Jacques R. Chamuel

Ultrasonic aircraft ice detector using flexural waves

A system for the detection of wing icing by monitoring variations in flexural waves transmitted through the outer plate material of an aircraft airfoil. The flexural waves in the plate of the wing airfoil are more subject to variation from the accumulation of ice on the wing than the compressional waves. The flexural waves are detected apart from the compressional waves, which tend to remain relatively constant, to provide an indication of icing. Changes in amplitude, phase or dispersion characteristics of the flexural waves are detected to indicate ice buildup, and, in one embodiment, these values are ratioed to the corresponding levels in the compressional wave in order to provide compensation for variations other than ice buildup. The ultrasonic waves may be coupled directly from a transducer to the airfoil plate or via an ultrasonic waveguide interposed between the transducer and the plate. The receiver for the ultrasonic waves to be detected may be positioned to receive direct flexural waves transmitted over a distance through the plate or flexural waves reflected from reflecting boundaries in the plate.

Contactless characterization of antisymmetric edge wave dispersion along truncated wedge using electromagnetic acoustic transducer

Accurate laboratory measurements are compared with approximate theoretical calculations on the dispersion of antisymmetric flexural edge waves propagating along the apex of a truncated 6061 aluminum wedge with an apex angle Θ=26.7°. The wedge waves are detected with a specially designed electromagnetic acoustic transducer in the frequency range 30–500 kHz. Phase velocity dispersion plots are obtained from gated sinusoidal signals and wavelength measurements averaged over 10–20 wavelengths. The general characteristics of the experimental phase velocity dispersion data closely matched the approximate theoretical parabolic model by McKenna et al. [IEEE Trans. Sonics Ultrason. SU‐21(3), 178–186 (1974)] derived for small apex angle. The measured dispersion curve was duplicated using a truncated wedge tip width 57 μm in the parabolic approximation calculations while the actual measured tip width was 62 μm Antisymmetric flexural wedge waves obtained from a sharp apex (3 μm) are practically nondispersive as expec...

Transient Scholte wave transmission along rough liquid–solid interfaces

Transmission characteristics of transient Scholte waves along periodic and random liquid–solid interfaces are demonstrated using laboratory ultrasonic models. These characteristics indicate that, for periodic interfaces, the transmitted Scholte wave is composed of an attenuated main pulse, which arrives first, followed by substantial energy at the Bragg frequency, which is delayed and spread over a wide time window. Random topographic variations in the liquid–solid interface eliminate the transmission of the late‐arriving components. The experiments are limited to a water ‘‘half‐space’’ over a high‐speed solid half‐space, in which case, most of the Scholte wave energy is in the water. The Scholte wavelength is comparable to the horizontal spatial wavelength in the surface but is much greater than the vertical scale of the spatial variations. Results from composite interfaces formed by placing thin parallel scatterers on a plane solid surface and from corrugated interfaces formed by directly machining groo...

Electro‐elastic self‐scanning crack detector

A contactless self-scanning electro-elastic nondestructive testing technique is described for determining in real time the presence, location, number and size of defects present on the surface of a material under test. In one embodiment the apparatus includes means for inducing eddy currents or current flow in the surface of the conductive material. A magnetostrictive delay line is disposed parallel to the direction of current flow and equidistant and in fixed spatial relation with the surface. The presence of a crack or defect in the surface proximate to the delay line creates transverse eddy currents or transverse currents in the material which interact locally with the magnetostrictive delay line to induce elastic waves in the delay line. The elastic waves are generated in the delay line only at locations corresponding to the edges of the defects. An ultrasonic sensor coupled to the delay line is used to detect the elastic waves travelling in the delay line. The location of a crack or fissure may be determined based on the time of arrival of the elastic waves at the sensor. The self-scanning line electro-elastic probe is not susceptible to the presence of elastic waves propagating in the material under test. The invention is applicable for inspection of flat and curved surfaces. Another elastic wave transmitting medium may be employed in place of the magnetostrictive delay line given appropriate excitation means. Additionally, the delay line may be fabricated as a two-dimensional sheet with ultrasonic sensors disposed at selected locations on the sheet to achieve rapid inspection of an area for defects, the location of defects being determinable based upon the time of arrival of induced elastic waves at respective sensors.

Nondestructive ultrasonic transducer

An extendable probe that permits nondestructive ultrasonic inspection of a workpiece for flaws is disclosed which provides information indicative of flaw presence and location. The probe includes a pair of waveguides capable of elastic wave transmission. A first waveguide is excited to produce elastic waves which travel along the waveguide to an end of the waveguide in elastic wave transmitting contact with the surface of the workpiece under inspection. A second waveguide is maintained in contact with the workpiece a selected distance from the first waveguide and a sensor is disposed on the second waveguide for reception of elastic waves. In the absence of workpiece defects intermediate the contact points of the first and second waveguides, elastic waves are transmitted from the first waveguide to the second waveguide through the workpiece to the sensor and an output signal representative of transmitted elastic waves is produced by the sensor. The presence of a crack or flaw in the workpiece between or proximate to respective ends of the waveguides is apparent as a variation in the amplitude of the sensor output signal. Inspection of relatively inaccessible remote surfaces is facilitated with the probe which is thin and extendable. The distance from the sensors to a workpiece flaw is determinable from travel time of elastic waves in the waveguides and the workpiece. Detection of flaws of varied orientation in the workpiece is achieved by pivotable orientation of the waveguide ends with respect to the workpiece.

