3 ms·

I wonder about the health aspect of this. It seems there is very little known about long-term exposure to high intensity ultrasound. Also, there could be a ris

I wonder about the health aspect of this. It seems there is very little known about long-term exposure to high intensity ultrasound. Also, there could be a risk of ear damage if a non-linear material came into the sound field, and producing distortion artifacts in the audible frequency range - given that about 1W/m^2 can be enough to cause damage.

EEGuy 13y ago
This, svantana. My dentist's ultrasonic dental plaque removing tool produces audible squeals reminiscent of analog tuning of an AM radio. That's one possible example of probable nonlinearities (in my gums an teeth) producing detectible audible power from ultrasonic energy transmission. No reference -- it's just what I hear every time I have my teeth cleaned. Granted an ultrasonic water stream (dental application) has different physical characteristics than an ultrasonic air pressure wave (ultrasound).
- etrautmann 13y ago
  It doesn't even have to be nonlinearities, could also be sidelobes of the fundamental ultrasound frequency. There's no reason to filter those out if it's not harmful, which I'd like to think was carefully verified.
etrautmann 13y ago
It can't actually harm your hearing, by definition. Hearing damage caused by high intensity sound is the result of mechanical transduction of sound waves to hair cells in your inner ear. When the amplitude of a certain frequency is too high, the cells responsible for turning those mechanical vibrations into electrical signals are physically damaged. Ultrasound is mechanically filtered, so it can't propagate into your cochlea and damage the hair cells. This is in contrast to something like photons, where UV or infrared light can absolutely damage your photoreceptors in your eye.
- marshray 13y ago
  No filter has an infinitely steep cutoff slope, it's a question of the 'degree' of attenuation. It may or may not be safe in practice, but if it is it's not "by definition". 50KHz is just two octaves above our normal range of hearing. She's claiming "charge laptop in 3.5 hours" levels of power transferred to a transducer "the size of a flash drive" a useful distance away. Now apply the inverse square law to estimate the necessary output power or assume a focused beam. Now imagine that flash drive is your ear, your eyeballs, or a pregnant lady.

EEGuy 13y ago

This, svantana. My dentist's ultrasonic dental plaque removing tool produces audible squeals reminiscent of analog tuning of an AM radio. That's one possible example of probable nonlinearities (in my gums an teeth) producing detectible audible power from ultrasonic energy transmission. No reference -- it's just what I hear every time I have my teeth cleaned. Granted an ultrasonic water stream (dental application) has different physical characteristics than an ultrasonic air pressure wave (ultrasound).

etrautmann 13y ago
It doesn't even have to be nonlinearities, could also be sidelobes of the fundamental ultrasound frequency. There's no reason to filter those out if it's not harmful, which I'd like to think was carefully verified.

etrautmann 13y ago

It can't actually harm your hearing, by definition. Hearing damage caused by high intensity sound is the result of mechanical transduction of sound waves to hair cells in your inner ear. When the amplitude of a certain frequency is too high, the cells responsible for turning those mechanical vibrations into electrical signals are physically damaged. Ultrasound is mechanically filtered, so it can't propagate into your cochlea and damage the hair cells. This is in contrast to something like photons, where UV or infrared light can absolutely damage your photoreceptors in your eye.

marshray 13y ago
No filter has an infinitely steep cutoff slope, it's a question of the 'degree' of attenuation. It may or may not be safe in practice, but if it is it's not "by definition". 50KHz is just two octaves above our normal range of hearing. She's claiming "charge laptop in 3.5 hours" levels of power transferred to a transducer "the size of a flash drive" a useful distance away. Now apply the inverse square law to estimate the necessary output power or assume a focused beam. Now imagine that flash drive is your ear, your eyeballs, or a pregnant lady.