Isolation from Electromagnetic Interference (EMI) for Research Instruments

The term electromagnetic interference (EMI) refers to the disturbance induced by an electromagnetic field that interferes with the exact performance of electrical equipment and causes trouble for precision research applications.

EMI can be produced from natural sources, like the sun or the Earth’s magnetic fields, or from man-made sources. However, most of the EMI is triggered by stray electrical or magnetic fields produced by electrical devices or machinery.

Effects of Electromagnetic Interference

EMI can negatively affect those applications, which assess the electrical characteristics of samples. Typical applications which determine electrical properties are Wifi testing, semiconductor probe stations, cell phone testing and electrophysiology testing.

These applications calculate minute levels of electrical current, hence any external source of electricity may induce error within the measurements. in addition, variable EMI can degrade the repeatability of these measurements.

Other types of sensitive applications are those that employ electromagnetic fields in their sensing mechanisms. Electron microscopy and MRI/fMRI happen to be the most common analytical methods in this category and come under transmission electron microscopy and scanning electron microscopy techniques.

Since the behavior and travel of electrons is vital to these sensing techniques, stray fields can present a major challenge. Normally, EMI fields appear as striations right through the images and manifest as sawtooth patterns along feature edges as shown in Figures 1 and 2.

SEM Image with no EMI Shielding

Figure 1. SEM Image with no EMI Shielding

SEM Image with EMI Cancellation

Figure 2. SEM Image with EMI Cancellation

Diagnosis of Electromagnetic Radiation

Since EMI usually manifests itself in ways that are difficult to identify, it is hard to diagnose electromagnetic radiation. Users can run tests incessantly without actually realizing that EMI is degrading the precision of measurements, and when the problem is identified it becomes hard to differentiate EMI from other sources of noise. Users mostly need to go through a troubleshooting process before they can detect an EMI issue.

Often, EMI sources can be distant from the point of installation. Since electromagnetic field causes EMI, it can extend across rooms and buildings through radiative coupling. At times, simply decoupling the instrument will not solve the problem.

Solutions to Solve EMI Issues

Similar to other types of noise sources, a number of solutions are available to overcome these issues. First, if possible, the source of the EMI should be turned off. If not, the source can be moved away from the instrument or else the instrument can be located at a distant point from the source of EMI. If these solutions are not practical, the EMI source can be separated from the surrounding environment. This can be achieved by appropriately grounding the machinery, building a Faraday cage around it, or positioning it in a room built from conductive material.

However, if these solutions are inappropriate, then the EMI should be dealt with at the instrument itself. First, users must ensure that the instrument is appropriately grounded. Then, a piece of conductive wire should be used to link the instrument to a ground, which is in turn is coupled to the Earth. Next, a Faraday cage should be constructed around the instrument. These cages are made of conductive material and comprise five- or six-sided boxes. They can efficiently disperse stray magnetic fields in the environment.

Conclusion

If all the above remedies fail, users can employ an active EMI cancellation system. EMI cancellation systems are capable of detecting electromagnetic fields at the instrument level and produce fields which cancel out the offending fields. These are the high-performance solutions, which are currently available to solve EMI issue.

About Herzan

Herzan provides high performance environmental solutions for precision research instruments. They include acoustic enclosures, vibration isolation systems, Faraday cages, and site survey tools. Herzan specializes in supporting nanotechnology research, but also offers solutions for product testing, in-vitro fertilization, and many other applications.

Herzan understands that every application and environment is different, so it collaborates with customers to create comprehensive integrated solutions that satisfy their unique demands.

Herzan was founded in 1992 by Ann Scanlan in Orange County, California. Originally, Herzan was established as an American subsidiary of Herz Company Ltd., a Japanese company specializing in vibration control. The name Herzan comes from the amalgamation of 'Herz' and 'Ann'.

This information has been sourced, reviewed and adapted from materials provided by Herzan LLC.

For more information on this source, please visit Herzan LLC.

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