Minimally privacy-violative human location sensor by ultrasonic radar embedded on ceiling

A system observing human daily activities that may violate privacy is unacceptable in our society. This paper proposes a minimally privacy-violative system for locating a person using ultrasonic radar embedded in the ceiling of a room. One of the presumable applications is a system for preventing aged people suffering from Alzheimer's disease from accidents. The proposed system can determine the 3D position of a person's head by assuming that the human head is an object that will move at a relatively high vertical position in a living area. The system does not input unnecessarily rich information such as images using a camera so that it can reduce the possibility for violating privacy. The authors constructed an experimental system that consists of 18 ultrasonic transmitters and 32 receivers which are embedded in the ceiling of a room. Experimental results confirmed the feasibility of the proposed system.