This article discusses mitigating the challenges related to radiation emission non-compliance while evaluating in-vehicle infotainment (IVI) displays per the guidelines set forth by CISPR 25 automotive electromagnetic (EM) compatibility standards. The research shows that IVI display systems infringe upon these standards, exhibiting radiation levels that exceed the permissible limits by 2.51 dB in the frequency band ranging from 555 to 960 MHz. In-depth analytical work pinpoints the root cause of this excessive radiation to be the printed circuit board assembly (PCBA) embedded within the IVI screens. To counteract this problematic scenario, the study described in this article finds that a fine-tuned adjustment of a conductive foam gasket solves the issue. The applied modifications substantially reduce radiative interference, allowing the system to comply with existing standards. The study reported in this article serves a dual purpose. First, it identifies the primary culprit behind the elevated radiation emission levels during CISPR 25 compliance assessments and second, it presents an effective remedial approach. The findings offer considerable practical implications for achieving regulatory compliance in the automotive electronics sector.
THE CHALLENGE
Addressing CISPR 25 Challenges in IVI Systems
The research described in this article advances the compliance of IVI displays with CISPR 251 automotive EM compatibility standards,2 identifying the PCBA as the primary source of non-compliance. To ensure standards compliance, a novel adjustment using conductive foam gaskets was introduced to reduce radiative interference significantly. This approach offers a model for similar diagnostics, contributing to the automotive electronics field by improving EM interference understanding in IVI systems. The findings propose practical solutions for maintaining regulatory adherence, impacting automotive design and testing and supporting the evolution of more refined EMC policies and standards. This research, aimed at enhancing vehicle safety and performance, provides a strategic framework for addressing EM interference, marking a significant advancement in automotive electronics.
Automotive Electronics Regulations
Radiated emissions regulations for automotive electronics vary globally but share core testing and implementation principles. The FCC in the U.S., ECE Regulation No. 10 in the EU and CISPR 25 internationally set crucial standards for minimizing interference and ensuring EM compatibility. Japan’s VCCI and China’s CQC contribute to a worldwide regulatory framework, ensuring the safety, reliability and compatibility of automotive electronics across regions to support global trade and consumer safety.
Radiated Emissions in Automotive Electronic Products
Radiated emissions from automotive electronics pose risks to safety, performance, regulatory compliance, brand reputation and economic success. Emissions can lead to health issues for occupants, impair critical vehicle functions like braking and navigation and disrupt data exchanges in connected vehicles. Compliance with international emission standards is crucial to avoid penalties, product recalls or bans that can damage brand image and lead to financial challenges. Conversely, meeting these standards enhances market competitiveness, consumer trust and economic benefits, highlighting the importance of rigorous testing and control measures in automotive electronics development.
The Origin of CISPR 25
CISPR 25, established by the International Special Committee on Radio Interference under the International Electrotechnical Commission (IEC), is a key international standard for EMI testing in vehicles, ships and engines. Created to address RF interference issues identified since 1934, CISPR 25 focuses on automotive and maritime sectors, evolving to manage the complexities of EM interference with the growth of automotive electronics. It has gained worldwide recognition, being incorporated into the regulatory frameworks of many countries to ensure EMI compliance and the standard plays a crucial role in mitigating EMI issues globally.
CISPR 25 Certification and Testing
CISPR 25, under the IEC, is essential for EMI testing in vehicles, ships and engines, focusing on integrity against EM disturbances. Globally recognized, it guides regulatory compliance, detailing procedures for conducted and radiated emission tests to ensure EM compatibility. The certification process involves preliminary review, testing in certified labs and result analysis, with ongoing updates reflecting new technology. CISPR 25 certification indicates EMC proficiency, enabling regulatory compliance and commercial success. This standard addresses the challenges of managing radiated emissions in automotive electronics, guiding manufacturers in adhering to EMC standards and solving issues.
RESEARCH BACKGROUND
Generating Radiated Emissions
Radiated emissions arise from electronic devices when current and voltage changes lead to EM wave propagation. This propagation is primarily due to rapid digital signal switching and clock oscillations. Power supplies, Wi-Fi, Bluetooth and mechanical components, like motors, also contribute to these emissions. Common-mode radiation, where current flows uniformly through conductors, is a significant emission source, amplified by antenna-like structures and resonant frequencies. Mitigating these emissions is vital for EM compatibility, ensuring products meet standards and maintain user safety and quality.
Mitigating Radiated Emissions
Mitigating radiated emissions during electronic device design and testing is crucial for regulatory compliance and product quality. The design phase involves minimizing high frequency component use, employing filters to limit unwanted frequencies, separating sensitive components from high frequency components and implementing comprehensive ground and power planes to reduce emissions. Selecting low-emission components and incorporating impedance matching enhances EMI mitigation.
Shielding Principles
Shielding involves the use of conductive or magnetic materials to encase devices. It blocks or absorbs EM waves from external and internal sources. The material choice, considering conductivity, device proximity and EM wave frequency, significantly influences shielding effectiveness. Effective shielding strategies include ensuring material-to-ground connectivity and minimizing enclosure openings. In this study, conductive foam gaskets effectively reduced radiation emissions in the 555 to 960 MHz frequency range from PCBAs. This demonstrates the role shielding plays in mitigating EM radiation, which is crucial for automotive electronics with high frequency applications.
Shielding acts as a barrier to block EM field transmission, reducing product emission and preventing external radiation interference. Shielding efficiency, measured in dB, is the ratio of unshielded to shielded wave amplitude. This ratio includes absorption losses, surface reflection losses due to impedance discontinuities and internal reflection losses. A high shielding efficiency value reflects a method that reduces radiated energy propagation. Clayton R. Paul3-5 has proposed examples of such methodologies, where gaskets are modified to prevent emission leaks.
EXPERIMENTAL DESIGN
Testing to verify radiated emissions involves EMC simulations and lab tests to identify and address excessive radiation, using shielding, filtering and grounding techniques to ensure compliance with standards like FCC, CE or CISPR.
Testing Radiated Emission Frequency Bands
Radiated emissions testing for automotive electronics mandates simulating real-world vehicle conditions, documenting operational parameters, like load and voltage and specifying device orientation in the test plan. Measurements need vertical polarization for frequencies up to 30 MHz and require both polarizations up to 2500 MHz, per CISPR 25:2016. Recommended antennas include the rod for VHF/UHF frequencies, biconical for wideband use, log-periodic for its broad range and directionality and horn for high gain in microwave bands. This structured approach ensures consistent, safety-compliant testing across the automotive industry. Table 1 shows some characteristics and applications of these antennas.
Radiated Interference Limitations – ALSE Method
According to the CISPR 25 standard, the absorber-lined shielded enclosure (ALSE)6,7 method for measuring radiated interference includes five distinct classes of limitations. Each class has its specific radiated interference limits, which are clearly outlined in the respective tables:
- Class 1 is the most lenient category, suitable for scenarios less sensitive to radiated interference
- Class 2 imposes stricter limitations than Class 1 and is commonly used for general vehicle components and modules
- Class 3, a medium-level restriction, is often considered the minimum acceptable standard by most vehicle manufacturers
- Class 4 includes more stringent limitations for applications that are particularly sensitive to radiated interference
- Class 5, the most rigorous category, is reserved for special applications with extreme sensitivity to radiated interference.
These classification levels enable vehicle manufacturers and suppliers to choose suitable restrictions for their needs, ensuring radio system stability across different environments. Figure 1 shows the ALSE radiated disturbance limits for various mobile service applications.
Figure 1 Examples of limits for radiated disturbances–ALSE method.
