetic fields for a given electrode geometry, placed in a test fixture, and experimentally analyzed. 2.2.5 Electromagnetic Devices for High Frequencies Building off of the current knowledge base and experience with ETCMs, the current investigators at Texas A&M University and Toyon Corporation (through a previous DARPA award) have identified several classes of devices – or building blocks – for high frequency applications. The discrete elements shown in the top of Figure 11 are device-level representations of common circuit elements that can utilize the dynamic mechanisms provided by the ETCMs. The upper left side of this figure show elements that can provide reactive impedance control using pressure driven systems, Electro-Fluidic Capacitors (EFCs) and Magneto-Fluidic Inductors (MFIs) – tunable capacitors and inductors – that derive their functionality from the position and concentration of nanoparticles. Similarly, using metallic-based ETCMs that can be controlled through their kinetic behavior and microstructuring in an AC field, we have demonstrated the ability to adjust the capacitance through the Electrophoretic Varactors (EVs) and resistive tuning and switching through the percolation of metallic nanoparticles into Dipolar Chain Rheostats (DCRs) (upper right of Figure 11). Combined, these elements use very novel concepts to

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achieve discrete networks with continuous tuning over a very wide range. This work will use the experience momentum from ongoing efforts to examine new embodiments of these technologies since the operation and performance of these devices relies on the architecture and topology of the device to exploit the material system. An example of a current MFI implementation – used primarily to demonstrate the proof of concept – can be seen in the lower half of Figure 11 along with the resulting forward transmission coefficient in log-magnitude format. The different curves within this plot demonstrate a filtering effect that was achieved by adjusting the ETCM (a mixture of NiFe - Permalloy) ‘plug’ position within the loose windings of an inductor – essentially adjusting the permeability and reactive impedance of the inductor. Using this in conjunction with microstrip line lengths (a very common monolithic transmission line used in high frequency applications) that connect to the inductor to the input and output ports a significant amount of reactive tuning was achieved. New devices will be investigated in the second and third year of this project. In addition to having very attractive application-based functionality, they will provide a means to accurately gauge the characterization of materials and systems discussed in previous sections.

Figure 11. Fundamental electromagnetic circuit elements – the Electro-Fluidic Capacitors (EFCs), Magneto-Fluidic Inductors (MFIs), Electrophoretic Varactors (EVs), and Dipolar Chain Rheostats (DCRs) – and a proof-of-concept example of the MFI and measured results at GHz frequencies. 2.3 Multiscale modeling and simulation of EM performance of colloidal-based materials structures (ETMCs) using a multi-scale and physics based framework. This research task will address the development of modeling methodologies for optimization of the integrated, multifunctional colloidal-based materials and devices by first focusing on understanding the mechanisms of colloidal assembly and second on predicting the resulting

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effective properties of the assembled structures. Hierarchical materials homogenization methods will be developed for the extraction of macroscopic electromagnetic properties of the custom designed colloidal material systems. These macroscopic properties are essential for expediting the subsequent, computer-aided electromagnetic analysis of the integrated colloidal suspension components. The key research sub tasks for this research thrust are the following: -Multiscale analysis of the electromagnetic response of colloidal suspensions under different patterning configurations. -Hierarchical multiscale modeling of the electrical resistivity, permittivity and magnetic permeability tensors of colloidal suspensions that require volumetric modeling in the subsequent, component design-oriented electromagnetic analysis. 2.3.1 EM modeling of colloidal suspensions An appropriate control of colloidal particle configuration can lead to reversible drastic changes of material properties by several orders of magnitude far beyond the tunable ranges of other conventional functional materials. We propose to pursue a computational study of colloidal phenomena by combining three models to simulate the directed assembly of colloidal particles and predict the resulting effective properties, and to bridge to the larger scale continuum constitutive model, all in close connection with the experimental investigation. The models employed include a diffuse interface field approach using in-house developed parallel computing code and two finite element-based models using the commercially available software COMSOL multiphysics®. The first level of modeling will be developed to characterize the short-range interactions between neighboring particles, and interactions between particles and electrode through electrokinetic flow, electroosmotic flow, electrophoresis and dielectrophoresis. A parametric study will then be completed to determine key parameters of fluid properties and colloid properties that will be used as input parameters for the other two models for particle assembly and property prediction. A second level of modeling will be used to simulate the colloidal particle microstructure evolution in microfluids driven by various forces of different physical origins: hydrodynamic force, Brownian motion, external field, field-induced dipoledipole interaction, and short-range inter-particle force, which depend on both particle configuration and particle shapes. No a priori constraint is imposed on possible particle configuration along evolution path, and each particle is free to translate and rotate under the constraint from microfluidic channels (microfluidic). The simulations will reveal process of particle self-assembly, explore contributions of different mechanisms and various relevant factors (particle shape and size, field amplitude and frequency, microfluidic and electrode geometries, etc.), and predict optimal controlling parameters for colloidal particle microstructure control and property tuning. The simulation results will be compared with the experimental measurements and the obtained particle configurations will be used in the next finite element model for property prediction. The third level of modeling will predict the effective properties of the assembled colloidal microstructures, such as the impedance of assembled colloidal microstructures as a function of applied voltage and frequency. A parametric study of this model will predict the capabilities of the microfluidic device such as maximum/minimum resistance, capacitance, and inductance. These three levels of modeling together will provide the microstructural basis for the hierarchical material homogenization. Our preliminary work using the first level of modeling considered gold particles suspended in an aqueous electrolyte solution and is shown in Fig 12. This work will be extended to include studies of different concentrations

