Ultrasonic examination of a thin, textured metal plate with Penrose tile structure consisting of pitched indentations.

A feasibility study is presented on the experimental application of ultrasound to examine rolled stainless steel plates having equidistant surface textures in two directions in the form of Penrose tiles. The specific problem of interest is investigating surface profile quality in terms of its equidistance and depth to monitor the manufacturing process. The goal is to eventually replace current time-consuming optical examination procedures with a reliable and rapid ultrasonic inspection technique. Two practical experimental setups are discussed and compared in this work: examining frequency spectra obtained from normal incidence pulse-echo measurements, and those obtained at Laue angle incidence. A thorough survey of ultrasonic methods precedes the experimental results to investigate such surfaces from a historical perspective.

Ultrasonic testing of the biomechanical properties of donation blood.

Background.Donated blood is routinely preserved for about six weeks. After that, a considerable amount of unused blood is discarded for safety. We carried out sequential measurements of the ultrasonic parameters (Velocity of propagation of ultrasound, its attenuation, and relative nonlinearity coefficient B/A) for red blood cells (RBCs) bags in their physiological preserving conditions in the blood bank, in a given experimental setup, to investigate the gradual deteriorations in the biomechanical properties of RBCs.Materials and Methods. We discuss our primary findings, which indicate the applicability of ultrasound techniques as a quantitative quick, non-invasive routine check for the validity of sealed blood bags. The technique can be applied during and beyond the regular preservation period, thus enabling deciding for each bag to either further preserve or withdraw.Results and Discussion. Considerable increases in the velocity of propagation (ΔV = 966 m s-1) and ultrasound attenuation (Δα= 0.81 dB C-1m-1) were detected to take place during the preservation time. Likewise, the relative nonlinearity coefficient showed a generally rising trend during the preservation period (Δ(B/A) = 0.0129). At the same time, a distinctive feature characteristic of a specific blood group type is realized in all cases. Due to the complex stress-strain relations and their reflection on the hydrodynamics and flow rate of non-Newtonian fluids, the increased viscosity of long-preserved blood may justify the known post-transfusion flow complications.

Learning the propagation properties of rectangular metal plates for Lamb wave-based mapping.

The inspection of sizeable plate-based metal structures such as storage tanks or marine vessel hulls is a significant stake in the industry, which necessitates reliable and time-efficient solutions. Although Lamb waves have been identified as a promising solution for long-range non-destructive testing, and despite the substantial progress made in autonomous navigation and environment sensing, a Lamb-wave-based robotic system for extensive structure monitoring is still lacking. Following previous work on ultrasonic Simultaneous Localization and Mapping (SLAM), we introduce a method to achieve plate geometry inference without prior knowledge of the material propagation properties, which may be lacking during a practical inspection task in challenging and outdoor environments. Our approach combines focalization to adjust the propagation model parameters and beamforming to infer the plate boundaries location by relying directly on acoustic measurements acquired along the mobile unit trajectory. For each candidate model, the focusing ability of the corresponding beamformer is assessed over high-pass filtered beamforming maps to further improve the robustness of the plate geometry estimates. We then recover the optimal space-domain beamformer through a simulated annealing optimization process. We evaluate our method on three sets of experimental data acquired in different conditions and show that accurate plate geometry inference can be achieved without any prior propagation model. Finally, the results show that the optimal beamformer outperforms the beamformer resulting from the predetermined propagation model in non-nominal acquisition conditions.

Assessment of a low-frequency ultrasound device on prevention of biofilm formation and carbonate deposition in drinking water systems.

A device generating low-frequency and low-intensity ultrasound waves was used for mitigating biofilm accumulation and scaling. Two systems were tested: a lab-scale plate heat exchanger operated with continuously recycled water and a continually fed flow-through drinking water pilot used for mimicking water circulation in pipes. Initial deposition of bacterial cells was not prevented by ultrasound wave treatment. However, whatever the tested system, both further calcium carbonate deposition and biofilm growth were markedly inhibited. Biofilms formed in reactors subjected to low-frequency and low-intensity ultrasound waves were weakly attached to the material. Even though the activity of bacteria was affected as shown by their lower cultivability, membrane permeability did not appear compromised. Ultrasound technology sounds very promising in both the mitigation of drinking water biofilm and carbonate accumulation.

Scanning Acoustic Microscopy Comparison of Descemet's Membrane Normal Tissue and Tissue With Fuchs' Endothelial Dystrophy.

