Acoustic interferometer

About: Acoustic interferometer is a research topic. Over the lifetime, 1493 publications have been published within this topic receiving 19355 citations.

Method and apparatus for measuring surface movement of an object using a polarizing interfeometer

Abstract: A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam A photon multiplier senses the phase shift and develops an electrical signal A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading

Simultaneous Nearby Measurements of Acoustic Propagation and High-Resolution Sound-Speed Structure Containing Internal Waves

Abstract: During the 2006 Shallow Water (SW06) experiment, simultaneous measurements were made of the sound-speed field as a function of range and depth associated with nonlinear internal waves and acoustic propagation at frequencies of 2-10 kHz over a 1-km path. The internal waves were measured by a towed conductivity-temperature-depth (CTD) chain to get high resolution. These measurements were coordinated so that the nonlinear waves could be interpolated onto the acoustic path, allowing predictions of their effects on the acoustics. Using the measured sound-speed field, the acoustic arrivals under the influence of the internal waves are modeled and compared to data. The largest impact of measured moderate amplitude internal waves on acoustics is that they alter the arrival time of the rays which turn at the thermocline.

A new definition for acoustic dose

Abstract: This paper discusses a recent proposal for definitions of acoustic dose and acoustic dose-rate. Acoustic dose is defined as the energy deposited by absorption of an acoustic wave per unit mass of the medium supporting the wave. Its time-derivative, acoustic dose-rate, Qm, in W kg−1 is central to the prediction of both rate of temperature rise and radiation force. These quantities have spatial and temporal dependency, depending on the local field parameters (acoustic pressure, particle velocity, intensity) and local material properties (absorption coefficient, αa, and mass density, ρ0). Spatial and/or temporal averaging can be applied where appropriate. For plane-wave monochromatic conditions in a homogeneous medium, Qm=2αaI/ρ0, (I is the time-averaged intensity), a simple expression which may also incorporate frequency dependencies of energy deposition. Acoustic dose and acoustic does-rate are exact analogues for Specific Absorption and Specific Absorption Rate (SAR), quantities central to radiofrequency (RF) and microwave dosimetry. Acoustic dosimetry in the presence of tissue/gas interfaces remains a considerable challenge.

Accurate measurement of interferometer group delay using field-compensated scanning white light interferometer

Abstract: Interferometers are key elements in radial velocity (RV) experiments in astronomy observations, and accurate calibration of the group delay of an interferometer is required for high precision measurements. A novel field-compensated white light scanning Michelson interferometer is introduced as an interferometer calibration tool. The optical path difference (OPD) scanning was achieved by translating a compensation prism, such that even if the light source were in low spatial coherence, the interference stays spatially phase coherent over a large interferometer scanning range. In the wavelength region of 500-560 nm, a multimode fiber-coupled LED was used as the light source, and high optical efficiency was essential in elevating the signal-to-noise ratio of the interferogram signal. The achromatic OPD scanning required a one-time calibration, and two methods using dual-laser wavelength references and an iodine absorption spectrum reference were employed and cross-verified. In an experiment measuring the group delay of a fixed Michelson interferometer, Fourier analysis was employed to process the interferogram data. The group delay was determined at an accuracy of 1×10(-5), and the phase angle precision was typically 2.5×10(-6) over the wide wavelength region.

X-ray diffraction by standing surface acoustic waves

Abstract: X-ray diffraction by standing surface acoustic waves was investigated under total external reflection conditions. A standing surface acoustic wave was formed on the surface of a YZ-cut of a LiNbO 3 crystal by superposition of two travelling surface acoustic waves. The diffracted X-ray radiation intensity was found to oscillate with twice the frequency of the surface acoustic wave excitation.