How Does A Transducer Work?

What is a Transducer?A good fishfinder depends on an efficient transducerto send and receive signals. The transducer is theheart of an echosounder system. It is the device thatchanges electrical pulses into sound waves oracoustic energy and back again. In other words, it isthe device that sends out the sound waves and thenreceives the echoes, so the echosounder can interpretor “read” what is below the surface of the water.

How Does a Transducer Work?The easiest way to understand how a transducerfunctions is to think of it as a speaker and amicrophone built into one unit. A transducer receivessequences of high voltage electrical pulses calledtransmit pulses from the echosounder. Just like thestereo speakers at home, the transducer thenconverts the transmit pulses into sound. The soundtravels through the water as pressure waves. When awave strikes an object like a weed, a rock, a fish, orthe bottom, the wave bounces back. The wave is saidto echo—just as your voice will echo off a canyonwall. When the wave of sound bounces back, thetransducer acts as a microphone. It receives thesound wave during the time between each transmitpulse and converts it back into electrical energy. Atransducer will spend about 1% of its timetransmitting and 99% of its time quietly listening forechoes. Remember, however, that these periods oftime are measured in microseconds, so the timebetween pulses is very short. The echosounder can

calculate the time difference between a transmit pulseand the return echo and then display this informationon the screen in a way that can be easily understoodby the user.

What Goes into the Making of a Transducer?The main component of a depth transducer is thepiezoceramic element. It is the part that convertselectrical pulses into sound waves, and when theechoes return, the piezoceramic element converts thesound waves back into electrical energy. Piezoceramicelements are most often in a disk form, but they mayalso be in the shape of a bar or a ring. A transducermay contain one element or a series of elementslinked together called an array. A transducer is madeup of six separate components:

• Piezoceramic element or an array of elements• Housing• Acoustic window• Encapsulating material• Sound absorbing material• Cable

Echosounder B744V transducer

Echo Echo

Transmit pulse Transmit pulse

Time (seconds)

How Does A Transducer Work?

How Does a Transducer KnowHow Deep the Water is?The echosounder measures the time betweentransmitting the sound and receiving its echo. Soundtravels through the water at about 1,463 m/s(4,800 ft/s), just less than a mile per second. Tocalculate the distance to the object, the echosoundermultiplies the time elapsed between the soundtransmission and the received echo by the speed ofsound through water. The echosounder systeminterprets the result and displays the depth of thewater in feet for the user.

How Does a Transducer KnowWhat the Bottom Looks Like?As the boat moves through the water, the echoes ofsome sound waves return more quickly than others.We know that all sound waves travel at the samespeed. When a sound wave in one section of the

sound field returns more quickly than another, it isbecause the wave has bounced off something closerto the transducer. These early returning sound wavesreveal all the humps and bumps in the underwatersurface. Transducers are able to detect whether abottom is soft or hard and even distinguish betweena clump of weeds and a rock, because the soundwaves will echo off of these surfaces in a slightlydifferent manner.

How Does a Transducer See a Fish?The transducer can see a fish, because it senses theair bladder. Almost every fish has an organ called anair bladder filled with gas that allows the fish to easilyadjust to the water pressure at different depths. Theamount of gas in the air bladder can be increased ordecreased to regulate the buoyancy of the fish.Because the air bladder contains gas, it is a drasticallydifferent density than the flesh and bone of the fish aswell as the water that surrounds it. This difference indensity causes the sound waves from theechosounder to bounce off the fish distinctively. Thetransducer receives the echoes and the echosounderis able to recognize these differences. Theechosounder then displays it as a fish.

Cable Housing Sound absorbingmaterial

Encapsulatingmaterial

Piezoceramic elementAcoustic window

Air bladder

Softbottom

Softbottom

Hard rocky bottom

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Can Fish Hear the Sound WavesProduced by a Transducer?No, the sound waves are ultrasonic. They are above(ultra) the sound (sonic) that human ears are able tohear. Humans can hear sound waves from 10 Hz to20 kHz. Most fish are unable to hear frequencieshigher than about 500 Hz to 1 kHz. The ultrasonicsound waves sent out by Airmar transducers havefrequencies ranging from 10,000 kHz to 2 MHz(200,000,000 Hz), clearly beyond the hearing of fish.However, most people can hear the transmit pulses ofour 10 kHz transducers; they sound like a series ofclicks.

What is Frequency?Frequency is the number of complete cycles orvibrations that occur within a certain period of time,typically one second. Sound waves can vibrate at anyone of a wide number of frequencies. The easiestway to understand frequency is to think of it in termsof sounds that are familiar. For example, a kettle drumproduces a low-pitched sound (low-frequency). That

is, it vibrates relatively few times per second. Whereas,a flute produces a high-pitched sound(high-frequency). It vibrates many more times persecond than a kettle drum. The frequency of soundwaves is measured in a unit called a Hertz. A Hertz isone cycle per second. For example: a 150 kHztransducer operates at 150,000 cycles per second.

