Inductive and Ultrasonic Multi-Tier Interface for Low-Power, Deeply Implantable Medical Devices

Abstract

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.

Ultrasonically powered piezoelectric generators for bio-implantable sensors: Plate versus diaphragm

“…Denisov and Yeatman (2010) performed a comparison between near-field inductive and acoustic power transfer concluding that near-field inductive power transfer is more efficient for larger devices with shallower tissue depths while acoustic power transfer is more efficient for smaller devices with deeper tissue depths. Sanni et al (2012) and Seo et al (2013) proposed hybrid systems where a larger inductive power transfer system transmitted power through skin and/or bone to a smaller in vivo acoustic plate-to-plate system. It is notable that the plate diameters of interest are, for the most part, decreasing with time.…”

Short-range remote powering for long-term implanted sensor systems in freely moving small animals

“…The power harvesting using piezoelectric materials is a solution for self-powered implantable systems [3]. However, the power harvesting from vibration is sensitive 978-1-4673-4642-9/13/$31.00 ©2013 IEEE [7], [8], [9].…”

“…Therefore, the transmitter output power level increases up to a few watts. Ultrasound is a suitable option for power transfer to deeply implants in the body [8]. The power transfer efficiency of ultrasound systems is very high in the water but not in the air.…”

Design of a CMOS System-on-Chip for Passive, Near-Field Ultrasonic Energy Harvesting and Back-Telemetry

“…In addition, unlike RF transmission, which is regulated according to FCC requirements, ultrasonic power delivery and transmission is only limited by the structure's mechanical compliance. In literature, several ultrasonic telemetry systems have been reported for use in metallic structures [21]- [23] and for in vivo applications [24]. In [15]- [20], passive ultrasonic telemetry systems have also been reported that eliminate the need for batteries on the sensors.…”