Interest
Proportion of Hacker News items mentioning "ultrasound" over time.
Mentions
Total number of Hacker News items mentioning "ultrasound" over time.
Ultrasound is sound with frequencies greater than 20 kilohertz. This frequency is the approximate upper audible limit of human hearing in healthy young adults. The physical principles of acoustic waves apply to any frequency range, including ultrasound. Ultrasonic devices operate with frequencies from 20 kHz up to several gigahertz. Read more on Wikipedia