Plasma Antenna

Plasma antenna represents a completely new technology of antennas that relies on plasma elements rather than on traditional metallic wires or elements. The feasibility of a plasma antenna is provided by plasma conductivity, that is given by free electrons obtained by gas ionization with the application of an intense electro -magnetic field. The fundamental base of plasma antenna is the use of an ionized medium as a conductor

2014 National Institute of Technology Sgr.

Report

Contents:

1. Introduction…………………………………………3

1.1 what is plasma?................................3

1.2 Definition of antenna……………………4

2. Plasma antenna………………………………………6

2.1 Theory of plasma antenna…………………… 6

2.2 Working of plasma antenna………………….. 6

3. Types of plasma antenna……………………………7

3.1 Gas Plasma Antenna ………………………7

3.2 Plasma Silicon Antenna……………8

4. Characteristics of plasma antenna………………..9

5. Comparision with convention antenna………….9

6. Advantages……………………………………………….10

7. Disadvantages…………………………………………..11

8. Applications ……………………………………………..12

9. Future scope……………………………………………13

10. Conclusion……………………………………………..13

11. References……………………………………………14

1. Introduction:

What is plasma?

Definition. Plasma can be defined as a set of quasi-neutral particles with free

electric charge carriers which behave collectively. In this definition, two terms

are very important:

(i) quasi-neutral. Meaning that there is the same quantity of positive and

negative particles so, as a whole, it behaves as a fluid without net charge.

(ii) collectively. Meaning that plasma as a whole is capable of carrying out

processes that generate electric and magnetic fields to which it can react. This

is one of the most important properties that lead to some unparallel

characteristics.

So basically, plasma is produced “when enough atoms are ionised to

significantly affect the electrical properties of a gas under normal conditions.”

It is not any alien form but only a state of ionisation, a state of matter. There

are eleven elements that exist as gas under normal conditions. Out of these,

group 18 elements are of prime importance (if we are analysing discharge

tubes) as they are inert. Plasma is much visible matter in the universe, being

about 99 per cent of all the matter. Besides astronomical plasma, we can

distinguish two main groups of plasma from laboratory point of view:

(i) Thermal plasma. Here electrons and ions are at thermal equilibrium. But

for this thermal equilibrium to exist, very high temperatures are required,

specifically in the range of 4000K-20,000K. But this equilibrium makes this

kind of plasma to be unfit for the antenna system application (welding, plasma

torches, sintering and etching).

(ii) Non-thermal plasma. Here ions and neutral particles are at lower

temperature as compared to electrons, or we can say that the electrons are

somewhat ‘hotter’ than ions. This fits for the antenna system application.

Examples:

The Sun Lightening

Fig. 1

Interaction of plasma with EM waves:

As we are interested in designing antenna systems, the interaction and

behaviour of plasma with EM waves must be investigated for better

understanding. As per some theses, various relations are set up (qualitatively)

to study their interaction. Plasma contains quasi-neutral particles, which

means they are highly conductive. For analysing interaction with EM waves,

four important parameters are conductivity, electrical permittivity, magnetic

permittivity and propagation constant.

Qualitatively, the interaction of plasma with EM waves can be formulated as:

1. Plasma with high-collision frequency behaves as a lossy medium. This is

due to the reason that with increase in plasma pressure and electron density,

the rate of collision increases, so considerable amount of energy will be lost.

(This is the reason why thermal plasma is unfit to be used in antennae.)

2. If W > Wp. EM wave frequency is greater than plasma frequency (an

inherent property of plasma), so wave propagates in plasma and the plasma

has dielectric properties which are electrically controllable.

3. If W < Wp. The propagation constant is imaginary. The wave is vanishing

with the plasma medium. The wave can be absorbed or reflected depending

on the collision frequency.

What is an Antenna?

