transponder consists of a dipole antenna with a Low Barrier Schottky Diode
HSCH-5340 of centred inductivity. The
transponder is 10.5 mg in weight and 12 mm in length. It consists of a silver
or gold wire with a diameter of 0.3 mm and a loop inductance of 1.3 nH (Fig. 22B,
23A). The dimensions of the wires, the loop and the conductive glue (two
component conductive epoxy, Chemtronics, Kennesaw, GA, 30152, USA) used to
connect the diode across the loop to the wire are very important and define the
strength of the harmonic signal. The loop is stabilized with nail polish. A
simple device can be used (Fig. 23B) to stretch and stiffen the silver wire in
order to produce a precise loop both with respect to loop diameter (0.35 mm)
and distance of the loop at the location where the diode is glued across the
loop (Fig. 23A). A laboratory-based calibration radar unit may be helpful for
estimating the quality of the transponders, but such a unit is not essential.
The calibration can also be performed in the field. The price for such a
custom-made transponder is about 20 €.
Fig. 23A. A collection of transponders. Notice the loop bridged by the diode, the nail polish for stabilizing the loop, the PVC tubing into which the wire is inserted, the number tag and the double sticky tape. (Photos: Christoph Grüter). B. A simple device for producing a loop with an inner diameter of 0.35 mm and a defined distance between the distance of the wire in the loop. One end of the wire is pulled below the horizontal wire, bent around the vertical filament above the horizontal wire and then strongly stretched.