A Sub-mm³ Ultrasonic Free-Floating Implant for Multi-Mote Neural Recording

Abstract

A 0.8 mm 3 wireless, ultrasonically powered, freefloating neural recording implant is presented. The device is comprised only of a 0.25 mm 2 recording IC and a single piezoceramic resonator that is used for both power harvesting and data transmission. Uplink data transmission is performed by analog amplitude modulation of the ultrasound echo. Using a 1.78 MHz main carrier, >35 kbps/mote equivalent uplink data rate is achieved. A technique to linearize the echo amplitude modulation is introduced, resulting in <1.2% static nonlinearity of the received signal over a ±10 mV input range. The IC dissipates 37.7 µW, while the neural recording front-end consumes 4 µW and achieves a noise floor of 5.3 µVrms in a 5 kHz bandwidth. This work improves sub-mm recording mote depth by >2.5x, resulting in the highest measured depth/volume ratio by ∼3x. Orthogonal subcarrier modulation enables simultaneous operation of multiple implants, using a single-element ultrasound external transducer. Dual-mote simultaneous power up and data transmission is demonstrated at a rate of 7 kS/s at the depth of 50 mm.

Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review

“…In recent years, thanks to the wireless power engineering, significant advancements have been achieved by integrating wireless methodologies to enable chronic in vivo implantable neural device in freely moving animals. Ultrasonic or induction based power supplies for signal and/or power communication [88], [133]- [136] are some of the most commonly used techniques for wireless interface. Integrating these wireless implantable devices with multichannel and/or optofluidic channel, while challenging, may enable simultaneous neural recording and stimulation or drug delivery.…”

“…Among others, Maharbiz et al studied the ultrasound based wireless neural implants as evidenced through their Neural Dust [144] and Stim Dust [145]. In one of the most recent studies [133], they developed a 0.8 mm 3 ultrasonically powered miniaturized wireless neural implant. The size of the recording IC is 0.25 mm 2 only and for both power and data transmission a single piezoceramic resonator was used, as pictured in Fig.…”

Fabrication of Injectable Micro-Scale Opto- Electronically Transduced Electrodes (MOTEs) for Physiological Monitoring

“…Therefore, recent efforts have focused on building micro-scale, tetherless implants. While microscale RF [6]- [8] and ultrasonic [9]- [11] systems have shown promise, their transduction mechanisms make scaling below a millimeter challenging. On the other extreme, optical imaging based on calcium/ voltage sensitive dyes/proteins allows noninvasive imaging at cell-scale resolution [1].…”

Injectable Nanoelectrodes Enable Wireless Deep Brain Stimulation of Native Tissue in Freely Moving Mice

“…A key challenge of such devices is powering, and wired-in powering can require that patients undergo surgical battery changes, every 3-5 years in the case of DBS devices (4). Instead, neural devices that are remotely powered have emerged using magnetic induction (5), opto-electric signaling (6)(7)(8), acoustic powering of piezoelectric materials (9)(10)(11)(12)(13)(14), magnetic heating (15), piezoelectric powering of LEDs (16,17), or magnetoelectric materials (18), instead of a wired-in battery.…”

“…Remotely powered devices using magnetic induction (5), or opto-electric signaling (6,7) thus far are limited in their tissue penetration depth, maximally reaching 1 cm and 6 mm, respectively (19). Ultrasound-powered piezoelectric devices are perhaps the most promising of these technologies, recently showing recording at multiple sites through 5 cm of tissue phantom material with a submm 3 device (10). Modulation with piezoelectric devices, however, has currently only been demonstrated in the peripheral nervous system using millimeter-scale devices, or in vitro (12)(13)(14).…”