Application Of Surface Waves Research Articles

Application of surface and normal ultrasonic waves for measuring the parameters of technical fluids: II. Density measurements

Application of surface and normal ultrasonic waves for measuring the parameters of technical fluids: II. Density measurements

Application of surface and normal ultrasonic waves for measuring the parameters of technical fluids: I. Shear viscosity measurements

The effect of a fluid on the surface waves moving in a waveguide along its boundary with the fluid is considered. The effect of the shear and volume viscosities of the fluid on the damping coefficient of such a surface wave is estimated. It is shown that the effect of fluids may be neglected at a measurement accuracy of about 10−3 if their shear viscosities are lower than 0.1 Pa s. At a higher viscosity, corrections that take into account the contribution of viscous losses to the measured damping coefficient of a surface wave should be introduced. A technique for calibrating a density sensor for low-viscosity fluids is described, and the densities of NaCl and saccharose solutions in distilled water are measured. The experimental results agree qualitatively with the theoretical estimates. It is noted that this method of measuring the longitudinal impedance of a fluid can use the same apparatus design in both the principle (pulsed) and the frequency range (1–10 MHz) for measuring the density, both viscosities, the velocity, and the sound absorption coefficient of a fluid. This design almost coincides with the apparatus used in the means of nondestructive quality control of materials and articles.

Application of ultrasonic surface waves in the detection of microcracks using the scanning heating laser source technique

This letter reports the application of the scanning heating laser source technique to detect microcracks that may be undetected by conventional methods. In the proposed approach, we monitor changes in the transmitted surface acoustic waves (SAWs) as a heating source is scanned over the crack. The experimental system for microcrack detection by a scanning heating laser source is obtained by exploiting the strong dependence of the transmission efficiency of acoustic pulses on the state of the contacts, whether open or closed, between the crack faces. Microcracks can be detected successfully by confirming the heating position at the point of maximal improvement of the transmission efficiency of the SAWs.

Parametric excitation of surface electron cyclotron X- and O- modes by alternating electric fields

Propagation of different electromagnetic surface waves (SW) is recognized as one of the most possible cause of undesirable plasma periphery heating, strengthening interaction between plasma column and walls of fusion device, impurity generation. This is found out clearly in experiments with ion cyclotron heating [1]. On the other hand in order to supply periodical operation of fusion devices, one can clean the devices inner surface. One of the prospective methods that can be used for this procedure is application both ion and electron cyclotron hardwares (without dismantling the whole device) for sustaining gas discharge, which can remove different contaminations from the chamber wall. The urgency of researches into parametric instability of SW at harmonics of cyclotron frequencies is caused as well by wide application of SW in various plasma technologies [2]. The present paper is devoted to development theory of parametric instability of slow surface Xand O-modes at electron cyclotron frequency for the model of semi-bounded plasma. Surface electron cyclotron O-modes (SECOM) were found theoretically [3] to propagate along plane plasmadielectric interface, when an external constant magnetic field is parallel to the plasma boundary and penetration depth of the modes is approximately equal to their wavelength. SECOM frequencies decrease if their wave number grows, their damping is determined by both collision (interaction between plasma particles) and kinetic (interaction between particles and plasma interface) mechanisms. Dispersion properties of surface electron cyclotron X-modes (SECXM) were studied theoretically in [4]. Unlike the SECOM they are unidirectional modes, their propagation coincides with direction of Larmor rotation of electrons on the plasma surface. They can propagate even along plasma-metal interface that makes them especially dangerous for destroying walls of fusion chambers. Sets of equations for these Xand O-modes are obtained by application of non-linear boundary conditions for their tangential magnetic field. Non-linear boundary conditions, which describe discontinuity of tangential component of their magnetic field are formulated by the aid of conception of existence of surface electric current, which is induced by the mentioned above external alternation electric field on the plasma interface. The reduced sets of equations for the Xand O-modes wave packets are obtained in approximation that the packets are composed by the main harmonic and two nearest satellite harmonics. EPJ Web of Conferences DOI: 10.1051/

Nonleaky surface acoustic waves on a textured rigid surface

Through a systematic theoretical analysis, we find that coarse corrugations textured on rigid surfaces are preferred to realize highly confined surface acoustic waves over a broad frequency range. To give a direct validation for the existence of the nonleaky surface waves, we have experimentally measured the dispersion relation. The experimental result agrees excellently with the theoretical one. Extensive applications of such artificial surface waves can be predicted because of the flexibility in design.