Purpose: To describe the application of scanning acoustic microscopy in the GHz-range (GHz-SAM) for qualitative imaging and quantitative characterization of the micromechanical properties of the Descemet's membrane and endothelial cells of cornea tissue. Methods: Investigated were samples of a normal tissue and a tissue with Fuchs' endothelial dystrophy (FECD, cornea Guttata). Descemet's membranes were fixed on glass substrates and imaged utilizing a focused acoustic lens operating at a center frequency of 1 GHz. Results: GHz-SAM data, based on the well-established V(z) technique, revealed discrepancies in the velocity of the propagation of Rayleigh surface acoustic waves (RSAW). RSAW were found to be slower in glass substrates with FECD samples than in the same glass substrates (soda-lime) with normal Descemet membrane, which indicates lower shear and bulk moduli of elasticity in tissues affected by FECD. Conclusions: Noninvasive/nondestructive GHz-SAM, is utilized in this study for the imaging and characterization of Descemet membranes, fixated on glass substrates. V(z) signatures containing sufficient oscillations were obtained for the system of Descemet membranes on glass substrates. The observed variation in the microelastic properties indicates potential for further investigations with GHz-SAM based on the V(z) technique.

Towards an Ultrasonic Guided Wave Procedure for Health Monitoring of Composite Vessels: Application to Hydrogen-Powered Aircraft.

This paper presents an overview and description of the approach to be used to investigate the behavior and the defect sensitivity of various ultrasonic guided wave (UGW) modes propagating specifically in composite cylindrical vessels in the framework of the safety of hydrogen energy transportation such as hydrogen-powered aircrafts. These structures which consist of thick and multi-layer composites are envisioned for housing hydrogen gas at high pressures. Due to safety concerns associated with a weakened structure, structural health monitoring techniques are needed. A procedure for optimizing damage detection in these structural types is presented. It is shown that a finite element method can help identify useful experimental parameters including frequency range, excitation type, and receiver placement.

Pulsed ultrasonic comb filtering effect and its applications in the measurement of sound velocity and thickness of thin plates.

An analytical and experimental study of the pulsed ultrasonic comb filtering effect is presented in this work intending to provide a fundamental tool for data analysis and phenomenon understanding in pulsed ultrasonics. The basic types of comb filter, feedforward and feedback filters, are numerically simulated and demonstrated. The characteristic features of comb filters, which include the formula for determining the locations of the spectral peaks or notches and the relationship between its temporal characteristics (relative time delay between constituent pulses) and its spectral characteristics (frequency interval between peaks or notches), are theoretically derived. To demonstrate the applicability of the comb filtering effect, it is applied to measuring the sound velocities and thickness of a thin plate sample. It is proven that the comb filtering effect based method not only is capable of accurate measurements, but also has advantages over the conventional time-of-flight based method in thin plate measurements. Furthermore, the principles developed in this study have potential applications in any pulsed ultrasonic cases where the output signal shows comb filter features.

Characterization of the geometry of microscale periodic structures using acoustic microscopy.

Periodic structures are very common in both scientific investigations and engineering applications. The geometry of the periodic structure is important for its designed functionality. Although the techniques such as optical and electron microscopy are capable of measuring the periodicity of microscale periodically-corrugated structures, they cannot be used to measure the height or depth of the corrugation. The technique of acoustic microscopy has been developed rapidly and it has been applied in the studies of steel integrated structures, ferro-elastic ceramics, human retina, semiconductors, composites, etc. In acoustic microscopy, V(z) curves have been used to investigate the visco-elastic parameters of thin sliced samples of composites, animal tissue, etc., while in this work it is applied in characterizing the geometry of periodically corrugated structures. The measurements of the geometry of periodic structures obtained using acoustic microscopy are compared with those obtained using optical microscopy, and the reliability of this acoustic technique is also examined.

Investigation of the origin of acoustic Wood anomaly.

In the spectrum of a broadband wave reflected from a periodically corrugated surface, spectral anomalies have been observed earlier and identified as acoustic Wood anomalies. A thorough investigation of the physical origin of the acoustic Wood anomaly is made through an experimental investigation and an examination of the existing theories. The existing explanations of acoustic Wood anomaly are reviewed and evaluated based on the analysis of the experimental results obtained from three types of interfaces: liquid-solid, solid-liquid and solid-air interfaces. In addition, spectral tips are observed and identified as another type of acoustic Wood anomaly. The investigation is based on time-frequency analysis and offers much more insight into this phenomenon than earlier research where only the frequency spectrum was considered.

Acousto-optic Bragg imaging of biological tissue.

