A low power RF harvester for a smart passive sensor tag with integrated antenna

The design and implementation of a low power RF harvester for use in smart passive sensor tags applied in structural health monitoring applications is presented. The tag operation is divided into two cycles: a standby mode cycle and a fully operational cycle. While in standby the tag requires only 5μA at 2.5V while any excess energy is stored in an accumulation capacitor and made available to the tag during full operation, where a low power commercial microcontroller responsible for sensor measurement and data transmission turns on. An optimized PIFA-type embedded antenna has been integrated in the design in order to enable tag operation near ground planes and metal structures. The system operates in the 430MHz band requiring a measured minimum input RF power of −5.8dBm. Tag operation has been tested by activating the onboard microcontroller. Indoor measurements as well as measurements with the use of a signal generator indicate full operation of the sensor tag for time intervals of 20ms for up to 4m distances with tag reader power of only 200mW.