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.


What are the dangers of radio frequency (rf)  and microwave exposure to humans?
Dangers to Humans of Radio Waves and Microwaves.

We can define the potential hazards of RF radiation in terms of:

1 Direct effects on people
(a) Thermal effects attributable to the heating of the human body due to the absorption of RF energy. At lower frequencies this includes heating due to excessive current densities in some parts of the body.

(b) Shocks and burns which may result from contact with conductive objects, e.g. scrap metal, vehicle bodies, etc., located in electromagnetic fields.

(c) The so called ‘athermal’ effects, if any, where it is postulated that the fields act directly on biological tissue without any significant heating being involved.

2 Indirect effects on people
Effects on people wearing implantable devices such as heart pacemakers, insulin pumps, passive metal plates and other related hardware due to interaction with some aspect of the implantable device. Some effects in this category affect the quality of life rather than physical health, e.g. interference with hearing aids and other electronic devices.

3 Effects on things in the environment
Ignition of flammable vapours and electro-explosive devices, e.g. detonators

Interference with equipment
Category 3 above may, of course, also involve people who may be present near the subject and may be affected by fire or explosion, people in aircraft where critical equipment is interfered with and the aircraft may be in jeopardy.

With the widespread use of mobile phones risks extend to interference with critical medical equipment in hospitals. Hence many people are likely to be affected in some way ranging from these obvious examples down to the merely irritating cases of interference with computers and domestic radio sets.

Before proceeding it is worth noting that a perceived ‘effect’ is not necessarily synonymous with ‘harm’ or ‘injury’. Our environment affects our bodies daily and some effects are of value, some harmful, and some have no apparent effect.

Some aspects of these topics may be differentiated in a general way in relation to the frequencies involved. Standards do tend to differ considerably in the detail of these.


An Introduction To Microsoft Hololens.
What is Microsoft Hololens?

Microsoft’s vision for the future is, it’s fair to say, one that not too many of us were expecting. Launched during the Windows 10 keynote with all the cloak and dagger reveal of a Jobsian ‘one
more thing…’ it became the headline story of the talk. this was undeniably a curve ball from the redmond giant.

But what kind of curveball exactly? Well, what it definitely is not is microsoft’s take on google glass.
holoLens is not an optical hUd and, while glass Explorers might be ridiculed and even viciously beaten for ‘exploring’ in public, you’d almost certainly be arrested if you approached a bank cashier wearing holoLens.

Yet that’s nothing to the trouble you’d be in should you even step near a petrol station or jittery downtown corner shop wearing oculus rift. Awesome it is. pretty it ain’t. and while it’s of closer comparison to holoLens than glass is, it’s still not quite the direct competitor to microsoft’s offering.

Rift locks you into a wholly virtual world whereas microsoft embraces the real world, showing its users pinning apps to living room walls and tinkering with projections of motorcycles.

Microsoft has effectively produced a micro pc that is hooked up to a set of high-definition holographic lenses, which it projects its 3d experience on 19 to. this, combined with spatial sound technology, creates wholly immersive Vr that promises to redefine Windows 10 apps… if the launch video is to be believed, anyway.

And that’s what’s making us very excited. Early hands-on reviews with development units have been both positive and profound. seen-it-all before technology journalists are genuinely excited about holoLens’s commercial, creative and educational potential.


How good is Panasonic CX850 TV?

Panasonic is really cranking the 4K at the moment, firstly with a slew of impressive 4K tVs, and secondly with the fact that it will introduce a range of 4K gadgets to support its panels, including a player that enables you to watch 4K content on and 4K cameras.

But ultra high-definition wrangling aside, the most exciting thing about panasonic’s tVs – specifically, its flagship 55-inch 4K LEd cX850 screen – is not so much what’s on the outside, but what’s on the inside.

Unlike the majority of television manufacturers, who are implementing android tV into their boxes, panasonic has made a shrewd move and plumped for the Firefox tV operating system.

Ignoring, for a moment, whether you prefer browsing the web via chrome or Firefox, mozilla’s os looks pretty spectacular, with an intuitive feel that makes it easy to find your way around and access the myriad of content – and voice command capabilities will further enhance this.

The new OS will also come with a range of extra nifty features, such as the ability to wirelessly exchange content like photos and videos from a smartphone, tablet or pc; and apps designed to notify you of new events, much as they would on a mobile.


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.


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

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.


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.


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.


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

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.