Advanced Materials Research Vol. 1037 (2014) pp 20-25 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.1037.20
Submitted: 09.08.2014 Accepted: 09.08.2014
New Optical Sensor Panel on Nanocomposite Base Sergey Panchenko1, a, Ibragim Suleimenov2,b, Zdenka Sedlakova3,c, Nikolay Semenyakin4,d 1 2
Al-Farabi Kazakh National University, Almaty, Kazakhstan
Almaty University of Power Engineering and Telecommunications, Almaty, Kazakhstan 3
Institute of Macromolecular Chemistry, Prague, Czech Republic 4
Kazakh-British Technical University, Almaty, Kazakhstan
a
[email protected],
[email protected],
[email protected],
[email protected]
Keywords: Optical Sensor Panel; Nanocomposite; Total internal reflection; Planar waveguide
Abstract. Paper describes the general construction of optical sensor panel on basis of nanocomposite. Appropriate nanocomposite material using industrially produced particles which provides needed optical contact is chosen. Detailed description of functional scheme of optical sensor panel is provided. Introduction Sensor panels of various types are widely used in all aspects of modern life. Among them PCs, mobile phones, tablet PCs, etc. Capacitive and resistive sensors are widely known [1]. Those types of sensors calculate coordinates of touch point due to change of electrical parameters of corresponding sensor area. Some another types of sensors based on different physical principles, in particular sensors [2] based on waves appeared in polyelectrolyte solutions [3, 4] was proposed too. The main disadvantages of known sensor panels are relatively high price of used components (for example, tin oxide is used for transparent sensor screen) and complicated technological process of theirs production. In this paper we show that there is the alternate sensor panel providing the same properties as widely spread sensor panels (capacitive and resistive) but proposed sensor panel could be made from cheap polymer materials and technological process is quite simple. The properties of polymer materials providing proposed construction of sensor panel are discussed. It is shown that using of composite material based on buthyl methacrylate (BMA) and 2-ethylhexyl acrylate, provides needed properties for implementation of proposed sensor panel. Optical sensor panel construction The operating principle of sensor panel is shown on fig. 1. Sensor panel consists of two flat film waveguides (1), (2) and intermediate layer (3) which prevents optical contact between (1) and (2) in initial (normal) state. Proposed intermediate layer (3) could be removed from construction under certain conditions. In this case layers (1) and (2) are placed directly one above another. The layer (1) provides propagation of optical band waves through whole area of sensor panel. The layer (2) is signal layer; its bottom surface can be coated with thin additional layer (4), which provides durable optical contact. The optical sensor panel of proposed type operates as follows: In initial state optical contact between layer (1) and layer (2) is absent. Optical contact emerges due to deformation of signal layer (2) under mechanical pressure (5). In this case we observe the secondary light source in signal film waveguide. The position of secondary light source can be determined by measuring light intensity in several discrete points. The appropriate diagram is shown in Fig. 2. Diagram contains the following construction elements:
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1)feeding flat waveguide (1) located under signal waveguide (2); 2)light sources (3) generating optical radiation in feeding waveguide; 3)light receivers (4) registering light intensity in discrete points.
Fig. 1. The operating principle of optical sensor panel based on flat film waveguides.; a) – initial (normal) state, b) – the appearance of secondary radiation source in signal layer under mechanical pressure Diagram also contains secondary light source (5) which appears due to optical contact between flat waveguides (1) and (2). From this picture we also can see that the difference of light intensity registered by light receivers (4) depends on coordinates of secondary light source. It gives us possibility to detect X and Y coordinates on the sensor panel.
Fig. 2. Diagram describing the detection of mechanical pressure point in sensor panel based on flat film waveguide It is obvious that efficiency of proposed construction depends on durability of optical contact between two layers and light scattering process which takes place in optical contact. In particular, in order to ensure durable detection of secondary light source coordinates by means proposed in Fig. 2 it is necessary that radiation pattern of secondary light source to be as symmetrical as possible. Using signal film based on nanocomposite material satisfies this requirement.
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Experimental Materials. Investigated polymers were synthesized from buthyl methacrylate (BMA) and 2-ethylhexyl acrylate (Aldrich) without additional purification and azobisisobutyronitrile (Aldrich). 2-Dimethylaminoethyl methacrylate (Aldrich), benzyl bromide (Aldrich), tetrahydrofuran, dioxane, methanol were used in order to synthesize cationic modifying compounds. Nanocor and Cloisite 20A (Southern Clay) were used in order to immerse silicate nanoparticles. Buthyl methacrylate (BMA) and 2-ethylhexyl acrylate (EHA) copolymers were used in experiments. Copolymers were obtained by method of radical copolymerization with azobisisobutyronitrile (AIBN) as initiator. Polymerization was performed in tetrahydrofuran solution. 2-ethylhexyl acrylate component was added to copolymer in order to increase the adhesion of signal film to feeding film (PMMA). Modifying cationic compounds were synthesized by alkylation of 2-dimethylamino ethyl methacrylate (DMAEMA) by benzyl bromide in solution of tetrahydrofuran. The reaction of this process is shown in Fig. 3. Br N N O
O
+
O
O
+ Br
Fig. 3. The scheme of reaction of synthesis of cation with quaternary ammonium group To perform the reaction there were mixed 0.1 mole of DMAEMA and 0.15 mole of benzyl bromide in environment of 250 ml of tetrahydrofuran. Reaction mixture was held in fridge. The precipitated quaternary ammonium salt was filtered and washed by tetrahydrofuran. Extracted components were cleaned by recrystallization in dioxan-methanol mixture and dried before the constant weight. Analysis results confirm the structure of modifier which corresponds to the chemical formula presented in Fig. 4. Results also show needed degree of purity of end product.
