The novel prevention technology of the standing wave by SWC (Standing Wave Canceller) SWC for passive RFID tags in all metallic shelf

Passive radio frequency identification (RFID) tag systems for the management of objects stored on a metallic shelf have a problem with “dead-spots”. These spots occur in low electric field area of the electromagnetic standing wave, causing degradation of the tag's readability [3], [4]. In this paper, we present standing wave suppression technology by employing the SWC (Standing Wave Canceller). The SWC is a conductive film or dielectric with reflectance (r), installed at a specific distance (Ls) from the reflecting wall. Thus, a part of the electric field is reflected at the SWC (Efr), while another part (Etr) with phase contrast (φ) penetrates into the SWC and is reflected at the wall. These are synthesized into the total reflection electric field (Er = Efr + Etr) at the SWC. When Efr and Etr are anti-phase with respect to each other, e.g., the SWC is installed at the position Ls = λg/4 (φ = π), Er is reduced and the standing wave is suppressed. Our SWC was able to improve tag readability, eliminating the dead-spot and saving power (4.7 dB) during tag-reading experiments in a metallic shelf.