A single‐feed circularly‐polarized patch antenna for reduced surface wave applications

AbstractA circularly polarized (CP) microstrip patch antenna design with single probe‐feed is proposed for reduced surface waves applications. The circular polarization is achieved by embedding a narrow slot at the center of a circular patch with an intersecting angle of 45 degrees relative to the feed position. Simulation results using the IE3D software facility have shown the capability of achieving circular polarization with high polarization purity while maintaining the reduction of surface waves and lateral waves. The simplicity of the design, together with the circular polarization characteristics and surface wave reduction indicate that this new antenna design is a promising candidate for applications including large patch antenna arrays and high precision GPS receiving antennas. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2675–2679, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24699

Characterization of ultrasonic Rayleigh surface waves in asphaltic concrete

This research examines the application of ultrasonic Rayleigh surface waves to the non-destructive evaluation (NDE) of asphaltic concrete in the frequency range 40–100 kHz. Two ultrasonic parameters, the phase velocity and amplitude attenuation, are considered to be sensitive to local compositional and structural variations and are measured. A wedge technique is used to generate Rayleigh surface waves in an asphaltic concrete beam with uniformly distributed aggregate, and this technique is shown to be effective in launching Rayleigh waves in this highly viscoelastic (absorptive) and heterogeneous medium. Three different ultrasonic detection setups using contact and non-contact transducers as receivers are examined and their results are compared. The experimental results show that the wedge generation technique along with an air-coupled receiving transducer with a finite-size aperture is the most reliable for characterizing Rayleigh waves in asphaltic concrete. It is also experimentally demonstrated that the proposed setup may be used to detect aggregate segregation in asphaltic concrete.

Analysis of Bloch-surface-wave assisted diffraction-based biosensors

A systematic study of Bloch surface wave (BSW) properties and applications in diffraction-based biosensors is presented. The design of such devices starts with the calculation of the BSW dispersion relation for a semi-infinite one-dimensional photonic crystal. We propose an approach in which polarization and 1DPC termination effects are simply described. Since in a realistic device the number of periods is limited, we investigate the issues arising from finite size effects and the choice of a structure substrate. Diffraction efficiency is studied as a function index contrast, multilayer termination, grating thickness, and number of periods. Numerical examples for Si/SiO2 and a-Si1−xNx:H periodic dielectric stacks are presented, showing that BSW can be exploited for the realization of efficient diffraction-based biosensors from the infrared to the visible range.

Feasibility of the surface-wave method for the assessment of physical properties of a dam using numerical analysis

A three-dimensional finite difference elastic wave model was developed to estimate the feasibility of surface wave applications in geotechnical problems. The wave motions calculated by the developed program in this study compare favorably with well known analytic solutions. The surface wave motions calculated from layered-dam type structures could be interpreted as an infinite layered structure using dispersion curves, but a special source of high energy (frequencies lower than 10 hertz [Hz]) is needed to assess the physical properties at depths on the order of tens of meters. A high-energy source in the low frequency band, however, can result in structural damage to a dam, which would limit field applications of the program. The dispersion curves calculated from the surface wave motion of homogeneous and center-core type dam models would result in fatal errors in the model if the conventional infinite layer structure is used in their interpretation. This is because the surrounding materials and boundaries of a dam create some distortion in the dispersion curve of the surface wave. It is strongly recommended to use a three-dimensional inversion model for correct interpretation and estimation of physical properties of dam materials when using the surface wave application for dam inspection.

