Traditionally, implants are powered by batteries, which have to be recharged by an inductive power link. In the recent years, ultrasonic power links are being investigated, promising more available power for deeply implanted miniaturized devices. These implants often need to transfer back information. For ultrasonically powered implants, this is usually achieved with on-off keying (OOK) based on backscatter modulation, or active driving of a secondary transducer. In this article, we propose to superimpose subcarriers, effectively leveraging frequency-shift keying (FSK), which increases the robustness of the link against interference and fading. It also allows for simultaneous powering and communication, and inherently provides the possibility of frequency domain multiplexing for implant networks. The modulation scheme can be implemented in miniaturized application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and microcontrollers. We have validated this modulation scheme in a water tank during continuous ultrasound and movement. We achieved symbol rates of up to 104 kBd, and were able to transfer data through 20 cm of water and through a 5 cm tissue phantom with additional misalignment and during movements. This approach could provide a robust uplink for miniaturized implants that are located deep inside the body and need continuous ultrasonic powering.

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Implantable devices need to communicate information to the outside world. For deep-seated miniaturized implants ultrasound communication can be favourable. However, implants need to operate during movement, and the selected communication scheme should be assessed accordingly. In this work, we implemented a simple protocol to transfer data packets based on On-Off-Keying (OOK) and Frequency-Shift-Keying (FSK) by backscatter modulation in ultrasonic communication links for deep implants.We then used it to compare FSK vs OOK encoding regarding the bit error rate during continuous ultrasound power transfer, and while moving, in a water tank setup. Our experiment shows, that sub-millimeter movements can have severe effects on OOK communication, but not for FKS. Therefore, FSK can allow for backscatter communication from deep implants regardless of their position and involved movements. The protocol can also be adapted to other backscatter modulation schemes in the future. @en

Recording neuronal activity triggered by electrical impulses is a powerful tool in neuroscience research and neural engineering. It is often applied in acute electrophysiological experimental settings to record compound nerve action potentials. However, the elicited neural response is often distorted by electrical stimulus artifacts, complicating subsequent analysis. In this work, we present a model to better understand the effect of the selected amplifier configuration and the location of the ground electrode in a practical electrophysiological nerve setup. Simulation results show that the stimulus artifact can be reduced by more than an order of magnitude if the placement of the ground electrode, its impedance, and the amplifier configuration are optimized. We experimentally demonstrate the effects in three different settings, in-vivo and in-vitro.@en

Safety is a critical consideration when designing an electrical neural stimulator, given the direct contact with neural tissue. This paper presents the design of a charge balancing system suitable for frequencies up to the kilohertz domain, to be used as an add-on system for stimulators over a wide range of frequencies, also covering nerve conduction blocking. It operates independently of the stimulator timing by continuously sensing the offset voltage, and applying a corrective current to the electrode, using the offset compensation technique. To ensure its stand-alone capability, the system is battery-powered, and includes a safety and start-up circuit. Electrical measurements verified the functionality of the circuit, demonstrating a residual offset of only 0.7 mV for 1 V biphasic pulses at 50 kHz. When tested for 20 kHz biphasic pulse at a 5 V amplitude, the offset was measured at -11.6 mV, which is still within the (commonly used) ±50 mV safety window.@en