Electromagnetic Media Sensor

Earth penetrators are now extremely effective in passing through layers of earth, sand, concrete, and reinforced material to reach hard targets. The penetrating munitions would be even more effective against hardened targets such as underground bunkers if the high explosive charge could be detonated at the optimum location inside the bunker. We propose to develop and test a simple electromagnetic (EM) sensor to control detonation of the high explosive charge. The EM sensor will measure the local dielectric constant (er ) of the surrounding material using a resonant antenna. For said, soil, concrete, and other terrestrial and construction materials, er is much higher than for air so detection of voids will be robust. In addition, the EM sensor will give an analog output signal which allows identification of various media types. An oscillator circuit generates RF energy which is radiated by the antenna. Variations in er modify the antenna resonant frequency, pulling the oscillator frequency or causing variations in reflected power which are measured as the sensor output. Proof of concept experiments will be performed with a realistic electronic package in a model penetrator body.