Henry A. Scarton

An acoustic diagnostic technique for use with electric machine insulation

Many of the electrical failures of large electric machines have mechanical precursors. This premise has led to the attempts described here to detect mechanical changes, such as groundwall delamination, by acoustic methods as a means of early detection of incipient failure. By optimally launching an ultrasonic wave into a stator bar and using the conductor as a waveguide, it has been shown possible to interrogate the groundwall insulation and the critical interface region adjacent to the conductor. Laboratory studies using an epoxy mica stator bar subjected to thermal cycling have demonstrated that the acoustic signatures obtained with this method are mirrored by conventional corona spectroscopy conducted simultaneously, although earlier damage is clearly discernible. Based on the results of this study, the acoustic technique appears to have substantial promise as an advanced detection tool. >

Some Parameters Affecting Tactile Friction

The friction of a sliding tactile contact was measured in an apparatus which simulated a keyboard. Results were taken for several materials. The friction coefficient was found to decrease with increasing load and with increasing speed. Experiments at varying humidity and surface roughness helped to define the friction mechanisms. It is concluded that tactile friction is predominantly adhesive, but modified by liquid bridging between the ridges of the skin and the counterface. Increased bridging due to higher humidity causes increased friction from viscous shearing effects, while increased roughness allows fewer bridges to form, decreasing the friction.

P1G-4 Through-Wall Communication of Low-Rate Digital Data Using Ultrasound

Wireless communication is ineffective for communicating through a solid steel wall due to the shielding effect of the metal. In some cases, holes can be made in the wall to allow wires to pass through, enabling the transport of electronic data. However, holes are often undesirable because they can reduce the integrity of the wall. This paper describes several approaches for using ultrasound to communicate low-rate digital data through a steel wall. The techniques minimize the complexity and power consumption of the communications hardware on the side of the wall from which the data is being sent, supporting applications in which a sensor may be either permanently embedded in a structure or is difficult to reach for servicing. Both pulsed and continuous-wave ultrasound techniques are described. Experimental data is presented showing the performance of the techniques when implemented using 1 MHz transducers mounted on a 15.24 cm (6 inch) thick steel wall. The results show that data rates on the order of 500 bits per second are readily available using simple communications techniques. Higher rates are possible if equalization is used to mitigate the effects of the multipath propagation within the steel block

A high-performance ultrasonic system for the simultaneous transmission of data and power through solid metal barriers

This paper presents a system capable of simultaneous high-power and high-data-rate transmission through solid metal barriers using ultrasound. By coaxially aligning a pair of piezoelectric transducers on opposite sides of a metal wall and acoustically coupling them to the barrier, an acoustic-electric transmission channel is formed which prevents the need for physical penetration. Independent data and power channels are utilized, but they are only separated by 25.4 mm to reduce the systems form factor. Commercial off-the-shelf components and evaluation boards are used to create realtime prototype hardware and the full system is capable of transmitting data at 17.37 Mbps and delivering 50 W of power through a 63.5-mm thick steel wall. A synchronous multi-carrier communication scheme (OFDM) is used to achieve a very high spectral efficiency and to ensure that there is only minor interference between the power and data channels. Also presented is a discussion of potential enhancements that could be made to greatly improve the power and data-rate capabilities of the system. This system could have a tremendous impact on improving safety and preserving structural integrity in many military applications (submarines, surface ships, unmanned undersea vehicles, armored vehicles, planes, etc.) as well as in a wide range of commercial, industrial, and nuclear systems.

