A passive sensor tag system, comprising: a passive electronic sensor tag having a sensor element and a sensor circuit, the sensor element configured to sense a change in a local environmental variable and to alter at least one of a fundamental electrical resonance frequency characteristic of the sensor circuit based on a change in state of the sensor element associated with the change in the local environmental variable, wherein the local environment variable is one of light, pressure, vibration, stress, and strain; an external readout including an external readout circuit configured to interrogate the sensor circuit of the sensor tag by generating a signal having a frequency and a voltage and transmitting the signal through an output antenna to an antenna of the passive electronic sensor tag, the transmitted signal coupling the sensor circuit and the external readout circuit, so as to read the fundamental electrical resonance frequency characteristic of the sensor circuit, wherein the external readout circuit includes a first analog-to-digital converter, ADC, sampling the signal before the output antenna and a second ADC sampling the signal after the output antenna, the external readout determining the impedance of the coupled system based on the sampling of the first ADC and the second ADC, the external readout determining the at least one of fundamental electrical resonance frequency characteristic of the sensor circuit based on an impedance of the coupled sensor circuit and external readout circuit, the external readout determining the change in the local environmental variable based on the alteration in the at least one fundamental resonance frequency characteristic of the sensor circuit, wherein the fundamental electrical resonance frequency characteristic is one of a fundamental electrical resonance frequency of the sensor circuit, a width of a resonance frequency response trough, and a width of a resonance frequency response crest. a passive electronic sensor tag having a sensor element and a sensor circuit, the sensor element configured to sense a change in a local environmental variable and to alter at least one of a fundamental electrical resonance frequency characteristic of the sensor circuit based on a change in state of the sensor element associated with the change in the local environmental variable, wherein the local environment variable is one of light, pressure, vibration, stress, and strain; an external readout including an external readout circuit configured to interrogate the sensor circuit of the sensor tag by generating a signal having a frequency and a voltage and transmitting the signal through an output antenna to an antenna of the passive electronic sensor tag, the transmitted signal coupling the sensor circuit and the external readout circuit, so as to read the fundamental electrical resonance frequency characteristic of the sensor circuit, wherein the external readout circuit includes a first analog-to-digital converter, ADC, sampling the signal before the output antenna and a second ADC sampling the signal after the output antenna, the external readout determining the impedance of the coupled system based on the sampling of the first ADC and the second ADC, the external readout determining the at least one of fundamental electrical resonance frequency characteristic of the sensor circuit based on an impedance of the coupled sensor circuit and external readout circuit, the external readout determining the change in the local environmental variable based on the alteration in the at least one fundamental resonance frequency characteristic of the sensor circuit, wherein the fundamental electrical resonance frequency characteristic is one of a fundamental electrical resonance frequency of the sensor circuit, a width of a resonance frequency response trough, and a width of a resonance frequency response crest.