Shielding refers to a variety of methods used to safeguard a delicate signal against external electromagnetic signals or to prevent a more robust signal from escaping and disturbing neighboring electronics. 

Fig: EMI Shielding

Shielding can be achieved through the following techniques:

• Conductive shields: Conductive shields are made of conductive materials like copper, aluminum, or steel. These shields can be applied as a box or wrapped around the electronic components to create a Faraday cage that blocks electromagnetic interference (EMI). When the EMI hits the shield, it induces an electrical current that flows on the surface of the conductive material and creates an opposite electromagnetic field that cancels out the EMI. This technique works well at higher frequencies, where the wavelength of the electromagnetic waves is smaller than the holes in the shield. They can be used in scenarios where a high level of shielding effectiveness is required, such as in medical or military applications. Conductive shields are also suitable for applications where the size and shape of the electronic component or PCB are irregular, and custom shielding needs to be designed.
• Absorptive shields: Absorptive shields are made of materials that can absorb EMI, such as ferrites or magnetic sheets. These materials have magnetic properties that allow them to convert electromagnetic waves into heat energy. The absorbed energy is dissipated as heat, preventing the EMI from reaching the sensitive electronic components. This technique is suitable for low and high-frequency EMI. It is cost-effective and can be used in scenarios where the size and shape of the electronic component or PCB are regular. Absorptive shielding materials can also be easily applied as a layer on the PCB or the electronic component, making them convenient to use.
• Reflective shields: Reflective shields are made of materials with high conductivity, such as metals. These shields reflect EMI away from sensitive electronics, similar to how a mirror reflects light. The reflective shield creates an opposite electromagnetic field that reflects the EMI away from the sensitive components. This technique works well at low and medium frequencies, where the wavelength of the electromagnetic waves is larger than the holes in the shield.

Grounding Techniques for reducing EMI and EMS:

Grounding involves connecting sensitive electronics to the ground to provide a low-impedance path for unwanted electrical currents to flow away from the system. Grounding can be achieved through the following techniques:

• Single-point grounding: In single-point grounding, all circuits are connected to a common ground point. This type of grounding is suitable for low-frequency circuits below 1 MHz, and it helps to prevent common-mode impedance coupling. Single-point grounding can be implemented as series-single-point grounding or parallel-single-point grounding. In series-single-point grounding, all the circuits are grounded in series, and in parallel-single-point grounding, all the circuits are grounded in parallel. The choice between these two depends on the specific application and the grounding requirements.
• Multi-point grounding: In multi-point grounding, each circuit is grounded separately to the nearest ground plane of low impedance. This type of grounding is preferred in high-frequency circuits operating above 10 MHz. The advantage of multi-point grounding is that it can reduce the ground impedance and provide a more effective ground return path for high-frequency signals.
• Hybrid grounding: Hybrid grounding is a combination of single-point and multi-point grounding techniques. This approach utilizes single-point grounding for low-frequency circuits and multi-point grounding for high-frequency circuits. This can provide the benefits of both types of grounding and ensure optimal grounding for the entire circuit.
• Floating ground: In a floating ground, there is no coupling loop between the circuits and the ground plane. This type of grounding is typically used in isolated power systems or circuits to prevent ground loops and common-mode noise. However, it is important to ensure that the floating ground is properly isolated and does not pose a safety hazard or cause interference with other circuits.

Click here to view the EMC Board Level Shields products.