Power, without the wires

Resonance
Induction works well for lower power and over short distances, but pumping in more juice – while creating a larger field – wastes most of the power because it extends in all directions, and any chargeable devices intercept only a part of it.

Resonance, also known as non-radiative electromagnetic energy resonant tunnelling (say that fast to impress a date), takes induction and attempts to extend its range, and more importantly, efficiency, by allowing electricity to almost ‘tunnel’ directly from one coil to another by relying on the resonant properties of each.

Say what?

Resonance has been explained in terms of musical instruments – strike a chord on an instrument such as a violin and the same vibrations can be felt in an adjacent violin, or so we’re told. All materials, objects, everything have a particular electromagnetic resonance. If a transmitter and receiver can be attuned to the same frequency, their resonant properties will allow electrons to jump directly between them instead of being wasted in a general magnetic field.

The magic ingredient with making resonant coils is the addition of capacitor at the end of the coils that allows them to be attuned to a particular frequency.

Resonance could provide enough power to drive a laptop or larger, and all from a transmitter coil up to metres away. Theoretically, with a number of transmitters placed throughout a house, an entire home could be driven by wireless power.

Radio
What about radio? After all, antennas pick up radio waves of particular frequencies and current is produced – that’s how you receive your JJJ.

Whereas resonance tries to make the transmission of power more efficient, advances in radio frequency-based power transmission focuses more on the reception.

A company called Powercast has developed radio transmission and receiving products that hinge on the receivers being able to capture up to 70% of radio frequency energy, compared to some 10% that a normal receiver might pick up.

One of the more interesting facets of Powercast’s products is that radio frequency noise works in its favour – the more reflections from walls and other objects, the more waves that reach the receivers and are turned into power.

However as usual range quickly dissipates effectiveness and, more importantly, the power produced is less than the other methods. While it may not be enough to power a laptop, it can recharge a phone, and probably enough to power wireless keyboards and mice – and that would be cool, a wireless mouse you never have to charge.

Resonance allows electrons to arc directly to matching resonant coils/

Future shocks
The most recent advances in wireless power are coming from a group of researchers at the University of Tokyo who have demonstrated a ‘power mat’ that drives anything placed on it – in this case a sealed LED, placed in a goldfish bowl with occupant goldfish and water, illuminated when the bowl is placed on the mat.

The technique uses induction, but like resonance, tries to focus the power just to where it’s needed. Here, the power mat consists of layers of coiled wire and new organic (pentacene) transistors, allowing the mat to direct power only to the coils that are needed.

Ultimately, all these methods are different sides of the same thing – electromagnetic waves. From radio frequencies to microwaves to light, there are different properties we tap into and each has advantages and disadvantages.

So when are our homes going to be fitted with these things in the walls so we can say goodbye to cables and plugs forever? It might eventually depend on a multitude of products – long range, resonant sources for charging computers and appliances, and short range weaker sources for handheld devices for example. Then there’s interference (at least, with induction) – radio and TV could be affected by local power transmitters.

One thing remains certain – the propensity for wires tangling themselves is a strong enough drive if there ever was one, to refine the technology of wireless power. Just think: How nice would your desk be without that tangle of wires behind it?