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With the growing number of electromagnetic compatibility (EMC) regulations, standards, and mandatory requirements both domestically and internationally, the importance of addressing EMC issues in electrical and electronic products has become increasingly recognized by governments and manufacturers around the world. Among the key tools used in EMC research and development, semi-anechoic chambers play a crucial role. In recent years, various industries in China have established EMC laboratories tailored to their specific product needs, including telecommunications, power systems, home appliances, and automotive sectors.
The National Bus Quality Supervision and Inspection Center introduced an EMC laboratory from Germany, which included a 3/5 m method semi-anechoic chamber, a conduction test shielding room, and a shielding amplifier room. The facility was completed in February 2005 and successfully passed the acceptance inspection by the Chinese National Accreditation Board for Laboratories (CNAL). During the planning and construction of the central 3/5 m semi-anechoic chamber, we accumulated valuable experience that can be shared and referenced by others in the field.
**1. Selection and Construction of the Overall Scheme for the Semi-Anechoic Chamber**
A semi-anechoic chamber is primarily designed to replace open-area test sites for measuring electromagnetic radiation disturbance and immunity. To simulate the propagation conditions of an open site—where only direct and ground-reflected waves are considered—the size of the chamber must align with the structural requirements of such environments. Common configurations include the 10 m, 5 m, and 3 m methods. There are multiple types of semi-anechoic chambers, varying in function, structure, materials, and installation style. The choice of solution depends on the user’s testing needs, the size of the test object, the required test level, and budget considerations.
First, it's essential to define the frequency range, whether the tests follow military or civilian standards, and whether the purpose is pre-compliance testing or third-party certification. Next, determine the maximum space the test object will occupy, the primary application criteria, financial constraints, and future expansion plans. This helps in selecting an appropriate and feasible testing environment and equipment configuration.
There are two main approaches to constructing a semi-anechoic chamber: modular assembly and welding. The assembled version uses profiled steel plates with bolt-on modules, connected with conductive gaskets to ensure RF shielding and electrical continuity. This design is lightweight, easy to assemble, and allows for future modifications. The welded version uses large steel plates joined together, offering better durability and higher shielding performance but at the cost of being less flexible and harder to disassemble.
Each manufacturer may use different shielding panel connection methods, so it's important to understand and compare these to ensure good electrical contact and sealing. The choice should also consider the actual construction timeline and other practical requirements.
**2. Mother Building and Infrastructure**
Setting up an EMC laboratory involves a systematic approach, starting with the design of the mother building, followed by the installation of the semi-anechoic chamber and test equipment. The mother building must be constructed first, taking into account factors such as floor space, structural load, power supply, air conditioning, and waterproofing. The ceiling height must be sufficient to accommodate the semi-anechoic chamber, conducted test shielded room, and other auxiliary facilities.
Adequate space should be reserved between the mother building and the chamber for installation, maintenance, and ventilation. The floor must support the weight of all shielding structures and mounting components, requiring careful construction. The ground must be flat, with minimal waviness over several meters, and meet high moisture control standards. A concrete pit is often needed for the turntable, and proper waterproofing is essential.
Before installing the chamber, the floor must meet certain humidity and grounding requirements. Each test chamber should have a low-resistance grounding point. Due to the complexity of interfacing between the chamber and the mother building, and the limited experience of domestic contractors, it's vital for civil engineering designers, construction teams, and chamber manufacturers to collaborate closely.
**3. Issues within the Darkroom Itself**
**3.1 Doors and Exits**
The darkroom typically requires two screened doors—one for personnel and one for the test object. Door designs vary, but they are usually chosen for ease of maintenance. Since the door is a major source of performance degradation, its lifespan and reliability should match that of the lab. The door leaf and frame often use a concave three-knife contact structure, with a soldering blade inserted into a spring-loaded finger piece on the frame to ensure good electrical continuity.
For personnel access, a hinged door with two leaves is common, connected via a lever mechanism to ensure smooth and tight closure. For larger objects like cars or motorcycles, sliding doors are preferred due to their larger opening size. These doors often include absorbing material and are sized based on the maximum dimensions of the test object. They may also feature a ramp or platform that automatically adjusts when the door opens or closes, ensuring a level surface inside and outside the chamber for safe handling of large items.
August 26, 2025