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of particles, shapes, sizes and alignment, as well as different material properties. Steady state and transient effects will be considered to determine response times for establishing patterning microstructures. (c)

(a)

(b)

Figure 12. The assembly depicted in model clusters of nanoparticles. (a) The model for the variable capacitance mode achieved at < 1KHz. (c) The model for variable resistance mode achieved at > 100KHz. The yellow highlighted sections in (a) and (c) denote the RVE, and the arrows show the field lines. (b) shows the corresponding experimentally obtained configurations. 2.3.2 Multiscale modeling of ETCMs The overall modeling effort of the proposed project involves physical phenomena occurring over a wide range of length scales which must be resolved or bridged. The largest length scale is that of the overall structure which is of the order 10-1-100m. However to predict and control the electromagnetic and mechanical constitutive properties of the composite materials at this macro length scale, one must take account of phenomena occurring at finer length scales. In particular, the macro scale composite material will have a complex heterogeneous microstructure affecting both its mechanical and electromagnetic properties. More specifically, the macro-scale structure will have a discrete distribution of meso-scale “controller elements” which in themselves have a complex heterogeneous microstructure with a hierarchy of critical length scales to resolve or bridge. These controller elements are to be strategically located in the macro-scale. In order to assist with the design of the integrated ETCMs approximate methods will be utilized, which will be used as a first order approximation of effective properties and for validation of design concepts. The proposed parametric studies will employ parameters such as orientation distribution functions of the nanoparticles, shape functions and volume fractions of the dispersed phases. The averaging methods will be applied to the low frequency limit (Lee, Boyd and Lagoudas, 2005) as a starting point for further numerical homogenization methods to be employed as explained in the paragraph above. While analytical homogenization for (linear) thermomechanical properties is a well established field with a vast literature, homogenization for electromagnetic properties has a much smaller literature. Averaging micromechanics approaches for aligned and randomly oriented inclusions will be employed to specifically determine the effective electrical conductivity, permittivity, and

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magnetic permeability of nanocomposites used as filler materials in capacitors and inductors. For example, the effective electrical conductivity can be obtained from the volume averages of the eff electric flux and electric field as Jσ  E , where J and E are the electric flux and field, eff respectively, σ is the effective electrical conductivity. For aligned nanotube or nanofiber composites with and without interphase coatings, these governing equations can be used to determine the nanocomposite effective axial and transverse electrical conductivities using the generalized self-consistent composite cylinders method. For nanocomposites consisting of randomly oriented nanotubes or nanofibers with and without interphase regions, the effective conductivity will be estimated by averaging over all orientations by c 2  (4) σ eff  σ 0  f    σ CCA  σ 0  ACCA sin    d d 4 0 0 where c f , σ CCA , and A CCA are the volume fraction, the effective conductivity, and the electric field concentration tensor, respectively, of the composite cylinder assemblage [Seidel and Lagoudas, 2006]. A similar methodology will be used to estimate other electromagnetic properties like effective permittivity and effective permeability. The ETCM embedded in a microfluidic channel, as shown in Fig. XYZZ is an intermediate scale (10-2-10-1)m component between the macro-scale (10-1-10-0)m of the structure and the meso-scale (10-5-10-4)m of the colloidal suspension. The ETCM has itself a hierarchical multiscale structure. The lowest scale to be resolved is that of the colloidal particle/fluid mixture (10-9-10-8)m. Numerical homogenization, as described previously, will be used to model the electromagnetic response of a unit cell of the particle/fluid mixture with electromagnetic field frequency dependence information coming from experimental studies. This frequency dependence determines alignment of the nano-particles which in turn determines whether the colloidal mixture behaves effectively like a conductor or a dialectric material. The next scale to model for the ETCM is that of the microvascular network unit cell (10 -6-10-5)m, as shown in Fig. 13, the critical information about the effective electromagnetic properties of the nanoparticle/fluid mixture having been determined from numerical homogenization of the nanoscale unit cell. This meso-scale unit cell incorporates a representative portion of the microvascular channel network filled with the nano-particle/fluid mixture. Its electromagnetic field frequency dependency will be inherited from the frequency dependency for the nanoparticle/fluid mixture used in the nano-scale unit cell analysis. Finally, the effective response of the entire device will be determined from numerical homogenization applied to the meso-scale unit cell and will be correlated with experimental results as described in the previous section.

