Sonar system

M.Nalecz, K. Kulpa, A. Piatek, Hardware/Software Co-designin DSP-Based Radar and Sonar Systems , International Radar Symposium 2004 19-21 Maj, Warsaw, Poland, pp. 137-142. 

The first practical device to make use of magnetostrictive technology, a sonar system developed by researchers at NSWC, used this property. The system consisted of magnetostrictive materials... 

As humans, we probably have a biased and somewhat exaggerated view of our status in the animal kingdom. Pride In our swollen forebrain and Its associated mental capabilities may blind us to the remarkably sophisticated abilities of other species navigation by birds, the sonar system of bats, homing by salmon, or the flight of a fly. 

SONAR allows the imaging of the seafloor and obstacles on it. An example of a side-scan sonogram mosaic of a mudslide is shown in Figure 3.5 (Prior and Coleman, 1978,1981). The soimd waves are emitted by a source and reflected off the seafloor and travel back to a receiver. The sound waves are produced by either active or passive systems. Active systems send out sound pulses. Passive systems monitor sounds emitted by the objects they are tracking. Ship-borne SONARs are active systems that are very powerful and can image seafloors and objects up to several kilometers from the source. The frequencies used in these systems determine their depth capabilities. A summary of some of the available side-scan sonar systems that are commercially available is presented in Table 3.8. 

Piezoelectricity links the fields of electricity and acoustics. Piezoelectric materials are key components in acoustic transducers such as microphones, loudspeakers, transmitters, burglar alarms and submarine detectors. The Curie brothers [7] in 1880 first observed the phenomenon in quartz crystals. Langevin [8] in 1916 first reported the application of piezoelectrics to acoustics. He used piezoelectric quartz crystals in an ultrasonic sending and detection system - a forerunner to present day sonar systems. Subsequently, other materials with piezoelectric properties were discovered. These included the crystal Rochelle salt [9], the ceramics lead barium titanate/zirconate (pzt) and barium titanate [10] and the polymer poly(vinylidene fluoride) [11]. Other polymers such as nylon 11 [12], poly(vinyl chloride) [13] and poly (vinyl fluoride) [14] exhibit piezoelectric behavior, but to a much smaller extent. Strain constants characterize the piezoelectric response. These relate a vector quantity, the electrical field, to a tensor quantity, the mechanical stress (or strain). In this convention, the film orientation direction is denoted by 1, the width by 2 and the thickness by 3. Thus, the piezoelectric strain constant dl3 refers to a polymer film held in the orientation direction with the electrical field applied parallel to the thickness or 3 direction. The requirements for observing piezoelectricity in materials are a non-symmetric unit cell and a net dipole movement in the structure. There are 32-point groups, but only 30 of these have non-symmetric unit cells and are therefore capable of exhibiting piezoelectricity. Further, only 10 out of these twenty point groups exhibit both piezoelectricity and pyroelectricity. The piezoelectric strain constant, d, is related to the piezoelectric stress coefficient, g, by... 

One of the most difficult adhesive problems involves the underwater sonar systems. Elastomers (29) (Neoprene rubbers) are adhered to metals with adhesives. The applications include cable sheath, vibration isolator and damper, acoustic absorber, sound reflector, sonar-dome window, and transducer boot. A poor bond at the Neoprene-steel interface could easily lead to saltwater penetration and corrosion, which eventually causes the failure of the sonar dome. 

Sonar systems. Instead of lowering a weight, these devices emit sound waves, which are reflected off the material surface and give a reading of the material level. Their accuracy is slightly better than the electromechanical system, but their primary advantage is that they give continuous readouts of material levels. Once installed and... 

Both electromechanical and sonar systems are volumetric in that they measure height of material in a silo and require the use of conversion tables to determine actual weight. For a more direct method, another system is used. 

Sonar system Sound navigation and ranging system... 

In addition to the various industries and uses identified for sonar and sound waves, the application of sonar helps to support and encourage research in a significant number of other industries and scientific fields. Power for sonar systems is vital, but space on ships or submarines is limited, so sonar development drives the pursuit of compact power sources. The effectiveness of the sonar depends on the power and focus of the beam produced by the transducer, which in turn promotes the exploration of more efficient and effective transmitting materials, as well as means of recognizing and collecting the return beam. The need for small computers to process the return data has created the demand for compact computer processors and data storage. 

Major Companies. The number of companies conducting research and development in sonar systems are few and often specialized. Because sonar systems are expensive and are typically used by large organizations, corporations, and national governments, they are not produced in great numbers and tend to be very costly. Sonar production is especially reliant on military sales, so countries prefer to reserve contracts for sonar sets to tbeir own domestic producers. The vital military nature of sonar also leads to the classification of some designs as national secrets. 

The performance of sonar systems can be assessed by the passive and active sonar equations. The major parameters in the sonar equation, measured in decibel, are as follows ... 

The figure of merit (FOM), a basic performance measure involving parameters of the sonar system, ocean, and target, is computed for active and passive sonar systems (in decibel) as follows ... 

FIGURE 17.42 Generic active sonar system. (Source Adapted from Knight, W., Pridham, R.G., and Kay, S.M. 1981. Digital signal processing for sonar. Proceedings of the IEEE 69( 11) 1454. IEEE 1981.)... 

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