In demand for low-loss wide-band communication devices, Potassium niobate (KNbO3) is now receiving renewed interests because it has been found to exhibit high electromechanical coupling. This paper describes the optimum cuts of KNbO3 for bulk acoustic waves (BAW) and surface acoustic waves (SAW) devices, with expectation of their application in the future. In addition, our recent works on growt...

Sound waves are mechanical waves and the behaviours of fixtures inside rooms are governed by rules in physics. These fixtures are classified into three groups: reflectors, diffusers and absorbers, and the physical properties are investigated. The important parameters in determining acoustic quality of rooms are introduced. On the other hand, it is shown that limitations exist on applying these ...

Development of a new, 3D, modal theory of low-frequency, long-range sound propagation through a fluctuating ocean, including both CW and transient acoustic signals. Comparison of theoretical predictions with NPAL experimental data. OBJECTIVES To develop a 3D modal theory of broadband sound propagation though a fluctuating ocean, including analysis of the coherence function for transient acousti...

Development of a new, 3D, modal theory of low-frequency, long-range sound propagation through a fluctuating ocean, including both CW and transient acoustic signals. Comparison of theoretical predictions with NPAL experimental data. OBJECTIVES To develop a 3D modal theory of broadband sound propagation though a fluctuating ocean, including analysis of the coherence function for transient acousti...

In this work, a model is proposed to predict acoustic waves generated in a homogeneous and isotropic cylindrical cavity by a laser line source. The Fourier series expansion is introduced for one spatial coordinate to solve this transient response problem. Theoretical displacements are obtained for an aluminum cylindrical cavity of internal diameter 40 mm. The corresponding displacements are obs...

Acoustics-based methods offer a powerful tool for sensing applications. Acoustic sensors can be applied in many fields ranging from materials characterization, structural health monitoring, acoustic imaging, defect characterization, etc., to name just a few. A proper selection of the acoustic wave frequency over a wide spectrum that extends from infrasound (<20 Hz) up to ultrasound (in the GHz–...

A hybrid technique is presented that simultaneously uses both electromagnetic and acoustic waves in a synergistic manner to detect buried land mines. The system consists of an electromagnetic radar and an acoustic source. The acoustic source causes both the mine and the surface of the earth to be displaced. The electromagnetic radar is used to detect these displacements and, thus, the mine. To ...

The linear stability of isothermal Bondi accretion with a shock is studied analytically in the asymptotic limit of high incident Mach number M1. The flow is unstable with respect to radial perturbations as expected by Nakayama (1993), due to post-shock acceleration. Its growth time scales like the advection time from the shock rsh to the sonic point rson. The growth rate of non-radial perturbat...

A compact femtosecond dual-oscillator pump-probe setup with 48 MHz-repetition rate, relying on asynchronous optical sampling, is presented. The relative timing jitter between both lasers over the whole pump-probe delay range is of the order of or lower than 500 fs. We demonstrate that both a picosecond temporal resolution and a 48 MHz spectral resolution combined with the fast acquisition rate ...

An analytical expression is derived for the temporal coherence of an acoustic field after multiple forward scattering through random three-dimensional (3D) inhomogeneities in an ocean waveguide. This expression makes it possible to predict the coherence time scale of field fluctuations in ocean-acoustic measurements from knowledge of the oceanography. It is used to explain the time scale of aco...