Do you want to block the sound from outside? Do you want to block the radio wave from outside? There seem to be a similar demand, but countermeasure against sound and radio wave is completely different.
Sound has longitudinal wave, and radio wave is transverse. The sound velocity is 340m/s, while the propagation speed of radio wave records 3x108m/s,106(million) times faster than sound.
As this show, sound and radio wave is alike but different, however, many constructions request the space which has both performances.
The purposes of electromagnetic shield are the following; (1) malfunction prevention of electronic equipment, (2) interference prevention of wireless telecommunications equipment, (3) effective use of radio wave, (4) prevention of information leak, (5) incoming prevention of PHS/ mobile phone.
For example, in a recording studio or TV/radio studio, the electromagnetic shield construction is carried out for the purpose of incoming prevention with a wireless microphone. Usually, to make the electric field strength level in the room less than the electromagnetic immunity level of broadcasting equipments (electromagnetic-noise performance value-resistant), 30dB (30MHz-1GHz) is considered as a target of electromagnetic shielding effectiveness.
In the mean time, many research/inspection institutes (psychology/aural laboratory etc.) or hospitals set the required efficiency higher for studios and anechoic chambers (greater than 60dB), naturally giving the priority over the shielding effectiveness than the acoustic performance .
To enhance the effect of electromagnetic shield, esetting a potential difference for 0dB, using the same materials for electric corrosion prevention and shielding the whole of interior completelyf are the basic concepts.
The electromagnetic shield specifications are decided by aimed eAmount of the decrease' and efrequency band' In many cases a copper sheet (foil) or aluminum foil is used because of its high electrically conductive, forming a electromagnetic shield layer with care for shielding of doors or windows and combining with several filters for equipment power supply and weak electric current, honeycomb filter for air conditioning ducts.
For confirming the shielding effectiveness, we take the insertion loss method which follows the eThe Measuring Method of EM Shield Effects at Construction Site (scheme)' by the Architectural Institute of Japan based on MIL-STD-285. We also confirm it by calculating the difference of the field strength level of the broadcasting radio wave (FM, TV station) between inside and outside of room.