Acousto-optic Bragg imaging is a technique that uses the interaction of light with ultrasound to optically image obstructions in acoustical fields. Existing reports of acousto-optic Bragg imaging based on transmission of acoustic fields through obstructions exhibit strong acoustic impedance mismatches manifested by poor image quality and missing details of physical structures of obstructions. In this work, the image quality was improved to exhibit detailed physical structures of an object by using an improved Bragg imaging system described in Sec. III below. This paper investigates the possibility of extending an acoustic Bragg imaging technique in transmission mode to image animal or plant tissues; a small azalea leaf is used as an illustration in this case. The Bragg image produced clearly shows the veins of the vascular azalea leaf serving as a proof of concept for cost-effective potential application of acoustic Bragg imaging of biological objects in the medical field. Moreover, acousto-optic Bragg imaging is potentially harmless to biological cells and is sensitive to density and elastic variations in the tissue.

Scholte-Stoneley waves on an immersed solid dihedral: generation, propagation and scattering effects.

Scholte-Stoneley wave propagation on a dihedral and more precisely the diffraction effects occurring at the corners, has since long been of high importance for nondestructive testing of materials and structures. Experimental investigations have been reported in the past. Simulations based on radiation mode theory have been published before, explaining the only situation for which the model is applicable namely rectangular corners. The current report describes an investigation applying finite element simulations. Results are obtained not only for rectangular corners but for any possible corner angle. The outcome is in agreement with reported experiments. Moreover a critical corner angle is found below and beyond which different diffraction phenomena occur. The study is performed for different isotropic solids.

Baseline subtraction technique in the frequency-wavenumber domain for high sensitivity damage detection.

This paper suggests a method for high-sensitivity damage detection. The method is based on pitch-catch measurements of Lamb waves combined with a baseline subtraction technique in the frequency-wavenumber domain. Small amplitude converted modes, generated during the interaction of propagating waves with damage, can thus be detected with minimal a priori information regarding their expected location in the frequency-wavenumber plane. This method is applied in the present paper to a case of notches with varied depth. Finite element simulations are carried out in the temporal domain to mimic results obtainable in real-world experiments. Two cases are studied, namely when each of the two pure fundamental modes are incident on a notch. The advantages of the method are detailed. The procedure to implement this method is described in the context of Structural Health Monitoring (SHM) or Non-Destructive Testing (NDT).

Ultrasonic geometrical characterization of periodically corrugated surfaces.

Accurate characterization of the characteristic dimensions of a periodically corrugated surface using ultrasonic imaging technique is investigated both theoretically and experimentally. The possibility of accurately characterizing the characteristic dimensions is discussed. The condition for accurate characterization and the quantitative relationship between the accuracy and its determining parameters are given. The strategies to avoid diffraction effects instigated by the periodical nature of a corrugated surface are also discussed. Major causes of erroneous measurements are theoretically discussed and experimentally illustrated. A comparison is made between the presented results and the optical measurements, revealing acceptable agreement. This work realistically exposes the capability of the proposed ultrasonic technique to accurately characterize the lateral and vertical characteristic dimensions of corrugated surfaces. Both the general principles developed theoretically as well as the proposed practical techniques may serve as useful guidelines to peers.

Air-coupled ultrasonic investigation of stacked cylindrical rods.

Measurement of the periodicities of diffraction gratings composed of stacked cylindrical rods is explored using an air-coupled ultrasonic technique. Acoustic Bragg scattering from three periodic structures is investigated by means of a polar scan. Consequently, Bragg angles and corresponding frequencies are obtained from angular spectrograms, using two different data acquisition approaches. According to the principle of Bragg scattering, the periodicities of the three periodic structures, which are equal to the diameter of the cylindrical rods, are determined. In order to evaluate the reliability of the technique and its accuracy, the obtained diameters are compared with those directly measured with a digital caliber. To show the robustness of the technique measurements are done with transducers of different quality.

A feasibility study of the use of bounded beams resembling the shape of evanescent and inhomogeneous waves.

Plane waves are solutions of the visco-elastic wave equation. Their wave vector can be real for homogeneous plane waves or complex for inhomogeneous and evanescent plane waves. Although interesting from a theoretical point of view, complex wave vectors normally only emerge naturally when propagation or scattering is studied of sound under the appearance of damping effects. Because of the particular behavior of inhomogeneous and evanescent waves and their estimated efficiency for surface wave generation, bounded beams, experimentally mimicking their infinite counterparts similar to (wide) Gaussian beams imitating infinite harmonic plane waves, are of special interest in this report. The study describes the behavior of bounded inhomogeneous and bounded evanescent waves in terms of amplitude and phase distribution as well as energy flow direction. The outcome is of importance to the applicability of bounded inhomogeneous ultrasonic waves for nondestructive testing.

