A compact wireless power transfer system at 915 MHz with supercapacitor for optogenetics applications

To facilitate sophisticated optogenetics research with minimal disruption to animal's behavior, a fully wireless optical stimulator module is desirable. This paper presents a compact wireless power transfer (WPT) system for optogenetics applications that is adapted to work in implanted condition with unstable and insufficient ambient RF energy field. The scope of this work is to design and implement a power transfer system architecture that is able to: 1) work over long distance, 2) achieve high power conversion efficiency and 3) provide stable output power for sufficient time duration. The designed WPT circuit operates at 915 MHz and achieves maximum power conversion efficiency of 50% at −15 dBm input power. With a compact circuitry design (12.20 × 13.22 mm), the obtained full power transmission efficiency was 0.329% at 20 dBm (100 mW) transmission power. Ex-vivo experiments indicated that when the WPT system was located 10 cm from the source, it retrieved a maximum of 0.324 mW in free space, and 0.112 mW if inserted inside porcine cadaver meat with 4 cm of thickness. At a distance of 1 m from the source, the system retrieved 17 μW in free space, and 1 μW in porcine meat. Furthermore, to sufficiently drive the LED, an advanced supercapacitor was utilized as an energy storage element. When fully charged, the system can supply the LED over 75 s with a total power of 2.45 W. The developed WPT system can be a viable solution to be applied in optogenetic experiments on laboratory animals for preclinical studies.