Why cell phones still show signals when the cell phone jammer is working?

When the frequency is low, electromagnetic interference mainly in near-field region, based on application of electric dipole and magnetic dipole near-field shielding theory. In the near field, with the interference of a different nature, the size of the electric and magnetic fields are quite different. High voltage low current main source of interference to the electric field, can only consider the neglect of electric field shielding magnetic interference; low-voltage high-current interference with the main magnetic field, magnetic field shielding can only consider the neglect of electric field interference.
As frequency increases, the ability to enhance the electromagnetic radiation, electromagnetic interference tends to far field for plane wave shielding theory based. Even cell phones still show signals when the    cell phone  jammer   is working, they can’t communicate anymore.In the far field, the electric field interference and magnetic interference can not be ignored, need to implement shielding of electric and magnetic fields. The conductive material can be used to good shielding and grounding, and can also play the electric and magnetic shielding of the dual role. Electromagnetic shielding and grounding and shielding are not linked. The real impact of the shielding effectiveness of the shield only two factors: one is the entire surface of the shield conductivity must be continuous, the other is not directly penetrate the shield conductor.
When the source of low frequency electromagnetic interference when using high magnetic permeability material, form a low reluctance path, so that the magnetic field lines within the limited shield to prevent the spread to shield the space to make the most of the magnetic field is concentrated In the shielding body. This  cell phone blocker has 1-year length of warranty.Shield the higher the permeability, thickness greater reluctance smaller, the better magnetic shielding. 3) In some cases, if the requirements of high frequency and low frequency electromagnetic fields have a good shielding effect, often composed of different layers of the metal shield.
1.3 electromagnetic shielding
Pure electric or magnetic field interference is rare, commonly referred to as electromagnetic interference is the existence of both electric and magnetic fields of high frequency electromagnetic interference. Free repairing for three years and life-long maintenance for this type of    cell phone  jammer. Electromagnetic shielding for sensitive equipment and sources of interference suppression when the distance generated by coupling electromagnetic field interference, it must be shielded electric and magnetic fields, usually in a good conductor of small resistivity materials, space, electromagnetic interference in the incident to the metal surface will of reflection and absorption of electromagnetic energy is attenuated, and thus play a role in shielding.
Electrostatic shielding and static magnetic shielding material is easy to achieve a good conductor, but in the alternating electromagnetic field, the electric and magnetic fields always exist in the same space, so the electric and magnetic fields must also consider shielding.Why cell phones still show signals when the    cell phone  jammer   is working? However, due to the different frequency, alternating electromagnetic interference [5,6] effects of different areas, practice should be treated differently.