An antenna is a device that sends or accepts electromagnetic waves. It

changes electromagnetic waves into electric currents, and electric currents

to electromagnetic waves. Antennas are used to send and receive waves

from the radio frequency of the electro-magnetic spectrum. Antennas

are used in radio and television broadcasting, spacecraft communication,

point-to-point radio communication like walkie-talkie system, hand

phones, radar, and wireless LAN.

An antenna is a setup of one or more electrical conductors, also called

elements. In the transmission of an antenna, a voltage is applied at the

antenna terminals to produce an alternating current (A.C) in the

elements, thus causing the elements to produce an electromagnetic field as an

effect. In reception, the reverse happens: an electromagnetic wave from an

external source induces an alternating current in the elements and a matching

voltage at the antenna's terminals. Some receiving antennas use shaped

reflective surfaces to collect the radio waves hitting them and direct or focus

them onto the elements.

How the antenna transmits signals:

First, a voltage is applied to the antenna terminal (in this case, the driven

element in the centre) to produce a potential difference in between the

opposite ends of the two conducting wires. When a potential difference exists,

there will be a flow of electrons, which in turn produces a current. Say that the

electrons from end A are moving towards end B at maximum speed. When

they reach end B, they will stop instantaneously. End B is now negatively

charged whereas end A is positively charged. The electrons are attracted to

the positive charges at end A and move back towards A at maximum speed.

Now, the charges at both ends are reversed. This back and forth movement of

the electrons produces an alternating current in the conducting wires. When

there is an alternating current in the metal conductors, electromagnetic waves

are produced. These waves are the signals being transmitted by the antenna.

How the antenna receives signals?

On the other hand, the entire process is reversed for the antenna to receive

signals. Electromagnetic waves from an external source reach the conducting

wires. The electromagnetic field is cut by the conducting wires, causing an

alternating current to flow in the conducting wires. Consequently, when there

is a current flowing in the wires, a voltage will exist too. The antenna receives

the alternating current as its signal.

2. Plasma Antenna:

Plasma Theory: A plasma can be generated from neutral molecules that are separated

intonegative electrons and positive ions by an ionization process (e.g., laser

heating or spark discharge). The positive ions and neutral particles are much

heavier than the electrons, and therefore the electrons can be considered as

moving through a continuous stationary cloud of ions and neutral particles.

Plasma Antenna Technology: A plasma antenna is a type of antenna in which the metal-conducting elements

of a conventional antenna are replaced by plasma. These are radio frequency

antennas that employ plasma as the guiding medium for electromagnetic

radiation.Plasma antenna is of two types: gas plasma antenna and plasma

silicon antenna [PSiAn].

3. Types of Plasma Antenna:

Gas Plasma antenna:-

It employs an ionized gas enclosed in a tube as the conducting element of an

antenna.When the gas is electrically charged or ionized to a plasma,it becomes

conductive and allowing radio frequency signals to be transmitted or

received. When gas is not ionized,the antenna element ceases to exit.

Alternatively the plasma can be used as a reflector or a lens to guide and focus

radio waves from another source.

1. When supply is given, gas gets ionized to plasma.

2.Plasma is energized.

3. Behaves as a conductor.

4. Generation of localized plasma.

5. Plasma acts as a mirror.

6. Reflects the beam.

Fig. 2

PSiAn Antenna: PSiAN consists of thousands of diodes on a silicon chip. When activated, each

diode generates a cloud of electrons – the plasma. At a high enough electron

density, each cloud reflects high-frequency radio waves like a mirror. By

selectively activating diodes, the shape of the reflecting area can be changed to

focus and steer a beam of radio waves. This “beam-forming” capability makes

the antennas crucial to ultrafast wireless applications, because they can focus

a stream of high-frequency radio waves that would quickly dissipate using

normal antennas.

3

4. Traditional Antenna Vs Plasma Antenna:

1. Unlike simple antenna, plasma antenna selects a beam avoiding the need for mechanical or manual alignment and realignment of fixed point to point communication links.