Laser diode acoustic noise reduction

A laser diode assembly and associated heat sink and excitation leads constructed to avoid the electromagnetic or magnetostrictive generation of stress or elastic wave disturbances in the diode, heat sink or associated components so as to maintain spectral purity in the diode laser emission. An improved laser diode assembly avoids the generation of elastic waves or vibrations within the leads, heat sink or associated structure of a laser diode by running excitation leads in a magnetic field cancellation arrangement to prevent magnetostrictively induced elastic waves in structure connected to the laser diode and to avoid vibration induced by coupling between the lead currents and external magnetic fields. The heat sink, electrical input and return leads and associated structure may be fabricated of a nonmagnetostrictive material to avoid magnetostrictively induced acoustic disturbances created by other magnetic field sources in the use environment of the laser diodes.

Shallow water acoustic studies using an air‐suspended water waveguide model

A novel experimental technique is introduced that allows multimode interference and coupling due to boundary topography and to the presence of scatterers in shallow water acoustic waveguides to be studied in the absence of radiation and elastic bottom effects. The air‐suspended water waveguide model consists of a water layer bounded above by air and below by a thin rubber membrane supported by pressurized air to counteract the weight of the water. Experimental data on the transmission of transient ultrasonic signals along the ‘‘perfect’’ waveguide are presented and compared with theory. Both experimental and numerical results are used to demonstrate that multiple nondispersed discrete pulses in a waveguide are equivalent to a summation of highly dispersed waveguide modes. Preliminary experimental results are also given demonstrating the propagation of transient acoustic waves in a free‐fluid layer waveguide with sloped or periodic boundaries.

Stress waves induced in graphite‐epoxy composite structures by current pulses

A technique to generate ultrasonic waves in graphite‐epoxy composite structures using electrical current pulses flowing in the structure is described. The difference between the thermal expansion coefficients of graphite and epoxy create large stress waves in response to localized heating by current pulses flowing in the individual graphite fibers. Experimental results are presented demonstrating the applicability of the method to nondestructive testing problems. The anisotropic elastic and electrical properties of a T‐300 graphite/DER‐332 epoxy composite plate were determined. In the experiments, a piezoelectric receiver transducer was used to detect the thermoelastic waves in the composite plate. Distinct ultrasonic waves were detected with 20 μsec current pulses below 50 mA.

Studies on the conversion of near‐grazing underwater ultrasonic waves in a sandy seafloor

Ultrasonic modeling results are presented supporting the hypothesis given by the author [J. R. Chamuel, IEEE Trans. Ultrason. Ferroelectr. Freq. Control, submitted Letter 10 April 1998] explaining the anomalous ultrasonic slow wave observed in water‐saturated sand [N. P. Chotiros, J. Acoust. Soc. Am. 97, 199–214 (1995)] using a layered elastic model. The rapid increase of the shear wave velocity of sand with depth causes the conversion of near‐grazing underwater acoustic waves into multiple coupled shear and compressional waves. Physical insight into the physical mechanisms is obtained from the refraction/conversion of broadband transient shear and compressional waves penetrating a layered solid with a low shear wave velocity. Polycarbonate/Plexiglas and wax/polycarbonate layered models were utilized. PP, PS, SP, and SS wave components were detected in the lower solid simulating the multiple features present in the anomalous acoustic sand data. In the effectively layered water/sand model, an underwater ac...

Experimental observations on liquid/solid interface waves

Elastic waves propagating at the interface between a liquid and a solid present interesting complex phenomena as the relative elastic properties of the liquid and the solid are varied. It is difficult to obtain a good physical interpretation of the mathematical solutions of the Stoneley wave equation. Experimental results are presented using limestone/water, aluminum/water, Plexiglas/water, and ice/water. A barrier was placed between source and receiver to isolate the Scholte wave from the water and pseudo‐Rayleigh waves. The experiments were repeated with a deep narrow cut made in the solid to stop the seismic waves. The measured Scholte (Stoneley) wave velocities agreed with Strick and Ginzbargs calculations (1956). For the limestone/water case, the barrier stopped the Scholte wave and did not affect the pseudo‐Rayleigh wave. The barrier did not stop the Scholte wave for the Plexiglas and ice cases. The deep narrow cut in the solid stopped the pseudo‐Rayleigh wave for the limestone/water case, and did ...