10 Researchers in Japan have developed a battery-less tag to guide UAVs in all weather conditions (writes Nick Flaherty). The MilliSign uses millimetre-wave (mmWave) radio signals from the bottom of a UAV to provide accurate positioning data from a battery-free tag on the ground. The key is that this operates in all weathers, when camera-based location systems struggle to provide accurate data. The researchers see this being used as a passive ground station for delivery UAVs to land safely. Conventional battery-less guidance systems using visual signs fail to work in poor weather because of low visibility. The need for all-weather operations with long-range readability therefore encourages the use of mmWave radar, which poses challenges in providing a Modifying the shape of its structures and arranging them like barcodes boosts the detection range and the number of bits that can be read from the tag. The design is based on a corner reflector (CR) array with a one-shot slant range-reading procedure with COTS mmWave radar. The shape of the CR units and their alignment decreases the tag’s size and expands the 3D reading range. The team also designed a signal processing pipeline that can automatically detect the position of a tag even in a noisy environment, by clustering a point cloud containing the reflection intensity information. This allows the tag to be detected and read with high accuracy, even in situations where a UAV is surrounded by obstacles such as walls, cars, and stairs, and allows automated tag detection to provide its landing location. Airborne vehicles All-weather tag guidance wide 3D reading range and low-cost operation. The researchers, at NTT and the University of Tokyo, designed a new type of RFID tag that measures 292 x 600 x 19 mm and stores 8 bits of data. The tag can be read by mmWave radar at frequencies from 30 to 300 GHz from a distance of more than 10 m and with a viewing angle of more than 30o in elevation and azimuth – nearly eight times that of conventional tags. The design means performance remains stable when visibility is poor and in multipath-rich environments. In conventional RFID, the radio wave reflection range is narrow as it uses a planar antenna, so the range that can be read from the air is limited. The new tag uses a more angular antenna, called a corner reflector, that has 3D reflectivity. December/January 2024 | Uncrewed Systems Technology The components for millimetre-wave detection
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