"Short Wave Sportfishing" wrote in message
...
On Mon, 21 Mar 2005 04:38:53 -0500, "Eisboch"
wrote:

~~ snippage ~~

Whatever floats your boat. Actually, I was trying to recall what limited
knowledge I have with ultrasonic nondestructive testing and how it may
(or
may not) apply in the moisture testing. Ultrasonics are used to test for
flaws or inclusions in welds, but can also be used for other materials to
measure thickness and changes in the density of the material. My bag was
thin films for optics and we but used many of the same laws (Snell's law
and
others) although we delt with the refractive index of a material rather
than
it's density. I donno ... just a thought.

Just so that I'm not missing something (which is possible - I'm not
the brightest bulb in the drawer), allow me to explain my thought
process here.

For one thing, water is relatively transparent to ultrasound under
normal conditions. It will reflect hard returns like thermoclines for
example and that is a density change I admit, but the distance from
the surface or transducer, the water is transparent. So in one sense,
yes, it does measure density.

However, when you are dealing with the presence of internal water in a
dense material, how to you measure it? To strain the bowl analogy a
little, what are you measuring for - the presence of a bowl or the
presence of water? If you reflect ultrasound into the bowl and get a
hard return, does that indicate that the entire bowl is solid or that
there is a hard bottom indicating the presence of a bowl?

To my simple mind, to test for the presence of water in any material
you start by measuring resistance to electrical signals (and the
argument can be made about density there also, but there is a subtle
difference). The more water, the less resistance and vice versa.

If you take a uncompromised piece of fiberglass as a base line, flip a
signal through it and use that as zero or base line, any changes have
to be due to decreased resistance to the signal.

Right?

Later,

Tom



No, actually I consider myself a middle of the road .... oh .... sorry ... I
forgot we were actually talking boats here.
Seriously - I don't know. I just never stopped to think about how a
non-invasive "moisture" meter worked.

Eisboch