Now compare the shielding effect of the sub-cover and non-sub-cover structures of electronic test instruments. From the equivalent circuit, it can be seen that the sub-cover structure affects one more level of attenuation, so the shielding effect is significantly improved. Now compare the shielding effect of the sub-cover and non-sub-cover structures of electronic test instruments. From the equivalent circuit, it can be seen that the sub-cover structure affects one more level of attenuation, so the shielding effect is significantly improved. It can be seen that the split cover structure is better than the common cover structure. The gap between the shielding box body and the cover is easy to leak. In order to reduce the leakage and enhance the shielding effect, a soft mesh shielding strip is placed between the upper and lower covers and the box body, and is bonded with conductive adhesive.
According to the external dimensions, its lowest-order resonance frequency f0 moment = 12L0E0 (1w) 2+ (1l) 2, f02 = 124P × 10-7 × 8.85 × 10-12 (10.28) 2+ (10.125) 2 = 132 (MHz ) This shows that its frequency meets the requirements.
Shielding effectiveness: SE = A + Rp = 1.31lfLrCr + 168-20lgLrfCr = 1.31 × 2 × 10-312 × 108 × 1 × 0.61 + 168-20lg1 × 12 × 1080.61 = 145.95dB, where the thickness of the shield L is 2mm, the material For aluminum. f is 1200MHz, L = 1, CD = 0.61.
Determination of the size of the heat dissipation hole: In the design of the whole machine structure, the choice of the size of the vent hole has a great influence on the shielding effect. When the area of ​​the vent hole is equal, the square hole leaks more than the round hole, and the rectangular hole is more than the square hole Big leak. The smaller the maximum line size of the hole, the smaller the leakage, so choose the round hole. And multi-round hole layout, according to the hole calculation shielding efficiency SE = 20lg (K / 2L), where: K = C / f = 3x108 / 1200x106 = 0.25mm, K / 100 is taken as the diameter of the heat dissipation hole, so the diameter of the hole is 2.5mm .The shielding of the module is in the whole machine, and each module also interferes with each other. The shielding of the module is very important. In the structural design, the upper cover is fixed at multiple points, the joints are uneven, and the shielding material is bonded.
Connector selection and installation: SMA series is used for the high-frequency interface, and rigid cables and cables composed of magnetic beads and shielding sleeves are selected for the cables, which play a greater role in solving the cable leakage field and improve the shielding effect.
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