What is the smallest possible sonar detection equipment?

There are some very small ultrasonic sensors in use today for purposes like fluid sensing that are very small (<1cm) across that combine a sound source (projector) with a sensor into a small transducer. These have limited transmit power and generally a very small range. read more

The Tritech Micron Sonar is the smallest digital CHIRP sonar in the world and is ideal for use by small ROVs, as a first-rate obstacle avoidance sonar in miniature form. read more

One useful small sonar is similar in appearance to a waterproof flashlight. The head is pointed into the water, a button is pressed, and the device displays the distance to the target. Another variant is a"fishfinder" that shows a small display with shoals of fish. read more