A low-cost millimeter wave interferometer for remote vibration sensing.

Remote sensing of ground vibration is a key tool in the detection of shallowly buried objects, such as land mines. Millimeter wave systems show promise for replacing laser Doppler vibrometers as the key sensing technology on the grounds of reduced cost and because they provide a larger (10 cm versus 1 mm), more robust sensor footprint. We have developed a double-conversion interferometer operating at 39 GHz that can be built for about $10 000. The system employs quadrature detection in order to provide reliable sensitivity over wavelength-sized changes in target range. Laboratory tests show that it can estimate sinusoidal ground motion from a 1 s time series with an uncertainty of about 5 μm. [ABSTRACT FROM AUTHOR]