# Problem of beam focus point Answered

Hi.

I have problem of beam focus point.

As I ask before, I'm in trouble of prove modeling and result.

I designed concave transducer and fire sine wave, 200kHz, 1 pulse with 1 MPa (sine 0.2e6 1e6 0 1)

Here is my design.

Geometric focal point place 42.8 mm and I expect beam focal point is placed before geometric focal point.

Because in acoustics, beam focal point is formed before geometric focal point.

But result is different.

beam focal point is formed after geometric focal point.

It's not right from acoustics perspective.

I attach my hole code and ask you see this problem.

thanks.

HJ.

--------------------

mp omp 32

symb radius = 63.e-3

symb x1 = 0.0

symb x2 = $x1 + 21.e-3

symb x3 = $x2 + 43.11e-3

symb x4 = $x2 + 100.e-3

symb y1 = 0.0

symb y2 = $y1 + 45.94e-3

symb y3 = $y2 + 2.e-3

symb freqint = 0.2e6

symb wavevel = 1500

symb wavemin = $wavevel / $freqint

symb nelem = 75

symb box = $wavemin / $nelem

symb i1 = 1

symb i2 = $i1 + nint ( ( $x2 - $x1 ) / $box )

symb i3 = $i2 + nint ( ( $x3 - $x2 ) / $box )

symb i4 = $i2 + nint ( ( $x4 - $x2 ) / $box )

symb indgrd = $i4

symb j1 = 1

symb j2 = $j1 + nint ( ( $y2 - $y1 ) / $box )

symb j3 = $j2 + nint ( ( $y3 - $y2 ) / $box )

symb jndgrd = $j3

grid $indgrd $jndgrd axix /* 2D (axisymmetric) (or axiy)

geom

keypnt 4 3

end

symb #read ESWT_matr.prjmat

c -------------------------------------------------------------------------

(this is contents of ESWT_matr.prjmat)

symb epvacm = 8.854e-12 /* dielectric constant for vacumn

symb freqdamp = 1.e6 if noexist /* specified frequency for damping model

symb rmu0 = 1.2566e-6

axis

form vctr

defn posx car2 0. 0. 0. 1. 0. 0. 0. 1. 0.

defn negx car2 0. 0. 0. -1. 0. 0. 0. 1. 0.

defn posy car2 0. 0. 0. 0. 1. 0. 0. 0. 1.

defn negy car2 0. 0. 0. 0. -1. 0. 0. 0. 1.

defn posz car2 0. 0. 0. 0. 0. 1. 1. 0. 0.

defn negz car2 0. 0. 0. 0. 0. -1. 1. 0. 0.

end

matr

c -------------------------------------------------------------------------

c air : Air, room temp

c -------------------------------------------------------------------------

c

type elas

wvsp on

prop air 1.24 343. 0.

elec air $epvacm

symb eps = $epvacm * 1.0

elec air $eps

thrm air 1005. 0.026

c --------------------------------------------------------------

c type : MISC :

c name : vacm :

c desc : Vacuum, also use Void :

c --------------------------------------------------------------

wvsp on

type elas

prop vacm 0 0 0

symb eps = 1

symb aeps = $epvacm * $eps

elec vacm $aeps

c --------------------------------------------------------------

c type : NONLINEAR :

c name : waternl :

c desc : Water - nonlinear for Type TISU :

c --------------------------------------------------------------

wvsp on

type tisu

prop waternl 1000 1500 0 0.1 0.0 0.0

5 -2e+08 2e+08

sdmp waternl $freqdamp db 0.002 0 1e+06 2 0.01 1

thrm waternl 4178 0.58 0.58 0.58 1.0 0 0 0

symb eps = 1

symb aeps = $epvacm * $eps

elec waternl $aeps

copy waternl waternl_1

end

c -------------------------------------------------------------------------

site

regn air

regn waternl $i2 $i4 $j1 $j3

regn vacm $i1 $i2 $j1 $j2

cyln waternl Z 0.0 1.0 $x3 $y1 $radius $radius 0.0 0.0 0.0 0.0

end

boun

side xmin absr stnd

side xmax absr stnd

side ymin symm all

side ymax absr stnd

end

func sine $freqint 1e6 0. 1.

calc

pres aprs

max aprs pmin pmax

end

plod

pdef pld1 func /* choose driving function and name 'pld1'

matr mtt1 vacm out

sdf2 pld1 mtt1 vacm waternl /* replace with actual matr names

end

prcs /* run process step

symb #get { step } timestep

symb simtime = 150.e-6 /* Simulation Time

c symb simtime = 3.e-3

symb nexec = nint ( $simtime / $step )

symb nloops = 75

c symb nloops = 300

symb nexec_loop = nint ( $nexec / $nloops )

grph

set imag avi /* Movie generation

end

proc plot save

exec $nexec_loop

grph

nvew 4 1

colr tabl data 6 /* Set color table for data

plot 1

mirr y

plot aprs

plot pmax

plot pmin

imag /* Save frame of movie - creates AVI in folder when model executes fully

end

end$ proc

proc plot $nloops

stop /* return to command prompt

## 5 comments

Chloe AllisonHi there,

I had a look at your model and it seems like the focal point is where it should be according to your diagram.

Best Regards,

Chloe

Hyunjae SongHi Chloe

I can get result looks like correct.

But when I find maximum data position, that is not 63 mm.

The maximum value place on 64.5 mm

Is maximum pressure place at 63 mm in data?

Chloe AllisonHi,

The maximum pressure is at 64.7 mm getting the data out of the solver but if you take into account the thickness of the transducer at the beginning then the focal point is less than 63 mm as you expected.

Best Regards,

Chloe

Hyunjae SongHi. Chloe.

That's what I'm asking you.

In Acoustics, beam focus must place in front of geometric focus.

Maximum pressure must place before 63 mm but you said focal point is 63.

You and I did simulation using 'waternl' which have B/A factor.

Then it can't be like that.

I want to know how can I fix it.

Thanks.

Chloe AllisonHi H.J,

If you look at the dimensions of the model in the *.flxprt file, they seem to be different to the ones in your diagram. Transducer length = 20.9 mm, Transducer height = 45.94 mm

(I changed the name of the transducer material to trans so it is easier to see)

I would go back and check the geometry so these values match your diagram.

Best Regards,

Chloe

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