Powering Implants

Midfield Wireless Powering for Implantable Systems
Efficient wireless power transfer across tissue is highly desirable for removing bulky energy storage components. Most existing power transfer systems are conceptually based on coils linked by slowly varying magnetic fields (less than 10 MHz). These systems have many important capabilities, but are poorly suited for tiny, millimeter-scale implants where extreme asymmetry between the source and the receiver results in weak coupling. This paper first surveys the analysis of near-field power transfer and associated strategies to optimize
efficiency. It then reviews analytical models that show that significantly higher efficiencies can be obtained in the electro-magnetic midfield. The performance limits of such systems are explored through optimization of the source, and a numerical example of a cardiac implant demonstrates that millimeter-sized devices are feasible.
MEMS-based Pressure Systems

Integrated Sensing Systems, Inc. (ISSYS), an Ypsilanti, MI company, has announced that “the U.S. Patent Office has granted a patent titled “System for monitoring conduit obstruction” (U.S. Patent No. 7,211,048), which covers the design and manufacturing of a wireless implantable sensing system for non-invasive monitoring of pressure and/or pressure gradients in a cardiac conduit.”
This is certainly not the first batteryless MEMS pressure monitoring device that we’ve seen around here. The EndoSure™ Wireless AAA Pressure Measurement System from CardioMEMS, Inc. has been 510(k)’ed by the FDA two years ago. What’s different about this system is its super-miniature size, designed to fit inside the diagnostic catheter for delivery into atrium, or into palliative shunts and conduits in pediatric heart patients, or into hydrocephalus shunts.
Company explains its technology:
Certain heart defects require implantation of a cardiac blood flow conduit in order to bypass valve aplasia or severe stenosis. One of the main issues with implanted cardiac conduits is that over time calcification or stenosis will occur and, in nearly all cases, occlusion will occur eventually. ISSYS’ novel implantable wireless sensing system allows physicians a means for accurate and non-invasive monitoring of conduit condition on a continuous basis. Using the data provided by ISSYS’ sensors, physicians can continuously monitor both pressure and blood flow rate within the conduit, in order to determine whether and when conduit revision is required. Furthermore, remote monitoring of conduit condition would simultaneously reduce the number of hospital and clinic visits while increasing the overall timeliness of treatment…
The pressure monitoring system consists of two major parts: an implantable, batteryless, telemetric sensor and a companion hand-held reader. The miniature implantable micro-device, suitable for implantation directly (via a custom catheter for minimally invasive, outpatient procedure), contains a MEMS pressure sensor along with custom electronics and an antenna for both wireless communication and tele-powering.
Using magnetic telemetry, the reader transmits power to the sensor and the sensed pressure is in turn transmitted back to the reader. Small size, optimized shape, and careful choice of materials ensure implant biocompatibility and non-thrombogenicity. Furthermore, the implant is delivered with a specially designed catheter as a low-cost outpatient procedure. Data collected by the sensor will be used by physicians to tailor treatment of the selected disease.