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1. An Application Comparison: Air Tables versus Negative Stiffness Technology
2. Featured Product: BM-10 Low Profile Isolator Used Where Vertical Space Matters
3. Featured Application: Motion in Review-Negative-Stiffness Vibration Isolation at Yale University
4. Upcoming Nanotechnology Meetings and Webinars
5. Our latest Ad
6. Your comments and suggestions
Comparison: Air Tables versus Negative Stiffness Technology
Negative-stiffness vibration isolators provide a significant improvement over air tables in vibration-sensitive environments
Excerpted from MR0 Today - June/July 2008
air tables have been around for the better part of a half-century,
their usefulness as an efficient method for vibration isolation
is now being seriously challenged by the more compact and
effective Negative-Stiffness vibration isolators
For almost forty years pneumatic vibration isolators have been the mainstay for stabilizing industrial and academia's most critical micro-engineering instrumentation. But, just as technology has been steadily migrating from micro to nano, so has the need for more precise vibration isolation in microelectronics fabrication, industrial laser/optical systems and biological research. These so called "passive system" air tables are now being seriously challenged by the newer Negative-Stiffness vibration isolators. Negative-Stiffness isolation is rapidly gaining popularity in industrial and laboratory environments, and to no small degree because of its ability to effectively isolate vibration in diverse and challenging environments.
An isolator is used to solve a problem, and how bad the problem is determines the solution you need. Since the 1960's air tables have been used for isolation. Basically cans of air, they are still the most popular isolators used. But, air tables with resonant frequencies at 2 to 2-1/2 Hz can typically only handle vibrations down to about 8 to 10 Hz, not quite low enough for optimum performance with modern nano-equipment. Also, greater isolation efficiencies are needed in the frequency ranges air isolators can handle.
For purposes of clarity in scanning probe microscopes and interferometers, air tables are an inefficient isolation solution. The air systems have been adequate up until a few years ago when better isolation was required.
Because of its very high isolation efficiencies, Negative-Stiffness vibration isolation systems enable vibration-sensitive instruments such as scanning probe microscopes, micro-hardness testers, profilers and scanning electron microscopes to operate in harsh conditions and severe vibration environments that would not be practical with top-performance air tables and other pneumatic isolation systems.
Negative-Stiffness versus Air Isolation
Following are ten key points which demonstrate the benefits of Negative-Stiffness isolators compared to air isolation systems:
#1: Low Hertz Perturbations
An air table will amplify vibrations in a typical range of 2 to 7Hz, this is because of the natural frequencies where air tables resonate. All isolators will amplify at their resonant frequency, and then they will start isolating. So, with an air table, any vibration in that range could not only fail to be mitigated, it could be amplified. The low cycle perturbations would just come straight through to the instrument.
Negative-Stiffness isolators resonate at 0.5Hz. At this frequency there is almost no energy present. It would be very unusual to find a significant vibration at 0.5Hz.
#2: Image Clarity
Negative-Stiffness vibration isolation can reduce vibration noise levels in Atomic Force Microscopes, for example, by a factor of 2 to 3 when compared with top-performance air tables. This is particularly significant for noise levels in the sub-Angstrom range. This results in clearer images and features not discernable with pneumatic isolation systems.
#3: Severe Vibration Environments
As nano-equipment use becomes more prevalent, lab sites are being set up in much more severe vibration-prone environments, such as upper floors of buildings and clean rooms. Such severe vibration locations are too extreme for pneumatic isolators to effectively do their job.
But Negative-Stiffness isolators perform well in such environments, producing much better images and data than can be obtained with even the best high-performance air tables.
#4: Harsh Environments - Vacuums, High/Low Temperature Extremes, Radiation
Air tables are not particularly compatible when it comes to operating in vacuums, extreme high and low temperatures, and radiation. Yet these harsh operating environments are often necessary when conducting research and testing, such as with cryogenic chambers in semiconductor research.
All metal Negative-Stiffness systems can be configured which are compatible with high vacuums and other adverse environments, such as extreme high and low temperatures, and radiation. With vacuums, for example, Negative-Stiffness isolators can be used right inside the vacuum chambers. This offers other advantages such as much lower payload weights, more compact systems, and eliminates problems associated with vacuum chamber feed-through.
#5: Compressed Air
Air tables require a constant supply of compressed air. This requires either a dedicated compressed air line to be plumbed in to your lab, a tank of pressurized gas or a small compressor.
Even if you are lucky enough to have a dedicated compressed air line your table's location is still limited by the length of air line you have. Large tanks of compressed gas have to be mounted very securely to minimize their danger. Changing the tanks can be quite difficult and inconvenient as well. Compressors are sources of both mechanical and acoustic noise and are very poor choices from a vibration standpoint.
If you can get your nano-environment mechanically isolated without having to deal with compressed air to run your vibration isolator, then you will be better off. The nice thing about Negative-Stiffness isolators is they do not require compressed air. They operate purely in a mechanical mode. One less thing you have to worry about when you are setting up your lab and working in it.
