Modelling A Linear Array Transducer

Hello, I have resolved the issue mentioned in the post. Now I am encountering a new problem: I have set the array elements at the xoffset position, but I am receiving very weak echo signals. Why is this happening, and how should I consider resolving it? Here is the code. Thank you for your reply.% 引导线性阵列示例
clearvars;

% =========================================================================
% 模拟
% ========================================================================
% 创建计算网格
Nx = 400; % x 方向的网格点数
Ny = Nx; % y 方向的网格点数
dx = 0.1e-3; % x 方向的网格点间距 [m]
dy = dx; % y 方向的网格点间距 [m]
kgrid = kWaveGrid(Nx, dx, Ny, dy);

% 定义介质属性
sound_speed_water = 1500; % 水声速 [m/s]
density_water = 1000; % 水密度 [kg/m^3]
sound_speed_acrylic = 2700; % 亚克力声速 [m/s]
density_acrylic = 1190; % 亚克力密度 [kg/m^3]
sound_speed_aluminum = 6300; % 铝声速 [m/s]
density_aluminum = 2690; % 铝密度 [kg/m^3]

% 创建时间数组
t_end = 45.5e-6; % [s]
kgrid.makeTime(sound_speed_acrylic, [], t_end); % acrylic

% 定义线性换能器的参数
num_elements = 36; % [阵元数量]
x_offset = 20; % [网格点]
element_width = 1; % 定义阵元宽度为1个网格点
source_focus = 0.13; % 聚焦深度 [m]
element_pitch = 0.3e-3; % 每个阵元的间距 [m]
source.p_mask = zeros(Nx, Ny);

% 计算发射阵元的起始位置
transducer_width = num_elements * (element_width + 2); % 发射阵元总宽度，包含间隔
start_index = round(Ny/2 - transducer_width/2); % y方向的起始位置

% 计算每个阵元的时间延迟
ids = (0:num_elements - 1); % 阵元索引
time_delays = -(sqrt((ids .* element_pitch).^2 + source_focus.^2) - source_focus) ./ sound_speed_water;
time_delays = time_delays - min(time_delays); % 归一化时间延迟

% 定义用于驱动换能器的音调脉冲属性
sampling_freq = 75e6; % [Hz]
tone_burst_freq = 7.5e6; % [Hz]
tone_burst_cycles = 1;

% 定义回波数据存储三维矩阵
num_scans = 128 - 36 + 1; % 扫描次数
num_time_points = length(kgrid.t_array); % 修正时间点数为 kgrid.t_array 的长度
echo_data = zeros(num_scans, num_elements, num_time_points); % 初始化三维矩阵

% 创建音调脉冲信号，为每个阵元生成时间序列
source.p = zeros(num_elements, length(kgrid.t_array)); % 初始化源信号矩阵
for i = 1:num_elements
pulse = toneBurst(sampling_freq, tone_burst_freq, tone_burst_cycles, ...
'SignalOffset', time_delays(i));
source.p(i, 1:length(pulse)) = 20 * pulse; %加了20倍更明显
end

% 分配输入选项
input_args = {'DisplayMask', source.p_mask};

% =========================================================================
% 定义传感器
% =========================================================================
sensor.mask = zeros(Nx, Ny); % 初始化传感器蒙版
sensor.record = {'p'}; % 记录声压

% =========================================================================
% 定义三层介质，包含孔缺陷
% =========================================================================
% 创建声速和密度的映射
sound_speed_map = zeros(Nx, Ny); % 初始化为零矩阵
density_map = zeros(Nx, Ny); % 初始化为零矩阵

% 设置水层的位置（上层）
water_height = round(10e-3 / dy); % 水层高度 10 mm
for i = 1:water_height
sound_speed_map(i, :) = sound_speed_water; % 水声速
density_map(i, :) = density_water; % 水密度
end

% 设置亚克力层的位置（中层）
acrylic_height = round(10e-3 / dy); % 亚克力层高度 10 mm
for i = water_height + 1:water_height + acrylic_height
sound_speed_map(i, :) = sound_speed_acrylic; % 亚克力声速
density_map(i, :) = density_acrylic; % 亚克力密度
end

% 设置铝层的位置（下层）
aluminum_height = round(20e-3 / dy); % 铝层高度 20 mm
for i = water_height + acrylic_height + 1:water_height + acrylic_height + aluminum_height
sound_speed_map(i, :) = sound_speed_aluminum; % 铝层声速
density_map(i, :) = density_aluminum; % 铝层密度
end

% 定义缺陷位置（孔）
radius = 1e-3; % 孔的半径
x_center = 300; % 网格中心
y_center = 200; % 孔在亚克力层中间
defect_region = makeDisc(Nx, Ny, x_center, y_center, round(radius/dx), 2 * pi);
sound_speed_map(defect_region == 1) = sound_speed_water; % 孔区域设置为水的声速
density_map(defect_region == 1) = density_water; % 孔区域设置为水的密度

% 更新介质属性
medium.sound_speed = sound_speed_map; % 使用有效字段
medium.density = density_map; % 使用有效字段

% 从第128个网格点开始进行扫描
start_scan_index = 128; % 设置起始扫描位置
for scan_index = 0:2:(2 * (num_scans - 1)) % 每次跨越两个网格
% 当前发射阵元的起始位置
current_position = start_scan_index + scan_index; % 网格位置从 128 开始

% 更新发射阵元的掩码
source.p_mask(:) = 0; % 清除之前的掩码
start_index = current_position - round(num_elements/2) * (element_width + 2); % 计算当前起始索引
for i = 0:num_elements - 1
% 仅在阵元位置设置掩码
source.p_mask(x_offset, start_index + i * (element_width + 2)) = 1;
end

% 运行模拟
sensor.mask = zeros(Nx, Ny); % 初始化传感器蒙版
sensor.mask(x_offset, start_index:start_index + (num_elements - 1) * (element_width + 2)) = 0; % 清空传感器蒙版
for i = 0:num_elements - 1
% 仅在阵元位置设置传感器蒙版
sensor.mask(x_offset, start_index + i * (element_width + 2)) = 1; %原来是x_offset，改成的100
end
sensor.record = {'p'}; % 记录声压

% 运行模拟
sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor, input_args{:});

% 存储回波数据，确保维度匹配
echo_data(scan_index / 2 + 1, :, :) = sensor_data.p; % 存储回波数据
end

% =========================================================================
% 可视化
% =========================================================================
figure;
plot(sensor_data.p(21,:));
xlabel('时间点');
ylabel('声压 [Pa]');
title('最后一次扫描的声压信号');

% 绘制特定扫描的接收到的信号（例如第5次扫描）
figure;
plot(squeeze(echo_data(5, :, :))); % 选择特定扫描和阵元的信号
xlabel('时间点');
ylabel('声压 [Pa]');
title('特定扫描的接收到的信号');

% 绘制所有回波数据的示例
figure;
stackedPlot(kgrid.t_array, squeeze(echo_data(5, :, :)));
xlabel('时间 [s]');
ylabel('回波信号');
title('所有数据的示例');

k-Wave

A MATLAB toolbox for the time-domain
simulation of acoustic wave fields