Magnetic field strength and flux density,remove emi shield iphone 4,emp generator 2014 youtube - 2016 Feature

Magnetic HysteresisThe lag or delay of a magnetic material known commonly as Magnetic Hysteresis, relates to the magnetisation properties of a material by which it firstly becomes magnetised and then de-magnetised.
We also know from the previous tutorials that the magnetic strength of an electromagnet depends upon the number of turns of the coil, the current flowing through the coil or the type of core material being used, and if we increase either the current or the number of turns we can increase the magnetic field strength, symbol H. The set of magnetisation curves, M above represents an example of the relationship between B and H for soft-iron and steel cores but every type of core material will have its own set of magnetic hysteresis curves. This is because there is a limit to the amount of flux density that can be generated by the core as all the domains in the iron are perfectly aligned.
Lets assume that we have an electromagnetic coil with a high field strength due to the current flowing through it, and that the ferromagnetic core material has reached its saturation point, maximum flux density. However, the magnetic flux does not completely disappear as the electromagnetic core material still retains some of its magnetism even when the current has stopped flowing in the coil. While other ferromagnetic materials have low retentivity (magnetically soft) making them ideal for use in electromagnets, solenoids or relays. If this reverse current is increased further the flux density will also increase in the reverse direction until the ferromagnetic core reaches saturation again but in the reverse direction from before. Then by constantly changing the direction of the magnetising current through the coil from a positive direction to a negative direction, as would be the case in an AC supply, a Magnetic Hysteresis loop of the ferromagnetic core can be produced. The Magnetic Hysteresis loop above, shows the behaviour of a ferromagnetic core graphically as the relationship between B and H is non-linear.
If the magnetisation current, i is increased in a positive direction to some value the magnetic field strength H increases linearly with i and the flux density B will also increase as shown by the curve from point 0 to point a as it heads towards saturation. Now if the magnetising current in the coil is reduced to zero, the magnetic field circulating around the core also reduces to zero. To reduce the flux density at point b to zero we need to reverse the current flowing through the coil.
An increase in this reverse current causes the core to be magnetised in the opposite direction and increasing this magnetisation current further will cause the core to reach its saturation point but in the opposite direction, point d on the curve. Again reversing the magnetising current flowing through the coil this time into a positive direction will cause the magnetic flux to reach zero, point f on the curve and as before increasing the magnetisation current further in a positive direction will cause the core to reach saturation at point a.
Then the B-H curve follows the path of a-b-c-d-e-f-a as the magnetising current flowing through the coil alternates between a positive and negative value such as the cycle of an AC voltage.
However, soft ferromagnetic materials such as iron or silicon steel have very narrow magnetic hysteresis loops resulting in very small amounts of residual magnetism making them ideal for use in relays, solenoids and transformers as they can be easily magnetised and demagnetised. Since a coercive force must be applied to overcome this residual magnetism, work must be done in closing the hysteresis loop with the energy being used being dissipated as heat in the magnetic material.
By adding additive’s to the iron metal such as silicon, materials with a very small coercive force can be made that have a very narrow hysteresis loop. Magnetic Hysteresis results in the dissipation of wasted energy in the form of heat with the energy wasted being in proportion to the area of the magnetic hysteresis loop. Rotating coils in DC machines will also incur hysteresis losses as they are alternately passing north the south magnetic poles. In the next tutorial about Electromagnetism, we will look at Faraday’s Law of Electromagnetic Induction and see that by moving a wire conductor within a stationary magnetic field it is possible to induce an electric current in the conductor producing a simple generator.
Hello Mohammad, Magnetic Hysteresis relates to the magnetic flux which lags the increases or decreases in magnetizing force.
