Biotelemetry

DIFFERENT TYPES OF BIO TELEMETRY SYSTEM

What is biotelemetry? Biotelemetry is an electrical measurement of

biological activities in living organism. It is used to monitor the patient who are in job

or work place and also monitor the athlete during practice to improve the performance.

ELEMENTS OF BIOTELEMETRY SYSTEM The transducer converts the biolog9ical

variable in to electrical Signal conditioner amplifies and modifies this

signal for effective transmission Transmission link connects the signal input

blocks to the read out devices by wire(or)wireless mean

Block diagram of a biotelemetry system

Design of bio-telemetry system The telemetry system should be selected to

transmit the bio-electric signals with maximum fidelity and simplicity.

The size and weight of the telemetry system

should be small.

It should have more stability and reliability The power consumption should be very small.

Radio telemetry systems  There are two types

1.single channel telemetry system 2.multichannel telemetry system • Single channel telemetry system: •

A miniature battery operated radio transmitter is connected to the electrodes of the patients

• Radio receiver which detects the radio signals and recovers the signals for further processing. • Receiving system can even be located in a room separate from the patient •

few hundred kHz to about 300mHz

Block diagram

Transmission of bio electric variables Active measurement:  bioelectric variables like ECG,EMG and EEG are measured directly with out using any excitation voltage Passive measurement:  Here the physiological variables like blood

pressure,temperature,blood flow etc are measured indirectly using transducer and excitation voltage

Tunnel diode fm transmitter

This circuit has higher fidelity an sensitivity Total weight is about 1.44gm with battery Radio frequency used - 100 to 250mhz Frequency response - 0.01hz to 20khz Input impedance - 300kilo ohms to mega ohms Temperature stability for carrier freq -0.05%/c Varactor diodes d which are voltage sensitive semi

conductor capacitors are used for freq modulation The signal is transmitted through the inductor L

Hartley type F.Mtransmitter In this circuit ,the capacitor c1 and inductor l1

form the tank circuit. Capacitor c2 are coupling capacitors T1 is the driver amplifier capacitor and T2 is the oscillating transistor. Amplitude of i/p signal varies from 10uv to several millivolts. Bandwidth of the signal is from 100hz to 1000hz.

Pulsed Hartley oscillator Pulsed Hartley oscillator for transmission of

temperature signals. To measure temperature , a thermistor is placed in the place of R1. To measure the pressure , the pressure changes should be given to move the core ‘m’ The transmitter is modulated by varying the rate of pulses of radio frequency oscillations. Continuous wave operation can be obtained by reducing the value of the resistor R1

Radio telemetry with a subcarrier When the relative position of transmitter to the body or

other conduction object changes,the carrier frequency and amplitude will change. To avoid this loading effect,the subcarrier system is needed. The signal is modulated on a subcarrier to convert the signal frequency to the neighbourhood of the subcarrier frequency. At the receiver end,the receiver detects the R.F. and recovers the subcarrier carrying the signal. All noise interference and loading effect can be separated by filters

Multiple channel telemetry system  There are two types : 1.Frequency division multiplex •

2.Time division multiplex

• Frequency division multiplex system: • Each signal is frequency modulated on a subcarrier frequency • Then these modulated subcarrier frequencies are combined to modulated

the main R.F. carrier.

 The frequency of the subcarriers has to be carefully selected to avoid

interference

 The low pass filters are used to extract the signals without any noise.

Time division multiplex telemetry system The transmission channel is connected to each

signal-channel input for a short time to sample and transmit that signal When all the channels have been scanned once a cycle is completed and the next cycle will start At the reciever end,the process is reversed If the number of scanning cycles per second is large and if the transmitter and the reciever are synchronized, the signal in each channel at the reciever side can be recovered without noticeable distortion.

Conditions The scanning frequency fn should be at least

greater than twice the maximum signal frequency fs. (i.e.)fn>2fssmax  Tn=1/fn=scanning period, and tn is the sampling time of each channel. Then the maximum channels that can be obtained is n=Tn/tn.

Problems in implant telemetry For long –term telemetry, implant telemetry is more

useful one. The whole electronic circuit is fully packed as a capsule. It is kept deep in the body to be closer to the signal source . For implement telemetry, the size and weight limitations are much serious and the reliability requirements is more critical. Body reaction: size, weight , surface condition and shave of the implant system will have effects on the body reaction. Meanwhile medical grade silastic ,teflon,glass and some metals which are used as enclosure causes like foreign body reaction on tissues.

Power supply two special types of power

supplies are used for long-term implant telemetry units along with mercury and lithium cells Environment power supply :Radio induction has been applied to transmit milliwatt of power to the telemetry unit for months. Microwatt power supply circuits using piezoelectric crystals placed on any blood vessels or aorta.