Takehiko Suginouchi

P1M-8 Acoustic Properties of Nanofoam and its Applied Air-Borne Ultrasonic Transducers

Nanofoam is a porous material called drying gel or aerogel. Nanofoam has a low density and a low acoustic velocity. Because of these properties, it was considered that nanofoam can realize high performance air-borne ultrasonic transducer. We applied nanofoam to two types of ultrasonic transducers. One is a matching layer type of ultrasonic transducer (ML-UT), and the other is refractive propagation type of ultrasonic transducer (RP-UT). The sensitivity of ML-UT was twenty times as high as conventional. And we confirmed the basic operation of RP-UT on the basis of the observation of the propagation of ultrasonic in the peculiar direction and broadband characteristics. The frequency bandwidth of RP-UT was more than three times as wide as conventional

Automatic Interference Elimination Algorithm for Ultrasonic Multiple Access Method

Ultrasonic sensing systems are currently used in automobiles and mobile robots. Recently, under conditions of multiple ultrasonic sensing systems operating in a small area, we proposed an ultrasonic multiple access method (UMAM) based on the spectrum-spread technology using M-sequence code. However, the effect of the UMAM depends on the preset threshold level. In this paper, we consider an automatic interference elimination algorithm for UMAM. Under conditions with a known interference-signal ratio, the normalized correlation function between two microphones can be used to investigate the effect of the threshold level in UMAM, and further, the optimal threshold level can be obtained from the maximum value of the normalized correlation function. Using a set of suitable training examples, the approximation function between the optimal threshold and the interference-signal ratio can be obtained. From the experimental results, the automatic interference elimination algorithm is a useful tool.

Investigation of novel phantom in consideration of acoustic and optical characteristics and development of assessment technique for minute change in thickness measured by ultrasound

For measurement of minute change in thickness using ultrasound, the phase tracking method based on the constraint least-squares approach has been developed. The value measured by this method has the order of sub-micrometer, and it is difficult to verify the precision of the value. We fabricated a novel phantom, which consisted of materials in consideration of the acoustic and the optical characteristics. The thickness of the phantom changed periodically and the change was measured by the ultrasound and laser simultaneously. We evaluated the proposed ultrasound measurement system with the value measured by the laser. From the experimental results, it was obtained that our ultrasound measurement system had an accuracy of about 0.2 /spl mu/m.

Quantitative assessment of the phase tracking method for measurement of the elastic characteristics of arterial wall

The minute change in thickness of the arterial wall during one heartbeat is measured by the phase tracking method based on the constraint least squares method that detects displacement of the arterial wall with high precision from the instantaneous phase of the reflected wave, and then the elastic characteristic is detected. However, a propagation-attenuation effect introduces the error due to the shift of the center frequency in the reflected wave. In this paper, using a modified quadrature detection method, the thickness change of the vessel phantom has been measurable by 0.5 /spl mu/m accuracy.