The Relationship and Differences Between EMC and EMI
As electronic products increasingly adopt low-power, high-speed, and highly integrated LSI circuits, these devices have become more susceptible to the threat of electromagnetic interference than ever before. Meanwhile, the proliferation of high-power household appliances and office automation equipment, coupled with the widespread use of mobile communication and wireless networks, has significantly increased sources of electromagnetic interference. These changes have compelled people to regard electromagnetic compatibility as an important technical issue that demands attention. This article will delve deeply into EMC and EMI.
What's the EMC and EMI?
The use of specific technical methods to allow various electronic and electrical devices within the same electromagnetic environment to operate normally without interfering with each other is known as Electromagnetic Compatibility (EMC).
According to the national standard GB/T4365-1995, EMC is strictly defined as the ability of nearby device or electronic system to function properly in its electromagnetic environment without causing intolerable electromagnetic interference to anything within that environment.
Electromagnetic compatibility encompasses two main aspects: electromagnetic interference (EMI) and electromagnetic susceptibility (EMS).
EMI refers to the interference caused by electromagnetic waves generated due to electromagnetic emissions effects when a computerized product is powered on, affecting surrounding electronic devices. EMS, on the other hand, refers to the electrical product's ability to resist harmful interference from external electromagnetic waves.
EMI includes aspects such as CE (Conducted Emission), RE (Radiated Emission), and PT (Interference Power Testing). Meanwhile, EMS encompasses ESD (Electrostatic Discharge), RS (Radiated Susceptibility), EFT/B (Electrical Fast Transient/Burst Immunity testing), Surge (Lightning Immunity testing), and CS (Conducted Susceptibility), among others.
Evidently, the purpose of EMC design is to ensure that the electronic devices or electrical systems crafted can achieve electromagnetic compatibility within their anticipated electromagnetic environments. In other words, the designed electronic devices or electrical systems must meet the dual capabilities stipulated by EMC standards.
The principles of electromagnetic interference (EMI)
Various forms of electromagnetic interference (EMI) are the primary causes affecting the compatibility of electronic devices. Therefore, understanding the sources of EMI is a crucial prerequisite for suppressing it and enhancing the electromagnetic compatibility of electronic products. The generation of electromagnetic interference can be categorized as follows:
Internal Interference
Mutual interference among internal electronic components.
(1) Interference caused by leakage from power interruption and insulation resistance through the working power supply lines.
(2) Influences resulting from impedance coupling of signals via ground lines, power supplies, and transmission wires, or mutual inductance between wires.
(3) Interference due to certain components within the equipment or system generating heat, which affects the stability of these components themselves and others.
(4) Interference caused by magnetic and electric fields generated by high-power and high-voltage components, affecting other components through coupling.
External Interference
Effects on circuits, electronic equipment, or systems originating from factors outside the electronic device or system.
(1) External high voltage or power interfering with electronic circuits, equipment,or systems through insulation leakage.
(2) Strong magnetic fields produced in space by external high-power equipment, which interfere with electronic circuits, electrical equipment, or systems through mutual inductance coupling.
(3) Interference caused by spatial electromagnetic fields affecting electronic circuits or systems.
(4) Interference stemming from unstable ambient temperatures causing changes in the parameters of components within electronic circuits, electrical equipment, or systems.
Propagation Paths of Electromagnetic Interference
When the radio frequency of the interference source is relatively high and the wavelength of the interfering signal is smaller than the structural dimensions of the object being interfered with, the interference signal can be considered a radiation field. The electromagnetic radiation outward in the form of plane electromagnetic waves and enters the pathways of the affected object.
The interfering signal can enter the affected system through leakage and coupling, via an insulating dielectric and common impedance coupling.
The interfering signal can also enter the system through direct conduction.
Measures to Improve Electromagnetic Compatibility
Improving the electromagnetic compatibility of electronic products involves basic methods such as grounding, shielding, and filtering to suppress EMI.
1.Grounding
Grounding refers to the electrical conduction path between electrical and electronic components within a system to a ground reference point. Beyond providing safety protection for equipment system, grounding also offers the essential signal reference ground needed for device operation. An ideal ground plane is a physical entity with zero potential and zero impedance, serving as a reference point for all signal lines in the circuit. No interference signals passing through it will cause a voltage drop. However, an ideal grounding plane does not exist, necessitating consideration and analysis of ground potential distribution, conducting grounding design practice and research, and finding an appropriate grounding potential.
The methods of grounding can be categorized into floating ground, single-point grounding, multi-point grounding, and hybrid grounding. For circuit systems, options include circuit grounding, power grounding, and signal grounding, among others.
2.Shielding
Shielding involves using a conductive or electromagnetic enclosure to isolate electromagnetic interference between the internal and external spaces. Its primary purpose is to suppress solar radiation interference across space. Shielding can be categorized into electromagnetic shielding, electrostatic shielding, and magnetic shielding. The design guideline of shielding can target either the source of interference or the object being interfered with. For the source of interference, the design aims to reduce its impact on surrounding devices; for the object being interfered with, it minimizes the effect of external electromagnetic waves on the device itself.
Active Shielding: This involves placing the source of interference inside the shield to prevent electromagnetic energy and interference signals from leaking into the external environment.
Passive Shielding: This involves placing sensitive equipment inside the shield to protect it from external interference.
3.Filtering
Filtering refers to a technique used to extract useful signals from original signals mixed with electromagnetic noise or interference. A filter solution is the component that achieves this task.
In reality, components themselves can generate various types of electromagnetic noise noise during operation. For example, a switching power supply is a strong source of interference, producing EMI signals that cover a wide frequency range and have significant amplitude. As these noises propagate along with the signal, they interfere with subsequent components, and this interference accumulates through each stage, potentially leading to the malfunction of the entire circuit. By applying filtering after a component that generates substantial noise and clearly interferes with downstream components, the noise can be removed, thereby reducing the interference on subsequent stages and allowing the system to operate stably.
Electromagnetic Compatibility Certification
The EMC certification of a product is based on the electromagnetic compatibility standards and corresponding technical requirements of the product. It involves testing requirement and confirmation by a certification body, which then issues a certification certificate and mark to demonstrate that the product to market meets the industry standards and technical requirements.
In China, EMC certification has been incorporated into the scope of the CCC certification (China Compulsory Certification), which is often referred to as "3C". The country implements a safety certification system for products with mandatory national or industry EMC standards, or those containing compulsory EMC clauses. These EMC-compliant products are subject to mandatory supervision in the market circulation field; without EMC safety certification, they cannot enter the marketplace.
For products adhering to recommended national or industry EMC standards, a qualification certification system is employed. Enterprises may voluntarily apply for certification through recognized certification bodies. Certification testing procedure must be conducted at EMC testing facilities accredited by the State Administration for Market Regulation.
