Ultrasound refers to waves with a frequency of 20Khz or higher, which has a characteristic of penetrating water. It is widely used in the medical field. The most representative use of ultrasound in the medical field is an ultrasound imaging apparatus using transmission and reflection of ultrasound. It is a device that obtains a cross-sectional image of the human body by visualizing the time and intensity of the reflected ultrasound while passing through the inside of the human body and passing through each organ.

A shock wave is generated when air is compressed in a very short time or when an object such as a bullet moves through the air at the speed of sound or faster than an aircraft. The pressure wave in the gas is usually transmitted at a constant speed such as sound in both the compressed part and the expanded part, but when the pressure changes rapidly, the expanded part changes gradually while the compression part changes abruptly, and the waveform is distorted. As the wave passes, a sudden increase in pressure, density, or velocity is felt. In electrical engineering, an impulse voltage, or current, is also called a shock wave. The impulse current, or voltage, refers to the generation of very high energy for a very short time.