Ultrasonic Reflection Coefficient Research Articles

Model and experimental analysis of oblique incident ultrasound in a tissue layer using doublet mechanics theory

The fundamental framework of doublet mechanics (DM) is used to analyze high-frequency ultrasound wave propagation in materials with discrete microstructure. Ultrasonic reflection coefficients were measured from a thin layer of tissue embedded between two glass substrates at oblique incidence. Theoretical calculations for the reflection coefficients of a multi-layered system at oblique angles are performed using both DM theory and the classical continuum mechanics theory (CCM). For example, at the frequency of 10 MHz at incident angle 8° in sample with 30 μm thickness, the discrepancy in the magnitude of the reflection coefficient between experimental results and theoretical prediction is 15.8% for DM but 79.0% for CCM; similar results at other frequencies and incident angle in the samples with 30 and 60 μm thickness have also been obtained, which demonstrates that the DM theory can better describe the wave propagation in tissue. The influence of the incident angles and tissue thickness are also discussed in this paper.

A Method for Ultrasonic Characterization of Density, Thickness and Velocity of Homogeneous Coating

This paper provides a nondestructive method for determination of the density, thickness and velocity of homogeneous coating from an inversion of experimental ultrasonic reflection coefficient amplitude spectrum (URCAS). The detailed analyses of the inverse algorithm and sensitivity of URCAS to the density, thickness and velocity are presented, and the sensitivity is identified as a basis for selecting the experimental data used in inversion. An example of the method and experimental measurement for comparison was given for an epoxy coating with the thickness of 0.277 mm. The relative errors between the inversion and reference value of the density, thickness and velocity were found to be 0.5 %, 3.97 %, and 0.97 %, respectively.

Measurements of coating density using ultrasonic reflection coefficient phase spectrum

A nondestructive method to determine the density of coating has been proposed in this paper based on the ultrasonic reflection coefficient phase spectrum (URCPS). A model was set up first to represent the ultrasonic waves reflected from a coating system at normal incident, and the relation between the extremum of URCPS and the coating density was established to provide the principle of determining the density. The ultrasonic method was validated on a series of ZrO2–7 wt.%Y2O3 (YSZ) coatings with various density. The specimens were prepared by electric beam physical vapor deposit (EB-PVD). After deposition, the specimens were irradiated using high-intensity pulsed ion beam (HIPIB) at different ion current density of 100 and 200 A/cm2 to change coating density. The coating densities of as-deposited and post irradiation by HIPIB were derived to be 4940–5030, 5200–5320 and 5390–5470 kg/m3, respectively. The relative error between the coating density measured by the ultrasonic method and Archimedean principle ranging from 2.53% to 6.11%, indicates that the proposed ultrasonic quantification method provides a reliable nondestructive way to determine coating density.

Simultaneous determination of the coating thickness and its longitudinal velocity by ultrasonic nondestructive method

The ultrasonic reflection coefficient amplitude spectrum (URCAS) has been extended to obtain the coating thickness and its longitudinal velocity at the same time on thick substrates. A model was set up first to represent the ultrasonic waves reflected from a coating system at normal incident, and the expression of URCAS was derived in order to obtain the coating thickness and velocity. Then, an inverse algorithm based on the Gauss–Newton method was introduced to determine the thickness and velocity by comparing the theoretical and measured URCAS. Experimental validation was conducted on the homogeneous epoxy coatings on the aluminum substrates and inhomogeneous ZrO2−7wt%Y2O3 (YSZ) coatings on the superalloy substrates. The relative errors of the thickness and velocity measurement were in the ranges of 2.15–2.35% and 2.67–4.40% for epoxy coatings, and between 5.33–5.96% and 8.95–9.66% for YSZ coatings. It is concluded that the URCAS combined with inversion technique can be applied to obtain the thickness and longitudinal velocity of coatings simultaneously.

Ultrasonic characterization of modified Cr 2O 3 coatings by reflection coefficient spectroscopy

Pores, microcracks and density of plasma sprayed Cr 2O 3 coatings before and after high-intensity pulsed ion beam (HIPIB) irradiation were investigated using the ultrasonic reflection coefficient spectroscopy (URCS). The URCS was analyzed based on an acoustic transmission model for the multi-layered structure. The longitudinal velocity in the coatings was calculated from the experimental URCS, and the attenuation coefficient expression was deduced by comparing the experimental and numerical fitting amplitude spectral lines. The longitudinal velocity of as-sprayed Cr 2O 3 coating is 2 002 m/s, and increases to 2 099 and 2 148 m/s after being irradiated by HIPIB with 1 and 5 shots. Correspondingly, the factor A changes from 0.046 to 0.026 and 0.020 and n from 1.702 to 1.658 and 1.649 in the attenuation coefficient expression of α= Af n . It is observed that the surface morphology of Cr 2O 3 coatings changes from rough and porous to smooth and uniform with the increase of shot number, which accords with the ultrasonic analyses reasonably. The URCS seems to provide a convenient and nondestructive method to characterize surface modification of the plasma sprayed coatings.

