Ultrasonic Microscopy Research Articles

Analytical model of the nonlinear dynamics of cantilever tip-sample surface interactions for various acoustic atomic force microscopies

A comprehensive analytical model of the interaction of the cantilever tip of the atomic force microscope (AFM) with the sample surface is developed that accounts for the nonlinearity of the tip-surface interaction force. The interaction is modeled as a nonlinear spring coupled at opposite ends to linear springs representing cantilever and sample surface oscillators. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a standard iteration procedure. Solutions are obtained for the phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) techniques including force modulation microscopy, atomic force acoustic microscopy, ultrasonic force microscopy, heterodyne force microscopy, resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), and the commonly used intermittent contact mode (TappingMode) generally available on AFMs. The solutions are used to obtain a quantitative measure of image contrast resulting from variations in the Young modulus of the sample for the amplitude and phase images generated by the A-AFM techniques. Application of the model to RDF-AFUM and intermittent soft contact phase images of LaRC-cp2 polyimide polymer is discussed. The model predicts variations in the Young modulus of the material of 24 percent from the RDF-AFUM image and 18 percent from the intermittent soft contact image. Both predictions are in good agreement with the literature value of 21 percent obtained from independent, macroscopic measurements of sheet polymer material.

Brittle wear of silicate materials by Hertzian rubbing contact

We studied the tribological properties of a structural series of 11 silicate materials to identify the main physical parameters that control the brittle wear of these materials. First, for each material we characterized Young's modulus E by ultrasonic microscopy, roughness σ by atomic force microscopy and crack pressure Pc by Hertzian indentation testing. Second, we measured the static and dynamic friction coefficients μS and μD, respectively, with a ball probe tribometer for each material and for three hardnesses of the ball probe. The experiments showed that crack density, which quantified the brittle wear of the materials, was controlled by an adimensional number, Cr = Pc/μSE. We show in this paper how this number takes into account the combined effects of the mechanical properties, the lubricating coating layer and the residual internal stresses of these materials.

Local Plastic Deformation and Failure Behavior of Nd:YAG Laser Welds in AA5182-O and AA6111-T4

An experimental methodology that quantifies tensile properties and damage accumulation in Nd:YAG laser welds in aluminum sheet metals is presented. Coupons identified as AA5182-O and AA6111-T4, with bead-on-plate and lap welds in various configurations, were quasi-statically strained to fracture in a miniature tensile stage. Two-dimensional strain fields, measured with a state-of-the-art digital image correlation (DIC) algorithm, served as the basis for the calculation of true stress–true strain behavior and the salient tensile properties of the weld materials. Scanning electron microscopy (SEM) analysis provided estimates of fracture strength, while ultrasonic microscopy was used to quantify weld porosity and establish a qualitative linkage with observed deformation behavior. Although containing substantial porosity, the AA5182-O all-weld material was found to have greater ductility than the AA6111-T4 material. The nominal strength of the AA5182-O/AA6111-T4 lap welds exceeded that of welds in AA6111-T4/AA5182-O, up to 50 pct strain. This suggests that bimaterial lap-weld strength at large plastic strains is dependent upon the placement of each Al alloy relative to the laser beam. Atomic force microscopy confirmed that fracture consistently occurred along weld/base metal interfaces, irrespective of the alloy type.

Nanoscale subsurface imaging via resonant difference-frequency atomic force ultrasonic microscopy

A scanning probe microscope methodology, called resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), has been developed. It employs an ultrasonic wave launched from the bottom of a sample while the cantilever of an atomic force microscope, driven at a frequency differing from the ultrasonic frequency by one of the contact resonance frequencies of the cantilever, engages the sample top surface. The nonlinear mixing of the oscillating cantilever and the ultrasonic wave in the region defined by the cantilever tip–sample surface interaction force generates difference-frequency oscillations at the cantilever contact resonance. The resonance-enhanced difference-frequency signals are used to create images of nanoscale near-surface and subsurface features. An analytical model is presented for assessing the RDF-AFUM phase signal resulting from near-surface variations in the sample contact stiffness and from the interaction of the bulk wave with subsurface structures. The application of the model to RDF-AFUM phase measurements of a 12.7μm thick film of LaRC™-CP2 polyimide polymer containing a monolayer of gold nanoparticles embedded 7μm below the specimen surface reveals variations in the Young modulus of the material of approximately 24% over regions roughly 10–35nm wide. The magnitude of the modulus variations suggests the occurrence of contiguous amorphous and crystalline phases within the bulk of the polymer. The RDF-AFUM micrograph indicates a preferential growth of the crystalline phase in the vicinity of the gold nanoparticles.

