Ultrasonic waves are those sound waves having frequency

Sound waves are classified based on their frequency relative to the human hearing range, which typically spans from 20 Hz to 20,000 Hz [t3][t5]. Ultrasonic waves, or ultrasound, are defined as mechanical sound waves with frequencies higher than the upper limit of human hearing, specifically exceeding 20,000 hertz (20 kHz) [t1][t4]. In contrast, sounds with frequencies below 20 Hz are termed infrasonic waves [t6][t8]. While humans cannot perceive ultrasonic frequencies, many animals like bats and dogs can hear them, with bats using frequencies up to 120,000 Hz for echolocation [t3]. In technology and medicine, ultrasonic waves are widely utilized for imaging (sonograms), industrial cleaning, and distance measurement due to their high frequency and short wavelength [t2][t6]. Therefore, the correct classification for ultrasonic waves is a frequency of more than 20 kilohertz.

Sources

1. [2] https://www.nps.gov/subjects/sound/understandingsound.htm
2. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC8954895/
3. [4] https://www.sciencedirect.com/topics/engineering/ultrasonic-range