
About Wave2000®
Wave2000®; is a standalone computer software program for computational
ultrasonics. It was produced to bring numerical simulation to the ultrasound
engineering community. This page provides some basic information about Wave2000® including
a general Program Overview, Hardware/Software/Memory
Requirements, and a brief description of the Wave Equation that
is being simulated.
Program Overview
Wave2000® is a standalone software package for computational ultrasonics.
It operates by solving the twodimensional (2D) acoustic (elastic and viscoelastic) wave equation
based on a method of finite differences. The solution is computationally intensive.
However, thanks to the ever increasing power and speed of computer hardware,
we at CyberLogic felt the time was right to bring such software packages to
the desktop and personal computer of the ultrasound engineer and researcher.
Wave2000® allows the user to compute the full acoustic wave
solution in an arbitrary twodimensional (2D) object, subjected to userspecified
acoustic sources. The program, besides simulating the complete spatial and
timedependent acoustic solution, allow the user to simulate ultrasound measurements
in a variety of source and receiver configurations. Wave2000® will prove
useful to researchers and applications engineers in such diverse fields as
nondestructive testing, materials evaluation, medical imaging and biological
tissue characterization. The software is useful also in basic mechanistic studies
and for academic applications. With Wave2000® the user can compute solutions
(e.g., scattered and reflected waveforms) to virtually an unlimited variety
of distinct physical problems without ever leaving the computer keyboard.
Wave2000® provides solutions to a broad range of 2D ultrasound problems.
The program allows the user to specify an arbitrary object which is ultrasonically
interrogated. The object is specified in a "PCX" image file. "PCX" is a "triedand
true" graphics file format which includes within it absolute size information,
a useful feature for the ultrasound simulations. The image data or object is
composed of individual pixels which can have 1 of 256 gray levels (0255).
Each pixel value represents a physical material (e.g., water, steel, etc.)
that is set by the user. Gray level 255 is reserved by Wave2000® to
denote void (i.e., vacuum). There is thus a vast variety of 2D structures which
can be processed using Wave2000®.
The 2D object or image can be generated either internally using Wave2000® "Geometry" routines
or externally using any graphics program (commercial or "inhouse") which can
output files in 8 bit monochrome "PCX" format. Additionally, the image may
be obtained from various scan modalities, for example CT or MRI slice data,
which has been converted to "PCX" format. Usually, a segmentation algorithm
of some kind would be necessary to properly associate various regions of the
image with a particular material (i.e., grey level). Although Wave2000® computes
solutions to 2D ultrasound problems, the solutions can be viewed as applying
to threedimensional objects which happen to be "quite long" in the dimensions
going into and out of the object plane. Of course, by "quite long" we mean
that the object extends from minus infinity to plus infinity, and that there
also is no change in the object crosssection along this dimension. Of course
this is hardly a "practical" experiment; nevertheless, the 2D simulations take
on a bit more "real world feel" when viewed in this "3D" way.
The attractiveness of Wave2000® is that it is very easy to generate
solutions to a wide variety of 2D ultrasound problems within a simple graphical
interface. The user has access to features designed to mimic reasonably closely
many practical situations. For example, there are source and receiver configurations
that the ultrasound engineer will notice are similar to real ultrasound experimental
configurations, for example the use of signals that characterize many transducer
generated waveforms. As one application, Wave2000® may be useful for
analyzing 2D wave propagation associated with transducerlike structures (e.g.,
layered) subject to various temporal (source) and static (boundary condition)
displacement boundary conditions, in the design of ultrasound transducers.
Wave2000® has the potential to generate new insights and approaches
to many problems in ultrasonics. For the first time, the user has the capability
to "experiment" to his or her heart's content, without turning on a pulserreceiver
or connecting a "BNC" cable. Indeed, the simulations can "run" while the user
is word processing a document or analyzing data from an earlier simulation.
The computer can work "around the clock" computing solutions to problems that
are difficult to perform in the laboratory or the field, but the results of
the simulations can provide important understanding and knowledge for future
experiments or for data already collected.
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Hardware, Software and Memory Requirements
Wave2000® is designed to run on any PC that has the Windows XP, Vista, 7 or 8 operating systems installed. Minimum hardware requirements
are extremely modest (for example 15 megabytes free hard disk space and 128
megabytes memory), although we recommend 1 GB or more memory for handling the
larger simulation models. (Detailed information on memory requirements can
be found in the 'Algorithm' topic of the Wave2000® User Guide Section
of the Help file.) Minimum graphics requirements are 256 color VGA and a compatible
mouse, but of course most systems will have hardware characteristics much higher
than these minimums. As noted, Wave2000® operates best with as much
RAM memory as possible, which allows problems of increasingly larger size to
be accommodated and avoids the need for virtual (disk) memory to be used. Note
also that Wave2000® supports multiprocessor systems, that allows
the program to potentially speedup the execution of the program. This is most
effective for "large" objects; experimentation by the user will determine when
multiprocessors can lead to faster execution times. The multiprocessors can
be either actual multiproccessor systems, or multicore processors, or both.