A magnetic field is a region in which a particle with magnetic properties experiences a force, and in which a moving charge experiences a force. To represent the field around a magnet we use a diagram which needs to obey some rules (or conventions) so that whoever uses it can interpret it correctly. The arrow shows the direction of the force that a free north pole, for instance a North pole with no South pole (which doesn't exist!) would feel. The spacing between the lines of flux tells you about the strength of field - as the lines get closer together, the field becomes stronger - for example, near the poles. Notice that in both cases the lines get further apart as you move away from the wire, this is because the magnetic field is getting weaker. Imagine you are screwing a corkscrew into or out of the page in the same direction as conventional current. There is a uniform field inside the centre of the coil; outside the field is the same as the field around a bar magnet. When two fields coincide they may cancel each other out and produce points where the magnetic field strength is zero.
Magnetic field strength is often called magnetic flux density and is given the symbol 'B' (obviously!?!). Magnetic field strength is defined as the force acting per unit current in a wire of unit length, which is perpendicular to the field. Either way, the reading on the scales will show how big this force is - so you have a measure of the force, F, due to the magnetic field and current. Absolute Permeability (μ) is the ratio of magnetic flux density (B) to magnetic field strength (H).
The absolute permeability is constant for non magnetic materials, as discussed previously, so a graph of B against H would be a straight line. Describe the inducing of an emf by relative motion between a conductor and a magnetic field. Discuss what is meant by the root mean squared (rms) value of an alternating current or voltage. Explain the use of high-voltage stepup and step-down transformers in the transmission of electrical power.
Suggest how extra-low-frequency electromagnetic fields, such as those created by electrical appliances and power lines, induce currents within a human body. Discuss some of the possible risks involved in living and working near high-voltage power lines. Conclusion: When a conductor moves with respect to a magnetic field (or visa versa) an electric current is induced. We need to think of magnetic field lines as magnetic flux (flux meaning something that flows).
When a conducting wire 'cuts' across the magnetic flux an induced current is produced.It doesn't matter whether it is the wire or the magnetic field that moves the result is the same.
Obviously then wires moving in opposite directions produce opposite induced currents and similarly for magnetic fields moving in opposite directions.
These factors inform many modern designs- motors, generators and dynamos all have many turns of wire inside them. The induced electromotive force across a conductor is equal to the rate at which magnetic flux is cut by the conductor. Considering a long straight wire cutting a magnetic field perpendicularly to the field lines. In this situation the work is done in moving the wire through the field and is converted in to electrical energy by doing so.
From our definition of magnetic flux cut, f, we can see that it is equal to B.A, where B is the magnetic field strength, or magnetic flux density, and A is the area that is cut.


If we are comfortable with this then we can start to think about flux cut by a coil of wire, or flux linkage.
Obviously the flux cut by a coil of N turns of wire will be N times as big as that cut by a single wire. The direction of any induced current (or induced emf) will be such as to produce effects which oppose the change that produces it. The amount of induced emf (and therefore current) will be affected by N- the number of turns in the coil, and f the magnetic flux cut. Try and plot a graph to show how the induced current varies as the coil rotates in the magnetic field.
Circuit currents and voltages in AC circuits are generally stated as root-mean-square or rms values rather than by quoting the maximum values. We can calculate the rms currents and voltages and then use them in circuit problems just as we do for dc. In order for this to happen and for us to be able to transmit large quantities of power over long distances we must be able to generate large voltages. A transformer is a device for increasing (steping up) and decreasing (stepping down) voltages. You may notice that the flux density increases in proportion to the field strength until it reaches a certain value were it can not increase any more becoming almost level and constant as the field strength continues to increase. Any further increase will have no effect on the value of M, and the point on the graph where the flux density reaches its limit is called Magnetic Saturation also known as Saturation of the Core and in our simple example above the saturation point of the steel curve begins at about 3000 ampere-turns per metre.
If we now open a switch and remove the magnetising current flowing through the coil we would expect the magnetic field around the coil to disappear as the magnetic flux reduced to zero. This ability for a coil to retain some of its magnetism within the core after the magnetisation process has stopped is called Retentivity or remanence, while the amount of flux density still remaining in the core is called Residual Magnetism, BR . Some ferromagnetic materials have a high retentivity (magnetically hard) making them excellent for producing permanent magnets.
