Design and Optimization of MEMS Based Piezo ...

Design and Optimization of MEMS Based Piezo-ElectricMicro Pump Jasti Sateesh1, K.Srinivasa Rao1, K. Girija Sravani1 , Koushik Guha2, KL Baishanab2 and R.Akshay Kumar1 1

Micro Electronics Research Group, Department of E C E, KL University, Guntur, A.P, India, 522502. 2 Department of ECE, national Institute of Technology, Silchar, Assam, India

Abstract— Controlled drug delivery in medical application plays a prominent role, that can be achieved by microdrug delivery devices. The efficient working of the controlled drug delivery system depends on the micropump in it. This paper presents theoretical, design and simulation analysis of piezoelectrically actuatedmicropump constructed using PZT-5H material, Quartz channel, and a PDMS membrane. The designed micro pump is analyzed for different structural, material changes by considering Turbulent and Laminar flows. The turbulent flow model is having a flow rate of 0.039 µ3m/s, while laminar flow is having 0.029 µ3m/s at a low operating voltage of 5V.

Index Terms— Drug delivery, Flow velocity, Flow rate, MEMS.

1. INTRODUCTION Delivering drug to a disease infected body is substantially important in curing the disease. Patients with diabetes should be continuously monitored for glucose in the blood, according to the glucose levels insulin should be supplied to fight with the produced glucose. There is a huge requirement of controlled drug delivery for therapeutic advantage. There are some conventional techniques for fulfilling this need. Tablets, capsules, injections, and subcutaneous injections comes with lot of wastage, take time to show impact. Treatment with injections is associated with a lot of side effects such as irritation, contamination, damaging of body tissues, a person needs to be trained to do the job of injection and controlled delivery is not possible. The Micro Drug Delivery System (MDDS) is an association of microneedle, micropump, microactuator and microvalve. Micropump for pumping the drug, microactuator for actuating the pumping and needle to deliver the drug to body and valves for directing the flow. Swan P. Davis analyzed the effects on a needle when it is inserting, after insertion and skin piercing force [1]. Seung-Joon Paik described in-plane microneedle for low insertion depth for invasive usage [2], Seiji aoyag by considering mosquito effect [3]. Microneedle array to extract samples for analysis and delivering the drug by [4] E.V.Mukharjee. Marrion Sausse and Rayan F. Donnelly guides the user about a hollow polymeric needle [5] and types, shapes of microneedles for a specific application [6]. Micropumps can be distinguished in two ways, Mechanical and non-Mechanical. Non-Mechanical deals with the properties of the liquid analyzed by Mehrdad Sheikhlouand [7], this technique is having bottlenecks in many ways. Mechanical micropumps relays on actuation and moment of layers that are in contact with the drug. Actuation technique judges flow velocity. Different types of actuation techniques are, Thermopneumatic O.C. Jeong [8], Pneumatic Meng.E [9] Bimetallic Zhan G [10], Laser beam radiation Maruo [11], Surface acoustic streaming Ogawa.j [12], Shape memory alloys [13,14]. E.makino and D.Reynaerts. Xiaotao Han analysed two electromagnetic coils exited to create a

magnetic gradient that pulls the drug particles down [15], Optical monitoring of local administration of the drug is presented principia Dardano[16], N. Kumar presented multiple inlets, outlet configuration using electromagnetic actuation[17]. Phase change actuation mechanisms are presented in Sim. W.Y [18], Bulk acoustic micropump with diaphragm structure is observed by Ersin Sayar[19]. Heating of liquid beneath the membrane to produce a bubble in order to deflect the membrane presented in N.M.Elman [20], osmotic pumps that use osmosis process when brought into contact with body fluids [21] Simmon Herrlich. Electrostatically actuated pump using 23V of excitation voltage is presented by [22], Drug excitation mechanism using electrokinetic properties of the liquid to be pumped is described by Aram J. Chang [23]. Drug delivery system reaching flow rate of 690µl/min is obtained by actuating the structure piezoelectrically with an input voltage of 100V is described by M.W. Ashraf [24]. Micropump actuated with piezo actuation which of length of 12mm is discussed by Li Cao [25], Valvless micropump which electric field of 500 V/mm is given by Qifeng Cui [26], Takalkar Atul S list the theoretical analysis of piezo electric effect [27], Piezoelectric pump with back pressure is described by Kan Junwu [28]. According to literature survey, the piezoelectricmicropumps have high back pressure, backflow and higher value of operating voltage. There is a need to decrease the power consumption by increasing the flow velocity. In this paper, we have designed and simulated piezoelectricmicropump by FEM Tool. In section 2, we have discussed the structure and in section 3, working of the piezoelectric pump. The performance analysis of micropump for drug delivery systems discussed in detailed dependent on turbulent and laminar flow in section 4 and followed by conclusions in section 5. 2.

