Chris / Geoff -
The KS-36000 tri-axle, bore-hole seismometer was developed to detect
underground nuclear explosions. The follow-on instrument is the KS-54000.
This is one method of detecting violations of the Nuclear Test Ban Treaty,
so I guess you could say that Department of Defense has an interest in
seismology.
Bob Hancock
Three Points, AZ
_____
From: psn-l-request@.............. [mailto:psn-l-request@............... On
Behalf Of ChrisAtUpw@.......
Sent: Saturday, September 23, 2006 14:54
To: psn-l@..............
Subject: Re: Border Patrol Use Of Seismic Sensors
In a message dated 23/09/2006, gmvoeth@........... writes:
I understand the US Border Patrol has used seismic sensors for a long time
now to watch certain areas of the border for intruders / interlopers and I
was wondering what is the sensors they are using (make and model or type or
manufacturer)?
Hi Geoff,
Probably 8 to 10 Hz See http://www.geospacelp.com/industry2.shtml#geo
HSJ, GS20 etc, are quoted for 'intruder detection', but I have no direct
knowledge.
I can imagine the military doing this too around nuclear sites and such
critical areas where sensitive information is being collected / stored.
Why can't a seismic sensor be built into a microchip somehow ?
You can't get the low noise and the high sensitivity, partly due to gas
interactions in very small spaces and partly due to intrinsic material
noise. You also have Brownian noise / kT / frequency considerations. This
may limit you to weights of about an ounce.
Have the experts in the field of science ever experimented here ?
I would have expected them to have tried quite hard. The hysteretic
limitations of materials are fundamental and inherent, so their success is
likely to be limited.
Horizontal seismometer noise may be limited by the earth tides amongst
other disturbances, which cyclically alter the slope of the ground / angle
of gravity slightly. This noise may be 20 dB above the minimum vertical
noise, but it is fairly broadband in it's effects. See the annual noise
plots from seismic stations.
So we make a highly sensitive vertical sensor, where the mass is
balanced by a spring force. The dimensions of the apparatus are temperature
dependant and the spring constant is temperature dependant, but neither are
strictly linear, or of comparable magnitude. In general, it may not be too
difficult to reduce temperature effects by a factor of 10, but any further
improvement gets progressively much more difficult. Throw in the fact that
springs do not behave truly elastically and the whole problem gets quite
difficult. Springs with a very low temperature coefficient are inherently
magnetic, which can add other sources of noise. The STS1 probably represents
about the best that can be done commercially.
Are there any military secrets related to Geology ?
Don't know of any, but I would doubt it, due to the known fundamental
limitations of the properties of materials.
Anyone here know anything about the future of vibration sensors sensitive
enough and low noise enough down to or below the seismic noise level ?
The only candidates that I know of are PZT piezoelectric crystals and
simple pendulum developments. PZT crystals have quite a high temperature
dependence. You need to hold the temperature very constant.
Since the output of coil / magnet induction sensors goes to zero as the
frequency goes to zero, the use of direct position sensors has become
commonplace. The use of very low drift / low noise / long life semiconductor
circuits is essential. Magnetic sensors (LVDT) may be limited to about
10^-10 m due to their inherent Barkhausen (domain switching) noise.
Capacitative sensors may, with considerable effort, give another couple of
orders of magnitude sensitivity, but they still depend on the expansion rate
of materials for their stability. Fused quartz coated with various metals
and silver plated Invar are known plate materials.
Using velocity damping derived by differentiating the position signal is
inherently noisy. Providing electromagnetic damping directly is quieter and
it is relatively easy to do with NdFeB or Sm/Co magnet arrays.
The move from coil springs of the LaCoste type to leaf springs of the
Streckheisen type enabled the 'parasitic vibration' responses to be reduced.
A bent sheet of copper plate close to a leaf spring may be used to stabilise
the temperature. Small NdFeB magnets may be stuck to the leaf spring to
provide inductive damping with the copper plate.
Some additional research may well be desirable on suspension systems and
on overall designs to minimise the effects of intrinsic noise. The
realisation that seismic sensors do not follow the 'standard' damping curve
has quite profound implications. Extending the period of 'simple' vertical
pendulums may offer significant advances, but high performance linear
capacitative sensors are needed. See
http://physics.mercer.edu/hpage/peters.html We may need to provide a 'build
it yourself' general purpose design; maybe a circuit board?
Regards,
Chris Chapman
Chris / Geoff =
–
The KS-36000 tri-axle, bore-hole
seismometer was developed to detect underground nuclear =
explosions. The
follow-on instrument is the KS-54000. This is one method of =
detecting
violations of the Nuclear Test Ban Treaty, so I guess you could say that =
Department
of Defense has an interest in seismology.
