Recent advancements in small, microscopic NDE sensor technologies will revolutionize how aircraft maintenance is done, and will significantly improve the reliability and airworthiness of current and future aircraft systems. A variety of micro/nano systems and concepts are being developed that will enable whole new capabilities for detecting and tracking structural integrity damage. For aging aircraft systems, the impact of micro-NDE sensor technologies will be felt immediately, with dramatic reductions in labor for maintenance, and extended useable life of critical components being two of the primary benefits. For the fleet management of future aircraft systems, a comprehensive evaluation and tracking of vehicle health throughout its entire life cycle will be needed. Indeed, micro/nano NDE systems will be instrumental in realizing this futuristic vision. Several major challenges will need to be addressed, however, before micro- and nano-NDE systems can effectively be implemented, and this will require interdisciplinary research approaches, and a systematic engineering integration of the new technologies into real systems. Future research will need to emphasize systems engineering approaches for designing materials and structures with in-situ inspection and prognostic capabilities. Recent advances in 1) embedded / add-on micro-sensors, 2) computer modeling of nondestructive evaluation responses, and 3) wireless communications are important steps toward this goal, and will ultimately provide previously unimagined opportunities for realizing whole new integrated vehicle health monitoring capabilities. The future use of micro/nano NDE technologies as vehicle health monitoring tools will have profound implications, and will provide a revolutionary way of doing NDE in the near and distant future.

This paper presents recent results based on the use of Surface Acoustic Waves (SAWs) for active sensors for health monitoring of a variety of structures. In the first example, SAWs were used in an acoustic waveguide effect in the fluid filled space between two surfaces. The effect was demonstrated for flat plates and for concentric cylinders. Pressure vessels with concentric cylinders are used in the power industry, where the position of an industrial lead screw is an improtant parameter. Wave travel over a length of up to 2 meters could be observed with little energy loss into the fluid. The second example, presents the use of Electromagnetic Acoustic Transducers (EMAT) for the rapid health monitoring of railroad wheels. In the third example, surface hugging wedges were used with conventional transducers to launch and detect SAWs for crack detection and mapping measurements on pressure vessel valve stems. The fourth example deals with health monitoring of living biomedical cells. In this case SAWs at hypersonic frequencies (1 GHz) were employed to image and monitor the health of the cells as the temperatures were raised. While these examples are still laboratory projects, some of them are finding their way into industrial applications.

Two scanning acoustic probe microscopy (SAPM) techniques have been developed for the nanoscale analysis of the interaction of acoustic modes on the surface of a solid. The scanning acoustic force microscope (SAFM) and the scanning acoustic tunneling microscope (SATM) are extensions to the scanning probe microscopy world utilizing the non-linearity of the respective interaction-distance curves in order to detect high-frequency signals, like acoustic waves or electric fields. SAFM and SATM measurements are presented that give an overview of past and present work in this field. With SAPM, acoustic wave properties of arbitrarily polarized surface acoustic wave (SAW) modes can be measured with sub-wavelength resolution and unmatched amplitude sensitivity. SAW dispersion measurements, scattering and diffraction, SAW transducer studies, studies of the crystal anisotropy, as well as atomically resolved images of the oscillating lattice will be discussed.

Over the last two centuries, engineers have learned how to determine material parameters that describe the properties of construction materials and the behavior of the materials under loading conditions. These parameters are measured from small specimens that are exposed to specific laboratory test conditions, sometimes far away from the real loading conditions for the materials in use. Engineering experience is required to use these material parameters for design and to guarantee material lifetimes of several decades for complex structures and systems, like for example, aircraft. Nano-structures having completely different chemical and physical property behavior than large scale devices possess, due to the extremely large surface to volume ratio along with quantum mechanical effects. Due to cost constraints and the speed of invention and business, there will not be unlimited time as in the past to create the necessary materials testing and characterization procedures and to develop the criteria for design and construction that guarantees reliability and a long lifetime for these new materials. A concept for an international scientist's network concerning characterization modeling and reliability of micro and nano materials will be presented. Objectives for the network are to assure safety and reliability of future products, to develop and harmonize noninvasive testing procedures, to develop training programs for nano characterization and modeling specialists, and for instance, to accelerate the process of application of nano materials.

