Noninvasive Material Characterization Research Articles

Noninvasive material characterization of biomaterials: Measuring viscosity and elasticity using ultrasound

The advent of tissue engineering has led to increased interest in the viscoelastic characterization of biomaterials. Gelatin Methacrylate (GelMA) is a particularly promising biomaterial, largely due to its tunability, yet the impact of different preparation parameters on the material’s viscoelasticity is not well understood. We characterized an array of GelMA scaffolds, fabricated by varying both GelMA concentration and ultraviolet (UV) lightexposure time. Pulse-echo ultrasound techniques were used to non-invasively determine the sound speed and attenuation of the scaffolds, revealing significant dependence on GelMA concentration. Steady shear rate tests in addition to strain- and frequency-controlled oscillatory shear tests were performed using a rotational rheometer (Model: DHR-2, TA Instruments) to ascertain the levels of shear-thinning and viscoelasticity at a wide range of strain rates, oscillation frequencies, and amplitudes. The rheological tests show moduli dependence on both GelMA concentration and curing time. Together, this acoustic and rheological characterization can be used to inform the selection of GelMA scaffolds in tissue engineering applications, and this method can be used as a guide for characterizing other polymeric hydrogels.

Noninvasive Acoustic Measurements in Cylindrical Shell Containers.

Acoustic time-of-flight (ToF) measurements enable noninvasive material characterization, acoustic imaging, and defect detection and are commonly used in industrial process control, biomedical devices, and national security. When characterizing a fluid contained in a cylinder or pipe, ToF measurements are hampered by guided waves, which propagate around the cylindrical shell walls and obscure the waves propagating through the interrogated fluid. We present a technique for overcoming this limitation based on a broadband linear chirp excitation and cross correlation detection. By using broadband excitation, we exploit the dispersion of the guided waves, wherein different frequencies propagate at different velocities, thus distorting the guided wave signal while leaving the bulk wave signal in the fluid unperturbed. We demonstrate the measurement technique experimentally and using numerical simulation. We characterize the technique performance in terms of measurement error, signal-to-noise-ratio, and resolution as a function of the linear chirp center frequency and bandwidth. We discuss the physical phenomena behind the guided bulk wave interactions and how to utilize these phenomena to optimize the measurements in the fluid.

Thermal Silicidation of Ni/SiGe and Characterization of Resulting Silicide Films Using Raman Spectroscopy and X-ray Diffraction

For advanced application specific devices, combinations of Si/Ge, Ge/Si, Si1-xGex/Si are frequently introduced in the device fabrication process. Epitaxy, condensation and annealing processes are commonly used for controlling the Ge content to a desired level. Strain and crystallinity can be affected by a small variation in composition or Ge content, which can result in device performance deterioration or failure. Thus, the composition, strain and crystallinity must be carefully monitored and controlled throughout the manufacturing process. The electrode formation process is also very critical for successful device fabrication. Any spikes and/or electrically active defects near junctions can be fatal to the device yield. Silicidation processes and resulting silicides must be investigated as much as possible using various non-invasive material characterization techniques.In this study, we report the thermal silicidation characteristics of Ni/Si1-xGex with various Ge content under different annealing temperatures in the range of 225oC ~ 400oC in N2 ambient. Thermal silicidation was performed in a stacked hotplate-based SAO-302LP system designed for 300mm wafers. For resulting silicide characterization, measurements of sheet resistance, Raman spectra, X-ray diffraction curves as well as scanning electron microscopy (SEM) observations were performed. We have studied Ge content and annealing temperature dependence on the resulting electrical and crystallographic silicide characteristics.Figure 1 shows 647nm excited Raman spectra and X-ray diffraction (XRD) curves from reference Si, and resulting silicide from Ni/Si0.75Ge0.25 before and after annealing under at 235oC, 310oC and 400oC.Raman spectra and sheet resistance measurements showed silicide formation and silicide layer thickening with increasing annealing temperature. XRD curves clearly indicated the change of crystalline phase of resulting silicide with annealing temperature increase. Various aspects of thermal silicidation and its characterization will be discussed at the conference. Figure 1

Electrical Impedance Spectroscopy (EIS) for Photovoltaic Materials: Possibilities and Challenges

Electrical Impedance Spectroscopy (EIS) is a noninvasive material characterization technique which provides the frequency response of the electrical impedance of materials under test as the signature of the material properties. EIS injects constant amplitude AC electrical currents and measures the developed potentials at different frequency points to calculate the complex electrical impedance. In EIS, the electrical impedance profile of a material is correlated with its structure and composition for material testing either online or offline. EIS is found as a fast, portable, user-friendly, and noninvasive technique and hence, it has been utilized for material characterization in a number of engineering fields and applied science areas. In the past few decades, EIS has also been used to characterize the photovoltaic materials. This paper reviews the possibilities and challenges of EIS technique applied for the characterization of the photovoltaic materials. The paper presents a brief discussion about the EIS technology, applications of EIS on PV materials along with the advantages and limitations of the technology. The paper concludes with the highlight of the recent trends of EIS based PV material characterization process mentioning the challenges of the technique.

