Theoretical Analysis of Acoustic Emission Spectra

Frequency analysis of acoustic emission spectra has been done by our group and others for several years now. Lloyd Graham presented some of the results in a previous paper. One would like, of course, to extract as much information as possible from these spectra. We hope, for example, that at least some fracture or failure processes, microscopic failure processes, will have distinctive frequency signatures: perhaps certain kinds of phase transformations or, as has been discussed, microcrack initiation by brittle fracture of intermetallic particles

Mechanism of Photostimulated Exoelectron Emission

This paper discusses the changes in photoyield of pure aluminum and binary aluminum alloys due to fatigue induced surface roughness in the energy range 5 to 11 eV. As evidenced by a surface replication technique, the roughness is caused by dislocation slip steps forming a near perfect grating on the surface. The grating causes a resonant coupling of incident photons to surface electromagnetic waves in the material, the decay of which can eject electrons if the resonance energy exceeds the material\u27s work function. The theory of this roughness induced photoyield will be briefly reviewed. The effects of fatigue softening and hardening, of oxide layer thickness, and of alloying on the photoyield as a function of photon incident energy will be reported

Concept and Mathematical Modeling of Acoustic Emission Source

Presently, most acoustic emission applications in nondestructive testing involve placing transducers on a large structure, a bridge or hydrocarbon cracking pressure vessel, then loading the structure and listening for the burst-type acoustic emissions that ensue, and ,finally using triangulation to locate the flaws whence came those bursts. This technique is very effective at locating defects, and that means that the typical, most studied acoustic emission parameters are just the number of events, the event rate, and to a somewhat lesser extent, the maximum amplitude . It might be the root mean square. amplitude, or some other amplitude that characterizes the acoustic emission, or an amplitude distribution, that is, the number greater than some threshold V. These are typical, widely used acoustic emission parameters, and they have been very successful in locating defects. In fact, if they hadn\u27t been, I don\u27t think I would be here today talking about fancier things in acoustic emission

Half-Space Radiation by EMAT\u27s

A Green\u27s function calculation of the far field radiation patterns of EMAT\u27s is presented. The approach is based upon (a) closed form expressions for the eddy current and static magnetic field distributions, established by the EMAT, which react to produce the driving Lorentz forces and (b) a Green\u27s function derived from the steepest descent approximation to the far field response of an arbitary surface point force on a half space. Numerical results are presented, illustrating the radiation patterns of the three common EMAT designs. Included are vertically polarized shear waves as radiated by both meander coil and periodic magnet EMAT\u27s and horizontally polarized shear waves as radiated by the latter

Calculation of the Response of Angle Beam EMATs to Flaws in the Far Field

In the design of a system for NDE, it is necessary to quantify the relationship of flaw size and orientation to transducer signal levels. This is particularly true for automated systems, in which the transducer coordinates cannot be adjusted by an operator to maximize the signal. This paper presents the result of a model calculation for the case of angle beam inspection using EMATs, which appear likely to find extensive use in such systems. Included in the model are calculations of the elastic wave radiation pattern in three dimensions for plates, calculations of the elastic wave scattering from cracks using existent approximate models, and calculation of the electrical response to the scattered wave. Transducer apodization is used to reduce spurious side lobe signals and blind areas where flaws are weakly detected. Emphasis is placed on the case of SH wave generation

Synthetic biology devices for in vitro and in vivo diagnostics

There is a growing need to enhance our capabilities in medical and environmental diagnostics. Synthetic biologists have begun to focus their biomolecular engineering approaches toward this goal, offering promising results that could lead to the development of new classes of inexpensive, rapidly deployable diagnostics. Many conventional diagnostics rely on antibody-based platforms that, although exquisitely sensitive, are slow and costly to generate and cannot readily confront rapidly emerging pathogens or be applied to orphan diseases. Synthetic biology, with its rational and short design-to-production cycles, has the potential to overcome many of these limitations. Synthetic biology devices, such as engineered gene circuits, bring new capabilities to molecular diagnostics, expanding the molecular detection palette, creating dynamic sensors, and untethering reactions from laboratory equipment. The field is also beginning to move toward in vivo diagnostics, which could provide near real-time surveillance of multiple pathological conditions. Here, we describe current efforts in synthetic biology, focusing on the translation of promising technologies into pragmatic diagnostic tools and platforms.United States. Defense Threat Reduction Agency (Grant HDTRA1-14-1- 0006)United States. Office of Naval Research. Multidisciplinary University Research InitiativeUnited States. Air Force Office of Scientific Research (Grant FA9550-14-1-0060)Wyss Institute for Biologically Inspired EngineeringHoward Hughes Medical Institut

Cryptic biodiversity effects: importance of functional redundancy revealed through addition of food web complexity

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117120/1/ecy2012935992.pd