Using ultrasonic wave reflection to measure solution properties

Ultrasonic wave reflection coefficients of aqueous solutions were measured using high-impact polystyrene as a buffer material to provide enhanced sensitivity over metal or ceramic buffer materials. The wave reflection values showed linear reduction when the concentration of chemical species in solution was increased, but a distinct relation between concentration and reflection coefficient was obtained for each solute species tested. However, more unified relationships were observed between reflection coefficient and other solution parameters – solution density, acoustic impedance, and P-wave velocity – that were consistent for all solution species. Based on this behavior an expression to compute solution density solely from reflection coefficient is derived, which can be applied to estimate solution density in solutions of unknown solute species and concentration when other measurements, such as wave velocity, are not possible.

Comparison between two ultrasonic methods in their ability to monitor the setting process of cement pastes

This paper presents the comparison between ultrasonic wave transmission (USWT) method and ultrasonic wave reflection (USWR) method in their ability to monitor the setting process of cement pastes. The velocity of ultrasonic longitudinal waves and shear wave reflection coefficient were measured simultaneously on cement pastes with different hydration kinetics. Even though both methods are able to reliably monitor the hydration process and formation of structure of an arbitrary cement paste, they monitor the setting process in different ways. The relationship between the velocity of longitudinal waves and shear wave reflection coefficient can be simplified into three characteristic phases and the end of the first phase can be used to define the beginning of the setting process of cement paste.

Ultrasonic Characterization of EB-PVD Thermal Barrier Coatings Irradiated by HIPIB

High-intensity pulsed ion beam (HIPIB) irradiation at 300 A/cm2 with a shot number of 1, and 5 was performed on the coatings and caused the modification of properties. Porosity and rough surface of EB-PVD (Electron Beam-Physical Vapor Deposition) deposited ZrO2-7%Y2O3 coatings with the thickness of 150 μm on heat-resistant steel have been characterized using the ultrasonic reflection coefficient phase spectrum. With increasing the shot number, the surface remelting and ablating filled gaps and caves between columns, and induced more uniform and compact structure. The ultrasonic measurement was investigated using immersion focusing pulse echo method with a 10 MHz transducer. The ultrasonic reflection coefficient related to frequency, velocity and attenuation coefficient were analyzed based on the acoustic transmission model in a multi-layered structure. For the as-deposited coating and coatings irradiated by HIPIB with the shot number of 1 and 5, the ultrasonic velocity changed from 2950 to 3170, and 3255 m/s respectively. The relationship between the attenuation coefficient and the frequency has been deduced based on the numerical fitting of the phase spectrum. The corresponded expressions are 1.35 α = 0.105 f , 1.2 α = 0.045 f and 1.14 α = 0.035 f , which displays that the attenuation coefficient decreases with the increasing of shot number. The ultrasonic results are in agreement with SEM observations, which have indicated that the coatings became denser and uniform with increasing the shot number. From the velocity and attenuation coefficient, the density, porosity, and microcracks of the coatings can be nondestructively evaluated utilizing the method of this paper.

Characterization Methodology of the Interface in Multilayer Composites

The quality of the interfaces in multilayer composites is a critical issue in the reliability testing of the composite product during the manufacturing process and in-service. Weak interfaces have often gone undetected and may become potentially defective at a later stage. One example is the interface between mold compound and silicon (MC/Si) in IC packaging. There is a desire to study the interface quality quantitatively, so the potential defective area can be evaluated and identified early. In this paper, a nondestructive evaluation methodology is proposed to measure the available strength of the interface by using ultrasonic reflection coefficients. It is known that interface degradation can be either due to poor manufacturing process and stress loading. Characterization of the interface quality of the MC/Si interface is first conducted by measuring longitudinal ultrasonic wave reflections from the interface samples fabricated under varying conditioning processes that simulate the degradation. A combined test that measures the reflection coefficient of the interface under stress load has also been conducted to quantify the effect of the load. Finally, it is shown that the overall effect on the reflection coefficient and available strength of the interface is derived and can be used as a quantitative indicator.

