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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 nanotechnology 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...
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 (www.the-scientist.com/news/display/40504/).
There's no universal fix, says David Platus, president of Minus K, a company that makes high-end vibration-isolation tables (see How It Works). 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.
User: Kurt Albertine, an anatomist at the University of Utah School of Medicine
Project: Electron microscopy of lung tissue samples
Problem: Low-frequency vibration causes double and triple images.
Solution: Albertine says the best solution for a scanning or transmission electron microscope is to put the machine on at least a one foot-thick slab of concrete. Most EM labs should be on the first floor or in the basement, he says. To further dampen vibration, users can load their microscopes on special dollies with thick rubber feet. Albertine recommends consulting with the microscope's manufacturer to find a solution. "They know their instruments, and they know how to optimize them despite a poor environment," he says.
User: Andrew Minor, a materials scientist at the National Center For Electron Microscopy, part of Lawrence Berkeley National Laboratory
Project: Imaging ceramics, polymers and nanowires at a resolution of a few Angstroms
Problem: "The vibration from your voice will make your image worthless," Minor says.
Solution: Minor's microscope rests on a floating, two-story concrete block. In September, his lab will begin using the most sensitive microscope in the world, able to resolve half an Angstrom. Such high-resolution microscopes are specially designed to limit vibration.
User: Larry Cohen, a neuroscientist at Yale University
Project: Imaging calcium- and voltage-dependent fluorescent dyes in live neurons with two-photon or epifluorescence microscopes
Problem: Even the slightest shaking can compromise the millisecond-timed measurements.
Solution: Cohen was among the first light microscopists to tackle vibration, beginning in the early 1970s. He started with air tables, which remain the industry standard and cost several thousand dollars, depending on size. The tables dampen up-and-down vibration well, says Cohen, but they have more trouble with side-to-side movements. On the advice of an engineer, Cohen mounted his microscope on top of motorcycle inner tubes resting on an air table. That solved most of the problems, but vibration still got through. He next bought a $5,000 table from Minus K that uses springs and flexors tuned to an instrument's precise weight, and it has solved his problems.
Brian Salzberg, a neuroscientist at the University of Pennsylvania who did a postdoc with Cohen in the 1970s, has gone even further to quell vibration in his lab. "The engineers, bless them, cleverly located all the air-handling equipment on the roof, so the building shakes," he says. As a fix, he rests his microscope on a $10,000 active isolation table produced by Halcyonics. The table electronically senses vibrations then mechanically cancels them out. To dampen vibration transmitted through the air, Salzberg shrouds his set-up in a soundproof curtain. "That combination works very well for us," he says.
Noise can come from sources other than vibration, Cohen cautions. Shot noise, related to the movement of photons, can overshadow vibrational noise. Moreover, when imaging live animals, breaths and heartbeats add still more noise. Those are problems isolation tables won't resolve.
User: Vicki Colvin, a physical chemist at Rice University in Houston
Project: While at Bell Labs, Colvin did holography, storing images and data onto pieces of plastic.
Problem: The lasers encoding the images were extremely sensitive to vibration; slight changes in temperature could compromise the process.
Solution: "As any physical scientist will tell you," Colvin says, "you get your best data in the middle of the night." At 1 a.m. temperatures in the lab steadied, and she was able to conduct her holography experiments in peace.
Atomic Force Microscopy
User: Holger Schmidt, an electrical engineer at the University of California, Santa Cruz
Project: Imaging nanoscale magnets used for data storage with an atomic-force microscope (AFM)
Problem: Vibration makes images blurry and useless.
Solution: Schmidt's microscope came with a floating air table that has worked well to stop vibration. AFM users demanding better isolation have been known to place their instruments in pits filled with sand or rubber chips. Another effective solution is to suspend the microscope in the air with bungee cords, says Colvin, who also does atomic-force microscopy at Rice.
Nuclear Magnetic Resonance
User: Stephen Lynch, a chemist at Stanford University who runs an NMR core
Project: Analyzing proteins and other macromolecules on a 600 MHz NMR instrument
Problem: The 14-Tesla magnet in his most powerful NMR is sensitive to even the slightest movements.
Solution: The machine is located in a basement; Lynch cautions against trying to set up an NMR on higher floors. Air-cushioned legs included with the NMR help to stop vibration from reaching the magnet. Slight changes in temperature can also create vibration, says Mark Kelly, who runs an NMR lab at UCSF. Even the sun shining through a window will cause problems, he says.
Selected Vibration Isolation Tables
• Suitable for most jobs and locations, from AFM to fluorescence microscopy
• Requires air/nitrogen tank or a compressor
|Passive mechanical tables|
Minus K Technology www.minusk.com
(table that can bear 200 lbs)
• Dampens down to ~0.5 Hz
• Tables are "tuned" to a specific weight (Salzburg solves that problem by tuning to a higher mass, then removing lead weights as new equipment is added.)
(table that can bear 200 lbs)
• Dampens down to 0.5 Hz
• Costs twice as much as air or passive mechanical tables