Gravity Geselleschaft
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Gravity waves passing through a piezo material such as crystalline quartz
or tourmaline cause varying charges across the crystal, resolvable to +one ten
thousandth of the charge on a single electron+ by a newly invented device, the
Quantum Dot Transistor (Elect. Eng. Times, June 24,'96)). A large phased array
of such detectors could be correlated to filter out noise to arbitrary levels of
sensitivity, and provide directionality. To avoid terrestrial noise, the array
could consist of a spread formation of small spacecraft using laser ranging to
monitor positions. Such a scheme may be sensitive enough for a practical "gravity
telescope".
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Homebrew Gravity Hacking-
To reduce non-gaussian interference, a global network of GPS
timebase-correlated cryogenically cooled crystals is proposed to allow
computational filtering of signal noise. Local arrays to allow effective
filtering of local noise. An array allows wave information such as phase as well
as simple periodicity.
This approach had potential advantages over traditional experiments
consisting of large metal rods with vibration transducers. One seeming advantage
is direct signal pickup by the antenna vs the use of a secondary transducer .
Alignment of the piezo crystal lattice with the gravity wave target-
It may be that a piezo crystal based gravity antenna allows better angular
resolution compared to previous designs. Potential off axis noise immunity,
combined with alignment at a tangent to the earth's surface, might greatly
mitigate gravitational noise from churning of the earth's interior (or even
the sun). With regard to angular resolution, a further intuition is that a high
aspect ratio is desirable for the crystal rod. It may be that a whisker shape,
alone or in an array, is best suited for experimentation. Arbitrarily large
antenna elements could be made by stacking piezo elements lengthwise, which may
prove necessary to achieve sufficient voltage sensitivity.
Active feedback control of the antenna-
The piezo effect works both ways- stress a crystal and a charge develops, or
charge a crystal and it stresses. (Piezo crystal behavior is based on a flexing
helical crystal lattice. As a kid I wondered why a little cloud in the shape
of a tornado could be faintly seen in a quartz/amethyst. It turns out that minor
impurities are sometimes carried along the crystallization front and deposited
in a ghostly image of the invisible structure.)
Variable stressing of the piezo antenna, by charging it, could offer a means
to tune it to specific resonances.
A key issue was how to deal with noise created by antenna dampening. It
would help if the antenna were resonant with the signal, but how does one build
a broadband tunable gravity antenna? One might use an array of variably tuned
antenna elements. A charge to the piezo crystal that changes its resonant
frequency might serve for fine tuning. A switched network of stacked crystals
might enable broad tuning.
Unstressing a crystal reduces its temperature and this might be a basis for
momentarrily reducing cryogenic temperature beyond what's otherwise practical.
Prestressing the crystal might allow more violent voltage and mechanical inputs.
A piezo stressed flywheel might hold together at monstrous RPM.
The original brainstorming group started from the premise that giant natural
crystals, as monstrous single molecules, may have unique properties otherwise
unavailable to science and engineering. Exploiting the fantastic precision of
such objects, down to the atomic scale, amounts to a sort of natural
nanotechnology.
A basic insight was that feeding a signal into a piezo crystal amounts to a "gravity
wave projector", albeit at a very weak level. This effect suggests several
cool applications. Communications might be possible between two crystals. Thus
the long awaited experimental confirmation of Einstein's prediction might be
determined at relatively low cost. An alternative is to just use the crystal as
a sensor using something like a big artillery piece to generate a gravity
pulse.
Phased arrays of crystal projectors could manipulate standing gravity waves
for such purposes as artificial gravity and "tractor beams". Gravity
wave emitter arrays could form the basis of future space propulsion systems.
A shaped stack of crystals can be pumped like a rail gun to build up
usable gravity pulses.
Date: Wed, 29 Apr 1998 13:57:54 -0700
From: jeremy rutman jeremy_rutman@bigfoot.com
To: gravity@zilker.net
Subject: piezo limits
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Wow-I was just in the dumps
(http://www.polycosmos.org/gravhack/mail.htm),
wondering what current limits on piezo sensitivity are
and thinking in any case interferometry is unbeatable.
Then I found:
RECORD NO.: 5408617 INSPEC Abstract No: A9623-8170C-069
AUTHOR: Fortunko, C.M.; Boltz, E.S.
CORP SOURCE: Mater. Reliability Div., Nat. Inst. of Stand. &
Technol.,
Boulder, CO, USA
TITLE: Comparison of absolute sensitivity limits of
various
ultrasonic and vibration transducers
SOURCE: Mater. Sci. Forum (Switzerland), Materials Science
Forum,
vol.210-213, pt.1, p. 471-8
ISSN: 0255-5476
"...of wide-band AE studies in metals. Furthermore, we find that
a new, conical, piezoelectric transducer, based on a
refinement of the NIST secondary-standard transducer,
appears to have sufficient sensitivity for such
applications. In particular, this new transducer is found to
exhibit absolute sensitivity that approaches the "thermal
rattle" limit in aluminum within 10 dB in the 250 kHz to 1
MHz region. Also, we show that the new transducer's noise
floor is below the noise floors of optical interferometers,
air-coupled capacitive transducers and EMATs"
First experiments-
The oldest traditions in fusion, aviation, and gravity wave reasearch, built experimental
devices with faint immediate hope. These devices were necessary
contemplation objects toward the detail engineering of true prototypes.
In this spirit I made crude devices from
cheap natural crystals, mountings, high voltage
sources, and commercial grade FETs. There was zero expectation of tangible results. The quick and dirty tests made with the hardware were almost purely ceremonial.
