From: Eugene Leitl (eugene.leitl@lrz.uni-muenchen.de)
Date: Mon Oct 26 1998 - 05:22:44 MST
Hara Ra writes:
> I read a book about 15 years on design of radio telemetry devices you put
> into gelatin sized capsules which pass through the digestive system. No, I
> don't recall the title, but "biotelemetry" is a good word to search for.
I have several of these on design of wireless biotelemetry devices,
endo radioprobes included. There are passive ones, which are
essentially oscillating circuits, and require a wobble generator to
measure the resonancy frequency, or active ones. The battery must
deliver better than >0.1 mW orelse the signal is detectable only in
less than 50 cm range. In Germany, 37, 169, 433, 456/466 MHz
frequencies are used, YMMV. The circuits themselves are
unbelievably simple (a cell, a transistor, a capacitor and
an oscillator circuit (inductivity/capacitor) is all you need
for temperature measurement, since resistancy of transistor's
pn-junction is a function of the temperature. pH monitoring is only
slightly more tricky (Sb/AgCl electrodes required, voltage is
generated from Mg/Sb pairs).
For one ultrashortwave tunnel diode sender (100..250 MHz) the
dimensions are given: mass (sans battery): 0.5 g, dimensions: 8 mm
diameter x 2 mm, range is a few meter.
On the mainstream side, many pets are marked with implantable
transponders, most vets and animal shelters being equipped with
according readers (reading purported to be fussy, since the thingies migrate
so much, you have to scan the entire animal body).
ciao,
'gene
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