Celebration of Floyd Dunn: Some remarks about his life, career, and accomplishments

No celebration of Floyd Dunn would be complete without some remarks about the life, career, and accomplishments of this remarkable scientist/engineer. Floyd had made significant scholarly contributions in six general themes, and you will hear about their impact to our welfare during the celebration. The six ultrasonic biophysics themes include absorptive processes, nonlinear phenomena, application in living systems, toxicity, measurement techniques, and ultrasonic microscopy. Floyd has been recognized for his accomplishments by being the recipient of most of the important national and international awards including National Academy of Sciences, National Academy of Engineering, ASA’s Gold Medal and Silver Medal in Bioresponse to Vibration, Acoustical Society of Japan’s Medal of Special Merit, IEEE’s Edison Medal, and election to Fellowship in six professional societies.

Image processing for scanning-type biological ultrasonic microscope considering its beam characteristics

We have been developing a biological ultrasonic microscope with a high lateral resolution. An acoustic pulse is transmitted by a scanning transducer to a substrate on which a thin slice of a tissue is embedded. The transducer has a minute curvature in order to focus an acoustic beam with a high frequency component. It may be fabricated by MEMS technology; however, from the point of view of engineering, it may not be easy to guarantee the reproducibility of beam pattern as specified. In a high frequency range, a small error in fabrication will lead to a big difference in beam pattern, which strongly affects the observed image. Using newly proposed methodology to observe a well-defined pin-hole, we found that each commercial single probe transducer with the same specification has a unique beam pattern. In addition, the pattern was not always concentric. Consequently, we proposed a method to compensate the image that was obtained using an eccentric beam pattern. A clearer image was successfully obtained after the compensation.

Analysis of Dominant Frequencies of Glass Fiber/Aluminum Laminates during Acoustic Emission Measurement

Dominant frequency characteristics of acoustic emission (AE) from single-edge-notched (SEN) glass fiber aluminum laminates (GFAL) under tensile loads were analyzed in relation to fracture mechanisms. The first and second peak frequencies expressed the characteristic changes of fracture processes in SEN-GFAL specimens such as macro-crack propagation and/or delamination between aluminum and fiber layers. On the basis of the above frequency analysis and of the fracture observation with ultrasonic through-scan and various microscopes, characteristic models for crack propagation of SEN-GFAL was proposed according to various orientations of fiber layer.

Multiscale mechanics of hierarchical structure/property relationships in calcified tissues and tissue/material interfaces

This paper presents a review plus new data that describes the role hierarchical nanostructural properties play in developing an understanding of the effect of scale on the material properties (chemical, elastic and electrical) of calcified tissues as well as the interfaces that form between such tissues and biomaterials. Both nanostructural and microstructural properties will be considered starting with the size and shape of the apatitic mineralites in both young and mature bovine bone. Microstructural properties for human dentin and cortical and trabecular bone will be considered. These separate sets of data will be combined mathematically to advance the effects of scale on the modeling of these tissues and the tissue/biomaterial interfaces as hierarchical material/structural composites. Interfacial structure and properties to be considered in greatest detail will be that of the dentin/adhesive (d/a) interface, which presents a clear example of examining all three material properties, (chemical, elastic and electrical). In this case, finite element modeling (FEA) was based on the actual measured values of the structure and elastic properties of the materials comprising the d/a interface; this combination provides insight into factors and mechanisms that contribute to premature failure of dental composite fillings. At present, there are more elastic property data obtained by microstructural measurements, especially high frequency ultrasonic wave propagation (UWP) and scanning acoustic microscopy (SAM) techniques. However, atomic force microscopy (AFM) and nanoindentation (NI) of cortical and trabecular bone and the dentin–enamel junction (DEJ) among others have become available allowing correlation of the nanostructural level measurements with those made on the microstructural level.

