Explanation of EMC test standards and measurement methods for automobiles | NEXTY Electronics, an electronic components and semiconductor trading company

Automotive technology is rapidly evolving due to the spread of autonomous driving and electric vehicles (EVs). As a result, onboard equipment is becoming more sophisticated and high-performance, making it increasingly important to comply with EMC (electromagnetic compatibility) standards.
This column provides engineers with easy-to-understand explanations of the changes in the EMC environment surrounding automobiles, the latest trends in international standards, and actual measurement methods.

Changes in the automotive EMC environment

Examples of changes in the automobile industry

In today's world, the use of wireless communications has expanded rapidly, and automobiles are now subject to a variety of wireless communications and electromagnetic waves while driving. Furthermore, the electronic control technology installed in automobiles is becoming more sophisticated in order to improve environmental performance, safety, and comfort. For autonomous driving, vehicles are now equipped with sensors in all directions, and with the spread of EVs, there are also increasing opportunities to connect vehicles to charging equipment. In order to respond to these technological innovations and environmental changes, automobiles are strongly required to comply with various EMC regulations.

Trends in international EMC standards

Major international EMC standards for automobiles

The main international EMC standards (CISPR *1 and ISO *2) for automobiles and their installed components are summarized below.

test			International Standards	Application point/measurement point	Test Frequency
Actual vehicle test	EMI	Wideband noise detection	CISPR12	Electric field measurement at a distance of 10m or 3m	30MHz～1GHz
		Narrowband Noise Measurement	CISPR12	Electric field measurement at a distance of 10m or 3m	30MHz～1GHz
		In-vehicle receiver protection	CISPR25	Measuring the voltage of your vehicle's ANTENNAS	150KHz to 2.5GHz
		Low-frequency radiated interference	CISPR36	Magnetic field measurement at a distance of 3m	150KHz to 30MHz
	EMS	General vehicle testing	ISO11451-1	ー	ー
		External radiation source method	ISO11451-2	Externally applied to the vehicle	10KHz to 18GHz
		Portable Transmitter Act	ISO11451-3	Applied by a portable transmitter	1.8MHz～5.85GHz
		BCI method	ISO11451-4	Apply to harness	1MHz to 400MHz
		Reverberation Chamber Method	ISO11451-5	Apply to harness/ECU	LUF (or 10kHz) to 18GHz
		Electrostatic Discharge Test	ISO10605	Apply to areas that can be touched by humans	ー
Component Testing	EMI	In-vehicle receiver protection	CISPR25	Electric field measurement at a distance of 1m Conducted Emission Measurement	150kHz to 2.5GHz
	EMS	General component testing	ISO11452-1	ー	ー
		Anechoic chamber method (ALSE)	ISO11452-2	Apply to harness/ECU	80MHz～18GHz
		TEM cell method	ISO11452-3	Apply to harness/ECU	10KHz to 200MHz
		BCI method/TWC method	ISO11452-4	Apply to harness	1MHz～3GHz
		Stripline Method	ISO11452-5	Applied to harness (and ECU)	10KHz to 400MHz
		Direct Power Injection (DPI)	ISO11452-7	Apply to CONNECTORS pin	250KHz to 400MHz
		low-frequency magnetic fields	ISO11452-8	Applied to ECU	15Hz to 150KHz
		Portable Transmitter	ISO11452-9	Apply to harness/ECU	26MHz～5.85GHz
		Low-Frequency Conduction	ISO11452-10	Apply to harness	0Hz, 15Hz to 150kHz
		Reverberation Chamber Method	ISO11452-11	Apply to harness/ECU	LUF to 18GHz
		Electrostatic Discharge Test	ISO10605	Apply to harness/ECU	ー
		General Exams	ISO7637-1	ー	ー
		transmission	ISO7637-2	Applying a pulse to POWER SUPPLIES line/measurement	—

List of EMC international standards

*1 CISPR: International Special Committee on Radio Interference
*2 ISO: International Organization for Standardization

Expansion of test frequencies in automotive EMC standards

In recent years, with the advancement of automotive electronics and wireless communication technology, the frequency bands covered by EMC testing have changed significantly. This is because the spread of millimeter-wave radar and 5G communications, as well as the introduction of electrification and wireless charging systems, require electromagnetic compatibility over a wider range of frequency bands than before. Below, we will explain the expansion of high- and low-frequency test frequencies.

