Wireless power transfer (WPT) or wireless energy transmission is the transmission of electrical power from a power source to a consuming device without using solid wires or conductors. Wireless transmission is useful to power electrical devices in cases where interconnecting wires are inconvenient, hazardous, or are not possible. In wireless power transfer, a transmitter device connected to a power source, such as the mains power line, transmits power by electromagnetic fields across an intervening space to one or more receiver devices, where it is converted back to electric power and utilized.

Wireless power techniques fall into two categories, non-radiative and radiative. In near-field or non-radiative techniques, wireless power is transferred over short distances by magnetic fields using inductive coupling between coils of wire or in a few devices by electric fields using capacitive coupling between electrodes. Applications of this type are electric toothbrush chargers, RFID tags, smartcards, and chargers for implantable medical devices like artificial cardiac pacemakers, and inductive powering or charging of electric vehicles like trains or buses. However, current focus is to develop wireless systems to charge mobile and handheld computing devices such as smartphones, digital music players and portable computers without being tethered to a wall plug.

In radiative or far-field techniques, also called power beaming, wireless power is transmitted by beams of electromagnetic radiation, like microwaves or laser beams. These techniques can transport energy longer distances but must be aimed at the receiver. Proposed applications for this type are solar power satellites, and wireless powered drone aircraft. An important issue associated with all wireless power systems is limiting the exposure of people and other living things to potentially injurious electromagnetic fields. Considering the safety of the end-users, non-radiative techniques have been given more prominence. Inductive coupling is the oldest and most widely used wireless power technology, and virtually the only one so far which is used in commercial products. Thus, today Wireless Power is more of magnetic resonance or inductive power transfer.

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Figure 1 : Inductive Coupling

In inductive coupling (electromagnetic induction or inductive power transfer, IPT), wireless power is transferred between coils of wire by a magnetic field. The transmitter and receiver coils together form a transformer as shown in Figure 1. An alternating current (AC) through the transmitter coil (L1) creates an oscillating magnetic field (B) by Ampere’s law. The magnetic field passes through the receiving coil (L2), where it induces an alternating EMF (voltage) by Faraday’s law of induction, which creates an AC current in the receiver. The induced alternating current may either drive the load directly, or be rectified to direct current (DC) by a rectifier in the receiver, which drives the load. A few systems, such as electric toothbrush charging stands, work at 50/60Hz so AC mains current is applied directly to the transmitter coil, but in most systems an electronic oscillator generates a higher frequency AC current which drives the coil, because transmission efficiency improves with frequency.

There are two alliances namely Wireless Power Consortium (WPC) and Power Matters Alliance (PMA) which fuel the spread of wireless charging all over the world. WPC have developed an interface standard for the inductive electric power transfer known as Qi (pronounced as Chee). WPC and PMA are backed by a number of big names in the mobile industry and these two standards are supported in Samsung’s new Galaxy S6 (Figure 2).

Figure 2 : Samsung’s Galaxy S6 supports both Qi and PMA standards, but the charger it sells is still based on inductive technology.

Figure 2 : Samsung’s Galaxy S6 supports both Qi and PMA standards, but the charger it sells is still based on inductive technology.

Both the PMA and Qi are based on inductive charging, which operates over short distances, less than 1cm, and usually uses magnets to hold your phone in the right place. Resonance charging, by comparison, operates over longer distances at the expense of less power as the distance increases, up to a couple of inches. This enables the technology to easily charge multiple devices at once. Each of these three standards delivers around 5W of power to your smartphone, which is roughly equivalent to using a 1 Amp wall charger.

Furthermore, PMA and the Alliance for Wireless Power (A4WP), the third largest group in the space, signed a collaborative deal earlier in the year. The agreement sees the two companies exchange patents, technologies and systems in order to facilitate a faster evolution and adoption of wireless charging technology. While the PMA prefers inductive charging, which is similar to Qi, A4WP’s Rezence standard makes use of magnetic resonance charging.

The main advantage of wireless charging is the convenience its got to offer to the end-user. The ease with which the smartphone gets charged after placing it over the wireless charger is just awesome. IKEA, a Swedish furniture company, have developed furniture with built-in charging spots (as seen in Figure 3) apart from the wireless chargers thus making the task of charging our smartphones much simpler and convenient.

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Figure 3 : Place your smartphone on the plus mark on the lamp-stand to charge wirelessly

Today people are overwhelmed with wide range of consumer electronics products which shape the convenience of today and drive the life of future. For instances, people prefer withdrawing cash from the nearest ATM instead of visiting their banks, people prefer shopping online using debit/credit cards instead of carrying cash along, in automobiles- people prefer central locking system instead of closing/opening all the doors manually and smart key wherein the ignition is activated without inserting a key but instead by pressing a starter button or twisting an ignition switch, etc. Similarly in the field of telecommunications, wireless charging enables the customers with charging of their smartphones with ease or convenience.

PowerSquare, an innovative start-up in the field of Wireless Power has developed wireless charging pad TANGO which is world’s first position free multi-device wireless charger. TANGO wireless charger offers a lot of convenience to the customers as their 2-Qi compatible smartphones can be charged wirelessly at the same time. For more information, please visit http://www.powersquare.com/ and grab your TANGO at http://www.powersquare.com/shop

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