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273 results on '"Hashimoto, Ken"'

38. First-Order Perturbation Analysis of Nonlinear Signal Generation in Surface Acoustic Wave Resonators on LiTaO 3 /SiO 2 /Si Structure Based on Coupling-of-Modes Theory.

Author

Hashimoto, Ken-Ya and Bao, Jing-Fu

Subjects
*ACOUSTIC surface waves, *ACOUSTIC resonators, *NONLINEAR analysis, *INTERDIGITAL transducers, *RESONANCE
Abstract

This article describes the first-order perturbation analysis of nonlinear responses in surface acoustic wave (SAW) resonators on the LiTaO3/SiO2/Si structure, where bulk wave radiation is negligible near the main resonance while the longitudinal resonances are not. The coupling-of-modes (COMs) theory is employed as the platform for both the linear and nonlinear response analyses. Stress and dielectric flux are assumed to be generated by nonlinear mixture of linear strain and electric fields proportional to the SAW displacement and applied voltage, respectively, and they are newly introduced to the extended COM equations as excitation sources. The simulated third harmonic (H3) responses agree well with the experimental ones including that caused by longitudinal resonances, and effectiveness of the present method is demonstrated. Furthermore, this theory is applied to the infinitely long interdigital transducer (IDT) to highlight the impact of longitudinal resonances. [ABSTRACT FROM AUTHOR]

Published
2022
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41. Double Busbar Structure for Transverse Energy Leakage and Resonance Suppression in Surface Acoustic Wave Resonators Using 42°YX-Lithium Tantalate Thin Plate.

Author

He, Yiwen, Wong, Yu-Po, Liang, Qi, Wu, Ting, Bao, Jingfu, and Hashimoto, Ken-Ya

Subjects
ACOUSTIC surface waves, ACOUSTIC resonators, DELOCALIZATION energy, ACOUSTIC surface wave devices, FINITE element method
Abstract

This article describes a new transverse edge structure with double busbar for surface acoustic wave (SAW) devices employing a 42°YX-lithium tantalate thin plate such as incredible high-performance (I.H.P.) SAW. This design offers good energy confinement and scattering loss suppression for a wide frequency range. First, preexisting transverse edge designs are reviewed, and their difficulties are pointed out using the dispersion relation for lateral SAW propagation. Then, numerical simulations are performed using the periodic 3-D finite-element method (FEM) powered by the hierarchical cascading technique, and effectiveness of the proposed structure is revealed. In addition, we also provide a possible solution to expand the frequency range giving well energy confinement and demonstrate effectiveness of manipulating the SAW slowness curve shape for transverse mode suppression. [ABSTRACT FROM AUTHOR]

Published
2022
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46. Efficient and Flexible Spatiotemporal Clutter Filtering of High Frame Rate Images Using Subspace Tracking

Author

Generowicz, B.S., Leus, G.J.T., Tbalvandanv, S. Soloukey, Van Hoogstraten, W. S., Strvdis, C., Bosch, J. G., van der Steen, A.F.W., De Zeeuwl, C. I., Koekkoek, S. K.E., Kruizinga, P., Hashimoto, Ken-ya, and Ruppel, Clemens

Subjects
Pixel, Computer science, clutter filter, Filter (signal processing), Iterative reconstruction, Doppler imaging, 01 natural sciences, 030218 nuclear medicine & medical imaging, 03 medical and health sciences, symbols.namesake, functional ultrasound, 0302 clinical medicine, subspace tracking, 0103 physical sciences, Principal component analysis, Singular value decomposition, symbols, Clutter, 010301 acoustics, Doppler effect, Algorithm, Eigenvalues and eigenvectors, Subspace topology
Abstract

Current methods to measure blood flow using ultrafast Doppler imaging often make use of a Singular Value Decomposition (SVD). The SVD has been shown to be an effective way to remove clutter signals associated with slow moving tissue. Conventionally, the SVD is calculated from an ensemble of frames, after which the first dominant eigenvectors are removed. The Power Doppler Image (PDI) is then computed by averaging over the remaining components. The SVD method is computationally intensive and lacks flexibility due to the fixed ensemble length. We propose a method, based on the Projection Approximation Subspace Tracking (PAST) algorithm, which is computationally efficient and allows us to sequentially estimate and remove the principal components, while also offering flexibility for calculating the PDI, e.g. by using any convolutional filter. During a functional ultrasound (fUS) measurement, the intensity variations over time for every pixel were correlated to a known stimulus pattern. The results show that for a pixel chosen around the location of the stimulation electrode, the PAST algorithm achieves a higher Pearson correlation coefficient than the state-of-the-art SVD method, highlighting its potential to be used for fUS measurements.

Published
2018

47. Regularized Capon Beamformer Using ℓ1-Norm Applied to Photoacoustic Imaging

Author

Paridar, Roya, Mozaffarzadeh, M., Basij, Maryam, Mehrmohammadi, Mohammad, Orooji, Mahdi, Hashimoto, Ken-ya, and Ruppel, Clemens

Subjects
minimum variance, norm regularization, Photoacoustic imaging, beamforming
Abstract

Delay-and-Sum (DAS), as a non-adaptive beamforming method, is one of the most common algorithms used in Photoacoustic imaging due to its simple implementation. The results obtained from this algorithm suffer from low resolution and high sidelobes. The adaptive Minimum variance (MV) method improves the image quality compared to DAS in terms of resolution and contrast. In this paper, it is proposed to add a ℓ1-norm regularization term to the conventional MV minimization problem and create a new sparse beamforming method, named Modified-Sparse-Mv (ms-Mv)algorithm. In fact, the sparsity of the output is forced to the beampattern by adding this new sparse added term, which results in more noise reduction and sidelobe suppression compared to MV. The minimization problem is convex, and therefore, it can be solved using an iterative algorithm. The results show that the proposed MS-MV method improves the signal-to-noise-ratio for about 5.36 dB and 6.44 dB compared to DAS and MV, respectively, for the designed wire phantom.

Published
2018

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