Acoustic interferometer

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

An acoustic monitoring system of the rip current based on passive reciprocal transmissions

Abstract: In the beach, the rip current is one of dangerous swift currents to carry swimming persons offshore. Sometimes, they are drowned because of this current. So it is desirable to detect and monitor the occurrence of the rip current in realtime. In general, the acoustic method is powerful at the view of underwater remote-sensing, and the reciprocal transmission is one tool to measure direct currents. But, usually acoustic transceivers are too expensive. Therefore, we propose an acoustic monitoring system combined with two acoustic transceivers and several sound reflectors for the measurement of the rip current. The core idea is shown in figure 1. An acoustic signal is transmitted by Tx 1 and/or Tx 2 and reflected by the sound reflector R 1 and received by Tx 2 and/or Tx 1 . The difference of travel times between forward transmission Tx 1 -R 1 -Tx 2 and reverse transmission Tx 2 -R 1 -Tx 1 is given by the following relation: δ t= 2VL/C2 or V=C2(2L)−1δ t where L is the distance between Tx 1 and Tx 2 , V is the velocity of the mean flow over the triangular area Tx 1 -R 1 -Tx 2 , and C is the sound speed over the area. This relation is applicable to the other sound reflectors in figure 1. The sound reflector R 2 gives a mean velocity of V 1 and V 2 . The sound reflector R 3 gives a mean velocity of V 1 , V 2 and V 3 . Therefore, this set of three different mean velocities is converted to a zonal current field. If the configuration is properly designed, the current field can be expected to monitor when and where the rip current will occur. The prototype of the monitoring system was designed and composed of two 14 kHz acoustic transceivers and a non-directional sound reflector. The acoustic test was carried out in the sea of Hiratsuka beach. As a result, it was found out that the bottom backscattering and reverberation of transmitted sound waves was stronger than expected ones, and disturbed receiving sound signals transmitted by each transceiver and reflected by sound reflectors in a short range. The reflected signals were detected at a range of 100m. The application of the replica cross correlation was successfully carried out. The result was effective to determine the precise travel time of direct and reflective waves. In order to resolve these problems properly, the frequency of sound waves should be changed to a higher frequency. A new acoustic monitoring system composed of an echo sounder, two broadband acoustic transducers and several sound reflectors for the measurement of the rip current is being developed. This system can use the 50kHz transducer for a long range and the 200kHz for a short range. The more detailed analysis will be discussed in the presentation.

Quantitative visualization of ultrasonic acoustic waves by means of digital laser speckle-technologies

Abstract: An original version of digital laser speckle photography has been used for visualization and quantitative diagnosis of acoustic waves in liquids in the megahertz frequency range. Standing acoustic waves were generated in tanks of special configuration which permitted obtaining analytical dependences of refraction angles of the probe laser radiation on the wave intensity. These refraction angles were determined experimentally by the change in contrast of the speckle fields arising in the scattered probe radiation and recorded by means of high-resolution digital CCD matrices. Quantitative diagnosis of the pressure and velocity fields in acoustic waves was carried out by measuring the deformation of the laser intensity correlation functions in recorded speckle fields.

System and method for measuring a fluid flow rate by processing of acoustic waves

Abstract: This system for measuring a flow rate includes a receiver of bulk acoustic waves, a first emitter of bulk acoustic waves in the fluid, intended to be arranged upstream of the receiver in such a way as to emit acoustic waves to the receiver, a second emitter of bulk acoustic waves in the fluid, intended to be arranged downstream of the receiver in such a way as to emit acoustic waves to the receiver, and a signal processing device designed to determine a flow rate value according to at least one characteristic of an electrical signal supplied by the receiver It further includes means for synchronizing the first and second emitters with each other in such a way as to generate destructive acoustic interferences between the acoustic waves that they emit before they are received by the receiver

Propagation of acoustic waves though periodic structures containing phase nonregularities

Abstract: The analysis of peculiarities of BAW and SAW propagation through the system of two reflecting Bragg structures (mirrors) separated by a gap providing non regularity of the phase of acoustic waves - an acoustic analog of a Fabri- Perot resonator is given.