1. Overview
Electron microscopes and other precision instruments have strict environmental vibration requirements. For example, electron microscopes require low-frequency vibration (0~30 Hz) in X, Y and Z axes to be less than 6 μm and high-frequency vibration above 30 Hz to be less than 12 μm. Low-frequency vibration below 20 Hz causes severe interference to electron microscopes. If the vibration exceeds these thresholds, ideal images cannot be captured when taking photos at magnifications above 10,000×.
For conventional Scanning Electron Microscopes (SEM) installed on upper building floors (2nd floor and above) or in locations with strong vibration sources (such as areas near underground subway lines), observation and imaging at magnifications above 30,000× become unfeasible. A vibration isolation system namely an anti-vibration table, is required to resolve this issue.
Field Emission Microscopes (FEM) operate at magnifications up to hundreds of thousands of times and demand even stricter vibration control. Satisfactory performance cannot be guaranteed even when placed on the ground floor, so anti-vibration tables are generally mandatory for installation.
Anti-vibration tables designed for electron microscopes are also suitable for other precision instruments. The AVI400 model from Switzerland’s Table Stable consists of two separate isolation pads and features extremely easy installation.
2. Working Principle
There are two types of anti-vibration tables: passive and active.
Passive anti-vibration solutions adopt rubber, metal springs, air springs and other materials. They deliver poor damping performance for low-frequency vibration below 20 Hz and may even trigger resonance of SEMs within the 0~20 Hz range, making them impractical for such applications.
Active anti-vibration systems utilize 3D sensors to detect external vibration transmitted along X, Y and Z axes. A PID controller generates control signals with equal amplitude and opposite phase, which drive actuators to produce internal counter-vibration of matching amplitude and opposite phase to offset or attenuate external vibration disturbances.
3. Model Selection
The actuators / isolation pads manufactured by Switzerland’s Table Stable are two elongated modules with compact size, lightweight design, simple installation and moderate pricing, which have gained wide adoption among domestic users.
4. Practical Performance
A customer’s EVO MA 25 SEM was installed on the 3rd floor and failed to capture clear images at magnifications above 10,000×. Since December 2012 the Swiss AVI-400 anti-vibration table has been deployed to maintain stable operation of the SEM, enabling high-quality imaging at 100,000-200,000×. Refer to the comparison images below:
Before Vibration Isolation
After Vibration Isolation
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