Selecting Frequencies

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Fish hearing frequency range

Human hearing frequency range

Airmar transducer frequency range

How Does a Customer DecideWhat Frequency is Needed?Airmar transducers are often designed for 50 kHz(50,000 cycles per second) or 200 kHz (200,000cycles per second). Transducers can be designed tooperate efficiently at any number of specificfrequencies depending upon the application andperformance requirements of the customer. Ahigher-frequency sound wave will give the user ahigher-resolution picture of what is present under thewater, but the range will be short. Fishermen in moreshallow lakes, who want a crisp clear picture of thebottom need a higher-frequency transducer.Low-frequency sound waves will not give the user asclear a picture of the bottom, but they have greaterrange for very deep areas where high-frequencysound waves cannot reach. A low-frequency unit willwork well in the depths of Lake Michigan or theocean.

A higher-frequency transducer will put out quicker,shorter, and more frequent sound waves. Like theripples made when a small pebble is thrown into stillwater, small waves of sound move evenly out andaway from the source. Because they are just smallwaves, they will not travel far, and small obstacles willcause them to bounce back. Higher frequencies aremore sensitive to small objects and will send backdetailed information which will show as crisphigh-resolution pictures on the echosounder screen.The range of high-frequency sound waves, however,is short. In fact, sound waves emitted by a 200 kHztransducer have a limited range of about 200 m

Selecting Frequencies

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50 kHz(600’). Now, think of the large waves created by alarge boulder thrown into still water. Low-frequencysound waves are like these large waves; they travelmuch farther than high-frequency waves. Butbecause low-frequency waves are so large, they washright over small obstacles. Low-frequency soundwaves are not as sensitive in detecting small fish orother small obstacles as are high-frequency waves,and although they can see to greater depths, theywill not send back detailed information or clear crisppictures.

This illustration shows the differences in beamwidth of atransducer operating at both 50 kHz and 200 kHz. Notice thedifferent way the fish appear as “marks” at each frequency.

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Transducer Style and Screen Images

In-Hull Transducers

Transom-Mount Transducers

Thru-Hull/External Transducers

M260 R199 / R299 / R399P79

B744V SS260 R99 / R209 / R309

P58 P66 TM258

Transducer Style and Screen Images

600 W 1 kW

600 W 1 kW

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Transducer Styles and Mounting Methods

Choosing the Right TransducerThere are three main considerations when selecting atransducer.

• Transducer mounting style• Type of boat and its hull material• Application or expectation for the transducer

Transducer Mounting StyleTransducers are typically mounted in one of threeways: through the hull, inside the hull, or on thetransom.

Through the HullThe transducers in this mounting style fall into twocategories. There are “flush” thru-hull sensors that sitflush or nearly flush with the boat hull. They arerecommended for smaller boats with a minimumdeadrise angle. And they are often installed on sailingvessels because they produce minimal drag.

External thru-hull transducers extend beyond thehull’s surface and usually require a fairing to aim thesound beam vertically. They are right for largerun-trailered vessels. When external mounts areinstalled with a High-Performance Fairing, thetransducer face is flush with the surface of the fairingand parallel to the waterline, resulting in a trulyvertical beam, putting maximum energy on thetarget. This installation, when mounted in “cleanwater,” forward of propellers and running gear,produces the most effective signal return, sincenothing on the vessel interferes with the transducer’sactive face.

Inside the HullAn in-hull transducer is installed inside a boat hullagainst the bottom and sends its signal through thehull. Some people prefer this mounting style, becauseit is not necessary to drill through the vessel. A unitcannot be damaged when a boat is trailered, thetransducer is not exposed to marine growth, andthere is no drag. Additionally, a transducer can beinstalled and serviced while the vessel is in the water.Most in-hull transducers are mounted inside a liquidfilled tank that is first epoxied in place. As long as thewater flow below the transducer is “clean”, it will givegreat high-speed performance.

On the TransomTransom-mounts are attached to the back (transom)of a boat hull. Trailered boats typically use thismounting style, since it is out of the way of the rollers.Some people prefer a transom-mount, because it iseasy to install and remove a unit—especially if akick-up bracket is used. Kick-up brackets move atransducer out of the way to prevent damage fromfloating debris when a boat is underway. Also, theyprotect the transducer when a boat is trailered, orwhen it is kept in the water for a long period of time.A transom-mount installation gives betterperformance than an in-hull at boat speeds below30 knots (34 MPH).

Transducer Styles and Mounting Methods

Plastic Bronze Stainless steel

Type of Boat and its Hull MaterialThe type of boat and the material used to make thehull must be taken into consideration when selectingthe transducer mounting style. Each has itslimitations.

