Products

Shielding - Types

Type of interference Type of protection (classified in order of effectiveness)

EMI (electromagnetic interferences)

Description: Interference similar to white noise. This interference on a membrane keypad results from the magnetic field produced by various devices near the keypad. The unit of measurement of EMI is the decibel.

Typical applications: medical, military, aeronautical, telecommunications.
  1. Copper mesh: completely protects the keypad, including LCD and LED windows. Effectiveness: 80 dB, from 1 MHz to 1GHz
  2. Aluminium foil: completely protects the keypad, excluding LCD and LED windows. Effectiveness: 50 dB, from 10 MHz to 10 GHz
  3. Polyester sheet screenprinted with a grid pattern of graphite and silver ink: completely protects the keypad, excluding LCD and LED windows.
  4. Shielded window, using ITO pulverization: selectively protects LCD windows. Effectiveness: 40 dB, at 100 MHz.

ESD (Electrostatic discharge)

Description: Interference caused by a discharge of static electricity. This interference on a membrane keypad results from the discharge caused by a user touching the keypad. The unit of measurement is the kilovolt (Kv).

Typical applications: various

Note: For ESD protection higher than 18 Kv, a special assessment of the project will be required in order to determine if the effectiveness of standard shielding types is adequate.
  1. Copper mesh: completely protects the keypad, including LCD and LED windows. Effectiveness: 80 dB, from 1 MHz to 1GHz
  2. Aluminum foil: completely protects the keypad, excluding LCD and LED windows. Effectiveness: 50 dB, from 10 MHz to 10 GHz
  3. Polyester sheet screenprinted with a grid pattern of graphite and silver ink: completely protects the keypad, excluding LCD and LED windows.
  4. Polyester graphic overlay: completely protects the keypad surface, including LCD and LED windows. Effectiveness: 2 Kv per thousandth of an inch of raw material.
  5. Free conductive trace surrounding the circuit: protects the periphery of the circuit.
  6. Shielded window, using ITO pulverization: selectively protects LCD windows. Effectiveness: 40 dB, at 100 MHz.

RFI (radiofrequency interference)

Description: Interference caused by the use of the keypad. This interference is negligible and is seldom taken into account. The unit of measurement of RFI is the decibel.
  1. Ferrite: absorbs the undesirable frequencies and releases the captured energy as small quantities of heat.
  2. Condenser or electronic filter: protection applied directly to the electronic module being used to receive the keypad.

Note: GGI International strongly recommends combining various types of protection methods.

  • Example 1: when using aluminium foil shielding connected on one or more traces of the tail, it is recommended to also include a free circuit trace surrounding the complete circuit.
  • Example 2: for a shielded window using ITO pulverization along with aluminium foil shielding connected on one or more traces of the tail, it is recommended to connect these two types of shielding to the same source of diffusion.

Additional notes: The reductions in intensity of the electric field are determined by the frequency, the conductivity of the shielding material and its thickness. Shielding Effectiveness (SE) is the degree to which shielding attenuates or reduces the energy of an irradiated electromagnetic field. The standard unit of measurement of SE is the decibel (dB). The value in decibels is the ratio of two measurements of the intensity of the electromagnetic field taken before and after the installation of the shielding apparatus.

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