◆Expansion of high-frequency test frequencies

・Immunity (EMS) test
With the spread of millimeter-wave radar and 5G communications, the test frequency has been expanded from the previous 1 GHz to 6 GHz.
On the other hand, there is also the issue of longer test times in order to ensure test quality.
・Emission (EMI) testing
Currently, CISPR12 for actual vehicles is limited to 1GHz, but discussions have begun to extend it to 6GHz, as with other product committees.

◆ Expansion of low-frequency test frequencies

・ISO standard trends
In the future, support for even lower frequency bands is expected to progress, with EMC requirements (such as supra-harmonics from power conversion devices and conducted emissions from AC POWER SUPPLIES ports) being added for the frequency range of 2 kHz to 150 kHz.
・Wireless charging system (WPT)
The need for electric field measurement is increasing, and test methods are being reviewed.

EMC measurement method

EMC measurement methods in the high frequency range: ALSE method and reverberation chamber method

What is the ALSE method?
ALSE stands for Absorber Lined Shielded Enclosure, and in Japanese it is called the "anechoic chamber method" or "ANTENNAS irradiation method." This is a typical measurement method used for immunity testing of automobiles and in-vehicle equipment (EMS) by irradiating an electromagnetic field from ANTENNAS in an anechoic chamber, and complies with the ISO 11452-2 standard. The frequency range covers high frequencies up to 18 GHz.
The ALSE method can only irradiate electromagnetic waves from one direction.

What is the reverberation chamber method?
The electromagnetic waves in the test area are diffused by the reflection of metal surfaces in the shielded chamber and the rotation of the stirrer, creating a homogeneous test environment in terms of electric field. Instead of the conventional method of irradiating electromagnetic waves from one direction, the electromagnetic waves are irradiated from all directions, enabling tests to be conducted under conditions closer to the real environment. This also significantly reduces test time. It is specified in ISO 11452-11 and other standards. It supports a frequency range up to 18 GHz, a high frequency region.

Both the ALSE method and the reverberation chamber method are EMC measurement methods compatible with the high frequency range (up to 18 GHz). Traditionally, the ALSE method was the mainstream, but in recent years, as automobiles have begun to be equipped with multidirectional sensors, there has been a demand for EMC measurement from all directions.
The ALSE method can only irradiate radio waves from one direction, so a turntable must be used for omnidirectional EMC evaluation, which poses the problem of long test times.To solve this problem, the reverberation chamber method was developed, which allows for more efficient automotive EMC measurements.

ISO11452-2 ALSE method
(Measurements in each direction are taken by rotating the turntable.)
ISO11452-11 Reverberation chamber method

Trends in EMC test standardization in the low frequency range

With the widespread adoption of electric vehicles, wireless charging systems (WPT) are moving from the development stage to the preparation stage for widespread adoption. This has led to an increased importance of EMC evaluation in the low-frequency range. While traditional EMC testing has focused primarily on the high-frequency range, WPT requires electric field measurements in the low-frequency range from a few kHz to several tens of MHz, and international standards are currently being developed. The low-frequency range of 2 kHz to 30 MHz is important for evaluating the power conversion devices used in WPT and the harmonics (supraharmonics) generated by their operation. To accurately measure these effects, CISPR11 is scheduled to standardize monopole ANTENNAS measurements at a distance of 10 m for the low-frequency range of 2 kHz to 30 MHz.

Summary of automotive EMC standards and measurement methods

In response to the rapid evolution of automotive technology in recent years, EMC countermeasures are becoming increasingly important. The EMC measurement range has expanded widely from low to high frequencies, and test methods are becoming more sophisticated, requiring electromagnetic wave evaluation from all directions. Engineers are required to understand the latest trends and take appropriate measures.
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