Sangki Lee

Design of IPMC actuator-driven valve-less micropump and its flow rate estimation at low Reynolds numbers

This paper presents the design and flow rate predictions of an IPMC (ionic polymer–metal composite) actuator-driven valve-less micropump. It should be noted that IPMC is a promising material candidate for micropump applications since it can be operated with low input voltages and can produce large stroke volumes, while having controllable flow rates. The micropump manufacturing process with IPMC is also convenient; it is anticipated that the manufacturing cost of the IPMC micropump is competitive with other technologies. In order to design an effective IPMC diaphragm that functions as an actuating motor for a micropump, a finite element analysis (FEA) was utilized to optimize the electrode shape of the IPMC diaphragm and estimate its stroke volumes. In addition, the effect of the pump chamber pressure on the stroke volume was numerically investigated. Appropriate inlet and outlet nozzle/diffuser elements were also studied for the valve-less micropump. Based on the selected geometry of nozzle/diffuser elements and the estimated stroke volume of the IPMC diaphragm, the flow rate of the micropump was estimated at a low Reynolds number of about 50.

Design and demonstration of a biomimetic wing section using a lightweight piezo-composite actuator (LIPCA)

This paper describes the design and evaluation of biomimetic wing sections, where the trailing edges of the wing sections are actuated by the piezoceramic actuator LIPCA (lightweight piezo-composite actuator). Thermal analogy based on linear elasticity was used for the design and analysis of the wing sections. In the actuation test of the wing sections, the effective deflection angle of the trailing edge was approximately five degrees at 300 V input. The predicted and measured actuation displacements agreed very well up to an input of 150 V. However, the real actuation displacement became larger than the estimated value for higher input voltages due to the material non-linearity of the lead zirconate titanate (PZT) wafer in the LIPCA. The biomimetic wing sections can be used for control surfaces of small scale unmanned aerial vehicles (UAVs).

A nine-node assumed strain shell element for analysis of a coupled electro-mechanical system

In the present paper, the formulation of a nine-node assumed strain shell element is modified and extended for use in analysis of actuator-embedded structures. The shell element can alleviate locking and has six degrees of freedom (DOFs) per node as a result of discarding the assumption of no thickness change. Mechanical–piezoelectric DOFs are coupled through the constitutive equation and the electric potential is assumed to be linear through the thickness of a piezoelectric layer. A finite-element program based on the formulation is generated and the code is validated though solving typical numerical examples. The results from the present work agree well with those from other references.

Analysis of multi-layered actuators using an assumed strain solid element

Abstract This paper presents an 18-node assumed strain solid element with mechanical–piezoelectric coupling. In the formulation, electric potential is regarded as a nodal degree of freedom in addition to three translations at each grid point. Since the assumed strain solid element is free of locking, the element can be used to analyze behavior of very thin actuators without locking. Using the solid element, we have analyzed the actuation performance of a composite multi-layered piezoceramic actuator and compared the result with measured data. The numerical estimation agreed well with the measured displacement for simply supported boundary condition and for low input voltage.

Piezoelectric Actuator-Sensor Analysis using a Three-dimensional Assumed Strain Solid Element

This paper presents a piezoelectric solid element that can be used for modeling thin sensors and actuators. The element has been extended from an eighteen-node assumed strain solid element that can alleviate locking in mechanical problems. For the fully coupled mechanical-piezoelectric formulation, the electric potential is regarded as a nodal degree of freedom in addition to three translations in the original element. Consequently, the induced electric potential can be calculated for a prescribed load and the actuation displacement computed for an input voltage. Since the assumed strain solid element can relieve locking, the proposed element can also be used to analyze the behavior of very thin actuators. In addition, a finite element code was developed based on the proposed formulation and typical numerical examples were solved for code validation. Parametric studies for the THUNDER actuator have been also conducted using the code, where specific combinations of materials used for the layers plus the curvature of THUNDER were both found to improve the actuation displacement.