2. The traditional antennas operate at lower frequencies whereas plasma antennas operate at very high frequencies. 3. Plasma antenna have no ringing effect associated with them whereas traditional antennas have this effect associated with them.

Fig. 4 Traditional antenna vs Plasma antenna

5. Features of Plasma Antenna:

1.Higher power:- This can be achieved in the plasma antenna than in the corresponding metal antenna because of lower Ohmic losses. Plasmas have a much wider range of power capability than metals.

2. Enhanced bandwidth:- By the use of electrodes or lasers the plasma density can be controlled. The theoretical calculations on the controlled variation of plasma density in space and time suggest that greater bandwidth of the plasma antenna can be achieved than the corresponding metal antenna of the same geometry. This enhanced bandwidth can improve discrimination. 3. Higher efficiency and gain-Radiation efficiency in the plasma antenna is higher due to lower Ohmic losses in the plasma.

4. Lower noise - The plasma antenna has a lower collision rate among its charge carriers than a metal antenna and calculations show that this means less noise. 5. Perfect reflector :- When the plasma density is high the plasma becomes a loss-less perfect reflector. Hence there exist the possibilities of a wide range of lightweight plasma reflector antennas.

6. Advantages of plasma antennas:

1. An important advantage of plasma antenna over a conventional antenna is

that the former is much lighter. These high-performance electronically-

steerable antennas are extremely lightweight and compact.

2. Free from mechanical parts, these maintenance-free plasma antennas are

ideally suited for a wide range of wireless communications.

3. Plasma antennas are invisible to radar. When the plasma antenna is not

turned on, radar will find it difficult to detect the antenna. Even if the plasma

antenna is turned on, it is invisible to signals above the plasma frequency. This

makes it hard for the plasma antenna signals to be intercepted or detected by

anyone other than the intended recipient. Clearly, this particular aspect of the

plasma antenna makes it ideal for use by the military to transmit and receive

secret instructions and information.

4. Plasma elements can be energised and de-energised in seconds, which

prevents signal degradation.

5. The plasma antenna is dynamically reconfigurable, which means that the

handlers of the antenna can freely change the frequency, gain, polarization,

power, directionality and beamwidth of the signal. The implications of this

advantage is that instead of needing multiple normal antennas, we can just

use a single plasma antenna, reducing cost and saving space.

6.The plasma antenna is capable of transmitting signals at an extremely fast

speed. In the plasma semiconductor antenna, by selectively activating certain

diodes, the handler is able to focus the electromagnetic waves produced into a

beam, which travels faster than a wave.

7.When a particular plasma element is not energised, its radiation does not

affect nearby elements.

8.. Plasma antenna can focus high-frequency radio waves that would dissipate

quickly if beamed by conventional arrays.

9.The plasma antenna allows for extremely short pulses, unlike a normal

metal antenna. When electricity is passed through a metal conductor, an effect

known as “ringing” occurs, that is an extra burst of electricity flow through the

conductor for an extremely short while when there is a sudden change of

input (like when the pulse is short). This wastes energy and causes unwanted

electromagnetic waves to be produced. With the plasma antenna, ringing is

totally eliminated.

7. Disadvantages:

1. The semi-conductor version of the plasma antenna is limited to high

frequencies, which makes certain applications difficult. For example, Wi-Gig

routers operating at 60Ghz cannot penetrate walls.

2. The ionizer increases power consumption. More energy is required to

ionize the gases or to make the silicon chips release electrons. Therefore,

plasma antennas actually use more power than normal antennas.

3. Plasma volumes must be stable and repeatable. When a gas is ionised, not

all 100% of the gas will ionise to become plasma. With silicon chips, it is

reasonable to say that the amount of electrons released by the silicon when

heated or charged will vary from time to time. Thus it is imperative that the

volume of plasma generated each time should be the same. The amount of

plasma existing during a transmission or reception should also be the stable

and not fluctuate. Only then will the electromagnetic waves transmitted be

stable.