Ultrasonic speed microscopy for imaging of coronary artery

We have been developing a scanning acoustic microscope (SAM) system for medicine and biology featuring quantitative measurement of ultrasonic speed and attenuation of soft tissues. In the present study, we will propose a new concept ultrasonic speed microscopy that can measure the thickness and ultrasonic speed using fast Fourier transform of a single pulsed wave instead of continuous waves used in conventional SAM systems. Six coronary arteries were frozen and sectioned approximately 10 μm in thickness. They were mounted on glass slides without cover slips. The scanning time of a frame with 300 × 300 pixels was 121 s and two-dimensional distribution of ultrasonic speed was obtained. The ultrasonic speed was 1720 m/s in the thickened intima with collagen fiber, 1520 m/s in lipid deposition underlying fibrous cap and 1830 m/s in calcified lesion in the intima. These basic measurements will help understanding echogenecity in intravascular ultrasound (IVUS) images. Imaging of coronary artery with the ultrasonic speed microscopy provides important information for study of IVUS coronary imaging.

Acoustic visualization of cold flakes and crack propagation in aluminum alloy die-cast plate

Acoustic images received at different depths of aluminum alloy (ADC12) die-cast plates containing coarse cold flakes were compared with microstructures at the same depth. The bright and dark regions in the acoustic images coincided with the oxide layer on the initially solidified surface of the cold flake and the body of the cold flake, respectively. These results show the ability of nondestructive detection of cold flakes by the ultrasonic microscopy. The specimens were then fabricated to contain the cold flake at a center, and subjected to three-point bending test. When the coarse cold flake existed apart from the tensile side surface of the specimen, a crack initiated at a small cold flake on the side surface and propagated in the specimen. In this case the bending strength was almost the same as the tensile strength (285 MPa) of the die-cast plate. When the cold flake existed on the tensile side surface or at a position less than 0.5 mm inside the surface, the crack propagated along the oxide layer of the cold flake. In this case, the bending strength decreased from the tensile strength when the cold flake approached the side surface. A relation between the bending strength and the position of the cold flake in the specimen was discussed from the standpoint of the fracture mechanics.

Integrated cantilever development for ultrasonic and acoustic scanning probe microscopy

Although conventional optical lever technology typically used for scanning probe microscope applications has proven high sensitivity, accuracy, and is cost effective for most applications involving micromachined cantilever deflection measurements, the frequency limitations and space needs limit its applicability to emerging ultrasonic-based scanning probe microscopy (SPM) applications. Recently, the fabrication of cantilevers integrated with actuation and sensing components has opened avenues for feedback-based driving of micromachined cantilevers at higher order resonance frequencies, while sensing average deflection without the need of an optical deflection pathway for average deflection sensing. The work presented here reviews recent efforts by our group in fabricating micromachined cantilevers with integrated ZnO actuation layers to induce cantilever deflection. These cantilevers are being fabricated for use in a heterodyne force microscopy system (HFM) to enable SPM imaging contrast based on viscoelastic response of a surface in contact with a micromachined tip, wherein active-feedback technology is being applied to maintain ultrasonic tip excitation at higher order cantilever resonances. The first- and second-pass fabrication results are presented and reviewed regarding cantilever release and ZnO actuator (and electrode) fabrication. Dynamic response data from these structures, measured via laser Doppler vibrometry, reveal the expected resonance structure for a cantilever of these dimensions.

High-frequency ultrasound annular array imaging. Part II: digital beamformer design and imaging

This is the second part of a two-paper series reporting a recent effort in the development of a high-frequency annular array ultrasound imaging system. In this paper an imaging system composed of a six-element, 43 MHz annular array transducer, a six-channel analog front-end, a field programmable gate array (FPGA)-based beamformer, and a digital signal processor (DSP) microprocessor-based scan converter will be described. A computer is used as the interface for image display. The beamformer that applies delays to the echoes for each channel is implemented with the strategy of combining the coarse and fine delays. The coarse delays that are integer multiples of the clock periods are achieved by using a first-in-first-out (FIFO) structure, and the fine delays are obtained with a fractional delay (FD) filter. Using this principle, dynamic receiving focusing is achieved. The image from a wire phantom obtained with the imaging system was compared to that from a prototype ultrasonic backscatter microscope with a 45 MHz single-element transducer. The improved lateral resolution and depth of field from the wire phantom image were observed. Images from an excised rabbit eye sample also were obtained, and fine anatomical structures were discerned.

