We report the development of a novel multi-tier interface which enables the wireless, noninvasive transfer of sufficient amounts of power as well as the collection and transmission of data from low-power, deeply implantable analog sensors. The interface consists of an inductive coupling subsystem and an ultrasonic subsystem. The designed and experimentally verified inductive subsystem ensures that 5 W of power is transferred across 10 mm of air gap between a single pair of PCB spiral coils with an efficiency of 83% using our prototype CMOS logic gate-based driver circuit. The implemented ultrasonic subsystem, based on ultrasonic PZT ceramic discs driven in their low-frequency, radial/planar-excitation mode, further ensures that 29 μW of power is delivered 70 mm deeper inside a homogenous liquid environment-with no acoustic matching layer employed-with an efficiency of 1%. Overall system power consumption is 2.3 W. The implant is intermittently powered every 800 msec; charging a capacitor which provides sufficient power for a duration of ~ 18 msec; sufficient for an implant μC operating at a frequency of 500 KHz to transmit a nibble (4 bits) of digitized sensed data.

This paper reports experimental results that are used to compare operation characteristics of lead zirconate titanate (PZT) piezoelectric ceramic discs operated in the radial mode. The devices are driven to radially vibrate at their lowest fundamental resonant frequency and thus transmit and receive power when immersed in a liquid phantom. A number of 1 mm × 10 mm (thickness × diameter) PZT discs are characterized experimentally within a propagation tank and results discussed. On the basis of these measured characteristics, a novel application is developed and reported for the first time. This consists of a tuned LC resonator circuit which is used at the receiving disc to maximize sensitivity as well as a Seiko start-up IC S-882Z which is employed to charge a capacitor that drives a PIC microcontroller (μC) once the voltage exceeds 2 V DC. We show that a mean input power of 486 mW RMS results in 976 μW RMS received over a range of 80 mm and that this is sufficient to periodically (every 60 s) power the μC to directly drive a red LED for 5 ms with a current of 4.8 mA/flash. This approach is suitable for low-power, periodically activated analogue bio-implant applications.

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Abstract-This paper describes a mixed signal subsystem for the inductive transfer of power and data to a fully-implantable medical device. The design includes circuits for the inductive power recovery and energy storage (charging), in addition to data recovery and demodulation. The data link is used to upload (at a data rate of up to 180Kbps) calibration and configuration data to the implanted device and integrates both error detection and correction on the recovered bitstream. The system incorporates an implanted Li-Ion micro-battery with supporting charging hardware to provide an uninterrupted power supply for autonomous deployment. This is to provide continuous operation without the requirement for an externally worn unit and additionally ensures registry (i.e. patient calibration) settings are maintained. The circuit has been implemented in a commercially available 0.35µm CMOS technology without requiring high-voltage device options.