WIRELESS POWER

INTRODUCTION

Wireless Power transfer was first demonstrated by Nikola Tesla in the 1890s, however it is only really in the last decade that the technology has been harnessed to the point where it offers real, tangible benefits to real world applications.  In particular, the development of resonant wireless power technology for the Consumer Electronics market, has seen charging by induction (wireless charging) deliver new levels of convenience for the charging of millions of everyday devices.

Wireless Power is commonly known by many terms, including Inductive Power Transfer (IPT), Inductive Coupling, Resonant Wireless Power, and Resonant Power Transfer. Each of these terms essentially describe the same fundamental process – the wireless transmission of electricity or energy from a power source to an electrical load, without connectors, across an air gap.  The basis of a wireless power system involves essentially two coils – a transmitter and receiver coil.  The transmitter coil is energized by alternating current to generate a magnetic field, which in turn induces a current in the receiver coil.

HOW DOES WIRELESS POWER WORK?

The basics of wireless power involves the transmission of energy from a transmitter to a receiver via an oscillating magnetic field.

To achieve this, Direct Current (DC) supplied by a power source, is converted into high frequency Alternating Current (AC) by specially designed electronics built into the transmitter.

The alternating current energizes a copper wire coil in the transmitter, which generates a magnetic field.  Once a second (receiver) coil is placed within proximity of the magnetic field, the field can induce an alternating current in the receiving coil.

Electronics in the receiving device then converts the alternating current back into direct current, which becomes usable power.

The diagram below simplifies this process into four key steps.

WIRELESS POWER TRANSFER DIAGRAM

1. The ‘mains’ voltage is converted in to an AC signal (Alternating Current), which is then sent to the transmitter coil via the electronic transmitter circuit.
2. The AC current flowing through the transmitter coil induces a magnetic field which can extends to the receiver coil (which lies in relative proximity)
3. The magnetic field then generates a current which flows through the coil of the receiving device. The process whereby energy is transmitted between the transmitter and receiver coil is also referred to as magnetic or resonant coupling and is achieved by both coils resonating at the same frequency. Current flowing within the receiver coil is converted into direct current (DC) by the receiver circuit, which can then be used to power the device.

WHAT IS MEANT BY “RESONANCE”?

The distance at which the energy (or power) can be transferred is increased if the transmitter and receiver coils are resonating at the same frequency.

This resonant frequency refers to the frequency at which an object naturally vibrates or rings – much like the way a tuning fork rings at a particular frequency and can achieve their maximum amplitude.

BENEFITS OF WIRELESS POWER

• Reduce costs associated with maintaining direct connectors (like those in the traditional industrial slip ring).
• Greater convenience for the charging of everyday electronic devices
• Safe transfer of power to applications that need to remain sterile or hermetically sealed
• Electronics can be fully enclosed, reducing the risk of corrosion due to elements such as oxygen and water.
• Robust and consistent power delivery to rotating, highly mobile industrial equipment
• Delivers reliable power transfer to mission critical systems in wet, dirty and moving environments.

Whatever the application, the removal of the physical connection delivers a number of benefits over traditional cable power connectors, some of which aren’t always obvious.  The video below highlights just some of the benefits and advantages of wireless power and offers an insight into a world where wireless power is widely integrated into industrial and mission critical environments.

FAQ’S

HOW EFFICIENT IS WIRELESS POWER TECHNOLOGY?

The overall efficiency of a wireless power system is the most important factor in determining its performance. The efficiency of a system measures the amount of power transferred between the power source (i.e. wall socket), and the receiving device. This, in turn, determines aspects such as charging speed and transmission distance.

Wireless power systems vary in regards to their level of efficiency based on factors such as coil configuration and design, transmission distance and coupling. A less efficient system will generate more emissions, and result in less power getting through to the receiver device.

Typically wireless charging technology for devices such as smartphones can reach upwards of 70%+ for power transfer. PowerByProxi can achieve over 90% wireless power transfer efficiency for their latest Proxi-Module platform, which transfers up to 100 watts of power.

HOW IS EFFICIENCY MEASURED FOR WIRELESS POWER TRANSFER?

Efficiency is measured in a general sense as the amount of power (as a percentage) that is transferred from the power source to the receiver device i.e. a wireless charging system for a smartphone with 80% efficiency means that 20% of the input power is being lost between the wall socket and the battery for the smartphone. The formula for measuring operating efficiency is:

CAN POWER BE TRANSMITTED THROUGH MATERIALS OTHER THAN AIR?

Yes. Power is able to be transmitted wirelessly through almost all non-metallic materials, including – but not limited to – solids like wood, plastics, textiles, glass and brick, as well as gases and liquids.

When a metallic or electrically conductive material (i.e. carbon fiber) is placed within close proximity of an electromagnetic field, the metallic object will absorb the power from the magnetic field, and heat up as a result. This, in turn, affects the efficiency of the system due to power being lost through absorption. This is how induction cooking works – inefficient power transfer from the cooktop creates heat to enable cooking. This post on wireless charging and induction cooking provides a detailed explanation on this relationship.