Samuel J. Wormley

Apparatus and method for detection of icing onset and ice thickness

An apparatus and method for detection of icing onset and ice thickness upon an accretion surface utilizing ultrasonic echo ranging techniques, including propagation of ultrasonic waves through a buffer block. A portion of the wave energy is reflected by reference reflection means and another portion of the wave energy is propagated to the ice accretion surface and to a reflecting interface. The reflecting interface is represented either by the accretion surface in absence of icing, or by a thin ice layer at the icing onset, or by the ice/air interface of an ice layer accreted upon the accretion surface. Reflected waves are transduced to electrical signals. Relative signal amplitudes and time delays provide measures of particular icing conditions upon the accretion surface, and are appropriately resolved into calibrated signals indicating icing onset, ice thickness, and ice accretion rate.

Apparatus and technique for reconstruction of flaws using model‐based elastic wave inverse ultrasonic scattering

An automated multiviewing ultrasonic apparatus and signal processing routine have been developed for utilization in nondestructive evaluation (NDE) of materials. The instrument has been developed to take advantage of recent advances in long and intermediate wavelength inverse scattering of elastic waves, and provides a 3‐D reconstruction of a flaw. Although the reconstruction obtained does not contain fine details of the flaw’s structure, it provides sufficient information about the flaw (size, orientation, and selected materials properties) so that failure‐predictive decisions can be made.

Measurement of texture and formability parameters with a fully automated, ultrasonic instrument

A fully automatic, ultrasonic instrument to measure texture and formability parameters on metal sheet is described. Arrays of EMAT transducers are used to transmit and receiveSo Lamb waves propagating at 0°, 45°, and 90° with respect to the rolling direction. By analyzing the frequency dependence of the phase of the received signals, the long wavelength limit of the velocities is obtained. Included is a discussion of this algorithm, and subsequent processing steps to predict the ODCsW400,W420, andW440. On steel, the prediction of drawability parametersr and Δr based on a correlation developed previously by Mould and Johnson is also discussed. Results of blind field trials at facilities of three suppliers/users of steel sheet for automotive applications and one supplier of aluminum sheet for beverage can production are reported. The former confirmed the Mould-Johnson correlation for lowr material but indicated that refinements are needed for modern steels with highr. The aluminum data suggest a correlation between W440 and the degree of four-fold earing.

Reliability of Reconstruction of Arbitrarily Oriented Flaws Using Multiview Transducers

Some basic problems associated with the reconstruction of arbitrarily oriented flaws using an automated multiviewing ultrasonic transducer system and its associated signal-processing algorithms are addressed. The effects of aperture size on the reconstruction reliability are investigated by computer simulation, and experimental results are presented for the reconstruction of arbitrarily oriented oblate and prolate spheroidlike flaws. The multiviewing capability of the system is used to determine a spatial data-acquisition pattern which improves the reliability of reconstruction by optimizing the illumination of the flaw surface by the multiviewing transducer and the signal-to-noise ratio of the scattering signal.

Elastic Wave Scattering from Multiple Voids (Porosity)

The purpose of the work described in this paper is the development of an ultrasonic measurement technique which provides a convenient way to detect dilute porosity conditions in materials and to extract certain properties of the flaw distribution which are important in failure prediction. Use has been made entirely of ultrasonic backscatter measurements; thus, the technique differs considerably from other investigations which lead to porosity determinations in that no reliance is placed upon either attenuation measurements or precise ultrasonic velocity measurements [1,2]. The technique thus possesses a distinct advantage for practical implementation, i.e., it is a “one-sided” measurement which does not require ultrasonic echo returns from an opposite face of the sample in order to be useful. At present, the work is limited to dilute porosity concentrations. Reasons for this limitation will become clear in the paper. With additional effort it is expected that this limitation can be removed and the work extended to larger concentrations.

