Topic 08 - About transducers

The physical device inside a transducer that creates the sound wave is a piezoceramic disc called the element. The element, when voltage is applied, vibrates - it distorts and reforms its shape in very rapid succession. This vibration occurs at a specific frequency and creates compression waves, or acoustic energy - sound waves. These waves travel outward from the element in a vaguely cone-shaped pattern and encounter targets along the way.


As this acoustic energy encounters targets such as fish or bottom structure, some of the beam will be attenuated (absorbed by the target), some will be reflected back at the transducer as an echo and some will be scattered. As the reflected echoes strike the transducer they cause a minuscule distortion in the shape of the crystal. This distortion of the crystal creates a small fluctuation of voltage, which can be detected and processed by the fish finder. The end result is an image on your display.


By measuring the time from when the sound wave is generated to when the return echo is received, we can learn the depth at which a target is encountered. The strength of the reflected echo can tell us about the size and density of the target. Some transducers are referred to as single-element transducers. This means that they contain a single piezoceramic disc that vibrates alternately at 50kHz and 200kHz, utilizing both operating frequencies.


When greater performance is desired or required, multiple element transducers are available that can significantly enhance the performance and sensitivity of your fish finder. A multiple-element transducer is one in which separate elements vibrate individually at their respective frequencies. Some high-end models utilize seven, nine or even fifteen 50kHz elements along with a large-diameter 200kHz element. The dedicated 200kHz element offers enhanced sensitivity in shallow water, while the greater surface area of the 50kHz array will receive echoes from deeper water with much more clarity and detail.


There are some important points that are true for every transducer installation. Acoustic noise is always present, and these sound waves can interfere with your transducers operation. Ambient (background) noise from sources such as waves, fish and other vessels cannot be controlled. However, carefully selecting your transducers mounting location can minimize the effect of vessel-generated noise from the propeller(s) and shaft(s), other machinery, and other fish finders. The lower the noise level, the higher the gain setting you'll be able to use effectively on your fish finder.


Always select a location where:


As a rule, no transducer should be located near a water intake or discharge opening, directly aft of any lifting strakes, steps or other obstructions or irregularities in the hull , or behind eroding paint (an indication of turbulence). The flow of water across the transducer face must be as smooth as possible in order to get the best performance while cruising.



Transducers used in smaller fish finders

Most standard transducers are designed for recreational fish finders and generally have a single element that resonates alternately at 50 and 200 kHz. Although these transducers are effective and inexpensive, greater performance can be had by matching your recreational fish finder with a high-performance transducer. These transducers are rated for a greater power output and contain an array of 50kHz elements along with one or more large-diameter 200kHz elements. An array of 50kHz elements allows for a very tight beam pattern, meaning there will be more energy on-target to produce return echoes. Also, the greater surface area of this array makes the transducer more sensitive to return echoes, enabling greater target resolution on the screen. The same is true of having one large, dedicated 200kHz element - its tighter beamwidth and greater sensitivity create a better performing transducer at all power outputs.