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TECHNICAL PAPERS

# Modeling and Design of an Optically Powered Microactuator for a Microfluidic Dispenser

[+] Author and Article Information
Mandar Deshpande

Micro- Systems Mechanisms and Actuators Laboratory, Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, 60607

Laxman Saggere1

Micro- Systems Mechanisms and Actuators Laboratory, Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, 60607saggere@ulc.edu

A comprehensive literature of light-driven actuation of liquids is presented in 9.

The actual dispensing rate requirement in the prosthesis could be even smaller and it depends on the concentration of the chemical dispensed. The dispensing rate assumed here is the bulk flow of liquid for the bench-top device.

Analytical solution for the transverse displacement obtained by this method is validated through a finite element analysis using ANSYS ® software, the details of which are discussed in a following section.

The full expressions for $CE$ and $CP$, which were obtained using Maple, are not reported here due to their somewhat unwieldy size.

The larger percent error between the analytical and the FEA results for the displacement for the combined loading case is attributable to the omission of electro-mechanical coupling effect in the analytical model for the displacement.

There is some ambiguity concerning the validity of $C=64$ for micro-scale flows in the literature. Some reports have suggested that for micro-scale flows, the value of $C$ must be taken to be about 20% less than the conventional value while others have used the conventional value, $C=64$(34,37-38). While the most appropriate value of $C$ must be determined through experiments for the specific geometry of the outlets, for this design, $C=64$ is assumed.

1

Corresponding author.

J. Mech. Des 127(4), 825-836 (Jan 18, 2005) (12 pages) doi:10.1115/1.1900749 History: Received June 22, 2004; Revised January 18, 2005

## Abstract

This paper presents systematic modeling and design of an optically powered piezoelectric microactuator for driving a microfluidic dispenser that could find a potential application in a retinal prosthesis. The first part of the paper treats a microactuator system comprised of a micron-scale piezoelectric unimorph integrated with a miniaturized solid-state solar cell. The microactuator design is tailored for driving a microfluidic dispenser to dispense a stored liquid chemical through its micron-sized outlet ports at a rate of about $1pl∕s$ when the integrated solar cell is irradiated by light at a power density of $3W∕m2$, corresponding to the requirements of the potential application. The microactuator system design is accomplished by first obtaining analytical models for the solar cell characteristic behavior and the microactuator displacements and then combining them to obtain the key dimensions of the microactuator through a design optimization. An analysis of the performance characteristics of the microactuator and a finite element analysis validating the analytical model for the microactuator’s displacements and the peak stresses under the operating loads are presented. The latter part of the paper presents a design of a microfluidic dispenser utilizing the optically powered microactuator and satisfying the desired input/output requirements. An analytical model integrating various energy domains involved in the system, viz. opto-electrical, piezoelectric, mechanical and hydraulic, is derived for the liquid flow through the dispenser’s micron-sized outlet ports. Finally, the energetic feasibility of the microactuator design obtained for the specified input and output criteria is also discussed.

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## Figures

Figure 12

Plot of the PZT (capacitor) voltage versus time for the three different solar cell collection areas

Figure 13

Dispenser deformations due to the actuator deflection and the chamber compliance

Figure 14

Variation of the volume flow rate through each outlet port, Qport(t) over dispensing time and average flow rate for the two design cases: (A) Design A and (B) Design B

Figure 15

Schematic arrangement of the outlet ports in the two designs

Figure 1

Optically powered microdispenser array concept for a novel biomimetic retinal prosthesis concept

Figure 2

The schematic of the dispenser structure (left) and its working principle (right)

Figure 3

Layout of the solar cell relative to the microactuator and the microdispenser

Figure 4

J–V curve of the solar cell with ηcell=16% and Jsc0=33.94mA∕cm2

Figure 5

Cross-sectional schematic of a circular piezoelectric microactuator

Figure 6

Free-body diagrams of the annular plate and the composite plate

Figure 7

Finite element analysis in ANSYS® (ver. 7.1): (A) The axisymmetric model of the microactuator showing stress distribution under a voltage load of V=0.4145volts at a scale of X:Y=1:2 (the axisymmetry is about the edge on the left-hand side—right-hand side edge is fixed). (B) Close-up of the stress distribution at the interface in the region circled in (A). (C) Element plot showing various material layers of a portion of the axisymmetric finite element model in (A).

Figure 8

Comparison of displacements at points along a diameter of the microactuator obtained by the analytical model and the finite element analysis for various loading cases

Figure 9

Open circuit voltage of the solar cell and the electric fields across the piezoelectric layers in the two designs considered as a function of incident irradiance in the range of 0.1–3W∕m2

Figure 10

Center point displacement and volume displacement of the microactuators in the two different designs as a function of incident irradiance in the range of 0.1–3W∕m2

Figure 11

(A) Solar cell powered piezoelectric actuator. (B) Simplified equivalent circuit representation of the actuator

## Errata

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