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Reference Information

Phased Array Technology

Most existing depthsounders and fishfinders in the marine market use a mature "fixed beam" technology which was originally developed during W.W. II to detect the presence and distance of submarines. Products using this technology usually have a transducer mounted on the rear of the vessel, making contact with the water. The transducer is connected to an electronic display module which is typically mounted near the boat's steering station.

These transducers are typically made up of a piezoceramic element which is encapsulated in a hydrodynamically shaped plastic or bronze case. The piezoceramic element has the important property in that it will vibrate when shocked with a high voltage electrical signal and will itself give off a small electrical signal when physically vibrated. If the display unit sends a large pulse of voltage down the cable to the transducer, the transducer will vibrate and the resulting acoustic vibrations will travel through the water until they strike an object, such as the bottom or suspended fish. When striking an object, a small amount of the acoustic energy is reflected and this "echo" returns and causes a small vibration in the transducer. The small vibrations in the transducer caused by the returning acoustic echo cause the transducer to send a small electrical signal back up the cable to the display unit. The user can then view the presence of, and distance to, these underwater objects.

The transducer element, depending on the physical characteristics of the piezoceramic element (thickness, diameter, etc.) has a fixed direction in which it is most efficient at sending and receiving acoustic signals. This direction is called the "beam angle" and is of critical concern to most knowledgeable fishermen, as the display will typically show only those targets that are within this beam angle. A large beam angle will show targets from a larger underwater area, but suffers from lack of resolution. That means that although several targets may be in the beam angle, the user can only determine their distance from the transducer, not their lateral position within the beam. For example, if one fish target is 10' below the boat at the far right edge of the beam angle, it will show the same display as if it were 10' below the boat at the far left edge of the beam angle. In addition, if fish are present at exactly the same depth but at different sides of the underwater beam, the transducer will receive echoes from both fish targets at the same time and the display will only show a single target. This is a serious limitation to the conventional technology.

To get around this limitation, several manufacturers have resorted to adding more piezoceramic elements to the transducer, each pointed in a different direction. By selectively using each piezoceramic element the transducer has the ability to point or look in as many different directions as there are piezoceramic elements. After approximately four elements, however, the transducer housing starts to become physically large and cumbersome. To date, manufacturers have put as many as five separate elements into the transducer to enable users a view in up to five different underwater directions. In the future, Interphase believes that this multiple fixed-beam approach has serious limitations, especially for use in more advanced products where maximum underwater coverage and resolution are important.

Development of New Technology

To get around these limitations and provide a sonar system that can achieve both outstanding coverage and good resolution, Interphase pioneered the use of Ultrasonic Phased Array Technology. In 1991 we received the prestigious IMTEC Innovation Award in recognition of the importance of this new technology to the marine industry. Although new to the sportsfishing and recreational marine industry, "phased array ultrasound technology" has proven its capabilities in the medical industry for many years. The amazing video images provided by medical ultrasound equipment are familiar to most people and clearly demonstrate the technology's ability to show highly defined images in a real-time or live-action mode. Interphase has taken this same technology and modified it for use in the marine market.

An acoustic phased array is a group of piezoceramic elements that are precisely sized and spaced. Each element will send and receive acoustic pulses as when used in the conventional single element technology. However, when all the elements in the array are sending or receiving acoustic energy at the same time, the entire array behaves like a single larger element with one important difference: the ability for the array to concentrate its acoustic energy in different directions depending on the different "phasing" of the signals applied or received by each element. Depending on the signal phasing to the array, acoustic beams can be directed in an almost unlimited number of directions. For example, using an 8 element phased array, the Probe is capable of steering the acoustic beam in over 90 different directions. Conventional fixed-beam technology would have required the use of at least 90 transducer elements, each pointed in a different direction. Such a transducer would be much too costly and bulky to be of any practical use in the marine market.

Since the acoustic beam in the phased array is steered electronically, requiring no moving parts, it can be quickly and reliably scanned and re-scanned over a large area. When displayed, the changing information between subsequent scans takes on an almost animated quality - showing, for example, the movement of underwater fish or the constantly changing bottom conditions.

In addition to its ability to electronically steer an acoustic beam, the phased array has other advantages over fixed beam technologies such as: allowing the user to adjust the transducer beam width, to scan large areas limited only by the physics of speed of sound through water (5,000 ft/sec.), and the ability to provide nearly real-time or live-action underwater views.

All Interphase sonar products are proudly made in the USA!