A novel cross-sectional characterization technique for nanomechanical profiling of low-k dielectrics has been developed based on ultrasonic force microscopy. So-called CS-UFM has been demonstrated on silicon-based, spin-on dielectrics (SOD) used for gap-fill in 0.15 μm trenches in an SiO₂ integrated circuit test structure. The SiO₂ trench walls were coated with a thin (~ 24 nm) plasma-enhanced, chemical vapor deposited (PECVD) silicon nitride layer. CS-UFM imaging clearly differentiated the SOD, SiO₂ and silicon nitride on the basis of elastic modulus. Variations in the elastic uniformity of the SOD and silicon nitride were observed. In addition, mechanical defects were identified within the SOD-filled trenches.

Martensitic transformation and degradation characteristics for Fe-Pd ferromagnetic shape memory alloy were investigated by the developed AFM (Atomic Force Microscope)/MFM (Magnetic Force Microscope) hybrid nano-characterization technique. In AFM martensitic transformation was detected by the changes of surface topography of martensite plates. In MFM martensitic transformation was detected by the changes of magnetic domain structures. This technique has an advantage that martensitic transformation characteristics such as martensitic transformation temperature and reverse transformation temperature can be measured at microscopic and nanoscopic small area. Degradation characteristics of martensitic transformation under cyclic loading were also detected by the changes of AFM and MFM images. In AFM images surface topography of martensite plates became flat and in MFM images the morphology of magnetic domain structures became unfocused under cyclic loading. Then it was found that the hybrid nano-characterization was very high sensitive technique to evaluate degradation for Fe-Pd ferromagnetic shape memory alloy.

7075 T651 aluminum alloy is frequently used in aircraft applications for its high strength to weight ratio. However, aircraft parts made of this alloy have been plagued by stress corrosion cracking (SCC). Retrogression and re-aging (RRA) is a post T651 two-stage heat treatment that provides improved SCC resistance with minimal loss in tensile strength. In this study, various forms of microscopy and mechanical testing are used to investigate how the RRA process affects the microstructure. The microscopic observations in this paper show that the precipitates in the aluminum alloy coarsen and that the grain boundary regions are depleted of copper and magnesium. The mechanical testing performed shows that the aluminum alloy decreases in strength and increases in conductivity when exposed to longer retrogression times prior to re-aging.

The detection and microscopic characterization of hidden corrosion has recently been a focus of several advanced NDE research efforts. A variety of approaches have been suggested, with laser ultrasonic (LU), scanning acoustic microscopy (SAM), thermography,and x-ray systems being four of the most promising NDE techniques. In this effort, a side-by-side comparison of each of these four techniques was conducted with the goal of assessing the detailed microscopic features of engineered and realistic hidden pitting corrosion reference samples. The reference samples included laser-etched cutouts and electro-chemically created surface pits ranging in size for 250 μm to 5 mm in surface extent, and depths of 25 μm to 1 mm. The effects of material loss/topography, corrosion-byproduct, and paint thickness levels were all addressed. Variations in measurement sensitivity, detectivity, and spatial resolution were studied, with particular attention being focused on the ability of the NDE technique to not only detect the hidden corrosion, but to provide any additional information regarding the microscopic nature of the corrosion area, its roughness, material loss levels, and pitting sharpness. In all cases, the NDE techniques provided an 'image' of the hidden corrosion areas, with some capability for assessing the internal structures of the pits from the measured signal levels or brightness levels of the measured image fields.

Two evaluation methods of nano-scale internal defects by ultrasonic atomic force microscopy (UAFM) is reviewed. The first one is a linear vibration analysis of the contact stiffness calculated from a finite element method analysis of a model including a subsurface gap. The second one is a nonlinear vibration analysis of a stiffening or softening spring representing the opening-and-closing behavior of the gap. These methods were verified by the resonance frequency mapping, the load dependence of the resonance frequency and the resonance spectra in UAFM on a subsurface gap in highly oriented pyrolytic graphite. It was proved that the proposed methods are useful for evaluating the crack closure/opening on the nano-scale.

