If you look at the medical studies of ultrasound exposure there are too many to even count. Let me just give the basics. Medical ultrasound is limited by law to exposure levels of 100mw to the square CM. At that level there has never been any proof of tissue damage. This is for imaging ultrasound. Studies DO show however that for fetal imaging the fetus is aware of the scan taking place. There is just no damage. There is another variety used for medical purposes which is in physical therapy. Their levels are much higher than used for imaging. The physical damage done to tissue by high levels of ultrasound is, in order, heating, cavitation. Imaging does not want either of these to occur. Physical therapy wants the heating to occur. Diagnostic ultrasound uses the range of 1 MHz to 7.5 MHz transducers for their purpose. Lower freqs give lower resolution but better penetration. Higher freqs, higher resolution but lower penetration. Most diagnostic equipment today does not use a single transducer but a phased array so that they can steer the beam to acquire the image. Many ultrasound technologists report that their hands feel better than their non ultrasound imaging counterparts which tends to lend credence to the fact that although there is no damage(?) some long term exposure effects are taking place. The effects taking place are akin to the physical therapy properties desired in the other ultrasound modality. In imaging it is essential that a coupling gel be used between the patient and the transducer to lessen the impact of the difference in impedance between the human skin and the transducer. High impedance interfaces disperse the ultrasound beam (attenuate it actually) to such an extent as to render imaging unusable without the gel. The gel is a very sophisticated formula and made explicitly for imaging taking into account the impedance of human flesh, transducer freqs, etc. Free air is a very good attenuator of diagnostic ultrasound also. Hope this helps Gary B. -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Chris Hunter Sent: Sunday, November 24, 2002 5:18 AM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE]:Physiological effects of ultrasound transducers The only physiological effects I've ever seen are those in cats and dogs - most of them hate bursts of ultrasound! The levels attainable with the little ultrasonic transducers (like the Murata ones from Maplin) are pretty low - there's no need to be concerned. Incidentally, ordinary electret microphone inserts work very well at ultrasonic frequencies, though you usually have to highpass filter the signal to prevent lower frequency sounds obliterating the ultrasonics. Chris ----- Original Message ----- From: "Steve Russell" To: Sent: Saturday, November 23, 2002 10:05 PM Subject: [EE]:Physiological effects of ultrasound transducers I'm about to start playing with some ultrasound transducers (for measuring distance). Is anyone aware of any studies, research, or other information about the physiological effects of ultrasound from these transducers? I know they are used in a variety of equipment, but I've found nothing that talks about possible hazards from exposure to ultrasound. I know ultrasound is used for foetal scanning, physiotherapy, Polaroid cameras, and so on, but there is no information about the levels used in such equipment, versus the output from transducers available from places such as Maplin in the UK. Thanks, Steve. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics