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What Is A Decibel? Why EMF Test Reports Use Decibels as a Unit of Measurement

What Is A Decibel? Why EMF Test Reports Use Decibels as a Unit of Measurement

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EMF shielding is when you reduce the strength of the EMF field with special barriers. These barriers come in the form of magnetic or conductive materials. One of the most common units people use to measure EMF shielding is the decibel. But what is a decibel?

Since most test reports use decibels to report values, it is important you understand how decibels measure EMF shielding.

Wait — Don’t Decibels Measure Sound?

Decibels don’t just measure sound. They measure a series of other physical properties that have varying intensities.

It’s true you’ll often hear people reference decibels when discussing the “loudness” of sound. But decibels don’t just measure sound. 

It’s easy to associate “decibels” with “sound.” This makes it harder for people to understand the unit of measurement behind the decibel itself. This can lead to confusion when you’re reading test reports on EMF shielding, since these reports often use decibels as a unit for measuring EMF attenuation, or shielding effectiveness.

So, What Is A Decibel, Really?

In its simplest terms, a decibel is a ratio, or a relationship between two numbers. This is similar to how percentages and fractions work, as they’re just ratios between two numbers. But unlike percentages and fractions, the decibel is a logarithmic ratio. This means that the decibel unit consists of two general parts: the ratio between two numbers, and the logarithm of that ratio.

As such, scientists use decibels to show changes in a property after taking measurements before and after a particular event. In the case of EMF shielding, the “event” is the addition of the EMF shielding.

Without getting into complicated math, just remember logarithms make it easier for people to work with complicated or large numbers.

Why Is The Decibel Unit Logarithmic?

Many people wonder why the decibel is a logarithmic unit; in other words, why can’t we express the unit as a percentage as opposed to a logarithm? Isn’t using logarithms overcomplicating the calculation of the measurement?

Some EMF test reports do actually present shielding effectiveness data in terms of percentages. But, in the case of measuring EMF shielding as well as acoustics, electronics, and optics, using logarithms actually can be more straightforward than using a simple ratio.

The main reason is because people find the numbers easier to work with, especially when the intensities of EMF radiation vary so greatly. Using decibels to measure EMF shielding reduces the need to use unnecessarily large numbers, since a small difference on a logarithmic scale can represent large leaps in EMF intensities.

Additionally, in the case of acoustics, scientists agree that the human ear perceives sound intensities on a logarithmic scale. As a result, using decibels in acoustics fits nicely with the natural way the human ear interprets sound.

Decibels in EMF Radiation Shielding

In the case of measuring EMF shielding, someone testing an electromagnetic field will try to reduce the field by arranging conductive or magnetic barriers around sources of EMF radiation. This is called EMF attenuation testing. The amount of EMF shielding that results depends on the size, volume, and the material used for shielding, along with the frequency of the source EMF radiation itself.

In order to understand what the decibel values on test reports mean, you need to understand the nature of the decibel. Generally speaking, we take the measurement of an EMF source before applying shielding and after applying shielding. Taking a logarithm of the ratio of these two numbers will result in the decibel value.

A measured decibel value during this process can tell you whether the shielding was successful in reducing EMF radiation by the amount you wanted.

By testing different materials and methods of EMF shielding, you can gauge the relative effectiveness of each shielding type. Using special formulas, you can even express the measured decibel value as a shielding percentage. A difference in a few decibels often means big jumps in shielding effectiveness.

As I mentioned previously, the decibel is a logarithmic ratio. For that reason, a boost in a few decibels in shielding effectiveness represents large boosts in EMF shielding percentage (EMF shielding effectiveness). Based on the formula from this handy article from LessEMF, for example, just a 20-decibel increase in shielding created in a 90 percent reduction in field strength.

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