Bob =
Hancock
Three Points, =
AZ
From:
psn-l-request@.............. [mailto:psn-l-request@............... =
On Behalf Of =
ChrisAtUpw@.......
Sent: Saturday, September =
23, 2006
14:54
To: psn-l@..............
Subject: Re: Border =
Patrol Use Of
Seismic Sensors
In a message dated 23/09/2006,
gmvoeth@........... writes:
I understand the US Border Patrol =
has
used seismic sensors for a long time now to watch certain areas of the =
border
for intruders / interlopers and I was wondering what is the sensors they =
are
using (make and model or type or =
manufacturer)?
Hi =
Geoff,
=
Probably 8 =
to 10
Hz See http://www.geospac=
elp.com/industry2.shtml#geo
HSJ, GS20 =
etc,
are quoted for 'intruder detection', but I have no direct =
knowledge.
I can imagine the military doing =
this too
around nuclear sites and such
critical areas where sensitive information is being collected / =
stored.
Why can't a seismic sensor be built into a microchip somehow =
?
You can't =
get the
low noise and the high sensitivity, partly due to gas interactions in =
very
small spaces and partly due to intrinsic material noise. You also have =
Brownian
noise / kT / frequency considerations. This may limit you to weights of =
about
an ounce.
Have the experts in the field of =
science
ever experimented here ?
I would =
have
expected them to have tried quite hard. The hysteretic limitations of =
materials
are fundamental and inherent, so their success is likely to be =
limited.
=
Horizontal
seismometer noise may be limited by the earth tides amongst other
disturbances, which cyclically alter the slope of the ground / angle of =
gravity
slightly. This noise may be 20 dB above the minimum vertical noise, but =
it is
fairly broadband in it's effects. See the annual noise plots from =
seismic
stations.
=
So we make =
a
highly sensitive vertical sensor, where the mass is balanced by a =
spring
force. The dimensions of the apparatus are temperature dependant and the =
spring
constant is temperature dependant, but neither are strictly linear, or =
of
comparable magnitude. In general, it may not be too difficult to reduce
temperature effects by a factor of 10, but any further improvement gets
progressively much more difficult. Throw in the fact that springs do not =
behave
truly elastically and the whole problem gets quite difficult. Springs =
with a
very low temperature coefficient are inherently magnetic, which can add =
other
sources of noise. The STS1 probably represents about the best that =
can be
done commercially.
Are there any military secrets =
related to
Geology ?
Don't know =
of
any, but I would doubt it, due to the known fundamental limitations of =
the
properties of materials.
Anyone here know anything about =
the
future of vibration sensors sensitive enough and low noise enough down =
to or
below the seismic noise level ?
The only
candidates that I know of are PZT piezoelectric crystals and simple =
pendulum
developments. PZT crystals have quite a high temperature =
dependence.
You need to hold the temperature very =
constant.
=
Since the =
output
of coil / magnet induction sensors goes to zero as the frequency goes to =
zero,
the use of direct position sensors has become commonplace. The use of =
very low
drift / low noise / long life semiconductor circuits is =
essential. Magnetic
sensors (LVDT) may be limited to about 10^-10 m due to their inherent
Barkhausen (domain switching) noise. Capacitative sensors may, with
considerable effort, give another couple of orders of magnitude
sensitivity, but they still depend on the expansion rate of materials =
for their
stability. Fused quartz coated with various metals and silver plated =
Invar are
known plate materials.
=
Using =
velocity
damping derived by differentiating the position signal is =
inherently
noisy. Providing electromagnetic damping directly is quieter and it is
relatively easy to do with NdFeB or Sm/Co magnet =
arrays.
=
The move =
from
coil springs of the LaCoste type to leaf springs of the Streckheisen =
type
enabled the 'parasitic vibration' responses to be reduced. A bent sheet =
of
copper plate close to a leaf spring may be used to stabilise the =
temperature.
Small NdFeB magnets may be stuck to the leaf spring to provide inductive
damping with the copper plate.
=
Some =
additional
research may well be desirable on suspension systems and on overall =
designs to
minimise the effects of intrinsic noise. The realisation that seismic =
sensors
do not follow the 'standard' damping curve has quite profound =
implications.
Extending the period of 'simple' vertical pendulums may offer =
significant
advances, but high performance linear capacitative sensors are needed. =
See http://physics.merce=
r.edu/hpage/peters.html
We may need to provide a 'build it yourself' general purpose design; =
maybe a
circuit board?
=
Regards,
=
Chris =
Chapman