To increase the efficiency of electronic devices their structures are getting smaller and the layered constructions are getting more complex. The inspection of these small and thin structures gives new demands on the NDT, especially in lateral and depth resolution. High-end X-ray tomography is one inspection method, which allows to detect cracks or delaminations. However, it is time consuming. Ultrasonic techniques are able to detect cracks, delaminations, and other inhomogeneities, too. Acoustic microscopy is the high-end application of ultrasonic techniques. Using frequencies between 1 MHz and 1000 MHz (1 GHz) it is possible to detect defects even in the submicron-range. In combination with scanning units with a resolution of 0.1 µm, modified transducers and special software microstructures of layered electronic devices can be inspected very fast. This method will be presented at several examples of semiconductor devices. It will be shown, that inline-inspection with acoustic microscopy is possible.

The material being used to construct interconnects in microelectronic circuitry is changing as developers switch from aluminum alloys to copper in order to make increasing smaller circuit wires. The performance of copper interconnects can be adversely affected by electromigration, precipitation formation, and changes in the grain microstructure of the wire. There is a need for characterization methods that can allow examination of the interconnects/wires and their grain structure in the nanometer range. One of the most powerful tools that are routinely used for characterization of nanostructured materials is the Atomic Force Microscope. The combination of AFM with ultrasonics (UFM) allows a near field acoustic microscopic image to be generated. By having the AFM tip detect the ultrasonic signal, the lateral resolution limitation of the acoustic wavelength that occurs in conventional acoustic microscopy can be overcome so that imaging with nanometer resolution is possible. In this paper, we present a qualitative comparison of AFM-UFM images on different forms of copper nanograins from two sources namely, ion beam deposited thin films samples containing polycrystalline sections and the aligned copper grains in the wires of an actual working microelectronic device. Images of the nanometer grain structure will be presented. Explanations for the image differences between samples will be discussed and possible applications are suggested.

Recent years have seen significant advances in both low and high energy X-ray microscopy. The image in X-ray microscopy is usually formed by differences in absorption of X-ray photons. Soft X-ray microscopy (energies below a few thousand eV) uses wavelengths under 10 nm. Since light wavelengths are approximately 500 nm, resolution is much better with X-rays. One can obtain nanoscale resolution with focused soft X-ray imaging of thin biological objects. To achieve high spatial resolution in high energy X-ray microscopy one can use focused parallel monochromatic beams produced by synchrotron radiation or one can use a microfocal X-ray source with high geometrical magnification of the image. For weakly absorbing objects the image contrast can be enhanced by X-ray refraction on inhomogeneities and phase contrast formation. The physical principles of the phase contrast technique are similar to those in optics and are based on X-ray interference. Modeling and experimental aspects of the phase contrast technique with a microfocal X-ray source and the effects of geometrical and material parameters are reviewed in some detail. Examples of phase contrast of porosity in a polymer layer and an aluminum weld are shown. The computer-simulated images are compared with images from experiment with a 5 μm microfocal X-ray source. Phase retrieval methods and phase map reconstruction from measured X-ray images are also discussed. Applications of the phase-contrast X-ray imaging include medical radiology, material science, and industrial radiography and tomography.

While solder joints of integrated circuits in BGA and uBGA packages can be tested with 3D-computed tomography, this process is time consuming and too expensive for anything but samples or small production volumes. This paper explores approaches to facilitate a 2D-imaging testing system for BGA and uBGA solder joints. Non-standard pad geometries can be used to cause a deformation of the solder balls during soldering; this deformation is detectable in a 2D-image. By integrating a compact X-Ray-source/detector unit into a reflow soldering station, controlling the quality of the solder joints in real-time during soldering will become possible. This information can then be fed back into the soldering station in order to optimize the soldering process.

