1. Design Management:
“Open”, “Save”, or “Delete”: open, save, or delete an existing design from server in your
folder. <br/><br/>
“Download”: save the current design to your local computer. <br/><br/>
“Upload”: open an existing design from your local computer. <br/><br/>
Why save a design on server? <br/><br/>
By saving a design on the server, you may open and work on it from anywhere. You
don’t need bring it with you. <br/><br/>
Why save a design on you local computer? <br/><br/>
It is a good practice to save a high confidential design on your own local computer. In
this way, no one get your design information. On your local computer, you have much
more freedom for the file management.
2. Frequency:
All the frequency parameters are in MHz. <br/><br/>
'Center Frequency': transducer working frequency. <br/><br/>
'Scan Start Frequency' and 'Scan Stop Frequency' frequencies determine the frequency
range within which the model will be simulated. It normally covers the maximal
bandwidth of the transducer. 'Scan Start Frequency' is always smaller than 'Scan Stop
Frequency'. <br/><br/>
The KLM simulation is conducted in frequency domain. The time domain curves are also
affected by the scan frequency range.
3. Aperture
All the geometry parameters are in mm. <br/><br/>
The current simulation program provides two types of aperture geometry: round
and rectangle. <br/><br/>
Radius is the only input parameter for the round aperture. <br/><br/>
Length and width are the two parameters for the rectangle aperture. <br/><br/>
Area of the aperture will affect the transducer impedance. The bigger is the area,
the lower is the impedance.
4. Load
'Front Load': the acoustic media in front of transducer. It is normally water having
an acoustic impedance of 1.5MRayl. <br/><br/>
'Back Load': the acoustic media in back of transducer. It can be ignored if the
transducer has a backing layer, which will attenuate all the backward acoustic
energy. Otherwise, it is normally air having an acoustic impedance near to zero.
<br/><br/>
'Target Impedance': It is normally a piece of metal having an acoustic impedance
above 20MRayl. <br/><br/>
'Target Distance': The distance from transducer surface to the target, in mm.
5. Transceiver
Transmit impedance affects all the time domain curves. Most transmitters have
50Ohm impedance. <br/><br/>
Receive impedance affects the receiving acoustic impedance and all the receiver
related time domain curves. Receive impedance may be go to kilo ohm range
when there is a very short cable connects transceiver and the transducer,
otherwise receive impedance should be the same as the cable characteristic
impedance to keep echo signal integrity. <br/><br/>
A cable will have transmission line effect when its length is longer than ten to
twenty percent of wavelength. At 1MHz, ten percent of wavelength is about 20
meter. <br/><br/>
The program provides Burst and Gaussian type of electrical excitation for the
simulation. For Burst excitation, number of burst cycle is required input. For
Gaussian type excitation, the input is percentage bandwidth. The higher is the
percentage bandwidth, the shorter is the waveform. Excitation time domain
waveform and its spectrum can be viewed in the graph window. <br/><br/>
The delay parameters only shift the time domain curves for better display.
6. Cable
<img src='Cable1.PNG'></img><br/>
A transmission line is represented by four parameters:
<ul><li>R: unit series resistance, &#937/m </li>
<li>G: unit shunt conductance, siemens/m </li>
<li>C: unit shunt capacitance, uF/m </li>
<li>L: unit series inductance, uH/m </li>
</ul>
Characteristic impedance and propagation constant are two most important
derivative properties from R, G, C, and L. <br/><br/>
<img src='Cable2.PNG'></img><br/>
When R and G are zero, the transmission line become lossless. The characteristic
impedance is totally determined by C and L. The propagation constant became a
pure imaginary number and thus there will be no loss when wave travels within it.
<br/>
<img src='Cable3.PNG'></img><br/>
For lossless transmission line, only the length and the characteristic impedance
are required inputs. <br/><br/>
For lossy transmission, in additional to input group of R, G, C, L, another group
of input including characteristic impedance and attenuation coefficient can also
determines its properties. As shown in the above equations, &#945 determines the
attenuation. <br/><br/>
The reflection coefficient at the load side of transmission line is determined by the
impedance mismatch between the characteristic impedance and the load. For a
given length of transmission line, the total equivalent impedance Z(d) can be
calculated by the following equations: <br/><br/>
<img src='Cable4.PNG'></img><br/>
When the impedances match, reflection coefficient will become zero. <br/><br/>
C and L can be found from the cable data sheet provided by vendor. G normally
can be ignored for most applications. R can be measured using a multimeter.
7. Backing Layer
Backing layers provide acoustic damping to the transducer as well as mechanical
support. Only one backing layer is needed for most applications and its impedance is
around 3 to 7 MRayl. Higher impedance will increase the bandwidth but decrease the
sensitivity. For Doppler application, where wide bandwidth is not necessary, air
backing may be good to achieve a high sensitivity. Backing layer should have a high
attenuation property.<br/><br/>
Input backing layer starts from active layer in the model. Click "Insr" to insert a new
layer in front of the current layer. The new inserted layer will be closer to the active
layer. Click "Add a Backing Layer" appends a new layer to the current last
layer.<br/><br/>
Thickness of each backing layer can be entered in unit of mm or wavelength. The
new enter data will overwrite the previous one. .<br/><br/>
To change material property, click " Material" button will pop a new window for
material input.
8. Active Layer
Active layer is the PZT layer. In this window the thickness is the only
input.<br/><br/>
Thickness of the layer can be entered in unit of mm or wavelength. The new enter
data will overwrite the previous one. .<br/><br/>
To change material property, click " Material" button will pop a new window for
material input.
9. Matching Layer
Matching layers provide acoustic coupling between the transducer and acoustic
media. Multiple matching layers are necessary to achieve wider bandwidth. Normally
a matching layer has a thickness around its quarter wavelength. The matching layer
impedance is the square root the multiplication of its neighbors: Z=sqrt(Z1*Z2).
<br/><br/>
Input matching layer starts from active layer in the model. Click "Insr" to insert a new
layer in front of the current layer. The new inserted layer will be closer to the active
layer. Click "Add a Backing Layer" appends a new layer to the current last
layer.<br/><br/>
Thickness of each matching layer can be entered in unit of mm or wavelength. The
new enter data will overwrite the previous one. .<br/><br/>
To change material property, click " Material" button will pop a new window for
material input.
10. TransLgd:
Bn
B1
PZT
Back
Load
PZT M1
0 
C0 
C0 C’
Mn Water
VC
Target
t
SA
t
1
  