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(a)

(b)

Figure 13. Unit cells of ETCMs, where different boundaries will results in different patterning: (a) Pointed electrode near a flat electrode, and (b) Conducting islands between planar electrodes.

3. Team and Timeline 3.1 The Team The Texas A&M University (TAMU) team includes Profs. Dimitris C. Lagoudas, Zoubeida Ounaies, Mike Bevan, and Gregory Huff. The above participating faculty contributes experimental and computational capabilities relevant to the proposed work in terms of established facilities at TAMU such as the Texas Institute for Intelligent Bio-Nano Materials and Structures for Aerospace Vehicles (TiiMS); the Center for Mechanics of Composites; the Electromagnetics and Microwave Laboratory; the Interfacial Colloidal Systems Laboratory; and the Electroactive Materials Characterization Laboratory. The resulting multidisciplinary research expertise spans multifunctional materials and structures for aerospace; mechanical, electrical and electromagnetic characterization of materials and structures; nano and micro-scale electric fielddriven assembly; and computational mechanics and multiscale modeling. The team members have a well-documented record of closely collaborating on a number of currently funded projects over the years. All four are currently engaged in a related DARPA-funded project on colloidal microfluidic systems to reversibly control physical properties through fluidic transport and directed colloidal assembly. In collaboration with Toyon researchers, microfluidic circuits with controllable electrical impedance will be integrated in reconfigurable antennas and smart skins. Additionally, the team will actively engage with AFRL researchers who are designing systems in which the aforementioned developments in active nanocomposites could lead to revolutionary design paradigms. Professor Dimitris Lagoudas Prof. Lagoudas is currently the Director for the newly established Texas Institute for Intelligent Bio-Nano Materials and Structure for Aerospace Vehicles funded by NASA. His

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research involves the design of multifunctional systems at nano, micro, meso and macro levels with appropriate methods developed to bridge the various length scales. This research will develop multifunctional hierarchical structural materials and systems. Lagoudas’ previous work ranges from analytical and experimental to applied research. Over the past decade, his research has been supported by various government agencies including NSF, ONR, ARO, AFOSR, and DARPA. He has collaborated with many industrial partners from industries such as Bell Helicopter - Textron, Lord Corp., Lockheed-Martin, Northrop Grumman, and Memory Technologies. He has also worked with several national labs, including AFRL, ARL, NRL, NASA, CDNSWC, NAWC, either directly or through Cooperative Research or Development Agreements. Professor Michael Bevan Prof. Bevan’s experimental work has focused on adapting and extending several advanced optical microscopy techniques to probe kT interactions between colloidal ensembles and patterned substrates to manipulate template directed self assembly processes. So far his group has: (1) identified methods for tuning van der Waals attraction between polymer coated colloids using specific ion effects, (2) developed microscopy methods to map micro-fabricated chemical and physical potential energy landscapes on various substrates, (3) implemented a multi-particle total internal reflection, video, and confocal microscopy experiment to measure particle-particle and particle-wall interactions on patterned substrates, and in the presence of external fields. Prof. Bevan’s modeling work has focused on implementing simulations and theories to solve longstanding problems with consistently understanding conservative and dissipative forces connected to the thermodynamics and kinetics of micro-structural evolution in interfacial colloidal systems. So far they have: (1) successfully described sources of seemingly anomalous interactions of colloids near surfaces, (2) developed a theoretical explanation for the dynamic transition of weakly attractive colloids at their percolation threshold. Professor Gregory H. Huff Prof. Huff, who joined TAMU from UIUC a few months ago, is lending his expertise in electromagnetics characterization and modeling, and design of large aperture reconfigurable antennas. Prof. Huff’s research interests involve the multidiscipline role of applied electromagnetics and the exploration of novel radiating systems and sensors. His current research in the Electromagnetics and Microwave Laboratory includes (1) the development of experimental techniques and analytical methods for the electromagnetic characterization and multi-port network representation (equivalent circuit, transmission line modeling, etc.) of novel materials and systems that facilitate their application into devices, (2) the analysis, design, and fabrication of reconfigurable and/or multi-function antennas, and the conformal integration of these radiators onto/into canonical structures and host chassis, and (3) the integration of reconfigurable devices into sensors, sensor platforms, multi-scale sensor networks, and communications platforms (as well as other areas that can fully exploit the behavior these high performance devices). Prof. Huff’s research also involves theory and design of other tunable devices for microwave and millimeter wave applications and the electromagnetic compatibility and packaging of high frequency components. Professor Zoubeida Ounaies Prof. Ounaies's research interests lie in the study of advanced material systems, including

