The answers below are intended for early material selection and project discussion. Real-world shielding should be validated in the finished assembly under the intended test conditions.
What does shielding effectiveness in dB mean?
Shielding effectiveness is normally expressed in decibels and compares the electromagnetic field or power before and after the shield. A higher dB value means greater attenuation under the stated test conditions.
Why should dB values never be read without the frequency?
Shielding effectiveness can change with frequency. A single headline value such as 80 dB is incomplete unless the test frequency or frequency range, sample configuration and test method are known.
Can I compare two suppliers by the highest dB number on their datasheets?
Not reliably. Comparison is meaningful only when the materials were tested under comparable conditions. Test fixture, specimen size, frequency, polarization, contact method and dynamic range can all change the reported result.
Does a high material dB value guarantee the same result in my enclosure?
No. Openings, seams, cable penetrations, poor electrical contact and installation geometry often dominate the performance of a finished enclosure. Material data should be treated as one part of the shielding design.