Abstract: Disclosed is an electromagnetic acoustic transducer, including a source of magnetic flux for establishing a static magnetic field, an electrical conductor for conducting an alternating current in the static magnetic field, and an electrically conductive, nonmagnetic shield disposed between the source of magnetic flux and the conductor.

Abstract: Disclosed is an electromagnetic acoustic transducer, including an electrical conductor adapted to carry an alternating current in a current plane, the current being conveyed by the conductor in uniformly spaced, parallel, and alternate directions at any instant, and a source of magnetic flux positioned to direct a static magnetic field parallel to the alternate directions, the transducer thereby being adapted to generate or detect a horizontally polarized shear wave in a ferromagnetic material. The transducer may be made unidirectional by adding a second electrical conductor adapted to carry a second alternating current 90.degree.

Abstract: A double drift IMPATT diode is formed from two semiconductors having different band gaps and carrier mobilities. The avalanche portion of the diode is created in the semiconductor having the lower band gap. The electron drift portion is created in the semiconductor having the higher electron mobility and the hole drift portion is created in the semiconductor having the higher hole mobility. This decreases the voltage required across the avalanche portion, decreases the series resistance, and thus increases the efficiency of the diode.

Abstract: An apparatus for characterizing a surface anomaly in an electrically conductive sample includes an oscillator with an amplifier for supplying gain to the oscillator, a feedback loop linking the input and output of the amplifier, a two port ferromagnetic resonator connected within the loop to modulate the level and frequency of oscillation of the oscillator in response to eddy currents induced in the surface of the sample by the resonator, a variable attenuator connected within the loop to adjust the power level of the oscillator, and an adjustable phase shifter connected within the loop for changing the total phase shift of the loop. A sensing circuit is operably connected to the output of the amplifier to monitor the resonance parameters of the oscillator.

Abstract: Disclosed is a nondestructive test device for detecting a flaw proximate to a welded seam in a pipe, including an electromagnetic acoustic transmitting transducer for generating a horizontally polarized shear wave in the wall of the pipe, a high frequency generator operatively connected to the transmitting transducer for energizing the transducer, an electromagnetic acoustic receiving transducer for responding to a horizontally polarized shear wave within the wall, an amplifier operatively connected to the receiving transducer for boosting the response signal of the transducer, and an indicating instrument for receiving and displaying the amplified response signal. In the test method disclosed, a horizontally polarized shear wave is generated in the wall, the pipe is monitored to detect a reflected horizontally polarized shear wave, and a time-dependent representation of the amplitude of the reflected wave is displayed.

Abstract: A charge coupled device has a semi-insulating semiconductor for a substrate. Resistivity of the semiconductor is at least 10.sup.6 ohm cm. A semi-conductive layer is grown epitaxially or is implanted on the substrate to form a thin, active, charge transport layer. A row of parallel, closely spaced gates on the charge transport layer provides individual storage wells in the charge transport layer. In a preferred embodiment, ohmic contacts adjacent the first and last gates in the row of gates provide a means for injecting a signal into the charge transport layer and a means for detecting the signal. Preferably, the substrate is semi-insulating GaAs and the gates are Schottky barrier gates.

Abstract: Disclosed is a method for measuring the depth a of a surface flaw in an object, including the steps of irradiating the flaw with an incident acoustic surface wave signal, detecting a reflected acoustic surface wave signal, including a first portion reflected from the surface edge of the flaw and a second portion reflected from the bottom of the flaw, and analyzing the interference between the first and second portions of the reflected signal to determine the depth of the flaw. The analysis may be carried out by Fourier transforming the reflected signals from the time domain to the frequency domain, selecting a frequency f.sub.n for which a maximum or minimum amplitude is detected independent of the angle of detection, and calculating the depth a from the formula a=nV.sub.r /2f.sub.n, where n is an integer, and V.sub.r is the speed of an acoustic surface wave in the object.

Abstract: A multiple cavity electro-optic tunable filter includes an ordered row of n electro-optically tunable plates (n=2, 3, 4 . . . ), each plate having an incident surface and an emergent surface, an incident reflective coating on the incident surface of the first tunable plate in the row, an emergent reflective coating on the emergent surface of the nth tunable plate in the row, and a series of (n-1) absorbent films, one of the films being disposed between each pair of adjacent plates in the row in mating contact with the adjacent surfaces of the adjacent plates.

Abstract: Disclosed is a nondestructive test method for inspecting an object, including the steps of generating a surface acoustic wave at a first location on the object, detecting a harmonic of the generated wave at a second location on the object, and relating the characteristics of the detected wave to the remaining useful life of the object. The amplitude of the detected harmonic may be compared to standard amplitude values to predict the percentage of fatigue life remaining in the object, or the amplitude may be used to estimate the size and density of cracks in the object. Additionally, the harmonic wave may be detected for a range of stress values, the amplitude differential between the maximum harmonic amplitude and the minimum amplitude under compression calculated, and the differential related to the remaining useful life of the object.