The effect of electro-mechanical coupling stiffness on the through-the-thickness electric potential distribution of piezoelectric actuators

This paper presents an analysis of the coupling effect on the behavior of piezoelectric wafers used for actuators and sensors. A fully coupled formulation for an eighteen-node assumed strain piezoelectric solid element is used to test the effect of full coupling stiffness on the electric potential distribution through the thickness of the actuator/sensor. Since the assumed strain solid element can alleviate locking, it can be used to analyze the behavior of very thin actuators without locking. In the formulation, the electric potential is regarded as a nodal degree of freedom in addition to three translations at each grid point. The electric potential is then prescribed for nodes at the top and bottom surfaces in the finite element model of a PZT wafer and is left unknown for the other nodes throughout the thickness. Consequently, the induced electric potential and actuation displacement can be computed for an input voltage. The effect of coupling stiffness on the through-the-thickness distribution of the electric potential is examined, considering parameters such as thickness and in-plane dimension. This research shows that full coupling stiffness only affects piezoelectric structures of specific thickness and shape. These new findings can be useful for precision sensor and actuator design.

Electromechanical flapping produced by ionic polymer-metal composites

An IMPC actuated flapping wing has been designed and demonstrated for mimicking flapping motion of a bird wing. The flapping wing can produce twist motion as well as flap up and down motions. For design of the wing, an equivalent beam model has been proposed based on the measured force-displacement data. The equivalent model is used to determine suitable IPMC actuator patterns that can create twist motion during up- and down-strokes of the wing. The IPMC actuator pattern is inserted in a wing-shaped plastic film to form a complete flapping wing. Experimental results show that the properly shaped IPMCs can create aniosotropic motion that is often required for producing effective thrust and lift forces in bird flight.

Equivalent Modeling for Shape Design of IPMC (Ionic Polymer-Metal Composite) as Flapping Actuator

In this work, flapping wings actuated by IPMCs are designed and simulated to mimick birds wing. In order for the wing to generate lift and thrust during flapping motion, the wing must be able to flap and twist at the same time. For design of such wings, shape of the IPMC actuator need to be designed such that the actuator can create bending and twisting motions during wing strokes. To determine the shape of the IPMC actuator, an equivalent bimorph beam model has been proposed based on the measured force-displacement data of an IPMC. The equivalent model and thermal analogy are used for numerical simulation of IPMC actuated wings to determine suitable shape of the IPMC actuator. In this way, we could select a best performing wing that can create the largest twist motion during flapping of the wing.

Performance analysis of a lightweight piezo-composite actuator considering the material non-linearity of an embedded PZT wafer

This paper analyzes the performance of lightweight piezo-composite actuators (LIPCAs) including the material non-linearity of the embedded 3203HD PZT wafer. For this analysis, we used a piezo-shell element code based on a nine-node assumed strain shell element formulation. The material non-linearity was included in the formulation due to the large observed discrepancies in the measured displacement and computed actuation displacement based on the linear analysis, especially at high input voltages. An experimentally extracted piezo-strain function of the PZT wafer and incremental formulation were incorporated into the linear finite element code to improve the accuracy of the estimated actuation displacement of the LIPCA. The non-linear piezo-shell program was used to estimate the non-linear performance of the LIPCA. The actuation displacement predicted from the non-linear code showed much better agreement with the measured data.

Dependency of electric field and mechanical stress on piezoelectric strain of PZT 3203HD

In this paper, material nonlinear behavior of PZT wafer (3202HD, CTS) under high electric field and tensile stress is experimentally investigated and the nonlinearity of the PZT wafer is numerically simulated. In the simulation, new definitions of the piezoelectric constant and the incremental strain are proposed. Empirical functions that can represent the nonlinear behavior of the PZT wafer have been extracted based on the measured piezo-strain under stress. The functions are implemented in an incremental finite element formulation for material nonlinear analysis. With the new definition of the incremental piezo-strain, the measured nonlinear behavior of the PZT wafer has been accurately reproduced even for high electric field.