Optical Bragg imaging of acoustic fields after reflection.

Bragg diffraction of x-rays occurs when the rays interact with a crystalline lattice at the appropriate angle. Bragg diffraction of visible light occurs when the light interacts at the Bragg angle with an ultrasonic field of the appropriate frequency. (The spacing between acoustic condensations and rarefactions acts like the planes in an atomic lattice.) If a beam of light is Bragg diffracted by an ultrasonic beam that previously has passed through an object, an image of the structure of the object is made visible in the diffraction field of the optical beam since there is a one-to-one mapping of the ultrasonic field onto the diffraction order. In many acoustic Bragg imaging applications, the sound field must pass through the object which is to be imaged. Ultrasonic attenuation at the very high acoustic frequencies needed for Bragg imaging (typically approximately 25-30 MHz) severely limits the nondestructive testing (NDT) applications of traditional acoustic Bragg imaging. In this paper, a reflection-based application of acoustic Bragg imaging is discussed which may have useful industrial and biomedical NDT applications.

Authors' Response to Strasberg's "Comment on 'Measurement of the frequency dependence of the ultrasonic parametric threshold amplitude for a fluid-filled cavity' " [J. Acoust. Soc. Am. 125, 1857 (2009)].

This letter is a response to Strasberg's recent paper, "Comment on 'Measurement of the frequency dependence of the ultrasonic parametric threshold amplitude for a fluid-filled cavity.'" The authors dispute the conclusions of Strasberg regarding the effect observed by Teklu et al. [J. Acoust. Soc. Am. 120, 657-660 (2006)] published previously in JASA.

Angular and frequency spectral analysis of the ultrasonic backward beam displacement on a periodically grooved solid.

The ultrasonic backward beam displacement, which has been shown to occur when a bounded beam is incident upon a periodically corrugated liquid-solid interface, is studied experimentally. This effect has been previously studied on a periodic water-brass interface at one particular frequency (6 MHz) and one corresponding angle of incidence (22.5 degrees), but the question has remained whether it would also exist at other frequency and angle combinations. The knowledge of whether this phenomenon is a coincidence or whether it will occur for other frequency and angle combinations contributes to a better understanding of the interaction of ultrasound with periodic structures and diffraction effects, in particular. Potential applications exist in the study of phononic crystals and in the non-destructive evaluation of materials. The present work reports results from recent experiments on the same periodically grooved brass sample that was employed in the first investigations of this phenomenon. Through the examination of frequency spectra in the form of angular and classical spectrograms, the experiments reported here show the backward beam displacement to occur for multiple angles of incidence and frequencies. Furthermore, evidence is shown as to the exact cause of the backward beam displacement, namely, a backward propagating Scholte-Stoneley wave.

Reflection of plane elastic waves in tetragonal crystals with strong anisotropy.

Propagation and reflection of plane elastic waves in the acousto-optic crystals tellurium dioxide, rutile, barium titanate, and mercury halides are examined in the paper. The reflection from a free and flat boundary separating the crystals and the vacuum is investigated in the (001) planes in the case of glancing acoustic incidence on the boundary. The analysis shows that two bulk elastic waves may be reflected from the crystal surface. The energy flow of one of the reflected waves in paratellurite and in the mercury compounds propagates in a quasi-back-direction with respect to the incident energy flow. It is proved that energy flows of the incident and reflected elastic waves are separated by a narrow angle of only a few degrees. It is also found that the relative intensity of the unusually reflected waves is close to a unit in a wide variety of crystal cuts. General conclusions related to acoustic propagation and reflection in crystals have been made based on the examined phenomena in the materials.

Increased efficiency of surface wave stimulation on the inaccessible side of a thick isotropic plate with superimposed periodicity.

Because of the growing number of applications of phononic crystals and other periodic structures, there is a renewed and growing interest in understanding the interaction of ultrasound with periodically corrugated surfaces. This paper presents a theoretical investigation of the transformation of ultrasound incident from the solid side onto a solid-liquid periodically corrugated interface. It is shown that it is possible to tailor the shape of a corrugated surface with given periodicity such that there is a significant amount of energy transformed into Scholte-Stoneley waves than if pure saw-tooth or sine-shaped surfaces were used. This permits the fabrication of periodic structures that can be patched on or engraved in body parts of a construction and enables efficient generation of Scholte-Stoneley waves. The study is performed for incident homogeneous plane waves as well as for bounded beams. Incident longitudinal waves are studied as well as incident shear waves.