Ultrasonic Beams with Bessel and Gaussian Profiles

A novel technique has been developed for generating ultrasonic beams with spatial profiles of amplitude governed by a truncated Bessel function or Gaussian function [1,2]. Bessel beams have very unique properties; in optics Bessel beams have been shown to be diffractionless (J. Durnin et al, 1987 [3,4]). In a related work, R. W. Ziolkowski et al [5] reported experimental measurements of “acoustic directed energy pulse trains” generated by synthetic line array of ultrasonic transmitters in water. However, a Bessel function ultrasonic transducer has never been reported before. Gaussian beams also have desirable properties; they are very easy to model analytically, and a circular Gaussian function ultrasonic transducer is free of near-field nulls and far-field sidelobes associated with conventional “piston source” transducers [6]. At least three designs of Gaussian transducers have been reported in the literature in the past 30 years [7–9]. We report a method in which piezoelectric ceramic elements are poled with nonuniform electric fields shaped like Bessel or Gaussian functions such that the resulting polarization (and hence the ultrasonic amplitude) follows that of the applied poling field. Like conventional piston source transducers, such Bessel or Gaussian transducers also possess the simple “parallel plate capacitor” configuration and can be packaged likewise. Beam profiles and propagation behavior of these Bessel and Gaussian transducers have been measured experimentally in an immersion tank and the results compared well with model predictions

Application of a Fourier Transform-Phase-Slope Technique to the Design of an Instrument for the Ultrasonic Measurement of Texture and Stress

This paper describes the development of an ultrasonic instrument to measure texture (preferred grain orientation), stress, and related physical properties in metal sheets in industrial environments. The technique is based on precise measurements of the speed of guided modes, including angular variations, and is made practical by the use of EMAT transducers, which require no couplant. The instrument is expected to find important initial applications in predicting sheet metal formability, either as a process control tool in the rolling mill or as a quality control tool in a stamping shop. Since the instrument will offer an improved measurement capability not presently available to industry, a much broader range of applications may develop, including measurements of stress and porosity in sheet and other simple geometries.

Two-dimensional ultrasonic tomography in nondestructive evaluation by using area functions

It is shown that the (normalized) area function based on the Born approximation offers a simple connection between the ultrasonic scattering response and the monochromatic ray sum in X-ray CT (computerized tomography). Because of this simple association, it is possible to apply the ultrasonic signals in the computationally direct and efficient parallel-beam X-ray CT algorithm to reproduce the vertical thickness function of an ultrasonic scatterer. The development of this imaging methodology is demonstrated for flaws of simple geometry; theoretical as well as experimental results for two model scatterers using this imaging technique are reported. Specifically, the area functions for a two-to-one spheroid and a circular cylinder are calculated and applied to a filtered backprojection algorithm of X-ray CT to obtain the vertical thickness function images. These images are then compared with the true vertical thickness functions of the targets based on their geometry. With theoretical data, this method was found to work very well. Even when experimental data containing creeping waves were used, the method produced satisfactory results for objects with continuously smooth surface.<<ETX>>

Technique for nonuniform poling of piezoelectric element and fabrication of Gaussian transducers

A new technique has been developed to polarize piezoelectric ceramic elements with a nonuniform electric field. Used as an ultrasonic transducer, the piezoelectric element will produce a corresponding nonuniform sound field. Ultrasonic transducers for generating specific field profiles can therefore be made by having a predetermined spatial pattern of polarization strength poled into the piezoelectric element. One of the desirable beam profiles is a Gaussian; it has the advantages of being free from near-field fluctuations and far-field sidelobes, and it is much easier to model than the usual piston transducers. This method was used to fabricate Gaussian beam transducers, and their measured field profiles compared well with the Gaussian beam model. Such transducers containing the built-in Gaussian amplitude profile can be electroded and mounted in the same manner as conventional piston transducers.<<ETX>>

Non-uniformly poled Gaussian and Bessel function transducers

A technique has been developed to polarize piezoelectric ceramic elements with spatially nonuniform electric fields. Used as ultrasonic transducers, these piezoelectric elements then produce nonuniform sound-field profiles corresponding to the spatially nonuniform polarization strength poled into the element. Gaussian transducers and Bessel function transducers have been built using this technique. The Bessel function transducer, of particular interest in achieving diffractionless beams was made to produce an ultrasonic beam profile approximating that of the Bessel function J/sub 0/(r) both in amplitude and in phase out to the third zero. The beam profiles of these nonuniformly poled transducers were mapped out in a water-immersion tank with a point probe and compared with beam profiles calculated with a Gauss-Hermite model excellent agreement was obtained. Such transducers containing prescribed field profiles can be electroded and mounted in the same manner as conventional piston transducers.<<ETX>>