Maximum-Likelihood Estimation for Passive Wireless Intermodulation Communication Sensors

The intermodulation communication principle has recently shown several advantages over other passive wireless sensor readout techniques. The advantages include a large readout distance and the possibility of using generic sensor elements. In this paper, we derive an algorithm to estimate the quantity measured by the wireless sensor from its intermodulation response and verify the algorithm experimentally with a passive wireless inclinometer sensor operating at 860 MHz. The results can be further used to realize a reader device for intermodulation communication sensors, maximize its operational parameters, and optimize the sensor structure for the best readout resolution.