tets for powering implantable biomedical devices t. dissanayake, d. budgett, a.p. hu, s. malpas and...
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![Page 1: TETS for Powering Implantable Biomedical Devices T. Dissanayake, D. Budgett, A.P. Hu, S. Malpas and L. Bennet](https://reader030.vdocuments.mx/reader030/viewer/2022032521/56649d575503460f94a35a4a/html5/thumbnails/1.jpg)
TETS for Powering Implantable Biomedical Devices
T. Dissanayake, D. Budgett, A.P. Hu, S. Malpas and L. Bennet
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Problems
• Coupling between internal and external components may vary according to orientation and posture
• Insufficient power -- implanted device won’t operate
– Charge an implanted battery
• Excess power – dissipated heat can cause tissue damage
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Power Regulation
• External– Preferred– Used in this design
• Internal• Heat dissipation
issue• Increased size • Increased weight
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Methods of Control• Magnitude Control
– Input voltage is varied to vary power delivered to the load
• Most common• Problem: mismatch of
resonant freq. of the sec. resonant tank and operating freq. of the external power converter
• Result: miss-match in freq. reduces power transferred– Increases Vin required– Decreases system efficiency
• Frequency Control• Operating freq. is varied
to vary power delivered• Tune/detune the secondary
pick-up• Effective power
delivered is regulated• RF link used to provide
wireless feedback from implanted circuit to external freq. controller
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TETS System Architecture
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nRF24E1 Nordic Transceivers• Detect DC output voltage
and transmit to the external transceiver
• The external transceiver processes the data and adjusts the duty cycle of the output PWM signal in order to vary the reference voltage
• Response time: 360 ms
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TETS Design
• Internal coil and the resonant capacitor were Parylene coated and encapsulated with medical grade silicon
• Implanted total weight: < 100 grams• Secondary coil held on sheep using three
loosely tied strings• Displacement– Axial: up to 10 mm– Horizontal: 10 – 20 mm– Power delivered: 5 – 25W (experiment: 10 W)
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In Vivo Sheep Testing:
ΔT = 3.8°CTmax = 38.4°CTest Time:24 hours
Experimental ResultsP = 10W; V = 23.5V; I = 0.425A
Freq. = 163 – 173 KHz
Thermistorsmeasure ΔT
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ASAIO Journal (1994, vol. 40)Adaptation of Tissue to a Chronic Heat Load
• Implanted constant heat flux devices into calves next to lung and muscle tissue– 0.04 W/cm2; 0.06 W/cm2; 0.08 W/cm2
• Initial:– ΔT = 6.4±0.6°C; 4.5±0.2°C; 1.8±0.2°C
• After 7 weeks: – ΔT = 3.7±1.2°C; 2.8±0.1°C; 0.8±0.1°C
• Adaptive response of the tissue to increase heat dissipation through angiogenesis (development of new blood vessels)
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nRF24E1-REELCost: $5nRF24E1-EVKITCost: $419
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Transceiver EVKIT Features
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There are mainly two types of TET transformers:1.Iron –core Upside: Little flux leakage
No radial or axial misalignmentNo magnetic flux cross-coupling by the nearby conductor
Downside: Difficulty in implantation
2.Air – coreUpside: Easy to implantationDownside: Some flux leakage
Radial or axial misalignment leads to decreased efficiency even no power output
Magnetic flux cross-coupling by the nearby conductor
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N N
NN
S S
S S
Proposed: Air core transformer to easy implantation,
Suggestion: can we put button magnets inside wound coils circle to realize self-alignment of primary and secondary coils both radially or axially?The coils center is filled with polyurethane which also wraps the button magnets inside
skin
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skin
DC/AC Converter
Primary CoilsSecondary Coils
RectifierBattery
Charging Circuit
Battery
Outside Body Inside Body
AMB AmplifierMotor ControllerHESA
Heart Pump
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Further
• Current power of the pump needed: 20 W?• What kind of coil to use? How do we choose
one? Material?• What electronics needed to make the
transceiver work? Difference b/w REEL and KIT.
• Which components can be bought, which have to be designed?