Re: Thermal Waves ?

[Bernard Cleyet <anngeorg@PACBELL.NET>]

Evidently the dissipation (diffusion) at high frequencies is sufficiently low
(small?) that one can use it for such imaging.  How is this essentially different
from A and B scan? (ultrasonic ruler for the eye or 2 D imaging for the fetus,
breasts lumps, etc.)

Ludwik!   http://www.eng.vt.edu/fluids/msc/super/super-f.htm   should do for your
question.

bc  who made carbon bolometers for "our" apparatus at UCSC

This posting is the position of the writer, and that of Landau, Ginzburg, Tiza,
Rudnick, et al.



Brian Whatcott wrote:

> At 07:44 AM 11/23/02, you wrote:
> > What is "second sound?"
> > ...
> > A sample is slowly scanned by a focused beam of laser light
> > of small power (not to burn anything at a focus). The beam
> > intensity is modulated by a mechanical chopper; that is how
> > the frequency can be chosen. Sound waves, produced at the
> > irradiated spot, are picked by a piezoelectric microphone.
> >
> > The signal is so small (microvolts) that a lock-in amplifier is
> > needed. The output voltage V, produced by the amplifier,
> > changes as the light beam goes from one spot on the surface
> > to another. The V(y,z) happens to be a good map of the
> > invisible structure below the shiny surface of a Si chip. The
> > n and p doped regions were recognizable in the illustration
> > as well as mechanical cracks and other defects. The speaker
> > said that instruments of that kind have been used in industry
> > since 1970's.
> > Ludwik Kowalski
>
> This technique is reminiscent of the acoustic microscope,
>   which can use signal sources as high as 100 MHz to illuminate
> opaque specimens at high resolution, and whose signal does
> not decay so rapidly as a thermal pulse would.
>
> In this connection, it always seemed a shame to me, that an
> underground house would need to be so deep in order to have
> the day's heating arrive at the coldest hour of night, that the
> temperature would already have stabilized to the unvarying
> seasonal average, the diurnal variation subsided to the
> noise level.
>
> Brian Whatcott
>    Altus OK                      Eureka!

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.