In this work, the laser intensity modulation method (LIMM) is applied to the investigation of the polarization distribution profile inside ferroelectric thin films. Here, a sinusoidal thermal wave is generated by a laser, thus causing a pyroelectric current. This current is influenced by the frequency and, hence, the penetration depth of the thermal wave inside the thin film as well as by the polarization state of this layer. The spatial polarization profile is then determined from the pyroelectric current spectrum by inverse solution of the appropriate FREDHOLM integral equation. Mathematically considered, this represents an ill-posed problem, which usually leads to numerically unstable solutions with an often severely disturbed waveform. Taking both profiles with larger gradients and superimposed noise at the pyroelectric current spectra into account, a TIKHONOV regularization method has to be employed to accomplish numerically stable and reliable results for the reconstructed polarization profiles. Based on the consideration of different typical polarization profiles, the influence of various regularization approaches was investigated, which determine the uncertainty of the reconstruction result. This work explains the effects of uncertainties of measurement due to data noise, non-optimal regularization parameters, material parameter variations and deviations of the thermal model and the influence of uncertainties due to non-optimal model assumptions. It will be shown that the lacking knowledge of precise thin film material parameters and noise inside the measuring setup represent the most decisive uncertainty sources for the LIMM method to determine polarization thickness profiles inside ferroelectric thin films.

One of the most critical aspects of developing and optimizing capacitive micro-machined transducer systems involves the introduction of appropriate stress levels in the membrane structures during the manufacturing process. Subtle variations in the elastic modulus levels and mechanical coupling can dramatically alter the dynamic vibratory response of the MEMS for ultrasonic applications. In this effort, two different optical interferometric NDE approaches were used to evaluate the static and dynamic characteristics of individual MEMS elements in an ultrasonic transducer array system for variations of applied stress. The interferometric techniques provided a detailed microscopic characterization of the physical motions and local microscopic positions of the MEMS transducer membranes. It was found that the flexural response levels of individual MEMS membrane structures due to increased electrostatic forces was directly coupled to the dynamic response of the micro-transducer, and could potentially be used for optimizing the efficiency and dynamic motion extent of the MEMS transducer array. The optical interferometric techniques both proved to be valuable micro-NDE characterization tools, and were perfectly suited for characterizing the dynamic and static responses of the MEMS ultrasonic transducer systems.

The rapid development of a wide variety of new devises in microelectronics, MEMS, NEMS and nano technology will lead to new challenges for their mechanical characterization and reliability assessment. Measurement of deformations and stresses in microscopic and even nanoscopic regions becomes a key issue. The authors make use of load state images captured by Atomic Force Microscopes (AFM) in order to measure object deformations. Out-of-plane deformation is determined from usual topography scans by computing surface profile differences. NanoDAC, a recently established approach, allows to meet these goals with regard to in-plane deformation. The method bases on cross correlations analysis performed on AFM scans, which are captured from thermally and/or mechanically loaded samples. Finally, local 3D displacement fields and in-plane strain fields are measured. A description of the basic principles and the capability of the technique are given. Furthermore, the authors demonstrate the potential of the mentioned method by its application to microcrack evaluation and the study of sensor and MEMS structure degradation. The first application corresponds to the measurement of crack opening displacement in the very vicinity of crack tips. As a consequence, fracture mechanics parameters are derived and allow to assess the defect with regard to possible crack propagation and component failure. This approach is used to study the influence of nanoscale material structures on crack behavior. The second example illustrates how the impact of thermal loading to the constitution of sensor or MEMS submicron layers is investigated by deformation analysis. The devices had been heated actively under the AFM. Degradation processes due to a severe thermal material mismatch were observed and monitored.