Machining crystals-
Preliminary work is underway to machine quartz cylinders
from natural samples. The Aztecs used reeds (!) with sand
abrasive and bow drills to machine quartz, so we will try brass
tubes on a machine lathe with a water-borne abrasive. The resulting
cylinders are to be polished to eliminate micro-flaws that as stress
concentrators promote violent mechanical failure of the crystal
under highly charged conditions.
A loose end is a comment at a Japanese gravity science Website (
http://www.icrr.u-tokyo.ac.jp/gr/English/theory/resonant.html ) that
piezo transducers on historic metal rod instruments did not work well
at cryogenic temperatures. I do not yet know if this applies only to
man-made ceramic piezo materials, or the magnitude of sensitivity
loss, if any, by supercooled quartz or tourmaline.
====included message=====
> 2) Please critique the following concept for a gravity wave
detector
> based on piezo effect-
>
> -Set up globally distributed network (an LBA to filter out local
> seismic and other noise) of machined giant quartz crystals
(available
> in 3' plus lengths or stack smaller crystals to long lengths) with
> crystal lattice precisely aligned with gravity wave source.
>
> -Proposed target source would be of a known period from
> electromagnetic evidence.
>
> -As gravity waves compress and stretch crystals along long axis a
few
> electrons should pop back and forth from a sensitive end mounted
> electrostatic pick up.
>
> -Use GPS timing signals to correlate the distributed nodes.
>
> -Use noise filtering techniques to sift for gravity wave signal.
>
Your scheme eliminates two major sources of error, seismic and
non-gaussian. Seismic is important at very low frequencies, say
lower than 100 Hz. Non-gaussian is the technical name for acts of
god, like a truck hitting your building, or a high energy cosmic ray
hitting your detector. Your scheme of putting multiple detectors at
different locations and then recombining the signal using timing info
etc. handles this nicely (although there could be problems with a
random event that effects the whole earth, say a sudden increase in
the solar wind leading to an increase in particles hitting the earth.
But still, millisecond timing should be able to eliminate these
events.)
However, at high frequencies, above 500 Hz or so, the major cause of
noise is thermal vibrations of the antenna. Regardless of the
material, its temperature causes noise. All operating antennas are
cooled to at least 4 K with liquid helium but even that is not cool
enough. The current goal is to cool a spherical antenna to 50 mK
using a dilution refrigerator.
Then you have noise from the damping in the antenna. The
dissipation/fluctuation theorem states that you will get noise from
any source of loss in a system. Since the antenna will always have
some loss (if you hit it, it won't ring forever) you will get noise
from that. So the goal is to minimize this. This is the famous "Q"
factor that we worry about so much. Using aluminum, current Q values
are around 10 million at 4 K. We need to have them up around 50
million.
That said, the problem with your quartz antennas might be the
ability, not just to construct them, but to do it in such a way to
get high Q. Using their piezoelectric properties to get an
electrical output, although a neat trick, is not that helpful. There
are currently mechanical transducers that can magnify the tiny
vibrations in an aluminum antenna enough without introducing too much
noise, that conventional electrical amplifiers can then amplify the
signal. Your scheme has the advantage of not requiring a second
mechanical system, which also needs to have a high Q. However, it
requires sophisticated knowledge of the mechanical properties of
quartz at low temperature. I don't know of anyone who has made
macroscopic objects out of quartz that have Qs of 10s of millions at
liquid helium temperatures. But if this a solved problem with an
industry capable of constructing such an antenna, it becomes an
attractive idea.
Gregg Harry gharry@wam.umd.edu
Active Damping/Exciting of piezo mass to manipulate bandwidth.-ds
http://www.nitehawk.com/Mystical.Crystal/atlcrpw.htm
================
A good background info. link-
http://www.piezo.com/histry.html
===============
http://www.pd.uwa.edu.au/Grav_Wave/AdvResMass.html
ADVANCED RESONANT-MASS GRAVITATIONAL WAVE
DETECTORS APPROACHING
QUANTUM LIMITED SENSITIVITY
Michael .E. Tobar
Australian International Gravitational Research Centre, Dept. of
Physics,
University of Western Australia, Perth, 6907, Australia
A large improvement is envisaged for the University of Western
Australia's (UWA) resonant-mass Gravitational Wave (GW) detector due
to a new type of parametric transducer constructed from low-loss
monocrystalline sapphire. Single pieces of crystals can be used as
both the resonant microwave transducer and a tuned resonant
mechanical mass. The sensitivity is determined by the acoustic losses
in the detector as well as the phase noise of the pump oscillator
driving the transducer. Newly developed cryogenic microwave
oscillators are now available with ultra-low noise levels of -165
dBc/Hz [1]. We project that this can be further reduced to -185
dBc/Hz with the advent of recent technology. Calculations suggest by
implementing this technology the noise temperature can be reduced
from a few mK to the order of micro Kelvin in a liquid helium
cryostat. This sensitivity can be achieved in the short term with
very little expense in comparison to the construction of an
interferometer, and is ideal for correlation experiments with the
proposed AIGO interferometer. Cryogenic sapphire transducer
technology presents a viable alternative to SQUID technology.
The quantum limit of a resonant mass at 4 K is of the order of a few
hundredths of a micro Kelvin. We show it is possible to measure such
a low noise temperature in a Sapphire Dielectric Bar Transducer
(SDBT).
[1] R.A. Woode, M.E. Tobar, E.N. Ivanov, D.G. Blair, An ultra-low
noise microwave oscillator based on a high-Q liquid nitrogen cooled
sapphire resonator, to be published in IEEE Trans. on UFFC, 1996.
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