Ultrasonic waves have frequencies greater than what approximate value?

Ultrasonic waves are defined by their high frequency, which exceeds the upper limit of human hearing. The general threshold for these frequencies is approximately 20,000 hertz (20 kHz). Therefore, any sound wave with a frequency above this value is classified as ultrasonic. This classification is crucial in the context of nondestructive testing (NDT) as ultrasonic testing (UT) utilizes these high-frequency waves to detect flaws in materials, providing insights into their structural integrity. Frequencies higher than 20 kHz facilitate better resolution and sensitivity when inspecting materials, making them ideal for applications in testing and evaluation.