A novel structure for chronically implantable cortical electrodes using polyimide bio-polymer was devised, which provides both flexibility for micro-motion compliance between brain tissues and the skull and at the brain/implant interface and stiffness for better surgical handling. A 5–10 µm thick silicon backbone layer was attached to the tip of the electrode to enhance the structural stiffness. This stiff segment was then followed by a 1 mm flexible segment without a silicon backbone layer. The fabricated implants have tri-shanks with five recording sites (20 µm × 20 µm) and two vias of 40 µm × 40 µm on each shank. In vitro cytotoxicity tests of prototype implants revealed no adverse toxic effects on cells. Bench test impedance values were assessed, resulting in an average impedance value of ∼2 MΩ at 1 KHz. For a 5 µm thick silicon backbone electrode, the stiffness of polyimide-based electrodes was increased ten times over that of electrodes without the silicon backbone layer. Furthermore, polyimide-based electrodes with 5 µm and 10 µm thick silicon backbone layer penetrated pia of rat brain without buckling that has been observed in implants without silicon reinforcement.

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.

We have developed acoustic-optic (AO) based display units for implementing a handheld hologram display by modulating light deflection through wide bandwidth surface acoustic wave (SAW). The developed AO device consists of a metal layer, a ZnS waveguide layer, SAW inter digital transducers (IDTs), and a screen for display. When RF power with a particular resonant frequency was applied to IDTs, SAW was radiated and interfered with confined beam propagating along ZnS waveguide layer. The AO interacted beam was deflected laterally toward a certain direction depending on Bragg diffraction condition, exited out of the waveguide layer and then directed to the viewing screen placed at a certain distance from the device to form a single pixel. The deflected angles was adjusted by modulating the center frequency of the SAW IDT (SAW grating), the RF power of SAW, and the angles between propagating light beam path along waveguide and radiating SAW. The diffraction efficiency was also characterized in terms of waveguide thickness, SAW RF input power, and aperture length. Coupling of mode (COM) modeling was fulfilled to find optimal device parameters prior to fabrication. All the parameters affecting the deflection angle and efficiency to form a pixel for a three-dimensional (3D) hologram image were characterized and then discussed.

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