Electron microscope site survey data interpretation – part 1

It is important to measure both vibration and magnetic field interference at different locations and heights when conducting a site survey, to see how signals change amplitude in all three axes. This helps to locate the cause of any problems, so that it is easier to implement measures to reduce or eliminate interference. It can be as simple as relocating the microscope, taking out the cause of the interference, or installing a cancelling system to improve microscopy performance as demonstrated in the following examples.

Power cables
Power cables run through many areas of a building and can be a common cause of interference for electron microscopes. The live wire in a power cable carries electric current to an appliance, while the neutral cable completes the circuit, to form a path for the current to flow back to the mains. These two wires should effectively cancel each other out but, as the currents in the wires get larger, the current difference between the wires grows and this leads to large magnetic fields.

Distribution boards
Distribution boards are essentially central hubs that distribute power around various circuits in a building or lab. They are a source of large magnetic fields, and every effort should be taken to place an electron microscope as far away as possible because, even at a small distance away. The interference levels are much higher than the tolerance level of the microscope.

Earth leakage current
In some instances, site surveys can actually uncover problems in the power supply. Large leaks down the earth wire produce huge magnetic fields, which can often be identified by turning off different areas of power supply. 

Lighting
Typically, lights are turned off in microscopy rooms during imaging, but occasionally lighting can still cause interference. In general, LEDs tend to be the best to use for electron microscopy labs, whereas fluorescent lights should be avoided. Changing the lights is often the simplest solution to overcoming the problem.

Trains and Trams
Trains produce interference that is far greater than the levels than can be tolerated by electron microscopes, depending on how far away the tracks are. The rate of train runtime can also determine the amount of disruption as regular activity – not only from vibrations as trains pass by, but also from magnetic fields running along the power lines – can affect instruments hundreds of metres away. 

Similarly, trams can also produce vibrations and magnetic fields that can be disruptive. The tram line itself is set on a hill and this influences the level of interference, based on whether a tram is going up or down the slope. However, in this situation, a microscope was still installed but with the addition of a magnetic field cancelling system to disrupt the impacts of interference. 

For further information on site survey services and magnetic field cancelling systems, contact us here.


About Spicer Consulting Limited

Since it was established in 1988, Spicer Consulting has built a world-wide reputation in magnetic field cancelling for Electron Microscopes and similar instruments. Today, working with equipment manufacturers and users alike, the company is recognised as an industry expert in maximising the performance of electron microscopes, electron beam lithography systems, CD metrology and focused ion beam tools. 

Spicer Consulting magnetic field cancelling systems protect sensitive equipment in the world's leading laboratories, universities and semiconductor manufacturing plants, as well as in the test facilities of electron and ion beam equipment manufacturers. Its magnetic field, vibration and acoustic analysis systems have been adopted as standard equipment for the conduct of site surveys by leading equipment manufacturers. Spicer Consulting is located in Stewartby, Bedfordshire, within the United Kingdom’s Golden Triangle of elite universities in London, Cambridge and Oxford.