Methods of Energy Transfer
Inductive Coupling
Inductive coupling is a method of energy transfer that involve the interaction of magnetic fields for two circuits through mutual inductance. When two conductors are configured in such a manner that the change in current through one wire leads to induction of a voltage across the ends of the other wire through the process of electromagnetic induction. It is important to understand that the inductances are linked by a common changing magnetic field. Mutual inductance is the measure of the amount of inductive coupling between the two conductors. The inductive coupling is increased in four ways; first through frequency which is directly proportional to the inductive reactance. Secondly, the distance that is between the disturbing and victim cables as well as the cable length that are parallel. Thirdly is the cable height in relation to the reference plane and lastly the load impedance of the cable or the disturbing circuit. Inductive coupling can be maximized through winding up two wires into coils and placing them close together on a common axis as the magnetic field of one coil passes through the other coil.
The two coils can be physically contained in a single unit especially the example of the primary and secondary side of a transformer and others may be separated. Coupling can be intentional or unintentional. Unintentional coupling is referred to cross-talk. Unintentional coupling is a form of electromagnetic interference. Generally, inductive coupling favors low frequency energy sources as the high frequency sources basically adopt capacitive coupling. The efficiency of the inductive coupling energy transfer is dependent in several factors which include, the inductor sizes, inductor shape, distance between coils, and the coil resistance.
Electromagnetic Radiation
Electromagnetic radiation is the transfer of electromagnetic energy through a vacuum by means of radiation. In other words, electromagnetic radiation is the electric and magnetic disturbance that travels through space at the speed of light. Electromagnetic energy is the only energy that can travel in a vacuum. The electromagnetic radiation has neither mass nor charge. it travels through the use of packets of radiant energy known as photons. Essentially, all objects that are warmer than the absolute zero at -273o C emit electromagnetic radiation. In the same way, objects reflect and absorb electromagnetic radiation that is emitted by other objects. All electromagnetic radiation follows the basic principles of the wave theory. Electromagnetic waves forms from the vibrations of electric and magnetic fields which involve perpendicular electrical and magnetic fields. The fields in the electromagnetic radiation have varying magnitude in a direction perpendicular to the direction in which the radiation travels. These fields travel at the same constant speed which is equivalent to the speed of light. The description of the electromagnetic radiation involves its frequency, wavelength and energy level. The wave characteristics of electromagnetic radiation involve the relationship of velocity to wavelength which is the distance of a single cycle. It also involves the frequency in that the number of cycles in a second are determined. Electromagnetic radiation of long wavelength is described to have a low frequency while on the other hand the radiation of short wavelength has high frequency. The long wavelength with low frequency at the electromagnetic spectrum is the radio waves. On the other hand, short wavelength with high frequency include the gamma rays. Other forms of radiation lie between these two extremes including Infrared, microwaves, ultraviolet and visible light.
Magnetic Resonant Coupling
Magnetic Resonant Coupling is a method that improves the performance of inductively couple energy transfer for large separation distances between coils through the use of resonant circuits. Few resonances are used in a resonant inductive coupling energy transfer system. resonance is the tendency to oscillate with large amplitude at a specific frequency. Two energy systems that have the same resonance tend to exchange energy between them. The resonance frequencies are combined with frequency of operation that in the frequency of the applied voltage which is equal to the resonance frequency of the system. Induced current in primary coil induces current in secondary coil when the coils operate at identical resonant frequencies. Primary coil induces high current amplification in secondary coil which allows for larger distances between the coils. At strongly coupled resonance frequencies, the maximum energy is transferred between energy systems. The utilization of resonance allows the transfer of more power at higher efficiency and over longer distances more than the non-resonated systems. Using magnetic resonant coupling, one coils can transfer energy to several receiving coils provided all their resonance is at the same frequency. When two coils are tuned to a particular frequency called resonating frequency, they absorb optimal energy through resonant coupling. This method of energy transfer offer power transfer up to ten times more than inductive coupling. The method does not require exact precision between the primary coils and secondary coils as inductive coupling and has low heat generation. The challenges with resonant inductive coupling involve the low efficiency and slower charging cycles compared to non-resonant inductive coupling. Another challenge of resonant inductive coupling involves the inability to transfer energy through solid objects.
