Quick mass production of homogeneous thin film material is required in paper, plastic, fabric, and thin film industries. Due to the high feed rates and small thicknesses, machine vision and other nondestructive evaluation techniques are used to ensure consistent, defect-free material by continuously assessing post-production quality. One of the fastest growing inspection areas is for 0.5-500 micrometer thick thin films, which are used for semiconductor wafers, amorphous photovoltaics, optical films, plastics, and organic and inorganic membranes. As a demonstration application, a prototype roll-feed imaging system has been designed to inspect high-temperature polymer electrolyte membrane (PEM), used for fuel cells, after being die cast onto a moving transparent substrate. The inspection system continuously detects thin film defects and classifies them with a neural network into categories of holes, bubbles, thinning, and gels, with a 1.2% false alarm rate, 7.1% escape rate, and classification accuracy of 96.1%. In slot die casting processes, defect types are indicative of a misbalance in the mass flow rate and web speed; so, based on the classified defects, the inspection system informs the operator of corrective adjustments to these manufacturing parameters. Thickness uniformity is also critical to membrane functionality, so a real-time, full-field transmission densitometer has been created to measure the bi-directional thickness profile of the semi-transparent PEM between 25-400 micrometers. The local thickness of the 75 mm x 100 mm imaged area is determined by converting the optical density of the sample to thickness with the Beer-Lambert law. The PEM extinction coefficient is determined to be 1.4 D/mm and the average thickness error is found to be 4.7%. Finally, the defect inspection and thickness profilometry systems are compiled into a specially-designed graphical user interface for intuitive real-time operation and visualization.

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Recent advances in metamaterials research has enabled the development of highly sensitive near-field microwave sensors with unprecedented sensitivity. In this work, we take advantage of the increase in the sensitivity to produce a compact, lightweight, affordable, and accurate measurement system for the applications of microwave imaging and material characterization. This sensitivity enhancement due to the inclusion of metamaterials opens the door for the use of inexpensive microwave components and circuits such as direct detectors while leveraging the high sensitivity of the metamaterial probe to deliver an overall accurate measurement system comparable to that of a traditional probe used in conjunction with a vector network analyzer. The sensor developed is composed of a metamaterial sensor with an RF direct detection circuit. In this work, two prototype measurement systems have been designed and tested. Measurement of small cracks in conductors and material characterization using the proposed system were performed. The results from the newly developed sensors were compared with the results from vector network analyzer measurements. Good agreement was obtained. The feasibility of a compact, lightweight, affordable, and accurate system has been demonstrated by using the developed prototypes.

Following Carslaw [1] and as discussed by Becker et al [2], the diffusion of ultrasonic energy in cement-based aggregates follow the heat diffusion equation. However, due to the finite size of the discs used in experiments by Becker, ultrasound energy is contained within the body for a longer period of time, as compared to [2]. Though the energy content of the disc in reality would eventually decay to zero, due to leaks and other mechanisms, a theoretical study of perfectly adiabatic case is useful to compare the residual energy values to material properties. As a particular example, the input energy sees multiple phenomena inside the material during propagation. The residual energy is this a combined effect of the multiple scattering, dissipative and diffusive processes. This objective of this thesis is to study the relationship between the residual spectral density and specimen geometry. The effort further aims to attribute the difference in the residual spectral energy density values in materials of similar geometry to the varying material properties of the heterogeneous materials. Finally, a study of the error propagation in the estimation is presented, along-with an analytical relationship showing the value of spectral energy density for discs of finite radius and height. Ref: 1. H. S. Carslaw, J.C.J., Conduction of Heat in Solids. 2nd ed ed. 1986: Oxford University Press, USA. 520 2. Becker, J., L.J. Jacobs, and J. Qu, Characterization of cement-based materials using diffuse ultrasound. Journal of Engineering Mechanics, 2003. 129(12): p. 1478-1484.

The objective of this research is the pursuit of a better characterization method for the air voids - particularly air-entrained voids - in fresh cement-based materials through the use of ultrasonics. The use of air-entraining agents (AEA's) to incorporate a stable network of air voids into fresh cement paste is common practice in the concrete industry. These particular air voids significantly improve durability of hardened cement paste through mitigation of stresses associated with freezing and thawing cycles. It is understood that the performance of entrained air voids in cement paste is dependent on their size and distribution, or spacing factor. However, conventional methods for qualifying air content, such as the Pressure, Volume, and Gravimetric Methods, only measure total air volume and cannot assess size or spacing. In this investigation, using matched pairs of transducers, ultrasonic pulses were transmitted through fresh cement paste specimens (0.0\% up to 0.6\% AEA by weight of cement). The received signals were recorded every five minutes during the first six hours and then every fifteen minutes thereafter. Analysis shows strong distinctions between specimens with and those without the AEA. Further research is needed into the distinctions among specimens with the AEA. However, the data suggest correlations between Vicat setting times, heat of hydration, and autogenous strain and ultrasonic metrics such as pulse velocity and peak frequency of the signal. The findings of this research should be most appropriate as a foundation for an inversion process and improved air-entrainment detection methods.