Accurate thickness measurement using a single terahertz pulse obtained in ambient atmosphere

Terahertz (THz) radiation suffers severe signal loss due to the high absorptivity of water vapor abundant in normal atmosphere, greatly limiting its potential in noninvasive material characterization. We propose a novel THz signal processing method that enables effective extraction of hidden sample information leading to accurate thickness determination. The thicknesses of multiple silicon wafers are measured using only a single THz pulse obtained in ambient atmosphere without any prior sample information. The results verify our proposed approach to achieve accurate and precise characterization of materials in a realistic environment.

A Non-Invasive Material Characterization Framework for Bioprosthetic Heart Valves.

Computational modeling and simulation has become more common in design and development of bioprosthetic heart valves. To have a reliable computational model, considering accurate mechanical properties of biological soft tissue is one of the most important steps. The goal of this study was to present a non-invasive material characterization framework to determine mechanical propertied of soft tissue employed in bioprosthetic heart valves. Using integrated experimental methods (i.e., digital image correlation measurements and hemodynamic testing in a pulse duplicator system) and numerical methods (i.e., finite element modeling and optimization), three-dimensional anisotropic mechanical properties of leaflets used in two commercially available transcatheter aortic valves (i.e., Edwards SAPIEN 3 and Medtronic CoreValve) were characterized and compared to that of a commonly used and well-examined surgical bioprosthesis (i.e., Carpentier-Edwards PERIMOUNT Magna aortic heart valve). The results of the simulations showed that the highest stress value during one cardiac cycle was at the peak of systole in the three bioprostheses. In addition, in the diastole, the peak of maximum in-plane principal stress was 0.98, 0.96, and 2.95MPa for the PERIMOUNT Magna, CoreValve, and SAPIEN 3, respectively. Considering leaflet stress distributions, there might be a difference in the long-term durability of different TAV models.

Graphene Based Terahertz Light Modulator in Total Internal Reflection Geometry

Modulation of visible light has been easily achieved for decades, but modulation of terahertz (THz) light still remains a challenge. To address this issue, the Fresnel equations have been developed to describe a conductive interface in a total internal reflection geometry and reveal a new approach for modulation. To demonstrate this new mechanism, a broadband device achieving a modulation depth greater than 90% between 0.15 and 0.4 THz, and reaching a maximum of 99.3% at 0.24 THz has been designed. The modulation is achieved by applying a gate voltage between −0.1 and 2 V to a graphene layer in a total internal reflection geometry. Compared to conventional designs, the high modulation is realized without assistance from metamaterial structures, resonant cavities, or multistacked graphene layers. Thus, the design is efficient and easy‐to‐fabricate and can be easily retrofitted to most existing THz systems. This work opens up a new avenue of research as the device has verified the theory and demonstrates how it can be used to make practical devices, bringing a promising new paradigm for THz modulation, thin‐film sensing, and noninvasive material characterization.

Advanced Spectral Imaging for Noninvasive Microanalysis of Cultural Heritage Materials: Review of Application to Documents in the U.S. Library of Congress

Hyperspectral imaging was originally developed for remote sensing and astronomical applications, but adaptations of this technology have been of great benefit to the preservation of cultural heritage. Developments in noninvasive analytical techniques have advanced the preservation of cultural heritage materials by enabling the identification and analysis of a range of materials, utilizing their unique spectral response to nondestructively determine chemical composition, and determining states of deterioration and change due to environmental conditions. When used as a tool for noninvasive characterization of cultural heritage, these spectral imaging systems allow the collection of chemical identification information about materials without sampling, which is a critical factor for cultural heritage materials. The United States Library of Congress has been developing the application of hyperspectral imaging to the preservation and analysis of cultural heritage materials as a powerful noncontact technique. It allows noninvasive characterization of materials, by identifying and characterizing colorants, inks, and substrates with narrow-band illumination to protect the object while also monitoring deterioration or changes due to exhibit and other environmental conditions. Contiguous illumination from the ultraviolet, visible, and infrared spectral regions allows the capture of lost, obscured, and deteriorated information. The resulting image cube allows greater capabilities for mapping and coordinating a range of complementary chemical and spectral analyses. The capabilities of this technique are illustrated by a review of results from analysis of the Waldseemüller World Map, the L'Enfant plan for Washington, D.C., and the first draft of the U.S. Declaration of Independence.

