To date there are several approaches for incorporating sensing capabilities into RFID. Active tags use batteries to power their communication circuitry, sensors, and microcontroller. Active tags benefit from relatively long wireless range and can achieve high data and sensor activity rates. However, the batteries required by active tags are disadvantageous for device cost, lifetime, weight, and volume. In contrast, passive sensor tags receive all of their operating power from external RF transmitting sources and are not limited by battery life. One attractive feature of passive sensor tags is the prospect of permanently embedding them in objects for structural monitoring. Another is their suitability for applications in which neither batteries nor wired connections are feasible, for weight, volume, cost, or other reasons. A limitation of purely passive sensor tags is the requirement of proximity to a RF transmitter. Since lower power consumption is one major trend in RF circuit design, a self-powered system by means of energy harvesting becomes very attractive. It can serve as the enabling technology for novel applications such as ambient intelligence. Using a power harvesting technique for wireless rechargeable battery smart sensor and enhanced RFID are the key elements for successfully distributing sensors across sensor networks.