To ensure electronic devices are immune to electromagnetic interference, manufacturers conduct EMC testing.
Radiated susceptibility testing evaluates the ability of a device under test to operate normally under an externally generated electromagnetic field.
IEC 61000-4-3 is the common reference to check the immunity of electrical and electronic devices against radiated electromagnetic energy.
When several electronic devices co-exist in an environment, it is important to avoid the intervention of electromagnetic interference
The vulnerability of electronic devices to electromagnetic interference is inherent and unstoppable. Electromagnetic fields are present everywhere and are capable of interfering with devices. The electromagnetic field generated by the device of interest also interferes with the fields in its vicinity. In both cases, there will be some abnormal functioning--it can be either in the device of interest or the device in its vicinity.
When several electronic devices co-exist in an environment, it is important to avoid the intervention of electromagnetic interference so that all associated devices operate normally. To ensure electronic devices are immune to electromagnetic interference, manufacturers conduct EMC testing. The conducted and radiated susceptibility of electronic devices can be determined using these tests. If the device passes testing, the product is ready to go on the market. If a device does not pass testing, the manufacturer must modify the design and include EMI mitigation techniques until the device of interest gets a pass certificate.
In this article, we will focus on radiated susceptibility in electronic devices, and the testing and standards that help mitigate this issue.
Electronic products are subjected to electromagnetic interference in the form of either conducted or radiated EMI. Conducted EMI gets transferred from the EMI source to a receiver via physical conduction paths such as wires, cables, traces, etc. When the interference affecting the devices takes no physical route and instead spreads through the air, the interference is called radiated EMI. When the device under consideration is affected by radiated EMI, it is said to have radiated susceptibility.
Devices with radiated susceptibility are often of poor quality or are defective. Radiated susceptibility becomes a challenge when unintentional electromagnetic fields interfere with power lines and signal lines in electronic products. If the electronic products are analog circuits, the tolerance to radiated EMI is less, and, therefore, they are influenced by electromagnetic field coupling. The long cables in electrical and electronic systems have high potential and the strong electromagnetic field coupling associated with them increases the susceptibility to radiated EMI. It is critical to regulate the radiated susceptibility of electronic or electrical end-products within acceptable limits. Radiated susceptibility testing helps designers have an understanding of the tolerance of a device to radiated EMI.
Radiated Susceptibility Testing
Radiated susceptibility testing evaluates the ability of a device under test to operate normally under an externally generated electromagnetic field. Radiated susceptibility testing is also called radiated immunity testing. This testing evaluates the performance of the cables and internal circuitry in the electronic device under test in an externally developed electromagnetic environment. The performance is assessed, and if the device operation continues to be unaffected, then it is considered to be immune to radiated EMI.
Radiated susceptibility testing analyzes the following:
- The field levels in the environment up to which the device continues to operate normally.
- The radiated electromagnetic field coupling with cables.
- The radiated electromagnetic field coupling with internal circuitry.
- The effectiveness of the enclosures and EMI shielding in mitigating radiated electromagnetic energy.
The test setup, measuring techniques, and testing equipment and auxiliary are arranged according to EMC standards. The entire test is conducted inside an anechoic chamber. The test instruments include an RF generator, RF power amplifier, directional coupler, transmitting antenna, power meter, and field probes. The externally inducted electromagnetic field of specified amplitude and frequency is transmitted using an antenna in the direction where the device under test is kept. The currents induced in the cables and circuits under the externally induced electromagnetic environment are proportional to the radiated field strength. If the currents induced in the device under test are greater than the acceptable limits, then it indicates that the circuit radiated susceptibility value is above the threshold, and the device receives a negative test result. The radiated field above which the device under test stops normal functioning is the susceptibility threshold. When operated below the susceptibility threshold, the device functions normally. The susceptibility threshold of the device is a function of the frequency and it varies from one device to another.
Radiated Susceptibility Standards
Various EMC regulatory bodies devise standards for conducting radiated susceptibility testing. IEC 61000-4-3 is a significant standard guiding the radiated susceptibility of a device under test. IEC 61000-4-3 is the common reference to check the immunity of electrical and electronic devices against radiated electromagnetic energy. According to IEC 61000-4-3, radiated susceptibility testing is performed in a semi-anechoic chamber with a frequency sweep from 80 to 1000 MHz. The testing setup, procedure, measuring techniques, and acceptable levels of RF energy given by IEC 61000-4-3 standards are followed by electronic manufacturers for determining the radiated susceptibility of their products.
The radiated susceptibility is an important parameter that defines the usability of an electronic device in an electromagnetic environment. Radiated susceptibility testing is conducted to determine the radiated susceptibility threshold of the device, and operation below this value is always safe.
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