Main Content

phased.IsotropicProjector

Isotropic projector element

Description

The phased.IsotropicProjector System object™ creates an isotropic sound projector used in sonar applications. An isotropic projector has the same response in all directions. The response is the radiated sound intensity per unit input voltage to the projector. You can change the response using the VoltageResponse property.

To compute the response of the isotropic projector for specified directions:

  1. Create the phased.IsotropicProjector object and set its properties.

  2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Description

example

projector = phased.IsotropicProjector creates an isotropic projector System object, projector.

projector = phased.IsotropProjector(Name=Value) creates an Isotropic projector object, projector, with each specified property set to the specified value. You can specify additional name-value pair arguments in any order as (Name1=Value1,...,NameN=ValueN).

Example: projector = phased.IsotropicProjector(FrequencyRange=[0 1000],BackBaffled=true) creates an isotropic projector element with its frequency range specified between 0 and 1000 Hz.

Properties

expand all

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

Operating frequency range of projector, specified as a 1-by-2 row vector in the form of [LowerBound HigherBound]. This property defines the frequency range over which the projector has a response. The projector element has zero response outside this frequency range. Units are in Hz..

Example: [0 10e3]

Data Types: double

Voltage response of projector, specified as a scalar or real-valued 1-by-K row vector. When you specify voltage response as a scalar, that value applies to the entire frequency range specified by FrequencyRange. When you specify the voltage sensitivity as a vector, the frequency range is divided into K-1 equal intervals. The response values are assigned to the interval end points. Then, the step method interpolates the voltage response for any frequency inside the frequency range. Units are in dB ref: 1 μPa/V. See Projector Voltage Response for more details.

Example: 10

Data Types: double

Back baffle response of projector, specified as false or true. Set this property to true to back baffle the projector response. When the projector is back baffled, the projector response for all azimuth angles beyond ±90 from broadside are zero. Broadside is defined as 0° azimuth and 0° elevation.

When the value of this property is false, the projector is not back baffled.

Usage

Syntax

resp = projector(freq,ang)

Description

resp = projector(freq,ang) returns the voltage response resp for the projector at the specified operating frequencies freq and in the specified directions ang of arriving signals.

Note

The object performs an initialization the first time the object is executed. This initialization locks nontunable properties and input specifications, such as dimensions, complexity, and data type of the input data. If you change a nontunable property or an input specification, the System object issues an error. To change nontunable properties or inputs, you must first call the release method to unlock the object.

Input Arguments

expand all

Voltage response frequencies of projector, specified as a positive real scalar or a real-valued 1-by-L vector of positive values. Units are in Hz.

Data Types: double

Direction of arriving signals, specified as a real-valued 1-by-M row vector or 2-by-M matrix. When ang is a 2-by-M matrix, each column of the matrix specifies the direction in the form [azimuth;elevation]. The azimuth angle must lie between –180° and 180°, inclusive. The elevation angle must lie between –90° and 90°, inclusive.

When ang is a 1-by-M row vector, each element specifies the azimuth angle of the arriving signal. In this case, the corresponding elevation angle is assumed to be zero.

Data Types: double

Output Arguments

expand all

Voltage response of projector, returned as a real-valued M-by-L matrix. M represents the number of angles specified in ang, and L represents the number of frequencies specified in freq. Units are in V/Pa.

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

expand all

beamwidthCompute and display beamwidth of sensor element pattern
directivityDirectivity of antenna or transducer element
isPolarizationCapableAntenna element polarization capability
patternPlot antenna or transducer element directivity and patterns
patternAzimuthPlot antenna or transducer element directivity and pattern versus azimuth
patternElevationPlot antenna or transducer element directivity and pattern versus elevation
stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object

Examples

collapse all

Find the response of an isotropic projector with default properties. Obtain the voltage response at five different elevation angles: -30°, -15°, 0°, 15° and 30°. All azimuth angles are set to 0°. The voltage response is computed at 2 kHz.

projector = phased.IsotropicProjector;
fc = 2e3;
resp = projector(fc,[0,0,0,0,0;-30,-15,0,15,30])
resp = 5×1

     1
     1
     1
     1
     1

Examine the response and patterns of an isotropic projector operating between 1 kHz and 10 kHz.

