Detection of sleeping and rising in care environment using sound-wave distance-measurement method at upper vocal register of 18–20 kHz

Abstract

Recently sensor network which connects many sensors via small-scale private wireless network such as ZigBee and Z-Wave has been studied. It will provide home/office-circumstance monitoring, i.e. taking care of old people, preventing crime and maintaining security. We have proposed novel movement detection for the elderly using precise sound / ultra-sound distance measurement without an invasion of privacy. In the previous paper, Tx and Rx transducers transmitted and received 40-kHz ultra-sound CWs. Distance information was obtained by IFFT based on the relative amplitudes and phases of received signals. But due to short wavelength at 40 kHz, sensitivity was a bit high. In this paper, to solve this problem we focus on detection of the elderly's sleeping and rising states by using 18–20-kHz sound waves at upper vocal register. We also developed automatic-measurement system which has function of sensor node and partial function of center node of ZigBee-based sensor network. Fundamental experimental results using the measurement system are illustrated. Comparison between results at 18–20-kHz sound and 40 kHz ultra-sound waves are also presented.