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Topic: Density sensor of solids (Read 22740 times) previous topic - next topic


It remains a dubious claim,  in my opinion.

There are many different ways in which wood "loses mechanical properties".   Abrasion,  rot,  fatigue, splitting, variations in moisture.
To assume this is related to "loss of mass",  or indeed "density",  seems naive.  Wood also shrinks and swells under various conditions,
which, by definition, affects the density.

You refer to wood rotting.  This usually involves the wood becoming wet.  Wood which has become wet,  and is rotting,  will
appear to have a higher density than it had when it was dry.

Then there are hundreds of species of wood to consider.


You refer to ultrasound testing of wood.   That's a good approach.   Sound wood will tend
to transmit sound,  unsound wood will tend to absorb it.   You can measure the rate of attenuation
of the ultrasound and draw conclusions from that.

Be that as it may,  there are many ways wood can become unsound,  without "losing mass", as you claim.


In thinking about this and some of my knowledge about materials, it seems to me a great deal of information about the density of material could be derived from sound waves. The frequency of sound traveling through dense material is different than when moving through lighter weight material. For example, we already know sound waves move faster through dense material. Also, working with various acoustic material, we know that spongy material absorbs sound. Higher density sponge rubber, for example, has a sound deadening effect while hard material can have a completely different sound response. Playing around with different frequencies and volume of vibrations through different materials, you could establish a record of the condition - density - of the material.

Suppose you might attach a piezo element to a piece of wood and cause it to vibrate at say, 20 kHz. By recording the vibration frequency and volume at some set distance from the emitter, through the material with a microphone or vibration sensor, you could conceivably establish a record of how the material might change over time. In speculating about it, fresh, 10% moist oak might have a readable difference if it were dried to 5%, or soaked to 15%. One could conceivably test a sample of dry-rotted wood or termite infested wood with the same device and eventually establish some sort of background record that would let you alert to the actual condition of the material in question. I know for a fact that wet wood transmits vibrations in an entirely different way than dry, so this method could establish "test points" in a structure to determine if the wood is suffering intermittent or continuous wetting in place that might be hidden from easy inspection, thus pinpointing serious conditions before they become a more extensive problem.

Just a thought.

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