Printed Loudspeakers
December 6, 2012, Printed Electronics USA, Santa Clara, CA— Arved C Hubler from Chemnitz University of Technology demonstrate new applications for printed actuators. A printed loudspeaker is the result of their research into applications for traditional printing and its use for electronics.
The school has been working on printed electronics for over a decade. Their first printed transistor appeared in ’03, followed two years later with the first integrated circuit. The first IC on paper took until ’07, followed by the first 3-D circuit in ’10. Last year, they produced a solar cell on paper.
Technologies are moving to more flexible substrates. Flexible content will include updates, layout and viewing, and some forms of artificial reality. Paper is nice for it handling and textures, is foldable, uses zero energy, and in most case is recyclable. All of these characteristics are important in the decision to make paper-based electronics and all of them will be merged in an ubiquitous flexible platform.
One issue for electronics is that the platforms like tablets and mobile devices cost many dollars to display any content, while paper costs cents to show content. The electronics devices are expected to have fairly long lives while the paper is considered disposable. Into this environment comes a new application, loudspeakers.
Possible applications are for smart packaging where sound-based logos can enhance the visual aspects. This combination will provide a channel for information, with security, and can present ads and technical applications that require sound. The value is that the speaker is on the product, so it doesn’t need a separate sound device or other platform.
The underlying technology is piezo-electronics. The other possible technologies for loudspeakers are moving coil, ribbon, magneto-static, and electro-static. These other technologies all require significant volume to produce sound, and need a rigid housing to hold the moving elements. In contrast, piezo just changes shape with the application of electricity.
Piezo materials can be easily printed on any substrate, and printing can add other active components at the same time. This design uses two conductive layers sandwiching a piezo material to make the speaker. The active layer is 16 microns thick and both surfaces radiate sound. The size, stiffness, and thickness of the substrate as well as the type of substrate all affect the sound.
This implementation has better response at the higher frequencies. A tweeter can be 16cm squared, while a mid-range speaker has to be 128cm squared. The 4cmx4cm speaker produces 50db at 2 kHz and 80dB at 10 kHz. The speaker can produce up to 90dB SPL or about as loud as a power mower. The frequency response is not very flat, and is a function of the underlying substrate and piezo materials. This version is stable over time, and is not greatly affected by absorbed humidity.
Future experiments will consider layer thickness and application methods and how they affect the frequency response. The speaker requires +/- 25 volts to produce sound, but is low energy, due to very low current draw. Higher levels of system integration will look at increasing output volume, improve frequency response, and integrate the amplifier with the speakers on the paper. Since the piezo materials can also generate electricity, a speaker and mike can be realized on a surface and the control electronics could also be integrated on to the paper.
In theory, one could create arrays for beam forming, but there are many challenges due to common the substrate and interference, the ability for acoustic programming, and the shapes of the transducers. The acoustic theories for individual shaped transducers are incomplete for soft substrates.
