Inductive charging

Inductive charging (also known as wireless charging or cordless charging) is a type of wireless charging that uses an electromagnetic field to transfer energy between two objects using electromagnetic induction, the production of electricity across a magnetic field. Inductive charging is usually done with a charging station or inductive pad. Energy is sent through an inductive coupling to an electrical device, which can then use that energy to charge batteries or run the device. It is the technology that enables smartphone wireless charging, such as the Qi wireless charging standard. Inductive charging (also known as wireless charging or cordless charging) is a type of wireless charging that uses an electromagnetic field to transfer energy between two objects using electromagnetic induction, the production of electricity across a magnetic field. Inductive charging is usually done with a charging station or inductive pad. Energy is sent through an inductive coupling to an electrical device, which can then use that energy to charge batteries or run the device. It is the technology that enables smartphone wireless charging, such as the Qi wireless charging standard. Induction chargers use an induction coil to create an alternating electromagnetic field from within a charging base, and a second induction coil in the portable device takes power from the electromagnetic field and converts it back into electric current to charge the battery. The two induction coils in proximity combine to form an electrical transformer. Greater distances between sender and receiver coils can be achieved when the inductive charging system uses resonant inductive coupling. Recent improvements to this resonant system include using a movable transmission coil (i.e., mounted on an elevating platform or arm) and the use of other materials for the receiver coil made of silver plated copper or sometimes aluminium to minimize weight and decrease resistance due to the skin effect. The transfer of power was the very first attempt using radio waves as a medium. Radio waves were first predicted in 1864 by James C. Maxwell. In 1888, Heinrich Hertz showed evidence of radiowaves using his spark-gap radio transmitter. Nikola Tesla believed that wireless power transfer was possible and probable. He built what was called the “Tesla Tower” which was a giant coil connected to a 200 foot high tower with a ball 3 feet in diameter. Tesla pumped 300 kW of power into the device; the coil resonated at 150 kHz. The experiment failed due to the fact that the power diffused in all directions. In the 1960s, much research was put into using microwaves to transmit power. William C. Brown made what he called a “rectenna”. This device received radio frequencies and converted them into a direct current. Brown succeeded but with low efficiency. Canada successfully flew a fuel-free model airplane in 1987 by transmitting a 2.45 GHz, 10 kW microwave to the model plane. There were also attempts to transfer power through induction. This was first used when, in 1894, M. Hutin and M. Le-Blanc proposed an apparatus and method to power an electric vehicle. However, combustion engines proved more popular and this technology was forgotten for a time. In 1972, Professor Don Otto of the University of Auckland proposed a vehicle powered by induction using transmitters in the road and a receiver on the vehicle. In 1977, John E. Trombly was awarded a patent for an 'Electromagnetically coupled battery charger'. The patent describes an application to charge headlamp batteries for miners.US 4031449  The first application of inductive charging used in the United States was performed by J.G. Bolger, F.A. Kirsten, and S. Ng in 1978. They made an electric vehicle powered with a system at 180 Hz with 20 kW.