Central Corneal Thickness Measurements Using Orbscan II Scanning Slit Topography, Noncontact Specular Microscopy, and Ultrasonic Pachymetry in Eyes With Keratoconus

To compare corneal thickness measurements using Orbscan II scanning slit topography, Topcon SP-2000P noncontact specular microscopy, and ultrasonic pachymetry in eyes with keratoconus. Central corneal thickness was measured in 22 eyes with keratoconus. Eyes with apparent corneal opacity were excluded. Scanning slit topography, noncontact specular microscopy, and ultrasonic pachymetry were used in this sequence. The acoustic equivalent correlation factor (0.92) was used for Orbscan readings. Three devices gave significantly different corneal thickness readings (P < 0.001, repeated-measure analysis of variance). Measurements with Orbscan scanning slit topography (449.5 +/- 43.2 [SD] mum) were significantly smaller than those of ultrasonic pachymetry (485.0 +/- 29.3 microm; P < 0.001, Tukey multiple comparison) and SP-2000P noncontact specular microscopy (476.7 +/- 28.3 microm; P = 0.002). There were significant linear correlations between ultrasonic pachymetry and scanning slit topography (Pearson correlation coefficient r = 0.741, P < 0.001), between scanning slit topography and noncontact specular microscopy (r = 0.880, P < 0.001), and between noncontact specular microscopy and ultrasonic pachymetry (r = 0.811, P < 0.001). In eyes with keratoconus, Orbscan II scanning slit topography system gave significantly smaller corneal thickness readings than the other 2 devices. Measurements taken by noncontact specular microscopy and ultrasonic pachymetry were comparable. Three devices showed significant linear correlations with one another.

Three-dimensional ultrasound biomicroscopy, environmental and conventional scanning electron microscopy investigations of the human zonula ciliaris for numerical modelling of accommodation

Biomechanical modelling of the accommodation process is a useful tool for studying the mechanism of accommodation and presbyopia and can aid in the development of accommodative lens-replacing materials. Existing biomechanical models, however, use a very simplified zonula structure. The aim of this study was to use three-dimensional ultrasonic imaging and scanning electron microscopy to provide a more detailed, three-dimensional description of the structure of the human zonula to improve the modelling of accommodation. Five human eyes were examined without invasive manipulation using a custom-made three-dimensional ultrasonic imaging technique that allows scanning of features with a spatial resolution of 30 microm. Environmental and conventional scanning electron microscopy (SEM) provided information to complement the ultrasonic images for use in development of a more anatomically correct finite-element model of the zonula structures. These data along with the material properties of the ocular tissue structures were used to construct an advanced geometric model for finite-element simulation of the accommodation process. Images were obtained through three-dimensional ultrabiomicroscopy (3D-UBM) of anatomical features heretofore not directly imagable in their native state. Ciliary processes and zonula structures were clearly separated by both the 3D-UBM and the SEM methods. It was found that fibres inserting on the anterior and posterior lens capsule emerge anteriorly at the ciliary body. Fibres emerging near the pars plana insert on the lens and the ciliary body. No X-shaped crossing fibres were found. Modelling of the accommodation process with both the simple and the more complex geometric models produced refractive power changes comparable with in vivo findings. The 3D-UBM allowed examination of zonula structures in their native state with minimized preparation artefacts. While these data were incorporated into a complex and more anatomically correct finite-element simulation of intraocular features including lens, zonular system and ciliary body it was found that a simplified zonular model is sufficient for the numerical simulation of the accommodation process.

On Evaluation Method of Damage Development for CFRP Laminates under Low Impact Energy (1st Report, Estimation of Residual Strength based on Static Bending Test after Occurrence of Damage)

Compression after impact (CAI) test has been applied as a representative method of the evaluation for the residual strength of CFRP laminates after the occurrence of cracks or delamination. As it has several problems such as the accuracy of load measurement, the strength dependency on attachment of specimen and so on, we have proposed an evaluation method of the static bending test without the special attachment instead of the compression test after impact. We used ultrasonic microscope and SEM to observe the damage states in CFRP laminates under the impact test with low energy and the static test. From these results, we have proposed three-point static bending test method, which can determine the equivalent static bending load for arbitrary impact load. It is recognized that the residual strength after the occurrence of damage can be evaluated by the proposed method. The method, which is presented, is more convenient than the conventional method like CAI.

