PSN-L Email List Message

Subject: Re: Instrument sensitivity
From: Geoffrey gmvoeth@...........
Date: Sun, 4 Mar 2012 22:28:48 +0000



Speaking on Musical Instruments may there be a sensor
used in electronic guitars or other like chellos
or bass instruments which may be used
for seismic also ?


I know these things are expensive.
A guitar pickup can be like 100.00 USD
and that makes it too expensive
for me to play with.



On 3/2/2012 12:49 PM, Randall Peters wrote:
> Of course a force equilibrium is necessary for a seismometer to operate, requiring for a vertical instrument that the weight of the inertial mass plus associated parts be balanced by an equal and opposite force provided by an element such as a (i) spring, or (ii) fluid through buoyancy, or (iii) magnetic force involving feedback to eliminate an otherwise unstable equilibrium because of Earnshaw's theorem.  And if really sophisticated, that upward force can be due to the Meisner effect (repulsion) involving a superconductor.  There is even the possibility of a superconducting force that is one of attraction rather than repulsion, involving the 'suspension' effect.  But no matter what the source of the balancing force, sensitivity is governed by the potential energy function that fully describes the physical properties of the opposing force pair.  The magnitude of the restoring force that brings the mass back to equilibrium after a disturbance is obtained by taking the deriv
ative of the potential.  The more shallow the potential, the longer is the period, and the sensitivity is proportional to the square of the period for such a system.  One possible means for obtaining a shallow potential and thus high sensitivity is based on the physics of an archer's compound bow.  The following link gives information (including photos) of one that was exhibited at the 'broadband conference' several years ago.  
> http://www.iris.edu/stations/seisWorkshop04/PDF/CompoundVerticalSeismometer.pdf
> There were some discussions of this approach here on the list-serve about three years ago; but perhaps the concept is worthy of a re-visit--especially for new readers of the ideas we generate.
> For one wanting additional physics to what can be gleaned from the site indicated above, there is also an article at
> http://physics.mercer.edu/petepag/combow.html
> 
> Randall Peters
> 
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