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Passive radio frequency identification (RFID) sensors are attractive in diverse applications where sensor performance is needed at a low cost and when battery-free operation is critical. We developed a general approach for adapting ubiquitous and cost-effective passive 13.56-MHz RFID tags for diverse sensing applications. In developed RFID sensors, the complex impedance of the RFID resonant antenna is measured and correlated to physical, chemical, or biological properties of interest. In contrast to known wireless sensors, developed RFID sensors combine several measured parameters from the resonant sensor antenna with multivariate data analysis and deliver unique capability for multianalyte sensing and rejection of environmental interferences with a single sensor. Theoretical calculations and experiments in an anechoic chamber demonstrate that the developed RFID sensors are immune to common electromagnetic interferences and the sensor/reader system operates within regulated emission levels. Performance of developed RFID sensors is illustrated in measurements of toxic industrial chemicals (TICs) in air with the detection limit (DL) of 80 parts per billion and in a non-invasive monitoring of milk spoilage. Sensors selectivity is demonstrated in the detection of different vapors with individual sensors. designs such as resonant inductor-capacitor [1,2], magnetoelastic [3], thickness shear mode [4], and surface-acoustic wave [5,6] transducers. Examples of detected physical parameters using these sensors Fig. 9. Results of extended-length experiment of the response of the RFID sensor for toxic volatile polar and nonpolar vapors TCE, MeOH, and Tol. (A) Sensor exposure to four replicate sets of 0-0.20 P/Po concentrations of three tested vapors. (B) Rapid response and recovery times of the sensor to three tested vapors. Insets show the response and recovery times of less than 1 min for 0.04 P/Po of TCE, MEOH, and Tol.

This paper describes the experimental hardware design and implementation for a delay hopped transmitted reference communication system.The hardware is designed to generate the delay hopped transmitted reference signal for a number of experimental conditions. It can be used either in ultra wideband pulse mode, ultra wideband noise mode, or in narrowband mode. We use the experimental hardware setup to conduct link experiments with a delay hopped transmitted reference communication system. Experiments were conducted in an indoor multi-path environment to test the viability of delay hopped transmitted reference for short-range indoor communications. The experimental results presented demonstrate that this modulation format is capable of transmitting data short range indoors with out line of sight transmission path with minimal transmitted RF power.