Synaptics Incorporated
Movement and presence detection systems and methods using sonar

Abstract:

A method for detecting presence of a person includes emitting, by a speaker of a device, a plurality of ultrasonic ping signals, receiving, by a microphone of the device, a plurality of reflected ultrasonic ping signals, and processing the received reflected signals to determine a presence of a person within a predetermined distance of the device. The processing includes determining changes in the reflected signals relative to the emitted signals by generating an impulse response by cross-correlating the received signals and the emitted signals, averaging the cross-correlated impulse response over a set time period, and generating a detection signal by subtracting the averaged cross-correlated impulse response from an instantaneous impulse response, applying a time gating function to select a portion of the detection signal corresponding to the reflected signal from the predetermined distance from the device, and applying gain compensation to the time gated detection signal to compensate signal falloff.