Analysis of Short-Period Rayleigh Waves Recorded in the Bohemian Massif Area During Celebration 2000 Experiment

The aim of this paper is to show the application of short-period surface waves recorded during deep seismic sounding experiment for constraining shallow velocity structure of the crust. Phase velocity of fundamental mode Rayleigh waves, observed along the CELEBRATION 2000 experiment profile CEL09, were obtained by a p-ω method and has been subsequently inverted for one-dimensional shear velocity models for the top 2 km. Multiple filter technique applied to one shot gather was used to carry out a joint inversion of phase and group velocity data and to provide γR data to be used for Qβ inversion. Validity of obtained VS and Qβ models was confirmed by the reflectivity method. Noticeably, no clear dispersive wawes were observed in the Tepla-Barrandian Unit. Quasi-2D model based on the individual 1D VS models is well correlated with the surface geology. Lower VS are observed in the Saxothuringian Zone in comparison to the Moldanubian Zone. In the vicinity of the Central Bohemian and Moldanubian Plutons, the near-surface VS values are relatively low, but below 1 km depth, they are higher than in surrounding areas. We interpret it as the result of the weathering and cracks within the granitoid rocks.

SAW device applications of longitudinal leaky surface waves on lithium tetraborate.

The possibility of high frequency SAW device applications of longitudinal leaky surface waves (LLSW) on lithium tetraborate (Li2 B4O7; LBO) is investigated in this paper. An electrical equivalent circuit model (ECM) is extended in order to consider effects of bulk wave scattering for the LLSWs. The equivalent circuit parameters used in the extended ECM for designing the LLSW devices are directly determined from numerically calculated dispersion curves. For applications of the LLSW, high frequency SAW filters on LBO with the Euler angles (0°, 47.3°, 90°) are demonstrated. As examples of the high frequency devices, 1.5 GHz and 1.2 GHz SAW filters using the mode are designed by using the extended ECM, and fabricated by using conventional patterning processes. One is for the filter of the global positioning system (GPS), another is for the 1.2 GHz band data transmission radio system in Japan. As a result, low loss SAW filters can be obtained easily without submicron fabrication techniques by using the LLSWs on LBO. Furthermore, the frequency response calculated by the extended ECM are in a good agreement with the experiments.

Application of seismic surface waves at a pre‐Columbian settlement in Honduras

Application of seismic surface waves at a pre‐Columbian settlement in Honduras

Application of seismic surface waves at a pre-Columbian settlement in Honduras

A technique to locate culturally significant features by means of mechanical stiffness contrasts using seismic surface waves was applied at a Pre-Columbian settlement along the Talgua River near the town of Catacamas, Department of Olancho, Honduras, Central America. This technique was adapted from geotechnical engineering, where it is used to establish layering of soil and rock. With this surface-based, non-intrusive technique, a stress pulse is applied at the ground surface and the resulting ground motion is sensed and recorded using a pair of geophones placed on the ground surface a short distance away. Through spectral analysis, the dispersive characteristics of the earth between the two geophones are determined. Anomalies were mapped by comparing dispersion “signatures” along linear arrays. For corroboration, electrical resistivity measurements were also conducted. Ground truth was established through excavations, during which several significant features were unearthed. The most valuable result of the geophysical investigation was the discovery that a thick layer of fill had been brought in to level the site. This documented that the Talgua Village was constructed on top of a massive modification of the natural landscape and implies a higher level of political power and complexity than suggested by the modest size of the surface mounds. Copyright © 1998 John Wiley & Sons, Ltd.

The influence of local irregularities on the propagation of Love waves

The propagation of Love waves in models with local irregularities (a canyon or an alluvial valley) related to general waste deposit problems in environmental geophysics is numerically investigated. The investigation is based on a direct boundary element method for calculating wave fields and on a Green's function technique for evaluating transmission, reflection and ‘diffraction’ coefficients for Love waves, incident on a local surface or subsurface irregularity in layered media. The present model studies reveal that the influence of local irregularities on the propagation of Love waves depends both on the geometry and material properties of the local irregularities and on the dynamic parameters of the incident Love waves. Local irregularities lead to strong scattering of Love waves whose wavelengths are comparable to the characteristic sizes of the irregularities. For Love waves having wavelengths which are very large compared to the characteristic sizes of irregularities the influence of these irregularities are negligible. In addition, Love waves incident on a local irregularity always undergo mode conversion. Part of the energy of the incident Love wave will covert to other Love wave modes and body waves. With respect to the application of surface waves in environmental geophysics, two results may be stressed: (i) Though the conversion of Love waves to body waves has been qualitatively anticipated in the past, its enormous strength quantified by the diffraction coefficients is interesting; (ii) Love waves are more sensitive to local velocity changes than to local density changes. For in situ measurements, this result leads to the conclusion that density is a less relevant quantity, although it may better characterize the material inside a waste deposit than velocity.