Ultrasonic apparatus and methods for the monitoring of melting, mixing and chemical reaction processes

Ultrasonic apparatus and associated methods for the in-line monitoring of melting, mixing and chemical reaction processes of materials inside an enclosed chamber having rotating elements associated therewith are presented. The chamber may be heated and the rotating elements may be blades and/or screws. The chamber may be a heating barrel and the materials may be polymer and polymer composites pellets, metal pellets and chemical compounds. Ultrasonic sensors, which are preferably coupled to a wall of the chamber, may be high temperature ultrasonic transducers attached to the external surface of the chamber or ultrasonic buffer rods embedded into the chamber and coupled to cooled ultrasonic transducers. These sensors are operated in the reflection mode and are placed over the rotating elements. The number and locations of the sensors depend on applications. The synchronization of the transmission of the ultrasonic signals and the associated data acquisition with the position of the rotating element may be accomplished by using a high speed multiple-record data acquisition system. The ultrasonic speed and attenuation in the material being processed, or the traveling time in the material and the amplitude of the ultrasonic signals reflected by the rotating element, the ultrasonic reflection coefficient or the amplitude of the ultrasonic signals reflected at the chamber-material interface or the buffer rod probing end-material interface, and the ultrasonic signals scattered by the material within the chamber, can provide information on the melting, mixing and chemical reaction of the materials.

The interaction of oblique incidence ultrasound with rough, partially contacting interfaces

The ultrasonic reflection coefficients of solid–solid interfaces, such as those found in fatigue cracks, are known to be a function of the compressive load. In this paper, the combined effects of crack face roughness and closure on ultrasonic detectability at oblique incidence are considered. Experimental results are described in which the pitch–catch reflection coefficients of compressively loaded steel–steel interfaces were measured over a range of frequencies (2–24 MHz) at both 45 and 60° incident angles. The results obtained are compared with quasi-static spring model predictions and the limitations of this model discussed. For the surfaces considered (R a ≈ 4 μm), the spring model was shown to be in agreement only at the lower end of the considered frequency range (i.e. 2–3 MHz).

Characterisation of IC packaging interfaces and loading effects

In IC packaging, the quality of the interfaces such as that between mold compound and silicon is a critical issue in the reliability testing during the manufacturing process and in-service. Weak interfaces have often gone undetected and may become potentially defective at a later stage. Furthermore, the stress due to mechanical or thermal loading may further deteriorate the interface quality, making the interface unreliable. There is a desire to study the interface quality quantitatively, so potential defects can be evaluated and identified early. In this paper, finite element analysis using multilayer interface model is used to study the reflection coefficient from the interface of varying quality. Different conditioning techniques were used to degrade the interface quality. Characterisation of the interface quality of the MC/Si interface was conducted using longitudinal ultrasonic wave propagation with contact transducers. A combined test that measures the reflection coefficient of the interface under stress load was also conducted to quantify the effect of the load. A nondestructive evaluation methodology is proposed that measures the available strength of the interface by using ultrasonic reflection coefficients, and it shows the correlation between the reflection coefficient and available strength of the interface can be developed and used as a quantitative indicator.

Monitoring of Lubricant Film Failure in a Ball Bearing Using Ultrasound

A lubricant-film monitoring system for a conventional deep groove ball bearing (type 6016, shaft diameter 80 mm, ball diameter 12.7 mm) is described. A high-frequency (50 MHz) ultrasonic transducer is mounted on the static outer raceway of the bearing. The transducer is focused on the ball-raceway interface and used to measure the reflection coefficient of the lubricant in the “contact” ellipse between bearing components. The reflection coefficient characterizes the lubricant film and can be used to calculate its thickness. An accurate triggering system enables multiple reflection measurements to be made as each lubricated contact moves past the measurement location. Experiments are described in which bearings were deliberately caused to fail by the addition of acetone, water, and sand to the lubricant. The ultrasonic reflection coefficient was monitored as a function of time as the failure occurred. Also monitored were the more standard parameters, temperature and vibration. The results indicate that the ultrasonic measurements are able to detect the failures before seizure. It is also observed that, when used in parallel, these monitoring techniques offer the potential to diagnose the failure mechanism and hence improve predictions of remaining life.

Nondestructive test methods in making and using vessels and plant

Diagnostic features are considered for the following: an ordinary vessel made of mild steel; a vessel with a jacket; a vessel made of corrosion-resistant steel; a vessel made from a bimetallic material; and enameled apparatus. The ultrasonic reflection coefficient is related to the thickness of the intermediate layer at various frequencies and various ratios of the scale thickness (oxide film) to the wavelength, and a study is also made of the dependence of the reflection coefficient for longitudinal waves on the layer thickness for lead, zirconium, and copper.

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.

