CN101076243A - Mask for preventing magnetic card from being demagnetized - Google Patents

Abstract

The invention is used for solving the issue that is that the high power electromagnetic field produced by mobile phone can caused the loss of information saved in the magnetic card when the mobile phone and magnetic cared are placed together. The manufacturing method comprises: setting up a foamed plastic layer between a first metal plate and a second metal plate; opening holes on the first metal plate and second metal plate; the holes on the first metal plate and second metal plate are in interleaved arrangement; the four edges of the first metal plate are connected to the four edges of the second metal plate.

Description

Prevent the screening arrangement of magnetic card demagnetization

Technical field

The present invention relates to the electromagnetic shielding apparatus, the screening arrangement of electromagnetic radiation of mobile telephone of especially decaying to the magnetic card demagnetizing action.

Background technology

At present, most magnetic card has adhered to a magnetic material and has come store information on a plastic cards, and magnetic stripe can lose efficacy under the electromagnetic field effect of certain intensity and cause losing of information.Chinese invention patent ublic specification of application CN1502278 discloses anti-magnetic field antistatic anti-electromagnetic radiation box of a kind of bank card and wallet.This invention is for the metal case type container, can protect magnetic card to avoid magnetic field and electric field effects in the environment.The content mentioned according to this description of the invention, this invention can prevent effectively that permanent magnet (magnet button, antitheft check door, nuclear magnetic resonance machine etc.) is to the destruction of the stored information of magnetic card in the life.Yet along with popularizing of present mobile phone, people's custom puts together mobile phone and the wallet that magnetic card is housed, and the permanent magnet that magnetic card has been mentioned by aforementioned invention by the main cause of demagnetization has been transferred to present mobile phone.People's mobile phone used in everyday, with GSM and CDMA mobile phone is example, their peak transmitted power is generally about 2W, average transmit power is about 250mW, so the large power, electrically magnetic field pulse that mobile phone produces at short notice can make (magnetic card) characteristic of the magnetic storage material that puts together change, and cause losing of magnetic card inner storag information, bring great inconvenience for people's life.In addition, since shielding box weight big, carry inconvenience, style is single, cost is higher, therefore can bring inconvenience to the user.When people wish to reach demagnetization-protected purpose, also need original wallet is replaced with this shielding box, caused the waste of existing resource.

Summary of the invention

The present invention is in order to solve the existing magnetic storage material that puts together with mobile phone, and the large power, electrically magnetic field pulse that produces because of mobile phone can cause losing of magnetic card inner storag information, brings great inconvenience for people's life; In addition, since shielding box weight big, carry inconvenience, style is single, cost is higher, therefore can bring inconvenience to the user; Also need original wallet is replaced with this shielding box when people wish to reach demagnetization-protected purpose, caused the problem of the waste of existing resource, a kind of screening arrangement that prevents the magnetic card demagnetization is provided, the concrete technical scheme that addresses the above problem is as follows:

The present invention is made up of first sheet metal 1, flexible cellular plastic layer 2 and second sheet metal 3, flexible cellular plastic layer 2 is located between first sheet metal 1 and second sheet metal 3, have hole 4 on first sheet metal 1 and second sheet metal 3, hole 4 on first sheet metal 1 and second sheet metal 3 is staggered, and the edge of first sheet metal 1 and second sheet metal 3 is connected.

First sheet metal 1 and second sheet metal 3 adopt copper material.

First sheet metal 1 of gauze screen of the present invention adopts copper shielding material to compare with adopting the irony shielding material with second sheet metal 3, and reflection loss is big, can reach the effective attenuation electromagnetic wave, the purpose in shielding mobile phone magnetic field.Because first sheet metal 1 and second sheet metal 3 adopt the metal copper sheet to make, electric conductivity is good, does not have the accumulation of electrostatic charge, can avoid the electrostatic breakdown data on magnetic card that produces because of friction.The present invention also has volume advantage little, easy to carry.

Description of drawings

Fig. 1 is a structural representation of the present invention, and Fig. 2 is the enlarged drawing of Fig. 1 I portion, and Fig. 3 is the partial sectional view of Figure 1A-A, and Fig. 4 is the enlarged drawing of Fig. 3 II portion.

Embodiment

Embodiment one: describe present embodiment in conjunction with Fig. 1, Fig. 3, Fig. 4.Present embodiment is made up of first sheet metal 1, flexible cellular plastic layer 2 and second sheet metal 3, flexible cellular plastic layer 2 is located between first sheet metal 1 and second sheet metal 3, first sheet metal 1 and second sheet metal 3 adopt copper material, evenly be installed with several holes 4 on first sheet metal 1 and second sheet metal 3, the hole 4 of first sheet metal 1 and second sheet metal 3 is staggered, and the edge welding of first sheet metal 1 and second sheet metal 3 is composited.

