Design and Optimization of Inductive Power Link for Biomedical Applications

Abstract

Powering biomedical devices is a major issue in the design of wearable and implantable electronics Chaimanonart et al. (2006); Chen et al. (2009); Kendir et al. (2004); Smith et al. (2002). Often, there is not space available for a battery that will last for the lifetime of the device, as batteries are limited both by total charge storage ability and number of recharge cycles Heller (2006). Replacement is often not an option, as the implant surgeries are both time consuming, require special expertise, and introduce the possibility of additional trauma to the patient. Percutaneous physical links Galbraith et al. (2007); Knutson et al. (2002) are prone to damage, because of the mismatch in material properties, scarring at the tissue interface Takura et al. (2006), and potential infections and skin irritation. In addition, these devices are difficult to keep sterile. An alternative is inductive links, which are coupled coils forming an air core transformer Hamici et al. (1996); Li et al. (2005); Liu et al. (2000); Sauer et al. (2005); Sivaprakasam et al. (2005); Theogarajan & Wyatt (2006); Wang, Liu, Sivaprakasam, Weiland & Humayun (2005). As diagrammed in Fig. 1, an inductive link consists of two components of electronics. Those located externally or physically detached from the subjects are referred as primary side electronics, e.g., external battery, power transmitter, power control units, etc. Those located under the skin (implanted electronics) or along with the subjects (wearable electronics) are referred as secondary electronics, including resonant amplifier, rectifier, regulators, and power management units. Power-transmission efficiency and system miniaturization are major design specifications to evaluate a power link. Given application related constraints, these specifications are inherently correlated and a careful trade-off analysis is required to achieve an optimal performance. This chapter is organized as follows. In Section 2, an introduction on power telemetry electronics is presented, followed by design analysis and simulation verifications. Section 3 focuses on inductor modeling, which correlates power efficiency with device size. Section 4 gives examples to quantify the achievable efficiency given design constraints. Design and Optimization of Inductive Power Link for Biomedical Applications