Laser-generated rayleigh waves in graphite/epoxy composites

This study explores the potential for application of laser-induced surface or Rayleigh waves on graphite/epoxy composites. Rayleigh waves were generated by a Q-switched ruby laser in the ablation regime and detected by a pinducer which permitted accurate phase-velocity measurements. The Rayleigh wave velocity was measured in various directions relative to the fiber direction. Experimental results agreed closely with numerical predictions in the thick plate, but showed some increase of phase velocity in the thin plate. Laser-generated Rayleigh waves, particularly along the fiber direction, showed good potential for applications in NDT.

Application of surface waves for antifouling

Marine fouling in ships and biofouling in condenser tubes, etc. cause numerous problems and a large reduction of fuel efficiency. Conventional methods include toxic paints and hull vibration. A nontoxic solution would be to excite Love waves on the surface and prevent the very first bio‐attachment on the surface. A thin PZT film with IDTs (InterDigital Transducers) flush mounted to the surface is used to launch these waves. Experimental results of this technique, which seems viable and cost effective, and most importantly, nontoxic, will be discussed.

Dispersion and attenuation of surface waves due to distributed surface-breaking cracks

Dispersion and attenuation of surface waves propagating over the free surface of a half-space containing distributed surface-breaking cracks are investigated. The 3-D problem of scattering of surface waves by a single surface-breaking crack is first formulated and the characteristic amplitude factor of the scattered surface wave is expressed in terms of the crack opening displacements. A relation between this amplitude factor and the scattered power flow is then derived. The scattering cross section is introduced as a measure of energy removal from the incident surface wave. By using energy considerations, the coefficient of attenuation is subsequently expressed in terms of the scattering cross section. Use of the Kramers–Krönig relation then yields an expression for the phase velocity. Numerical results are given for both the coefficient of attenuation and the phase velocity, as functions of the crack density, a characteristic length dimension of the crack and the frequency. The theoretical framework provided in this paper may lead to a novel application of surface waves for the detection and characterization of fatigue damage of metals under cyclic loading.

Application of surface acoustic waves to direct measurement of the parameters of superfluid helium thin films

The authors propose an acoustic method to measure directly the density of the normal component in thin films of superfluid helium. The effect of the helium film on the velocity and the penetration depth of Love and Gulyaev-Bleustein shear surface waves is analysed. The advantage of the method based on the application of shear surface waves is that the change in their velocity, as is shown, is proportional to the normal component density and the helium film thickness.

Nonreciprocal surface waves

Some surface waves have the property that a simple reversal of the direction of propagation leads to a surface wave with a different frequency. In this paper we explore the properties of such nonreciprocal waves for a variety of excitations and structures. For a semi-infinite geometry the nonreciprocity can be quite dramatic. For example in some magnetic systems, a surface wave exists for propagation in one direction, but no surface wave exists for propagation in the reverse direction. In thin films, it is generally the localization of the surface wave which is nonreciprocal. Thus a surface wave travelling along the + x axis may be localized at the upper surface of the film, while a surface wave travelling along the - x axis is localized at the lower surface of the film. We will discuss nonreciprocal surface excitations which occur in a variety of systems. The elementary properties of nonreciprocal surface plasmons, polaritons, phonons and magnons are derived. We briefly review some of the applications of nonreciprocal surface waves to practical signal processing devices. Finally we discuss the microscopic origin of nonreciprocity.

Piezoelectricity in thin film materials

The need for efficient ultrasonic transducers in the 100 MHz to several GHz frequency range has stimulated the development of a number of transducer structures using piezoelectric thin films. Starting in the early 1960’s with primarily longitudinal bulk mode transduction in CdS films, the piezoelectric thin film transducer technology has progressed over the years to the controlled generation and detection of both longitudinal and shear waves in films of CdS, ZnO, and other materials. While most of the early work was directed towards bulk waves, the more recent strong interest in SAW devices has encouraged the use of piezoelectric thin films, primarily ZnO, in this arena also. A combination of experimental work and theoretical studies has generated a rather comprehensive understanding of the structure and behavior of piezoelectric thin films for both bulk and surface wave applications.