Vibration Isolation Technology Explained

Vibration before and after Isolation

This page is dedicated to explaining the basic concept of vibration and technology used to suppress its affects on high precision microscopes and other tooling that vibration creates detrimental problems in quality and performance.  For a more detailed overview, Contact Us and request our Vibration Technology handout.

Vibration is a mechanical movement around an equilibrium point. In other words, it is a mechanical phenomenon where a dynamic external force is applied onto structures or floors, causing the oscillation motion that repeats itself after an interval of time. Among the sources of vibration, the low frequency vibration is not perceptible during daily activities, and can adversely affect high-performance metrology tools in the fields of semiconductors, display manufacturing, electron microscopy, photonics and life sciences.

Classification of Vibration

Periodic noise is defined as the known magnitude of the excitation acting on a vibratory system at any given time. It is generally caused by rotating machinery. Random noise is caused by unpredictable excitation such as wind velocity, road roughness, foot and vehicular traffic, and ground motion during various activities.

Periodic and Random Vibration Noise

Sources of Vibrations in Laboratories

  • Ground vibrations indicate all the factors that cause vibrations on a floor. The factors include foot and vehicular traffic. external noises. wind blowing against building, seismic activity, HVAC systems and many other types of mechanical equipment in the nearby vicinity depending on how the building either dampens those vibrations or transmits them doe to the building construction.
  • Acoustic noises are the factors that directly apply a force to a payload, such as loud noise, wind blowing from fans or the opening and closing of doors.
  • A direct force is a force that directly applied to a payload on a platform, including cables connecting all the equipment and motorized linear stages.
sources of vibration in a laboratory

Natural Frequency and Resonance

The natural frequency is the frequency at which the system resonates or oscillates when the system is not disturbed by an external force. A higher stiffness and a lower mass indicates the high natural frequency and a lower stiffness and a higher mass indicates the low natural frequency.  As will be explained later, isolation solutions also have resonant frequency.

Resonance occurs if a forced frequency coincides with a natural frequency of the system resulting in large oscillations. Frequency at which the response amplitude is a relative maximum is known as resonant frequency. Materials like elastomers and springs often used for vibration isolation can actually make the vibration of the payload worse if their natural or resonant frequency is near the same frequency as the vibration to be attenuated.

Vibration Isolation

Vibration isolation is defined as the process to isolate an object from sources of vibration. The theory of vibration isolation is to make the natural frequency of the system lower than the forced frequency and to suppress the resonance at the natural frequency of the system. As technology advances. a vibration isolation technique is essentially required to isolate vibrations from high-performance metrology tools.

Transmissibility (T) indicates the ratio of the amplitude of the vibration transmitted to an isolated payload to that of the exciting vibration. The efficiency of the vibration isolation improves with the lower natural frequency, meaning the lower transmissibility is the better vib