Electronic polymer devices and test structures based on PEDOT/PSS were fabricated in a fully CMOS compatible process. The resistivity of PEDOT/PSS polymer films is dependent on film thickness. The resistivity increases with decreasing film thickness for polymer film thicknesses between 190 nm and 380 nm. The resistivity differs by a factor of ~3 depending on film thickness. The evaluation of the specific contact resistivity depending on the choice of the metallization leads to a difference of the specific contact resistivity by a factor of 190. The specific contact resistivity does not follow the Schottky-Mott law and thus indicates a non-ideal behavior of the metal PEDOT/PSS interface. The lowest average specific contact resistivity was obtained for silver with an average value of 0.14 Ωcm² and the highest specific contact resistivity was obtained for platinum. Even the lowest specific contact resistivity for silver is still very high when compared with low resistivity ohmic contacts to silicon. However, the specific contact resistivity is expected to have a significant drawback for overall device performance. Possible future applications of MEMS and electronics based on polymers will be for simple devices like transistors, ID tags, thermistors, acceleration and pressure sensors as well as radiation and UV detectors.

The degradation of a polymer coating and predicting the coating lifetime, based on physica properties and distribution within the coating of the polymer binder, pigments, and fillers, are economically very important. As technologies advance, allowing control of coatings at the nanoscale level, methods such as Monte Carlo can be used not only to predict the behavior of a nanodesigned coating with time but also to design coatings, such as optimizing pigment particle distributions or optimum hard and soft phase distributions of the binders in multiphase systems for maintaining the desired property with time. Erosion of the coating surface was simulated using Monte Carlo techniques where terrestrial solar flux is the initiator for polymer segment cleavage and removal. The impact on the sensitivity of the polymer adjacent to the detached polymer segment can be increased or decreased in the model based on the chemistry and surface energy of the remaining polymer matrix. Multiple phases with varying sensitivity to degradation can be modeled. The Monte Carlo generates a statistically similar surface topography and chemistry of the coating. The results of the Monte Carlo model are compared to measurable properties; such as gloss, fracture toughness, and wetting contact angle, using various published correlations of the property to the surface topology. The simulated properties change through the lifetime of the coating in ways that are consistent with observed behavior. Apparently, complicated changes in many properties can be described by the repeated application of simple, random processes.

A detailed microscopic characterization of stress-corrosion cracking (SCC) processes has been conducted for electro-chemically pitted AA 2024-T3 aluminum dogbone specimens in a high-cycle fatigue environment. The measurements were done in-situ using scanning laser ultrasonic detection of Rayleigh waves propagating along the material surface. Detailed microscopic NDE evaluations of crack extent and position, crack growth rates, and local crack depth were made based on near-field ultrasonic scattering signatures. A variety of electro-chemically generated corrosion pits were studied, where variations of pit depth, pitting surface area, and pit volume loss were correlated to fatigue life, crack initiation, and crack growth rates. The measurement technique provided an advanced crack 'imaging' capability that proved to be a very useful NDE tool for the micro-characterization of crack growth processes, and provided a wealth of information regarding the micro-features of the cracks whcih are currently not available with any other advanced NDE technique.

In frequency modulated continuous wave sensor systems for object distance measurement, use of the fast Fourier transformation for frequency estimation is widely adopted because of its comparably low execution time and available implementations. Inherent resolution restrictions make modern state-space based frequency estimators a viable alternative to this approach. Estimation of the correct model order, crucial to accurate distance measurement when used in a setup with an unknown number of targets, may be avoided by using active transponders. In this paper, application of a state-space frequency estimator is investigated with the use of measurement data in a system with an a priori known number of active targets. Evaluation results are analyzed and compared to performance of the Fourier transformation.

A computer program, called TERRA (Thickness Evaluation of Roads by RAdar) was recently developed for estimating pavement layer thicknesses from ground penetrating radar (GPR) data. This program incorporates decision criteria for automated detection of layer interfaces, computation of layer thicknesses and a segmentation algorithm for delineating segments based on layer thicknesses. The Florida Department of Transportation (FDOT) initiated the present field study for an initial assessment of TERRA. Radar and core data were collected from several flexible pavement sections of Florida's roadway system. These sites were selected to represent the present Florida in-place mixes (Superpave and Marshall mixtures) and different asphalt layer thicknesses, which varied from approximately 50 to 300 mm (2 to 12 in). Radar data were collected at both highway speeds and in stationary mode. This paper presents a description of the data collection effort as well as the subsequent analysis and findings.

