pISSN: 1229-7607 eISSN: 2092-7592

Regular Paper

Copyright 2010 KIEEME. All rights reserved. http://www.transeem.org65

DOI: 10.4313/TEEM.2010.11.2.065

TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS

Vol. 11, No. 2, pp. 65-68, April 25, 2010

Author to whom corresponding should be addressed: E-mail: kjlim@chungbuk.ac.kr

Keywords: Piezoelectric micro-pump, Valveless pump, Extensional vibration mode, Peristaltic motion

The operation principle of a traveling wave rotary type ultrasonic motor can be successfully applied to the fluidic transfer mechanism of the micro-pump. This paper proposes an innovative valveless micro-pump type that uses an extensional vibration mode of a traveling wave as a volume transportation means. The proposed pump consists of coaxial cylindrical shells that join the piezoelectric ceramic ring and metal body, respectively. In order to confirm the actuation mechanism of the proposed pump model, a numerical simulation analysis was implemented. In accordance with the variations in the exciting wave mode and pump body dimension, we analyzed the vibration displacement characteristics of the proposed model, determined the optimal design condition, fabricated the prototype pump from the analysis results and evaluated its performance. The maximum flow rate was approximately 595 μL/min and the highest back pressure was 0.88 kPa at an input voltage of 130 Vrms. We confirmed that the peristaltic motion of the piezoelectric actuator was effectively applied to the fluid transfer mechanism of the valveless type micro pump throughout this research.

Received January 26, 2010; Revised February 25, 2010; Accepted March 16, 2010

Hyun-Hoo KimDepartment of Display Engineering, Doowon Technical University College, Paju 413-861, Korea

Design of a Valveless Type Piezoelectric Pump for Micro-Fluid Devices

1. INTRODUCTION

Micro-pumps have unique characteristics that are able to transport minute, as well as accurate, amounts of liquid or gas. Hence, micro-pumps are appropriate in dealing with chemical and biological substances by analyzing the system as a micro-fluid flow control appliance [1]. These devices generally consist of one or more chambers created by the deformation of the actuator and check valves in order to manage the fluid flow. However, check valves installed within micro-pumps raise prob-lems such as pumping performance degradation via abrasion, fatigue and valve blocking, etcetera [2,3]. In order to solve the critical problems, extensive research and development upon valveless type pumps have been conducted. A valveless micro-pump, first proposed by Stemme and Stemme, used a diffuse/nozzle structure, which was a substitution for the ability of the

check valves [4]. Also, Bar-Cohen and chang [5], introduced the peristaltic pump using a flexural vibration mode of a traveling wave. This paper proposes an innovative valveless micro-pump type that uses an extensional vibration mode of a traveling wave as a volume transporting means. The proposed pump consists of coaxial cylindrical shells that join the piezoelectric ceramic ring and metal body, respectively. The main feature of this pump does not require the valves because the peristaltic action produces a tightly closed space that may play an important role by causing a squeezing effect. Also, when the input power is turned off, the sliding interface, formed between the coaxial shells against each other, stops the flow of fluid. Therefore, a self-locking action is automatically produced like a closing operation of the conven-tional check valves. In order to verify the operation principle of the proposed pump model, a numerical simulation analysis was conducted. Modal and harmonic analysis was carried out during its design phase and, based on the simulation results, we made a prototype micro-pump and tested its performance.

Jin-Heon Oh, Jae-Hun Yoon, Eui-Hwan Jeong, and Kee-Joe Lim

College of Electrical and Computer Engineering, Chungbuk National University, Cheongju 361-763, Korea

Trans. Electr. Electron. Mater. 11(2) 65 (2010): H.-H. Kim et al.66

2. OPERATION PRINCIPLE

The operation principle of a traveling wave rotary type ultra-sonic motor can be successfully applied to the fluidic transfer mechanism of a micro-pump. Figure 1 illustrates the operation principle of the traveling wave rotary type ultrasonic motor. Piezoelectric ceramic elements are used as vibrators and posi-tioned at appropriate distance from one another for traveling wave excitation. Points on the surface of the stator ring move within elliptical trajectories and bents propagate as it stands in accordance with the passage of time. The metal disk or ring, which is pressed on the stator, is rotated by the tangential force at the contact surface [6].

