Wave2000 Example #1:
Layered media measurements using pulse-echo ultrasound.
The figure below and associated legend represent a layered ultrasound propagation
problem. Wave2000 has a pseudo-color display related to material definitions
which is shown here. Thus, in this model there are three material layers making
up the overall object, aluminum, titanium and chromium, going from left to
right across the screen. Also shown is a 0.5 cm transducer located at the center
of the left side of the object. This transducer has been defined in Wave2000
to operate in pulse-echo mode.
Wave2000 generates "step-by-step" images of the propagating ultrasound
wave. The ultrasound "movie" below displays a 1 MHz sine wave with
a Gaussian envelope propagating into the layered structure from the left
surface. The diffraction spreading of the wave from the transducer can
be seen, while the wave is reflected and transmitted at the boundaries
of the layers. The boundaries are displayed as a light pixel value proportional
to the gradient between the two regions.
Wave2000 plots and/or saves all transducer source and/or receiver data. The
figure below displays a receiver plot associated with this layered simulation
model. The graph shows the measurements associated with the pulse-echo receiver.
As may be seen, the source waveform (in blue) is displayed at the very beginning
of the plotted signal. The reflected waveform measured by the receiving portion
of the pulse-echo transducer is shown in red. On this curve, the first identifiable
waveform is the reflection from the first (aluminum/titanium) interface, occurring
at about 4 us. Following that, the next main portion of the waveform is the
reflection associated with the second (titanium/chromium) interface, occurring
at about 8 us. The last well defined reflection is that associated with the
vacuum portion of the object (i.e., the reflection associated with the chromium/vacuum
interface at the right side of the object), and occurs at about 11 us. You
can also observe the presence of later arriving signal energy, representing
multiple reflections as well as mode conversions. Note that the stated arrival
times are the round trip travel times for the ultrasound signals.
In Wave2000, ultrasound simulations can be easily adapted to model various
changes to the interrogated object. For example, Wave2000 can model
the effects of non-parallel material layers as easily as it simulates this
parallel interface model. It is interesting to note in this example that
the source transducer gives rise to a significant amount of diffraction
spreading and as a result a related amount of non-normal incidence of the
ultrasonic wavefront onto the boundaries (and the associated shear waves
generated by mode conversion). These phenomena are all accounted for in
a Wave2000 simulation.