Vibration is mechanical energy carried through a physical structure in wave form. Vibrations are generated by a wide array of natural and man-made sources. The behavior of vibrations are heavily influenced by the structures through which they travel.
Vibrations affect research instruments in different ways. For imaging tools, they can degrade image quality. Vibrations will manifest themselves by blurring the image or creating jagged lines along the edges of features.
Vibrations can cause significant issues for instruments which measure force, like nanoindenters and tensile testers, or which utilize force in their sensing mechanism, such as scanning probe microscopes or microbalances. For example, vibrations are a notorious source of AFM noise. When vibrations are present, sensitive instruments will produce inaccurate results. If the displacement of the vibrations exceeds the resolution level of the instrument, the vibrations can render the instruments useless.
Vibrations can also frustrate precision manufacturing processes. Applying thin coatings, such as in hard disc applications, or taking precise weight measurements requires low environmental noise levels.
Some vibrations are readily apparent, like when a truck passes. Others are much more subtle. Often vibrations that are too small for humans to sense are too large for research instruments to handle. This is especially true when the instruments are operating at the nanoscale. In these cases, researchers will need to employ some sort of vibration measurement equipment to provide external verification of noise levels.
Once troublesome vibrations have been detected, it can still be difficult to identify their source. Vibrations can travel through the ground for miles. Vibrations from noisy machinery can easily transmit throughout an entire building. A site survey should be conducted to try to determine the source of noise. You can do this by identifying the frequency level of the offending vibrations. That information can be used to narrow down the potential sources. Taking measurements in multiple places and comparing power levels will help you find the source. This can be a time-consuming, trial-and-error process.
Poor construction can often amplify and multiply the troublesome vibrations. A building constructed without the demands of precision research in mind can often result in resonances and a confusing vibration profile. Desks and tables that are not rigidly constructed can also increase vibration issues.
Selecting vibration isolation systems can sometimes be a difficult process. Individual instruments have particular sensitivities which may not be well characterized. Noise levels are hard to gauge unless a site survey is performed. Isolation systems should be selected in consultation with the instrument maker and experts in the field of noise reduction. For more information on this process, please read our Tutorial on Choosing an Isolation System.
The first step in eliminating troublesome vibrations is to identify the source and, if possible, remove it. If the source can’t be eliminated, then it should be isolated from the building. This can be accomplished by adding damping rubber under the feet or decoupling it from the building using hose, cable, or duct extensions.
If the above measures are insufficient, isolation must be added to the sensitive instrument itself. Adding mass is a good first step in this direction. Increasing the mass of a system increases its impedance, which means it will take more energy to move it. If additional isolation is needed, simple rubber mats or feet can be added under the instrument or table.
If these rudimentary efforts fail, a more complex isolator will need to be employed. Passive isolators like bungees, air tables, or negative stiffness isolators are the next level of isolation. These can usually provide a higher reduction factor at a moderate cost.
For extremely high precision applications or very noisy environments, an active vibration control system should be used. These high performance vibration isolation systems continually sense and damp incoming vibrations. Since these systems lack a low frequency resonance, they are well equipped to handle the noise profile of even the worst environments.