RESUMEN

Single modality wireless power transfer has limited depth for mm-sized implants across air / tissue or skull / tissue interfaces because they either suffer from high loss in tissue (RF, Optical) or high reflection at the medium interface (Ultrasound (US)). This paper proposes an RF-US relay chip at the media interface avoiding the reflection at the boundary, and enabling efficient wireless powering to mm-sized deep implants across multiple media. The relay chip rectifies the incoming RF power through an 85.5% efficient RF inductive link (across air) using a multi-output regulating rectifier (MORR) with 81% power conversion efficiency (PCE) at 186 mW load, and transmits ultrasound using adiabatic power amplifiers (PAs) to the implant in order to minimize cascaded power loss. To adapt the US focus to implant movement or placement, beamforming was implemented using 6 channels of US PAs with 2-bit phase control (0, 90, 180, and 270°) and 3 different amplitudes (6-29, 4.5, and 1.8 V) from the MORR. The adiabatic PA contributes a 30-40% increase in efficiency over class-D and beamforming increases the efficiency by 251% at 2.5 cm over fixed focusing. The proof-of-concept powering system for a retinal implant, from an external PA on a pair of glasses to a hydrophone with 1.2 cm (air) + 2.9 cm (agar eyeball phantom in mineral oil) separation distance, had a power delivered to the load (PDL) of 946 µW. The 2.3 × 2 mm2 relay chip was fabricated in a 180 nm high-voltage (HV) BCD process.

RESUMEN

Inductive powering for implanted medical devices, such as implantable biosensors, is a safe and effective technique that allows power to be delivered to implants wirelessly, avoiding the use of transcutaneous wires or implanted batteries. Wireless powering is very sensitive to a number of link parameters, including coil distance, alignment, shape, and load conditions. The optimum drive frequency of an inductive link varies depending on the coil spacing and load. This paper presents an optimum frequency tracking (OFT) method, in which an inductive power link is driven at a frequency that is maintained at an optimum value to ensure that the link is working at resonance, and the output voltage is maximised. The method is shown to provide significant improvements in maintained secondary voltage and system efficiency for a range of loads when the link is overcoupled. The OFT method does not require the use of variable capacitors or inductors. When tested at frequencies around a nominal frequency of 5 MHz, the OFT method provides up to a twofold efficiency improvement compared to a fixed frequency drive. The system can be readily interfaced with passive implants or implantable biosensors, and lends itself to interfacing with designs such as distributed implanted sensor networks, where each implant is operating at a different frequency.

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RESUMEN

Inductive powering of implantable medical devices involves numerous factors acting on the system efficiency and safety in adversarial ways. This paper lightens up their role and identifies a procedure enabling the system design. The latter enables the problem to be decoupled into four principal steps: the frequency choice, the magnetic link optimization, the secondary circuit and then finally the primary circuit designs. The methodology has been tested for the powering system of a device requirering a power of 300mW and implanted at a distance of 15 to 30mm from the outside power source. It allowed the identification of the most critical parameters. A satisfying efficiency of 34% was reached at 21mm and tend to validate the proposed design procedure.

RESUMEN

Instrumented hip implants were proposed as a method to monitor and predict the biomechanical and thermal environment surrounding such implants. Nowadays, they are being developed as active implants with the ability to prevent failures by loosening. The generation of electric energy to power active mechanisms of instrumented hip implants remains a question. Instrumented implants cannot be implemented without effective electric power systems. This paper surveys the power supply systems of seventeen implant architectures already implanted in-vivo, namely from instrumented hip joint replacements and instrumented fracture stabilizers. Only inductive power links and batteries were used in-vivo to power the implants. The energy harvesting systems, which were already designed to power instrumented hip implants, were also analyzed focusing their potential to overcome the disadvantages of both inductive-based and battery-based power supply systems. From comparative and critical analyses of the methods to power instrumented implants, one can conclude that: inductive powering and batteries constrain the full operation of instrumented implants; motion-driven electromagnetic energy harvesting is a promising method to power instrumented passive and active hip implants.

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