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In this paper, a solution for electromagnetic compatibility guarantee based on the combination of metal shielding and circuit components distance estimation methods is presented. The electromagnetic noises generated from a working radio-electronic unit can expand into the space and act on other around radio-electronic units. An EMC guaranteed radio-electronic unit by the suitable technique method will not cause the electromagnetic noise to others. In opposition, it will not be under electromagnetic action from another one. Due to the power of electromagnetic noise, the metal shielding, distance estimation or other technique methods should be used to guarantee EMC. Every method has own advantage as so as weakness for detail radio-electronic unit, so it is necessary to choose a suitable method to guarantee EMC for them, the combination of metal shielding and distance estimation is a choice, for example. The proposed solution has been evaluated by using CST (Computer Simulation Technology) software and EMxpertEHX analyzer in oscillator circuit context. The simulated results on CST show that the proposed solution decreases the electromagnetic radiation about of 39.1 dB at frequency 500 MHz in comparison to results when nothing electromagnetic compatibility methods are not used. The experimental results on the oscillator circuit are presented. The electromagnetic radiation reduction of the oscillator circuit is about of (25 - 30) dB. In comparison to individual metal shielding and distance estimation methods, the effectiveness of the proposed solution for electromagnetic compatibility guarantee is significantly increased.

Nowadays, with the huge development of science and technology, the radio-electronic units (REUs) must be in guarantee not of the desired operation efficiency but electromagnetic compatibility (EMC) also before to use (refs. [

In this paper, we propose a solution to combine both mentioned above methods to guarantee EMC. Before investigation the SE of proposed solution, the metal shielding as well as distance estimation are investigated individually in detail by the CST software (ref. [

The main parameter to determine the influence of the metal sheath on EMF is SE related to the ratio of the incident and transmitted electric (magnetic) intensities, which are given as (ref. [

S E e = 20 lg | E i E t | (1)

S E h = 20 lg | H i H t | (2)

where E i , E t ( H i , H t ) are the incident and transmitted electric (magnetic) intensities, respectively.

Beyond Equation (1) and Equation (2) given above, as shown in

S E [ dB ] = R [ dB ] + A [ dB ] + B [ dB ] (3)

where,

R dB = 168 + 10 log 10 ( σ r / μ r f ) (4)

is the reflection in far field (ref. [

R e , dB = 322 + 10 log 10 ( σ r / μ r f 3 r 2 ) (5)

R m , dB = 14.57 + 10 log 10 ( f r 2 σ r / μ r ) (6)

are the reflections of electric and magnetic sources in near field, respectively (ref. [

A dB = 20 log 10 e t / δ = 20 t δ log 10 e = 1.314 t f μ r σ r (7)

is the absorption (ref. [

B = 20 lg ( 1 − e − 2 t / δ ) , (8)

is the re-reflection (ref. [

of material. t [ cm ] is the thicknees of material. r [ cm ] is the distance between radiation source and metal sheath. The re-reflection B will be meaningful if A ≤ 15 [ dB ] (ref. [

All the results above show that the metal shielding is easy to design, but it needs to eliminate slits and to choose suitable size of holes if they are that depends on technology. So to enhance or perfectly guarantee EMC it is necessary to use distance estimation between RE modules or units combined to metal shielding. As know, the EMF changes with propagation distance, but differently for near and far fields. For the far field, Inverse Distance Method (ref. [

E ( R ′ ) [ dB ] = E ( R ) [ dB ] + 20 lg ( R / R ′ ) (9)

The near field is more complex than far field. The field parts change inversely not linear to distance as 1 / r , but nonlinear as 1 / r 2 or 1 / r 3 (

The boundary between near and far fields is where the ratio E / H = Z w called wave impedance is approximately equal to internal impedance of free space η 0 (ref. [

Consider an aluminium (Al) sheathed box (ASB) with size of 16 × 10 × 3 cm and thickness of sheath of 2 cm (

A second ASB with size of 10 × 10 × 3 cm is placed in distance of d from the first one. The CST will be used to evaluate SE for different cases as: single ASB, single ASB with holes in the sheath, two ASBs with different distance one from other. The EMC will be simulated and evaluated at frequency changing from 1 MHz to 1 GHz. Beside using CST to evaluate the SE of proposed solution, the oscillation circuits and power supply with output voltage of 5V is experimentally evaluated using measurement equipment EMxpertEHX consisting from EMxpert software and EMSCAN scanner (

Using Equation (3) and aluminium sheath with t = 0.2 [ cm ] , μ r = 1 and σ r = 0.61 at frequency from 500 kHz (ref. [

From

However, the ASB is not always closed tight; instead, there are slits or small holes and apertures used for air ventilation or for cable installation, really. If the slits and holes are not suitble designed, the radiation signal leakage may overcome the standard limit as of CISPR-22 then causes inexpectant effects.

For the case of ASB with three apertures of different size of 3 × 1.5 cm , 2 × 1.0 cm and 1 × 0.5 cm the EF intensity decreases about 23.1 dB, 48.2 dB and 57.3 dB in comparison to that of inshielding case measured at 500 MHz frequency. This situation is similar to the case measured at a distance of 2 cm (

Using Equation (9) and what described in

From

Let a second ASB with size of 10 × 10 × 3 cm is placed in distance of d from the first one. The distribution of the EF around both ASBs is simulated and illustrated in

the distance between two ASBs, the EF intensity inside second ASB-frequency characteristics with different distances are simulated and illustrated in

Although EF intensity decreases with the increase of distance, but it does not reject the influence one on other if both of ASBs are in operation regime. This phenomenon is proved when observing the power supply is placed close to the oscillator circuit without shielding (

From the EF distribution in the plane of scanner (

EF intensity is relatively hight and unhomogeneous depending on the circuit power of the individual electronic elements. At some positions, it rises to 90 dBuV.

However, the EF intensity reduces significantly when both units are metal sheilded and placed in distance of 10 cm one from other, i.e. is under the EMC guarantee (

From

It is clear that the electromagnetic noises from radio-electronic units should not act one on other, means the EMC is guaranteed when they are shielded with high SE and placed in a suitable distance.

Based on Computer Simulation Technology, EMxpertEHX equipment, Inverse Distance Method, the EMC is simulated and tested followed to CISPR-22 standard. The EMC guarantee is investigated by two methods, metal shielding, distance estimation and then combination of them. The EMC is also experimentally evaluated for power supply and oscillator circuit. Although both methods are not new, but combination of them enhances the effectiveness to guarantee EMC, moreover the obtained results give us clear image about EMC, which can be used to test the capability to guarantee EMC of REUs in detail.

The results give us a hint to combine simulation and testing tools to automatically evaluate EMC of the REUs with different mechanical configurations, electronic designs at different estimated distances in the future.

The authors declare no conflicts of interest regarding the publication of this paper.

Truong, N.D., Van Nghia, T., Chinh, B.D. and Quy, H.Q. (2019) Combination of Metal Shielding and Distance Estimation for Electromagnetic Compatibility Guarantee. Journal of Electromagnetic Analysis and Applications, 11, 135-147. https://doi.org/10.4236/jemaa.2019.119009