A new sensing technology might realize a system that determines whether the driver of a vehicle is nodding off at the wheel, drunken or under the influence of an illegal drug and whether abnormalities such as cardiac arrest and irregular pulse are occurring to a patient lying on a bed in need of nursing care.
The sensing technology was co-developed by Hiroshima University, the University of Tokyo and Delta Tooling Co Ltd. When embedded in the backrest of a seat, it can detect the sound and vibration of the cardiovascular system. Because the sensor can be embedded in a seat and bed, it does not have to be attached to a driver or a person in need of nursing care. As a result, the sensor is not removed by the driver or patient, and it does not make the wearer feel discomfort.
The key to the development of the technology was a measure to prevent the sound and vibration of the cardiovascular system from being obscured by noise. Though the sound and vibration of the cardiovascular system become APW (aortic pulse wave) after being transmitted to the skin surface of the back, they could not be directly measured with a conventional stethoscope, piezoelectric device, microphone or air pack sensor because of the large influence of noise, said Toshio Tsuji, professor at the Institute of Engineering, Hiroshima University
Moreover, in the case of an auto seat, such sound and vibration should be monitored even when the car is running. However, in such "active" cases, noise is even larger than in "static cases." Therefore, the researchers decided to amplify only an about 20Hz frequency component of the APW.
In fact, the APW consists of an about 1Hz pulse wave component and about 20Hz vibration component. On the other hand, the frequency of noise such as of a running vehicle is usually 10Hz or lower. Therefore, the researchers considered that it is possible to drastically reduce the influence of noise by amplifying the 20Hz vibration component and detecting it with a microphone.
In view of this, the researchers developed a sensor that consists of a three-dimensional (3D) knit (net), bead foam body and microphone and can be embedded in the backrest of a seat. The 3D net absorbs a locally-applied force in the thickness direction but hardly absorbs a broadly-applied force in the thickness direction. In other words, it can amplify and transmit a locally-applied vibration such as of the APW in the thickness direction while dispersing the pressure applied to the backrest by the human body.
The bead foam body is a material with a large spring constant. It is possible to make a microphone-equipped oscillator that easily vibrates only in the thickness direction by vertically supporting the oscillator with the material.
By making such structural improvements, the researchers amplified about 20Hz signals, which are the main components of the APW, by about 463% by making them resonate and enabled to detect the signals with a microphone while preventing them from being obscured by noise.© Japan Today