Towed arrays

Ferroelectric—polymer composite devices have been developed for large-area transducers, active noise control, and medical imaging appHcations. North American Philips, Hewlett-Packard, and Toshiba make composite medical imaging probes for in-house use. Krautkramer Branson Co. produces the same purpose composite transducer for the open market. NTK Technical Ceramics and Mitsubishi Petrochemical market ferroelectric—polymer composite materials (108) for various device appHcations, such as a towed array hydrophone and robotic use. Whereas the composite market is growing with the invention of new devices, total unit volume and doUar amounts are small compared to the ferroelectric capacitor and ferroelectric—piezoelectric ceramic markets (see Medical imaging technology). 

Background data from the Multiple Towed Array Detechon System (MTADS) showed numerous anomalies in one of the fill areas. Except for one part done by the District of Columbia, the area adjacent to the railroad... 

Laser Fluorimeter As 2i source of biological information we propose the use of a multi-station (up to 12 sampling locations) towed sea water laser fluorimeter for water quality analysis specific to selected hydrocarbons which might be present in the area. The laser excites elements of the plankton population and that of calibrated hydrocarbons (e.g. breakdown products of munitions contents) present in the water. The fluorescent spectra are received through a fibre optic cable, split and counted through specific filters. From this data a direct correlation of the effects of pollution on the plankton population can be made. The system would be towed in conjunction with the multi-sensor towed array. 

Towed Array Cable with a number of underwater microphones used to detect underwater objects across a range of aquatic environments. 

Variable Depth Sonar Similar to a towed array, but a variable depth sonar has a motorized fish at the end of the array to permit the array to... 

One type of sonar transducer, primarily used in the surveillance community, is a low-frequency active source. The tonpilz design is commonly used for such projectors at frequencies down to about 2 kHz (a tonpilz at this frequency is almost 0.75-m long). For frequencies below 2 kHz, other types of transducer technology are employed, including mechanical transformers such as flexing shells, moving coil (loud speaker) devices, hydraulic sources, and even impulse sources such as spark gap and air. Explosives are a common source for surveillance, and when used with towed arrays make a very sophisticated system. 

A common array, shown in Figure 17.46(a), is a single linear line of hydrophones that makes up a device called a towed array, which in the oil exploration business are often called streamers. The line is towed behind the ship and is effective for searching for low-level and low-frequency signals without interference from the ship s self-noise. Figure 17.46(b) shows a more sophisticated bow array (sphere) assembly. 

Towed array sonar is a system of hydrophones towed behind a submarine or a surface ship on a cable. It mainly consists of a source array and a receiver array. In order to ensure its detection range and positioning accuracy, the source array is always hundreds of meters long and contains thousands of similar components. 

Ferroelectric polymers continue to show excellent application in underwater towed arrays. Because of the ease in forming ferroelectric polymer into a variety of shapes and geometries, PVDF has been featured in towed array applications as planar elements, coaxial lines, and cylindrical elements. The towed array applications have included military and seismic uses. 

During the 1980s, Raytheon Company manufactured a selected number of towed array sensors [Sj. These sensors consisted of multiple homopolymer PVDF elements connected electrically in parallel to form an extended line sensor. The individual elements were constructed from electroded and bonded PVDF sheets stacked in mechanical series and electrically in parallel to simultaneously boost both the capacitance and sensitivity. The anisotropy of the homopolymer is exploited in these extended sensors by aligning the low (3,2) axis sensitivity along the towed axis. This results in an array that, by design, will suppress flow noise and vibration strum while being most sensitive in the normal direction. 

Innovative Daaaduoets Incorporated. ST-5 solid towed array. Product data sheet. Fort Worth. TX. 1994. 

MTADS Multi-sensor Towed Array Detection System... 

The structure of ferrihydrite has been the object of numerous studies in the past and several different structures have been proposed. The main difficulty affecting elucidation of the structure is the low degree of order. The original models of Towe and Bradley (1967) and Chukhrov et al. (1976) are based on XRD data and involve a defective hematite structure based on an hep array of anions with vacant Fe sites and a considerable amount of water. The Fe ions are distributed randomly over the interstices and there is more OH and H2O and less Fe in ferrihydrite than in hematite, i. e. there is a lower Fe/O ratio (< 2/3). 

Perhaps the most important new approach to chemical measurements has been the use of sensors for oceanic chemistry. Sensors comprise a transducer and its supporting electronic instrumentation. The key feature of sensors is their ability to monitor the concentration of a particular analyte continuously, so that the dimension of time can be added to the traditional three dimensions of spatial measurements. An example of a sensor is a pH electrode, coupled with a high-impedance voltmeter and a means of standardization and temperature compensation in situ. In principle, such a sensor can monitor pH continuously for days at a time while transferring the data to a recorder or memory device. One can contemplate towing an array of sensors at various depths simultaneously, obtaining three-dimen-o tin us d ta t. i Dr v e th two- imensional data a ail-... 

More efficient techniques for underwater search need to be developed. These techniques should make use of integrated suites of instruments, including visual (video cameras and laser line scanning equipment) and other sensors (e.g., magnetometer arrays) to support the search and reduce the need for divers. Boat-towed platforms rather than free swimming underwater vehicles would appear to be preferable for integrated underwater survey systems. 

As fundamental as these textural parameters are, unfortunately, we are faced with an often bewildering array of techniques and equipment used to evaluate aspects of texture, and an equally diverse and sometimes confusing system of nomenclatures. Although over twenty years have passed since Potter et al. (1980) contended that our understanding of tow to measure and interpret texture lags far behind that of composition, it is still valid to say that sediment textural analysis, particularly of fine-grained material, is at the petrographic frontier of sedimentary studies. 

Seismic energy pulses are created through the Aquapulse system by confining the detonation of a mixture of propane and oxygen in an elastic-walled container. The combustion products are vented indirectly to prevent the formation of bubble pulses. Four Aquapulse units are commonly towed in a rectangular array behind a vessel and are fired simultaneously at depths from 11 to 15 m (Dobrin, 1976 Kearey et al., 2002). 

Take a series of sweeps with the towed sensor arrays and gather all physical, chemical and biological data... 

A wide array of fiber tows (each of which consists of hundreds of filaments) are used for composite tape manufacturing. The diameter of filaments are usually in a range from 6 to 8 pm for carbon fibers (CF) and from 10 to 17 xm for glass fibers (GF). Also, aramid fiber (AF) tows or other polymeric fibers in this range of diameters are available. The... 

FIGURE 17.46 (a) Schematic of a towed line array. (Source Urick, R.J. 198 i. Principks of Underwater Sound, p. 13. McGraw-Hill, New York.) (b) bow array assembly for the seawolf submarine (SSN-21). (Source NUWC. 1991. Division Newport, BRAG 1991 presentation. Naval Undersea Warfare Center, New London, CT.)... 

The bipolar trickle tower reactor has already been mentioned (Fig. 2 26). Here, the electrolyte falls, under gravity, down a packed column containing a bipolar array of electrodes. In order to maintain trickle flow (and hence, minimize bypass currents) the flow rate is restricted High flow rates cause flooding while tow values result in incomplete wetting of the electrodes. 

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