Passive wireless sensors for chemical and biological agents and wireless systems including the passive wireless sensors

A wireless system for detecting an exposure of a wireless sensor to an analyte, the wireless system comprising an interrogator module including an interrogator card that sends interrogation pulses having an interrogation frequency to a wireless sensor and receives response pulses having a response-pulse frequency from the wireless sensor, wherein the wireless sensor comprises:

• a sensor receiving antenna configured to receive the interrogation pulses;
• a DC converter electrically coupled to the sensor receiving antenna;
• a relaxation oscillator circuit electrically coupled to the DC converter, the relaxation oscillator circuit comprising a capacitance element that defines the response-pulse frequency;
• and
• a sensor transmitting antenna electrically coupled to the relaxation oscillator circuit, the sensor transmitting antenna being configured to receive response pulses from the relaxation oscillator circuit and to transmit the response pulses to the interrogator module at the response-pulse frequency;
• wherein:
• the capacitance element of the relaxation oscillator circuit comprises an interdigitated capacitor comprising a first capacitor plate including a plurality of parallel first-plate fingers and a second capacitor plate including a plurality of second-plate fingers, a capacitor-finger gap defined between the first-plate fingers and the second-plate fingers, each of the first-plate fingers extending between two of the second-plate fingers to form an interdigitated structure of the interdigitated capacitor;
• the interdigitated capacitor is coated with a detection layer of a functional material having a detection-layer dielectric constant that defines an IDC dielectric constant of the interdigitated capacitor, the detection layer completely covering the interdigitated capacitor and filling the capacitor-finger gap;
• and
• the detection-layer dielectric constant changes when the functional material is exposed to the analyte, thereby changing the response-pulse frequency of the relaxation oscillator circuit to an analyte-exposure frequency indicative of the exposure of the functional material to the analyte.