Abstract: Disclosed is a method for generating an ultrasonic wave in a material, utilizing a transducer adapted to induce a higher than fundamental mode wave in the material and a signal generator adapted to drive the transducer at a frequency above the cutoff frequency below which the higher mode wave will not propagate. For a horizontal shear wave, optimal transducer efficiency is obtained by selecting a driven frequency between a minimum cutoff frequency f.sub.c =v.sub.s n/2t and an upper frequency sufficiently close to f.sub.c to drive the transducer with at least a preselected increase in efficiency.

Abstract: Disclosed is an electromagnetic acoustic transducer for generating and detecting an elliptically polarized ultrasonic wave in an electrically conductive material. The transducer includes a row of uniformly sized, adjacent, alternately oriented permanent magnets, which establish a periodic magnetic field. Coaxially wound around the row is a first coil for inducing an alternating current perpendicular to the field and perpendicular to the periodic direction, while a second coil is wound around the coil orthogonal to the first coil to induce an alternating current perpendicular to the field and parallel to the periodic direction. An ultrasonic ellipsometer includes such a dual coil transmitting transducer for generating an elliptically polarized wave and a dual coil receiving transducer for detecting the wave after it has propagated through an electrically conductive medium.

Abstract: A method and an apparatus are provided for ultrasonically inspecting a cylindrical object. The object is placed between the poles of a magnet to create a circumferential magnetic field in the object. A group of electromagnetic transducers (EMAT's) are placed adjacent the material so that the transducers scan the entire object when it is rotated. When an RF signal is applied to the transducers, elastic waves are generated in the material. These elastic waves reflect from defects in the material and these reflections are received by the transducers.

Abstract: The transducer is constructed from individual transducer elements arranged in an array and configured to exhibit a predominant, longitudinal mode transversely to the array. The elements are interconnected through thin flexible sheets. Each element is individually damped, and the transducer as a whole is electrically damped through resonance with the clamped capacitance and dissipation. Electrical control permits in-phase operation of all transducer elements or control with preselected phase differences.

Abstract: An electromagnetic transducer is provided for ultrasonically inspecting conductive material as the material moves relative to the transducer. A coil is positioned in the field created by a magnet so that the conductors of the coil are transverse to the magnetic field. The coil is located predominately near the leading side of the magnet where flux is concentrated as the magnet and material move toward each other.

Abstract: A method and device which are suitable for the in-place inspection of pipelines are provided. A completely self-contained, mobile inspection station is placed inside a pipeline. The station runs through the pipe and transmits Lamb waves within the pipe wall, receives reflected and transmitted portions of the waves, and records the amplitude and phase of the received waves. The recorded information is analyzed to determine the location and nature of discontinuities in the pipe.

Abstract: Stress in a material is measured using electromagnetically generated, transverse elastic waves. A correlation is known to exist between the difference in velocity of orthogonally polarized transverse waves in the type material being measured and stress in the material. An electromagnetic transducer is used to generate orthogonally polarized waves traveling through the part at different velocities as a result of anisotropic stress in the part. The difference in velocity between the polarized waves is measured and compared to the correlation to obtain the stress existing in the part.

Abstract: Stress is detected by magnetostrictively generating vibrations which are detected at a location spaced from the region of generation. The efficiency of the generation is indicative of stress if the region is magnetically biased to less than maximum amplitude for the vibrations as produced. Preferably, the needed bias for generating vibrations at a constant level is used as stress indicator. Due to reciprocity of magnetostriction, the efficiency of generating magnetic oscillations by means of elastic vibrations in a biased region can be detected.