Kohsuke Tsuruta

Blind signal separation with undersampled signals for frequency modulated echoes

Ultrasound technology in medical examinations has developed further in recent years. Above all, the system monitoring the fetal well-being with ultrasonic echoes becomes most popular in obstetrics. However, it retains several problem that the observed echoes may include the information of the maternal body, and acoustic transfer functions are affected by the fetal movement. This paper proposes a novel monitoring system utilizing blind signal separation (BSS), which is a method for recovering a set of source signals from their mixtures without any knowledge about the mixing process.

Spatio‐temporal gradient signal processing for reconstructing scattered wave fields

This paper presents a subspace signal processing method which detects the scattered sound waves based on the spatio‐temporal gradient analysis over the Lamb wave field. The proposed method has an ability to classify the surface acoustic wave field through the rank of the covariance matrix defined over the four‐dimensional vector space which is spanned by the following components: a vertical displacement, its vertical velocity, and a pair of shear strains of the plate surface. The covariance matrix provides the information about cracks. When a unique sound source exists on the surface without any cracks or scatterers, the rank of the covariance matrix is reduced to two. Increasing the rank up to three, however, one or more scatterers exist on the surface. Therefore, by the singular value decomposition (SVD) of the covariance matrix, optimal, orthonormal bases are obtained. In formulating the scattered wave field by the unknown object, its best reconstruction, in the LMS sense, can be obtained by the sum of...

Spatio‐temporal gradient signal processing for detecting subsurface cracks

This paper presents a crack characterization method by spatio‐temporal gradient analysis over the Lamb wave field. The surface ultrasound waves that propagate in the direction of the layer are potential candidates of nondestructive testing (NDT) methodology. The proposed method has an ability to classify the surface acoustic wave field through the rank of the covariance matrix defined over the four‐dimensional vector space which is spanned by the following components: a vertical displacement, its vertical velocity, and a pair of shear strains of the surface. The covariance matrix provides the information about cracks. The determinant of the covariance matrix, therefore, is proposed as the index of homogeneity of the object surface. In this study, the computational process in the wave field near the cracks is discussed and their physical meanings are investigated through FDTD‐simulations and acoustic experiments.

Resolution enhancement algorithm utilizing multiple reflections for image reconstruction in the conduit

In the acoustical endscopy, due to the physical limitations, the transducer array is composed of a small number of elements and each interspacing is larger than the acoustical wave length that is called a sparse array system. In such case, the volumetric image reconstruction process becomes ill‐posed caused by the interference of the reverberation in the tube. Consequently, the reconstructed image is interfered by widely spread strong spurious lobes. This paper proposes a novel volumetric image reconstruction algorithm for a 3D sparse aperture acoustical holography, which visualizes the forward‐looking image in the conduit tube. The proposed algorithm utilizes prior knowledge about both field, object, and observed signal as (1) the support of the object is limited within the conduit, and (2) the multiple reflected wave field scattered by the object is statistically independent of the reverberation in the tube. The proposed sparse array acoustical imaging system utilizes, therefore, the multiple reflected ...