A scratch intersection based material removal mechanism for CMP processes is proposed in this paper. The experimentally observed deformation pattern by SEM and the trends of the measured force profiles (Che et al., 2003) reveal that, for an isolated shallow scratch, the material is mainly plowed side-way along the track of the abrasive particle with no net material removal. However, it is observed that material is detached close to the intersection zone of two scratches. Motivated by this observation, it is speculated that the deformation mechanism changes from ploughing mode to shear-segmentation mode as the abrasive particle approaches the intersection of two scratches under small indentation depth for ductile metals. The proposed mechanistic material removal rate (MRR) model yields Preston constant similar to those observed experimentally for CMP processes. The proposed model also reveals that the nature of the slurry-pad interaction mechanism, and its associated force partitioning mechanism, is important for determining the variation of MRR with particle size and concentration. It is observed that under relatively soft pads, small particles and low particle concentration, the pad undergoes local deformation, yielding an increased MRR with increasing particle size and concentration. At the other extreme, the intact walls of the surface cells and the connecting cell walls between the surface pores deform globally, resembling a beam or a plate, and a decreasing trend in MRR is observed with increasing particle size and concentration. The predicted MRR trends are compared to existing experimental observations.

We discuss in this paper the underlying physics of a residual bias phenomenon, whereby the metalized Mylar films of air‐coupled film transducers accept and retain a residual electrostatic charge. Experimental measurements to demonstrate and quantify this effect are reported here, along with a hypothesis of the mechanism of charge transfer and embedding. The measurements show the amplitude performance of the capacitive film transducers as a function of applied bias voltage and frequency. Factors such as humidity and decay time also play roles in the acquisition and holding of charge on a film. We hypothesize that charge transfers from the conductive backplate and collects on the non‐metalized side of the film. The charged films therefore are electrostatically attracted to the transducer backplate even with no applied voltage bias. Typically, an externally applied bias voltage is needed to charge the capacitor. With a persistent residual bias effect, these air‐coupled capacitive film transducers could be used like conventional piezoelectric transducers with no biasing required. This effect has substantial implications for the operation of air‐coupled film transducers.

In this work ultrasonic models and measurements are used to characterize a number of the important elements of an ultrasonic measurement system as well as the entire system. Ultrasonic measurement models for predicting the response from reference reflectors are described, including a new ultrasonic measurement model recently developed to simulate the ultrasonic response of an infinitely long cylindrical cavity. The reference reflectors considered include spherical pores, flat-bottom holes and side-drilled holes, which are commonly used in nondestructive evaluation studies. These reflectors are employed in a series of modeling/experimental studies to assess where approximate and more exact scattering models are needed and to estimate the significance of beam variations over the reflector surface. Model-based simulated flaw responses are compared to experimentally determined flaw responses from these reference reflectors and the accuracy of the models is discussed.;The role that an ultrasonic piezoelectric transducer plays in an ultrasonic measurement system can be described in terms of the transducer's input electrical impedance and its sensitivity. A new model-based method for simultaneously determining the impedance and sensitivity of commercial ultrasonic immersion transducers is developed. This method is based on a pulse-echo setup and relies only on electrical measurements. It is demonstrated that sensitivities obtained with this new method agree well with the sensitivities obtained using a more complex three-transducer method originally developed for lower-frequency acoustic transducers that has been used in many previous studies. The influence of the pulser/receiver settings on the transducer electrical impedance and sensitivity is also discussed. Cabling effects present are compensated for in the new pulse-echo method.;The transducer impedance and sensitivity measurements obtained using this new pulse-echo method are combined with measurements/models for all the other electrical elements in an ultrasonic measurement system to determine a system transfer function that characterizes the effect of all the electrical and electromechanical components in the system. It is shown that by combining the system transfer function with models of the acoustic/elastic process present in a measurement system it is possible to accurately simulate the output voltage of the entire ultrasonic measurement system.

