Extending the remote distance of LC passive wireless sensors via strongly coupled magnetic resonances

This paper presents an approach to extend the remote distance of inductive-capacitance (LC) passive wireless sensors via strongly coupled magnetic resonances. The use of an intermediate resonator (repeater) for enhancing the magnetic resonance results in multiple peak frequencies of a readout system. A coefficient matrix method is used here to analyze the effects of the repeater theoretically, including frequency splitting and sensitivity decay. The circuit simulation results agree well with the analytical analysis. An interrogation approach to avoid sensitivity decay is proposed by summing the two peak frequencies. A varactor-based LC passive voltage sensor is wirelessly measured with three different repeaters and without the repeater, respectively. It is shown that the remote distance of the passive wireless sensor with the repeater can be improved to 180% without sensitivity decay.