What Is A Sonar Transducer?

20 Feb What Is A Sonar Transducer?

What is a sonar transducer?

No matter what make or model fishfinder you have, there is a sonar transducer at work inside. Regardless of whether you have a new FishHunter fish finder that connects to an iPhone or Android device, or an old-school boat mounted unit, the bit of advanced electronics that makes the whole thing work is called a transducer.
The transducer itself is a piezoelectric crystal or nowadays more likely it’s a synthetic crystalline material that transforms electrical energy into mechanical energy (sound) and back again. Let me break it down into simple science.


sonar tranduscer is piezoelectric crystal
You remember that Disney movie, The Dark Crystal, which had all those Muppets and… well…  This science has nothing to do with that story. But some of the best transducers are mineral crystals!
A transducer is any substance that converts one form of energy into another form of energy.


Many different types of energy can be converted by transducers into other forms of energy including electromagnetic, photovoltaic, electrical, mechanical, chemical energy, and acoustic and thermal energy, and more. Today the term transducer generally means the use of a sensor or a detector of some kind, but any system which changes energy from one form into another is considered transductive.
dark crystal movieTransducers are found everywhere today and have been helping our society for the last hundred years. They’re widely used in all types of everyday things, including antennae, microphones, speakers and magnetic tape heads, and especially in measuring devices like hydrogen meters, pH meters, electrostatic meters, all types of audio transmitters and receivers.
Ultrasonic transducers transmit sound waves through air and these were used in early television remote controls and garage door openers. Those same ultrasonic transducers now are mounted on new luxury vehicles as echo location systems to help drivers determine the distance from the rear of a car to the concrete curb.
In the case of sonar, the transducer is usually a single mineral crystal lattice that converts electricity into high frequency sound by vibrating the crystal lattice. Another device called a hydrophone is often used to collect the return sounds, and another device measures the differences in the data which is fed to an imaging processor for display.


Piezoelectric crystals change shape when electrified.  They will expand or contract when subjected to DC current across their lattice structure, depending on the placement of the electrical leads that apply the voltage.  USING DC CURRENT, the amount of voltage applied and the orientation of the mineral will cause the crystal lattice to expand.  When the polarity of the charge is reversed, the crystal will contract in the opposite way.  So when scientists USE AC CURRENT or alternating current it causes the crystal to expand and contract, and vibrate, rapidly. These vibrations make sound. The sound waves travel through a medium (salt water or freshwater) and bounce off whatever is hard enough to return the sound waves back to the associated ‘listening’ device.
A hydrophone is historically what was used to detect the returning sound wave and report it as another form of energy, often an electrical signal.


The Best FishFinders Have High Quality Transducers with Cultured Piezoelectric Crystals

Any anomalies in the mineral crystal lattice will cause the associated electronic device to work improperly, so lots of care is taken when growing the crystals. The science of creating these semiprecious gemstones is a well-funded field of study.  Much like Star Trek Voyager episode where the search for dilithium crystals takes the crew to strange new worlds, our own search for the best piezoelectric crystals on Earth is equally intense.
Table sugar crystals are piezoelectric.  Although relatively easy to find, in that of the 32 different crystal structures, 20 exhibit piezoelectric properties, the piezo crystals we have and can make ourselves are not very efficient.
After World War II, the Japanese discovered a new class of synthetic materials, called ferroelectrics, which exhibit piezoelectric constants many times higher than natural materials. This led to intense research to develop barium titanate and later lead zirconate titanate materials with specific properties for particular applications, including echo location devices and sonar fish finders.


MacGyver would grow Rochelle Salt Crystals. It would take about 10 – 14 days, and perfect conditions, but he would grow the salt crystals from three drug store ingredients: cream of tartar, sodium carbonate (soda ash) and distilled water.  Rochelle Salt crystals are white and look like rock salt and are piezoelectric. With crystals in his hand, MacGyver would then smash apart a ‘quartz’ clock radio and use the guts to charge the rocks and send out his first PING. Then he has to build another rig to listen for the return, which might somehow feed into his iPhone or android device to make a digital readout, or any TV tube or flat screen – the writers would gloss over the six weeks of machine programming it would take to create even the most basic display, because he is MacGyver.
If you were in business making a better Fishfinder, you would probably put your scientists to work on improving the transducer and or the related audio sensors, and more specifically focus on making better piezoelectric crystals, better than  barium titanate or lead zirconate titanate crystal arrangements. In the not so distant future, such crystals will be grown in space to take advantage of low gravity environments.