This research work is focused on the development of a spherically focused (no-mirror) capacitive-film air-coupled ultrasonic transducer and a leak location array sensor for long-endurance spacecraft. For the development of a spherically focused capacitive-film air-coupled ultrasonic transducer, two transducers have been designed, fabricated, and their performance characterized, using a spherically deformed backplate and film. One has a 10-mm diameter and 25.4-mm geometric focal length, and another has a 50-mm diameter and 50.8-mm geometric focal length. Both spherically focused transducers have frequency spectra centered at 805 kHz with -6-dB points at 400 kHz and 1200 kHz. By performing rigorous feasibility tests; a flexible copper/polyimide circuit board material is employed as a backplate in place of the conventional silicon substrate. Utilizing its deformability and ease of microfabrication, we have demonstrated that spherically focused air-coupled ultrasonic transducers can be made to function without the need of an external focusing device, such as a zone plate or an acoustic mirror. We have also invented a simple and easily applied method to conform the metalized polymer film onto a spherically curved backplate, while suppressing wrinkling on the film. Good agreement has been shown between measurement and theory, suggesting that our transducers behave as ideal spherically focused piston transducers;For the development of a leak location array sensor for long-endurance spacecraft, we have developed and experimentally demonstrated a sensitive and reliable means to locate an air leak in a plate-like structure. The goals of this work are accomplished by developing a sophisticated leak location algorithm and a two-dimensional PZT array sensor. The proposed leak location algorithm is highly effective in finding the direction of the leaks, using a minimal number of sensors, and needing less computation time while still achieving high accuracy. In addition, it accounts for the multi-mode dispersive characteristics in a plate-like structure, and utilizes structure-borne noise generated by turbulence at an air leak. This leak location algorithm is implemented by a prototype of a 64-element array sensor.

We demonstrate an array sensor method intended to locate leaks in manned spacecraft using leak‐generated, structure‐borne ultrasonic noise. We have developed and tested a method for sensing and processing leak noise to reveal the leak location involving the use of a 64‐element phased‐array. Cross‐correlations of ultrasonic noise waveforms from a leak into vacuum have been used with a phased‐array analysis to find the direction from the sensor to the leak. This method measures the propagation of guided ultrasonic Lamb waves passing under the PZT array sensor in the spacecraft skin structure. This paper will describe the custom‐designed array with integrated electronics, as well as the performance of the array in prototype applications. We show that this method can be used to successfully locate leaks to within a few millimeters on a 0.6‐m square aluminum plate.

Micrometeorite hits can create air leaks in manned spacecraft. Leak-generated-guided ultrasonic waves can be monitored within the platelike spacecraft skin to detect and locate leaks. Cross-correlation techniques allow measurement of the deterministic behavior of the leak-generated noise. Measured leak-into-vacuum cross-correlations of noise signals from two adjacent transducers are recorded as the transducer pair is rotated to determine the relative phase delay as a function of rotation angle. The direction to the leak is found from the variation of phase with angle or from synthetic aperture analysis. The leak is then located through triangulation from two or more sensor-pair locations.

Past research has conclusively shown that long fiber structural composites possess superior specific energy absorption characteristics as compared to steel and aluminum structures. However, destructive physical testing of composites is very costly and time consuming. As a result, numerical solutions are desirable as an alternative to experimental testing. Up until this point, very little numerical work has been successful in predicting the energy absorption of composite crush structures. This research investigates the ability to use commercially available numerical modeling tools to approximate the energy absorption capability of long-fiber composite crush tubes. This study is significant because it provides a preliminary analysis of the suitability of LS-DYNA to numerically characterize the crushing behavior of a dynamic axial impact crushing event;Composite crushing theory suggests that there are several crushing mechanisms occurring during a composite crush event. This research evaluates the capability and suitability of employing, LS-DYNA, to simulate the dynamic crush event of an E-glass/epoxy cylindrical tube. The model employed is the composite "progressive failure model", a much more limited failure model when compared to the experimental failure events which naturally occur. This numerical model employs (1) matrix cracking, (2) compression, and (3) fiber breakage failure modes only. The motivation for the work comes from the need to reduce the significant cost associated with experimental trials. This research chronicles some preliminary efforts to better understand the mechanics essential in pursuit of this goal. The immediate goal is to begin to provide deeper understanding of a composite crush event and ultimately create a viable alternative to destructive testing of composite crush tubes.

