Acoustic proximity sensing

An acoustic proximity sensor comprising:

• a substrate having a cavity;
• a first microphone disposed inside the cavity;
• and
• a processing system configured to receive a first signal from the first microphone and to analyze the first signal to estimate a resonant frequency of the cavity;
• wherein the processing system is further configured to use the resonant frequency to calculate a distance from the cavity to a surface.

A robot comprising:

• a base;
• a finger operably connected to the base;
• an end effector attached to the finger and incorporating a pretouch sensor, wherein the pretouch sensor comprises:
• a first microphone disposed in a cavity;
• a second microphone disposed outside of the cavity;
• and
• a processing system configured to receive a first signal from the first microphone and a second signal from the second microphone, and to use the first and second signals to estimate a resonant frequency of the cavity;
• wherein the processing system is further configured to use the resonant frequency to calculate a distance from the cavity to a surface.