One way to reduce this residual flux density to zero is by reversing the direction of the current flowing through the coil, thereby making the value of H, the magnetic field strength negative.
Reducing the magnetising current, i once again to zero will produce a similar amount of residual magnetism but in the reverse direction. Starting with an unmagnetised core both B and H will be at zero, point 0 on the magnetisation curve. However, the coils magnetic flux will not reach zero due to the residual magnetism present within the core and this is shown on the curve from point a to point b.
If the magnetising current is reduced again to zero the residual magnetism present in the core will be equal to the previous value but in reverse at point e. Then ferromagnetic materials have memory because they remain magnetised after the external magnetic field has been removed.
This heat is known as hysteresis loss, the amount of loss depends on the material’s value of coercive force. Materials with narrow hysteresis loops are easily magnetised and demagnetised and known as soft magnetic materials.
Hysteresis losses will always be a problem in AC transformers where the current is constantly changing direction and thus the magnetic poles in the core will cause losses because they constantly reverse direction. As said previously, the shape of the hysteresis loop depends upon the nature of the iron or steel used and in the case of iron which is subjected to massive reversals of magnetism, for example transformer cores, it is important that the B-H hysteresis loop is as small as possible. The hysteresis loop shows the B-H curve with an AC magnetizing force with flux density B on the vertical axis and field intensity H on the horizontal axis. So pop a magnet at X in the field (see diagram) and it would align itself with its North pole pointing along the arrow.
The turning motion of the corkscrew is in the same direction as the field arrows need to be. Apply the corkscrew rule to different sections of the coil (below) and you should see that at all points, the field is to the right on the inside of the coil and to the left outside. Permeability varies dynamically for magnetic materials such as iron or steel, based on a number of factors including the currently applied magnetic field strength, the previous magnetisation of the material, and on the current magnetic flux density. A A  Neither should theA  mattress be be treated with any chemicals or fire retardants.A  How buying the wrong mattress can make you ill.
Next follows some case history examples then we'll talk about those other types of unseen energies;A  the man-made electromagnetic variety and how these can also affect a house or building and the well-being of those inside. Tomasz M Janowski concerning zones of geomagnetic field disturbances (magnetic anomalies) in Poland and the health of 309 cows kept in cow stalls in a buildingA  measuring 91 x 24 meters in area. A A  Neither should theA  mattress be be treated with any chemicals or fire retardants.A  Such mattresses are hard to find. This is the magnetic field cut by a wire of length l, moving a distance x, in a magnetic field B. We can think of a coil of wire being linked to the magnetic flux it cuts, thus giving rise to the term flux linkage.
If we can keep moving electric currents low in overhead power lines then we can reduce resistance, heat generation and thus heat losses. This coercive force reverses the magnetic field re-arranging the molecular magnets until the core becomes unmagnetised at point c. Opposite directions of current result in opposite directions of field lines +H and -H, and likewise, opposite polarities of flux density produce +B or -B. In this example, we've cut a coil in half and are looking at it from the side - so the conventional current comes out of the page at the top and into the page at the bottom. If you make your fingers point in the same direction as the conventional current around the coil - your thumb points towards the end of the solenoid that is the North pole. The relative permeability of air is very similar to that of a vacuum, so it is normally assumed that μr=1 for air.
Magnetic materials demonstrate effects such as hysteresis and saturation, as illustrated by a B-H Curve.
As you can see the magnetic contours of this bed size area (6a€™x4a€™) are very gentle and slightly undulating showing an overall geomagnetic anomaly of 582 nT (nano Tesla). Cows kept in three of these stalls suffered ill health problems over and above a ratio that might be normally expected. However in the UK a small specialist mattress companyA  in Mid Wales, 'Abaca Organic' make such a product.