THEORETICAL MODEL

Any fluid in liquid form will move when it experiences Gravitational force, when there is height difference between the inlet and outlet and/or under influence of force we apply. The flow that is gained by the liquid under influence of above mentioned forces depends on several constraints. The optimization of the flow velocity, linked with dimensions of the structure,

piezoelectric material properties and the viscosity of the liquid used. When Piezoelectric materials are supplied with voltage excitation, atoms inside the materials experience electrical pressure which causes the atoms to balance themselves, bringing a structural change. Piezoelectricity mathematically described within a materials constitutive equation (1), which defines how the piezoelectric materials stress (T), strain (S), Charge-Density displacement (D), Electric field (E) interact. The Piezoelectric constitutive law S=SE×T+dt×E (1) D=d×t+ET×E

Matrix „d‟ in the equation contains the piezoelectric coefficients for the material Static Displacement change in length of the structure can be given as in equation (2)

(4) Liquid that flow in a tube has both laminar flow and Turbulent flow. Reynolds numbers gives the clear idea about the flow in a tube. The Reynolds number is less than 105 the flow is laminar, if exceeds it is Turbulent flow. The velocity at which liquid flow changes from laminar to turbulent flow is generally referred to as Critical Velocity. The transition time between laminar to turbulent that occurs is transition flow. In micro channels we can observe laminar flow, but at bendings it is possible to be the flow is turbulent. Turbulent flow is dependent on the velocity of flow, the area of the surface in contact with the liquid and temperature, it does not dependent on pressure. The laminar flow is dependent on Velocity of flow, liquid density, temperature, area of surface in contact and nature of the surface, not dependent on pressure Flow rate can be calculated by finding the velocity of the liquid. Velocity of liquid V=

(5)

(2) ∅f = Flow Rate d31 = Transverse Piezoelectric large signal deformation coefficient

Ac = Area of channel 3.

l =Length of the piezoelectric material V = Voltage applied h = Height of the piezoelectric material. This structural change influences the liquid to move. When liquid is in motion, the forces acting on it (3) are gravity, pressure, viscosity, Turbulence, Surface tension and compressibility. (3)

STRUCTURE OF MICRO PUMP AND CONCEPT OF WORKING

The structure of micropump is as shown in the figure. The micropump consists of Piezoelectric material is placed on two electrodes, one is treated as ground and the other is an active electrode. On top of piezoelectric layer, PDMS is material is placed to support bending on PZT. The channel with inlet and outlet is placed on PDMS membrane which is assumed to be made up of quartz.

F (g,p,v,t,s,e) = Gravity, Pressure, Viscous Force, Turbulent Force, Surface Tension, Compressibility Viscosity of a liquid can be determined as the ratio between shearing stress to velocity gradient Reynolds number is the ratio of Force of inertia to Force of Viscosity (4) Reynolds Number Nr = Force of Inertia/ Force of Viscosity Fig. 1: Structure of Micropump The inlet width is 20 µm and outlet width is changed

from 5 µm to 40 µm. When a voltage is applied to the electrodes the piezoelectric material undergoes structural deformation, which vibrates the membrane in order to pump the drug out of the channel. The dimensions of the structure are given in table 1 Table 1: Dimensions of the structure S.No Parameter Dimensions(µm) 1 Channel width 500 2 PZT Disc 700×30 3 Inlet width 20 4 Outlet Width 10 5 Electrode 500×20 4.

