Vibration isolation: Negative stiffness vs Pneumatic Systems

For decades, pneumatic air tables have been the workhorse for reducing vibrations in cleanrooms for manufacturing and research, where critical micro-engineering instrumentation is employed. But just as technology has steadily pushed the boundaries into nano-applications in microelectronics fabrication, industrial laser/optical systems and biological research, so has the need become ever more necessary for improved precision in vibration isolation.

Increasingly, pneumatic air tables are taking a back seat to the more recent technology of negative-stiffness vibration isolation, which over the past 20 years since its introduction, has proven itself in thousands of applications throughout industry, government and academia, including some of the most diverse and challenging environments, such as cleanrooms.

Vibration Sources
Vibration can be caused by a multitude of factors. Every structure is transmitting noise. Within the building itself, the heating and ventilation system, fans, pumps and elevators are just some of the mechanical devices that create vibration. Depending on how far away the cleanroom equipment is from these vibration sources, and where in the structure the equipment is located, whether on the third floor or in the basement, for example, will determine how strongly the equipment will be influenced. External to the building, the equipment can be influenced by vibrations from adjacent road traffic, nearby construction, loud noise from aircraft, and even wind and other weather conditions that can cause movement of the structure.

Vibrations in the range of 2 hertz (Hz) to 20,000 Hz will influence sensitive equipment. But these internal and external influences primarily cause lower frequency vibrations, which are transmitted through the structure, creating strong disturbances in precision equipment used in cleanrooms.

Vibration Isolation
Used extensively in semiconductor manufacturing, biotechnology, the life sciences, and other fields that are very sensitive to environmental contaminants - such as dust, airborne microbes, aerosol particles, and chemical vapours - cleanrooms provide an enclosed environment with a controlled level of contamination that is specified by the number of particles per cubic metre at a specified particle size.

Equipment employed inside the cleanroom must be designed to generate minimal air contamination including vibration isolation equipment, which can range from relatively simple rubber blocks, metal springs and breadboards, to highly efficient air systems, active electronic systems, and negative-stiffness systems - constructed with more advanced technologies and materials for higher precision vibration isolation.

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Press Release

New Ultra-Thin CT-2 Low-Frequency Vibration Isolation Platform Adapts to Space Constraints in Critical Micro- and Nano-Microscopy

Press Release: Minus K Technology has announced the new ultra-thin, low-height model CT-2 passive isolator - the successor to the CT-1 offers better horizontal performance with additional payload ranges for heavier instruments. The completely passive tabletop unit is just under 2-3/4 inches in height, yet delivers 1/2 Hz vertical natural frequency, and ~1-1/2 Hz horizontal natural frequencies - considerably more low-frequency vibration isolation performance compared to air tables and active systems. The CT-2 utilizes Minus K's breakthrough patented technology that led to a Laser Focus World 2019 Innovation Award

The new Negative-Stiffness CT-2 ultra-thin, low-height, low-frequency vibration isolation platform mitigates space constraints in microscopy applications.

Full release...

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Ultra-Low Vibration Lab at University of Michigan Facilitates Nanoengineering Discoveries Engineering a Vibration Isolation Solution

The Ultra-Low Vibration Lab (ULVL) is a part of the new Center of Excellence in Nano Mechanical Science and Engineering (NAMSE) – a recent addition to the G.G. Brown Laboratories on the North Campus of the University of Michigan in Ann Arbor. Noel Perkins, former associate chair for Facilities and Planning with the Department of Mechanical Engineering, describes this addition as a “building-within-a-building”. The Nanoengineering Lab, located on the ground floor, contains eight ultra-low-vibration chambers for nanoscale metrology, mechanical, temperature and interference testing.

The chambers are structurally isolated from the balance of the building. Vibration isolation tables are mounted on pillars that are part of an 8-ft-thick seismic mass, which is isolated from the chamber floors. Even researchers footsteps wont disturb experiments. With the emergence of nanotechnology and nanoengineering of the last two decades, a relatively small number of institutions and agencies have been able to construct facilities for ultra-sensitive measurements, and I know of none that are focused on the mission of a mechanical engineering department, said Edgar Meyhofer, professor of mechanical engineering and biomedical engineering at the university.