Fig. 4. Nanoparticle modifier formula (2-(methacryloyloxy)ethyl-dimethylbenzylammonium bromide) The necessity of using of modifier is caused by properties of nanoparticle source (Nanocor). Nanocor clay is natural layered silicate, more precise natural Na+ montmorillonite (MMT), which is hydrophilic and cannot mix with used polymers in molecular level.
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In order to make these layered nanoparticles compatible with polymer systems counter ions, in our case Na+ located between adjacent layers, must be replaced by molecules, which will make surface of nanoparticles organophilic. Organophilic MMT was prepared as follows. 10 g of Na+ MMT were dispersed in 60 ml of distilled water, after it was allowed for swelling for 24 hours under stirring at room temperature. Then compound was heated up to 700°C and stirred for one hour. After cooling, the compound was slowly added solution of quaternary ammonium salt with concentration equal to 3 concentrations of Na+ MMT by ion exchange capacity. After stirring during for 30 min at room temperature, the compound was held in fridge for 24 hours. Then filtered compound was washed several times by deionized water in order to remover the rest of source components. The final product (O-MMT) was derived by drying. At the next stage polymerization of BMA and EHA in presence of obtained earlier O-MMT was = 2:1). performed in solution of tetrahydrofuran and water (THF:H2O 2,2-Azobis(2-methylpropionitrile was used as initiator. The scheme of immersion of nanoparticles in polymer chain is shown in Fig. 5. End product was dried and dissolved in chloroform (5% of polymer weight). Polymer films were obtained by evaporation of chloroform solution. All synthesized films have needed for experiments homogeneity and transparency (up to 3% of nanoparticle concentration).
Fig. 5. The scheme of nanoparticle immersion in polymer chain Methods. A special setup (Fig. 6) was designed in order to investigate durability of optical con-tact between polymer films produced in Materials section and industrial PMMA glass.
Fig. 6. The diagram of experimental setup Setup contains special handlers (1) which hold PMMA bar (2). The light generated by white LED (3) was radiated through butt of bar. Light receiver (4) is located at opposite butt of bar. Polymer film
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sample under investigation (5) was located on the top of the bar. Mechanical pressure was created by spring (6) with average force about 1.5 Newton. This value corresponds to typical mechanical pressure of sensor panel user. It also should be noted that there is no intermediate layer which discussed in section 1, so we have simpler construction. Results and Discussion Main results of optical contact quality investigation. Fig. 7 shows the dependence of optical signal intensity in relative units from time at instant when we create mechanical pressure on signal film. We can see on figure the decrease of light intensity after applying mechanical pressure (t= 4s). Light receiver can detect this stepwise decrease. On the other hand we observe secondary source of light in signal layer. Findings shows that using flat films produced accordingly subsection 2.1 actually provides durable optical contact needed for design of proposed sensor panel.
Fig. 7. The dependence of optical signal intensity at the moment of applying mechanical pressure. Copolymer composition BMA: EHA = 90:10 Functional diagram. Functional diagram of sensor panel is shown on Fig. 5. Present diagram was tested by means of computer simulation software Proteus VSM. Calculations take into account obtained levels of light intensity and errors caused by non-ideal radiation pattern of secondary light source. These errors were investigated during experimental series. At this stage of work the error in determining the coordinates of point of mechanical pressure is about 5%. Even such level of error permits using proposed sensor panel as keyboard located on screen of tablet PC or other device. Sensor panel is controlled by microcontroller, which provides various types of interface to mobile device. Current implementation operates via USB interface as standard HID device. It is possible to integrate current scheme with Bluetooth module and use wireless communication. The main operating principle of sensor panel is to measure light intensity with four light receivers (1) and then compare values on X1 and X2 channels to calculate x-coordinate, Y1 and Y2 positions to calculate x-coordinate. Controller software takes into account radiation pattern in order to consider light attenuation in signal film.
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USB, Bluetooth (HID profile) x1 Controller y2 x2
1
y1 2
1
1 y x 1
Fig. 5. Functional diagram of sensor panel Conclusion As we see from this work, synthesized from production-ready materials composite has properties permitting to implement optical sensor panel. This type of sensor panel can be produced from low cost polymer materials and technological process is not complex. References [1] Schöning, J., Brandl, P., Daiber, F., Echtler, F., Hilliges, O., Hook, J. & von Zadow, U. (2008). Multi-touch surfaces: A technical guide. IEEE Tabletops and Interactive Surfaces, 2. [2] Suleimenov, I., Mun, G., Ivlev, R., Panchenko, S., & Kaldybekov, D. (2012). Autooscilla-tions in Thermo-responsive Polymer Solutions as the Basis for a New Type of Sensor Pa-nels. AASRI Procedia, 3, 577-582. [3] Dolayev, M., Panchenko, S., Bakytbekov, R., & Ivlyev, R. (2014). The Principle of Recor-ding Information in Distributed Environments via Suleimenov-Mun's Waves.Advanced Materials Research, 875, 642-646. [4] Panchenko, S. V., Obuhova, P. V., Chezhimbaeva, K. S., Tsoi, A. M., Shaikhudinova, A. A., Eligbaeva, G. A., & Dolayev, M. (2013). Prospects of Using Waves of Suleimenov-Mun in “Green” Energetics. World Applied Sciences Journal, 22(10), 1460-1464.
