Hi,
I always had a hard time understanding the gain problem of kwave in phased-array ultrasonic focusing. I used 1MPa pressure source signal to stimulate my 64 elements to focus. Why is the maximum value of p_rms at the focus only 5*10e4Pa?I just did a little experiment where I emitted a 10Pa pulse at source.p_mask(32,32,1)，a pulse signal with an amplitude of 0.03pa was received at the sensor.mask(32,32,32),it's down 333 times.
medium.sound_speed = 1500*ones(Nx,Ny,Nz) ; medium.density = 1000*ones(Nx,Ny,Nz);
So,how do I get the right focus gain?
k-Wave
A MATLAB toolbox for the time-domain
simulation of acoustic wave fields
Focusing gain problem
(8 posts) (2 voices)-
Posted 4 years ago #
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in addition ,dx=1.5e-3,f=1MHz
Posted 4 years ago # -
Hi Jack,
It looks like your driving frequency is not supported by the grid. To meet Nyquist and make the PML work effectively, you need at least 3 points per acoustic wavelength. If c = 1500 m/s and f = 1e6 Hz, then lambda = 1.5 mm. Thus you need at dx <= 0.5 mm.
Brad.
Posted 4 years ago # -
Hi Bradley，
My mistake.In fact,my dx is 1.5e-4m,so how to explain this phenomenon?Posted 4 years ago # -
Is there anyone can explain the problem,dx=1.5e-4m,thanks
Posted 4 years ago # -
Hi jackYANG,
The focusing gain will depend on the size and curvature of your transducer elements, the driving frequency, and the distance from the elements to your detection position. It's plausible that if you have small elements and you're a long way away, you could have a much lower pressure due to the spreading of the wave. If you have disc or bowl shaped elements, there are analytical formula for the pressure on-axis. You could use these to calculate the expected pressure from each element at your expected focus to check your values.
Brad.
Posted 4 years ago # -
Hi Brad,
Thank you very much for your answer.But I still have a question that has been puzzling me,Kwave (spherical wave) of acoustic wave in three-dimensional space with the increase of propagation distance, how sound pressure will change, if the medium is water, under the condition of linear, according to the simulation, I do a small sound pressure fell sharply, how to achieve the sound pressure amplitude attenuation with the propagation distance for normal, such as water under the weak attenuation of sonic basic little change along with the propagation distance (personal opinion).jackYANG
Posted 4 years ago # -
Hi jackYANG,
For a point source, the pressure will decay with 1/distance. You can check this by making your source mask a single point, and then recording the pressure at two points along the axis away from the source, and comparing the amplitude (be sure to have absorption and nonlinearity turned off).
Brad.
Posted 4 years ago #
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