MAGNETIC CLASSIFICATION OF MATERIALS BASIC INFORMATION AND TUTORIALS

Magnetic Classification of Materials
What Are the Magnetic classifications of Materials?


Material Type Description

Nonmagnetic No magnetic reaction.

Diamagnetic Induced dipole moment opposes applied field.
Repelled by bar magnet.
Very weakly magnetic.

Paramagnetic Induced dipole moment aligns to applied field.
Attracted by bar magnet.
Weakly magnetic.

Ferromagnetic Induced dipole moment aligns to applied field.
Attracted by bar magnet.
Very strongly magnetic.
Has memory and so can be used to create permanent magnets.
High electrical conductivity.

Ferrimagnetic Type of ferromagnetic material.
Induced dipole moment aligns to applied field.
Attracted by bar magnet.
Very strongly magnetic.

Ferrites Type of ferrimagnetic material.
Induced dipole moment aligns to applied field.
Attracted by bar magnet.

Very strongly magnetic.
Low electrical conductivity.

Superparamagnetic Material mixture: ferromagnetic particles suspended in a plastic binder.
Induced dipole moment aligns to applied field.
Very strongly magnetic.
Has memory, which allows for uses in audio, video, and data recording.

SMALL LOOP ANTENNA BASIC INFORMATION AND TUTORIALS

What is small loop antenna?
Small loop antenna defined.



Large loop antennas are those with overall wire lengths of 0.5λ to more than 2λ. Small loop antennas, on the other hand, have an overall wire length that is much less than one wavelength (1λ).

According to a Second World War US Navy training manual such antennas are those with an overall length of ≤0.22λ. Jasik’s classic 1961 text on radio antennas uses the figure ≤0.17λ, while John Kraus (1950) used the figure ≤0.10λ.

An amateur radio source, The ARRL Antenna Book, recommends ≤0.085λ for small loop antennas. For the purposes of our discussion we will use Kraus’s figure of ≤0.10λ.

A defining characteristic of small loops versus large loops is seen in the current distribution. In the small loop antenna the current flowing in the loop is uniform in all portions of the loop. In the large loop, however, the current varies along the length of the conductor, i.e. there are current nodes and antinodes.

The small loop antenna also differs from the large loop in the manner of its response to the radio signal. A radio signal is a transverse electromagnetic (TEM) wave, in which magnetic and electrical fields alternate with each other along the direction of travel.

The large loop, like most large wire antennas, respond primarily to the electrical field component of the TEM, while small loops respond mostly to the magnetic field component. The importance of this fact is that it means the small loop antenna is less sensitive to local electromagnetic interference
sources such as power lines and appliances.

Local EMI consists largely of electrical fields, while radio signals have both magnetic and electrical fields. With proper shielding, the electrical response can be reduced even further.

COAXIAL CABLE CAPACITANCE CALCULATIONS BASIC INFORMATION AND TUTORIALS

How to calculate the capacitance of coaxial cable?

Coaxial Cable Capacitance Calculation Explained.

A coaxial transmission line possesses a certain capacitance per unit of length. This capacitance is defined by:

C = 24ε / log(D/d)          pF/Metre

where

C is the capacitance

D is the outside conductor diameter

d is the inside conductor diameter

ε is the dielectric constant of the insulator.

A long run of coaxial cable can build up a large capacitance. For example, a common type of coax is rated at 65 pF/metre. A 150 metre roll thus has a capacitance of (65 pF/m) (150 m), or 9750 pF. 

When charged with a high voltage, as is done in performing breakdown voltage tests at the factory, the cable acts like a charged high voltage capacitor. 

Although rarely if ever lethal to humans, the stored voltage in new cable can deliver a nasty electrical shock and can irreparably damage electronic components.

TRANSMISSION LINE NOISE BASIC INFORMATION AND TUTORIALS

What is transmission line noise?
Transmission Line Noise Defined.



Transmission lines are capable of generating noise and spurious voltages that are seen by the system as valid signals. Several such sources exist.

One source is coupling between noise currents flowing in the outer and inner conductors. Such currents are induced by nearby electromagnetic interference and other sources (e.g. connection to a noisy ground plane).

Although coaxial design reduces noise pick-up compared with parallel line, the potential for EMI exists. Selection of high-grade line, with a high degree of shielding, reduces the problem.

Another source of noise is thermal noise in the resistances and conductances of the line. This type of noise is proportional to resistance and temperature.

There is also noise created by mechanical movement of the cable. One species results from movement of the dielectric against the two conductors.

This form of noise is caused by electrostatic discharges in much the same manner as the spark created by rubbing a piece of plastic against woollen cloth.

A second species of mechanically generated noise is piezoelectricity in the dielectric. Although more\ common in cheap cables, one should be aware of it.

Mechanical deformation of the dielectric causes electrical potentials to be generated.

Both species of mechanically generated noise can be reduced or eliminated by proper mounting of the cable. Although rarely a problem at lower frequencies, such noise can be significant at microwave
frequencies when signals are low.

VOLTAGE STANDING WAVE RATION BASIC INFORMATION AND TUTORIALS

What is Voltage standing wave ratio (VSWR)?
Voltage standing wave ratio (VSWR) Defined.