Abstract: Disclosed is an acoustic wave sensor, including an acoustic wave oscillator having a resonant frequency which is modulated according to changes in a physical variable and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal. As a surface acoustic wave pressure sensor, the sensor includes a housing defining a cavity therein, an opening in the housing communicating with the cavity, a surface acoustic wave transducer attached to the housing to close the opening and adapted to deflect in response to a pressure differential across the transducer, an amplifier coupled to the transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of the loop in response to the deflection, and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal.

Abstract: A polyimide foam is provided which has improved resistance to crumbling and to high temperatures. The foam is produced by reacting polymethylene polyphenylisocyanate (PAPI) with benzophenone-3,3',4,4'-tetracarboxylic acid dianhydride (BTDA) in the presence of furfuryl alcohol and concentrated phosphoric acid (PA). The ratio of PA to PAPI, (PA/PAPI), must be approximately 20 to 26% by weight.

Abstract: A semi-open method for growing an epitaxial layer on a substrate by increasing the pressure, refluxing the volatile components, contacting the substrate with the melt solution, and reducing the solution temperature.

Abstract: In this monolithic detector array, a signal processing layer is epitaxially formed directly on an active detector layer. The active detector layer is supported by a transparent substrate. The three layers are made of intrinsic semiconductors of the same conductivity type (e.g., n-type). The semiconductor forming the active layer has a smaller bandgap than the signal processing and substrate layers. A plurality of vias of opposite conductivity type (e.g, p-type) extend through the signal processing layer into the active detector layer where they form p-n junctions with the active detector layer. These p-n junctions collect charges generated by the radiation and the vias conduct these charges to the signal processing layer where gates, AC background suppression circuitry, and a charge coupled device process the photogenerated signals.

Abstract: Disclosed is a method of connecting a first component, including a first electrical conductor, to a second component, including a second electrical conductor, which involves the steps of positioning the first component proximate to the second component to establish a juncture area, covering the juncture area with an insulating layer to form a smooth surface transition between the first and second components, and depositing a third conductor across the insulating layer and in electrical contact with the first and second conductors.

Abstract: Disclosed is a method for evaluating a discontinuity in an object. As used to measure the depth of a surface discontinuity in a plate type of object, the method includes the steps of generating a horizontally polarized shear wave in the object directed substantially along the axis of the discontinuity, passing the generated wave through an aperture to diffract the wave prior to its arrival at the discontinuity, detecting the wave after it has propagated through the discontinuity, and calculating the depth of the discontinuity by correlating the phase and amplitude of the detected wave to the phase and amplitude of a similar wave propagated in a region of the object which is free of discontinuities.

Abstract: A band of material is formed by plating the material onto a cylindrical cathode sandwiched between a pair of insulating end pieces and is supported in a plating bath spaced a short distance from an anode. The cathode is rotated about its axis to provide uniform, reproducible mass transport to the plating surface. In order to determine the tensile properties of the plated material, the band is removed from the cathode and pulled apart in a tensile machine. During tensile testing, the band is held using a pair of pins and clevis, or it is formed into a strip and gripped in a standard fixture. In order to determine the stress condition of the plated material, the band is cut open and its change in diameter measured.

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 optical filter for transmitting light in a narrow bandwidth centered about the wavelength .lambda., including a birefringent half-wave crystal defining an optical path through the crystal and normal to the optical axis of the crystal, the thickness of the crystal effecting a 180.degree. phase change between the fast and slow components of light of wavelength .lambda. along the optical path; a first polarizer preceding the crystal in the optical path and having a first polarizing plane rotated 45.degree. about the optical path from the optic axis of the crystal; a first reflective surface preceding the first polarizer in the optical path and normal to the optical path; a second polarizer following the crystal in the optical path and having a second polarizing plane rotated 90.degree. about the optical path from the first polarizing plane; and a second reflective surface following the second polarizer in the optical path and normal to the optical path.

Abstract: Disclosed is an optical filter, including a plurality of adjacent layer pairs, each pair having an incident and an emergent surface and including a first dielectric layer having a thickness t and a refractive index n, a second dielectric layer, adjacent to the first layer, having a thickness t and a refractive index n, and a control electrode disposed between and in electrical contact with the layers. The filter further includes a plurality of ground electrodes disposed on the layer pairs to electrically contact each incident and emergent surface, a source of electric potential, and a switch for connecting the source between the control electrodes and the ground electrodes, whereby light having a wavelength .lambda.=4nt will be reflected by the filter upon closing the switch and thereby applying the electric potential in opposite directions across the first and second layer pairs. The plurality of layer pairs may include m layer pairs, with the thickness of each dielectric layer in the ith pair (i=1, 2, 3 . .

Abstract: A method and apparatus are provided for automatically controling the strain rate during superplastic forming of a blank of material into a part. The method and apparatus produce a part in a minimum time by deforming the material in its optimum superplastic conditions. A relationship is determined between time and the pressure required to form the blank against the configured surface of a die at a strain rate which causes the blank to flow superplastically. The blank is positioned in the die and held at a temperature at which the material exhibits superplasticity. Pressure is automatically applied across the thickness of the blank in accordance with the previously determined relationship between time and pressure until the part is formed. The apparatus comprises conduits connected to a die and to a high pressure gas. Valves in the conduits regulate the pressure applied to the blank. A controller receives command signals from a programmer which is programmed with the desired time vs pressure relationship.