Wave2000® is a "memoryhungry" program; this is simply the nature
of the acoustic problem which is being simulated. To aid the user in assessing
the memory requirements for a particular simulation model, we can provide the
following approximate relationships.
The simplest approach for approximating memory needed is to multiply the number
of finite difference grid elements, N, by 30; this is the amount of memory
required in bytes (plus some additional "fixed" program overhead which can
usually be neglected in comparison to the 30 x N quantity). As an example,
if an object image is 3 cm x 4 cm and the pixel resolution ("Pixels/mm") is
10 pixels/mm, the number of pixels in this image will be 300 x 400 = 120,000
pixels. Now if we assume that the finite difference grid elements generated
by Wave2000® are coincident with the number of image pixels (i.e., Grid/Pixel
= 1), then the memory required is 30 x N = 30 x 120,000 = 3.4 megabytes.
Another perspective on memory requirements can be gained by determining the
memory needed as a function of object size in terms of wavelengths. In the
example above, it was assumed the the grid size was coincident with object
image pixel size, i.e., both were 0.1 mm square (10 pixels/mm). For the case
of a problem in which the minimum wavelength is about 1 mm, this 0.1 mm size
for the finite difference grid element should provide a reasonably accurate
solution. We may extend this reasoning for a more generic assessment of memory
requirements as follows. Assuming that we would like to have a grid element
dimension 10 times less than the minimum wavelength, then that implies that
100 x 30 = 3000 bytes for a square object 1 wavelength on a side. If one has
a square object which is 10 wavelengths on a side, then using the same relative
grid dimensions, Wave2000 would require about 10,000 x 30 = 293 kilobytes of
memory. One may also extend this approximation to any number of (minimum) wavelengths
to evaluate memory requirements. Assuming a rectangular object Q wavelengths
by R wavelengths in overall dimensions, and again assuming 10 grid elements
per wavelength, then the memory required for this model is approximately 30
x 100 x Q x R = 2.93 Q x R kilobytes. It is useful to also point out that the
minimum wavelength is inversely proportional to the frequency of the source
waveform. Therefore, if a simulation with a 1 MHz source waveform requires
1 megabyte of memory, then changing to a source waveform operating at 2 MHz
will generally require four times as much memory, or in this case 4 megabytes,
to be used. (This assumes that the same size object is used in both cases.)
Thus the user may want to carry out as many of his or her simulations as possible
with relatively low frequency sources, in order to reduce computational overhead.
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Wave Equation
The specific acoustic equation that is simulated in a Wave2000® simulation
is given by:
In the above equation, which applies in an isotropic elastic region,
ρ = material density [kg/m^3],
λ = first Lame constant [N/m^2],
μ = second Lame constant [N/m^2],
η = shear viscosity [Ns/m^2],
φ = bulk viscosity [Ns/m^2],
∇ = the gradient operator,
∇ • = the divergence operator,
∂ denotes the partial differential operator,
t = time [s],
and
w is a two dimensional column vector whose components are the x and y components of displacement of the medium at location (x,y), that is
w = [wx(x,y,t) wy(x,y,t)]'
where ' denotes matrix transpose. Wave2000 solves the above equation within each homogenous grid element of the object, and computes (and displays) the displacement vector at the intersection of 4 grid elements at each time step of the simulation. As noted above, the simulation explicitly satisfies the stress and displacement boundary conditions across each and every grid element of the simulation model. Additional information on the acoustic wave equation including the viscous loss component (i.e., the viscosity tensor) can be found in the excellent book by B. A. Auld entitled Acoustic Fields and Waves in Solids, Vols. 12, 2nd Edition, Krieger Publishing Company, Malabar, Florida, 1990.
Wave2000® does not implement "raytracing" or other "nongeneral" methods
in simulating ultrasound measurements. Rather, it is a comprehensive engineering
software package designed to compute the full and accurate solution to
practically any 2D ultrasonic problem. Wave2000® simulates data that
you would measure on the lab bench or in the field. In addition, it has an
easy to use graphical user interface allowing you to begin simulating complex
ultrasound problems in a matter of minutes after receiving your Wave2000® software.
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For features available in Wave2000®, you can look at Wave2000 page. For additional information, you may want to review several of our Wave2000
Examples. In addition you can download the program and obtain a free
time limited license for program evaluation by registering
with us and logging in. Information on pricing is
also available. Please Contact Us to discuss your
intended application(s) or for any other additional information you would
like to have on Wave2000®.
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