The idea to measure vibration with
ultrasound is surely relatively old. But we know only one such work,
made about 20 years ago in Wroclaw (at the Technical University). Even a
patent application was made.
We have proposed this idea in a project made for Prof. Zygmunt Pawłowski
for the Music Academy in Warsaw. Some years ago he has made a pioneer
work, measuring vibrations of the head and face of singing people, using
optical holography. We have proposed to use for this purpose acoustical
method and have had a success.
The method has some advantages in comparison to other methods for
contactless measurement of vibrations:
1. The shape and the kind of the surface, that vibrate does not matter.
2. It is possible to measure from relatively large distance (even some
meter are possible)
3. Electronics, that is necessary for this method is relatively simple
and not expensive. This allows to build devices, that can measure the
picture of vibration of larger surfaces, using many channels. Similar
devices using laser vibrometry would be very expensive.
4. It is possible to measure exactly the amplitude of vibrations.
The sensitive of the method is now in the region of 0.1 micrometer
vibration amplitude, but it can be improved.
There are also some disadvantages of this method: It is sensitive to
strong movements of the air. But it seems, that it can be also improved
from this point of view.
The first prototypes, that we have created some years ago was based on
the measurement of phase of continuous wave. Now we have a product, that
is based on pulse analysis and described here
