Ultrasonic transducers for navigation

Abstract

Free space ultrasonic ranging is attractive for applications such as gesture recognition and robotic navigation. Unlike optical ranging technologies, ultrasound based solutions are insensitive to ambient illumination and can therefore be used in- and outdoors. Using time-of-flight, ultrasound rangers work over distances of up to a few meters and achieve sub-mm resolution. Using arrays, objects can be localized in three dimensions. Transducers consist of 400μm Aluminum-Nitride membranes sandwiched between actuation electrodes batch fabricated on Silicon wafers. Unlike capacitive transducers which require actuation voltages in excess of 100V, piezoelectric devices are compatible with low-voltage actuation. At the 200kHz resonance frequency, the wavelength at atmospheric pressure is 2mm, ideal for compact arrays. The transducers do not dissipate static power and are therefore ideal for battery powered applications. Energy consumption is dominated by the low-noise readout amplifier and is on the order of 1μJ per channel including analog-digital conversion and signal processing, enabling video-rate object tacking at less than 1mW power dissipation. A prototype system consisting of seven transducers on a 1mm grid operates up to a 750mm range and ±35o angle span with ±3.5mm accuracy and ±3o worst case angle error.