Battery-Free Love-Wave-Based Neural Probe and Its Wireless Characterizations

Abstract

A wireless Love-wave-based neural probe that utilizes a one-port reflective delay line was developed for both reading and stimulating neurons in the brain. Poly(methyl methacrylate) (PMMA) as a waveguide layer and gold (Au) electrodes were structured on the top of a 41° YX LiNbO3 piezoelectric substrate, following the parameters extracted from coupling-of-mode (COM) modeling. For a one-port reflective delay line, single-phase unidirectional transducers (SPUDTs) and three shorted grating reflectors were employed, which made possible the implementation of a wireless and battery-free neural probe. The fabricated Love-wave-based neural probes were wirelessly measured using two antennas with a 440 MHz central frequency and a network analyzer. Sharp reflection peaks with a high signal-to-noise ratio were observed from the reflection peaks. The probe was immersed in 0.9% saline solution while applying input DC voltages. Good linearity, high sensitivity, and reproducibility were observed depending on DC applied voltage, in the range from 0 to 500 mV. The sensitivity obtained from the DC firings (artificial neural firings) was ∼0.04 µs/VDC, indicating that this prototype probe is very promising for the wireless reading and stimulation of neural firings in in vivo animal testing.

Wireless neural probes based on one-port SAW delay line and neural firing-dependent varicap diode

“…For further decrease in the insertion loss, the single phase unidirectional transducer (SPUDT) configuration can be considered as an another alternative because the SPUDT deters bidirectional acoustic radiations and directs all acoustic waves to flow to only one direction toward the shorted-grating reflector and split-type reflectors, thus minimizing the insertion loss. But in our previous effort for SPUDT configuration, difficulties in minimizing the fabrication errors and in impedance matching were additional concerns owing to smaller pitch size in SPUDT and larger capacitance [18].…”

“…2). The propagating SH wave is partially reflected by split-type reflectors, reconverted into EM waves by IDTs, and then the EM energy is transmitted to the network analyzer through the antenna [15][16][17][18][19]. The varicap diode interconnected with sharp metal tips via opamp was electrically linked to split-type reflectors on one-port SAW reflective delay line for neural firing detection.…”

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

“…[23][24][25] The COM modeling is an efficient and widely used method of simulating diverse types of SAW devices. [13][14][15][16][17]26) All the device parameters affecting the results were taken into account, which include a bidirectional IDT structure with open-circuit grating reflectors, the reflection effect from the edge of the probe sidelines, and the impedance variation effect due to the PVDF-TrFE ferroelectric capacitive electrode connected to the IDT-type reflector. The mixed P-matrix and FFT program were used for obtaining the reflection coefficient S 11 in the time domain.…”

“…The propagating SH wave is partially reflected by IDT-type reflectors, reconverted into EM waves by IDTs, and transmitted to the network analyzer through the antenna. [13][14][15][16][17] The copolymer poly(vinylidene-fluoride-trifluoroethylene) (PVDF-TrFE) ferroelectric capacitive electrodes were connected to IDT-type reflectors on the one-port SAW reflective delay line for neural firing detection. Any electrical firings will change the capacitance at the capacitive electrodes, resulting in changes in reflection peaks at the measurement system.…”

Development of wireless, chipless neural stimulator by using one-port surface acoustic wave delay line and diode–capacitor interface

“…However, these wired neural probes have many issues such as signal attenuation and distortion and noise addition while passing a long wired cable, sanitation concerns due to the manual operation of chips, frequent battery replacement, and a limited activity scope of a training animal owing to the use of wired cables, which cause stress to the animal. [10][11][12][13][14][15][16][17][18][19][20] To solve these issues, a wireless neural probe system has been suggested. With the introduction of wireless neural probes, the abovementioned problems were to some extent resolved, but there are still many issues to be solved, which include the heaviness of chips mounted on the animal's cortex surface, signal distortion, and noise synthesis through wireless electronic circuits consisting of thousands of transistors, and installation of a battery with a finite lifetime to operate the wireless electronic circuits and the probe.…”