http://en.wikipedia.org/wiki/Proximity_fuzeThe device described in World War II patent works as follows: The shell contains a micro-transmitter which uses the shell body as an antenna and emits a continuous wave of roughly 180–220 MHz. As the shell approaches a reflecting object, an interference pattern is created. This pattern changes with shrinking distance: every half wavelength in distance (a half wavelength at this frequency is about 0.7 meters), the transmitter is in or out of resonance. This causes a small oscillation of the radiated power and consequently the oscillator supply current of about 200–800 Hz, the Doppler frequency. This signal is sent through a band pass filter, amplified, and triggers the detonation when it exceeds a given amplitude.
Is it feasible to reproduce this circuit ?
Like this? There are lot of similar circuits. The major issue is to fit into something small enough for our small projectiles. Under 20mm diameter.
http://electronic-schematic.blogspot.co ... ector.html