The Design of Automobile Electromagnetic Noise to Suppress Interference Electric Wave

Generally speaking, electromagnetic noise is difficult to eliminate, but various measures can be taken to suppress electromagnetic noise to a level that does not cause electromagnetic interference. It is often difficult to use a simple method to solve the electromagnetic noise problem, so it is best to use several different combinations.

1. General requirements

The suppression of automobile electromagnetic noise can be carried out in the receiver, but due to the receiving frequency, the propagation mode of the interference wave and other various actual conditions, it is more difficult to take measures at the receiver. Since the electromagnetic noise of automobile electrical equipment can interfere with other communication equipment and various electronic equipment, it should be considered to suppress the electromagnetic noise generated by the automobile electrical equipment itself. The characteristics and levels of electromagnetic interference waves generated by various electrical appliances on the car are different, so the suppression method of interference should also conform to its characteristics and levels. The basic measures such as damping, shielding, filtering and connection can be used in the design of suppressing interference radio waves, and four conditions must be met: â‘  There is a good suppression effect. â‘¡ Does not hinder the performance of the automotive electrical equipment itself. â‘¢High reliability and easy to use. â‘£The price is reasonable.

Second, the electromagnetic noise suppressor

At present, the suppressors used in automobiles at home and abroad are basically composed of resistors, inductors, capacitors, so-called R, I, and C, such as resistors, shielded wires, capacitors, interference suppression coils, and interference suppression filters.

Three, methods

shield

Shielding is the most direct way to establish an electromagnetic barrier between two areas to protect the circuits in the system from damage by the electromagnetic environment.

There are many forms of shielding, which can be partitions, box-type enclosures, or cable or connector shields. The effectiveness of shielding is expressed in terms of shielding effectiveness. It is not only related to the shielding material, but also related to the thickness of the material, the frequency of application, the distance from the radiation source to the shielding layer, and the shape and number of discrete shielding layers.

Shielding has two main purposes: One is to limit the radiated electromagnetic energy to a specific area (called active shielding). Active shielding refers to the structure where the interference source is inside and prevents the interference wave from leaking to the external space. It must be grounded, and the smaller the grounding resistance, the better. The second is to prevent radiated electromagnetic energy from entering specific areas (called passive shielding). Passive shielding refers to a structure where the interference source is outside and prevents interference waves from entering the shielded space.

The steps of shielding design are: ① Determine the interference level and energy density to be shielded; ② Estimate the allowable signal level on the other side of the shielding layer; ③ Combine the product structure and housing design, select a detailed shielding design plan. The design principles of shielding are: ① High-frequency electric field shielding should use copper, aluminum, magnesium and other good conductive materials to obtain maximum reflection efficiency. ② Use magnetic materials such as iron and nickel-iron high-permeability alloys for low-frequency magnetic field shielding to obtain maximum absorption efficiency. ③The shielding layer with sufficient thickness can shield the electric field of any frequency, and has a high shielding efficiency. ④Multilayer shielding (including chassis and cable) can provide high shielding effectiveness in a wide frequency band, but cost and other performance requirements (such as cable deflection) must be considered. ⑤All joint surfaces used to seal the gap must be clean, and there must be no non-conductive coating. ⑥ In order to maintain the shielding effectiveness of the housing, conductive linings, spring washers, waveguide attenuators and grids should be added to the necessary threading holes.

connection

The connection is to establish a low-impedance path between the two metal surfaces. This path can be established between the ground reference and components, circuits, shields and structural parts. The purpose of the connection is to establish a uniform electrical structure, that is to try to make the path of the radio frequency current uniform on the structure, to avoid generating potential between metal parts, thereby causing interference.