EMF Meter: difference between AC magnetic, AC electric, and RF Measurements

Question

let's consider this EMF Meter. Regarding its description, I have some doubts regarding what it is physically trying to measure:

• Detects all three types of EMF pollution: AC magnetic, AC electric, and RF/microwave

Aren't all of them electromagnetic waves hence the same thing?

• AC Magnetic Mode covers 40 Hz – 100 kHz with range of 0.1 – 100.0 milligauss (mG)
• AC Electric Mode covers 40 Hz – 100 kHz with range of 1 – 1000 volts per meter (V/m)

In a free space electromagnetic wave, E and B fields amplitudes are related by the free space impedance. So, aren't these two measurements equivalent? Are both Modes the same measurement with just the impedance conversion factor, or should I decide to use the AC Magnetic Mode in some cases and the AC Electric Mode in others?

• RF Mode covers 20 MHz – 6 GHz with range of 0.001 – 19.999 milliwatts per square meter (mW/m2)

Again, I imagine this mode actually measures the same phenomenon as before but it is a power measurement instead of a field measurement. Why is the power measurement preferred for higher frequencies and field measurements for lower frequencies?

Answer 1

No they are not the same thing.

As a simple first order model:

They are magnetic only waves (B) without electric field (E), electric field only waves (E) without magnetic field (B), and when they both appear simultaneously as a single electromagnetic wave with E and B, that's RF.

Nearby the device, i.e. in the near field, you generally have E and B separately, they have not merged into single RF wave yet. Far away the device, i.e. in the far field, you can only measure the merged electromagnetic RF waves, as it's too far to measure E and B separately.

As the distance of the transition zone between near and far fields depends on frequency of the radiation, it means that high frequencies of E and B become RF more near the device and low frequencies are still separate E and B fields near the device as they have not become RF yet.

So at low frequencies you have no RF yet so best to measure separate E and B fields, and at high frequencies you don't have separate E and B fields any more so best to measure RF.

Answer 2

The EMF meter is measuring the fields that might be considered hazardous to humans. Low frequencies generally won’t cause heating of the human tissue. As we go higher in frequency, this can cause heating - we are familiar with microwave ovens. Since it can cause heating, we’re concerned with the power. 1milliWatt of 2.4GHz won’t do much to us, but once we start getting into Watts, then the concern begins. 700Watts like the average microwave oven, we know what it can do.

With the lower frequencies, the fields are of interest. We know magnetic fields have an effect at the atomic level but we’re really not sure what long term exposure to high magnetic fields does to us. Personally I’d want to keep my distance from extended exposure to mains distribution transformers due to the magnetic fields.

Similarly with high electrostatic fields it’s not something we should have extended exposure to.