POWER EFFICIENT WIRELESS DATA LINKS FOR BIOMEDICAL IMPLANTS
Presented by:
Arun Vargis Thomas
S7-T1,
#12
CET

OVERVIEW
Biomedical implants
Relevance of power efficient implants
Technology used
Implementation
Performance
Conclusion.

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BIOMEDICAL IMPLANTS
A device fitted inside human body to check the internal conditions.
Mostly electronic.
Size kept as minimum as possible.


IMPORTANCE OF POWER- EFFICIENT IMPLANTS
Battery Life of implants is Limited.

Prevention of Tissue damage.


Wireless Links
Near field and far field links
Used to transfer power as well as Data.
Separately optimised .

A NEURAL PROSTHESIS SYSTEM
FEATURES
Inductively coupled.
A bidirectional half-duplex link.
Power consumption reduction using
IMPEDANCE MODULATION TECHNIQUE
High Uplink data rate at a low bit error rate.

IMPEDANCE MODULATION
Primary network is driven by a sinusoidal current source, iin=Iinsin(w0t).
Operated at a frequency w0 where both the source and load networks oscillate.

IMPEDANCE MODULATION

Zin=R1(1+k2Q1Q2)=R1(1+m) is the basic input impedance equation.
Digital data changes Q2 of load network during uplink.
Source voltage is amplitude shift keyed (ASK).


BLOCK DIAGRAM
Data from brain


ELECTRODES


IMPLANTED DEVICE
Wireless uplink

EXTERNAL RECEIVER
O/P ANALYSIS

UPLINK DATA WAVEFORMS
EXTERNAL TRANSCEIVER-TRANSMISSION
TX is high.
The method used is On-Off Keying.
Oscillator voltage is shifted using input data.
Inductor coupled to implant network.
All receiver circuits are turned off

INTERNAL TRANSCIEVER(IMPLANT)

IMPLANT-TRANSMISSION
TX is high.
The data is used to switch the load Q factor.
Q variation coupled to external system via inductive coupling.

IMPLANT-RECEPTION
TX is low.
Switch M2 is held at permanent off condition.
Demodulation using envelope detector.
Comparator.

DOWNLINK DATA

HOW POWER EFFICIENT??
Impedance modulation technique.


Receiver circuits are turned off during transmission.

Performance of the system

PERFORMANCE SUMMARY
Link distance: tested up to 5cm.
Resonant frequency: 25 MHz
Uplink data rate: 1Mbps-5.8Mbps(at 2cm)
Downlink data rate: 15kbps to 300kbps(at 2cm)
External power consumption: 2.5mW(uplink)/1.5mW(downlink)
Internal power consumption: 100µW(uplink)/140µW(downlink)
Bit error rate : < 10-6 for a 2 cm page link and of the order of 10-3 for a
5 cm link

CONCLUSION
Impedance Modulation makes the internal implant system extremely low power consuming.
Excellent bit error rate reduction can be achieved at page link distances upto 5 cm

REFERENCES
Soumyajit Mandal, Rahul Sarpeshkar, “Power-efficient impedance modulation wireless data links for biomedical implants.”, IEEE Trans.Biomed.Eng.,Vol.2.No.4.Dec 2008 .
Maysam Ghovanloo, Khalil Najafi, “A wideband Frequency Shift Keying Wireless Link for Inductively Powered Biomedical Implants”, IEEE Trans. Circuits and Systems.Vol.51.No.12.Dec 2004.
Michael Catryffe, Bart Harmans, Robert Tuerf, “An inductive power system with integrated Bidirectional data transmission”, Science Direct, Feb2004.

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