## Extremely Low Frequency Electro Magnetic Field Sensing (Part 3)

Part 1234, 5

This post deals with the sensing antenna which can increase the sensitivity of the MicroELFEMF application

One of the difficulties posed when sensing ELF frequencies is antenna size. This is because the antenna must be at least a substantial fraction of the size of the wavelength of the frequency of the EM waves. Simply put, a 1 Hz signal would have a wavelength equal to the distance EM waves travel through the antenna’s wire in 1 second. For ELF, this is very slightly slower than the speed of light in a vacuum. As used in military applications, the wavelength is ~3.0 10^8 m/s (1) divided by 50 or 60 Hz, which equals ~6.0 10^6 m to ~5.0 10^6 m. That’s long wire!
For pratical reasons, we will use a piece of wire which is a fraction of the base length. The antenna that I used is obtained after halving 25 times the theoritical wire length! Just kidding! Just use a piece of 17 cm of copper straight wire.

Here is an illustration of the ELF EMF application that is using a GLCD display. Note that the base radiation is quite high in this room. The left part of the display shows the real time signal while the right part contains the frequency domain plot, so as to say the frequency spectrum plot.

(1) The speed of light in vacuum is equal to 299792458 m/s. The speed of the light in a metal medium is about 5% slower than in vacuum, which is about 284802835 m/s.

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