Showing papers on "Standing wave published in 1973"

Low-loss reflection coatings using absorbing materials

Abstract: A class of multi-layer reflectors using a plurality of low-loss reflective elements composed of absorbing materials in the form of thin films is described wherein the differences between the absorption indices of the materials are used to obtain reflecting boundaries. The class of reflector structures are designed in such a manner that when light is directed onto the structure, a standing wave is generated throughout the structure. Absorbing materials in the nodes of the standing wave do not absorb but absorbing materials in the antinodes provide enhanced absorption.

Orthogonal resonant filter for planar transmission lines

Abstract: The conductor pattern on a dielectric substrate includes a rectangular element of finite thickness whose two surface dimensions are chosen so that each is one-half the wavelength of a desired frequency. Accordingly, the element will support two resonant orthogonal standing waves and external coupling to each wave may be provided independently. Common coupling to both waves may also be provided so that the dual resonant structure may be used as a three-port device for frequency combining and separating and is particularly well-suited for frequency conversion applications. A two-port arrangement permits generation of specific filter characteristics.

On the mechanism of sound production in organ pipes

Abstract: It is shown that both the Cremer‐Ising and Coltman mechanisms for sound production in organ pipes are comprehended by a more general approach, based on conservation of linear momentum. By calculating force per unit area exerted by the jet on a control volume containing the mixing region, and equating this to the difference in pressure along the pipe axis, it is possible to derive an expression for acoustic particle velocity in the standing wave as a function of the jet driving flow spectrum. The momentum model of the jet‐pipe interaction is able to explain the Coltman radiation symmetry effect, and also accounts for the role of entrained air in sound production. Additional spectral interaction terms, not previously noted, are found to play a significant role in the production of sound‐pressure fluctuations in the pipe. The fluctuating lift force at the edge is found to contribute to the sustenance of the pipe‐cavity oscillation below resonance, opposing it above resonance. In the near vicinity of the resonant frequency, edgetone effects are relatively small.

On the stability of nonlinear cold plasma waves. Part 2

Abstract: In part 1 (Infeld 1972), it was shown that a nonlinear stationary wave in a cold plasma is marginally stable to all perturbations that are functions of the spatial direction parallel to the direction of propagation only. The stability analysis is extended here in part 2 to include general spatial variations. Within the limitations of the treatment, it is found that, for wave amplitudes up to maximal value (onset of trapping), the wave is marginally stable. Hence one would expect these large-amplitude cold plasma waves to exist in practice.The one-dimensional analysis of part 1 is also extended to include waves with relativistic velocities, and such waves are again found to be marginally stable.

On the form of the highest progressive and standing waves in deep water

Abstract: The form of a progressive gravity wave on deep water, which generally must be found by numerical integration (Michell 1893) is shown to be approximated with remarkable accuracy by a single term. Six consecutive waves are transformed conformally so as to surround the point corresponding to infinite depth. The free surface then corresponds closely to the boundary of a hexagon. In a similar way the profile of a standing wave is closely approximated to by transforming four consecutive waves conformally and taking the profile as the boundary of a square. The profile agrees closely with that calculated by Penney & Price (1952) and with the experiments of Taylor (1953).

Material suspension within an acoustically excited resonant chamber

Abstract: A method for positioning an object within a chamber, which is especially useful in performing manufacturing operations under zero gravity conditions, including applying sound waves within the chamber in different directions and at a frequency for each direction that establishes a standing wave pattern so that the object is automatically urged towards the intersections of the nodes, or locations of minimum pressure.

On mass transport induced by interfacial oscillations at a single frequency

Abstract: The to method of matched asymptotic expansions is employed to calculate the mass tre sport velocity due to combinations of small amplitude oscillatory waves propagatir, at a single frequency in fluid systems with density and viscosity dis-continuities. Interfacial boundary layers are considered in terms of the curvilinear coordinate system described by Longuet-Higgins(1). The order of magnitude of the mass transport velocity calculated for a general oscillatory disturbance is the same as that calculated for interfacial progressive waves by Dore(2). For standing waves, the time-averaged motion of the fluid particles forms a cellular structure in each fluid layer; the mass transport velocity due to modal interactions is associated with a similar structure.