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high performance composites and multifunctional materials. Current research activities encompass processing and characterization of smart materials; development of new electroactive nanostructured composites; experimental characterization of the constitutive behavior of ferroelectric materials such as PZT and PVDF; and the development of new methods to characterize materials’ behavior. Recently, the focus in Dr. Ounaies’s laboratory has been on incorporating nanoinclusions such as carbon nanotubes and ceramic powders to control and enhance the electrical and electromechanical properties of polymer nanocomposites. Sensing and actuating capabilities of carbon nanotube-reinforced electroactive polymers have been investigated to improve controlled responses upon various external stimuli. Nanotube-based sensors promise increased sensitivity and high response time. Such devices would rely on the intimate coupling of chemical and biological recognition and electrical transduction. This work resulted in the first high-temperature piezoelectric polymers and polymer composites. Examples of applications include integrating the sensors and actuators into composite structures for aerospace; one focus is on the development of a fully adaptive, fully integrated wing structure with embedded and distributed multifunctional sensors and actuators for unmanned aerial vehicles. Additionally, the carbon nanotube-based composites can be used as chemical sensors or biosensors for detection and monitoring, owing to the coupling between chemical or biological recognition and electrical properties. 3.2 Time Plan and Budget The total requested amount is $300k for three years. Most of the budget will support graduate students, travel, supplies, and a modest amount will go towards a portion of the PIs summer salary. In planning the budget, the PIs agreed to dedicate the majority of it to student support; however, the investigators are fully committed to be engaged with the proposed research and will accomplish that by leveraging existing funds they have.

Thrust 1 Thrust 2 Thrust 3 Total

FY08

FY09

FY10

$100k

$100k

$100k

4. Facilities Texas A&M University is a Research I institution as well as a land, space and sea grant institution and is well instrumented and equipped to meet the technical and equipment needs of this proposal. Most of the micro-fabrication work will be conducted at the TAMU Material Characterization Facility (http://www.chem.tamu.edu/cims/instruments.html). Very small mask features (2 m or less), and focused ion beam or dry reactive ion etching techniques may require outsourcing some parts of device fabrication to the NSF Sponsored fabrication facilities at Cornell and/or Northwestern Universities. Additional facilities in the departments of Chemical, and Mechanical Engineering, and Physics include a complete machine shop with full-time dedicated personnel to assist in the design and construction of custom-made laboratory

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equipment. Chemical and biochemical synthesis and support is also available. The Electroactive Materials and Characterization Laboratory Capabilities include: • Dielectric spectroscopy using a Hewlett Packard HP4194A Impedance Analyzer (frequency 10Hz to 100 MHz) and a QuadTech High Precision LCR Meter (frequency 10 Hz to 2 MHz) coupled with a Sun EC10A temperature chamber (–180ºC to 400ºC). The system is automated using a custom LabView control interface. • Broadband Dielectric and Impedance Spectroscopy - Novocontrol Technologies. • Thermally Stimulated Current (TSC) technique using SETARAM TSC 3000. The set-up includes a test cell with variable electrode sizes and shapes, a temperature chamber with capability from –150ºC to 400ºC, a power supply up to 500V, and completely automated system operation. • Dynamic Mechanical Analysis - TA Instruments RSA III • High speed video capture for displacement measurement and actuator characterization, from Motion Capture Technologies. • Equipment for casting, drying and curing polymer films. Materials and Structures Laboratory Capabilities include: • MTS axial servo-hydraulic test systems with load capacities from 20 to 100 KIP • Adelaide axial-torsional, electro-mechanical test system with axial and torsional loading capacities up to 20 KIP and 10,000 in-lbs, respectively • MTS high-rate, open-loop, servo-hydraulic test system with actuator speeds up to 60,000 in/sec and impact energies up to 24,000 in-lbs. • Extensometers for ambient and high temperature strain measurement, including: MTS axial and diametral extensometers, an MTS biaxial extensometer, and an assortment of MTS axial clip gauges offering a wide range of capacities.

• • •

Temperature chambers and furnaces to suit a variety of isothermal and transient temperature testing requirements for elevated temperature research. Leica optical microscope [with Bright field, Dark field, Polarized Light, Polarization Contrast, Differential Interference Contrast, and high-resolution CCD Camera for Digital Imaging] Differential Scanning Calorimeter - Perkin Elmer Pyris 1

Nanomaterials and Advanced Composites Lab (NACL) Capabilities include:

• • •

Equipment for the processing and dispersion of nanoconstituents. Cast molding facility for the fabrication of nanocomposite specimen of various geometries to meet different test requirements. Vacuum-assisted resin transfer molding (VaRTM) facility for laminated fiber-reinforced composite fabrication. A temperature-controlled infusion table allows for the infusion of laminates at elevated temperatures.

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•

Miniature mechanical testing stage for in-situ tension and flexural testing of small specimen (within an SEM, environmental chamber, Raman spectrometer, etc.)

