WAVE REFLECTION IN PIEZOELECTRIC HALF-PLANE

The assumption of quasi-static electric field in the problem of wave reflection in piezoelectric half-plane results in missing an independent electric wave mode at the piezoelectric boundary, which leads to oversimplified solutions of reflected waves in a strong piezoelectric medium if only elastic bulk wave boundary conditions are considered. The paper presents a novel solution to address the issue by using the inhomogeneous wave theory and introducing a virtual reflection wave mode in addition to the elastic bulk wave modes. The virtual wave is assumed to satisfy the Snell's law as well as the piezoelectric boundary condition and can be treated in the same way as the elastic bulk waves. The analysis results show that this virtual wave always propagates along the boundary for any incident angle and can be treated as a pseudo surface wave. The energy transmission analysis reveals that this surface wave transmits zero energy and does not violate the energy conservation between the incident and the reflected elastic bulk waves. In addition, the analysis also reveals an interesting result that the quasi-transverse, not the quasi-longitudinal, incident wave will be fully reflected and no quasi-longitudinal reflected wave will be generated if the incident angle is beyond a critical angle.

Download Full-text

A technique to eliminate the azimuth ambiguity in single-well imaging

Geophysics ◽

10.1190/geo2013-0310.1 ◽

2014 ◽

Vol 79 (6) ◽

pp. D409-D416 ◽

Cited By ~ 8

Author(s):

Yi-de Zhang ◽

Hengshan Hu

Keyword(s):

Wave Reflection ◽

Incident Angle ◽

Imaging Techniques ◽

Fluid Pressure ◽

Displacement Component ◽

P Wave ◽

Reflected Waves ◽

Single Well ◽

The Media ◽

Two Sides

Single-well imaging has been a technique increasingly used in the detection of near-borehole geologic structures. The azimuth of a geologic structure, however, cannot be uniquely determined with acoustic signals recorded in the borehole alone, due to the azimuth ambiguity existing in current imaging techniques. We eliminated such ambiguity by revealing the relevant acoustic principle underlying the P-wave reflection behavior. When a P-wave excited by a transducer in the logging tool impinges upon a planar interface, the P-wave reflection coefficient (RC) of the displacement is opposite in sign to that of the normal stress or fluid pressure, regardless of the incident angle and the parameters of the media on the two sides. The derived relation about signs of RCs was validated by finite-difference solutions for reflected waves from a near-borehole plane fault. With this newly discovered reflection principle, one can eliminate the azimuth ambiguity of any interface outside a borehole by checking if the waveforms of pressure and the displacement component are both changed in polarity after reflection. Furthermore, because the pressure and displacement are observable quantities and the waveform of the acoustic source is known in acoustic logging, it is convenient to implement the data acquisition for this technique, which is a major advantage over other techniques. We expounded and exemplified our new technique by numerical simulation.

Download Full-text

Sound reflection of acoustic porous metasurfaces under uniform mean flow

INTER-NOISE and NOISE-CON Congress and Conference Proceedings ◽

10.3397/in-2021-2182 ◽

2021 ◽

Vol 263 (4) ◽

pp. 2601-2608

Author(s):

Renhao Qu ◽

Jingwen Guo ◽

Yi Fang ◽

Siyang Zhong

Keyword(s):

Surface Wave ◽

Critical Incident ◽

Incident Angle ◽

Low Frequency ◽

Noise Attenuation ◽

Mean Flow ◽

Background Flow ◽

Reflected Waves ◽

Acoustic Performance ◽

Sub Wavelength

Acoustic metasurfaces are artificial 2D structures with a sub-wavelength thickness that can realize some exotic properties such as non-trivial refraction, broadband and low frequency absorption. However, most relevant studies are still in a static medium, hindering their realistic applications in aviation, where background flow exists. To address it, the effects of mean flow on the acoustic performance of metasurfaces, which is designed based on the generalized Snell's law (GSL) to achieve anomalous reflections, are systemically studied. Firstly, an analytical model of GSL taking the effect of background uniform mean flow into account is built, in which the wavenumbers of both incident and reflected waves are corrected. Then, taking an acoustic porous metasurface for instance, the effectiveness of the derived model is validated by numerical simulations. Results reveal that the reflected waves are deflected in the presence of background flow. The critical incident angle, at which the incident sound wave is converted to surface wave, decreases with the increasing flow velocity. Since the converted surface wave can only propagate along the metasurface, there is little sound energy radiated into far field, which is benefit for the noise attenuation in the presence of flow.

Download Full-text

Reflection and Transmission of Waves in Pyroelectric Body

Volume 13: Sound, Vibration and Design ◽

10.1115/imece2010-37732 ◽

2010 ◽

Author(s):

Xiaoguang Yuan ◽

ZhenBang Kuang

Keyword(s):

Surface Wave ◽

Boundary Conditions ◽

Wave Vector ◽

Interface Plane ◽

Bulk Wave ◽

Two Dimensional ◽

Reflection And Transmission ◽

Bulk Waves ◽

Temperature Waves ◽

Wave Vector Component

The reflection and transmission theory of waves in pyroelectric medium is studied in this paper. In general in an infinite homogeneous pyroelectric medium there are four bulk wave modes: quasi-longitudinal, two quasi-transversal and temperature waves. However there are five boundary conditions in the reflection and transmission problem of the pyroelectric medium. In this paper we find that the surface wave will be revealed to satisfy the boundary conditions with other four bulk waves. The surface wave has the same wave vector component with the incident bulk waves on the interface plane. The two dimensional reflection problems of waves at the interface between the semi-infinite pyroelectric medium and vacuum is researched and an numerical example is given.

Download Full-text