Non-Invasive Characterization for Long-Term Preservation of Cultural Heritage

ABSTRACTDevelopments in non-invasive analytical techniques advance the preservation of cultural heritage materials by identifying and analyzing substrates and media. Spectral imaging systems have been used as a tool for non-invasive characterization of cultural heritage, allowing the collection of chemical identification information about materials without sampling. The Library of Congress has been developing the application of hyperspectral imaging to the preservation and analysis of cultural heritage materials as a powerful, non-contact technique to allow non-invasive characterization of materials, by identifying and characterizing colorants, inks and substrates through their unique spectral response, monitoring deterioration or changes due to exhibit and other environmental conditions, and capturing lost and deteriorated information. The resulting image cube creates a new “digital cultural object” that is related to, but recognized as a distinct entity from the original. The range of data thisobjectcontains encourages multidisciplinary collaboration for the integration of preservation, societal and cultural information.

ARFI Imaging for Noninvasive Material Characterization of Atherosclerosis Part II: Toward In Vivo Characterization

ARFI Imaging for Noninvasive Material Characterization of Atherosclerosis Part II: Toward In Vivo Characterization

ARFI Imaging for Noninvasive Material Characterization of Atherosclerosis Part II: Toward In Vivo Characterization

Seventy percent of cardiovascular disease (CVD) deaths are attributed to atherosclerosis. Despite their clinical significance, nonstenotic atherosclerotic plaques are not effectively detected by conventional atherosclerosis imaging methods. Moreover, conventional imaging methods are insufficient for describing plaque composition, which is relevant to cardiovascular risk assessment. Atherosclerosis imaging technologies capable of improving plaque detection and stratifying cardiovascular risk are needed. Acoustic radiation force impulse (ARFI) ultrasound, a novel imaging method for noninvasively differentiating the mechanical properties of tissue, is demonstrated for in vivo detection of nonstenotic plaques and plaque material assessment in this pilot investigation. In vivo ARFI imaging was performed on four iliac arteries: (1) of a normocholesterolemic pig with no atherosclerosis as a control, (2) of a familial hypercholesterolemic pig with diffuse atherosclerosis, (3) of a normocholesterolemic pig fed a high-fat diet with early atherosclerotic plaques and (4) of a familial hypercholesterolemic pig with diffuse atherosclerosis and a small, minimally occlusive plaque. ARFI results were compared with spatially matched immunohistochemistry, showing correlations between elastin and collagen content and ARFI-derived peak displacement and recovery time parameters. Faster recoveries from ARFI-induced peak displacements and smaller peak displacements were observed in areas of higher elastin and collagen content. Importantly, spatial correlations between tissue content and ARFI results were consistent and observable in large and highly evolved as well as small plaques. ARFI imaging successfully distinguished nonstenotic plaques, while conventional B-mode ultrasound did not. This work validates the potential relevance of ARFI imaging as a noninvasive imaging technology for in vivo detection and material assessment of atherosclerotic plaques. (E-mail: russbehler@unc.edu)

Validity of a closed‐form diffusion solution in approximation for reflectance imaging with an oblique beam of arbitrary profile

Determination of optical parameters of turbid media from reflectance image data is an important class of inverse problems due to its potential for noninvasive characterization of materials and biological tissues, which demands rapid modeling tools to generate calculated images. We treat the problem of reflectance imaging with homogeneous semi-infinite turbid media as a boundary-value problem of diffusion type in the P1 approximation to the radiative transfer equation. A closed-form solution has been obtained for an oblique incident beam of arbitrary profile and its accuracy has been examined against a Monte Carlo method and measured data. We find that the diffusion solution provides a sufficiently accurate tool to rapidly calculate reflectance images for samples of large or moderate scattering albedo illuminated by a beam of arbitrary profile as long as the anisotropy factor remains less than 0.7 and single scattering albedo larger than 0.8. The closed-form solution can thus be used as a part of a forward modeling toolbox to determine optical parameters from reflectance image data in combination with other method such as the Monte Carlo simulation.

