k-Wave Toolbox |

## Steering A Linear Array Example

On this page…
Overview Defining the linear array and input signal Running the simulation

### Overview

This example demonstrates how to use k-Wave to steer a tone burst from a linear array transducer in 2D. It builds on the Simulating Transducer Field Patterns Example.

- open the file in the MATLAB Editor
- run the file in MATLAB

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### Defining the linear array and input signal

The source mask is defined by creating a binary mask with the desired source points set to 1.

    % define source mask for a linear transducer with an odd number of elements
    num_elements = 21;      % [grid points]
    x_offset = 25;          % [grid points]
    source.p_mask = zeros(Nx, Ny);
    start_index = Ny/2 - round(num_elements/2) + 1;
    source.p_mask(x_offset, start_index:start_index + num_elements - 1) = 1;

The input signal to each element is then created using the function `toneBurst` with a geometrically steered temporal offset that varies across the source.

    % define the properties of the tone burst used to drive the transducer
    sampling_freq = 1/dt;   % [Hz]
    steering_angle = 30;    % [deg]
    element_spacing = dx;   % [m]
    tone_burst_freq = 1e6;  % [Hz]
    tone_burst_cycles = 8;

    % create an element index relative to the centre element of the transducer
    element_index = -(num_elements - 1)/2:(num_elements - 1)/2;

    % use geometric beam forming to calculate the tone burst offsets for each
    % transducer element based on the element index
    tone_burst_offset = 40 + element_spacing*element_index*sin(steering_angle*pi/180)/(medium.sound_speed*dt);

    % create the tone burst signals
    source.p = toneBurst(sampling_freq, tone_burst_freq, tone_burst_cycles, 'SignalOffset', tone_burst_offset);

A plot of the input signals for each transducer element is shown below.

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### Running the simulation

Visualisations of the pressure field at two different times for steering angles of +30 and -20 degrees are shown below.

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© 2009-2014 Bradley Treeby and Ben Cox.