Echo SONAR

Medical Ultrasound Many of us have first seen our unborn children or grandchildren thanks to medical ultrasound technology. This application is somewhat related to sonar in that both use pulse echo methods to send and receive signals. However, in this short-range application, transducer arraj can be designed to form images. 

Geography, Geology Pulse/echo techniques are used in the location of mineral and oil deposits and in depth gauges for seas and oceans. Echo ranging at sea has been used for many years (SONAR). 

In navigation and target detection, a scanning active sonar can be used to provide a realistic visual picture of sound-reflecting objects around the source. The scanning beam is rotated, and the reflected beams show the position of objects in a given plane as echo blips . Another display is required to show the depth/altitude of the object observed... 

Sonar and imaging technologies are based on sending out ultrasound pulses and receiving the echoes. The resolution capabilities depend upon the emitted pulses being sharp, and the sharper the pulse the more Fourier components it has. Therefore, for a transducer to emit and detect a sharp pulse it must be able to respond to a wide frequency range - that is it must have the broad band characteristic associated with low mechanical Q. The very lossy nature of the polymer phase endows the composite with this (Q < 10). 

At great ocean depths or in areas with poor visibility other devices may be employed. Sonar may be used to determine the location of large or encrusted objects by calculating the time it takes echoes to bounce off them. Underwater cameras may be towed by the boat to take pictures of a site in water with good visibility. 

Asdic Anglo-French anti-submarine detection device, forerunner of Sonar, named after the Anti-Submarine Detection Investigation Committee. It comprised a transmitter/receiver which sent out undersea sound impulses and picked up the echo if an impulse struck an object. By measuring the time lapse between transmission and reception of the echo, the range of the target could be calculated. 

Rock Intrusive in sedimentary rocks side scan sonar, echo sormding Magnetic... 

A minelayer with a remotely controlled submarine, one-manned submersible, was chartered. It was equipped with scanning sonar, echo sounder, low-light cameras, headlamps and manipulators and conducted by cable. The submarine was brought down to the group of five wrecks and a video film was made. 

Sub-Bottom-Profiler This system is another multi-frequency acoustic system which is comparable to a seismic monitoring system of low seabed penetration capability. The acoustic emissions are frequency-modulated and the pulse rate is adjustable to suit the local requirements. The echoed signal can be recorded and processed into a display-form similar to the side-scan-sonar. It produces information about the thickness of sedimentation and can plot the contour of the seabed below the sedimentation layer. 

Sonar Sound navigation ranging a method of recording the echo, or return of sound waves emitted by a sound device located in a submarine or similar vehicle. 

To facilitate the transmission of sound into the water, shipboard sonars are mounted in large plastic bilges near the bow, requiring the relocation of the ship s anchors to avoid hitting them. Because of the distinctive sound, the return echo used on an active sonar beam to find a submerged object was known as pinging the target. 

Reverberation/clutter Inhomogeneities, such as dust, sea organisms, schools of fish, and sea mounds on the bottom of the sea, which form mass density discontinuities in the ocean medium. When an acoustic wave strikes these inhomogeneities, some of the acoustic energy is reflected and reradiated. The sum total of aU such reradiations is called reverberation. Reverberation is present only in active sonar, and in the case where the object echoes are completely masked by reverberation, the sonar system is said to be reverberation limited. 

B.4.2 Multibeam sonar or multibeam echo sounder (MBES) 578... 

Objects and obstacles located on the seabed give a sharp reflection of these pulses and create an acoustic shadow on their lee side. Thus, an image is obtained similar to an aerial photo at sunset, where shadows are accentuated, so that protrusions can be detected and an estimation of their height can be made. An absolute height measurement cannot be performed with the side scan sonar, for this echo sounding or multi-beam techniques are required. 

The multibeam is sometimes referred to as Swath echo sounder. The multibeam is in principle equal to the side scan sonar and the sub-bottom profiler, except that... 

The sonar equation is of fundamental impoitance in all ultrasonic and acoustic systems although it is more widely used in sonar design than in other applications. It is used to predict the voltage level, Rx> of an echo from a target given an electrical voltage drive, 7, to the transmitter. In simplified form it is... 

Pulsed irltrasoimd is rrsed for inspection purposes including medical imaging, sonar, acoustic microscopy, and nondestmcdve evalrrahon. In a pulsed system a transducer is placed in contact with a sample, electrical driving signals are sent to the transdncerto make pulses of irltrasonic waves, which enter the sample and echoes from internal scatterers are collected by a receiver, processed, and displayed for interpretation (see Fig. 8). 

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