Medical Developments - March 2009
Motion in Review
Negative-Stiffness Vibration Isolation
By Dr. David L. Platus, President and Founder, Minus
K Technology, Inc.
LED BY PROFESSOR LAWRENCE E. COHEN PH.D.OF YALE UNIVERSITY'S
DEPARTMENT OF CELLULAR AND MOLECULAR PHYSIOLOGY, the
small lab in room BE58 at the Yale School of Medicine has
been conducting research on neuronal activity in brain cells
to develop methods for imaging brain activity, and then
uses these methods to study the brain. The university has
been developing the method for imaging brain activity for
42 years, but it was not until several years ago that the
lab opted to move to a higher level of vibration isolation
technology to support its microscopy-imaging.
It is not unusual for universities, and industry for that
matter, to have to deal with vibrations that compromise
the imaging quality and data sets that they acquire through
microscopy. Although it is certainly the desire of every
lab to rid the unwanted vibration, conventional systems
such as air tables, have not been successful in providing
an adequate level of vibration isolation for ultra-sensitive
equipment measuring at the Angstrom and micron levels.
Such was the case with Cohen's lab at Yale, where air tables
had been the mainstay for the lab's vibration isolation
for many, many years. But now, for adequate isolation to
conduct its neuronal research at the micron level, the air
tables were not able to provide the vibration isolation
needed for the lab's research.
"Monitoring many neurons or regions simultaneously
can improve our understanding about how nervous systems
are organized," Cohen continues. "For example,
the cells in your spinal cord have to get information from
your toe, and also send information to your toe. That signal
is a propagated electrical wave of membrane potential, and
dyeing that membrane can provide an optical signal that
is used to measure that propagated wave."
The lab uses a high-speed camera to view these changes.
It has a speed of 2,000 frames-per-second with very high
quantum efficiency, which is the quantity of photons that
get converted into electrons. The camera has a quantum efficiency
of about 0.9, which converts almost all the photons into
| In the lab's
optical monitoring of brain activity, each pixel in
the recording receives light from a small portion of
neurons which have been stained by microinjection of
the dye into the brain. After waiting for the dye to
spread into the processes, the dye can be used to monitor
changes in membrane potential in dendrites and axons.
When a low magnification objective is used to form an
image of a vertebrate preparation on the lab's 464 element
photodiode array, or 80 x 80 pixel CCD camera, each
pixel receives light from hundreds or thousands of neurons.
It is also using a variety of microscopes to conduct
this research including a laser scanning 2-photon microscope
and an optical microscope. At this time, only the optical
microscope is set on the Negative-Stiffness vibration
isolation system, built by Minus K Technology.
Yale University has implemented this Minus K Negative-Stiffness
Vibration Isolator in their Department of Cellular
and Molecular Physiology.
"Measuring in the dimension of microns still requires
vibration isolation because it is so small,'' Cohen says.
''Any small movement in the lab environment makes a big
effect. If you are viewing at 10 , and it vibrates by 10
, then you are in big trouble.
"We were using air tables before, but the Negative-Stiffness
isolator is much better," Cohen continues. "It
reduces the vibration by a larger faction because it reduces
the vibration in the X/Y plane just as well as in the Z
plane, where the air table does not do well at all on the
Negative-Stiffness isolators employ a unique - and completely
mechanical - concept in low-frequency vibration isolation.
Vertical-motion isolation is provided by a stiff spring
that supports a weight load, combined with a Negative-Stiffness
mechanism. The net vertical stiffness is made very low without
affecting the static load-supporting capability of the spring.
Beam-columns connected in series with the vertical-motion
isolator provide horizontal- motion isolation. The horizontal
stiffness of the beam-columns is reduced by the "beam-column"
effect. (A beam-column behaves as a spring combined with
a Negative-Stiffness mechanism.) The result is a compact
passive isolator capable of very low vertical and horizontal
natural frequencies and very high internal structural frequencies.
The isolators (adjusted to 1/2Hz) achieve 93% isolation
efficiency at 2 Hz; 99% at 5 Hz; and 99.7% at 10 Hz.
Putting up with lab vibration noise problems for any amount
of time, let alone for a period of years, can only be costly
in terms of lost production, and will certainly inhibit
the progress of the research. tmd
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