Understanding the function of a transducer
How does a Fish Finder's transducer operate?
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.
Sound travels through water at a known speed. Consequently, we can calculate the depth of a target by measuring the time it takes for acoustic energy to travel to and from a target. The strength of the reflected echo can tell us about the size and density of the target.