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A methodology to extract sensor data from underground, in-situ, multi-frequency soil content sensors is presented. The underground sensor, that contains a small metamaterial inspired antenna that doubles up as a sensing element, measures the impedance of the surrounding soil by sending multiple signals of known frequencies in the range 1–40 MHz and comparing the magnitude and phase of reflected signal...
A key challenge to underground, in-situ soil sensing with wireless interface is the antenna size. Smaller operating frequency supports lower path losses but enhances the wavelength and hence the size of standard monpole (8.2 cm in height at 915MHz) or rectangular microstrip patch antenna (11.5 cm × 9.3 cm at 915 MHz), which is prohibitive for underground sensors. Lowering the frequency below 915MHz...
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