Sources of microseismic P waves

Abstract: Origin ofP waves detected earlier in microseisms of very quiet locations in the USSR is discussed in detail. It appears that the most pronounced sources ofP waves are tropical cyclones over the Pacific. The amplitude of the force in the source for a medium power typhoon is found to be of the order of 1016 dynes. The effective source area is estimated as 104–105 km2 approximately. The shape of the amplitude spectrum ofP wave corrected for the absorption in the mantle does not contradict with the standing wave theory of microseisms generation. Results of observations at various epicentral distances give strong evidences of the predominant attenuation of the fundamental Rayleigh mode as compared with higher Rayleigh modes andP waves in the frequency band of 0.3–0.15 cps.

Standing wave acoustic parametric source

Abstract: A piston type transducer in combination with a thin wall waveguide which is terminated by a thin plug of pressure release material to form a resonant cavity. The transducer is driven simultaneously at two closely spaced high intensity, high frequency signals. The two frequencies are chosen to be either neighboring resonances or to be within the bandwidth of a single resonance. A low frequency acoustic wave is generated by the nonlinear interaction of the two high frequency standing waves in the fluid within the resonant cavity and radiates omnidirectionally into the surrounding medium through the thin walled waveguide.

A Method of Analyzing Transient Waves by Space-Time Cross Spectra

Abstract: Spectral formulas for analyzing transient waves are presented. Cross-spectral analysis of space-Fourier coefficients isolates travelling waves and standing wave oscillations, and provides statistical information concerning their structure and energetics.

The measurement of small changes in ultrasonic velocity and attenuation

Abstract: Ultrasonic velocity and attenuation are defined by the solution A = Ao, e−az cos (kz-wt) (1) for an ultrasonic wave propagating in the zdirection with a propagation constant k = 2π/λ = 2πf/v, a radian frequency w = 2πf, and an attenuation coefficient a In these definitions, λ = wavelength, f = frequency, and v = phase velocity In this traveling wave, the measurable quantities generally are v and a If one creates a standing wave by superposing two oppositely directed traveling waves within a reflecting plenum, then the standing wave is described by a resonant frequency and a wavelength which give v, and by a decrement which yields a In this paper only traveling wave methods for waves of infinitesimal amplitude will be treated Methods for measuring small changes in v and a will be described

Temporal growth of a plasma oscillation.

Abstract: A plasma oscillation excited due to beam plasma interaction forms sometimes a standing wave between electrodes. The oscillation is suppressed by modulating the beam with high frequency signal as previously reported. When the modulation is removed, the oscillation begins to grow. From displays of this phenomenon on an oscilloscope the growth rate is directly observed. Indirect method based on a van der Pol equation is also tried for the same oscillation. The results are compared with the theory.

Method and apparatus for determining the cross section of material using a sound field

Abstract: Method and apparatus by which the approximate cross section of filamentary or wire form material is determined, wherein the material is passed through a sound field having standing waves of at least two different frequencies and sound pickups for detecting the frequencies so that the cross section of the material may be determined by changes in amplitude or phase of at least one of the waves. One standing wave serves to provide an indication of the cross section of the material while another standing wave adjusts the zero point of the measuring arrangement.

Nonlinear damping of standing waves on shallow water

Abstract: The amplitude of a standing wave on shallow water has been observed as a function of the excitation frequency (ω) in conditions where nonlinear effects are important. It is found that the peak of the normal resonance curve is flattened, due to extra damping caused by resonant, nonlinear generation of a wave having an oscillation frequency of 2ω. The experimental observations are in good agreement with the theoretical model presented in the paper.

