We have studied about non-contact measurement of human body surface displacement by breathing using the ultrasonic pulse-echo method. The displacement by breathing can be determined by continuously measurement of the distance to the human body surface. In the case of a standing human, however, there are the displacement by body movement in addition to that by breathing. Furthermore, displacements by breathing and body movement are equal to or smaller than the wavelength of airborne ultrasound. Therefore, measurement of the displacement by only breathing using airborne ultrasound is typically difficult. We have proposed a measurement method of the displacement by breathing of a standing human. First, the SNR of the echo reflected from the body surface is improved by M-sequence pulse compression in the proposed method. Then, displacements of the front and back of the human body are estimated by tracking phase differences of echo signals. After that, displacement by body movement is canceled by difference between the front and back displacements. In this paper, the displacement by breathing of the standing volunteer was measured by the proposed method. When the volunteer is breathing, the displacement by breathing whose frequency was approximately 0.13 Hz could be measured.
Pulse compression using a maximum-length sequence (M-sequence) can improve the signal-to-noise ratio (SNR) of the reflected echo in the pulse–echo method. In the case of a moving object, however, the echo is modulated owing to the Doppler effect. The Doppler-shifted M-sequence-modulated signal cannot be correlated with the reference signal that corresponds to the transmitted M-sequence-modulated signal. Therefore, Doppler velocity estimation by spectrum-pattern analysis of a cyclic M-sequence-modulated signal and cross correlations with Doppler-shifted reference signals that correspond to the estimated Doppler velocities has been proposed. In this paper, measurements of the position and velocity of a moving object by the proposed method are described. First, Doppler velocities of the object are estimated using a microphone array. Secondly, the received signal from each microphone is correlated with each Doppler-shifted reference signal. Then, the position of the object is determined from the B-mode image formed from all cross-correlation functions. After that, the velocity of the object is calculated from velocity components estimated from the Doppler velocities and the position. Finally, the estimated Doppler velocities, determined positions, and calculated velocities are evaluated.
An acoustic method that can be used in air has the potential to allow for a fast and accurate characterization of objects in air. Nevertheless, it is difficult to identify acoustic signals from small objects clearly because of environmental noise and the scattering of sound on the object surface. Therefore, a sensing system that enables the measurement of small objects in air must be developed. In this study, we performed the localization of small objects of size comparable to the sound wavelength using an M-sequence signal and the phase information of received signals in a noisy indoor environment. Using the M-sequence signal, we are able to improve the SN ratio and to measure in a stable manner the reflected waves that cannot be detected using a conventional impulse. The arrival direction information was used to extract signals reflected by targets from unwanted signals of the floor or ceiling. Using an M-sequence signal and the arrival direction information, the position detection of small objects in the indoor environment was enabled.
In the quantitative diagnosis using ultrasound, existence of the high or low echo which was indistinguishable from speckle serves as an index of diagnosis. In this study, we tried to clarify the relation between the scattering condition in the tissue and the probability density function of echo amplitude. Parameters to estimate the scattering condition were derived by Q-Q probability plot at computer simulation models and the clinical data of liver fibrosis. In the simulation model of heterogeneous medium, the result of Q-Q plot became a curve and the curvature was dependent on the difference of the scatterer density of two intermingled media. In the clinical data of liver fibrosis, curvature was large when many fibers were contained. On the other hand, curvature was small when cysts or minute blood vessels were intermingled in the speckle and the whole distribution function was able to be approximated by k-distribution. Moreover, the crooked point of the Q-Q plot was changed depending on the scatterer density of a mixture part. These results show that the mixture rate and scatterer distributions of two different distribution functions can be recognized parametrically in the liver in which minute diseased tissue was intermingled.
Because of a growing need for unconstrained medical monitoring for unobtrusively observing individuals in a living space, we have been studied about non-contact measurement of vital information such as respiration and heartbeat using airborne ultrasound. In previous study, the measurement system of small displacement using the M-sequence-modulated signal and tracking phase difference of reflected signals from the target has been proposed. The measurement of respiration and heartbeat of the target in a standing position using a pair of the loudspeaker and the microphone has also been performed. However, body position cannot be measured using a pair of the loudspeaker and the microphone because the system can measure the distance to the body only. In this paper, we describe a basic study of the measurement of body position, respiration, and heartbeat. In the system, using microphone array, body position was estimated by synthetic aperture processing. In addition, small body-surface velocity by respiration and heartbeat were measured by tracking phase difference of reflected signals.
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