Transducer Glossary

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Acoustics

The science dealing with the transmission of sound waves

Amplitude Shading

A method of reducing the side lobe levels in a transducer array. The shading usually causes the main beam to broaden by applying different voltages to the elements of the array.

Attenuation

To lessen, weaken, or diminish (i.e. to weaken a signal)

Beacon (Acoustic)

An underwater device which continually sends out a repetitive signalat a preset frequency. Pingers are used to mark locations or objects underwater for later recovery or relocation. The amount of time a pinger can be deployed is dependent on its battery life.

Beam Pattern

Beam patterns show the relative amplitude of the acoustic pressure (generated or received) as a function of direction relative to the transducer. For reciprocal transducers the transmit and receive beam patterns are basically the same. Beam patterns are three-dimensional.

Beam Steering

The method of steering the main lobe of a transducer to a certain direction.

Beam Width

The width of the main beam lobe, in degrees, of the transducer. It is usually defined as the width between the "half power point" or "-3dB" point.

Blanking Distance

Minimum sensing range in an ultrasonic proximity sensor. Blanking distance is a function of the ring down time of the transducer as the transducer must ring down before it can receive the sound reflected from the target.

Damping

Materials, design, and mounting techniques used to reduce ringing in the transducer.

dB (Decibel)

A unit of measure used to express the volume of a sound

Doppler

Technique for calculating the relative velocity between two points by measuring the shift in frequency of a sound wave transmitted from one point to the other.

Directivity Index

The value in dB of ten times the common logarithm of the directivity factor. The directivity factor is the ratio of the sound intensity produced by a test transducer on a specific axis to that of a point source that is putting out the same acoustic power. Since the specific axis is usually one of maximum radiation, the DI in usually greater than zero.

Echo Location

Determining the location of a target relative to the sensor face by means of measuring the time it takes for a sound wave to travel to the target and be reflected back to the sensor.

Efficiency

In a projector efficiency is defined as the ratio of the acoustic power generated to the total electrical power input. Efficiency varies with frequency and is expressed as a percentage.

Frequency

The number of cycles per second of a wave (i.e. sound wave)

Hydrophone

A hydrophone converts acoustic energy into electrical energy and is used in underwater passive systems for listening only. Hydrophones are usually used below their resonance frequency over a much wider frequency band where they provide uniform output levels.

Hydrophone Directivity

The beam width of a hydrophone determines its directivity. A narrow beam will give it greater directivity, i.e. allow determination as to the direction a sound wave is coming from.

kHz (kilohertz)

Unit of frequency, equal to one thousand hertz or cycles per second.

Level Sensor

Same as a proximity sensor except with the surface of a fluid or bulk solid as the target.

Main Lobe

The main acoustic beam in a directional transducer. There are other, smaller lobes called side lobes that are located around the main lobe

Maximum Response Axis

The MRA or acoustic axis of a transducer is defined as the direction in which the acoustic response has its maximum value.

Omnidirectional

Sending or receiving sound waves in or from any direction. 360 degrees receiving capability

Open Circuit Voltage

The OCV is the level of the electrical output per one micropascal of acoustic input.

Piezo-electric ceramic

A material made of crystalline substance which creates charges of electricity by the application of pressure and vice versa.

Pinger

See Beacon (Acoustic)

Projector

A projector converts the energy from a power amplifier (generator) into an acoustic pressure output. Projectors are usually driven near their resonance frequencies where they provide the highest acoustic output. Projectors are sound sources.

Proximity Sensor

Ultrasonic sensor designed to measure the distance from the sensor face to a target.

Receiver

Transducer used to intercept the acoustic wave reflected back from the target. Can be same as transmitter.

Resonant Frequency

The frequency at which a piezo-electric ceramic will vibrate most efficiently i.e. will produce the highest output with the least amount of voltage applied.

Ringing

Analagous to the ringing of a bell, it is the rise and decay time before and after the transducer reaches maximum amplitude. Expressed as the mechanical Q of the transducer which is the number of cycles it takes to get up to 90% of maximum amplitude, or down to 10% above zero amplitude.

Side Lobe

Smaller acoustic beams located around the main lobe.

Sonar

Word is derived from "sound navigation and ranging." It describes a devise that transmits frequency sound waves in water and registers the vibrations reflected back from an object. It is used in detecting objects such as submarines, locating schools of fish, or determining water depth.

Source Level

Sound pressure (acoustic power) in dB referenced to 1.0 microPascal measured at 1 meter (one foot in air) from the sound source.

Sub-bottom Profiling

Determining the sedimentary structure of the ocean floor by utilizing sound waves.

Target Strength

A measure of the percentage of the acoustic energy hitting the target that is reflected back to the transducer.

"Time-of-Flight"

Technique for calculating the distance to a target by using the timing of the return echo from the target and the speed of sound in the medium between the target and the sensor. Used in echo location and ultrasonic flowmeters.

Transducer

In acoustics this term is used to describe an antenna which converts electrical energy into sound wave and vice versa.

Transmitter

See "Projector".

Transponder (Acoustic)

A devise that automatically transmits sonar signals when actuated by a specific sonar signal from an interrogator. Transponders are used to mark or track objects or sites underwater. They are programmed to be in a continuous passive (listening) mode until they receive a valid signal from a transponder interrogator.

Transmit Current Response (TCR)

The level of the acoustic output referenced to one meter (one foot in air) per one amp input

Transmit Voltage Response (TCR)

The level of the acoustic output referenced to one meter (one foot in air) per one volt input

ÁPa (microPascal)

A unit of pressure used in acoustics

Ábar

A unit of pressure used in acoustics


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