G Vandevoorde’s research while affiliated with KU Leuven and other places

The applicability of micro-systems, designed to contain monitoring or actuating devices is often hampered by accessibility. For systems with low power demands, the use of inductive links for wireless energy and data transfer to the remote system is a widely acknowledged solution. Design strategies that optimise towards power transfer efficiency for given geometric constraints, have been proposed. With the introduction of more power consuming components, such as small dc motors, in micro-systems, a demand was created for inductive links with high power transfer possibilities combined with a high overall efficiency. This paper describes the design considerations for such high energy inductive links. An inductive link is presented, capable of transferring 20 W of power over a distance of 1 cm with an overall efficiency of 80%. In addition, ongoing developments will be outlined, such as data-transmission and external voltage regulation.

For many years, transcutaneous energy transfer (TET) systems have been developed for energizing total artificial heart systems. Although such a basic system can be developed without too much design effort, optimization toward high power transfer efficiency forces the introduction of novel system topologies and design strategies. In addition, for medical applications, the thermal impact of a TET system on the biological tissue should be taken into account, resulting in limitations on usable coil geometries. This article presents a TET system that has been developed for a power transfer of 25 W over a distance of 1 cm with minimal dimensions of 1 x 6 x 4 cm for the external driver and 5 x 3 x 1 cm for the internal electronics. The coil geometries have a thickness of 2 mm and a diameter of 6 cm. An overall system efficiency of 80% was achieved for an internal load of 25 W.

This paper proposes a system for the detection of hip prosthesis loosening by means of a vibration analysis technique. Although this technique has been adapted before, the novelty presented here lies in the fact that the monitoring is done inside the prosthesis itself, offering better measurement results. Thus, an implantable monitoring system is required, involving low power consumption and miniaturization. Monitoring is done by a miniature, capacitive accelerometer. The monitoring system is equipped with a telemetric link, to provide data transmission from the implant to a PC, where the data are analyzed. The system is powered inductively, since it is intended for long-term implantation.

A microsystem for wireless long-term measurement of the intraocular pressure is presented. The sensing element is a novel distributed parallel-resonant inductive-capacative circuit, with a pressure-dependent resonance frequency. This circuit is based upon a twofold on-chip deposited inductor. The high Q inductor is deposited by electrodeposition of copper on a micromachined chip incorporating a pressure-sensitive diaphragm. Test structures were fabricated and characterized. Q factors of 30 at 45 MHz and inductance values of 0.4 µH are obtained for 3×3 mm2 structures.