Ultrasonic proximity sensors emit and receive sound waves. The carrier signal is a high frequency, inaudible sound wave. They detect the presence of the target object in one of two configurations.

Lots of frogs around the world use a scream to scare off predators but scientists have found frogs in the Brazilian Atlantic Forest that can scream at an ultrasonic ... but no sound came out.

Some plants emit a mournful melody using ultrasonic clicks when they become ... and a recording of 'the sound made by a dehydrated tomato' was played near one of the tomatoes.