Validating Fluctuational Electrodynamics
When heat travels between two separated objects, it flows differently at the smallest scales distances on the order of the diameter of DNA, or 1/50,000 of a human hair. For example, heat radiates 10,000 times faster at the nanoscale. Researchers have been aware of this for decades, but they have not understood the process. Now, at ULVL, researchers have measured how heat radiates from one surface to another in a vacuum at distances down to 2 nanometers. "We've shown for the first time, the dramatic enhancements of radiative heat fluxes in the extreme near-field," said Reddy. "Our experiments and calculations imply that heat flows several orders of magnitude faster in these ultra-small gaps." Reddy and Meyhofer led the work. A paper on the findings was recently published in the international journal of science, Nature.

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Professor Holger Müller's Group at UC Berkeley is focused on advancing experimental quantum technology to push the sensitivity of experiments to new levels, and to perform precision measurements of fundamental constants. The groups work uses methods from atomic, molecular and optical physics. One project is the development of a transportable, multi-axis atom interferometer, named miniG.

MiniG was designed to research how quantum interference can be used to measure gravity outside of the laboratory. When cooled to just above absolute zero, the atoms form the focus of a portable quantum gravimeter.

Gravimeters, used to measure gravitational acceleration, have been successfully applied for metrology, geology and geophysics. MiniG uses an atom interferometer to measure the effect of gravity on clouds of atoms that are first trapped and cooled. Interferometry inherently depends on the wave nature of the object. Particles, including atoms, can behave like waves. Atom interferometers measure the difference in phase between atomic matter waves along different paths.

We use atoms that are laser-cooled to millionths of a degree above absolute zero, said Xuejian Wu, a post-doctoral scholar, involved in the development of miniG at the Müller Group. With pulses of light, we drive each atom into a quantum superposition of having been kicked with the momentum of photons, or not kicked. The atoms, in two places at one time, are in a superposition of recoiling backwards or staying still. By manipulating the state of the atoms using one of two types of such light pulses, we steer the matter waves' paths and recombine the matter waves at the end of the experiment.

Atom interferometry has become one of the most powerful technologies for precision measurements, and atomic gravimeters, based on atom interferometry, are extremely accurate and have long-term stability.

Current atom interferometers, however, are too complicated to operate in a miniature package or under field conditions. Berkeleys mini-G was engineered to resolve this issue.

In this project, we are developing a mobile atom interferometer using a single-diode laser system and a pyramidal magneto-optical trap, continued Wu. This allows the device to be smaller, simpler and more robust than conventional atom interferometers.

Vibration Isolation

Measurements of atomic precision require isolation from ambient vibrations coming from internal and external sources. As measurements are being done at a smaller and smaller level, those vibrations that are present will start to dominate, and the need for more effective isolation increases.

Although the Müller Groups research laboratory is situated in the basement of a building on the Berkeley campus, it is still influenced by vibrations from the buildings HVAC system.

For several years now we have been using Negative-Stiffness vibration isolation for our research projects, continued Wu.

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Featured Product: BM-4 Bench Top Vibration Isolation Platform

• Can also be made cleanroom and vacuum capatible.
  
• Vertical natural frequency of 1/2 Hz or less can be achieved over the entire load range.
  
• Horizontal natural frequency is load dependent. 1/2 Hz or less can be achieved at or near the nominal load.
  
• See Performance for a typical transmissibility curve with 1/2 Hz natural frequency.
  

Pricing & sizes for BM-4

Specifications (pdf)

The United States Bowling Congress (USBC) is the national governing body of bowling, as recognized by the United States Olympic Committee. It is a membership organization that provides standardized rules, regulations and benefits for certified bowling leagues and tournaments. The USBC is one of the worlds largest sports and recreation membership organizations, in the United States serving approximately 1.4 million bowlers that participate in USBC-certified leagues and tournaments on both the national and local levels.