Thru-Hull/External MountThru-hull transducers will work with any engine type:inboard, outboard, or I/O. And these transducers areright for power and sailboats alike. There are thru-hullunits for every hull material.

Thru-hull units are not recommended in twosituations.• Plastic thru-hull housings cannot be used in a

wooden boat. Wood swells as it absorbs water, soit may crack the housing.

• Bronze thru-hull housings cannot be used inaluminum boats. The interaction between thealuminum and the bronze, especially in thepresence of salt water, will eat away thealuminum hull and/or the bronze housing.

In-Hull MountIn-hull transducers will work with any engine type:inboard, outboard, and I/O. These transducersperform well on both power and sailboats.

Thick aluminum hulls are not recommended forin-hull installations, because there is too much signalloss transmitting through the metal. In addition, this

Transom-MountTransom-mount transducers can be used with anyhull material. However, they will not work on a vesselwith an inboard engine due to the turbulenceforward of the sensor. And because of excessiveheeling, transom-mounts are not recommended forsailboats.

installation will not work on wooden boats or coredfiberglass hulls (foam, balsa wood, or plywood layerssandwiched between an inner and an outer skin).These materials contain air bubbles that reflect andscatter sound pulses before they reach the water.

Some in-hull transducers, such as the P79, can beused on small aluminum-hull boats up to 6.7 m (22’)with a hull thickness of 0.38 mm (0.150”) or less. Inthese installations, the transducer face is epoxieddirectly to the hull.

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Transducer Styles and Mounting Methods

B744V P66

DST800

R99

Application or Expectation for the Transducer

Cruising and SailingIf time on the water is spent sailing or cruising, ahigh-power transducer is not needed. Single-frequency200 kHz transducers with 200 W to 600 W RMSpower will be more than enough in this application.Accurate depth readings will range from 61 m to152 m (200’ to 500’) depending on the depthinstrument.

Recreational FishingIf the application is recreational fishing, a 600 Wtransducer will do the job. These transducers haveenough power to read bottom in over 305 m (1,000’)of water and have 50 kHz and 200 kHzdual-frequency capability. Typically matched withsmall to mid-size fishfinders, a 600 W transducer isperfect for bottom fishing, marking bait, and markinggame fish.

Tournament Sport FishingA 1 kW to 2 kW transducer is a must for tournamentsport fishing. These powerhouses will give the user acrystal clear screen on medium to large fishfinders.The multiple elements that make up the transducercan distinguish schools of fish as closely-spacedindividual targets and can distinguish fish close to thebottom. These transducers are so precise; fish are nolonger concealed by their surroundings.

Many of the 1 kW and 2 kW transducers have Airmar’sexclusive Broadband Ceramic Technology. The200 kHz element produces the highest resolutionavailable today without sacrificing sensitivity.

Commercial FishingThese transducers are available in frequencies from24 kHz to 200 kHz and power from 1 kW to 4 kW.Units feature high-efficiency designs producingsuperior fishfinding and clear and distinct images ofboth the bottom and closely-spaced fish.

R199SS260

Transducer Styles and Mounting Methods

Navigation/Ocean Survey/Custom

CommercialFishing

TournamentSport Fishing

CS229

RecreationalFishing

Cruising andSailing

M42

Navigation/Ocean Survey/CustomAirmar offers custom engineered transducers forconsumer, commercial, and scientific applications.Airmar designs and manufactures transducersranging in frequency from 10 kHz to 2 MHz andpower outputs ranging from 100 Watts to10,000 Watts depending on the specific application.Typical applications vary from portable units forharbor survey to custom fishfinder transducers tomulti-frequency arrays used in deep-sea sounding.Transducer arrays of more than 100 piezoceramicelements have been designed and manufactured.Airmar can produce dual-beam and split-beamtransducers, phased-array transducers, SWATH andForward Looking Sonar Transducers—all built to thecustomer’s specifications. Airmar also can supply awide range of flow sensing transducers.

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600 W vs 1,000 W High-Performance Units

B744V600 W

SS2601 kW

Transducer Comparison: 600 W versus 1 kWThe photos below clearly show the screen resolution differences between a single-element 600 W transducer and amultiple-element 1 kW transducer.