Embodiment two: the hole 4 of opening on first sheet metal 1 of present embodiment and second sheet metal 3 is square hole, and the length of side of square hole is 1.2mm～2mm.

Embodiment three: the spacing of the adjacent square hole 4 of present embodiment is 0.6～2mm.

The determining of the spacing of first sheet metal 1 of device and the length of side of the square hole 4 of second sheet metal 3 and square hole 4 should satisfy electromagnetic wave energy pad value SE, and to meet or exceed this index of 40dB be principle.

Embodiment four: the thickness of present embodiment device is 0.6～1mm.

Embodiment five: it is a that present embodiment takes away the hole parameter _s=1.2mm, d _w=0.6mm, t _w=d _w=0.6mm is as the perforate parameter of shield blade, and screening effectiveness is SE _Min=41.75dB, SE _Max=125.19dB.

Experiment shows, the shielding action of electromagnetic field of high frequency is depended primarily on the size of metal surface reflection loss and absorption loss sum, and for different materials: the conductivity of metal (as: copper) is big more, and reflection loss is big more; The magnetic permeability of metal (as: iron, nickel) is big more, and absorption loss is big more.Under the condition of millimeter magnitude, when frequency electromagnetic waves incident, the difference of the total screening effectivenesss that cause because of material is different can be ignored at material thickness.But, reflection loss and absorption loss in screening effectiveness proportion also the thickness with gauze screen is relevant, reflection loss is not subjected to thickness effect; The absorption loss proportion reduces along with reducing of thickness.When shielding thickness was reduced to the 0.1mm order of magnitude, the proportion of absorption loss can reduce greatly, therefore, should mainly consider the metal material of copper that adopts reflection loss big when this device of design.Flexible cellular plastic 2 can be converted into heat energy to electromagnetic energy, thereby further absorbs electromagnetic energy.Flexible cellular plastic 2 with first sheet metal 1 and second sheet metal 3 at interval certain distance, can further strengthen sheet metal to the attenuation of Electromagnetic effect.The hole 4 of first sheet metal 1 and second sheet metal 3 adopts the mode of mutual dislocation to arrange, and is theoretical and experimental results show that this kind arranged screening effectiveness is improved.

During use, two screening arrangements are laterally put into two bank note layers of wallet respectively,, can reach and prevent that mobile phone magnetic field from making the purpose of magnetic card demagnetization the wallet closure.Its principle is: when incident electromagnetic wave arrives screening arrangement; because twice decay and 2 pairs of absorption of electromagnetic wave of flexible cellular plastic layer through first sheet metal 1 and second sheet metal 3; electromagnetic wave obtains effective attenuation; the electromagnetic wave that passes screening arrangement has been not enough to magnetic card is produced demagnetizing action; thereby protected magnetic card; make it not by demagnetization, prevented the information dropout of magnetic card.If the length of side of copper shield blade square hole 4 is a _s, square hole 4 edge spacings are d _w, the thickness of device is t _w, get t usually _w=d _wAccording to the electromagnetic shielding theory, can calculate under the condition of the single-layer metal film perforation length of side and Edge Distance vertical incidence shielding electromagnetic waves usefulness SE _MinAnd SE _Max, SE _MinWhen shielding in certain band limits, screening arrangement is to the screening effectiveness of frequency electromagnetic waves, SE _MaxBe the i.e. screening effectiveness of single-layer shield device when frequency goes to zero of limiting case.Screening effectiveness can be amid a sharp increase when being mapped to screening arrangement when electromagnetic wave is oblique.The good shield effectiveness of electromagnetic shielding field defined is meant that electromagnetic wave energy pad value SE meets or exceeds 60dB, the present invention has the copper material shield blade of at interval two-layer certain distance, choose the requirement that single-layer metal sheet screening effectiveness index satisfies 40dB, screen effect takes place in each layer simultaneously, thereby screening arrangement bulk shielding usefulness SE is reached more than the 60dB, realized electromagnetic effective shielding.Therefore choosing of screening arrangement parameter should be taken all factors into consideration its practicality characteristics, i.e. not light, the materials saving of frangibility, weight etc., and binding data is embodied in: a _s/ d _wValue is as far as possible greatly to realize materials province, lightweight requirement; d _wRelatively should be not too small, otherwise screening arrangement is lost easily.The electromagnetic frequency values f=of the modern most now mobile phone radiations of the electromagnetic frequency values of most mobile phone radiations of enchashment ω/2 π=1800MHz then can obtain the some groups of a that meet the shielding properties index by calculating _sA _sAnd d _wValue.

Table 1: listed screening effectiveness SE _MinAbout 40dB, a _s/ d _wValue is not less than 1 mesh parameter.

