Journal of Mechanical Science and Technology 25 (11) (2011) 2763~2768 www.springerlink.com/content/1738’494x DOI 10.1007/s12206’011’0718’z Piezoelectric electro’active paper (EAPap) speaker † Jaehwan Kim 1 , Gyu’Young Yun 1 , Jung’Hwan Kim 1 , Jinyi Lee 3 and Joo’Hyung Kim 2,* 1              !"#$ % 2       &’( #$!"#) % 3     * +    &’( #$!"#) % (Manuscript Received June 4, 2011; Revised July 6, 2011; Accepted July 6, 2011) ’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’  Film type piezoelectric speaker using cellulose electroactive paper (EAPap) in audible range was studied by acoustic characterization. The speaker was fabricated by depositing thin metal electrodes on both sides of EAPap. The local piezoelectric behavior of thin EAPap surface was visualized at 6 kHz and 221 Hz. The performance of EAPap film speaker as a function of size was evaluated in the audible frequency range, resulting in enhancement of speaker performance in low frequency range. From the measurement of geometric effect of EAPap speaker on audible performance, the circular type speaker shows better performance than rectangular one. Therefore we suggest that the piezoelectric EAPap has a potential for acoustic applications. %’*: Cellulose; Electro’active paper (EAPap); Piezoelectric; Speaker; Stretching effect !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!   Sound is an important surrounding nature to transfer infor’ mation as a function of wave propagation of pressure gener’ ated from various sources. A speaker as an electro’acoustical transducer can generate various sounds by converting input electrical signal via air media. In general, a conventional speaker consists of diaphragm, voice coil with magnet, spiders and a frame. It also requires a certain space due to its volumet’ ric structure. According to reproducing frequency ranges, a speaker is classified as tweeter, mid’range driver, woofer, or full range drivers Due to the interaction between the magnet and the voice coil to generate the movement of the coil for’ ward and back, different sizes and volumetric spaces are addi’ tionally required. To overcome these fundamental working physics and structural constraints, a sheet type speaker using piezoelectric elements has been suggested [1, 2]. Due to its very simple structure, a plate’type speaker will revolute or replace the conventional speaker concept [2, 3]. Recently the prototypes of thin film speaker made of polyvinylidene fluo’ ride (PVDF) [4, 5] and flat speaker [6] were demonstrated for acoustic speaker applications. Compared to other piezoelectric polymers obtained from a chemical process, cellulose is an abundant natural material from common natural resources such as plants, cotton and seaweed. Very recently, cellulose’based electroactive paper (EAPap) has been discovered and has started to receive much attention due to its huge potential for various piezoelectric sensors as well as actuators [7, 8]. From a material viewpoint, cellulose is composed of two different regions which are disordered amorphous and ordered crystalline areas shown in Fig. 1. Also, regenerated cellulose consists of layer by another layer as a multi layered structure. Cellulose itself possesses a piezoelectricity in well ordered area due to structural non’ centrosymmetry of cellulose fibrils [9]. Also, the combination † This paper was recommended for publication in revised form by Associate Editor Heung Soo Kim * Corresponding author. Tel.: +82 62 230 7063, Fax.: +82 62 233 6896 E’mail address: joo’hyung.kim@chosun.ac.kr © KSME & Springer 2011 Fig. 1. Schematic of cellulose film shows disordered region and or’ dered regions in the cross’sectional view. The right figures present the surface and cross sectional SEM images of regenerated piezoelectric cellulose film after stretching process.