Frequently asked questions
Do the Aarronia materials reflect or absorb RF signals?
The materials sold by Aaronia reflect RF signals. This means that the RF is effectively blocked from the desired area but does not reduce the signals outside the area.
Do I need to ground the Aaronia materials?
The materials sold by Aaronia do not need to be grounded to be effective at higher frequencies (mobile phone frequencies) but for complete protection against low frequencies, it is much better to ground the materials.
What do you mean by grounding?
This is an electrical term to describe whether something is electrically connected to earth. It is like the green and yellow wire you sometimes see connecting water pipes and provides an electrical path for any built up voltages to conduct safely away into the earth. When required this should be carried out by a competent electrician.
Do any of your materials require special joining or bonding together to form a secure enviroment?
A good join between any adjoining sheets of material is required to ensure continuity of the screening effectiveness. It should not be necessary to provide special bonding between the sheets as long as they overlap and touch according to the installation guidelines in the data sheets.
Will I get double the performance if I put two layers together?
In short, No. You will get an increase in effectiveness if you leave a gap between the two layers but it will still not be as high as twice the attenuation and the effectiveness depends on the gap and the frequency being blocked. Putting two layers touching each other will offer no better attenuation than one layer.
What is attenuation?
Attenuation is a measure of the effectiveness in reducing a signal. The higher the number, the better it reduces the signal. Attenuation is measured in decibels (dB) and is a logarithmic scale which means that effectiveness doubles for every 3dB. I.E. 0dB has no effect, 3dB will halve the signal passing through, 6dB will quarter the signal going through (half of a half), 9dB will pass one eighth (half of one quarter) and so on.
I have seen that some competitive materials state 99% blocking or 99.9% blocking. How does this equate to dB and attenuation?
This is a different way of stating the effectiveness of a material without using technical terms but can be very misleading. 99% blocking means that 1% of the signal can pass through. In terms of dB, 0dB gives 0% blocking, 3dB gives 50% blocking, 6dB gives 75% blocking and so on (see FAQ on attenuation). To achieve 99% blocking you only need to have 20dB attenuation. Aaronia Shield offering 50dB attenuation equates to 99.999% and X-Dream offering 100dB equates to 99.999,999,99% so you can see that the percentage scale becomes fairly meaningless quite quickly which is why we prefer to use the dB scale. Every 10dB is approximately 90% reduction.
Isn’t dB used to measure sound rather than RF?
The dB unit is used in a lot of different ways and environments. Technically, a dB measurement is actually a ratio comparing a measured level to a reference level and usually has a suffix (following symbol) to define the reference. For example when measuring sound the unit should be properly specified as dBA which tells us our reference level is a sound of a particular intensity. RF power can be measured as dBW which is dB reference to 1 Watt or dBm which dB referenced to 1 milliWatt. A dB attenuation can be subtracted directly from a defined power. I.E. If a power is defined as 50dBW and you use Aaronia Shield to protect, the resulting power in the protected are would be 50dBW – 50dB = 0dBW. In power terms that is 100,000Watts reduced to 1Watt!
The Ofcom states dBW for mobile phone mast outputs but then talks about W/m2 for exposure and then you mention dB. I am confused with all these units and how they fit together. Is there a relationship between them?
All transmitters are measured in dBW which is a measure of the power that is transmitted from the antenna or mast. Once that signal leaves the antenna it spreads out across an area and is more properly measured as a power density in units of W/m2 (Watts per square metre). You will not encounter the full power effect from a mobile phone mast unless you are actually touching the antenna part of it as the signal reduces (very dramatically) as it travels away from the mast. For example, a GSM mast transmitting at the maximum level allowable in UK will be working at 62dBm (32dBW or about 1,500 Watts). The power density or field strength 1 metre from the mast would be 236 W/m2. 2 metre from the mast that would be 50 W/m2 and 4.5 metres away it would only be 10 W/m2. By the time it has travelled to mobile phone several hundred metres away it is a very small signal.
I have seen some dB numbers specified which are negative (I.E. -67dBm). What does this mean?
Negative numbers in the dBm scale refer to increasingly smaller numbers. For example -100dBm is a lot smaller than -10dBm which is smaller than 0dBm. They are not negative powers but just smaller than the reference number. The reference for dBm is 1 milliWatt and in the same way that +3dBm is 2mW, -3dBm is ½ or 0.5mW. Negative dBm uses the same factors as positive dBm but instead of multiplying by the numbers you divide by them. -10dBm is 1/10 or 0.1mW and so on. The dBm scale is a convenient way of documenting large numbers (or numbers with large numbers of zeros after the decimal point) in a meaningful and useable format.