INTRODUCTION
What Are Vibrations? Vibrations are the transmission of mechanical energy in wave form through a physical structure. The behavior of vibrations is greatly affected by the physical structures through which they transmit.
Vibrations are created by several natural and man-made sources, including building sway, foot traffic, moving parts within instruments, pumps and other machinery, HVAC equipment and ventilation, vehicle traffic and seismic movement.
EFFECTS OF VIBRATIONS
Research instruments are affected by vibrations in many different ways. Vibrations can deteriorate image quality for imaging tools by blurring the image or generating jagged lines along the edges of features.
Vibrations can significantly affect measurements of equipment that quantify force such as tensile testers and nanoindenters, or that apply force in their sensing method such as microbalances or scanning probe microscopes.
Sensitive devices will deliver inaccurate results due to the presence of vibrations. The instruments may become useless if the displacement of the vibrations is more than the equipment’s resolution level. Precision manufacturing processes are also affected by vibrations. Low environmental noise levels are essential in precise weight measurements and in the application of thin coatings.
CHALLENGES OF VIBRATION ISOLATION
Vibrations are often so small that they are not in the audible range of humans, but large enough that they cannot be handled by research instruments, especially when the measurements are on the nanoscale. These cases may require the deployment of certain vibration measurement instruments that externally verify noise levels.
Identifying the source of troublesome vibrations is again a challenge even after their detection because they can traverse miles through the ground. Vibrations generated from noisy machinery can easily propagate across a whole building.
It is often necessary to conduct a site survey to identify the source of noise by detecting the frequency level of the problematic vibrations. This data is useful in limiting the potential sources. The source can be identified by comparing power levels and taking measurements in different points. However, it is a highly time-consuming trial-and-error process.
The offending vibrations can be amplified and multiplied by poor construction. Resonances and a confusing vibration profile are the results of a building constructed without considering the requirements of precision research. Vibrations issues can be increased if tables and desks are not rigidly constructed.
SOLUTIONS FOR VIBRATION ISOLATION
Sometimes, the selection of vibration isolation systems itself is a challenging process because the specific sensitivities of individual instruments may not be well defined. It is difficult to gauge noise levels without conducting a site survey. It is necessary to take the advice from instrument manufacturers and experts in the noise reduction field for selecting isolation systems.
The first step to prevent offending vibrations is the identification and possible elimination of the source. If it is not possible to eliminate the source, then it must be isolated from the physical structure by placing damping rubber under the feet or detaching it from the structure utilizing cable, hose, or duct extensions.
If vibration is not controlled by these measures, then it is necessary to add isolation to the sensitive equipment itself. The addition of mass to a system raises its impedance, which, in turn, increases the energy required to move it. More isolation can be achieved through the addition of simple rubber mats or feet under the equipment or table.
If these simple measures fail, then it is necessary to use a more complex isolator such as passive isolators, which include air tables, bungees, and negative stiffness isolators. These passive isolators are capable of providing a higher reduction factor at a reasonable cost.
An active vibration control system must be employed for very noisy environments or extremely high precision applications. These high performance vibration isolation systems can continually detect and damp incoming vibrations. They can effectively deal with very noise environments as thanks to their low frequency resonance.
