数值解
close all,clc,clear all
z = 1.5;
f1 = 2.5e3;
f2 = 15e3;
B1 = f2-f1; % 带宽15-2.5=12.5KHz
T = 0.719e-3; % 脉宽0.719ms
k = 1.7e7; % K=B/T
Fs = 10*15e4; % 采样率
N = 1; %控制窗口长度
c = 1480; %Speed of sound in water
t = 0:1/Fs:N*T-1/Fs;
z_temp = 0:z/length(t):z;
A = 1;
P0 = 1;
w = 2*pi*5*f2;
% K = B/T;S
Beta = 1.2; % Coefficient of non-linearity
c = 1480; % Speed of sound in water
rho = 1.07; % Density of medium
alpha = 0.4; % Absorption Coefficient of ultrasound carrier
s = 1; % Cross sectional area in metres^2
Et = A*cos(2*pi*(f1*t+k*t.^2/2)); %包络
Y = abs(fft(Et));
Y_nom = (Y-min(Y))/(max(Y)-min(Y));
f = Fs*(0:length(Y_nom))/length(Y_nom);
% figure;plot(t,Et);title('发射信号包络时域波形图'),xlabel('t (s)'),ylabel('幅度')
%% 某一位置,变化的时间
t_temp = 0;
Et_delay = A*cos(2*pi*(f1*(t