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: An electromagnetic transducer is provided which transmits and receives ultrasonic waves from a metallic part predominately in only one direction. At least two rows of permanent magnets are placed adjacent each other in a side-by-side relation. The N-S axes of the magnets are substantially parallel and adjacent magnets in each row have opposite polarity so that two periodic magnetic fields are created. The adjacent magnets are off-set by one-fourth period. Coils wrapped around each row of magnets are driven in phase quadrature in order to generate a unidirectional elastic wave in the metallic part. In another embodiment, sets of three rows of magnets are offset by one-sixth period and driven in 60.degree. phase shift.

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 magnet is used to create a static magnetic field adjacent to the surface of a conductive material. At least one conductor runs through the magnetic field. When a pulse of current flows through the conductor, an elastic wave is generated in the material. In a preferred embodiment, a row of individual permanent magnets is used to create a periodic magnetic field. One side of a coil is placed in the periodic magnetic field so that a sheet of current moves transverse to the magnetic field when a pulse of current flows through the coil. When the coil is oriented parallel to the row of magnets, a horizontal shear wave is generated in the material. When the coil is oriented transverse to the row of magnets, a Lamb wave is generated in the material.

Abstract: At least one of several transducers on a piezoelectric substrate is externally short-circuited by a series resonance circuit for suppression of triple transit echoes. The resonance circuit is additionally connected to an amplifier via a high input or output impedance. In multi-transducer systems any two transducers are prevented from communicating via echo signals by such resonance circuits. In filter cascades several resonance circuits may be included in the interstage coupling circuit or between the input and output amplifiers on the one hand and the cascade on the other hand.

Abstract: A surface acoustic wave filter has a Lithiumniobate substrate of parallelogram configuration, which is bonded to a header having similar acoustic impedance. The substrate has three transducers arranged along its long sides at particular spacings destined to suppress triple transit echoes. The short sides are oblique and surface portions adjacent thereto are covered by surface waves attenuating paddings. Two such filters are cascaded on the same header.

Abstract: Two piezoelectric filters are cascaded for suppression of bulk waves while mutually reinforcing surface wave band pass filtering. Each filter has an apodized central transducer and two outer transducers. In one instance the two outer transducers on one filter differ from the two outer transducers of the other filter with regard to bulk wave generation and reception. In another instance one filter provides asymmetric transmission and symmetry is restored by a wave slow-down for surface waves only. In still another instance the slow-down pad is provided also, but the signals in the two outer transducers are electrically inverted.