Ultrasonic signals are sound waves that have a frequency higher than the upper limit of human hearing, typically above 20,000 hertz (20 kHz). These signals are used in various applications, including medical imaging, where they help create images of internal body structures through techniques like ultrasound. In addition to medical uses, ultrasonic signals are employed in industrial settings for cleaning, welding, and detecting flaws in materials. They can also be used in animal communication, as some animals, like bats and dolphins, utilize ultrasonic frequencies for navigation and hunting.