2262 超音波スペクトロマイクロスコピーによるボールSAWデバイスの簡便な異方性評価法(S26-4 非破壊評価とモニタリング(4),S26 非破壊評価とモニタリング)

2262 超音波スペクトロマイクロスコピーによるボールSAWデバイスの簡便な異方性評価法(S26-4 非破壊評価とモニタリング(4),S26 非破壊評価とモニタリング)

Improvement of the Precision of Ultrasonic Microscope for Biological Tissue Using the Automatic Extraction of the Reference Signals

This paper deals with the precision of the ultrasonic microscopy for biological tissue characterization. The estimation error of sound speed influenced by the selection of reference points for obtaining the reference signal is described. In well known scanning type microscope, a focused ultrasonic signal is irradiated to the glass substrate on which a thin sliced tissue is attached. The reflected signal from the front surface of the tissue is compared with the signal from the glass substrate on which no tissue is attached. As the scanning plane and glass substrate are not completely in parallel, it is necessary to locate the glass surface at each measuring point. For this purpose, several reference points on which no tissue is attached are selected in the view field. The equation of the plane representing the glass surface is consequently obtained using the reflection at these reference points. However, the glass surface has an apparent surface roughness. This brings an estimation error of the equation of the plane. This error can be reduced by increasing the number of reference points. In order to extract a sufficient number of reference points automatically, an algorithm using the reflected wave was proposed to discriminate the points where the glass surface is exposed. Although the estimation error of sound speed with three reference points was as large as 31 m/s (as the double of standard deviation), it was reduced into as small as 16 m/s, when 1000 reference points had been automatically extracted.

Automated defect recognition of C-SAM images in IC packaging using Support Vector Machines

Ultrasonic C-mode scanning acoustic microscopy (C-SAM) is widely used in the semiconductor industry for reliability testing and product inspection due to its ability to nondestructively detect defects in IC packaging. However, image interpretation and defect identification depend largely on the experience of operators, and there is no defect recognition system; this is partly due to current recognition systems, which are based on computer vision algorithms and are not robust for C-SAM images. A new robust defect recognition system and its application to C-SAM images are described in this paper. The iconic domain of two-dimensional C-SAM grey-level image analysis based on the non-linear Mumford-Shah model is used, and defect recognition is achieved through the use of Support Vector Machines (SVMs). The system is verified through experiments on a sequence of C-SAM images corrupted by synthetically generated noise, bias and different shape. The remarkable defect recognition rates achieved indicate that Support Vector Machines (SVMs) are suitable for IC package defect identification.

Non-destructive evaluation of the interface between silicon dies and copper leadframes in integrated circuit packaging

The silicon die and copper leadframe in integrated circuit (IC) packaging are bonded together by die attach adhesive, and the quality of the interface is a critical issue in the reliability of IC packaging. Common defects such as cracks and delaminations can be detected using the C-scan ultrasonic microscopy method with sufficient confidence. However, weak interfaces due to weak adhesion and poor cohesion have often gone undetected, to subsequently become potential defective areas. In this paper we present experimental work to evaluate the quality of the interfaces that typically exist in IC packages using longitudinal ultrasonic wave propagation with contact transducers. Three different conditioning processes, varying curing, moisture exposure and pre-curing moisture contamination, are used to degrade the interface bonding the silicon die and copper leadframe. Ultrasonic reflection coefficients from the interface are then measured. The results show that the reflection coefficient depends strongly on the interface quality, and can be used as a quantitative indicator to characterize the bond quality.

Lattice dynamics in VO2 near the metal-insulator transition

Abstract We present a comprehensive experimental study of the lattice dynamics in the vicinity of the metal-insulator transition in VO2 by means of combined use of Raman spectroscopy and ultrasonic microscopy. Single crystalline samples of high quality particularly allow quite a complete determination of all Raman modes in the insulating phase at the Γ-point and the observation of an optical soft mode. In addition, the elastic behavior has been successfully investigated by measuring the propagation velocity of ultrasonic surface waves microscopically excited in various crystal directions. Our study reveals a striking coincidence of strong lattice softening attributable to certain acoustic branches and the occurrence of the optical soft mode, which precedes the metal-insulator transition over more than 100 K on approaching the critical temperature.