Virtual Cable: Beam-Direction Converter for IoT Communications inside a Motor

In the automotive and robotics industries, there is an increasing demand for sensing conditions inside metal housings such as engines and motors. The inside of metal housings is narrow and complex, and wiring from the outside of the metal housing to the sensor is difficult due to safety considerations and limitations on the range of movement. To overcome these limitations, wireless communication to transmit sensor data outside of a metal enclosure is a possible solution. However, this solution suffers from reflection and multipath inside the metal enclosure, resulting in a large propagation loss of radio waves. In this study, we reduced the propagation loss by developing a direction changer that combines a small spiral antenna and a small directional antenna made of a printed circuit board to limit the direction and radiation angle of radio waves, thereby suppressing the reflection and scattering of radio waves. Experiments using a test device imitating a motor confirmed that the proposed method improved the received signal strength indicator by approximately 30 dB compared to that obtained without the direction converter.