Hi everyone
I simulate the ultrasound pressure and intensity distribution for a cylindrical transducer, the transducer, sensor mask, and the result is like below.
For the profile of distribution, it is really interesting. Does anyone know is there any principle of ultrasound physics that explain this?
Sorry for the fail of uploading. Here is another try from imageshack
Sorry for the fail of uploading. Here is another try from imageshack
Hello all
I set all the parameters, like attenuation coefficient, as close as to the real water. Then, when I increase the excitation amplitude(in MPa), the uniformity of the intensity distribution becomes better.
Is there any explanation for this?
Hi cge,
A couple of things to check:
1) Are you using a pressure or velocity source?
2) What is your source frequency, and how close is it to two points per wavelength? Do you see the same behaviour if you use a lower frequency?
3) Have you switched off the PML in the z-direction, i.e., by setting the optional input 'PMLAlpha', [2, 2, 0]?
Brad.
High Brad
Sorry for the late reply.
I am using a pressure source, a sine wave with an amplitude of 0.6MPa
The source frequency is 1.5 MHz
Media alpha power is set to 2
Media attenuation coefficient is set to 0.0022
Media propagation speed is set to 1540 m/s, density is the 1000 kg/m^3
I didn't swiched off the PML at Z direction, I set the PMLAlpha to 10 with thickness at 3 direction being 10 respectively.
The last firgure is for RMS pressure and average intensity has the similar profile.
Recently, I carried out a measurement of the cylindrical transducer, the result of pressure distribution is quite similar to the simulation result of a flat square transducer. The measurement was carried out using hydrophone.
For the distribution in the last figure, I remove the data of internal distribution in the figure.
According to my literature study and measurement, it seems that the simulation above is for a shear wave , which experience huge attenuation in water, rather than longitudinal wave. However I didn't set anything about the type of wave generated. Also, the waves generated in simulation for flat square and flat disk transdcuers(with their surface perpendicular to Z direction), were longitudinal waves. In my measurement for real transducer, it seems that the wave generated is albo longitudinal waves.
Does this related to the k-wave simulation tool?
Hi cge,
I'm not exactly sure what you are trying to simulate. Are you trying to replicate your experiment? From your figures above, it seems you have a square source and a cylindrical sensor mask.
A couple of things to check:
1) Is your source frequency close to two points per wavelength?
2) What do you see if you plot the pressure rather than intensity?
The current release of k-Wave only simulates longitudinal waves. This is valid if you are trying to model ultrasound waves in a fluid.
Brad.
Hi Brad
Yes, I am trying to replicate the experiment.
Here I am using a cylindrical source and a square sensor mask. So that I can know the distribution along the circle at certain height.
For the pressure plot, it is just the same.
I don't understand what do you mean by the source frequency close to two points per wavelength. Does that mean there are two grid contained per wavelength?
Best Regards
The frequency is 1.5MHz, with propagation speed to be 1540 m/s
I set the dx=dy=dz=0.25mm, the wavelength is 1.02 mm, will this affect?
Another thing is that for the flat square and flat disk simulation, especially the flat disk one, the simulation results matches with measurement and theories of beamforming for flat disk simulation quite well.
I think the cylindrical one(generating waves on its side wall as shown in previous figure) can be described by a square disk equiavelent model since if you cut the cylindrical one along one of its ridge and put the side wall on a plane, it is a square.
My measurement support this. But still I am wondering why I can't directly get the simulation result for the cylindrical one
Moreover, for the simulation of flat disk and flat square transducer, I am still using the settings identical to the cylindrical one. i.e:
attenuation coefficient=0.002 exponent power=2
propagation speed=1540m/s; frequency=1.5Mhz
dx=dy=dz=0.25mm
But for these simulation, the result is quite normal
Hi cge,
Perhaps you could post your code and a sketch of the experiment, and I can take a look.
Brad.
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