Keywords: adaptive structures, shear actuation, piezoelectric bimorphs, valve-less micro-pumps, concept designs, finite element analysis.

Micro-pumps are micro-fluidic devices that can be used in several domains such as in medical, inkjet printing or gluing applications. They differ mainly by the driving and inlet-outlet valves mechanisms. Piezoelectric actuation was proposed since the mid-eighties [1] for the actuation of the membrane (or diaphragm)-based micro-pumps. The transverse mode, that uses the so-called piezoelectric strain constant, is the most used [1,2,3]. It consists of actuating the membrane in bending (up/down) so that a cavity is created. This causes a variation (decrease/increase) of pressure which flows (pumps) the fluid. Recently, the longitudinal mode, that uses the so-called piezoelectric strain constant, has been also proposed [4]. For this, a piezoelectric stack actuator, replacing the traditional patch one, acts on the membrane in order to displace it up-down and to vary the pressure of the fluid. This driving mechanism was combined with unimorph actuators as active valves instead of the passive check valves [1,3] or diffuser nozzles [2] (hence valve-less) proposed in the previous designs.

Alternatively for the membrane-based micro-pump designs, a new generation of micro-pumps has been proposed where piezoelectric bimorphs (or benders) directly form a cavity and a fluid can be transported within the enclosed volume by imposing an adequate driving electric signal [5,6]. Both longitudinal and transverse modes have been numerically investigated using piezoelectric fibre composites (PFC) with inter-digitated electrodes (IDE) [5] and classical bulk piezoelectric patches [6], respectively. These micro-pumps have no valves, no dead volume and can work in both directions, forwards and backwards. Theoretically, they are also self-priming and bubble-tolerant. However, these extension (longitudinal and transverse) -mode micro-pumps require a multilayer (piezoelectric, passive, shim) structure that adds two design parameters, namely the active-passive layers thickness and stiffness ratios. Besides, the PFC/IDE based design requires a high actuation voltage (1000V) that limits its application range.

The present contribution aims to present a new valve-less piezoelectric micro-pump design that uses the so-called shear-actuation mechanism (SAM). Contrary to the classical extension actuation mechanism (EAM) [7], here the initial poling and actuation electric field directions have to be perpendicular [8]. This new design exploits the recently proposed shear bimorph concept [9] that benefits from the several advantages of the SAM, in particular the low and homogeneous stresses both inside and at the actuator interfaces [10]. Several designs, through variations of the electric signal, actuators stiffness, electrode numbers and boundary conditions, are proposed and evaluated using finite element analyses in order to assess their performance according to the generated maximum displacement and cavity volume. Estimations of the energy consumption, as well as capillary forces, are also given for the basic design.

1

H.T.G. Van Lintel, F.C.M. Van de Pol, S. Bouwstra, "A piezoelectric micropump based on micromachining of silicon", Sensors and Actuators, 15, 153-167, 1988. doi:10.1016/0250-6874(88)87005-7

2

A. Ullmann, "The piezoelectric valve-less pump - performance enhancement analysis", Sensors and Actuators A, 69, 97-105, 1998. doi:10.1016/S0924-4247(98)00058-2

3

M. Koch, N. Harris, A.G.R. Evans, N.M. White, A. Brunnschweiler, "A novel micromachined pump based on thick-film piezoelectric actuation", Sensors and Actuators A, 70, 98-103, 1998. doi:10.1016/S0924-4247(98)00120-4

4

D.G. Lee, S.W. Or, G.P. Carmen, C.H. O'Neill, "Piezoelectric hydraulic pump with innovative active valves", in Proceddings of the SPIE's 9th Annual International Symposium on Smart Structures and Materials, San Diego (CA, USA), March 2002. doi:10.1117/12.474689

5

M. Sester, C. Poizat, "Simulation techniques for piezoelectric composite materials and their applications to smart structures", in N. Wereley (Ed.), Proceedings of the SPIE's 7th Annual International Symposium on Smart Structures and Materials, 3985, 750-758, 2000.

6

C. Poizat, B. Thielicke, O. Benevolenski, "From bending actuators to a peristaltic micropump", in E.A. Lipitakis (Ed.), Proceedings of the 6th Hellenic Conference on Computer Mathematics and its Applications, LEA Publishers, Athens, 1, 141-148, 2004.

7

M. Gall, B. Thielicke, A. Huart, "Development of a peristaltic micro-pump based on PZT bending actuators", in Proceedings of ACTUATOR 2006, Bremen, Germany, June 14-16, 2006.

8

A. Huart, "FE analysis of a piezoelectric micropump", Joint Supméca (Saint Ouen, France) Engineering Thesis and Fh-IWM (Friburg, Germany) Internal Report W4/2005, September 2005.

9

C. Poizat, A. Benjeddou, "On analytical and finite element modelling of piezoelectric extension and shear bimorphs", Computers and Structures, in press. doi:10.1016/j.compstruc.2005.01.005

10

A. Benjeddou, "Shear-mode piezoceramics advanced materials and structures: a state of the art", Mechanics of Advanced Materials and Structures, accepted. doi:10.1080/15376490600809336

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