Wireless Power : Transfer Electricity without Wires

The wired world

It has taken about a century of digging and cabling, to network the world together. Electricity grids around the world use wires to take electricity from where it is generated to deliver it to where electricity is needed. These setups typically involve the massive plants, transmission towers, and the number of pylons on the distribution grid. When electricity was being introduced, wiring up so many places, across the world, seemed like a daunting task. Wires, were however relatively cheap, as well as efficient, and so wired electricity became the de facto standard of distributing electricity.

Wireless power in itself is not a new idea, it had been conceptualized more than a century ago, only never really implemented. In 1893, the Chicago World Fair brought together trends from around the world. It was also one of the earliest large scale demonstrations on the uses of electricity. Nikola Tesla won a bid to arrange for electricity for the entire fair (Thomas Edison and JP Morgan were his competitors). Here, the attendees saw the earliest public demonstration of wireless electricity transmission, a setup by Tesla. Tesla’s approach used something known as electrostatic induction. The method involves suspending two sheets of metal from the ceiling, one on either side of the room, and creating an alternating electrostatic field between them. This allows light bulbs to light up anywhere within a room.

Tesla’s vision for wireless power was to juice up devices anywhere in an environment, without the devices being tethered to wires. Even in 1893, the fact that bulbs were tethered to wires, making them immobile, was considered a problem. Over the years, many successful methods to deliver energy over distances wirelessly have been developed. Fundamentally, wireless transfer of information was considered similar to the wireless transfer of energy. Applications for these have been many. These included remote control devices, vehicles in a closed environment and communication.

About two decades ago, a range of electronic devices and household appliances started showing up in the market. These ranged from digital cameras and spare television sets to vacuum cleaners. All of these needed plug points, and the number of points often fell short. A typical user would face a number of problems, with just the wires. Sometimes the plugs would be of a different standard than the socket, almost every device had a unique adaptor that was not compatible with anything else, and running a number of devices at the same time became difficult. In an environment where the density of power-hungry devices is large, the wiring invariably became a tangled mess that nobody could navigate. A cramped office with computers lined up on a table, is a perfect example of this.

While wireless power over large distances is not going to be feasible any time soon, there are two areas where users stand to benefit a lot from wireless power. Wireless power is great for sending a large amount of power over small distances, as in charging all devices in a single room, or household, and sending a small amount of power over large areas, say, all the walkie-talkies on a construction site. A company called Splashpower toyed around with early prototypes of wireless energy transfer as early as 2001. Demonstrations of technologies have been around since 2008, showing up at conferences such as CES, and are expected to be implemented by 2011.

Near range wireless power

The technologies for existing near-range wireless electricity transmission are all based on the principle of induction. Induction is a phenomenon that causes electricity to be created when there is a change in a magnetic field. There are many kinds of inductive phenomena, including electromagnetic and electrostatic induction. Wireless transfer of a small amount of energy to and from devices using these methods, is pretty common already. The tags in retail outlets, for example, use this technology, as do some smartcards and the devices that detect shoplifting. In some highly-specific applications of electricity, which can be potentially harmful, some of these technologies are used to power devices that do not require much electricity. Examples of such applications range from electric cookers to electric toothbrushes.

Companies such as WiPower are trying to up the ante a bit, by allowing consumer electronics such as cameras, laptops, PMPs, mobile phones and even televisions to charge up wirelessly. WiPower uses a form of electromagnetic induction known as “resonant coupling”. Resonance occurs when an object vibrates at a greater amplitude because of some kind of waves. These waves may be magnetic, electromagnetic, acoustic or any other variety – resonance occurs for all of them. Music from a stringed instrument, breaking a glass with a high-pitched voice, or vibrating windows when a certain frequency is playing on speakers are all everyday examples of resonance.

A coil of wire, attached to a power source, can relay electromagnetic waves over to another coil of wire, attached to a device. The inductive coupling uses electromagnetic resonance, and the receiver coil generates electricity. Tightly-coupled induction tunes the coil of wire embedded within a device so finely to the coil which is the source, that the orientation, location and distance to the object become very important. Loosely coupled induction however, does not have these limitations, but suffers from a small fall in the efficiency of the power transmission (about 10 per cent when compared to tightly coupled induction). Both these technologies have their own unique set of problems. Tightly-coupled induction cannot be used to power up multiple devices at once, because the size of the coils on both the transmitter and the receiver should be of a similar size. Loosely coupled induction renders many devices that it charges useless, as the electro- magnetic energy interferes with some of the communication features in the device, such as GSM or radio.

A comparison of efficiency vs the range of standard wireless technologies

This kind of resonant coupling, is a great compromise between efficiency and mobility. Other kinds of wireless electricity technologies either need the devices to be too close to the source, or cannot charge up any device in a reasonable amount of time. The inductive coupling approach also is the lowest cost solution, and can be cheaply deployed in a number of ways. The coil to charge a device can be either embedded within the device itself, replacing the battery unit, or added to the back of a device as an additional sleeve, which is connected to the power unit of the device. The sleeve approach is great for transition between a wired domestic, office and public environments, to a wireless one. The device can be charged using traditional methods where wireless chargers are not available. The charging can be done in the form of mats, that can charge multiple devices at once. These sources can be embedded, within say the tables of cafes or the walls of homes.