The Microscopy and Imaging Center – MIC Capabilities include:

• • •

Several SEM systems, including a new high resolution FE-SEM (2nm resolution) with OIM and heated/cooled loading stage capability Zyvex Model S100 nanomanipulator. TEM, HREM and X-Ray diffraction equipment

Materials Characterization Facility Capabilities include:

• • • • • •

Raman/FT-IR/NSOM Microscope for advanced optical spectroscopy (high spectral resolution for Raman and fluorescence measurements) Far-field and near-field scanning optical microscopy with spatial sensitivity to subwavelength resolution. Digital Instruments Nanoscope Atomic Force Microscope/Scanning Tunneling Microscope Class 1000 clean room and lithography facilities TriboIndenter nano-indenter Electron Beam Lithography: JEOL JSM 6460 SEM with Nabity NPGS Lithography option. Line widths of 18nm have been demonstrated

Surface Engineering Research Laboratory The facilities available at TAMU for surface engineering research include: AFM, energy dispersive X-ray spectroscopy, X-ray diffraction, ESCA, LEED, atomic absorption spectroscopy, FT-IR spectroscopy, differential scanning calorimetry (DSC), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), mass spectroscopy, and scanning tunneling microscopy. The facilities are operated by highly trained personnel. Computing Facilities Texas A&M University Supercomputing Facility Other major equipment in investigators’ laboratories related to this work: • Zeiss inverted confocal scanning laser microscope – 3D dynamic imaging • Zeiss inverted fluorescence microscope with CCD camera – fluorescence and general imaging • Zeiss upright microscope with PMT & CCD camera – single particle and ensemble TIRM • Brookhaven static/dynamics light scattering goniometer/autocorrelator – particle shape, size, and interactions • Brookhaven ZetaPALS – particle sizing and electrophoresis • Paar Physica MCR 300 rheometer – rheological measurements

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Electromagnetics and Microwave Laboratory • HP 8510C Vector Network Analyzer 1. 45 MHz - 50.0 GHz 2. 75 GHz - 100 GHz • Orbit/FR Automated Antenna Measurement System (includes an HP 85360A distributed frequency converter from 2-40 GHz) • 40' indoor anechoic chamber • 10' active antenna mini-anechoic chamber automated measurement system • Microwave circuit etching facilities (mechanical and chemical) • Access to Cray and Silicon Graphics supercomputers • Cryogenic testing of superconducting microwave circuits through 40 GHz • Microwave software 1. 2.5-D EM Simulators: IE3D, Sonnet, Momentum 2. 3-D EM Simulators: Fidelity, CST Microwave Studio, Ansoft HFSS 3. Microwave CAD: Agilent ADS, HPEEsof Series IV, Cadence/SpectreRF

5. References 6. Biographies DIMITRIS C. LAGOUDAS, Ph.D., P.E. Professional Preparation Aristotle University of Thessaloniki, Greece Mechanical Engineering Diploma, 1982 Lehigh University, Applied Mathematics Ph.D., 1986 Cornell University (postdoctoral) Applied Mathematics and Theoretical and Applied Mechanics 1986-88 Research Interests D.C. Lagoudas is the Director for the Texas Institute for Intelligent Bio-Nano Materials and Structure for Aerospace Vehicles funded by NASA. His research involves the design of multifunctional systems at nano, micro, meso and macro levels with appropriate methods developed to bridge the various length scales. This research will develop multifunctional hierarchical structural materials systems that will carry structural loads; store electrical energy; assist in thermal management; and protect against low and high velocity impact. Additionally, multifunctional porous shape memory alloys at the micro scale will be developed and then integrated into smart structures relevant to multifunctional lightweight space applications. He has taught graduate courses on Micromechanics, Mechanics of Active Materials, Damage Mechanics, Continuum Mechanics, Theory of Elasticity, and Plasticity and Inelastic Behavior of Composites. Over the past decade, his research has been supported by various government agencies including NSF, ONR, ARO, AFOSR, and DARPA. He has collaborated with many industrial partners such as Bell Helicopter - Textron, Lord Corp., Lockheed-Martin, Northrop Grumman, and Memory Technologies. He has also worked with several national labs, including AFRL, ARL, NRL, NASA, CDNSWC, NAWC. Appointments Texas A&M University, College Station TX 77843-3141 John and Bea Slattery Chair, September 2004 25

Director, Texas Institute for Intelligent Bio-Nano Materials and Structure Center, August 2002 Chair, Faculty of Materials Science and Engineering, August 2002-August 2003 Associate Vice President for Research, May 2001-May 2004 Ford Professor, October 1999 – August 2004 Director, TEES Center for Mechanics of Composites, September 1998-December 2001 Full Professor of Aerospace Engineering, September 1998-present Associate Professor of Aerospace Engineering, July 1992- September 1998 Relevant Publications: 1. LEE, J.S., BOYD, J.G., and LAGOUDAS, D.C., 2005, “Effective Properties of Three-Phase ElectroMagneto-Elastic Composites,” Int. J. of Eng. Sc., Vol. 43, 790-825 2. Hadjiev, V.G., Lagoudas, D.C., Oh, E.-S., Thakre, P., Davis, D., Files, B.S., Yowell, L., Arepalli, S., Bahr, J.L. and Tour, J.M., 2005, “Buckling Instabilities of Octadecylamine Functionalized Carbon Nanotubes Embedded in Epoxy,” Comp. Sci. and Tech., Vol. 66, 128-136. 3. Oh, E.-S., Lagoudas, D.C., Slattery, J.C., 2005, “Thermodynamics of two-dimensional, singlecomponent, elastic, crystalline solids: SWNTs,” Phil. Mag. Vol. 85, 2249-80. 4. Chen, C.-C, Bisrat, Y., Luo, Z.P., Schaak, R.E., Chao, C.-G, Lagoudas, D.C., 2006, Fabrication of single crystal tin nanowires by hydraulic pressure injection,” Nanotech., 17, 367-374. 5. Seidel, G.D. And Lagoudas, D.C., 2006, “Micromechanical Analysis of the Effective Elastic Properties of Carbon Nanotube Reinforced Composites,” Mech. of Mater., 38,884-907.

