Professor JANG Jyongsik of SNU's School of Chemical and Biological Engineering and his research team recently invented a transparent and flexible speaker using graphene electrodes and PVDF film. This cutting-edge speaker is expected to have diverse applications, attached to various surfaces such as car windows and computer monitors.

Graphene, the main material of this research, conducts electricity well, and is shock-resistant and light. In order to coat graphene onto PVDF film, the research team first put graphene oxides (GO) into an inkjet printer, because graphene itself does not dissolve in water well. GO are not charged with electricity when sprayed evenly by an inkjet printer. Then, the film, both sides of which are plated with GO, is sprinkled with a particular material (a deoxidizing agent) heated in an oven at 90 degrees Celcius. The deoxidizing agent is attached thinly to GO by steam, which makes the film charged again with electricity.

This film speaker, whose film itself plays the role of a diaphragm, is smaller in volume than a traditional speaker containing a separate diaphragm inside. Under electro-stimulation, the inner electrons of PVDF film line up in the direction of positive and negative poles. When this is charged with alternating current voltage, the poles of which alternate from positive to negative every moment, the film makes sound by contracting and expanding. Through this process, this tiny 60 to 70 micrometer thick (about 1/1000th of a milimeter) object functions properly as a speaker.

This transparent speaker provides a wide range of sound, from a low-pitched tone (100 Hz) to the highest sound that a man can hear (20 kHz), which is greater than the sound range that a traditional thin-film speaker made of other materials offers.

It is also expected to be used to reduce noise, because it absorbs sound. Thus, when attached to windows, it may convey sound inside clearly while minimizing the noise from outside. Jang explains this invention is particularly notable in that a uniform and flat electrode was successfully created. Their results were published in Chemical Communications on July 11, 2011.

Written by LEE Tae Joon, SNU English Editor, leetjoon@hanmail.net   ?
Proofread by Brett Johnson, SNU English Editor, morningclam2@gmail.com