C0 
C '   2  sinc   
kt 
 0  
:1
 
  kt 
 0C0 Z C
1/ 2

  
 sinc 


 20 
As shown in the above figure, ultrasound transducer is represented by a three-port
network with two acoustic ports and one electrical port. The electrical port connects to
the transceiver and the acoustic port connects to acoustic media in both back and front of
the transducer. <br/><br/>
All the acoustic layers including backing layer, PZT layer, matching layer and acoustic
media are simulated by segments of transmission lines. The wave speed of the
transmission line is the acoustic speed of the material. The length of the transmission line
is the thickness of the corresponding layer. <br/><br/>
In addition to the transmission line segments, one transformer and two capacitors are
critical to the model. It can be seen from the equations that the piezoelectric coefficient
Kt is the main factor in addition to the geometry parameters. <br/><br/>
KLM simulation output can be divided into two categories: frequency domain and time
domain information. The frequency domain information includes the transducer transmit
electrical impedance and receiving acoustic impedance. The time domain information
includes impulse response for both transmit and receive, and two-way pulse echo under
given excitation. <br/><br/>
Considering a cable and matching electrical network may be inserted in between the
transceiver and the transducer, impedance or time domain curved can be checked at
multiple points along the electrical path. <br/><br/>
The KLM model doesn’t consider the aspect ratio of the transducer. Most material
properties provided by vendors are obtained from bulk volume and they will be true only
when transducer is in a large disk shape. When the aperture size is smaller compared to
about 5 times of wavelength, the material properties may need to be adjusted to achieve
more accurate simulation results.