As long as there have been cell phones, users have been looking for simpler ways to keep them charged besides having to plug them in to an electrical outlet with a cord.
Charging pads, plug-in power extenders and other options can be used, but researchers are continuing to look for new and more innovative methods, including wireless charging using sound waves or even ultrasound waves.
Experiments to use sound waves to wirelessly charge cell phones have been tested in the past, with the most recent attempts being conducted at England's Queen Mary University of London (QMUL), according to the school.
Meanwhile, a start-up called uBeam has been working for several years to perfect a method by which it uses ultrasound to move electricity from a source into a wireless device, from a smartphone to a tablet or other device.
At Queen Mary University of London, the idea of using sound to charge phones has been a project between researchers at the school and a team from Nokia, according to an Aug. 15 report from the school.
The idea came out of research done last year by researchers from the school's engineering and materials science departments, which found that playing pop and rock music improved the performance of solar cells, according to the school. Those original findings were published in the journal Advanced Materials with the Imperial College London.
"Developing this research further, Nokia worked with the QMUL team to create an energy-harvesting prototype (a nanogenerator) that could be used to charge a mobile phone using everyday background noise—such as traffic, music and our own voices," the school reported. "The team used the key properties of zinc oxide, a material that when squashed or stretched creates a voltage by converting energy from motion into electrical energy, in the form of nanorods."
Those nanorods then "respond to vibration and movement created by everyday sound, such as our voices," the school reported. "Electrical contacts on both sides of the rods are then used to harvest the voltage to charge a phone."
One of the primary researchers on the project at the school, Dr. Joe Briscoe, said that the experiments could someday lead to products that could charge mobile devices using sound waves to move energy.
"Being able to keep mobile devices working for longer, or do away with batteries completely by tapping into the stray energy that is all around us is an exciting concept," he said in a statement. "This collaboration was an excellent opportunity to develop alternative device designs using cheap and scalable methods. We hope that we have brought this technology closer to viability."
Previous experiments by Nokia to use radio waves to charge cell phones were reported back in 2009.
uBeam and Ultrasound
The uBeam project to find a better wireless device charger takes a different direction from the sound wave project by using ultrasound waves. The concept was first shown publicly by its organizers about three years ago during a science fair sponsored by The Wall Street Journal and its All Things Digital unit.