MICHAEL A. BEVAN Professional Preparation Lehigh University, Chemical Engineering, B.S., 1994. Lehigh University, Chemistry, B.S., 1994. Carnegie Mellon University, Chemical Engineering, Ph.D., 1999. University of Melbourne-Australia, Chemistry/Chem. Eng./Math, postdoc, 1999-2001. University of Illinois at Urbana-Champaign, Material Science/Physics, postdoc, 2001-2002. Appointments Assistant Professor of Chemical Engineering, Texas A&M University, August 2002-present. Honors/Awards 1.NSF Presidential Early Career Award for Scientists and Engineers (PECASE), 2005. 2.NSF CAREER award, Engineering Directorate, CTS Division, 2004. 3.Beckman Fellowship, national award by Arnold and Mabel Beckman Foundation, 2001. 4.Henkel Fellowship, national award by ACS Colloids & Surfaces Division, 1998. Five publications most closely related to the proposed project 1. Self-diffusion in Sub-Monolayer Colloidal Fluids Near a Wall, Anekal, S.G.; Bevan, M.A. J. Chem. Phys. Vol. 125, 034906, 2006. 2. Mapping Patterned Potential Energy Landscapes with Diffusing Colloidal Probes, Wu, H.; Everett, W.N.; Anekal, S.G.; Bevan, M.A. Langmuir Vol. 22, 6826-6836, 2006. 3. Dynamic Signature for the Equilibrium Percolation Threshold of Attractive Colloidal Fluids, Anekal, S.G.; Bahukudumbi, P.; Bevan, M.A. Phys. Rev. E Vol. 73, 020403, 2006. 4. Interpretation of Conservative Forces from Stokesian Dynamic Simulations of Interfacial and

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Confined Colloids, Anekal, S.G.; Bevan, M.A. J. Chem. Phys. Vol. 122, 034903, 2005. 5. Hindered Diffusion of Colloidal Particles Very Near to a Wall: Revisited, Bevan, M.A.; Prieve, D.C. J. Chem. Phys. Vol. 113, No. 3, pgs. 1228-1236, 2000. Five other significant publications 1. Diffusing Colloidal Probes of Protein and Synthetic Macromolecule Interactions, Everett, W.N.; Wu, H.; Anekal, S.G.; Sue, H.; Bevan, M.A. Biophys. J. Vol. 92, 1005-1013, 2007. 2. Equivalent Temperature and Specific Ion Effects in Macromolecule Coated Colloid Interactions, Fernandes, G.; Bevan, M.A. Langmuir Vol. 23, 1500-1506, 2007. 3. Role of Polydispersity in Anomalous Interactions in Electrostatically Levitated Colloidal Systems, Pangburn, T.O.; Bevan, M.A. J. Chem. Phys. Vol. 123, 174904, 2005. 4. Inverse Density Functional Theory as an Interpretive Tool for Measuring Colloid-Surface Interactions in Dense Systems, Liu, M.; Bevan, M.A.; Ford, D.M. J. Chem. Phys. Vol. 122, 224710, 2005. 5. Measurement and Interpretation of Particle-Particle and Particle-Wall Interactions in Levitated Colloidal Ensembles, Wu, H.; Pangburn, T.O.; Beckham, R.E.; Bevan, M.A. Langmuir Vol. 21, No. 22, 9879-9888, 2005. GREGORY H. HUFF, Assistant Professor Professional Preparation University of Illinois, Electrical Engineering, B.S., 2000 University of Illinois, Electrical Engineering, Applied Electromagnetics, M.S., 2003 University of Illinois, Electrical Engineering, Applied Electromagnetics, Ph.D., 2006 Appointments and Positions Texas A&M University NASA-GRC (LERCIP)

2006 – present 2005 (summer)

Awards IEEE H. A. Wheeler Applications Paper Award (2004) Listed below are references relevant to the work on this project. 1. G. H. Huff, J. Feng, S. Zhang, and J. T. Bernhard, “Directional reconfigurable antennas on laptop computers: Simulation, measurement and evaluation of Candidate Integration Positions,” IEEE Transactions on Antennas and Propagation, vol. 52, pp 3220 – 3227, Dec. 2004. 2. G. H. Huff and J. T. Bernhard, “Integration of packaged RF MEMS switches with radiation pattern reconfigurable square spiral microstrip antennas,” IEEE Transactions on Antennas and Propagation, vol. 54, Part 1, pp. 464 – 469, Feb. 2006. 3. G. H. Huff, et al., “Modeling of Ferroelectric thin films and materials for microwave devices and antennas,” Proc. 2005 IEEE/URSI International Symposium on Antennas and Propagation, Washington, DC, July 2005, vol. URSI, p. 178.