8. Applications: 1. The plasma antenna has high potential to be used in the military sector, as it

is hard to be detected by radar. This is good for the military to send and

receive top secret documents or instructions.

2. As signals radiated by a plasma antenna is hard to intercept and therefore

hard to be blocked, the plasma antenna is said to be resistant to electronic

warfare, a strategy commonly employed by enemy countries.

3 .The plasma antenna can be used in radio and television broadcasting. The

signals emitted by the plasma antenna tend to be stronger than the signals

emitted by the normal metal antenna, thus causing the radio waves to last

longer without damping and being extinguished. The consequence of this

implication is that radio broadcasting companies no longer need to build so

many relay stations and towers to relay the signal to further areas.

4. Another market application for the plasma antenna is to be installed on

ships and submarines. Submarines require stealth to complete the mission of

its crew, and so having a plasma antenna would be of great benefit. For fishing

ships that require echolocation to locate the position of fish in deep sea, the

plasma antenna will also be advantageous.

5. One very relevant application of the plasma antenna is in wireless Internet,

like Wi-Gig. Wi-Gig provides faster Internet connection to users than is

provided by Wi-Fi. A faster Internet connection means that users will be more

productive and save time. The economy of the country can be improved as

more work can be done in a shorter time. Activities like downloading

podcasts, movies and music at fast speeds can be done even using wireless

Internet connection. This is clearly an advantage for mobile users.

6. Another application of the plasma antenna is its role in improving public

safety networks.

7. It is also possible that plasma antennas can be used in space

communication. Plasma antennas which prove to be lighter than normal

antennas can serve as communication devices on jet planes, commercial

planes, and even space shuttles. For example, scientists and researchers

working at the NASA Glenn Research Centre have filed and received a patent

for a slotted antenna waveguide plasma source.

8. Future Scope: Growing need for speed of communication network along with data handling

capacity are the major forces helping to explore new vistas of transmission

and reception. With the wireless generations moving from 2G to 3G, 4G, 5G

and so on, the real benefit of upgrading the Wi-Fi networks is to get them to

run faster. Wi-Fi usually can manage 54 megabits of data per second. The

fancied Wi-Fig (a graphical user interface for configuring wirless connection)

would handle up to 7 gigabits per second. This would mean downloading a TV

show in a matter of seconds. The advances in plasma antenna technology are

expected to play a great role in the desired speed and capacity-handling

capabilities of communication networks.

10. Conclusion: In conclusion, the plasma antenna works according to the same principles and

physics laws as the normal antenna, with plasma replacing the metal

conductors of the normal antenna. But because the conducting material used

is plasma, it affords some advantages over a normal antenna. The most

notable advantage of the plasma antenna is the fact that it is practically

invisible to radar and can release short pulses of signals. Therefore, the

military of US is currently racing to implement the plasma antenna into their

existing systems.

Also, another advantage of the plasma antenna is that it can pave the way

towards faster wireless Internet, which is certainly needed by most users

nowadays, whether it be for entertainment or business purposes.

11. References:

1. M. Moisan and Z. J. Zakrzewski, “Plasma sources based on the propagation

of electromagnetic surface waves.

2. Alex Theodore Anderson, 2011. Plasma Antennas. Artech House Papers

from Conference Proceedings.

3. http://www,electonicsforu.com/circuitarchives/plasma antenna/view.php.

4. Alex Anderson, E. P. Pradeep, Experimental and theoretical results with

plasma antennas," IEEE Transactions on Plasma Science,.

5.http://www.ukessays.com/plasmas /antennas/viewpage.1204.cicuitory.php.asp

6.http://www,plasmaantennas.com//ltd.experimentalckt.viewpage//.

7. Kraus J.D., “Antennas for all applications”, second edition, “Tata McGraw-Hill

1988”.

8. Balanis C.A. “Antenna theory analysis and design” second edition, “John Wiley

&sons, Inc 1997”.