Vibration noise 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 and their material characteristics.
- Building sway
- Foot traffic
- HVAC equipment and ventilation
- Moving parts within instruments
- Pumps and other machinery
- Seismic movement
- Vehicle traffic
Vibrations affect research instruments in different ways depending on the type of sensitive components embedded within the instrument and how they are supported. For imaging tools, vibration noise can degrade image quality severely as vibrations will manifest themselves by blurring the image or creating jagged lines along the edges of features.
Vibrations can cause significant issues for instruments measuring force, like nanoindenters and tensile testers, or instruments utilizing force in their sensing mechanism, like scanning probe microscopes or microbalances. For example, vibrations are a notorious source of noise and image distortion for atomic force microscopes (AFMs). When vibrations are present, sensitive instruments will produce inaccurate results or indiscernible data. If the vibration displacement exceeds the resolution level of the instrument, the vibrations can render the instruments useless.
Vibrations can also frustrate precision manufacturing processes, such as hard disk applications or precision weight measurements. To optimize the manufacturing output of these applications, it is required that they operate at low environmental noise levels.
Some vibrations are easy to identify, like when a truck passes and the ground floor slightly shakes. Others are much more subtle and harder to discern. Often vibrations that are too small for humans to identify are too large for research instruments to handle. This is especially true when the instruments are operating at the nano-scale level. In these cases, researchers employ vibration measurement equipment to provide external verification of noise levels to understand the extent of the problem.
Even when vibrations have been characterized within a room, it can still be challenging to identify the primary source(s) of vibration. Vibrations can travel through the ground for miles, making it harder for researchers to locate if the source of the vibration originates from their lab or subsequent areas beyond their lab. Vibrations from noisy machinery can easily transmit throughout an entire building, leading to complications for many research instruments on different floors. A site survey should be conducted to determine the level of noise in the lab to understand the extent of the problem. You can do this by identifying the frequency level of the offending vibrations and their respective amplitudes. Performing these measurements can also narrow down the potential sources of vibration. Taking measurements in multiple places and comparing amplitude values will help you find the source or the vicinity of where the source is located. This can be a time-consuming, trial-and-error process, but one that may be necessary when an instrument’s measurement capabilities are rendered useless.
Poor construction can often amplify and multiply the troublesome vibrations. A building constructed without the requirements of precision research in mind can often result in resonances and an obfuscated vibration profile. Desks and tables not rigidly constructed can also increase vibration issues.
In addition to the trouble caused by not making these considerations, selecting a vibration isolation system can become a difficult process. Individual instruments have unique sensitivities that may not be well characterized. Noise levels are hard to gauge unless a site survey is performed and many times this is not the case for a wide range of instrumentation. 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 cannot be eliminated, then the noise source should be isolated from the building. Isolating the noise source from the building can be accomplished by adding damping rubber under the feet of the instrument or decoupling the instrument from the building using hose, cable, or duct extensions.
If the above measures are insufficient, isolation solutions must be added to the sensitive instrument itself. Adding mass is a good first step in this direction as 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 initial efforts fail, a more complex isolator is recommended to address the inherent vibrations in the lab. Passive isolators like bungees, air tables, or negative stiffness isolators are the initial next level of isolation as they provide higher vibration isolation at a moderate cost.
For extremely high precision applications or very noisy environments, an active vibration control platform should be used as they are designed to address broad frequency isolation in all six degrees of freedom (0.5 – 1,000 Hz). These high performance vibration isolation systems continually sense and damp incoming vibrations to ensure uniformed measurements for sensitive instruments. Since these systems lack a low frequency resonance, they are well equipped to handle the noise profile of the worst environments and the most demanding instruments.