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4. T. L. Roach, G. H. Huff, J. T. Bernhard, “A comparative study of diversity gain and spatial coverage: Fixed versus reconfigurable antennas for portable devices,” Microwave and Optical Technology Letters, vol. 49, pp. 335 – 339, March 2007. 5. G. H. Huff and J. T. Bernhard, “Electromechanical beam steering of a trough waveguide antenna using cantilever perturbations,” Proc. 2005 Antenna Applications Symposium, Allerton Park, Monticello, IL, Sept. 2005, pp. 152 – 165. 6. G. H. Huff, K. Heiptas, and J. T. Bernhard, “Reconfigurable microstrip antennas in phased arrays: performance and potential,” Proc. 2004 PIERS, Nanjing, China, August 2004, p. 92. 7. G. H. Huff, T. L Roach, and J. T. Bernhard, “Conformal integration of broadside to endfire radiation reconfigurable antennas onto canonical structures,” Proc. 2004 IEEE/URSI International Symposium on Antennas and Propagation, Monterrey, CA, July 2004, vol. URSI, p. 178. 8. K. Hietpas, G. H. Huff and J. T. Bernhard, “Investigation of phased array beam steering using reconfigurable antennas,” 2004 IASTED International Conference on Antennas, Radar and Wave Propagation, Banff, Canada, July 2004, pp. 68 – 71.

ZOUBEIDA OUNAIES ACADEMIC PREPARATION The Pennsylvania State University, Mechanical Engineering, B.S. (1989) The Pennsylvania State University, Mechanical Engineering, M.S. (1991) The Pennsylvania State University, Engineering Sc. and Mech., Ph.D. (1996) PROFESSIONAL APPOINTMENTS January 2005 Assistant Professor, Aerospace Engineering and Materials Science and Engineering, Texas A&M University, College Station, TX. 2002-2004 Assistant Professor, Mechanical Engineering, Virginia Commonwealth University, Richmond, VA. 1999.2001 Senior Staff Scientist, Advanced Materials and Processing, ICASE, NASA LaRC, Hampton, VA. RESEARCH INTERESTS Active materials and nanocomposites; Coupling mechanical-electrical-chemical phenomena in polymeric materials; Electrical and dielectric properties of polymers and polymer composites; Processing and characterization of electroactive nanocomposites for sensing/actuation in aerospace and biomedical applications. Ounaies, Z., Park, C., Lillehei, P., and Harrison, J., “Dielectric, Piezoelectric and Mechanical Characterization of SWNT-Polyimide Composites”, accepted in Journal of Thermoplastic Composite Materials, Special Issue on Nanocomposites I. Kim J., Yun S.*, and Ounaies Z.,”Discovery of cellulose as a smart material”, Macromolecules, 39, no. 12, pp.4202-4206, 2006.

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Yun S.*, Kim J., and Ounaies Z., “Single-walled carbon nanotube/polyaniline coated cellulose based electro-active paper (EAPap) as hybrid actuator”, Smart Materials & Structures, 15, no. 3, pp. N61-N65, 2006. Park, C., Ounaies, Z., Wise, K., and Harrison, J., “In Situ Poling and Imidization of Amorphous Piezoelectric Polyimides”, Polymer, Volume 45, Issue 16, pp. 5417-5425, 2004. Ounaies, Z., Park, C., Wise, K., Siochi, E. and Harrison, J., “Electrical Properties of Single Wall Carbon Nanotube Reinforced Polyimide Composites”, Composites science and technology, 63, no. 11, pp.1637-1646, 2003. Park, C., Ounaies, Z., Watson A., Crooks, R., Smith Jr, J., Lowther, S., Connell, J., Siochi, E., Harrison, J., and St.Clair, T., “Dispersion of Single Wall Carbon Nanotubes by In-Situ Polymerization Under Sonication”, Chemical Physics Letters, 364 (3-4) pp. 303-308 (2002).

