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Design and characterization of a passive harmonic sensor embedded in sand

This paper demonstrates the suitability of the harmonic back-scatter approach for narrow-band, embedded remote structural health monitoring. A passive harmonic repeater was embedded and characterized at a depth of 15 cm in a sand box with inserted metal bars. The harmonic repeater comprises electrically-small 3-D receive and transmit antennas and a passive diode-based frequency doubler. The repeater operates by receiving a 2.4 GHz signal and transmitting back a signal at 4.8 GHz.