Chipless wireless neural probes based on one-port surface acoustic wave delay line and neural-firing-dependent capacitors

A wireless, battery-free neural probe system was developed for reading neural signals in the brain using a one-port surface acoustic wave (SAW) reflective delay line, neural-firing-dependent capacitive electrodes, two antennas, and a network analyzer as a measurement unit. The one-port SAW reflective delay line supersedes the existing complex wireless transceiver system composed of a few hundreds of transistors and a heavy rechargeable battery and makes battery-free, wireless measurements possible. The multicapacitive electrodes placed on a sharp shank were electrically connected to the corresponding interdigital transducer (IDT)-type reflectors on a one-port SAW reflective delay line. Each electrode on the sharp shank was made using a copolymer poly(vinylidene–fluoride–trifluoroethylene) (PVDF–TrFE) ferroelectric material sandwiched between two metals. As electrical pulses were applied to the capacitive electrode, overall impedance perturbations between the IDT and the external capacitive electrode system were observed, resulting in amplitude changes in the reflection peaks in the time domain depending on the magnitude of the electrical pulses. Good linearity and sensitivity were observed at the amplitude variations in terms of applied electrical pulses. Coupling-of-modes (COM) modeling and impedance matching simulations were also performed to predict device performances and compare experimental results.