Microscopy & Microtechniques


Vibration control in electron microscopy suites Adam Fox, Mason UK


Vibration isolation products are designed and engineered for a variety of scenarios. Scientific laboratories and the equipment typically found within them are often sensitive to vibration. However, for electron microscopes, the conventional methods of isolation are often insufficient. This article describes how scientists at Cardiff University resolved the challenge of operating a large electron microscope less than 100 metres from a major trainline, by partnering with vibration control engineering specialist, Mason UK.


At Cardiff University, a disused railway yard has been converted into a state-of-the-art scientifi c facility, which now contains world-leading scientifi c research establishments. As well as an ‘occulus’ staircase, the new Cardiff Innovation Campus is also home to a large electron microscope.


A challenging specifi cation


Equipment like this is highly sensitive to vibration. According to guidance from the manufacturer, anything above VC-E level would impair the functioning of the equipment. Imaging and analysis at the atomic level means that any external interference that causes a deviation greater than the dimensions of the atom can be a major problem. The new electron microscopy facility is located close to a busy road and just 75 metres from a major trainline, both a passenger and freight line in constant use.


passing into the structure of a building where it can manifest as noise, but they can also protect sensitive equipment from interference caused by outside sources of vibration. Often the ideal solution for low frequency applications, they offer superior performance to rubber mats or pads.


Spring mounts are frequently combined with inertia bases. Inertia bases range from simple steel frames through to large concrete fi lled frames to provide inertial mass. The basic principle is that the increased mass will reduce vibration, lower the centre of gravity and thereby reduce rocking and increase thrust resistance. When combined with the correct acoustic isolation system, inertia bases are the most effective anti-vibration technique for machinery.


Despite the versatility of spring mounts, they would be ineffective at providing the desired level of vibration control, such were the engineering demands of this project. ‘‘Springs are effectively stressed metal wires, which have multiple vibration response modes. While this is often not an issue as we are dealing with extremely low levels of vibrational power, it can become a problem for very sensitive applications,’’ explained Adam Fox, Director at Mason UK.


Thermo Fisher scanning electron microscope


In addition, when springs are engineered to become softer and softer, and therefore more receptive to lower frequencies of vibration, it becomes a challenge to place something on top of them when stability is required. ‘‘With softer springs, relatively small changes in loading can lead to excitation. Although rubber and spring combinations can add damping, this also reduces isolation performance and multiple degrees of freedom remain, which means some vibration frequencies can be amplifi ed,’’ added Adam.


Laboratory building and adjacent trainline


Early site surveys confi rmed that the vibration from the trains would interfere with the performance of the equipment unless mitigative solutions were implemented. The acoustic consultant working on this project, Colin Gordon Associates, therefore designed a very tight specifi cation to ensure that VC-E levels would be achieved, despite the vibration-generating activities in the area.


The contractor, Bouygues UK, brought Mason UK on board to try and meet the challenging design criteria in the specifi cation. ‘‘Mason proved to be a very knowledgeable and competent specialist,’’ recalled Ashley May, Senior Design Manager with Bouygues UK. ‘‘They delivered excellent advice, design, installation and post installation support on this project and went the extra mile with assistance, even after the completion of the contract.’’


The limits of conventional measures


Spring mounts are often effective at isolating mechanical and electrical equipment, or protecting sensitive instrumentation. They can prevent vibration from equipment from


Air springs


Air springs are rubber bellows, pressurised with a gas like nitrogen. They are specifi ed in projects like the Cardiff Innovation Campus, where very high levels of isolation are called for. Equipment is mounted on an inertia base and the air springs are pressurised to raise the base from the fl oor.


‘‘Air springs are self-levelling and have very little resonant response, therefore providing a high level of stability and higher levels of isolation than can be provided by rubber or spring isolators,’’ explained Adam. ‘‘They can typically achieve natural frequencies of sub 2Hz, but it is possible for well-engineered systems to go even lower.’’


Typical applications for air springs include sensitive medical equipment like MRI scanners, or high precision imaging equipment such as electron microscopes. However, this kind of technology, and the expertise required to design and install it, is a very niche area of engineering. There are very few companies that can offer air springs as an option. Air springs are also not a standard, off-the-shelf product. Mason UK designed a bespoke system that was built for the electron microscopy suite at the Cardiff Innovation Campus, working toward the criteria in the specifi cation.


INTERNATIONAL LABMATE - FEBRUARY 2023


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