Abstract
Deeply implanted biomedical devices (DIBDs) are a challenging application of wireless power transfer because of the requirement for miniaturization while minimizing patient exposure to tissue heating. This article proposes a capacitively coupled conductive power transfer method for DIBDs, which allows for the safe transfer of power into the body while using minimum implant volume. The method uses parallel insulated capacitive electrodes to couple uniform current flow into the tissue and implants. Analytical analyses are presented, which result in a two-port network that describes circuit operation. The two-port network is further simplified for typical DIBD applications where coupling to the external electrodes is low. This results in a simple circuit model of power transfer for which the parameters are easily obtained by experimental measurements. The proposed circuit model has been validated using circuit coupled finite-element analysis (COMSOL) and benchtop experiments using a tissue phantom. In addition, the safety aspect of the method has been evaluated via COMSOL simulation of the specific absorption rate for various implanted receiver dimensions and implantation depths. Finally, a completed power supply, unaffected by the implantation depth, running at 6.78 MHz, delivering 10 mW deep into the body while meeting the IEEE C95.1 basic restriction is presented.
Highlights
Active biomedical implants require power to operate
Based on the low coupling simplification and the prior work showing that tissue behaves mainly as a conductor, we propose a new model of C-TET, namely Capacitively Coupled Conductive Transcutaneous Energy Transfer (CCCTET)
The results illustrated in Fig. 17.a,b,c are obtained in COMSOL for a fully tuned system operating at the maximum power transfer point
Summary
Active biomedical implants require power to operate. The power requirement of such devices, ranging from microwatts to tens of watts [1], can either be supplied by implanted energy storage units, via percutaneous (through the skin) drive lines, or wireless power transfer. BecerraFajardo et al used high-frequency burst currents, followed by rectification to extract the envelope and deliver microstimulation of nerves This technology could be suitable for deep implantation and miniaturisation [15]. An alternative approach is to capacitively couple volume conduction power transfer by applying a dielectric coating to the external and/or implanted electrodes. This replaces the metal-electrode double-layer capacitance with capacitance formed about an insulator. Coated power electrodes can be used to prevent stimulation currents coupling to the power receiving circuitry due to their high impedance at low frequency This could prevent the loading of the stimulator, enable the use of current steering approaches [19], or enable simultaneous optimisation of stimulation/recording electrodes and volume conduction power transfer.
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