Showing papers on "Acoustic interferometer published in 1968"

Transmission Fringes in Reflection Multiple-Beam Interferometry

Abstract: Transmission fringes in reflection multiple-beam interferometry are obtained independently of the characteristics of the coating of the reference surface by coupling a two-beam interferometer to the multiple-beam interferometer.The two-beam interferometer is defined by the reference surface of the multiple-beam interferometer and one additional mirror in a Twyman configuration.

Amplification of acoustic waves in a coupled semiconductor‐piezoelectric ceramic system

Abstract: Amplification of longitudinal acoustic waves traveling in a thin piezoelectric ceramic plate was achieved by electrically coupling the elastic waves to the drifting carriers in an n‐silicon plate. Amplification up to 15 dB/cm in the 2‐MHz range was obtained, and the system was also operated as a tunable oscillator and mixer in the 0.5‐ to 4‐MHz range. In addition, these experiments also enabled us to measure the drift mobility of majority carriers in silicon.

Finite‐Amplitude Acoustic Waves in Dielectric Crystals

Abstract: Acoustic waves at microwave frequencies show significant nonlinear effects at power densities of 10 W/cm2. These effects have been studied using Bragg diffraction of light from the harmonic components of the acoustic waves. With this technique, direct harmonic analyses of the waves have been obtained without the need for calibrated broad‐band transducers. The following effects of finite amplitude waves propagating in quartz have been observed: variation of the attenuation of the fundamental with power level; the presence of the second through fifth acoustic harmonics; the growth and decay of these harmonics as a function of the distance traveled by the acoustic wave; and the behavior of the second harmonic after reflection from a stress‐free surface. The growth of the harmonics assures that they were generated in the bulk of the solid. Similar effects have been observed in MgO and MnF2. The experimental observations have been compared with theoretical predictions and estimates of the relevant third‐order ...

Microwave investigation of acoustic waves in low-pressure plasma

Abstract: This paper deals with measurements of changes in electron concentration in acoustic waves excited mechanically in a low-pressure slightly ionized plasma by means of a microwave method. The measurements were performed by means of a rectangular resonator in the 3 GHz band. Periodic changes in the rhythm of the acoustic frequency of the electron concentration have been measured. A hypothesis of the origin of the changes in electron concentration has been suggested.

Ion waves in a partially ionized gas in an external electric field

Abstract: The propagation of longitudinal acoustic waves in the ion gas in an external electric field is studied theoretically. The results are compared with properties of waves in space without the external field. The phase velocities, damping factors and the influence of parameters of the gas on the properties of ion waves is discussed.

Generation and Detection of Acoustic Waves in Pulsed Electrical Discharges

Abstract: Electroacoustic resonances excited in a cylindrical plasma tube are very sensitive to minute changes in electron density and temperature and can therefore be used to detect sound waves. The principle of detection is that in the ordinary acoustic mode, the neutral particles, electrons, and ions move in phase with the same relative density changes. It is demonstrated experimentally that the acoustic transient detected at a certain distance from the negative glow of a pulsed electrical discharge is superposition of a direct pulse and a pulse that has been reflected from the cathode surface. From the perturbations of the electroacoustic resonances, relative density changes of the order of 1% in the acoustic transient are deduced.

Amplification and Attenuation of Acoustic Waves in Nonhomogeneous Steady Flows

Abstract: An investigation of the interaction between acoustic waves and steady‐flow fields was stimulated by the problem of combustion instability in rocket engines. A one‐dimensional analysis of traveling acoustic waves in flows of an inviscid, nonconducting, perfect gas, containing mass and heat sources, reveals the existence of a coupling between acoustic waves and non‐homogeneous steady‐flow fields. This coupling allows energy transport between the wave and the flow field, resulting in either amplification or attenuation of the wave, depending on the gradients of the steady‐flow variables and on the propagation direction. Results of experiments with nonuniform velocity fields are in agreement with theoretical predictions. In particular, an air jet discharging into a straight organ pipe and a converging air flow through a tapered pipe, are found to attenuate waves propagating through the pipes. [This work was supported by the U. S. Air Force Office of Scientific Research.]

Interaction of acoustic waves with burning surfaces of condensed systems

Abstract: The principal topic of the linear theory of the acoustic burning stability of solid propellant systems is the possibility of amplifying acoustic pressure waves reflected from a burning surface. The investigation of reflected acoustic waves reduces to the study of the reorganization of the physico-chemical processes in the combustion zone, caused by harmonic pressure disturbances, and to the calculation of the acoustic perturbation of the rate at which the gas flows off the burning surface. The reflectivity of the combustion zone is characterized by the value of the acoustic admittance.