Noninvasive assessment of human jawbone using ultrasonic guided waves

The problem of detecting defects in jawbones is an important problem. Existing methods based on Xrays are invasive and constrain the achievable image quality. They also may carry known risks of cancer generation or may be limited in accurate diagnosis scope. This work is motivated by the lack of current imaging modalities to accurately predict the mechanical properties and defects in jawbone. Ultrasonic guided waves are sensitive to changes in microstructural properties and thus have been widely used for noninvasive material characterization. Using these waves may provide means for early diagnosis of marrow ischemic disorders via detecting focal osteoporotic marrow defect, chronic nonsuppurative osteomyelitis, and cavitations in the mandible (jawbone). Guided waves propagating along the mandibles may exhibit dispersion behavior that depends on material properties, geometry, and embedded cavities. In this work, we present the first study in the theoretical and experimental analysis of guided wave propagation in jawbone. Semianalytical, finite-element (SAFE) method is used to analyze dispersion behavior of guided waves propagating in human mandibles. The geometry of the cross section is obtained by segmenting the computed tomography (CT) images of the jawbone. The cross section of the mandible is divided in two regions representing the cortical and trabecular bones. Each region is modeled as a linear Hookean material. The material properties for both regions are adopted from the literature. The experimental setup for the guided waves experiment is described. The results from both numerical analysis and guided waves experiment exhibit variations in the group velocity of the first arrival signal and in the dispersion behavior of healthy and defected mandibles. These results shall provide a means to noninvasively characterize the jawbone and accurately assess the bone mechanical properties. Our study is not aimed at characterizing the bone density in human mandibles. Rather, it is aimed to assess bone mechanical properties and defects that cannot be diagnosed by X-ray or other imaging modalities. This work may pave the way to the development of inexpensive noninvasive devices to detect small defects in human mandibles.

Crystallographic texture analysis of archaeological metals: interpretation of manufacturing techniques

Neutron probes and high energy X-rays are sources of primary importance for the non-invasive characterization of materials related to cultural heritage. Their employment in the characterization of archaeological metal objects, combined with the recent instrumental and computational developments in the field of crystallographic texture analysis (CTA) from diffraction data proves to be a powerful tool for the interpretation of ancient metal working techniques. Diffraction based CTA, when performed using penetrating probes and adequate detector coverage of reciprocal space, for example using large detector arrays and/or ToF mode, allows simultaneous identification and quantification of crystalline phases, besides the microstructural and textural characterization of the object, and it can be effectively used as a totally non-invasive tool for metallographic analysis. Furthermore, the chemical composition of the object may also be obtained by the simultaneous detection of prompt gamma rays induced by neutron activation, or by the fluorescence signal from high energy X-rays, in order to obtain a large amount of complementary information in a single experiment. The specific application of neutron CTA to the characterization of the manufacturing processes of prehistoric copper axes is discussed in detail.

ARFI imaging for noninvasive material characterization of atherosclerosis

Cardiovascular disease (CVD) is the leading cause of death in the United States, with 70% of CVD mortalities the result of sequelae of atherosclerosis. An urgent need for enhanced delineation of vulnerable plaques has catalyzed the development of novel atherosclerosis imaging strategies that use X-ray computed tomography, magnetic resonance and ultrasound modalities. As suggested by the pathophysiology of plaque development and progression to vulnerability, insight to the focal material, i.e., mechanical, properties of arterial walls and plaques may enhance atherosclerosis characterization. We present acoustic radiation force impulse (ARFI) ultrasound in application to mechanically characterizing a raised focal atherosclerotic plaque in an iliac artery extracted from a relevant pig model. ARFI results are correlated to matched immunohistochemistry, indicating elastin and collagen composition. In regions of degraded elastin, slower recovery rates from peak ARFI-induced displacements were observed. In regions of collagen deposition, lower ARFI-induced displacements were achieved. This work demonstrates ARFI for characterizing the material nature of an atherosclerotic plaque.

X-ray phase contrast tomography with a bending magnet source

X-ray radiography and x-ray tomography are important tools for noninvasive characterization of materials. Historically, the contrast mechanism used with these techniques has been absorption. However, for any given sample there are x-ray energies for which absorption contrast is poor. Alternatively, when good contrast can be obtained, radiation damage from an excessive dose may become an issue. Consequently, phase-contrast methods have in recent years been implemented at both synchrotron and laboratory facilities. A range of radiographic and tomographic demonstrations have now been made, typically utilizing the coherent flux from an insertion device at a synchrotron or a microfocus laboratory source. In this paper we demonstrate that useful results may be obtained using a bending magnet source at a synchrotron. In particular we show that the same beamline can be used to make and characterize a sample made by x-ray lithographic methods.

Overview of applications of micromagnetic Barkhausen emissions as noninvasive material characterization technique

In this concise overview, the physical principles of magnetic Barkhausen effect will be briefly discussed and its recent applications in material characterization will be considered. There are new trends in micromagnetic Barkhausen effect emissions and its applications in the material characterization area. These emissions take place in magnetic materials subjected to changing applied magnetic field, and can be used, for instance, to study noninvasively surface characterization of materials. Since these emissions are quite sensitive to changes in the microstructure and subsurface stress states in magnetic materials, various applications of these of micromagnetic emissions have been found in areas such as nuclear, aerospace, and automotive technologies which use magnetic materials.