k-Wave

1. ChiaChin Li
   

   Member
   Joined: Mar '11
   Posts: 5

   Hi,

   According to Photoacoustic signal generation,
   P_initial = (Pulse laser energy)*(absorption coef.)*(Grueneisen coef.)
   I assume that pulsed laser energy and absorption coefficient are independent with Temperature. And Grueneisen coefficient is direct proportion with temperature.
   So I expect that I can simulate the result of PA signal peak values raise with temperature in direct proportion.

   I wanted to simulate PA signal changes in different cases of temperature(25-55 degree C: raising value of initial pressure and sound speed with temperature), absorption(25,50,83.33,250,500 cm^(-1): size of initial pressure spot), and ultrasound transducer(fc=5,10,25,50MHz) used for signal detection.

   The signal flow of my 1D simulation:
   http://imgur.com/Yoe34

   And the 1D simulated result in different absorption at 25 degree C:
   http://imgur.com/IW0SF

   Then I record the peak value of PA signals from 25 to 55 degree C, and make the PA signal changes as a function of temperature:
   http://imgur.com/v9p1B

   But the slope of PA signal and temperature as a function of center frequency showed strange tendency:
   http://imgur.com/XdqsC

   I thought the result in final picture(http://imgur.com/XdqsC) should be constant of center frequency. But it shows surprising result. Did I do any wrong settings? Could you help me solve my problem?

   Thanks a lot.

   Chia-Chin

   Posted 12 years ago #

2. bencox
   

   Developer
   Joined: Mar '10
   Posts: 285

   Dear Chia-Chin,

   Apologies for the delay in replying, we've both been away.

   The graphs of the slope vs centre frequency don't seem to agree with the previous graphs showing the amplitude changes as a function of temperature. Are they from the same data set?

   There are a couple of things we can think of straight off:

   Do you still see the change in the slopes when you don't include the sound speed change with temperature? Is it just a function of the temperature dependence of the sound speed?

   There will be some dispersion associated with the absorption which may change the shape of the pulse a bit (although this may not be a large effect).

   Ben

   Posted 12 years ago #

3. ChiaChin Li
   

   Member
   Joined: Mar '11
   Posts: 5

   Hi Ben,

   I repeat my simulation without speed change. And all the slopes were the same in different absorption and frequency response of US transducers used for detection. The sound speed as a temperature function is:

   speed = 1.40238742e3 +T_current*5.03821344 -T_current^2*5.80539349e-2 +T_current^3*3.32000870e-4 -T_current^4*1.445379e-6 +T_current^5*2.99408365e-9; %[m/s]

   (from: http://resource.npl.co.uk/acoustics/techguides/soundpurewater/content.html#BILANIUK )

   And it seems like that the dispersion associated with the absorption will not effect the slopes. But from the equation of PA signal generation, the peak value of detected PA signal should not change with different sound velocities. What information of my simulation should I offer to you to solve my problem?

   Thanks for your help!

   Chia-Chin

   Posted 12 years ago #

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