Vibration Control: How to control vibration noise for superresolution microscopes

From site surveys to active vibration control, steps can be taken to keep your superresolution microscope stable and ready to collect data.

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REID WHITNEY

From site surveys to active vibration control, steps can be taken to keep your superresolution microscope stable and ready to collect data.

Vibration noise commonly disrupts the workflow of researchers who are using superresolution microscopes, limiting their progress on processing samples or collecting usable data. The presence of vibration noise can significantly impact the cost and time required to complete a microscope-based research project. Consequently, it is important to understand the key steps in controlling vibration noise:

• Step 1. Characterize ambient vibration noise

• Step 2. Investigate mitigation solutions

• Step 3. Isolate the source of vibrations

• Step 4. Isolate the microscope from vibrations

By following these steps, researchers can become more efficient in their workflow and get back to what matters most: their research.

Characterize ambient vibration noise

Site surveys. Site surveys help define the noise profile of a room, measuring vibration, acoustic, and/or electromagnetic interference (EMI) noise across specific measurement profiles (see Fig. 1). Site surveys are often performed by an environmental consultant or specialist in the field using a data-acquisition system and sensors (such as accelerometers, microphones, and magnetometers). These measurements capture environmental noise within a moment in time to gain a preliminary understanding of the baseline noise of a room.

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FIGURE 1. As indicated by this site information form, successfully performing a site survey requires essential information that includes room details, local noise sources, microscope details and positioning, and how the site survey is performed.

A site survey is performed to understand noise as it relates to a microscope’s noise tolerance or maximum allowable environmental specification, which is determined by the manufacturer to ensure the microscope runs optimally. The noise collected is contrasted with the microscope noise specification to determine if the environment meets specification or requires alternative measures to bring the environment within specification.

Data logging. When the variance in noise within a given lab is low, a site survey that measures noise within a single moment in time is sufficient to understand the noise profile of a room. However, if periodic noise sources or difficult-to-determine noise events are present, data logging is a more-relevant approach for researchers to consider.

Data logging is a type of site survey in which environmental noise is measured over an extended period (for example, 24 hours or greater). This process is done to identify noise that occurs periodically—information that can help shape the type of vibration-control approach ultimately chosen. Data logging can be performed locally or monitored remotely. One difficulty with data logging is matching specific data with individual events. In addition, the level of difficulty can depend on what data-logging hardware and/or software is used.

Investigate mitigation solutions

Relocating the microscope. The most affordable and common avenue to address noise is to find a new location for the incoming microscope that includes a lower ambient-noise floor. Doing so relieves the researcher from finding mitigation solutions for the noise source or the microscope, which typically costs money for a solution and time away from performing research.

The primary reason that researchers do not pursue this option is a lack of choice when it comes to lab space with lower noise profiles. Choice can be determined by either the nearby labs having similar noise issues, or lack of available space in general to situate the microscope.

Relocating the noise sources. The second mitigation solution, which is often addressed by microscope manufacturers in the preliminary planning phase, is to relocate noise sources that accompany a microscope to a different room. Whether it be loud scroll pumps, air generators, or electronics cabinets, accessory hardware not critical during data collection is best located in a separate room or closet decoupled from the microscope’s workspace.

Changes to the lab. The third, and often most costly, mitigation solution is to modify the architecture of the lab itself, whether it be modifying the flooring underneath the microscope, adding acoustic paneling to the walls, or including radio-frequency (RF) shielding in the room. Changes to the lab may provide a complete solution, but at a considerable cost.

The primary benefit of this option is that not only will the individual microscope being affected benefit from this change, but surrounding microscopes will benefit as well.

Isolate the source of vibrations

If mitigation solutions are not possible, isolating the source of vibrations is the next step in controlling vibration noise in the lab. Similar to modifying the lab or relocating noise sources, isolating vibrations at the source can greatly benefit all microscopes within the lab (albeit not equally). Vibrations emanating from loud equipment such as HVACs, pumps, universal protocol converters (UPCs), and so on may impact certain microscopes more than others because of their inherent sensitivity at individual frequencies, which is why isolating vibration sources to determine their overall effectiveness and impact is difficult.

