When current flows in a charged conductor, it produces an electromagnetic field at about 90 degrees to the conductor. This current changes the direction of flow a number of times and at a particular frequency. These electromagnetic lines may pass through another conductor in the same circuit which produces voltage. This is the basic concept of coupling which transfers energy from one part of the circuit to the other. While this is unfavorable if it happens accidentally and induces noise or crosstalk, coupling may be deliberately added to the circuit for certain functions. All of this at the macro level is also applicable to the tiny circuits on printed circuit boards. This is because electromagnetic interference (EMI) can cause malfunctioning in the already complex boards with several components and wires. There are various types of coupling, and the right one can be chosen depending on the application requirement and the path taken by the EMI to travel from source to destination. This post discusses various EMI coupling methods and the use of PCB shields to prevent unintended coupling.
EMI Coupling Methods
While electromagnetic coupling can actually introduce noise, the same technique can be applied for the benefit of the circuit. Also known as transformer action, it is often used in transformer coils to produce alternating current (AC). This creates electromotive force, electrically isolates the transformers and couples them magnetically. Here are some commonly used coupling methods in various scenarios and based on the type and direction of EMI.
- Conductive coupling: Conducted EMI is introduced when energy flows through two charged conductors in a circuit creating an electromagnetic field around them. This may happen due to design and installation faults which may induce EMI through connected cables. While shielding of cables, grounding or circuit boards, and isolation of signals are key aspects in mitigating this type of EMI, conductive coupling may help. This is done through common-impedance coupling which comprises conductive transfer between source and receptor.
- Inductive coupling: This is applied when EMI is produced by a created magnetic field. Here, source EMI couples over the magnetic field at the receptor end. Based on the concept of electromagnetic induction, current is induced in the receptor at the required intensity based on variations on current and inductance between source and receptor.
- Radiative coupling: External EMI may travel via air to the target. Here the source and target devices may be distantly located from each other, wherein noise is often radiated. Hence, radiative coupling is used to mitigate EMI. These are high-frequency microwave signals, and widely used in radio frequency interference (RFI) induced applications.
- Capacitive coupling: This is applied in case EMI is generated due to distributed capacitance. Also known as exchange coupling, here the signals are transmitted across various levels through the electromagnetic field of two unit circuits.
What is Unintended Coupling?
While coupling is deliberately implemented to mitigate EMI, unintended coupling that occurs in a circuit may even damage its functioning due to noise. This is one of the major issues in PCBs and more so as their designs have become increasingly complex owing to several components, layers, and wires. Coupling may happen due to fluctuations in frequencies and voltages. Importantly, this issue may not be visible or easily predictable always, and if it goes unnoticed may result in chip failure. So, the best solution is prevention, and this issue can be settled efficiently at the design stage by using PCB EMI shields. These are metal shields used to protect the board and they are absolutely effective in avoiding unintended coupling altogether.
If you are an OEM or a PCB manufacturer that needs premium quality EMI shields for your boards, make sure you partner with the right manufacturer and supplier of PCB EMI shields. Ensure they specialize in design and can offer you customized and flexible PCB shields. XGR Technologies offers SnapShot ™ EMI shields that offer excellent shielding effectiveness from below 1 GHz to 12 GHz. As well as consistent isolation across a wide frequency range. These shields are made of plasticized metal and hence are flexible, lightweight, and can be removed and reinstalled easily. The shields have non-conductive interior surface which reduces electromagnetic coupling with traces of the circuit that helps prevent noise and enhances efficiency and safety. You can contact XGR Technologies team today to know more about these EMI shields or share your requirements.
