A transformer that converts currents and voltages is one of the most essential elements of an electric circuit. In the simplest case, the transformer consists of two galvanically separated, fixed coils without a ferromagnetic core. This transformer core is considered an air core transformer.
In any form of simple material, two coils (known as windings) are wound. In certain instances, cylindrical or rectangular cardboard shape is wrapped with wire coils, this core material is air.
Since the transfer of energy from one circuit to another through a transformer, a transformer without a steel magnetic circuit is widely used in electrical engineering. We might have various applications, but most of the time we ‘re supposed to convert the AC voltage. That is the very name of the device, taken from the Latin term transform-transform.
Such a conversion is required, for example, because the voltage of the energy source is different from the voltage expected for the energy receiver. Primary and secondary winding wounded on a non-magnetic strip where there is a flow connection between primary and secondary winding through the air.
Difference between Air Core and Iron Core Transformer
The reciprocal inductance effect is much weaker in the air core than in the iron core, i.e. the resistance of the generated flux is large in the air medium where, as in the iron core, it is smaller. However, hysteresis and eddy current losses, which are common in iron core situations, are less or more completely eliminated in the air core shape of the transformers.
High-frequency Air Core Transformer
The transformer core composition depends on voltage, current and frequency. Also included are size limitations and construction costs. Air and soft iron are widely used for core materials. That material is suitable for different applications and not suitable for other applications. Air core transformers are usually used at high frequency (over 20 kHz) from the source of the voltage. Iron-core transformers are usually used when the source frequency (less than 20 kHz) is small. A soft-iron core transformer is extremely useful when the transformer is small yet effective.
The iron core transformer has greater transmitting power than the air-core transformer. Sheets of transformer laminated core steel quickly discharge heat, thus allowing for effective power transmission. Many of the transformers you’ll find have laminated steel cores in Navy equipment. These laminations are separated from a non-conductive material, such as a varnish, and shaped into a core. It takes about 50 of these laminations to become one core thick. Laminations have the effect of minimizing certain losses that are addressed later in this segment. A significant thing to note is that the most effective core of the transformer is one that has the fastest path for the most flux lines with the lowest energy loss.
Principles of operation and application of air transformer
The air transformer is a method for transforming electrical current parameters without physical contact between the components. In other terms, the energy is transmitted wirelessly across the air.
Although the air environment is a low current conductor in natural circumstances (standard temperature, absence of ions treated differently), the usage of air transformers as sources of additional current or voltage is counterproductive. Another factor is the conversion of AC frequency, where no significant energy costs are required. The devices called are therefore designed to relay currents of various frequencies during the propagation of radio signals.
The air transformer is a device with a conditional “air core” a distance that divides the main and secondary windings according to the operating system. The wire windings are wound on a rectangular base made of a condenser board or another insulator for the durability of such a distance, where the main conductive medium is air.
They are reduced to two groups:
Impedance is used to coordinate the values of the voltage drop at the source and consumer of the load in order to ensure the most efficient energy transfer.
Insulating, which is used for safety reasons to isolate parts of the equipment from an energy source.
They induce a secondary voltage, the value of which is comparable to the inductance of the electrical system. The core material is therefore characterized by the highest magnetic permeability. Such materials also include glass, porcelain, mica and certain types of plastics.
Air Core Transformer Design
The core is used in transformers to the magnetic flux and to reinforce the connection between the primary and secondary windings. The usage of diamagnetic materials guarantees the avoidance of hysteresis and vortex disturbances and disruptions of the electromagnetic field in the system as this contributes to a reduction of the efficiency of the radio signal.
In addition to the quiet operation, the wireless transformers are also lightweight. This kind of transformer is, therefore, suitable for portable, lightweight electronics and high-frequency applications.
According to the basic design, the air Transformers are divided into cylindrical and toroidal. Reasonable options for core material give the following products:
- The device’s high performance.
- No power failure during transformation.
- Stability of the ratio of primary to secondary voltage.
How to make and assemble an air transformer?
Pre-determined with core material. Using electrical cardboard, it is necessary that its performance characteristics comply with the following standards of IEEE.
Thickness, mm, no less than-2.1 … 2.3. Right now.
Density: g / cm 3, no less than 1,0 … 1.13. 1.14.
Tensile strength, MPa, not less than-103 … 111. 112.
The power of bending, MPa, is no less than-34 … 41.
Electrical strength, kV / mm, no less than-12 … 13.
Percent relative humidity-8 ± 2.
The insulated copper wire coils are placed either on a plastic sheet or on a hollow toroid. For the adopted core configuration, its resistance moment is assumed to be the greatest at a given external cross-section distance, providing the required mechanical support for winding. Copper winding around the toroid can be taken to different points from which the secondary voltage is removed, if necessary.
In order to maintain continuous resonance in the tuning circuit, an additional capacitor is often attached to the winding. Magnetic flux flows through the air around the winding and through the air in the hollow core.
In order to match the value of the voltage drop over the main copper winding correctly, a protective winding is often used. It is attached to the antenna receivers and properly grounded.
Toroidal cores have many features that make an advantage over cylindrical cores because the effect of vagal coupling is limited. This type is used especially for high-frequency applications.
Air Core Transformer Efficiency
In fact, most of the transformers are made of cores. For high performance, the coupling coefficient should be as close as possible to 1. If the magnetic fluxes of the coils are not fully closed, that is, if any of the fluxes are scattered, the energy transmission loss decreases. Yes, these are the same dissipation losses of the transformer, usually expressed as dissipation inductance.
But, if there’s low efficiency in a coreless transformer, why is that? The irony is that the magnetic components commonly utilized in the manufacturing of core materials (ferromagnets, ferrimagnets, magnetodielectric) have a non-linear magnetizing curve. In other terms, the accuracy of the waveform transmitted across such a transformer leaves plenty to be desired. And at times, that is extremely necessary.
In addition to the dependence of the magnetic properties of the core on the magnetic field, there is frequency dependence. Cores made of special materials with low magnetic permeability are used to reduce this dependence.
However, neither special materials nor non-magnetic clearance completely solves the issue. Often, the removal of the core from the transformer only serves to produce the desired result. It’s the same Coreless Transformers or Air Core Transformers. Do not equate coreless transformers with air-cooled transformers, often referred to as air transformers.
Occasionally, the core can not be utilized owing to the design characteristics of the transformer. But let’s find the right thing. Transformers without a core will, most commonly, are encountered by specialists interested in receiving and transmitting antennas. Transformers are used to link the feeder to the antenna. Not necessarily without a heart, but they’re performed very frequently.
Here are the Applications
Quite probably, the others noticed something on the tv viewing antennas. The coil, in overt form, was uncommon there, and more often than not it was only a bit of U-shaped metal. The corresponding transformer compared the wave impedance of the antenna with the wave impedance of the wire. The alignment of the balanced loop antenna with the unbalanced cable was also assured. Yes, air-core transformers have often been used for this purpose, although more frequently than not for individual antennas. In addition, a coaxial cable transducer may also be powered by a transmitting antenna.
I do not list experiments with a transmitting antenna in vain. The truth is that strong broadband transmitters have specifications for matching antenna transformers that are very difficult to implement using magnetic cores. In these situations, coreless matching transformers are used to minimize signal distortion. Here’s the evidence of amateur design.
Contactless credit cards, contactless keys/badges, NFC tags for smartphones, RFID tags work in the same way.
Sure, these coils are also called antennas, but this is not necessarily accurate. These are, in essence, the coils, the toroidal transformer windings without a core. They include both the power of the built-in chip and the transmission of information.
Here is an experimental video from youtube explaining about air core and iron core coils