A Sub-Millimeter Lateral Resolution Ultrasonic Beamforming System for Brain Stimulation in Behaving Animals

In this paper, we present a second-generation wireless ultrasonic beamforming system, aiming for a truly wearable device for brain stimulation in small behaving animals. The fully-integrated, battery-operated system enables a self- contained untethered system. The system is partitioned into two parts for weight distribution: (1) a 1D capacitive micromachined transducer (CMUT) array on a separate head-mountable flexible printed circuit board (PCB), (2) a rigid back-mountable PCB including electronics such as a custom ASIC, a power management unit, a wireless module, and a battery. The newly developed ASIC not only enables a compact electronic system (30.5 mm x 63.5 mm) but also generates 3.4 times higher acoustic pressure (1.89 MPa_PP), which corresponds to a spatial-peak pulse-average intensity (I_SPPA) of 33.5 W/cm², at a depth of 5 mm, compared to the first-generation ASIC. The full width at half maximum (FWHM) of the pressure is estimated to be 0.6 mm, achieving a sub-millimeter lateral resolution by using 5-MHz focused waves.