With the exception of light-based sensors, that change their light interaction properties, all sensors require some power in order to operate and provide a signal to a remote source. Light-based systems are readily blocked by typical obstructions such as buildings, trees, and vegetation. Some wireless systems require the use of on-board circuitry that temporarily charges up a battery or capacitor in the presence of an externally applied RF radiation, then use this electrical energy to re-transmit signal. This method is bulky, expensive, and can only transmit data at short distances. The need for a powered sensor/transmitter severely limits the deployment of such sensors in large scale such as over large geographic regions or as part of the civil infrastructure.
University researchers have developed an antenna system that changes the nature of its transmission and reception of electromagnetic radiation based on local environmental conditions. It may use this feature to transmit local environmental information by wireless means without the need for power. The sensor system described in this invention requires no power, but may be interrogated remotely by wireless means. The simplicity of the device and passive operation means the device can be deployed over large regions while still enabling remote readout. Furthermore, since the interrogating system may use directional antennas, the interrogating radiation may be highly localized, e.g., through the use of a "pencil beam". Thus the location of the sensors may be determined by the interrogating system, allowing true geographic mapping of the sensor networks.
|United States Of America||Issued Patent||7,570,169||08/04/2009||2005-514|