A mm-Sized Free-Floating Wirelessly Powered Implantable Optical Stimulation Device

• Published in: IEEE transactions on biomedical circuits and systems 2019-08, Vol.13 (4), p.608-618
• Main Authors: Jia, Yaoyao, Mirbozorgi, S. Abdollah, Lee, Byunghun, Khan, Wasif, Madi, Fatma, Inan, Omer T., Weber, Arthur, Li, Wen, Ghovanloo, Maysam
• Format: Article
• Language: English
• Subjects: Action Potentials; Algorithms; Animals; Biomedical optical imaging; Brain; Capacitors; Carrier frequencies; CMOS; Coils; Computer Simulation; Electric Power Supplies; Electrodes; Energy storage; Female; Floating; Free-floating; implantable; inductive link; Instantaneous current; Light effects; Light emitting diodes; Magnetic fields; Microtechnology; mm-sized; Models, Theoretical; Neural prostheses; Neuromodulation; On-Off Keying; Optical Devices; Optical resonators; Optical sensors; optogenetic switched-capacitor based stimulation; Optogenetics; Photic Stimulation - instrumentation; Power control; Prostheses and Implants; Proto-Oncogene Proteins c-fos - metabolism; Rats, Sprague-Dawley; Sheep; Stimulated emission; Stimulation; Surgical implants; System on chip; Telemetry; Visual cortex; Wireless power transmission; Wireless Technology; μLED array
• ISSN: 1932-4545; 1940-9990
• DOI: 10.1109/TBCAS.2019.2918761

This paper presents a mm-sized, free-floating, wirelessly powered, implantable optical stimulation (FF-WIOS) device for untethered optogenetic neuromodulation. A resonator-based three-coil inductive link creates a homogeneous magnetic field that continuously delivers sufficient power (>2.7 mW) at an optimal carrier frequency of 60 MHz to the FF-WIOS in the near field without surpassing the specific absorption rate limit, regardless of the position of the FF-WIOS in a large brain area. Forward data telemetry carries stimulation parameters by on-off-keying the power carrier at a data rate of 50 kb/s to selectively activate a 4 × 4 μLED array. Load-shift-keying back telemetry controls the wireless power transmission by reporting the FF-WIOS received power level in a closed-loop power control mechanism. LEDs typically require high instantaneous power to emit sufficient light for optical stimulation. Thus, a switched-capacitor-based stimulation architecture is used as an energy storage buffer with one off-chip capacitor to receive charge directly from the inductive link and deliver it to the selected μLED at the onset of stimulation. The FF-WIOS system-on-a-chip prototype, fabricated in a 0.35-μm standard CMOS process, charges a 10-μF capacitor up to 5 V with 37% efficiency and passes instantaneous current spikes up to 10 mA in the selected μLED, creating a bright exponentially decaying flash with minimal wasted power. An in vivo experiment was conducted to verify the efficacy of the FF-WIOS by observing light-evoked local field potentials and immunostained tissue response from the primary visual cortex (V1) of two anesthetized rats.