1Mhz ultrasonic _physical_ therapy devices are under $100, https://pmc.ncbi.nlm.nih.gov/articles/PMC3810427/ https://pmc.ncbi.nlm.nih.gov/articles/PMC3810427/ (

1Mhz ultrasonic _physical_ therapy devices are under $100, https://pmc.ncbi.nlm.nih.gov/articles/PMC3810427/ https://pmc.ncbi.nlm.nih.gov/articles/PMC3810427/ (2012) > Applications of ultrasound in medicine for therapeutic purposes have been an accepted and beneficial use of ultrasonic biological effects for many years. Low power ultrasound of about 1 MHz frequency has been widely applied since the 1950s for physical therapy.. In this overview, the Bioeffects Committee outlines the wide range of therapeutic ultrasound methods, which are in clinical use or under study, and provides general guidance for assuring therapeutic ultrasound safety.