When an RF cable is mismatched, i.e. connected to a load of a different impedance to that of the cable, not all the power supplied to the cable is absorbed by the load. That which does not enter the load is reflected back down the cable.

This reflected power adds to the incident voltage when they are in phase with each other and subtracts from the incident voltage when the two are out of phase. The result is a series of voltage – and current – maxima and minima at halfwavelength intervals along the length of the line.

The maxima are referred to as antinodes and the minima as nodes. The voltage standing wave ratio is the numerical ratio of the maximum voltage on the line to the minimum voltage: VSWR = Vmax/Vmin.

It is also given by: VSWR = RL/Z0 or Z0/RL (depending on which is the larger so that the ratio is always greater than unity) where RL = the load resistance.

The return loss is the power ratio, in dB, between the incident (forward) power and the reflected (reverse) power. The reflection coefficient is the numerical ratio of the reflected voltage to the incident voltage.

The VSWR is 1, and there is no reflected power, whenever the load is purely resistive and its value equals the characteristic impedance of the line. When the load resistance does not equal the line impedance, or the load is reactive, the VSWR rises above unity.

A low VSWR is vital to avoid loss of radiated power, heating of the line due to high power loss, breakdown of the line caused by high voltage stress, and excessive radiation from the line. In practice, a VSWR of 1.5:1 is considered acceptable for an antenna system, higher ratios indicating a possible defect.

DOPPLER EFFECT BASIC INFORMATION AND TUTORIALS

What is Doppler Effect?
Doppler Effect Defined.



Doppler effect is an apparent shift of the transmitted frequency which occurs when either the receiver or transmitter is moving. It becomes significant in mobile radio applications towards the higher end of the UHF band and on digitally modulated systems.

When a mobile receiver travels directly towards the transmitter each successive cycle of the wave has less distance to travel before reaching the receiving antenna and, effectively, the received frequency is raised.

If the mobile travels away from the transmitter, each successive cycle has a greater distance to travel and the frequency is lowered. The variation in frequency depends on the frequency of the wave, its propagation velocity and the velocity of the vehicle containing the receiver.

In the situation where the velocity of the vehicle is small compared with the velocity of light, the frequency shift when moving directly towards, or away from, the transmitter is given to sufficient accuracy for most purposes by:

fd = (V/C )ft

where
fd = frequency shift, Hz
ft = transmitted frequency, Hz
V = velocity of vehicle, m/s
C = velocity of light, m/s

Examples are:
• 100 km/hr at 450 MHz, frequency shift = 41.6Hz
• 100 km/hr at 1.8 GHz – personal communication network (PCN)
frequencies – frequency shift = 166.5Hz
• Train at 250 km/hr at 900MHz – a requirement for the GSM pan-
European radio-telephone – frequency shift = 208 Hz

When the vehicle is travelling at an angle to the transmitter the frequency shift is reduced. It is calculated as above and the result multiplied by the cosine of the angle of travel from the direct approach.

LG EG9900 4K TV GADGET REVIEW AND DESCRIPTION BASICS

LG EG9900 4k TV

Curved TVs are hotter than Oman in summer right now, but while they’re perfect for watching two-abreast, when there’s a room full of people, those in the middle can’t see diddly. Lg’s revolutionary bendable screen could solve that irksome problem by adapting to your needs with its flexible display.

Instead of pigeon-holing you with either flat or curved, Lg’s bendable tV can, rather brilliantly, do both. When it’s just you and a friend, go curved for maximum immersion.

When you’ve got friends around, a wave of the tV’s remote will make the display instantly flex into a flat position, so everyone gets a slice of the action.

LG is really pushing the organic technology found inside its panels, and the Eg9900 features the same oLEd spec, giving this screen impeccably bright and vibrant colours and perfect blacks. With ‘just’ a 4K resolution to contend with, you can lap up all that glorious 4K content rearing its head right now.

Yes, its 77-inch screen is a little bit gargantuan, but the cool, bendable technology will eventually trickle down to the smaller models, so you won’t necessarily have to build a man cave to justify your rather ott purchase, though you should.

THE FRAUNHOFER AND FRESNEL ZONES BASIC INFORMATION AND TUTORIALS

Each electromagnetic field can be divided into four zones: the near zone, the intermediate zone, the far zone, and the plane-wave zone. The near zone is the portion of the field close to the source. It is defined as the region where stored energy is much greater than any radiating energy. The far zone is the region where:

1) the stored field energy is much less than the radiating energy,

2) the wave impedance is approximately ho = 120p, and 3) the electric and magnetic fields are perpendicular to one another.

The intermediate zone is the region between the near and far zones. The plane-wave zone is the region in the far zone where the radiation can be approximated as plane waves.

This last zone is different from the others because its definition depends on the size of the receiving antenna.

Just as a basketball’s surface appears curved to a human but relatively flat to a tiny microorganism on the surface, and the Earth’s surface appears flat to a walking human, the apparent flatness of a curved wavefront depends on the relative size of the observer.

In optics, the plane-wave zone is called the Fraunhofer zone, and the combination of the three other zones is called the Fresnel zone.