Graphene has enjoyed considerable publicity even in its infancy. Graphene is a form of carbon consisting of planar sheets with the atoms arranged in a honeycomb-shaped lattice.
Graphene may possibly be the future replacement for silicone. It’s a two-dimensional material that measures just one atom thick and has a breaking strength 300 times greater than steel. In an earphone with almost no specialized acoustic design, a graphene diaphragm performs the same as a high quality commercial one. Instead of being artificially damped, the graphene diaphragm can be damped by air itself.
Using a 3-D printer, it will be possible to print graphene circuitry and immediately upgrade a component in a device or build a component from scratch. This will save a considerable amount of money as speaker companies spend a lot of funds creating the perfectly balanced speaker diaphragm.
Researchers at the University of California, Berkeley have created the first ever graphene audio speaker – an earphone. Without any kind of optimization, the researchers show that graphene’s superior physical and electrical properties allow for an earphone with a frequency response that is comparable to or better than a pair of commercial Sennheiser earphones.
A loudspeaker, earphone or headphone works by vibrating a paper diaphragm, otherwise known as a cone, creating pressure waves in the air around the listener. Different sounds are created based on the frequency of these pressure waves. Human ears can usually hear frequencies between 20 Hz and 20 KHz. The quality of a speaker depends on how well it produces sounds equally within this scale.
The Berkeley graphene earphone is made from a 30nm-thick, 7mm-wide sheet of graphene. This diaphragm is then sandwiched between two silicon electrodes, which are coated with silicon dioxide to prevent any shorting should the diaphragm be driven too hard. By applying power to the electrodes, an electrostatic force is created, which causes the graphene diaphragm to vibrate, creating sound. By oscillating the electricity, different sounds are created.
Most diaphragms must be damped to avoid objectionable frequency responses. As stated previously, a graphene diaphragm requires no damping, because graphene is so strong. The lack of damping demonstrates that the graphene diaphragm is very energy efficient, which would be important for reducing the power usage of smartphone and tablet speakers.
A speaker diaphragm is essentially a simple harmonic oscillator with an inherent mass and restoring force that determines the way it vibrates at different frequencies. Most diaphragms need to be damped to broaden the range of frequencies over which they perform. Damping quickly becomes a complex and expensive procedure and produces power inefficiencies.
To avoid damping engineering, the diaphragm needs to be very thin and light with a small spring constant so that the air itself damps its motion. This is tricky given how weak and fragile most materials become when they are thin. Graphene is the ideal contender because it is electrically conductive, has an extremely small mass density, and can be configured to have very small effective spring constant.
Unlike conventional speakers that require mechanical moving parts to compress air and generate sound waves, thermoacoustic speakers work by rapid heating and cooling of a conductor that causes expansions and contractions of the air which, in turn, generates sound. The concept of a thermoacoustic speaker has been around for a long time, but progress was delayed because we did not have suitable materials or fabrication methods.
Graphene has shown to be the solution due to its high thermal conductivity, very low heat capacity and its ability to form free-standing membranes. It has been shown that single and multiple layers of graphene can generate thermoacoustic sound on a range of substrates.
A graphene-based system can work on flexible substrates and by changing the overall shape of a flexible substrate, the thermoacoustic graphene speaker can focus sound in interesting ways, bringing about interesting applications in medical ultrasound, where acoustic emitters with complex geometries can be realized to focus sound waves.
Graphene has extremely low mass density and high mechanical strength, which are significant qualities for efficient wide-frequency-response electrostatic audio speaker design. Low mass ensures good high frequency response, while high strength allows for relatively large free-standing diaphragms necessary for effective low frequency response.
The graphene-based electrostatic audio speaker is straightforward in design and operation and has excellent frequency response across the entire audio frequency range (20 Hz ~ 20 kHz), with performance matching or surpassing commercially available audio earphones. A direct recording of the song “Sound of Silence” by Simon&Garfunkel played through the graphene loudspeaker can be found here.
Graphene could be made using 3-D printers by using a technique known as vapor deposition to leave a thin film of the graphite-based conductor on sheets of PVDF (poly vinylidene fluoride). By sandwiching the PVDF between graphene electrodes and applying a current from a sound source, researchers are able to create a flat and transparent loudspeaker that could be integrated into windows or screens; but don’t expect this low-power sound source to replace your hi-fi, as it relies on the distortion-prone piezoelectric effect, and it probably won’t sound much better than the earpiece on your cell phone.
In other news regarding graphene, Samsung announced its developing “a breakthrough synthesis method” that will speed up the commercialization of graphene. Samsung, which developed the new process at its Advanced Institute of Technology in partnership with Sungkyunkwan University, says the new method is “one of the most significant breakthroughs in graphene research in history.” What does this mean for consumers exactly? Samsung says graphene’s flexibility, high heat conductibility, and durability make it a perfect option for small devices like wearables and devices with flexible displays.
The Samsung team is the first to grow a large-scale, impurity-free sheet of graphene that maintained its electric properties. The process involved growing the graphene in multiple places on a specially treated layer of Germanium, the smaller pieces of graphene would then merge together to form the large sheet.
Processor manufacturers like Intel and Qualcomm are paying particular attention to the potential of graphene because it allows electrons to flow through it 100 times easier than they do in silicon. It’s hoped that this level of electrical conductivity will enable processors made from graphene to continue Moore’s Law long after silicon has reached the end of its own usability.
However if graphene is mass marketed in the near future, it will bring higher quality sound for a much cheaper price on conventional devices. Expect cutting edge audio progression in technology. There will be changes coming.
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Len Calderone – Contributing Editor
Len has contributed articles to several publications. He also writes opinion editorials for a local newspaper. He is now retired.