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Power Mapper Shows UHF Signal Strength, to Help Users Properly Install RFID Systems

EPix is selling its handheld device worldwide, offering users a simple means of measuring a reader's ultrahigh-frequency RF signals, as well as locating transmission dead spots.
By Claire Swedberg
May 30, 2012British electronics firm ePix Ltd. is selling a handheld device that a user can operate in order to ascertain the level of RF transmission from a reader before, during or after the installation of a radio frequency identification system. In that way, the operator can determine not only whether tags can be read, but how strong the RF signal is at any location in the vicinity of that reader.

Dave Mapleston, ePix's founder, envisioned and then built the device, the Power Mapper, while teaching an RFID course at the University of Cambridge, approximately three years ago. "I could only explain the theory of RFID radio wave propagation," he says, rather than demonstrate any theory to the students by showing them where RFID waves were or were not transmitted. "Teaching RFID is not easy, and becomes very complex when the radio waves are enclosed in small spaces," he explains. "Radio waves aren't as simple as people think." Mapleston wanted to demonstrate the waves' behaviors to his students, rather than simply describe them.


The Power Mapper is a battery-free device that measures a UHF RFID reader's signal strength.

To that end, Mapleston tried utilizing existing technologies, such as LED meters, but was dissatisfied since they can detect the presence of an RF wave but not indicate signal quality. He says he created the Power Mapper "after some research into precise antenna matching and small radio-integrated detector circuits," which he used to build his solution.

According to Mapleston, RF waves are polarized, meaning they are oriented in certain directions, and are emitted from a reader in "thin strips." The tags will receive power, instructions and data from the RF signals in these strips, within about 20 feet of an interrogator's antenna. However, he notes, an RF field's strength can be affected by a large presence of metal, as well as the reader antenna's angle and the distance involved. Interference nulls (dead spots) appear between those strips, through which RF signals do not travel, thereby leading to an inability to read a tag in certain positions. What's more, he says, to achieve the greatest read range, the polarization of the tag's antenna should match that of the reader's signal.

To minimize the presence of any such nulls in an interrogator's transmission, users typically learn the best arrangement of RFID readers and antennas through trial and error. If tags cannot be read at particular locations, users simply adjust the reader antenna and try again. "It's guesswork," Mapleston says. "They don't know if they are reading a tag well or poorly."

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