Test Wave Coexisting with a Large-Amplitude Electron Plasma Wave

Abstract: The behavior of a small test wave launched simultaneoualy with a large- amplitude electron plasma wave is calculated by treating the test wave as a slow modulation of the larger wave's amplitude and phase. Test-wave experiments show agreement with the calculation when the test-wave frequency is between the large wave's frequency ( omega₀) and omega₀-4 pi /T, where T is the maim wave's transit time through the experiment. When the spontaneously unstable lower sideband frequency is within this range, the sideband's slow amplitude oscillations agree with the calculation. (auth)

Radiation from travelling wave circular loop antenna in compressible electron plasma

Abstract: The radiation properties of perfectly conducting filamentary circular loops of arbitrary dimensions immersed in a uniform isotropic, compressible electron plasma are studied theoretically. The current distribution on the circumference of the loop is assumed to be a travelling wave with arbitrary phase propagation constant. The far zone fields of the circular loop are obtained and the radiation resistance is then evaluated for both the electromagnetic and electroaeoustic modes. From these general results, the problem is reduced to that of the circular loop in vacuum and the consequent results are found to tally with those available in literature. From the detailed study of fields and radiation resistances as put out in this paper, it is shown that the radiation resistance of both the modes is higher in the case of travelling wave loop than in the case of standing wave loop. It is, therefore, concluded that loop antennas on Bpttco vehicles may be fed with travelling wave currents rather than with t...

Standing waves in an open pipe: A nonlinear initial-boundary value problem

Abstract: Transient disturbances in a column of gas in an open tube are described using a nonlinear theory which includes both amplitude dispersion and wave interactions. For reflection from an open end, the theory must include the second nonlinear correction to the characteristic to distinguish the linear and nonlinear travel times. The initial value problem is reduced to solving a functional difference equation which determines the signal on a boundary. When the signal is damped by allowing radiation of energy at the boundaries, it may be possible to prevent shock formation.

Servo control positioning apparatus including a standing wave detector

Abstract: Apparatus for effecting relative positioning between two mechanical members in accordance with digital (or analog) commands includes a standing wave supporting, electrical wave propagating structure terminated other than by its iterative impedance. The wave structure is mechanically fixed to one mechanical member, and a probe is coupled to the wave structure and fixed for translation with the other mechanical member. A voltage controlled oscillator excites the wave structure developing a standing electrical wave therein -- the wave pattern node positioning being determined by the input digital command. Feedback servomechanism apparatus then responds to the potential induced in the probe (or, by superposition, that on the wave structure) for positioning the probe at the requisite standing wave null point. In accordance with one aspect of the present invention, the wave propagating structure is sealed, and the probe disposed external thereto, to preserve measuring accuracy.

Wave forces on a submerged vertical plate

Abstract: A vertical plate of finite length and depth is attacked by gravity waves in water of finite depth. The forces and moments acting on the plate are computed by using the theory of linearized waves. The forces depend on three dimensionless parameters combining the draft, length, water depth and wave length and on the angle of attack. The problem is reduced to the solution of two infinite linear systems of equations. Numerical solutions are presented for different particular combinations of the parameter values. In most of the cases the standing wave approximation yields sufficiently accurate results.

Position sensing transducer including an electrical wave propagating structure of varying electrical length

Abstract: A position sensing transducer employs a standing wave supporting electrical wave propagating structure, and probe apparatus coupled thereto, each affixed to different mechanical members adapted for relative translation therebetween. The wave propagating line is terminated other than by its iterative impedance, and feedback circuitry including a voltage controlled oscillator is employed to vary the electrical length of the wave line such that a node in the resulting standing wave pattern is developed at the probe position. The oscillator output frequency thus provides a direct measure of physical probe positiong vis-a-vis the wave line termination, and thereby also of the relative displacement of the two mechanical members. In accordance with a further aspect of the present invention, the transducer may be included in a servomechanism arrangement to automatically position the mechanical members in a prescribed physical relationship along the controlled axis.

Normal mode analysers for standing waves on liquids

Abstract: This paper shows how it is possible to analyse standing waves on a fluid surface into normal modes by means of a measuring device. For waves with prescribed symmetry, the area of fluid in contact with strips of suitable geometry gives a signal proportional to the amplitude of a desired mode. When there are no special symmetry conditions the analyser takes the form of suitably shaped lozenges distributed above the fluid surface. The capacitance between the lozenges and the fluid surface is proportional to the volume between the surface and the analyser, which in turn depends on the amplitude of a given normal mode in the surface wave. The geometry of the desired mode determines the shape and distribution of lozenges in the analyser. It is noted that a volume analyser can also be used for exciting a desired set of normal modes on a fluid surface.