Penetration-free system for transmission of data and power through solid metal barriers

This paper presents a novel system capable of simultaneous high-power and high data-rate transmission through solid metal barriers using ultrasound. By co-axially aligning a pair of piezoelectric transducers on opposite sides of a metal wall and acoustically coupling them to the barrier, an acoustic-electric transmission channel is formed which prevents the need for physical penetrations. Independent data and power channels are utilized, but they are only separated by 25.4 mm (1 in) to reduce the systems form factor. Commercial off-the-shelf components and evaluation boards are used to create real-time prototype hardware and the full system is capable of transmitting data at 12.4 Mbps and delivering 50 W of power through a 63.5 mm (2.5 in) thick steel wall. A synchronous multi-carrier communication scheme (OFDM) is used to achieve a very high spectral efficiency and to ensure that there is only minor interference between the power and data channels. Also presented is a discussion of many potential enhancements that could be made to greatly improve the power and data-rate capabilities of the system. This system could have a tremendous impact on improving safety and preserving structural integrity in many military applications (submarines, surface ships, UUVs, armored vehicles, planes, etc.) as well as in a wide range of commercial, industrial, and nuclear systems.

Apparatus for treating flowing working gases particularly to reduce the noise in operation thereof

A device for treating flowing working gases in order to reduce their operational noises and in most instances also to increase their operating efficiency comprises a flowing working gas operating device which has a discharge conduit with at least one discharge opening for the outflow of the working gas. A check valve is associated with the discharge and includes an elastic valve member movable to close the opening when the flow thereof decreases to a predetermined amount for example as determined by the reduction of pressure of the gases so as to prevent any back flow into the conduit which is likely to produce noise. The elastic member may comprise an ordinary rubber band which is preferably held in position by a guide member so that when the pressure of the working gas is sufficient the gases will flow out of the discharge conduit and will be directed through one or more chambers so as to cause the gas to flow into a whirling vortex flow and preferably in a substantially annular path so as to order the gases and to thereby increase their efficiency of operation.

The method of eigenvalleys

A computer-aided contour search technique for finding the complex roots of infiniteor finite-order complex transcendental equations, called the Method of Eigenvalleys, is presented. The method is used to solve a dispersion relation, which arises in the theory of linear wave propagation in viscous compressible liquids.

Free vibrations of rectangular cantilever plates. Part 1: out-of-plane motion

An analysis of the free in-plane vibrations of a cantilevered rectangular plate is performed by means of a variational approximation procedure. The problem is treated by first obtaining the exact solution for waves in the plate satisfying the equations of plane stress including in-plane inertia with two opposite edges traction free. The solution results in a set of dispersion curves. A number of the resulting waves are used in what remains of the variational equation, in which all conditions occur as natural conditions. Roots of the resulting transcendental equation are calculated, which yield the eigensolutions and associated eigenfrequencies. The results are compared with results obtained using FEM, and good agreement is shown.

Acoustic emission analyzer

A periodic structure such as a diffraction grating is disposed on the surface of an object from which acoustic emissions are to be detected. A plane monochromatic light beam is incident on the periodic structure and forms a number of Bragg diffraction orders at predetermined angles. A detector positioned to intercept one of the diffraction orders receives light whose frequency has been Doppler shifted by surface motion on the object. A reference beam, also incident on the detector heterodynes with the Doppler-shifted beam so that the Doppler component can be recovered. In one embodiment, the reference beam is also incident on the surface and itself produces Bragg diffraction orders. The geometry produces up Doppler in the Bragg diffraction orders from one beam and down Doppler from the Bragg diffraction orders from the other beam and selected Bragg diffraction orders from both beams are heterodyned in the detector.

The Relationship Between Standing Waves, Pressure Pulse Propagation, and Critical Flow Rate in Two-Phase Mixtures

A two-fluid model is presented that can be used to predict the celerity andattenuation of small-amplitude harmonic disturbances in bubbly two-phases flow.This frequency-dependent relationship is then used to predict the propagationof small-amplitude pressure perturbations through the use of Fourierdecomposition techniques. Predictions of both standing waves and propagatingpressure perturbations agree well with existing data. The low andhigh-frequency limits of the celerities predicted by the model are examinedand their relationship to critical flow rate is demonstrated. Somelimitations of the interfacial pressure model employed in conventional criticalflow analysis are exposed and the implications to the prediction of criticalflow rate are discussed.