Barkhausen noise measurements were used to determine the thickness of several micrometer thick zinc coatings on steel wires. Barkhausen noise is a broadband frequency signal ranging from several KHz to MHz. By comparing the attenuation of the noise through the zinc layer for different frequencies, it is possible to determine the thickness of the Zn coatings. An advantage of the method is that the attenuation of the signal can be calculated if the conductivity of the coating layer is known. Therefore, no calibration procedures are required.

Sensors for online monitoring of the heat treatment of aluminum alloys have been developed. The correlation between heat treatment parameters of Al 7075, the microstructure of the materials and NDE measurements has being studied systematically. By establishing correlations to the process parameters, it was assumed to be possible to devise a technique that provides not only insight into the aging process but also act as a quality control method for process verification. Multi-frequency eddy current allows compensation for environmental influences along with the ability to perform measurements at elevated temperatures and is therefore suitable for process monitoring.

Synchrotron-radiation imaging serves as a powerful tool for the non-destructive material characterization of metallic foams. The foaming process is visualized in situ by real-time radiography in projection image sequences. The temporal evolution of foam expansion from early pore formation over pore growth up to the collapse of the foam structure are reported. Ex situ microtomography is applied to the study of statistical distribution properties at the early foaming stages. Various image processing and analysis techniques yield quantitative results concerning pore nucleation and their early formation, film rupture and foam drainage. The similarities and differences of the metal foaming process with respect to the precursor material, its processing steps and process parameters are determinable.

This paper presents complex permittivity measurement of material using dielectric ring resonator. The method descried in the paper uses the perturbation method of dielectric ring resonator. In the conventional method, the value of one parameter in the formula of the perturbation method had been obtained using a standard sample and it was assumed as a constant. In our proposed method, it is obtained by the analytical solution of the dielectric ring resonator. Thus the measurement accuracy by the proposed method has been greatly improved. The proposed method was used to measure the permittivity of the sample of sawdust, of which the moisture content is from 0 to 120% on dry basis. The values of complex permittivity obtained by using HE₂₁₁ mode and TE₀₁₁ mode are in good agreement. By the proposed method, the maximum difference for real and imaginary part of permittivity using the two modes are 5.8% and 5.0%, respectively. It was shown that the results are much better than that by the conventional method.

Recently there is an increasing interest in laser beams with radial symmetry in polarization. Due to the cylindrical symmetry in polarization, these beams have unique focusing properties, which may find wide applications in a variety of nanometer scale applications, including high-resolution metrology, high-density data storage, and multi-functional optical microtool. In this paper, simple method of generating cylindrically polarized beams is presented and their potential applications to nondestructive nano-characterization are discussed. A high resolution surface plasmon microscope and a surface plasmon enhanced apertureless near-field scanning optical microscope are proposed. An automatic scanning microellipsometer that uses the cylindrical symmetry to enhance the signal-to-noise-ratio in high-spatial-resolution ellipsometric measurement will also be presented.

Crack initiation and growth characteristics of solder joints under fatigue loads are investigated using piezomechanical actuation. Cracks in solder joints, which can cause failure in microelectronics components, are induced via piezoelectricity in piezo-ceramic bonded joints. Lead-zirconate-titanate ceramic plates and eutectic Sn-Pb solder bonded in a double-lap shear configuration are used in the investigation. Electric field across each piezo-ceramic plate is applied such that shear stresses/strains are induced in the solder joints. The experiments show that cracks initiate in the solder joints around defects such as voids and grow in length until they coalesce with other cracks from adjacent voids. These observations are compared with the similar thermal cycling tests from the literature to show feasibility and validity of the current method in investigating the fatigue characteristics of solder joints. In some specimens, cracks in the piezo-ceramic plates are observed, and failure in the specimens generally occurred due to piezo-ceramic plate fracture. The issues encountered in implementing this methodology such as low actuation and high processing temperatures are further discussed.