Set the projector parameters and obtain the voltage response at five different elevation angles: -30°, -15°, 0°, 15° and 30°. All elevation angles at 0° azimuth angle. The voltage response is computed at 2 kHz.

projector = phased.IsotropicProjector('FrequencyRange',[1,10]*1e3);
fc = 2e3;
resp = projector(fc,[0,0,0,0,0;-30,-15,0,15,30]);

Draw a 3-D plot of the voltage response.

pattern(projector,fc,[-180:180],[-90:90],'CoordinateSystem','polar', ...
    'Type','power')

Find the beamwidth of an isotropic underwater projector at 10 kHz.

First, create an isotropic projector element.

projector = phased.IsotropicProjector('FrequencyRange',[10 12000])
projector = 
  phased.IsotropicProjector with properties:

    VoltageResponse: 120
     FrequencyRange: [10 12000]
        BackBaffled: false

Then, use the beamwidth object function to plot the 3 dB beamwidth of the projector.

[bmw,angs] = beamwidth(projector,10000,'dbDown',3)
bmw = 360
angs = 1×2

  -180   180

Because the projector is isotropic, there is no 3 dB down point.

Examine the response and patterns of an isotropic projector at three different frequencies. The projector operates between 1 kHz and 10 kHz. Specify the voltage response as a vector.

Set up the projector parameters, and obtain the voltage response at 45° azimuth and 30° elevation. Compute the responses at signal frequencies of 2, 5, and 7 kHz.

projector = phased.IsotropicProjector('FrequencyRange',[1 10]*1e3, ...
    'VoltageResponse',[90 95 100 95 90]);
fc = [2e3 5e3 7e3];
resp = projector(fc,[45;30]);
resp
resp = 1×3

    0.0426    0.0903    0.0708

Next, draw a 2-D plot of the voltage response as a function of azimuth.

pattern(projector,fc,[-180:180],0,'CoordinateSystem','rectangular', ...
    'Type','power')

Figure contains an axes object. The axes object with title Azimuth Cut (elevation angle = 0.0°) contains 3 objects of type line. These objects represent 2 kHz, 5 kHz, 7 kHz.

Compute the directivity of an isotropic projector in different directions. Assume the signal frequency is 3 kHz. First, set the projector parameters.

fc = 3e3;
projector = phased.IsotropicProjector('FrequencyRange',[1,10]*1e3, ...
    'VoltageResponse',[100,110,120,110,100]);
patternElevation(projector,fc,45)

Select the angles of interest to be constant elevation angle at zero degrees. The five azimuth angles are centered around boresight (zero degrees azimuth and zero degrees elevation).

ang = [-20,-10,0,10,20; 0,0,0,0,0];

Compute the directivity along the constant elevation cut.

d = directivity(projector,fc,ang)
d = 5×1

     0
     0
     0
     0
     0

The directivity of an isotropic projector is zero in every direction.

Examine the azimuth pattern of an isotropic projector at 30° elevation. The frequency range is between 1 kHz and 10 kHz. Specify the voltage response as a scalar.

Set the projector parameters.

fc = 3e3;
projector = phased.IsotropicProjector('FrequencyRange',[1,10]*1e3, ...
    'VoltageResponse',-115);
patternAzimuth(projector,fc,30)

Plot a smaller range of azimuth angles using the Azimuth parameter.

patternAzimuth(projector,fc,30,'Azimuth',[-20:20])

Plot an elevation cut of the directivity of an isotropic projector at 45° azimuth. Assume the signal frequency is 3 kHz.

Create the isotropic projector object and call the pattern object function.

fc = 3e3;
projector = phased.IsotropicProjector('FrequencyRange',[1,10]*1e3, ...
    'VoltageResponse',70);
patternElevation(projector,fc,45)

Plot a smaller range of elevation angles using the Elevation parameter.

patternElevation(projector,fc,45,'Elevation',-20:20)

More About

expand all

References

[1] Urick, R.J. Principles of Underwater Sound. 3rd Edition. New York: Peninsula Publishing, 1996.

[2] Sherman, C.S., and J. Butler. Transducers and Arrays for Underwater Sound. New York: Springer, 2007.

[3] Allen, J.B., and D. Berkely. “Image method for efficiently simulating small-room acoustics”, Journal of the Acoustical Society of America. Vol. 65, No. 4. April 1979, , pp. 943–950.

[4] Van Trees, H. Optimum Array Processing. New York: Wiley-Interscience, 2002, pp. 274–304.

Extended Capabilities

Version History

Introduced in R2017a