We developed a battery-free wireless headphones prototype as part of our fun activities. Learn what we found out and our ideas of potential for them.

The ecosystem of personal devices we use is continuously changing. These kind of devices need to evolve into smart, easy to use and comfortable items we can carry with us without problems. This is why manufacturers are continuously implementing improvements in their designs for lower size, lower power consumption and hassle-free battery charges.

As an example, new wireless battery charging devices are already available in the market. You simply bring your phone on top of these devices and it will start charging without you having to connect your phone to a cable. See the Nexus Wireless Charger as an example.

Incorporating RF energy harvesting in the loop

As you already know, we have been proposing RFID as a means to develop battery-free sensor and actuator solutions. Energy harvesting from RF fields allows for other components to work properly without the need of wires and batteries.

When power consumption of the devices to work with is low, this approach has proved to work. All kinds of sensors and actuators can be embedded in RFID tags to deploy anywhere. These are completely dead until a user comes nearby with the proper reader, activates the sensor and gathers the information.

Although powering up a device such as a smartphone or charging up batteries is too much of a challenge for UHF RFID technology – power transferred is too high for this technology – there are other creative solutions that could be applied.

Battery-free headphone prototype

We at Farsens decided to go for a fun challenge: wireless battery-free headphones.

The idea was to be able to broadcast an audio signal to wireless headphones without the need of batteries on them. For that purpose you don’t even need a standard UHF RFID reader but a simple Voltage-Controlled Oscillator (VCO) would do – since the is no signal back from the headphones to the reader; it is a one way communication system.

Battery-free headphones architecture

Battery-free headphones architecture

We ended up manufacturing a first prototype to prove the idea. A signal of audio files from a computer was sent to the headphones. A good analog audio signal was received at the headphones with actually very nice quality.

Commercial solutions employ lots of electronics to improve quality of the signal. The output of the prototype is not anywhere near of entertainment industry standards at the moment but it was just a fun experiment in a lab environment. Results were actually a lot better than expected which made us think about potential uses.

Would RF energy harvesting based battery-free headphones be useful?

What about implementing wireless and battery-free headphones for blind people in public services? Imagine a train in which these kind of service is available: blind people can get a headset to warn them when they arrive to their destination.

What about cultural environments? Cities could use battery-free headphones to promote their main spots. A tourist with the proper headset getting close to a spot embedding a VCO would start receiving the audio for that specific spot, be it an sculpture, a building or any other asset.

I bet you can come up with different uses for this kind of solutions. Let us know if you are willing to work on any of them!