Ultrasonic assessment of rough surface contact between solids from elastoplastic loading–unloading hysteresis cycle

An ultrasonic method to characterize the elastoplastic contact between two rough surfaces is presented. Ultrasonic experiments are performed on three different interfaces formed by aluminum surfaces with different levels of roughness. The frequency-dependent ultrasonic reflection coefficient from the interface is measured during loading and unloading cycles as a function of pressure, from which the ultrasonic interfacial contact stiffness is reconstructed by the least-squares inversion procedure. It is shown that one should distinguish between the ultrasonic (dynamic) interfacial stiffness and static interfacial stiffness for rough surfaces in elastoplastic contact (they are identical for purely elastic contact). It is shown that ultrasonic stiffness is associated with local unloading stiffness. An elastoplastic micromechanical model is used to describe the plasticity-induced hysteresis in the ultrasonically measured interfacial stiffness during loading–unloading cycles. The topographic parameters of the interface contact are reconstructed by matching the model-predicted results with the experimentally determined ultrasonic stiffness. Using these parameters the real area of contact, which is not directly measurable, is predicted during loading–unloading cycles using the model.

High-resolution ultrasonography for analysis of age- and disease-related cartilage changes.

Because of their limited spatial resolution, current clinical noninvasive imaging modalities (radiography, computed tomography, conventional echography, and magnetic resonance imaging) are able to detect only the late stages of the cartilage degradation. To detect early lesions and follow their evolution in time with imaging, higher resolution is necessary. Recent work suggest that high-frequency ultrasound may serve as a useful means for the investigation of cartilage matrix structural changes occurring under various experimental and clinical circumstances, like the growing process and osteoarthritis. In this chapter, an experimental 50-100-MHz ultrasound scanner is described for high-resolution echographic imaging of articular cartilage. The procedures of data acquisition and signal processing are detailed for the quantitative evaluation of ultrasonic reflection and backscatter coefficients, which have been reported to be sensitive to subtle surface and internal disease-related alterations. Further technological developments and miniaturization of the echographic probes may lead to extension of this technique to the study of living small animals or to the clinical field in combination with conventional arthoscopy.

Ultrasonic evaluation of the silicon/copper interfaces in IC packaging

The silicon die and copper lead-frame in integrated circuit (IC) packaging are bonded using a die attach adhesive, and the quality of the adhesive interface is a critical issue in the reliability testing of IC packaging and during the manufacturing process. Common defects such as cracks and delamination can be detected using the C-mode ultrasonic microscopic method with sufficient confidence. However, a weak interface due to weak adhesion and poor cohesion has often gone undetected and may become a potential defect at a later stage. There is a desire to study the interface quality quantitatively, so that any potentially defective area can be evaluated and identified early. This paper describes work in evaluating the quality of the interfaces that typically exist in IC packages by using longitudinal ultrasonic wave propagation with contact transducers. An interface spring model is used to predict the ultrasonic reflection coefficient relationship with varying interfacial spring constants. Experimental results of normal incidence reflection coefficients are obtained from the two-layered specimen bonded with die attach adhesive under varying conditioning process that simulates the degrading of the interface. Good qualitative agreement between the measurement and the prediction is obtained, and shows that the reflection coefficient depends strongly on the interface quality. The study demonstrates that the quantification of the interface quality is possible, using the reflection coefficient as a criterion.

The measurement of contact pressure in machine elements using ultrasound

This paper describes a study of the use of ultrasound to measure the pressure between two machine elements in contact. Relationships between ultrasonic reflection coefficient and pressure have been found both empirically and via a numerical contact model. The numerical contact model was used to predict the stiffness of the interface. This stiffness was then converted to ultrasonic reflection coefficient via a quasi-static spring model. The quasi-static spring model was shown to be valid for surface finishes in the range 0.5–2.1 μm and ultrasonic frequencies up to 31 MHz. Ball–flat contacts, similar to those found in contacting machine elements, were scanned using a focused ultrasonic transducer. Using the relationship between ultrasonic reflection coefficient and pressure, the contact pressure distribution over the contacts was found. Very good agreement was found between the calculated contact pressure distribution and that predicted by Hertzian contact theory, indicating that ultrasound is a viable method for measuring the contacts in real machine elements, both at the prototype development stage and in situ.

Ultrasonic characterization of the interface between a die attach adhesive and a copper leadframe in IC packaging

The silicon die (chip) and the copper leadframe in IC packaging are bonded by a die attach adhesive, and the quality of the interface is a critical issue in the reliability of IC packaging as well as during the manufacturing process. The common defects such as cracks and delamination can be detected using the C-mode scanning acoustic microscopy. However, a weak interface due to poor adhesion often goes undetected and may become a potential defective area at a later stage. This paper describes the work done to evaluate the quality of the weak interface between a die attach adhesive and a copper leadframe. An interface spring model is used to predict the ultrasonic reflection coefficients. Normal incidence reflection coefficients are measured from a two-layer specimen bonded with a die attach adhesive. The quality of the interface in the samples and its degradation are affected by copper oxidation, and by applying shear stress loading. It is shown that the reflection coefficient depends strongly on both the interface quality and stress loading, indicating that a nondestructive characterization of the interface is possible and the reflection coefficient can be used as a criterion.