Table 1: list different a _s, d _wDuring value, each sheet metal is the screening effectiveness of 1800MHz vertical incidence ripple to frequency

a s(mm)	d w(mm)	a s/d w	SE min(dB)	SE max(dB)
					1.3	1.0	1.3	42.80	131.82
1.3	0.8	1.6	41.89	128.78
					1.4	1.0	1.4	41.79	131.44
1.2	0.6	2.0	41.75	125.19
					1.4	0.8	1.8	40.85	128.35
1.5	1.0	1.5	40.85	131.07
					1.4	0.7	2.0	40.24	126.43
1.8	1.6	1.1	40.23	136.47
					1.6	1.0	1.6	39.95	130.71
1.9	1.8	1.1	39.94	137.76
					1.7	1.2	1.4	39.89	132.90
1.5	0.8	1.9	39.87	127.95
					2.0	2.0	1.0	39.64	138.89
1.9	1.6	1.2	39.52	136.21

Data are calculated by following (1)～(7) formula in the last table:

The inductance L of grid _SFor:

$L_S=\frac{{\mathrm{\&mu;}}_0{\mathrm{<figure-callout\; id="2"\; label="a\; S"\; filenames="A20071007235400083.png,A20071007235400084.png"\; state="\{\{state\}\}">a</figure-callout>}}_S}{2\mathrm{\&pi;}}\ln [1-\mathrm{EXP}(-\frac{\mathrm{\&pi;}{d}_W}{a_S})]---\left(1\right)$

A in the following formula _sBe mesh centre distance, d _wIt is mesh edge distance.

The resistance R of grid _SFor:

$R_S=\frac{4a_S}{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="d\; W"\; filenames="A20071007235400083.png,A20071007235400084.png"\; state="\{\{state\}\}">d</figure-callout>}}_W^{}{\mathrm{\&sigma;}}_W}---\left(2\right)$

σ in the formula _WBe the conductivity of metal,

TE ripple transfer function T in the vertical incidence TEM ripple ₁With TM ripple transfer function T ₂Be respectively:

${\left|T_1\right|}_1=\frac{2\mathrm{\&omega;}{L}_s}{\sqrt{Z_0^2+{\left(2\mathrm{\&omega;}{L}_S\right)}^2}}={\left|{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="A20071007235400083.png,A20071007235400084.png"\; state="\{\{state\}\}">T</figure-callout>}}_2\right|}_1(\mathrm{\&theta;}=0)---\left(3\right)$

ω in the formula=2 π f, f is the incident wave frequency, $Z_0=\sqrt{\frac{{\mathrm{\&mu;}}_0}{{\mathrm{\&epsiv;}}_0}}$ Be the characteristic impedance of air, μ ₀Be the magnetic permeability of medium when being vacuum, ε ₀Be the dielectric constant of vacuum, θ is the incident angle of ripple.

Consider the limit of ω → 0, can obtain

${\left|T_1\right|}_2={\left|{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="A20071007235400083.png,A20071007235400084.png"\; state="\{\{state\}\}">T</figure-callout>}}_2\right|}_2=\frac{2R_s}{\sqrt{Z_0^2+{\left(2R_S\right)}^2}}---\left(4\right)$

The lower bound SE of shield effectiveness _MinWith upper bound SE _MaxBe respectively:

SE _min＝-201g|T| ₁ (5)

SE _max＝-201g|T| ₂ (6)

So shield effectiveness SE satisfies following formula:

SE _min＜SE＜SE _max (7)

Claims (5)

1, prevents the screening arrangement of magnetic card demagnetization, it is made up of first sheet metal (1), flexible cellular plastic layer (2) and second sheet metal (3), it is characterized in that flexible cellular plastic layer (2) is located between first sheet metal (1) and second sheet metal (3), first sheet metal (1) and second sheet metal (3) adopt copper material, have hole (4) on first sheet metal (1) and second sheet metal (3), the hole (4) of first sheet metal (1) and second sheet metal (3) is staggered, and first sheet metal (1) is connected with the edge of second sheet metal (3).

2, the screening arrangement that prevents the magnetic card demagnetization according to claim 1 is characterized in that the hole (4) on first sheet metal (1) and second sheet metal (3) is square hole, and the length of side of square hole is 1.2mm～2mm.

3, the screening arrangement that prevents the magnetic card demagnetization according to claim 1 is characterized in that adjacent holes (4) spacing is 0.6～2mm.

4, the screening arrangement that prevents the magnetic card demagnetization according to claim 1, the thickness that it is characterized in that device is 0.6～1mm.

5, the screening arrangement that prevents the magnetic card demagnetization according to claim 1, it is characterized in that taking away the hole parameter is a _s=1.2mm, d _w=0.6mm, t _w=d _w=0.6mm is as the perforate parameter of shield blade, and screening effectiveness is SE _Min=41.75dB, SE _Max=125.19dB.

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