High contrast air-coupled acoustic imaging with zero group velocity Lamb modes

The well known zero in the group velocity of the first-order symmetric (S1) plate wave mode has been exploited in air-coupled ultrasonic imaging to obtain significantly higher sensitivity than can be achieved in conventional air-coupled scanning. At the zero group velocity point at the frequency minimum of the S1mode, a broad range of wavenumbers couple into the first-order symmetric mode at nearly a constant frequency, greatly enhancing transmission at that frequency. Coupled energy remains localized near the coupling point because the group velocity is zero. We excite the mode with a broadband, focussing, air-coupled transducer at the frequency of the zero group velocity point in the S1 mode. By exploiting the efficient coupling at the zero group velocity frequency, we have easily imaged a single layer of Scotch tape attached to a 6.4-mm thick Plexiglas plate and 3.2-mm Teflon inserts in a composite laminate

Towards Intelligent Databases

This article is a presentation of the objectives and techniques of deductive databases. The deductive approach to databases aims at extending with intensional definitions other database paradigms that describe applications extensionaUy. We first show how constructive specifications can be expressed with deduction rules, and how normative conditions can be defined using integrity constraints. We outline the principles of bottom-up and top-down query answering procedures and present the techniques used for integrity checking. We then argue that it is often desirable to manage with a database system not only database applications, but also specifications of system components. We present such meta-level specifications and discuss their advantages over conventional approaches

Multimode Dispersion Compensated Pulse-Echo Guided Wave Inspection

Obtaining temporal/spatial resolution in guided wave measurements comparable to that of bulk wave measurements is impeded by the complicating effects of multimode dispersion. Transport of signals by multiple dispersive modes of propagation can transform an initially compact transient into an extended, visually unintelligible wavetrain. Guided mode inspections therefore tend to restrict measurements to regimes for which a single mode can be generated with minimal dispersion, consequently restricting the achievable temporal/spatial resolution of the measurement. The objective of the work reported here is to remove such restrictions, through implementation of wavefield measurements which accommodate the total complexity of multimode dispersed signals. Temporal and spatial Fourier analysis of guided wave fields enables a full identification of individual mode contributions. It is therefore conceivable that, given measurements taken over an appropriate spatial array, processing could be implemented to effectively remove the effects of multimode dispersion, enabling operation in frequency regimes currently associated with bulk wave measurements. This paper will report on work which is exploring this possibility. Results will be presented demonstrating array-based MHz regime plate wave measurements, generating 10 or more modes, in which individual modes are isolated, effects of dispersion are removed, and temporal resolution of the original transmitted pulse is restored. Examples of application will be presented, and factors determining the effectiveness of temporal resolution restoration will be discussed

Evaluation of Clinical and Ultrasonographic Parameters in Psoriatic Arthritis Patients Treated with Adalimumab: A Retrospective Study

Objectives. The aim of this study was to evaluate clinical and US-PD parameters in PsA during adalimumab treatment. Methods. A retrospective study has been conducted in forty patients affected by moderate-to-severe peripheral PsA. Clinical, laboratory, and US-PD evaluations were performed at baseline, after 4, 12, and 24 weeks of treatment. They included erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), visual analogue scale (VAS), Health Assessment Questionnaire (HAQ) modified for Spondyloarthritis, Psoriasis Area Severity Index (PASI) score, the 28-joint Disease Activity Score (DAS 28), and US-PD assessment. US-PD findings were scored according to a semiquantitative scale (ranging 0–3) for synovial proliferation (SP), joint effusion (SE), bone erosions (BE), and PD. Results. Data obtained for clinical, laboratory findings and US-PD evaluation showed statistical significant improvement in all the measures performed except for BE. A significant parallel decrease in SE, SP, and PD values were demonstrated. Conclusion. This study demonstrated that US-PD is a valid technique in monitoring the response to adalimumab in moderate-to-severe PsA

Air-coupled, focused ultrasonic dispersion spectrum reconstruction in plates

This paper presents and demonstrates a noncontact method for measuring the Lamb wave dispersion spectrum of a plate. Noncontact air-coupled source and receive transducers are used with line-focus mirrors and 50–700 kHz broadband apparatus for simultaneous measurement over a broad spectrum of refractive angles and multiple guided modes. Broadband, wide-angle wave forms are measured as a function of position. The Fourier transform of these wave forms from the t – x domain to the v – k domain gives an approximate spectrum of the dispersion relation. We measure the dispersion spectra of Lucite™, aluminum, balsa wood, and a carbon fiber epoxy laminate, and show that the measured spectra agree well with the dispersion relation calculated from Lamb wave theory

Wednesday Evening Session XIX ‘Town Meeting on a Working Group in NDE’

The following record of the Wednesday evening problem session at th effort Magruder Inn, Williamsburg was transcribed from audio tapes made during the presentations and discussion

MOSAIC: A Scalable reconfigurable 2D array system for NDT

This paper documents the development of a scalable 2D array system, or Mosaic that can be targeted at a wide range of NDT applications by way of a reconfigurable tile that can be tessellated to form arrays of any size and shape. Close coupling permits utilization of excitation voltages as low as +/-3.3V with insertion loss of 48dB on reflection from an aluminum back wall at 73mm achieved using 2D arrays without decoding

The Influence of Thin Bonding Layers on the Leaky Waves at Liquid-Solid Interfaces

This paper presents theoretical and experimental results on the problem of bounded acoustic beam reflection at the Rayleigh angle from a fluid-solid interface which is loaded by a thin solid layer. The theoretical development exploits the framework of existing theory to yield a simple, analytic model which is reasonably accurate for thin layers. It is shown that the influence of the layer is contained entirely in the dispersive Rayleigh wavespeed and the thickness-dependent displacement parameter Δs. Measurements of the reflected acoustic field amplitude have been performed on several samples of stainless steel loaded with a thin copper layer. We have found reasonably good agreement between the theoretical model calculations and experimental measurements for ratios of the layer thickness to the Rayleigh wavelength as large as 0.3. Beyond this value, some disparity is observed, particularly in the calculation of the thickness-dependent Rayleigh wavespeed

Impeded Growth of Magnetic Flux Bubbles in the Intermediate State Pattern of Type I Superconductors

Normal state bubble patterns in Type I superconducting Indium and Lead slabs are studied by the high resolution magneto-optical imaging technique. The size of bubbles is found to be almost independent of the long-range interaction between the normal state domains. Under bubble diameter and slab thickness proper scaling, the results gather onto a single master curve. On this basis, in the framework of the "current-loop" model [R.E. Goldstein, D.P. Jackson and A.T. Dorsey, Phys. Rev. Lett. 76, 3818 (1996)], we calculate the equilibrium diameter of an isolated bubble resulting from the competition between the Biot-and-Savart interaction of the Meissner current encircling the bubble and the superconductor-normal interface energy. A good quantitative agreement with the master curve is found over two decades of the magnetic Bond number. The isolation of each bubble in the superconducting matrix and the existence of a positive interface energy are shown to preclude any continuous size variation of the bubbles after their formation, contrary to the prediction of mean-field models.Comment: \'{e}quipe Nanostructures Quantique