Frequencies Number of Beam RatedElements and Width RMS PowerConfiguration (@-3dB) (W)

45° 600 W

12° 600 W

Frequencies Number of Beam RatedElements and Width RMS PowerConfiguration (@-3dB) (W)

50 kHz-AE 19° 1 kW

200 kHz-BH 6° 1 kW

50 kHz

200 kHz

Single-element600 W transducer

High-performance1 kW transducer

50 kHz

200 kHz

50/200 kHz-A

600 W vs 1,000 WPerformance

Xducer ID™ FeatureAirmar’s exclusive Transducer ID feature allowsechosounders to query the connected transducergathering important operating characteristics. With thisdata, the echosounder and transducer function as aprecisely-tuned system. A Transducer ID enabled sensorcontains an embedded microcontroller thatcommunicates with the connected echosounder via asingle conductor in the transducer cable. The principaldata transmitted is intended to identify the type andconfiguration of the transducer. Then the echosoundercan alter its parameters of operation to optimizeperformance and to protect the transducer fromoverdrive. The Transducer ID feature also providesimportant information to installers and technicians suchas serial number and housing style. Listed below is asummary of the information that the Transducer IDfeature can provide to future fishfinders.

•Airmar part number•Housing style•Serial number•Ceramic elementconfiguration•Date of manufacture•Acoustic window• Impedance matchingconfiguration•Nominal frequency(s)•Best transmit frequency(s)•Power rating•Beam pattern

The image above shows the depth and beamwidthdifferences between the single-element, 600 W, B744Vand the multiple-element, 1 kW, SS260.

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Transducer ID™

High-Performance FairingAchieve maximum fishfinder performance by installing an Airmar transducer with a High-Performance Fairing. EachHigh-Performance Fairing is custom designed to match its transducer model. The fairing assures a vertical beamwhich results in strong return echoes. Additionally, the streamlined shape reduces drag and minimizes turbulenceover the face of the transducer. At speeds above 30 knots (34 MPH), screens continue to display clear images andsolid bottom tracking.

Without High-Performance Fairing With High-Performance Fairing

The photos above show a boat-test comparison of a transducerinstalled with a High-Performance Fairing versus a standardfairing. The same transducer model was used. One transducerwas installed on the port side of the boat with a High-PerformanceFairing, and the other was installed on the starboard side with astandard fairing. Using a switchbox, we were able to swap fromone transducer to the other. At speed, the significant resolutionand clarity on the fishfinder screen when using the transducerwith a High-Performance Fairing is clearly depicted.

200 kHz, 25 knots (29 MPH) 50 kHz, 36 knots (41 MPH)50 kHz, 23 knots (26 MPH)

Without afairing, thebeam isangledimproperly.

With a fairing,the beam isangledproperly.

Advantages of a High-Performance Fairings

High-Performance Fairing OnlyHigh-Performance Fairing

Standard FairingHigh-Performance Fairing

Standard Fairing

Benefits of Broadband Transducer Technology

Airmar is the first to introduce affordable BroadbandTransducers. This is an enabling technology thatprovides better fish detection today and will lead todramatic advances in echosounder performance in thefuture. While these transducers are more costly tomanufacture, the present and future benefits are huge.

Broadband Transducers enhance fish detection onvirtually all of today’s fishfinders. They give betterdefinition; it is far easier to distinguish among individualfish and between fish and the bottom.

Airmar achieves superior results by using a new ceramicmaterial. It lets transducers operate over a range offrequencies while maintaining sensitivity. TheseBroadband Transducers are, by definition, low-Qdevices. In other words, they exhibit very low ringing.There is little variation from transducer to transducer.Additionally, Broadband Transducers are relativelyimmune to the effects of aging, so their frequencyrange remains stable over time.

Benefits TodayManufacturers now market echosounders that canadjust operating frequency and power output. Whilethese are premium products, the designs are aprecursor of things to come. With the ability to adjustfrequency, an echosounder can operate Airmar’sbroadband ceramics anywhere in the 160 kHz to260 kHz band. By selecting different operatingfrequencies, two or more high-frequency sounders canwork simultaneously without interference. Thefrequency also can be adjusted to the mission.Lowering the operations frequency increases thebeamwidth and depth capability; raising the frequencynarrows the beamwidth, increases echo definition, andimproves high-speed performance.

Future BenefitsHere is where it gets really exciting. In today’sfishfinders, good fish detection is obtained bytransmitting a long pulse. This puts more energy on thetarget. With a long pulse, closely-spaced fish cannot beseparated—you get a big blob. Fish close to the bottomappear attached to the bottom and are difficult orimpossible to detect.

Airmar’s broadband transducers enable frequencymodulated (FM) transmissions; a.k.a. CHIRP or codedtransmissions. Using FM transmissions, you can achieveboth the benefits of long pulse, more energy on target,and short pulse, segregation of closely-spaced fish andidentification of fish on or close to the bottom. This isbecause the coding of the transmission is known andthe return echoes are similarly coded. The technique isalso known as pulse compression. In summary,fishfinders of the future with FM transmissions will havedramatically improved target resolution andsignal-to-noise ratio. Airmar’s broadband transducertechnology will enable this to happen.

Figure of Merit

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