Piezoelectric ceramics are widely used to generate ultrasonic waves. By transmitting ultrasonic waves from piezoelectric ceramics and measuring the time it takes for the reflected waves to be received by the piezoelectric ceramics, it is possible to measure the distance to an object. Ultrasonic waves propagate with little loss in water, air, and solid objects, so distances can be measured in a variety of environments. Underwater, it is used for fish detection and seabed exploration; in the air, it is used for vehicle detection, autonomous robots, and in solid objects, for a wide range of applications such as defect inspection.