7

Zinc Oxide(Zno2)

1.91×105

8

Ammonium Hydrogen Phosphate[(Nh4)2hpo4]

1.93×105

9

Aluminum Nitride [Ain]

1.92×105

From Fig.2 it can be concluded that when the outlet width changes, the flow velocity varies. Increasing of width diminishes the flow. When the outlet width is reducing, backflow is getting high at 5µm maximum backflow is happening, no drug is reaching the outlet. So the Minimum width of the channel must be 10µm

RESULTS AND DISCUSSIONS

As per Reynolds number, at the critical velocity the flow of liquid changes from laminar to turbulent. The designed structure assumed with no slip condition at wall as the liquid in contact with the boundary wall does not have any flow. As the piezo disc in the design is excited with 5V input supply, the deformation occurs in the structure. The structure is simulated with different dimensional changes and with different materials. A. Performance analysis dependent on Turbulent flow Changing of piezo material has a slight effect on outflow velocity, it can be neglectable. The Simulated values of Flow velocities considering different piezo materials is given in table 2.

Fig.2: Flow velocity when outlet width is changed The channel width and dimensions are vareid, producing similar effects as outlet, increasing of channel width decreasing the flow velocity.

Table 2: Flow velocity for different piezoelectricmaterials S. No

Materials

Flow Velocity(µm/S)

1

PZT-5H

1.9×105

2

PZT-4D

1.9×105

3

PZT-2

1.9×105

Fig.3: Flow velocity when channel width is changed

5

4

Rochelle Salt

1.93×10

5

Quartz Rh

1.92×105

6

Tellurium Dioxide(Teo2)

1.91×105

The simulated results of turbulent flow are shown in Figure 4. velocity of the fluid when 10µm of outlet is considered(4a), it is evident from fig 4(b) the channel width is scaled down, backflow is high as the liquid repels back by the boundary walls of the outlet4(b).

Fig .4(a): Flow Velocity when outlet width is 10µm When width changed to 20µm increases the forward flow. So, optimal flow rate can be achieved when the width of inlet is 20µm and channel width of 30µm.

Fig 5(a): Flow Velocity at channel width of 10 µm The flow velocity is increasing as the outlet width is decreasing as illustrated in the Fig 5(a), whereas channel length is decreased back pressure is increasing in turn causing the back pressure. At channel width of 30µm and outlet width of 20µm the pumps is having optimal flow velocity as shown in fig5(b).

Fig. 4(b): Flow Velocity when outlet width is changed to 5um B. Performance analysis dependent on Laminar flow The viscosity of the pumping liquid increases with the presence of bio-species, hence it acquires laminar flow. The assumption for simulation is taken as the viscosity of the liquid is high and it possess laminar flow, no slip condition is taken at the wall boundary.

Fig. 6: Flow velocity when the outlet width is changed Fig.6 plots the effects when the outlet width is changing, the inlet and channel are kept constant. Increasing of outlet is decreasing the flow on other hand increasing the back flow. Channel width is increased gradually causing substantial decrease in flow velocity.

Fig 5(a): Flow Velocity at outlet width of 10 µm Fig. 7: Flow velocity channel width is changed

The channel width is varied as shown in the graph, an E. V. Mukerjee, S.D. Collins, R.R. Isseroff and R.L. Smith increase of channel width decreases the velocity. “Microneedle array of transdermal biological fluid extraction Changing of piezo materials has a neglectable effect. and in situ analysis”, Sensors and Actuators A (2004) 267Comparing both achieved Turbulent and Laminar flow 275. O.C Jeong S. S Yang, Fabrication and test of a theromopneumatic rates, Turbulent is having high value 0.039µ3m/s than micropump with a corrugated p+ diaphragm”, sensors and laminar 0.029µ3m/s 5.

CONCLUSION

In this paper, we have designed, simulated, and analyzed a Micropump actuated with piezoelectric actuation technique for different scaling factors of inlet, outlet, and channel widths. The simulations are carried out by considering turbulent and laminar flows. When the turbulent flow is considered and the dimensions of outlet and channel change is impacting on the flow velocity, the optimal pump is achieving a high flow rate of 0.039µ3m/s. When the Laminar flow is considered in the channel, the dimensions of the outlet and channel are scaled up, flow velocity is going down, the flow rate achieved by considering laminar flow with optimal dimensions is 0.029µ3m/s. As the laminar flow is also having good flow rate this pump can be used with high viscous fluids having biospecies. However proposed micropump provides flexible and controllable drug delivery at the operating voltage is 5V. ACKNOWLEDGMENT The Authors would like to thank NPMASS for providing necessary computer tools

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