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).