Moving a coil of wire in a magnetic field varies the amount of flux that links it, thus gives rise to a varying induced current.
This will become easier once you're over 18 as you will be allowed to drink wine and will therefore have knowledge of a corkscrew. The problem was initially resolved by moving these unhealthy cows to other cow stalls in the complex where they recovered. If this varying magnetic field links with a coil of wire, then an induced current will be produced in this coil. Within our evolutionary history our bodies own magnetic field has integrated with this magnetic field which is responsible for controlling amongst other things, circadian rhythms, mood changes and certain hormone production such as melatonin and serotonin.


However the healthy cows that were placed in these three cow stalls soon succumbed to ill health problems. The second geomagnetogram (G2) was taken above a sprung mattress from a lady suffering from chronic fatigue syndrome and severe depression, and has a magnetic anomaly of 22,435.4 nT.
The sprung mattresses I have measured so far over the past two years have had magnetic anomalies between 4,000 and 61,000 nT. The bottom line is that nature neverA  intended us to sleep on such a disturbed site as shown in figure G2 which has been artificially produced by the bed being placed near to a radiator ( causing the high spike to the right of the graph)A  and the springs causing the rest of the disturbed site. The reason for these abnormally high magnetic abnormalities is a result of the bed springs intensifying the magnetic flux of these fields, made worse by the interaction of high magnetic fields around the bed and house from numerous electrical appliances, extension cables running under the bed and transformers placed near to the bed.
It accumulates in the body and combines permanently with tissues, and inhibits activity of some enzymes. Our forefathers sleeping on straw or feathered mattresses in houses devoid of any electrical fields or microwave energy would not have experienced such geomagnetic disturbances. Each static magnetic field bump or sink on geomagnetogram (G2) may speed up or slow down body fluids (blood and lymphatic) in exposed areas such as the brain, heart, lung, liver, legs etc. The report concluded that the micro element disorders in the animals staying in the geopathic stalls was the primary cause of the many diseases and even death of the organism. Sleep time exposure to the same sharp variations of magnetic fields for years may induce some chronic health effect. Blood tests especially leukocyte count and the amount of toxic metal found in hair analysis were also indications that the animals were suffering from the detrimental affects of long term exposure to these geopathogenic sites. The World Health Organization in a health criteria report recognizes interactions between variations in static magnetic fields in cellular tissues to include an induction of electrical potentials and magneto hydrodynamic effects in the circulatory systems and by direct stimulation of nerve and muscle cells even under extremely weak thresholds. At our current stage of knowledge it is difficult to explain the mechanism these geomagnetic disturbances have on living organisms. The Cliff of Tears It is important not to underestimate the value of the earth's natural geomagnetic field (DC Field) which interacts with our bodies in many positive waysA  This DC field rarely shows an anomaly above or below 2% of its normal strength which differs according to the latitude in which you live. However there are instances in nature where abnormal magnetic anomalies exist usually due to a sudden change in mineralogy or geological structure over a short distance.
One instance of this is in the USA, at a place called Gyngywamp, near Croton, Connecticut knownA  as 'The Cliff of Tears' where visitors to this site very frequently become depressed, gums start to bleed and nose bleeds occur.
Polish Academy of Sciences June 1996 Studies conducted using various methods, are evidence that the earth's magnetic field plays an important role in the activity of living organisms as it affects the course of Physico-chemical reactions in the organism.
A disturbed geomagnetic field alters, among other things, the evolutionary shaped permeability of cell membranes and the magnetic orientation of micro elements. Indeed, in the town nearby, doctors and nurses are familiar with this sudden onset of illness in visitors to this old Indian sacred site. This can affect the whole plant or animal organism and thus the physiological status of the organism, the central nervous system and neuro-psychical phenomena. The causation seems to be that within a few meters the geomagnetic DC field varies from 330 milligauss at an 80 degree dip to 700 milligauss at a 59 degree dip. The influence of a disturbed geomagnetic field on the living organism is slow and cumulative in time and can cause dysfunction of the organism, but after it stops the dysfunction can regress.
