There are several different types of wireless radio frequency identification (RFID) tags that are truly zero-power radios. Currently, most unpowered wireless RFID tags only have a range of a few meters. There are longrange, low-powered tags that draw energy either from a battery or some other form of localized power. A passive, or zero-power, radio receiver uses no direct electrical power, but makes sole use of the power available from a transmitter via the radio spectrum.
Commercial applications for short-range, zero-power radio receivers are already common for RFID tags used in applications ranging from low-cost theft prevention devices in stores and libraries, to somewhat more expensive devices used to track shipping containers and pallets in warehouses.
A long-range, truly zero-power radio receiver has until now been unavailable. Such a radio receiver could solve a number of communication-related problems. Right now, cellphones continually turn their radio receiver circuitry on and off to listen for attempts to be contacted by the cellular base station. Similarly, global positioning system (GPS) receivers cycle their receivers on and quickly off to keep track of changes in location. A long-range, zero-power radio receiver with sufficient sensitivity would greatly extend battery life in wireless mobile applications.
Sandia National Laboratories has developed the Zero-Power Receiver, an unpowered signal receiver that detects and responds to very weak signals using pyroelectric devices as impedance transformers and/or demodulators. In some embodiments, surface acoustic wave devices (SAW) are also used.
The miniature radio receiver can be integrated easily into a wide range of devices to provide continuous wireless connectivity. The underlying principle behind the Zero-Power Receiver is that the powered radio frequency electronics used in most wireless receivers can be replaced with electronics that require no power supply or battery. Using this technology, a short-range radio receiver (<100 m) can be built that uses no power other than the received RF signal. A longer-range radio receiver can also be built that uses only DC amplification, for a total power consumption that is about 10,000 times lower than a conventional radio receiver operating at a comparable range.
The Zero-Power Receiver directly demodulates an amplitude-modulated wake-up signal sent from a transmitter. The amplitude modulation can be sent using pulse coding to provide a unique device-selective turn-on signal to the Zero-Power Receiver. It uses Sandia’s patented pyroelectric demodulator to provide direct RF-to-baseband conversion over a wide RF input frequency range and modulation bandwidths. The input impedance of the pyroelectric demodulator provides a match to 50-Ohm circuitry over a very wide bandwidth, ultimately only limited by the electronics packaging that contains the device.
This technology solves multiple communication issues. When incorporated into a cellular phone or GPS, it eliminates the need for the device to constantly power on and off waiting for contact — greatly extending battery life. It can also greatly increase range and decrease size of currently available RFIDs.
Potential applications include cellular devices, wearable electronics, home automation, automotive control and sensing, biomedical devices, wireless RFID tags, animal tracking studies, and national security.