Critical to the initiatives of the USBC is its Department of Equipment Specifications and Certification, which encompasses testing and research of bowling equipment to set standards and enhance the sports credibility.

“There are two sides to bowling – the recreational, and the more competitive,” said Tom Frenzel, Research Engineer with the USBC. “Our focus is on research, testing, standardization and certification of bowling equipment used for leagues and tournaments.”

“Basically, any piece of equipment that touches the bowling lane comes though this department to be evaluated, and determined whether or not it should be allowed to be used,” added Frenzel. “This includes bowling pins, bowling balls, lane panels, lane conditioners, gutters, and kick-back walls in the pin deck.”

To this end, the department uses a number of research and testing methodologies to ensure that not only do these products meet established specifications, but that they are manufactured to within a 4 Sigma quality manufacturing limit, which means within a 0.6 percent defect rate. Essentially, ensuring that 99.4 percent of all bowling products used for certified leagues and tournaments are within designated specifications.

Minus K Negative-Stiffness vibration isolator,
under a 3D laser-scanning, digital confocal microscope.

Surface Roughness of Bowling Balls
One area of ongoing research and testing at USBC concerns surface roughness of bowling balls.

Since the early 1990s, better bowling ball coverstocks have been developed. These coverstocks find more friction on the lane, and inevitably hook more. They also disrupt the oil pattern on the lane more, which tends to reduce friction. So the USBC engineering team is trying to better understand the implications of these factors, and better control their outcomes.

It has become popular to sand bowling balls with different grits of sand paper, explained Frenzel. This practice has helped us see how the sanding level on a ball affects its surface layer, then we compare this back to how it performs on the lane.

The rougher you get the ball, the more the ball will hook, and the more friction it will find, continued Frenzel. The friction will define how the ball accelerates. So more friction means more acceleration, which just means it is changing its speed quicker, or in less time. It is really hooking sooner versus later, or taking less time to hook.

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Bad Vibrations: How to Keep the Effects of Environmental Bounce Out of Your Data

(2007 legacy article) - Whether it's an NMR or a two-photon microscope, scientists love toys - at least when they work. Sometimes the most mundane things bungle technology: environmental vibrations from cars driving by, central air conditioning, the voices of the operators, and even the ocean. As instruments become more sensitive, subsonic rumblings become more insidious, particularly for nano-technology applications. With many instruments, such as atomic-force and electron microscopes, cutting down on vibration is essential to collecting good data. "You could spend a million or two million on a microscope and have it rendered useless because of vibration," says Kurt Alberline, an anatomist at the University of Utah School of Medicine, who runs an electron microscopy lab.

When researchers suspect vibration is wreaking havoc on their data, they should identify the origin of the noise or get an environmental engineer to find it, say scientists who regularly deal with vibration. For example, Vicki Colvin, a chemist at Rice University in Houston, noticed images moving around in a circle on her transitional electron microscope. "It was like a ghost," she says. Colvin discovered that an air duct was causing the problem and spent $1.20 on a shield to divert air away from the scope. "The easiest way to get rid of vibrational noise is to stop it at its source." says Larry Cohen, a neuroscientist at Yale University.

The design of a building is critical to the vibration that reaches an instrument, says Ahmad Soueid, senior vice president at HDR Architecture in Omaha, Neb., which has designed more than a dozen nanotech laboratories. Isolating air-handling equipment from laboratories and using special joints that redirect vibration to the ground are some of the fixes his firm uses. Recently, concerns over vibration plagued a $250 million NIH facility under construction in Baltimore. Initial reports indicated the building's quivers could render confocal microscopes useless, although later measurements suggested most instruments will work with proper dampening

There's no universal fix, says David Platus, president of Minus K, a company that makes high-end vibration-isolation tables. Solutions vary, from cheap rubber pads that rest under instruments, to the air-cushioned tables that have been around for 50 years, to tables that sense vibration and cancel it out. "The more sensitive the instrument, the better isolation you need." he says.

