A. Above 30 kHz.
B. Below 20 KHz.
C. Over 300 kHz.
Brief Facts about Frequency of Ultar Sound Waves:
Ultrasound waves have a frequency of above 20kHz. In scientific terms “ultrasound” means all acoustic energy with a frequency that is above human hearing i.e. (20,000 hertz or 20 kilohertz). Typical diagnostic sonographic scanners operate in the frequency range of 2 to 18 megahertz, hundreds of times greater than the limit of man.