Abstract-This paper reviews some popular techniques to harvest energy for implantable biosensors. For each technique, the advantages and drawbacks are discussed. Emphasis is placed on the inductive links that are able to deliver power wirelessly through the biological tissues and enable bidirectional data communication with the implanted sensors. Finally, high-frequency inductive links are described, focusing also on the power absorbed by the tissues.Index Terms-Energy harvesting, implantable biosensors, inductive powering, remote powering.

Recent advances in microelectronics and biosensors are enabling developments of innovative biochips for advanced healthcare by providing fully integrated platforms for continuous monitoring of a large set of human disease biomarkers. Continuous monitoring of several human metabolites can be addressed by using fully integrated and minimally invasive devices located in the sub-cutis, typically in the peritoneal region. This extends the techniques of continuous monitoring of glucose currently being pursued with diabetic patients. However, several issues have to be considered in order to succeed in developing fully integrated and minimally invasive implantable devices. These innovative devices require a high-degree of integration, minimal invasive surgery, long-term biocompatibility, security and privacy in data transmission, high reliability, high reproducibility, high specificity, low detection limit and high sensitivity. Recent advances in the field have already proposed possible solutions for several of these issues. The aim of the present paper is to present a broad spectrum of recent results and to propose future directions of development in order to obtain fully implantable systems for the continuous monitoring of the human metabolism in advanced healthcare applications.

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Abstract-An approach based on multi-layer spiral inductors to remotely power implantable sensors is investigated. As compared to single-layer inductors having the same area, multi-layer printed inductors enable a higher efficiency (up to 35% higher) and voltage gain (almost one order of magnitude higher). A system conceived to be embedded into a skin patch is designed to verify the performance. The system is able to transmit up to 15 mW over a distance of 6 mm and up to 1.17 mW where a 17 mm beef sirloin is placed between the inductors. Furthermore, the system performs downlink communication (up to 100 kbps) and uplink communication based on the backscattering technique (up to 66.6 kbps). Long-range communication is achieved by means of a bluetooth module.Index Terms-Energy harvesting, implantable sensors, inductive link, multi-layer spiral inductors, remote powering.

Abstract-A wearable device to power implanted sensors by means of an inductive link is presented. The system, having size 69 × 40 mm 2 , is designed to be embedded into a skin patch and located over the implantation area. The system can transfer up to 15 mW within 6 mm in air. Tested with a 17 mm thick beef sirloin placed between the inductors, the device is able to deliver up to 1.17 mW. Downlink communication with the implanted sensors is performed at 100 kbps by using amplitude modulation. Uplink communication is performed at 66.6 kbps by using load modulation. Long range communication between the system and remote devices is enabled by a bluetooth module. The system is powered by two rechargeable lithium-ion polymer batteries and has an autonomy of 10 h in stand-by mode and about 1.5 h in transmitting mode.