In this thesis ultrasonic Lamb wave measurements are performed to detect material nonlinearity in aluminum sheets. When a Lamb wave propagates, higher harmonic wave fields are generated and under certain conditions the second harmonic is cumulative. When these conditions hold the Lamb waves are serviceable for material nonlinearity measurements. For generation, a wedge transducer combination is used. The detection of the Lamb wave are performed with either a laser interferometer or a second wedge transducer combination and the results are benchmarked. A short time Fourier transformation (STFT) is applied to the detected signal to extract the amplitudes of the first and second harmonics. A relative ratio of the first and second harmonics is deduced from nonlinear wave theory to assign the nonlinearity of the material. To verify the capability of the measurement setup and to show that cumulative second harmonics are generated, measurements for different propagation distances are performed. Further measurements on plasticly deformed specimens are carried out to examine the change of the material nonlinearity as a function of plasticity.

The objectives of this thesis are to develop and validate laser ultrasonic inspection methods for on-line testing of microelectronic devices. Electronic packaging technologies such as flip chips and BGAs utilize solder bumps as electrical and mechanical connections. Since they are located hidden from view between the device and the substrate, defects such as cracks, voids, misalignments, and missing bumps are difficult to detect using non-destructive methods. Laser ultrasonic inspection is capable of detecting such defects by utilizing a high power laser pulse to induce vibrations in a microelectronic device while measuring the out of plane displacement using an interferometer. Quality can then be assessed by comparing the vibration response of a known-good device to the response of the sample under inspection. The main limitation with the implementation of laser ultrasonic inspection in manufacturing applications is the requirement to establish a known-good reference device utilizing other non-destructive methods. My work will focus on developing a method to inspect flip chip devices without requiring a previously established reference. The method will automatically examine measurement data from a large sample set to identify those devices which are most similar. The selected devices can then be utilized to compose a hybrid reference signal which can be used for comparison and defect detection. Current trends in the electronic packaging industry continue to drive toward increased solder bump density, making it increasingly difficult to generate strong ultrasonic signals in these stiffer devices. To overcome this difficulty, I propose a new excitation method which places the source of ultrasound at the inspection location for each test point on the device surface. This ensures that the same power is available for each inspection location while also increasing the signal to noise ratio. The hardware implementation of this method reduces the system complexity and required automation, which can significantly reduce equipment cost and inspection time. The implementation of the proposed excitation method in conjunction with the use of a hybrid reference signal for defect detection will improve the utility of the laser ultrasonic inspection technique to on-line inspection applications where no other non-destructive methods are currently available.

The long-term goal of this research is to assist in the development of a fast, accurate, and low-cost nondestructive inspection prototype for solder joints in integrated circuits (IC). The goal of the work described in this thesis is to develop a fully automated system to maintain the signal strength of the vibrometer that would reduce the testing time while maintaining or improving the quality of the defect detection results. The ability to perform the inspections in an automated manner is very important in order to demonstrate the ability of the defect detection system to be used for online inspection without the need of an operator. The system was able to find the maximum signal strength (at a single point on the surface of a flip chip) nearly five times faster than Polytec's commercial system with a search time of approximately 2.1 sec. When integrated into the nondestructive inspection prototype, the system described in this work was found to approximately reduce the data acquisition time per test location by four times, with a minimum data acquisition time of 8.5 sec and an average time of 15.4 sec, while maintaining the same level of quality of results obtained by a skilled operator when manually maintaining the signal strength of the vibrometer. Hardware was developed that retrofitted a vibrometer's focusing head at the end of a fiber optic cable to a motorized linear stage. This stage controlled the standoff distance between the focusing head and the IC's surface with a fixed focal length, which allowed the spot size of the laser to be adjusted while searching for a desired signal strength. Numerous tests were conducted to determine the search parameters, which led to a search time of approximately 2.1 sec. This time was found to be dependent on the surface finish of the IC being inspected. It was also found that to achieve a desired signal intensity strength, not only does the standoff height of the focusing head, which determines the laser spot size, need to be controlled, but also the exact location on which the laser is reflecting off the IC.

Thesis (Ph.D.)--Tufts University, 2004. / Adviser: Masoud Sanayei. Submitted to the Dept. of Civil Engineering. Includes bibliographical references (leaves 300-305). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (M.S. in Civil Engineering)--University of Maryland, College Park, 1992. / "A scholarly paper submitted to Assistant Professor Ian Flood." Description based on title screen as viewed on April 16, 2009. Includes bibliographical references (p. 49-52). Also available in print.