The antenna mode of cell phone jammer is omnidirectional and four-channel

It is the use of high-frequency magnetic shield in the opposite direction under the effect of the eddy current magnetic field with the original cancel the interference of high frequency magnetic field weakened, because the shield grounded to achieve the electric field shielding. The thickness of the shield not too large, and the skin depth and structural strength is the major consideration. 2 calculate the shielding effectiveness of shielding effectiveness (SE) is defined as: the electromagnetic field in the same location without shielding of the electromagnetic field strength and increases the shield after the ratio of the electromagnetic field strength. Difference between former and latter strength forcell phone jammeris no less than 20 dB.Common decibels (dB) said. SE = A + R + B (1) where: A is the absorption loss; R for the reflection loss; B for the loss of multiple reflections. 2.1 electromagnetic wave reflection loss due to air resistance and electromagnetic shielding metal is different from the incident electromagnetic wave produces reflex. The wave impedance of air in different areas of the field source and the field is not the same, were calculated as follows. Magnetic field source in the near-field reflection loss R (dB) for the formula: μr is the relative permeability; σr relative conductivity; f the wave frequency (Hz); D as the radiation source to shield distance (cm). It is the working directivity of cell phone jammer.Electric source in the near-field reflection loss R (dB) for the electromagnetic field source in the far-field reflection loss R (dB) for the R = 168-10log10 (μrf / σr) 2.2 absorption loss when the electromagnetic wave into the metal shielding of electromagnetic waves in shielded metal to spread, due to attenuation resulting from absorption. Absorption loss A (dB) to (4) where: d is the thickness of shielding material (mm). 2.3 multiple reflection loss of electromagnetic waves in the shielding layer multiple reflections between the loss of B (dB) for the formula: Zm is the electromagnetic impedance of the metal shield; Zw is the wave impedance of air. When A> 10dB, the general loss of multiple reflections can be neglected. 2.4 Calculation Example field shielding effectiveness of different source materials from the shield (thickness 0.254mm) 30cm away the shielding effectiveness (dB) results in Table 1. The antenna mode of cell phone jammer is omnidirectional and four-channel.Table 1 in the near-field and far-field cut-off point for the λ/2π, λ is the wavelength of the electromagnetic field. Field source from the shield of different materials (0.254mm) from the field sources in Table 1 shield of different materials (thickness 0.254mm) 30cm away copper-frequency shielding effectiveness dB / Hz magnetic shielding integrity of the near-field 3.1 is not complete if the shield , will lead to leakage of electromagnetic fields. In particular, electromagnetic shielding, which uses high-frequency magnetic shield in the opposite direction under the effect of the eddy current magnetic field with the original cancel high frequency magnetic field to weaken interference.The working power supply of cell phone jammer is AC 220V/3W. If the shield is not complete, the effect of reducing eddy current, which greatly reduced the effect of shielding. 3.2 The shielding effectiveness of shielding materials and electromagnetic shielding applications progress, to promote the continuous development of the form of shielding materials, and no longer limited to single-metal flat patterns, shielding effectiveness is also rising. Pay special attention to application of different shielding materials and shielding effectiveness of different applications. 3.2.1 Metal flat metal plate made of electronic equipment chassis, only durable, but also has electromagnetic shielding effect.