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7. Current and Pending Support DIMITRIS LAGOUDAS

CURRENT SUPPORT Nanotechnology and Materials Systems, NSF - REU Site, Co-PI, $250,000, 3/1/05 – 2/28/08, 0.0 mo/year New Mathematical Tools for Next Generation Materials, NSF-IGERT, Co-PI, $ 2,817299.00, 06/01/06 – 05/30/11, 1 mo/year. Thermo-Mechanically Enhanced Interfaces with Multifunctional Nanoparticles, NSF, PI, $347,131, 09/01/06 – 08/31/09, 1 mo/year. Magnetic Field-Induced Phase Transformation in Magnetic Shape Memory Alloys with High Actuation Stress and Work Output, ARO, Co-PI, $368,047, 07/19/06 – 12/31/07, 1 mo/year. Microfluidic Systems for Reconfigurable RF Surfaces and Systems, DARPA, Co-PI, 10/01/06 - 06/30/07, 1 mo/year. Thermomechanical Processing and Modelling of High Temperature SMAs for Multifunctional Engine Components, NASA, co-PI, $580,765, 12/01/06 – 11/30/09, 1 mo/year. Multi-Scale-Modeling and Characterization of Carbon Nanotube Reinforce Multi Functional Composites as New Lightweight, Durable Materials for Improved Subsonic, Fixed-Wing Vehicle Performance, NASA, PI, $562,403, 01/22/07 – 21/01/10, 1 mo/year. Thermomechancial Fatigue Characterization and Finite Element Analysis of 60-NiTi SMAs, Boeing, PI, $29,858, 01/07 – 05/07, 0 mo/year. Shape Memory Alloy for Vibration Isolation and Damping of Large-Scale Space Structures, AFOSR, PI, $158,320, 01//01/07 – 05/30/07, 1 mo/year. PENDING Novel Manufacturing and Modeling Approaches for Multi-Scale Monolithic and Hybrid Phase Transforming, NSF NIRT, Co-PI, $1,400,000, 05/01/07 – 04/0/11, 1 mo/year. Toward the Design of Bio-Inspired Micro Aerial Vehicles, AFOSR, Co-PI, 05/01/07 – 04/30/11, 1 mo/year. MICHAEL A. BEVAN CURRENT SUPPORT Microfluidic Systems for Reconfigurable RF Surfaces and Systems, DARPA, Co-PI, 10/01/06-06/30/07, 1 mo/year. Diffusing Colloidal Probes of Protein and Synthetic Macromolecule Interactions, Co-PI, NSF, $100,000, 08/01/06-07/31/08, 0 mo/year. Ensembles of Levitated Diffusing Colloids as Novel Biomolecular Probes, The Robert A. Welch Foundation, PI, $150,000, 06/01/04 – 05/31/07, 1 mo/year. CAREER: Direct Measurement and Manipulation of Colloidal Interactions and Dynamics in Template Directed Photonic Crystal Assembly, NSF, PI, $400,000, 02/01/04 – 01/31/09, 1 mo/year.

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PENDING Collaborative Research: Microfluidic Chaotic Mixing in Complex Fluids, NSF, PI, $230,000, 01/01/08-12/31/10, 1 mo/year. Diffusing Colloidal Probes of Protein-Protein Potentials of Mean Force on Arrays, The Robert A. Welch Foundation, PI, $150,000, 06/01/07 – 05/31/10, 1 mo/year. Multi-Dimensional Interfacial Colloidal Crystallization, ACS Petroleum Research Fund (type AC), PI, $135,000, 07/01/07-08/31/10, 1 mo/year. NER: Nanoparticles as Active Surface Probes: Models and Experiments to Develop Diffusing Colloidal Probe Microscopy, NSF (University of Massachusetts, Amherst), CoPI, $130,000, 07/01/07-06/30/08, 1 mo/year. NIRT: Development of Approaches for the Hierarchal Assembly of Active Nanostructures for Optical and Electronic Device Applications, NSF (Texas Tech University), Co-PI, $1,250,000, 07/01/07-06/30/11, 0.5 mo/year. ZOUBEIDA OUNAIES CURRENT SUPPORT Collaborative Research: Multifunctional Performance of Carbon Nanotube-Polymer Composites, NSF, PI, $150,828, 1/05-9/07, 1.0 mo/year. Graduate Student Support, Texas Institute for Intelligent Bio-Nano Materials and Structures (TiiMS), PI, $40,000, 1/05-present, 0.0 mo/year. Active Nanocomposites, AFOSR, PI, $390,000, 6/06-5/09, 0.0 mo/year. Nanostructured Electroactive Composites, NASA LaRC, PI, $90,000, 9/05-9/07, 1.0 mo/year Microfluidic Systems for Reconfigurable RF Surfaces and Systems, Toyon Research Corporation/DARPA, co-PI, $200,000, 10/06-6/07, 1.0 mo/year Reversible Control of Anisotropic Electrical Conductivity Using Colloidal Microfluidic Networks, DARPA, co-PI, $100,000, 11/05-12/06, 0.5 mo/year Active Nanocomposites: Development of Sensors and Actuators for Future Aerospace Applications, Texas Space Grant Consortium, PI, $10,000, 10/06-6/07, 0.5 mo/year CAREER: Development of “Smart” Structural Polymer-Nanocomposites based on Interfacial Coupling and Local Field Enhancement, NSF, $400,000, 5 years PENDING NIRT: Active Electromechanical Nanostructures Without the Use of Piezoelectric Constituents, NSF, 1.425M, 3 years

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