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Omnidirectional Wireless Power Transfer for Millimetric Magnetoelectric Biomedical Implants

Wei Wang, Zhanghao Yu, Yiwei Zou, Joshua E Woods, Prahalad Chari, Yumin Su, Jacob T Robinson, Kaiyuan Yang

TL;DR

An omnidirectional WPT platform for millimetric bioelectronic implants, employing the emerging magnetoelectric (ME) WPT modality, and “magnetic field steering” technique based on multiple transmitter (TX) coils is presented.

Abstract

Miniature bioelectronic implants promise revolutionary therapies for cardiovascular and neurological disorders. Wireless power transfer (WPT) is a significant method for miniaturization, eliminating the need for bulky batteries in devices. Despite successful demonstrations of millimetric battery free implants in animal models, the robustness and efficiency of WPT are known to degrade significantly under misalignment incurred by body movements, respiration, heart beating, and limited control of implant orientation during surgery. This article presents an omnidirectional WPT platform for millimetric bioelectronic implants, employing the emerging magnetoelectric (ME) WPT modality, and magnetic field steering technique based on multiple transmitter (TX) coils. To accurately sense the weak coupling in a miniature implant and adaptively control the multicoil TX array in a closed loop, we develop an active echo (AE) scheme using a tiny coil on the implant. Our prototype comprises a fully integrated 14.2 mm3 implantable stimulator embedding a custom low power system on chip (SoC) powered by an ME film, a TX with a custom three channel AE RX chip, and a multicoil TX array with mutual inductance cancellation. The AE RX achieves negative 161 dBm per Hz input referred noise with 64 dB gain tuning range to reliably sense the AE signal, and offers fast polarity detection for driver control. AE simultaneously enhances the robustness, efficiency, and charging range of ME WPT. Under 90 degree rotation from the ideal position, our omnidirectional WPT system achieves 6.8x higher power transfer efficiency (PTE) than a single coil baseline. The tracking error of AE negligibly degrades the PTE by less than 2 percent from using ideal control.

Omnidirectional Wireless Power Transfer for Millimetric Magnetoelectric Biomedical Implants

TL;DR

An omnidirectional WPT platform for millimetric bioelectronic implants, employing the emerging magnetoelectric (ME) WPT modality, and “magnetic field steering” technique based on multiple transmitter (TX) coils is presented.

Abstract

Miniature bioelectronic implants promise revolutionary therapies for cardiovascular and neurological disorders. Wireless power transfer (WPT) is a significant method for miniaturization, eliminating the need for bulky batteries in devices. Despite successful demonstrations of millimetric battery free implants in animal models, the robustness and efficiency of WPT are known to degrade significantly under misalignment incurred by body movements, respiration, heart beating, and limited control of implant orientation during surgery. This article presents an omnidirectional WPT platform for millimetric bioelectronic implants, employing the emerging magnetoelectric (ME) WPT modality, and magnetic field steering technique based on multiple transmitter (TX) coils. To accurately sense the weak coupling in a miniature implant and adaptively control the multicoil TX array in a closed loop, we develop an active echo (AE) scheme using a tiny coil on the implant. Our prototype comprises a fully integrated 14.2 mm3 implantable stimulator embedding a custom low power system on chip (SoC) powered by an ME film, a TX with a custom three channel AE RX chip, and a multicoil TX array with mutual inductance cancellation. The AE RX achieves negative 161 dBm per Hz input referred noise with 64 dB gain tuning range to reliably sense the AE signal, and offers fast polarity detection for driver control. AE simultaneously enhances the robustness, efficiency, and charging range of ME WPT. Under 90 degree rotation from the ideal position, our omnidirectional WPT system achieves 6.8x higher power transfer efficiency (PTE) than a single coil baseline. The tracking error of AE negligibly degrades the PTE by less than 2 percent from using ideal control.

Paper Structure

This paper contains 18 sections, 11 equations, 27 figures, 1 table.

Table of Contents

  1. Introduction
  2. Principles of Omnidirectional WPT
  3. Multi-Coil Adaptive Power Transfer via Active Echo
  4. Mutual Inductance Cancellation in Multi-Coil TX
  5. Circuit and System Implementation
  6. System Overview
  7. AE Transmitter in the Implant SoC
  8. Multi-Channel AE Receiver (RX)
  9. Low Noise Analog Front End
  10. Peak Detector and Data Converter
  11. Polarity Detector
  12. Experimental Results
  13. Active Echo (AE) Transmitter Testing
  14. Three-Channel AE Receiver Testing
  15. Mutual Inductance Cancelled TX Coil Array
  16. ...and 3 more sections

Figures (27)

  • Figure 1: Selected applications of wirelessly powered bio-implants and the sensitivity to angular rotations of various WPT modalities burton_wireless_2020piech_wireless_2020yu_magnetoelectric_2022.
  • Figure 2: Magnetic field distribution at the implant's site when (a) turning on one TX coil, and (b) optimally configuring the two coils.
  • Figure 3: HFSS simulation setup and results of magnetic field steering: the power of TX1 is 1W, and the power of TX2 changes from 1W with the opposite current phase to 1W with the same phase.
  • Figure 4: Principle of Active Echo (AE) to enable adaptive omnidirectional magnetoelectric wireless power transfer.
  • Figure 5: Prototypes of implant: (a) Unfolded implant board with storage cap, ME film, and AE coil assembled; (b) Implant with an mm-scale plastic package and aligned ME film and AE coil; (3) Implant encapsulated with medical epoxy for cardiac pacing and neurostimulation.
  • ...and 22 more figures