Which frequency is associated with ultrasonic waves?

Ultrasound is acoustic (sound) energy in the form of waves with a frequency above the range of human hearing and thus inaudible.

Ultrasound is acoustic (sound) energy in the form of waves with frequencies above the range of human hearing. The human ear can detect a maximum frequency of approximately 20 thousand cycles per second $(20,000 \mathrm{Hz})$. This is the point at which the sonic range ends and the ultrasonic range begins. Ultrasound is used in a variety of applications including electronics, navigation, industrial, and security. It is also used in medicine to examine internal organs.
As a result, the ultrasonic frequency range exceeds $20,000 \mathrm{Hz}$.