After several months the healthy cows were moved in to the geopathogenic stalls and were observed to undergo a reverse process as their hair turned gray, matted, and became poorly rooted in the skin.
To varying degrees the health consequences of staying above one of these geopathically stressed locations can be replicatedA  in our own homes by the choice of mattresses we use.A  The bottom line is, if you suspect your sleeping site is being disturbed by an unusually high magnetic anomaly then buy a bed that has a wooden base and place there upon a mattress that has no springs and make sure it is not placed near a radiator or other heavy metal object.
My Own Research Many of the readings I have taken from mattresses slept on byA  people suffering from frequent miscarriage and Chronic Fatigue Syndrome (CFS) showed similar readings to the anomalies in the polish cow stalls. Unnatural Alterations in the Earth's Geomagnetic Field A second and equally important influence on the sequence of mitosis is the role in which the normal earth's geomagnetic field (DC field) influences the formation and production of a healthy pregnancy.
It appears that the exposure of a dividing cell to an inhomogeneous DC magnetic field causes a physical force to be exerted on the chromosomes or on one of the other microscopic structures associated with mitosis, resulting in structural abnormalities in the chromosomes.
The geomagnetic field is an important regulating factor for the whole organism of the human being. Many biochemical reactions, the oxidation process, the efficiency of the immune system and the regulation of the hormone system, are dependent on the surrounding condition of the geomagnetic field. A so called disturbed zone, or geomagnetic anomaly, exists as part of the constant flux of the eartha€™sA  field, producing in its natural state localized areas where homogeneous and inhomogeneous fields meet. Should the human body especially during sleep, be exposed to an inhomogeneous geomagnetic field over an extended time, then a great health risk is introduced every day to the body. This presents a measurable stress to the immune system especially during sleep when the body needs to relax.
The degree of how extreme these geomagnetic anomalies are, whether increasing or decreasing, coincide with the degree of risk to the health. It is important, therefore, to know what the actual situation is concerning the sleeping and working pace. To measure the geomagnetic field over the sleeping place is the best way to be informed about any health risk factors. The first symptoms are vegetative syndromes, drowsiness, waking up, feeling a€?offa€™ , chronic aches and pains, headaches and depression. Ferro-magnetism and Dia-magnetism Geomagnetic effects are created depending on whether a material repulses, attracts or is neutral to the eartha€™s magnetic lines of force. These are the highly magnetic materials: iron, magnetite (found in blood), nickel, and cobalt. Also some minerals are affected such as: manganosite, pyrite, basalt, platinum and aluminium.
Today houses have wires, metal conduit, and heating piping all with local and specific magnetic permeability properties. The geomagnetograms I produce can show a very disturbed sleeping site according to the density of a metal object placed near to or under the bed. Other structures I have found such as a metal girder from a room conversion below the bedroom and a bed placed above a large metal boiler in the kitchen below have also influenced a high magnetic anomaly. Also springs during manufacture can become highly magnetized if they come into close contact with other magnetic objects or electric fields.
Biological Effects Most of the research in to the biological effects of sleeping above an abnormally disturbed geomagnetic field (could be your mattress) has been carried out in Germany by Dr.
Ludger Mersmann who is a bio-physicist at the Technical and Medical Research Centre Wassenach Germany.
Studies with mice remaining in geopathogenic places are observed to have smaller litters, decreased weight and try to escape from the geopathic zones. Other German studies of animals kept in geopathogenic zones showed adverse effects on health and sudden death.The proportion of lymphocytes in the total white blood cell count dropped sharply as the animals stayed in geopathogenic stalls. Possible to prove hypothesis that cows staying in geopathogenic stalls area was a factor that caused ill health.According to a hypothesis of Krzywda et al.



Long term food storage 25 years later
Describe the disaster preparation and recovery planning


Comments to “Magnetic field strength and flux density”

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