We have developed and tested in the laboratory a method for in-orbit detection and location of air leaks in manned spacecraft that uses only a small number of sensors distributed arbitrarily on the inner surface of the spacecraft skin. Then, structure-borne ultrasound in the range of 300–600 kHz is monitored from each of the sensors. When cross correlations between measured sensor waveforms indicate the presence of a leak, these correlations are compared with a large dynamically generated database of simulated correlations to locate the leak on the pressure vessel. A series of experimental tests were performed and at worst the method identified some false locations, but the true location of the leak always appeared.

Heat transfer plays an important role in the design of efficient thermoelectric (TE) devices. Currently, a TE device constructed from bismuth-telluride with figure of merit, ZT, of unity can achieve an ideal efficiency of about 12%. However, the efficiency achieved in practice is less than 5%. This difference between the ideal and the actual efficiencies can largely be attributed to heat transfer. A numerical study based on three-dimensional CFD analysis was performed to investigate natural convection and radiation heat transfer that take place in the space between the thermoelectric legs in thermoelectric (TE) modules. Parameters studied include staggered and non-staggered arrangement of the TE legs, length of the legs, spacing between legs, and difference between the hot and cold temperatures. Results obtained show natural convection and radiation can both be important. Radiation increases in importance as surface emissivity increases. Also, radiation heat transfer increases as leg length shortens, leg spacing, and temperature difference increases. This data will be used to guide design. Results also show that there is net transfer of heat to TE legs from the hot walls of the cavity. This presents a new design opportunity.

A guided ram-air parachute, or parafoil, offers a lightweight and efficient means for the autonomous placement of payloads to specified ground coordinates. The technology has a wide variety of applications, including advanced precision airdrop operations and the safe return of high altitude balloon or sounding rocket payloads. Current systems rely on complicated and expensive sensor suites, and computationally intensive guidance and control algorithms. In the present work, an integrated guidance, navigation, and control scheme is presented which utilizes inexpensive "off-the-shelf" sensors and computationally simple guidance, navigation, and control (GNC) algorithms. The GNC scheme is intended for implementation on a Peripheral Interface Controller (PIC). The GNC scheme is intended to serve as the primary GNC scheme for a small-scale parachute system, but could equally well serve as a backup for a more complicated system in the event of CPU or sensor failure. Navigation data is collected from a GPS receiver and a 3-axis digital compass, sampled at 1 Hz and 2.5 Hz, respectively. The wind speed and heading are estimated using the supplied navigation data and an estimate of the vehicle airspeed. It is shown that an estimation accuracy of better than 3 ft/s for velocity and 10 degrees for heading can be achieved without additional filtering. A linear proportional feedback controller is designed to control the vehicle course angle. It is shown that the effect of the slow sample rate of the navigation sensor data acts as a filter in the forward loop and contributes non-minimum phase zeros to the closed-loop dynamics. The guidance algorithm generates a series of inertially fixed waypoints consisting of three distinct phases: initial homing, energy management, and final approach. The algorithm requires no a priori information about the wind profile. A six degree-of-freedom model is used to evaluate the performance of the integrated GNC algorithm. Monte-Carlo simulations were conducted for a number of wind profiles which were specifically chosen to test various design parameters. The combined results show a circular error precision (CEP) landing accuracy of 115 ft. It is shown that the primary factors limiting landing accuracy are the maximum actuator deflection and the low system bandwidth.