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EMS Structural simulation of valveless micro-pump based on Electromagnetic actuation

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Applications

Introduction

Micro-electro-mechanical systems (MEMS) are a highly growing field. They enable the investigation of micro-scale devices in various applications such as biomedical industries which involve imbedded microfluidic devices. Micro pumps are one of the essential MEMS components for the microfluidic system and have a significant potential in chemical control of Nano-liter flows for drug delivery as well as chemical analysis and mixing.

Micropumps, based on Electromagnetic-actuation, are the common integrated devices that have been applied to the needs of biomedical applications. These micro-pumps gave rise to a new emerging microfluidic field requiring a compact method of actuation to produce the needed flow. One of the commonly used micro-pumps is the valveless-actuated one.

Micro-valveless-actuated pump

The structure of the micro-valveless pumping mechanism is studied in this paper. It comprises an electroplated permanent magnet mounted on a flexible PDMS membrane and a base glass substrate holding a fixed micro coil. Such type of micro pumps allows to create a significant driving flow pressure. In the pumping operation, fluid is driven through the pump by applying a current to the micro coil such that an electromagnetic force is established between the coil and the magnet causing a resulting deflection of the PDMS diaphragm. The PDMS is specially chosen as the membrane material since it has good flexibility characteristics.

Consequently, the large diaphragm deflection allows the rate to be easily controlled under low electrical current and frequency.
Figure 1 shows a real prototype of the micro-pump and a schematic illustration of the whole actuation mechanism.
 

 A picture of the fabricated micro-pump [1] a). and its schematic illustration b).

Figure 1 - A picture of the fabricated micro-pump [1] a). and its schematic illustration b).

Modeling and problem description

The magnetostatic module of EMS coupled to the structural study is used in this analysis. It enables the computation and the visualization of the mechanical deflection of the flexible membrane exposed to the magnetic loads, which is produced by the coil-magnet interaction.
The design of the proposed micro-pump is shown in figure 2.

a): 3D isometric view of the micropump b): cross-sectional view of the micro- pump

Figure 2 -  a): 3D isometric view of the micropump b): cross-sectional view of the micro- pump.
 

The following tables define the dimensions of the main model components`:

Table 1 - PDMS diaphragm design
Material Radius (µm) Thickness (µm) Elastic limit force (µN)
PDMS 1950 80 315
Table 2 - Coil design
Material Inner Radius (µm) Outer Radius (µm) Width (µm) Turns Resistance (?)
Copper (Cu) 1250 1725 25 10 3.23
 
Table 3 -  Magnet design
Material Radius (µm) Thickness (µm) Distance from coil base (µm)
CoNiMnP 1150 20 620

Material Properties

Table 4 - Material properties
Material Density
(Kg/m au cube)
Magnetic permeability Electrical conductivity
(S/m)
Elastic Modulus
(Pa)
Poissons ratio Magnetization
Coercivity (A/m)
Remanence (T)
Copper (Cu) 8900 0.99 5.7 E+07 Not required      
    Not 

    required
PDMS 1030 1 0 0.75 E+6 0.49
Glass
Not required
1 0
Not required
CoNiMnP 1.88 0 47700
0.3

Electromagnetic Inputs:

The inductor coil is defined as solid coil supporting a current input range of 0.4 - 1 A rms.

Mechanical boundary conditions

Fixed boundary conditions are applied to lateral cylindrical surface of the PDMS membrane, as shown in the figure 3:

Applied mechanical boundary conditions

Figure 3 - Applied mechanical boundary conditions

Meshing

Top and isometric view of the meshed model
Figure 4 - 
Top and isometric view of the meshed model
 

Results

To achieve the required actuation force and diaphragm deflection fixed by the reference [2], a series of numerical simulations were executed, using EMS tool, for different current inputs in the range of 0.4A-1A. The corresponding obtained results are presented in the figures below.
The figure 5 shows the variation of the resultant magnetic force versus the applied current inputs (0.4 A to 1A). A good coherence is observed between the reference [2] results and those obtained from EMS tool.

Magnetic force variation versus current inputs for both Reference [2] and EMS results.

Figure 5 - Magnetic force variation versus current inputs for both Reference [2] and EMS results.
 

Under the effect of the magnetic force acting on it, the PDMS-diaphragm is bending upwards. It attains a maximum deflection of 15.08 µm under 16.5µN corresponding to a current input of 0.9A (Figure 6).

The obtained results are well responding to the desired membrane displacement mentioned in the Reference [2]. It improves the ability of the micro-scale pump to achieve a significant membrane deflection under reduced energy consumption.

Resultant deflection of the PDMS membrane for a current input of 0.9A
Figure 6 - Resultant deflection of the PDMS membrane for a current input of 0.9A
 

A second comparison between Ref [2[ simulation, analytical [2] and EMS results is represented through the figure 7. It is showing the 2D plot variation of the membrane deflection versus the obtained magnetic force for the current range [0.4A..1A].
It confirms the good agreement between the different results and the ability of EMS simulation tool to estimate the magneto-mechanical behavior of the micro-pump actuation under low current.

Variation of membrane displacement versus the magnetic forces
Figure 7 - Variation of membrane displacement versus the magnetic forces.

Conclusion

The theoretical model of the micro-valveless-pump proposed by the Reference [2] has been investigated through the Magneto-structural analysis of EMS software. The obtained mechanical results validate the computed analytical ones given by the paper.
Thus, EMS enabled to confirm the established electromagnetic actuator design which is satisfying the micro-pump requirements. The micro-pump is capable to produce a sufficient actuating force to achieve the desired diaphragm deflection which responds well to the biomedical applications` needs. 

Reference

[1]- Lee, Chia-Yen, Hsien-Tsung Chang, and Chih-Yung Wen. "A MEMS-based valveless impedance pump utilizing electromagnetic actuation." Journal of Micromechanics and Microengineering 18.3 (2008): 035044.
[2]- Chang, Hsien-Tsung, et al. "Theoretical analysis and optimization of electromagnetic actuation in a valveless microimpedance pump." Microelectronics journal 38.6-7 (2007): 791-799.