Dear Chris,

I suppose by "a few feet" I mean at least one and preferably 5-10.

The problem with ultrasound is that the transducers are quite thick - I
have to keep the thickness down to about 3-4 mm.

I have a telemetry transmitter on there already, which is working fine,
but I need to tell it when to transmit. If it is out of range the data
will be lost (not to mention wasting power). So it needs to know that it
is within range. At the moment I simply press a switch, but it would be
nice to automate this. I don't want to incorporate an RF receiver
because that would require be a big increase in size and power -
basically it's not an option. I was wondering about an RFID tag, and I
still think that's probably the best option. Do you know what sort of
range you can get with them?

Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
Dept. of Biomedical Engineering, Pangborn 105B
Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287
Email: kirtley@cua.edu
http://engineering.cua.edu/biomedical

Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
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