What is the best way to shield sensors against electromagnetic interference?

1 What is EMI?

EMI, or unwanted electrical or magnetic noise, can interfere with the normal operation of a device or circuit. It can originate from external sources, such as power lines, radio waves, or other electronic devices, or from internal sources like switching components, motors, or wires. The effects of EMI on sensors vary depending on the frequency, intensity, and duration of the noise. These effects may include reduced signal quality and accuracy, increased noise and distortion, erratic or unstable behavior, loss of communication or data, and degradation or failure of components.

2 How to measure EMI?

To measure EMI, you need to use a device called a spectrum analyzer, which can detect and display the frequency and amplitude of the noise. You can also use an oscilloscope, which can show the waveform and the time domain of the noise. By measuring EMI, you can identify the source, the type, and the level of the interference, and determine how it affects your sensor. You can also use these devices to test the effectiveness of your shielding methods.

3 How to shield sensors against EMI?

There are two main types of shielding methods: passive and active. Passive shielding involves using materials or structures to block or reduce EMI, such as metal enclosures, shields, or screens. You can also use ferrite beads, cores, or clamps to filter out high-frequency noise from wires or cables, or twisted-pair or coaxial cables to reduce EMI from external sources. Active shielding involves using devices or circuits to cancel or compensate EMI, such as differential or balanced signals. Additionally, you can use amplifiers, filters, or converters to boost, isolate, or convert your signal to a less susceptible form. Digital signal processing (DSP) techniques can also be used to remove noise from your signal.

4 How to choose the best shielding method?

When selecting the best shielding method, several factors should be taken into consideration, such as the type and level of EMI, the frequency and bandwidth of the sensor signal, the sensitivity and accuracy of the sensor, the cost and complexity of the shielding solution, and its compatibility and performance with the sensor and system. It is important to weigh up the benefits and drawbacks of each shielding method, as well as to test it under realistic conditions to ensure it meets your expectations.

5 How to improve your shielding design?

To improve your shielding design, you should minimize the sources and paths of EMI, use proper grounding and bonding techniques, appropriate connectors and terminations, and shielding materials and devices that match your signal impedance and frequency. Additionally, it is important to avoid loops, gaps, or discontinuities in your shielding, use shielding methods that complement each other, and monitor and evaluate your shielding performance. By following these best practices, you can enhance your shielding design and ensure that your sensors work reliably and accurately in the presence of EMI.