A disruptive solution for sensing the activity of electrical devices connected to the home power line, based on the use of a long range UHF RFID system, is proposed. The solution uses a flexible RFID tag sensor wrapped around the power cord of the electrical device to be sensed. In addition to the identification of the device, the RFID tag has the unique property of detecting the status change, that is, the ON/OFF state of the device. A preliminary prototype using an external sensing acquisition block realized on a PCB connected to a flexible substrate holding the RFID antenna, have been realized and successfully tested. A sensing range of approximately 5-6 m using a regular RF reader operating in the UHF band, have been obtained, despite the close proximity of the power cord.
The idea is to wrap, around the power cord of the electrical device to be sensed, a flexible RFID tag which has the unique property of detecting the current impulse appearing along the power cord at each switch ON/OFF of the device and storing this information in the memory of the RFID chip. Therefore, the status information could be transmitted with the ID of the tagged device when placed in the range of a standard RFID reader operating in the UHF band. The energy of the current impulse, coupled through an optimized antenna design, is found sufficient to activate the RFID chip and to write the information of the status change in the chip memory, for example by modifying one bit value in the memory.
A cost effective solution for wireless sensing of home electrical devices have been designed realized and successfully tested. The solution uses commercial off-theshelf components and costs approximately $4 or $5 which is almost 10 time less than the commercially available solutions for monitoring electrical devices.
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