Backscatter communication, which utilizes reflection of radio wave, is used in wireless systems composed of highly-functional base stations (reader/writer) and low-functional nodes, such as RFID and radars. The nodes of backscatter communication have neither oscillators nor amplifiers to transmit radio wave by themselves, but enable node-to-reader/writer communication by changing ON/OFF of antennas or phase of reflected waves with analog circuits. Low-power nodes, such as LSI, can be activated with radio wave transmitted from reader/writer, thus realize wireless communication systems with battery-less nodes.
Backscatter communication is commonly used to swiftly recognize nodes’ identifiers or relative position from reader/writer. Wireless sensing with backscatter communication is also enabled by recent low-power MEMS sensors. Directors’ research teams especially focus on structural health monitoring (SHM) of industrial machinery and public infrastructures. Purposes of SHM are detection and prediction of structures’ troubles and faults. There are many works in SHM area, but current SHM requires installation/uninstallation of sensors with wires before/after an inspection, because it needs completely-synchronized sensor data from multiple sensors. It results in long interval between inspections, limited number of sensors, and also low inspection accuracy.
Against this problem, directors’ research teams propose a novel wireless communication system, Multiple Subcarrier Multiple Access (MSMA), which allows numerous battery-less backscatter sensors to transmit their sensor data simultaneously by digital signal processing separating mixed signals at reader/writers. Currently our work is supported by Japanese government (Ministry of Internal Affairs and Communications, SCOPE), and realizes completely-synchronized sensor data streaming from 10 backscatter sensors. Applying this technology on SHM eliminates installation/uninstallation of sensors, and its small-form-factor sensors enable high-frequency inspections and in-operation inspections with higher accuracy. Improved inspection frequency and accuracy realize predictive maintenance of structures based on analyses of mass sensor data.