In a piezoelectric ring of the actual motor, the vibration ampli-tude of the traveling wave increases towards the outer perimeter, as shown in Fig. 2(a) [7]. Therefore, the side wall of the elastic metal body ring, installed on the piezoelectric ceramic plate, ex-cites the extensional vibration mode in its radial direction along the propagation of the traveling wave, as shown in Fig. 2(b). The space formed by this motion is used as a platform for the transportation of fluids. The proposed pump consists of coaxial cylindrical metal shells bonded with annular type piezoelectric

ceramic plates in order to make full use of the extensional vibra-tion mode effect. The inner shell is a ring and the outer shells are two semi-circle type parts, as shown in Fig. 3. Because the pro-posed micro-pump uses coaxial cylindrical shells, the slide con-tact surface between the inner and outer shells is able to make chambers via the proper operation mode setting.

Fig. 1. Operation principle of a traveling wave rotary type ultrasonic motor.

(a)

(b)

Fig. 2. Vibration mode excitation via traveling wave propagation.

Fig. 3. Shape of the proposed micro-pump model.

<Inner shell> <Outer shell>

Fig. 4. Deformation of the inner and outer shell (i.e. 5 wave mode).

(a)

(b)

Fig. 5. Vibration characteristics in accordance with the wave mode and length ratio analysis results.

67Trans. Electr. Electron. Mater. 11(2) 65 (2010): H.-H. Kim et al.

3. VIBRATION ANALYSIS

A numerical simulation analysis for the proposed model was implemented in order to verify the pump operation mechanism. Finite element modeling software, ATILA, was used for this pro-cess. Modal and harmonic analysis were both carried out for the inner and outer shells of the pump, respectively. According to the wave mode and variation of the pump body shape, the distribu-tion of both the vibration amplitude and operational frequency was changed. Figure 4 roughly illustrates the deformation of the inner and outer shells under the operation condition. When the traveling wave occurs, excitation of extensional vibration mode in radial direction is confirmed. (i.e. white arrows)

The variation of both the extensional vibration amplitude and resonance frequency due to the wave mode and elastic body length ratio is presented in Fig. 5, respectively. Body length ratio defines the proportion between the height and width for the elastic metal body. The widths of the inner and outer metal body were fixed to 5 mm and the height of it was modified. Analysis of the wave mode was executed under a 1-length ratio condition, and analysis on the length ratio was fulfilled under a 5-wave mode condition.

4. EXPERIMENTS

A prototype valveless micro-pump was fabricated in accor-dance with the simulation result. The 5-wave mode and 3-length ratio type model was selected due to the relatively high vibration amplitude and low operational frequency characteristics. Piezo-electric ceramic plates, manufactured via the conventional fabri-cation method, were bonded to the inner and outer metal shells, respectively.

The exact composition of piezoelectric ceramics was produced using 0.9Pb(Zr0.51Ti0.49)O3-0.1Pb(Mn1/3Nb1/3Sb1/3)O3 + 0.05Cr2O3.

In order to remarkably increase the dielectric and piezoelectric properties, Leadoxide(PbO) - Zirconate(ZrO2) - Titanate(TiO2) and Manganate(MnO2) - Niobate(Nb2O5) - Antimonate(Sb2O3) were mixed [8]. Also, Cr2O3 was added to raise the value of the mechanical quality factor (Qm) and to drop the dielectric loss(tanδ ). The mixing ratio was determined by considering the morphotropic phase boundary (MPB) in order to maximize the piezoelectric characteristics. Its prominent properties are shown in Table 1. This piezoelectric ceramic material has a high electro-mechanical coupling factor (kp), a high mechanical quality factor and a low dielectric loss. Therefore, we are able to determine that it can also successfully be used in other piezoelectric devices. The components and dimensions of a prototype pump are pre-sented in Fig. 6.