#6: Location Selection for Vibration-Sensitive Equipment
Let's face it, air tables are big, bulky structures, they take up a lot of lab space. The high-performance air tables are even bigger. This can become a limiting factor when laying out the equipment in your lab.
Negative-Stiffness isolators are available in high-performance bench top configurations, considerably more compact than air tables and easy to move around. They are also available as workstations, tables and floor platforms where these configurations are required.
#7: Load Adjustment
Low-frequency passive vibration isolators are somewhat sensitive to small changes in weight loads, as well as to large displacements. Pneumatic systems utilize leveling valves to mitigate the problem.
Negative-Stiffness isolators provide a very simple manual adjustment to accommodate variations in weight loads. For applications where manual load adjustment is not practical they provide an auto-adjust system that maintains the isolator in a precise vertical equilibrium position.
#8: Scanning Probe Microscopes
Scanning Probe Microscopes (SPMs) have vibration isolation requirements that are unparalleled in the metrology world. The vertical axis is the most sensitive for most SPMs. They can also be quite sensitive to vibrations in the horizontal axes. In order to achieve the lowest possible noise floor, on the order of an Angstrom, isolation is always used.
Bench top air systems provide limited isolation vertically and very little isolation horizontally. Negative-Stiffness isolators provide increased isolation performance for SPMs over air tables, while offering better ease-of-use and no facility requirements.
Negative-Stiffness isolators have the flexibility of custom tailoring resonant frequencies vertically and horizontally.
#9: Laser/Optical Equipment
Laser and optical systems, whether used in an academic lab or in an industrial environment, are very susceptible to vibrations from the environment. These instruments almost always need vibration isolation. Traditionally, large air tables have been the isolators preferred for optical systems, but Negative-Stiffness isolators are becoming a popular choice. Negative-Stiffness isolators provide 10 to100 times the performance of air tables, depending on the vibration frequency.
Laser based interferometers are extremely sensitive devices that are capable of resolving nanometer scale motions and features. They often have very long mechanical paths which makes them even more sensitive to vibrations. The sophisticated modern ellipsometry techniques that allow this high performance rely on low noise to be able to detect fringe movement. Properly isolating an interferometer will allow it to provide the highest possible resolution.
Optical profilers have similar sensitivity to vibrations. Optical component systems are often quite complex. The long optical paths can lead to angular magnification of vibrations. Optical air tables can make the problems worse since they have a resonant frequency that often matches that of floor vibrations. Negative-Stiffness 0.5Hz isolators provide isolation in these environments when air tables simply cannot.
#10: Maintenance and Expense
Because Negative-Stiffness isolators utilize simple elastic structures and viscoelastic materials that deform, their isolation performance does not degrade with micromotions typical of laboratory floors and fabrication rooms, as do conventional pneumatic isolators.
Cost-wise, Negative-Stiffness isolators are comparably priced to air isolators or lower priced for many applications.
The Need for a Better Vibration Isolation Solution
The need for vibration isolation will continue to increase in importance as the precision of research and test applications embraces smaller and smaller magnitudes of scale.
As industrial researchers and universities continue to broaden their nano-tech work, necessitating more sensitive equipment and expanded lab facilities, vibration-handicapped environments will become more prevalent, and a better vibration isolation solution will be required than what has been available for the past almost half-century with air tables. It appears Negative-Stiffness vibration isolation will fill that void.
The full article can be found at: http://minusk.com/content/in-the-news/mro_today_june-july_2008.html
BM-10 bench top platform offers 10-100 times better performance
than a full size air table in a package only 4.6 inches
tall and 12 inches wide and deep. It also does this without
any air or electricity!
This vibration isolation platform is extremely easy to use and offers extreme performance. It offers a 1.5Hz horizontal natural frequency and our signature 0.5 Hz vertical natural frequency. There are only two adjustments. The BM-10 is perfect for new generations of small SPM's that require the highest performance in a very compact system.
This is the thinnest, smallest footprint, most portable, and most user-friendly isolator ever offered that is capable of delivering this level of performance.
The curve below shows the vertical ½ Hz performance of the BM-10. It offers 10-100 times better performance than an air table in a package many times smaller.
Minus K's BM-10 Bench Top Vibration Isolator
transmissibility curve with 1/2 Hz natural Frequency
The horizontal isolation performance of the BM-10 is the same as that of the BM-6.Applications have included the full spectrum from Scanning Probe Microscopes (AFM, STM, NSOM, etc) and Laser/Optical systems through neurosciences, electronics, and even audio reproduction.
Because Minus K products can be used under vacuum conditions and require no power for their operation, they have been used in applications ranging from ground tests of spacecraft to sensitive experiments where there can be no stray electromagnetic fields.
Negative-Stiffness Vibration Isolation at Yale University
Excerpted from Today's Medical Developments - March 2009
Motion in Review
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 electrons.
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.
"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 X/Y plane.
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.
The full article can be found at:
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