Since the technology has been around for a while, and is a low cost solution, why are we not seeing more wireless devices around? When asked this question, the WiPower team told us that “The major hurdle to mass adoption has been the difficulty and cost of integrating wireless power technology into consumer electronic products. Large OEMs are very interested in the technology, but have generally found it too complex and expensive to replicate in high volume manufacturing environments. “ The initial cost of such devices would be high, and it is an overhead that consumers may not be willing to pay extra for. For example, if a manufacturer comes out with a camera that charges wirelessly, will the buyer pay extra for a mat that can charge the camera, and maybe other devices from manufacturers who follow the same standard? It is easier to market a wireless television, that does not need to be tethered to a power source.

Uniden Power Pad Australia

There is currently a gap between wireless technologies, and its implementation, as manufacturers will have to rethink the way they make their devices. “WiPower has attempted to bridge this gap by providing companies with a wireless power Design Kit. The Design Kit allows engineers to explore WiPower’s technology, and discover how simple and cost-effective it is to design into a variety of applications. With WiPower’s wireless power system, consumers will be able to charge multiple devices in any position on a single charging pad. The technology is also easily integrated into furniture so that people will be able to enjoy clean, wireless spaces at home, the office, etc.” The WiPower design specifications are available to manufacturers, and orders can be placed for the transmitter and receiver elements to integrate into any manufacturing process. The receiver units are designed in such a way, that they can be potentially retro-fitted into existing consumer electronic products. One of WiPower’s greatest innovations is in the charging pads. The pads are configured in a way that they can calculate the amount of charge necessary for the device, and relay only that much power to the receiver.

Long range wireless power

The technologies for long-range wireless electricity transmission, a possibly more exciting domain, include radio waves, microwaves, and even lasers. The technologies are not that difficult to decipher or understand. For example, to use lasers to provide wireless power, you need to simply point a sufficiently powerful laser at a solar panel. It is easy to envision a network of lasers instead of wires, but there is the question of efficiency. While in controlled spaces, the efficiency is pretty good, over a large grid or deployment on a large scale is not yet practical. However, a small amount of charge can be “cast” over a large area, powering up devices that are willing to accept that charge.

A Powerharvester module, is tiny enough to be embedded almost anywhere

Wirelessly relaying small, but steady amounts of power have their own unique set of advantages. Powercast is a company that specializes in something known as “trickle power”, a model of wireless power transmission that allows power to be relayed over radio waves in small quantities. They make Power harvester Receivers, that can “harvest” electricity and power devices, and Power caster Transmitters, that are sources of power for the receivers. The use of Powercast for consumer technologies is very limited. According to Powercast, “Our technology provides micro-power and will not be suitable for most consumer devices, and especially devices like mobile phones that require fast recharging. Wireless power for consumer devices will primarily be based on induction and will work for higher power, short range applications.” Powercast has demoed a few trickle power consumer applications though, including LED Christmas lights and remote controls that charge up wirelessly. Trickle power, however, has a range of applications when it comes to applications on a larger scale, especially in the industrial sector. “We are focused on power over distance for industrial applications such as wireless sensors for trickle charging batteries or battery-free sensors. Wireless sensors enabled by Powercast technology will provide greater life and reduced maintenance (from not having to change batteries) to wireless sensors for a range of applications including energy management, building automation, location tracking, and defense.” This has many implications for a number of sectors. Any kind of monitoring on a system, through small cameras, infra-red sensors, or other kinds of sensors, can be done through a Powercast setup. All the walkie-talkies in an area can be remotely powered using a trickle charge. Smart RFID tags, similar to the tags embedded in consumer goods, can be used to track, say all the animals in a national park, and monitor their health at the same time.

Powercast’s system is built in such a way that any number of Powercasters can transmit power to any number of power receivers, configured within the same grid. This allows for great flexibility at the point of deployment, and scales well when more units have to be added to any given configuration. “Powercast has many innovations related to sending and receiving power over distance. Our RF Power harvester components work over a wide operating range which makes them useful for many applications as opposed to a design that only works in a narrow operating range of input power and device load,” according to Harry Ostaffe Director, Marketing and Business Development, Powercast. Powercast has teamed up with at least 200 companies for developing and implementing the trickle power technology, and also sells kits that can be used to develop applications.

A wireless world

Apart from the convenience aspect of the technology, there are many other advantages as well. The environment stands to benefit tremendously if this is implemented on a large scale. The large number of adapters and wires will be done away with, as well as devices such as multi-plug points. The packaging material used to deliver these wires along with the device can also be done away with. Batteries, that are terribly harmful to the environment can be replaced by discreet wireless power sources. The cost of materials used to make these wires and batteries and running the factories that do all of this can also be done away with. This kind of technology can greatly reduce the hazards of working with devices that use wires and plugs in explosive environments, in hospitals and in combat situations. When it comes to industrial applications, wireless power to sensor networks, or tagged networks not only simplifies implementation, but also allows for the components of a network to do more. For example, trickle charged smartcards or RFID tags can be configured to collect and relay information, as they can be wirelessly powered. Deploying networked nodes in the atmosphere for collecting weather information, underwater, or even in outer space becomes more efficient as each module can be powered up at a distance. Widespread use of wireless power technologies, is however, still some time away.