In order to operate the prototype pump, we constructed a driving system. This system is composed of two channel function generators producing two phase voltages having 90 degrees of phase difference for traveling wave excitation within the piezo-electric ceramic plates, the power amplifier for the voltage mag-nitude increase and the oscilloscope for the voltage input state check. Figure 7 shows a diagram of the operating system.

The performance of the proposed micro-pump was measured in terms of the pump limits for flow rate and back pressure. Fig-ure 8 shows the experimental situation of the prototype pump performance test. For the case of the flow rate data acquisition, the measuring method used an accumulated amount of water by utilizing the pumping operation for a specified period of time. Also, the determination of pump back pressure was measured by the height of pumping water into the vertical tube. The maxi-mum flow rate was 595 μL/min and the highest back pressure was 0.88 kPa at an input voltage of 130 Vrms. Additionally, we veri-fied that the fluid flow direction was easily changed via the phase control between the two input voltage sources. The flow rate or

(a)

(b)

Inner shell Inner diameter 20 mm Outer diameter 30 mm

Outer shell Inner diameter 30 mm Outer diameter 40 mm Angle of arc 172°

Fig. 6. Components and size dimension of a prototype pump.

Fig. 7. Prototype pump driving system diagram.

Fig. 8. Performance test of prototype pump.

Table 1. Dielectric and piezoelectric properties of piezoelectric ce-ramic.

Items Symbol Unit Measured value Electromechanical coupling factor kp % 58 Mechanical quality factor Qm 1500

Piezoelectric constant d33 pC/N 340

d31 pC/N -120

Frequency constant Np Hz·m 2100 Relative dielectric constant ε33/ε0 1300

Trans. Electr. Electron. Mater. 11(2) 65 (2010): H.-H. Kim et al.68

the back pressure characteristic of a prototype micro-pump is shown in Fig. 9.

5. CONCLUSIONS

This paper proposes an innovative valveless piezoelectric mi-cro-pump type that is able to transport fluid by an extensional vi-bration mode of a traveling wave. This pump has the body shape of a coaxial cylinder, and is able to form multiple chambers due to vibration. In accordance with the variations in the exciting wave mode and pump body dimension, we analyzed the vibra-tion displacement characteristics of the proposed model, deter-mined the optimal design condition, fabricated the prototype pump from the analysis results and evaluated its performance.

The maximum flow rate was approximately 595 μL/min and the highest back pressure was 0.88 kPa at an input voltage of 130 Vrms. We were able to confirm via this research that the peristaltic mo-tion of the piezoelectric actuator could be effectively applied to the fluid transfer mechanism for the valveless type micropump.

ACKNOWLEDGMENTS

This work was supported by the Korea Research Founda-tion Grant funded by the Korean Government (KRF-2008-313-D00376).

REFERENCES

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[2] J. C. Rife, M. I. Bell, J. S. Horwitz, M. N. Kabler, R. C. Y. Auyeung, and W. J. Kim, Sens. Actuators A 86, 135 (2000) [DOI: 10.1016/s0924-4247(00)00433-7].

[3] M. M. Teymoori and E. Abbaspour-Sani, Sens. Actuators A 117, 222 (2005) [DOI: 10.1016/j.sna.2004.06.025].

[4] E. Stemme and G. Stemme, Sens. Actuators A 39, 159 (1993) [DOI: 10.1016/0924-4247(93)80213-z].

[5] Y. Bar-Cohen and Z. Chang, Proc. SPIE, vol. 3992 (Newport Beach, CA, USA 2000 Mar. 3, International Society for Optical Engineering) p. 669. [DOI: 10.1117/12.388190].

[6] T. Sashida and T. Kenjo, An introduction to ultrasonic motors (Oxford University Press, Oxford, 1993). p. 10.

[7] T. Sashida and T. Kenjo, An introduction to ultrasonic motors (Oxford University Press, Oxford, 1993). p. 127.

[8] K. J. Lim, S. Y. Lee, J. S. Lee, M. J. Lee, and S. H. Kang, J. Electro-ceram. 13, 449 (2004) [DOI: 10.1007/s10832-004-5140-9].

Fig. 9. Flow rate with the variation in back pressure for the character-istic of a prototype micro-pump.