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Example Causes of Bad Vibrations:
Automotive
Buildings
Columns
Computers
Elevators
Engines/Motors
Floors
Freeway & Road Traffic
Generators
HVAC (Heating & Air Conditioning Issues)
Machinery
Mechanical Entities
Plumbing, Piping
Pneumatic factors
Seismic Waves (including from ocean waves)
Trains & Subways
Transformers
Winds Against Buildings
(Examples with Hz...)

Minus K vibration isolation systems can be designed for very heavy payloads. The following are some typical isolator dimensions. The 10,000 lb and 25,000 lb isolator dimensions are approximate and are based on preliminary designs.

XM-1: 10,000 lb capacity: 20"W x 20"D x 22"H

The James Webb Space Telescope is the largest cryogenic instrument telescope to be developed for space flight. It is a large-aperture infrared space telescope and the scientific successor to NASA's Hubble Space Telescope and used a set of six custom heavy capacity Minus K vibration isolators for ground testing.

The ground testing confirmed the telescope and science instrument systems will perform properly together in the cold temperatures of space. Additional test support equipment including mass spectrometers, infrared cameras and television cameras were also supported by Minus Ks heavy capacity vibration isolators which allowed engineers to observe the testing.

Each of the isolators was designed for 10,000 lbs. and the total payload supported from the top of the Johnson Space Center vacuum Chamber A was 60,000 lbs.

The isolators allowed NASA to simulate the telescopes performance in space while preventing all the ground-based disturbances, such as the pumps and motors, and even traffic driving by from interfering with the ground testing. Case study: NASA James Webb Space Telescope (JWST).

Vibration Criterion (VC) Curves-Lab Analysis
Codes and curve descriptions for different vibration environments and solutions.

The VC (Vibration Criteria) curves were developed in the early 1980s by Eric Ungar and Colin Gordon. They were originally developed as a generic vibration criteria for vibration-sensitive equipment for use in the semiconductor, medical and biopharmaceutical industries, but have found application in a wide variety of technological applications.

The criteria takes the form of a set of one-third octave band velocity spectra, together with the International Standards Organization (ISO) guidelines for the effects of vibration on people in buildings. The criteria apply to vibration as measured in the vertical and two horizontal directions.

The NIST-A criterion was developed for metrology, but has gained popularity within the nanotechnology community. The NIST-A criterion is a very difficult criterion to meet at some sites with significant low-frequency vibrations.

The VC curves are now widely accepted throughout the world as a basis for designing a facility to meet the requirements of a group of highly vibration sensitive equipment used close together.

University of Michigans Ultra-Low Vibration Lab (ULVL) was completed in 2014. After the construction, a vibration survey was done on the Ultra-Low Vibration Lab chambers. The measurements demonstrated that even when a single vehicle was driving on a nearby street, the vibrations exceeded the NIST-A specifications necessary for the ULVL.

The University of Michigan ordered seven customized tabletops and 31 custom Minus K Negative-Stiffness vibration isolators with pedestals provided for the eight Ultra-Low Vibration Lab chambers.

Customized Minus K Technology Negative-Stiffness vibration isolation table installed in one of the Ultra-Low Vibration Lab chambers

The final vibration survey by Colin Gordon Associates (CGA), after installation of the customized Minus K Negative-Stiffness isolators and tables, showed the measured vibration levels in all ULVL chambers from VC-K to VC-M at frequencies above 2.5 Hz, well below the NIST-A Vibration Criterion required.

"VC-M is the lowest we have ever measured, though we werent able to measure below 2.5 Hz because our most sensitive sensor wont go lower, due to sensor noise floor," said Hal Amick, Vice President of Colin Gordon Associates.

The updated VC Curve on Minus K's website shows these lower curve levels that were measured by CGA and have already assisted University of Michigans ULVL with two major scientific milestones.

Vibration site surveys can tell you a lot about how to
specify equipment for vibration isolation in your laboratory.

Updated VC Curve on Minus K's website...