Human Location Estimation in Bathrooms Using the Doppler Effect of 25-kHz Spatial Ultrasound

Bathrooms are slippery, and their hard floors and walls pose a high risk of injury from falls. Drowning accidents caused by a transient loss of consciousness due to changes in blood pressure are also common. To mitigate these accidents, a system is needed to monitor a bather’s location and request appropriate assistance when an accident occurs. This paper proposes a technique for human location estimation in a bathroom using spatial ultrasound, which utilizes the phase changes in signals caused by the Doppler effect. In an evaluation experiment where a bathroom was divided into four sections to estimate the location of the subject, we achieved an average accuracy of 90.8% when the bathtub was filled with water.