ECE 5320 Mechatronics

Assignment #01: Literature Survey on Sensor and Actuators

Topic: SONAR (SOund NAvigation and Ranging)

Prepared By:

Lee GardnerDepartment of Electrical and Computer Engineering

Utah State University

Outline– Reference list

– To probe further

– Major applications

– Basic working principle illustrated

– A typical sample configuration in application (application notes)

– Major specifications

– Limitations

– And many more relevant issues in applications (such as, how to choose, cost information, where to buy etc.)

Reference List

• Mechatronics Handbook• HowStuffWorks.com• Sonar Made Simple, Ridgesoft LLC 2003

www.ridgesoft.com/articles/sonar/SonarMadeSimple.pdf

• Sonar Theory and Application, Imagenex Model 85 Color Imaging Sonar User’s Manual. http://www.imagenex.com/sonar_theory.pdf

Major Applications

• Object distance measurement.

• Object proximity detection

• Vehicle motion coordination and movement/location mapping

• Detection, Classification, Localization, Identification– Passive: just listen

• biological monitoring

– Active: transmit and listen (echolocation)

• surveying (side-scan), depth sounding, imaging, fisheries

Major Applications Cont…Active Sonar:Benefits

Control of signal band. Direct access to range and

azimuth. Matched filter gain.

Drawbacks Two-way transmission loss Large power requirement. Negative impact on marine

mammals. Source position and

intention visible to all.

Passive Sonar:Benefits

Minimal power requirement.

Minimal impact on marine mammals.

Clandestine surveillance.Drawbacks

No range information. Mini-submersibles and

divers are very quiet with respect to ambient.

No matched filter gain.

Basic Working Principle

• Sonar works by transmitting a wave (sound wave) and listening for the echo of the sound.

• The received wave is measured and analyzed for changes in amplitude and phase.

• The delay in the return of the “ping” and the speed of sound can be used to determine the distance of the closest object detected.

Basic Working Principle Cont…

Basic Working Principle Cont…

• The distance to the nearest object can be calculated by dividing the elapsed time

Distance = Elapsed_Time/(2 * Speed of Sound)

• The factor of 2 comes from the fact that the wave traversed the distance from sensor to object twice.

• Speed of Sound varies and is dependant on:– Temperature– Salinity– Depth/Elevation

Transmission Loss (TL)

• Describes the “weakening” of the intensity of sound due to a source at some point in the transmission medium

• Affected by:– Spreading– Propagation details– Absorption– Forward reflection losses (boundaries)

• TL = 10log10(I0/I1) dB (here I0 is SL)

Working Model

• In many cases the sonar image of a target will closely resemble an optical image of the same object.

Working Model Cont…Imaging Sonar

Imaging Sonar

• Fan shaped beam• Scans surfaces at shallow angles, usually

through a horizontal angle• Displays color images or pictures• Complete echo strength information for each

point• Primarily for visual interpretation

Imaging Sonar Cont…

Characteristics necessary for visual image• The angle through which the beam is moved

is small• The fan-shaped beam has a narrow angle• The transmitted pulse is short• The echo return information is accurately

treated

Working Model Cont…Profiling Sonar

Profiling Sonar

• Narrow pencil shaped beams• Scans surfaces at a steep angle usually on a vertical

plane• Displays individual points or lines• Accurately cross-sections a surface• Echo strength for each point higher than a set threshold• Digitizes a data set for interfacing with external devices• Data set is small enough to be manipulated in a small

computer• Primarily a measurement tool

Working Model Cont…

Sonar Image Interpretation

• Image of a target will closely resemble an optical image of the same object.

• A sonar image will always have less resolution than an optical image.

• Rough objects reflect sound well in many directions and are therefore good sonar targets.

• Smooth plane surfaces, may be difficult to see with a sonar.

Image Interpretation Cont…

• It is often useful to scan targets from different positions.

• An unrecognizable target from one direction may be quite easy to identify from another.

• Usually the relative elevations of the targets are not known, only the range from the transducer.

• Two targets displayed in the same location on the screen may be at different elevations.

Image Interpretation Cont…

Image Interpretation

• You might see a target on the bottom, and a target floating on the surface in the same place.

• By analyzing the shadows you can estimate the height of objects above the bottom.

• Reverberation (clutter) is interference in an active sonar return due to scattering from non-targets– Interfaces

• Bottom roughness, bottom “features,” sediment volume inhomogeneities

• Surface roughness, bubbles

– Volume (fish)

Major Specifications

• Range: The longest distance detectable from an object.

• Sensitivity: Ability to detect subtle changes in detected object

• Bandwidth: The range to detect motion and movement in the object by measuring Doppler shift.

• Accuracy: The difference in the detected range to the actual range.

Major Specifications Cont…

• Precision: Ability for the sensor to repeat results given a particular accuracy.

• To avoid interference, sonar arrays must be fired sequentially

• Noise susceptibility and filtering.• Coverage area

Limitations

• Generally only used for under water applications• Noise susceptibility can skew results• High precision and accuracy sonar equipment are too

expensive for consumer use.• Some objects are “invisible” to sonar and difficult to

detect.• Precise image reconstruction is difficult do to very low

resolution echo’s

Cost

• Cost varies widely on use and application.• Generic sonar systems can be made cheaply.• High accuracy and specialized sonar systems can

be very expense. Usually only used by military and industry.

• Precision Budget can grow extremely high for high-end systems.

Where to Buy

• Many retailers (digikey etc…) have sonar sensors available for consumer purchase.

• Specialized and high end sensors available through industry channels.

• http://www.mstarlabs.com/adwds/adsonr01.html• http://www.wg-plc.com/international/security/underwater_

surveillance_system.html