Vibration-damping solutions to consider. Vibration-absorbing materials such as passive springs or sorbothane rubber can reduce the amount of vibration transferred into the surrounding environment, lowering the overall noise profile of the room and solving vibration issues for some types of equipment. If the vibration noise issue is structural (for example, building resonances), there isn’t much to be done to isolate the source. However, locating the microscope closer to a load-bearing wall that has more structural support will result in lower amplitudes than locating the microscope in the center of a room.

Microscopes can be the culprit, too. It is important to remember that microscopes can induce vibration-caused noise directly into their measurements that arise from loose hardware or poor cable management. If caught early, this situation can be easily and cost-effectively addressed. Even if a microscope is supported by a vibration-control system, vibrations imparted directly to the microscope will not be mitigated, as vibration-control systems primarily address floor vibrations.

Isolating microscopes

There are a variety of vibration-control solutions available, depending on the type of vibration noise local to the environment and the inherent sensitivities of the supported microscope (see Fig. 2). These solutions vary in terms of frequencies isolated, technological features included, and cost. Some of the most common solutions include:

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FIGURE 2. Many options are available for isolating microscopes from vibrations; these options vary in cost, complexity, and capability.

Passive vibration control (composite materials). Materials such as sorbathane and other damped rubber materials provide a passive form of damping by reducing higher frequency vibrations from being transferred into the microscope. The technology and cost behind these solutions are minimal, making them perfect for microscopes not operating at maximum precision or needing to focus on samples at high magnification (10,000X or greater).

Passive vibration control (bungee system). Bungee-based passive systems work well as an affordable vibration-control solution when coupled inside an acoustic enclosure. Bungee systems can vary in terms of their performance, as their elasticity can be tuned to the vibrations needing to be isolated. One reason why a researcher would not use a bungee-based passive system is that they do not offer low-frequency vibration control (<5 Hz) or broad frequency control in environments that are particularly noisy at many frequencies.

Passive vibration control (air-based). Air-based passive vibration-control systems are the most popular solution in terms of vibration control in the lab. Robust workstations exist that provide considerable rigidity, density, and vibration control, while more-affordable desktop solutions provide researchers with considerable control in a simpler form factor.

Air-based workstations provide better low-frequency vibration-control performance than do desktop form factors. However, the cost can be 2–3X higher. This cost-to-performance ratio provides researchers with the opportunity to determine whether the cost is justified based on the sensitivities of their microscope and the local noise of their environment.

Active vibration control (piezoelectric sensors/actuators). Active vibration-control systems are often the chosen solution for superresolution microscopes and other microscopes requiring absolute precision (see Fig. 3). These systems are unique in that they isolate all rotational modes of vibrations (all six degrees of freedom) below 5 Hz, which passive systems are unable to do. Many active vibration-control systems isolate down to about 1 Hz, with only a few isolating between 0.5 and 0.7 Hz.

Additionally, active vibration-control systems are unique because they adapt to a changing environment—a result of their core technology of piezoelectric sensors, actuators, and control electronics. The local vibration noise is measured by the internal sensor, which is transmitted to the control electronics to be converted to an out-of-phase inverse force, which is then translated through the actuators to provide the vibration-controlling effect. This process is known as a feedback loop, which is only present in active vibration-control systems.

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FIGURE 3. Active vibration-control systems use piezoelectric sensors, actuators, and control electronics to dynamically respond to vibrations in the environment and provide an out-of-phase inverse force to the top plate.

Vibration control improves microscope efficiency

Vibrations are an unavoidable nuisance in labs around the world and spending time to control them is never the goal of the researcher. Even deciding on a solution to mitigate these issues is only a means to an end, which is getting back to performing research with the microscope necessary to do so. Correctly understanding vibration issues and how to address them from the start helps researchers to save time in investigating a solution, save money from not having to try out multiple mitigation solutions, and return to their workflow.

Reid Whitney is vice president at Herzan, Laguna Hills, CA; e-mail: reid@herzan.com; www.herzan.com.

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