What makes an antennae?
Let's first discuss how to spell antennae.
Thanks to the proliferation of American literature and media in Australia, we have ended up with this hybridised language where sometimes it matters which way the word is spelled, and sometimes it doesn't.
Antennae qualifies as a 'doesn't'.
In the US and Canada, antenna is a singular, while antennae refers to a plural. At least, it does when referring to insect antennae.
Metallic antennas, like are used practically everywhere, are antennae or antennas, depending on your own preference.
To the point however, what actually defines an antennae?
'Antennae' refers to an object which transmits or receives electromagnetic radiation.
It 'radiates' this energy thanks to a few fundamental laws of physics.
As you may well know, most things have a 'charge' associated with them. This is generally due to a lack, or surplus, of charged particles of either polarity (i.e. positive or negative). When these charges are moved from one place to another, the associated field undergoes acceleration (or deceleration), which gives rise to changing magnetic fields. This is the underlying premise of Maxwells' equations - the defining equations of the modern era.
The trick is to design the object such that these fields are superimposed (i.e. stack) rather than cancel out.
Antennae operate on a frequency, which often dictates the length and style of an antennae. In geophysical applications, the frequencies range from sub-ELF (3-30 Hz) to Mid-UHF (300 - 3000 MHz) depending on the method of geophysics being employed. Grounded-source (< 1 Hz), and magneto-telluric (measured in seconds, (i.e. 1/Hz) due to such low frequency) operate with low frequencies and resolve very-deep targets (at very low resolution), while ground penetrating radar has applications in concrete scanning, in the GHz range (but only 'sees' several centimetres depth).
My main focus is on low-frequency antennae, therefore I will talk about controlled-source EM (Magneto-telluric does not have a dedicated antennae, as it is a passive source method!).
The 'grounded' source refers to a pit of conductive material, such as aluminium foil buried and soaked in saline-water solution. This lowers the contact resistance allowing greater current to be transmitted and thus greater voltage into the earth. i.e. Ohm's law. Greater voltage in means higher voltages out, which means less-stacking and better signal-to-noise.
We beget the question of whether a grounded-source is technically an antennae though.
There's an incredible amount of literature behind antennae design - obviously, as it's a keystone of our way-of-life. The link below gives, in my opinion, the best, most succinct, and approachable explanation of antennae theory and design.
The authors complimentary site of Maxwells Equations is also fantastic.
Link: http://www.antenna-theory.com/basics/main.php
Thanks to the proliferation of American literature and media in Australia, we have ended up with this hybridised language where sometimes it matters which way the word is spelled, and sometimes it doesn't.
Antennae qualifies as a 'doesn't'.
In the US and Canada, antenna is a singular, while antennae refers to a plural. At least, it does when referring to insect antennae.
Metallic antennas, like are used practically everywhere, are antennae or antennas, depending on your own preference.
To the point however, what actually defines an antennae?
'Antennae' refers to an object which transmits or receives electromagnetic radiation.
It 'radiates' this energy thanks to a few fundamental laws of physics.
As you may well know, most things have a 'charge' associated with them. This is generally due to a lack, or surplus, of charged particles of either polarity (i.e. positive or negative). When these charges are moved from one place to another, the associated field undergoes acceleration (or deceleration), which gives rise to changing magnetic fields. This is the underlying premise of Maxwells' equations - the defining equations of the modern era.
The trick is to design the object such that these fields are superimposed (i.e. stack) rather than cancel out.
Antennae operate on a frequency, which often dictates the length and style of an antennae. In geophysical applications, the frequencies range from sub-ELF (3-30 Hz) to Mid-UHF (300 - 3000 MHz) depending on the method of geophysics being employed. Grounded-source (< 1 Hz), and magneto-telluric (measured in seconds, (i.e. 1/Hz) due to such low frequency) operate with low frequencies and resolve very-deep targets (at very low resolution), while ground penetrating radar has applications in concrete scanning, in the GHz range (but only 'sees' several centimetres depth).
My main focus is on low-frequency antennae, therefore I will talk about controlled-source EM (Magneto-telluric does not have a dedicated antennae, as it is a passive source method!).
The 'grounded' source refers to a pit of conductive material, such as aluminium foil buried and soaked in saline-water solution. This lowers the contact resistance allowing greater current to be transmitted and thus greater voltage into the earth. i.e. Ohm's law. Greater voltage in means higher voltages out, which means less-stacking and better signal-to-noise.
We beget the question of whether a grounded-source is technically an antennae though.
There's an incredible amount of literature behind antennae design - obviously, as it's a keystone of our way-of-life. The link below gives, in my opinion, the best, most succinct, and approachable explanation of antennae theory and design.
The authors complimentary site of Maxwells Equations is also fantastic.
Link: http://www.antenna-theory.com/basics/main.php
Comments
Post a Comment