This paper discussed modeling, design, fabrication and characterization of a new cantilever-type electrostatic zipping actuator. The actuator was designed to achieve high displacements and fabricated using multi-layer polysilicon foundry fabrication process PolyMUMPS. The high out-of-plane displacement is to satisfy the requirements in specific optical applications. In this paper we presented the design considerations in displacement, electrostatic forces and electrostatic stability. The electrostatic force between the curved cantilever and the bottom electrode on the substrate pulls the cantilever down. With a warped cantilever, the force closes the gap from the anchor end and gradually the zipping effect actuates the entire cantilever without increasing the biasing voltages. Previous electrostatic zipper actuators require a thin layer of dielectric material on top of the bottom electrode to prevent electrical shorting. They may have an issue with electrical breakdown of the thin dielectric layer due to the film quality. We designed a new mechanical structure to avoid the electrical shorting problem without a layer of dielectric material. Our analysis and experimental results demonstrated that the proposed design can withstand high voltages without shorting and is capable of high deflection.The vertical displacements of different device configurations were found ranging from 30.4µm to 450µm while the actuation voltages varied in the range from 12V to 45.3V for complete actuation. The pull-in voltages for various configurations were analyzed and presented.
Optical fibers coated with various non-magnetized ferromagnetic materials and actuated by external magnetic fields were designed and characterized to demonstrate the feasibility for remote scanning. Cobalt, iron, nickel, and samarium-cobalt powders were used to enable the actuation. Silica optical fibers were coated with a mixture of 70% enamel paint and 30% various ferromagnetic materials. The static and dynamic measurements were preformed under the remote control of an electromagnet. Experiments with different ferromagnetic materials and different suspended fiber lengths of 3.2 cm, 4.2 cm, 5.2 cm, 6.2 cm, and 7.2 cm were performed to compare with theory. The static displacements, dynamic displacements and resonant frequencies of the actuation were measured.
This paper discusses modeling, design, fabrication and characterization of an optical scanner based on cantilever-type electrostatic zipping actuators. The electrostatic actuator has been designed to achieve high displacements for large optical scanning angles at lower actuation voltages. The zipping actuators are fabricated using multi-layer polysilicon foundry fabrication processes. The electrostatic force between the cantilever and the bottom electrode on the substrate pulls the cantilever down. With a warped cantilever, the force closes the gap from the anchored end and gradually the zipping effect actuates the entire cantilever. In our design, mechanical structures are arranged to avoid electrical shortcircuit. With various annealing temperatures, the warped angles are controllable. The cantilever serves as a reflective surface and the high out-of-plane displacement is used to steer a reflected laser beam for imaging and scanning applications. In this paper we present the design considerations in electrostatic zipping actuator displacement and control as well as the arrangement for optical scanning.
A compact fiber optic scanner for biomedical applications such as optical coherent tomography has been designed, fabricated and tested. The scanner is designed as an in vivo device and composed of an optical fiber coated with nickelpowder loaded paint for external magnetic actuation. The compactness of the imaging device makes it suitable for applications where size, precision and low power consumption is critical. We have previously demonstrated the principles utilizing magnetic actuation for the fiber scanner coated with magnetic gel. This work focused on verification and optimization of the scanner operation. The magnetic properties of the nickel particle mixed with paint were characterized using an alternating gradient magnetometer. The optical scanner is externally actuated by an electromagnet and so it does not require a voltage or current supply in the probe itself. The displacements of the scanner were recorded using a position sensitive detector. The result showed a 0.8-mm displacement under the influence of a static magnetic field of 17.6 KA/m in a fiber with a moveable length of 4.2cm. Dynamic analysis showed a displacement of 0.83mm with an input current amplitude of 41mA and a magnetic field of 2.4 KA/m. The measurements are in good agreement with the theoretical lumped-element calculations. Finite-element analysis was performed and the results agree with the theoretical and experimental results. The static and dynamic displacements of the fiber optic scanner depend on the thickness and length of the magnetic coating. Thus, scanners for different displacements and operating frequencies can be designed by varying the coating thickness and length.
In this paper, we present design, modeling, fabrication, testing techniques and experimental verification for a bidirectional thermal actuator. The actuation principle is based on the asymmetrical thermal expansion of pseudo-bimorph microstructures due to the difference in the electrical resistance of two stacked poly-silicon layers. Bi-directional actuation is achieved depending upon the application of currents on either the top or bottom layers. Various designs were fabricated using the commercial foundry process PolyMUMPS and characterized with a reflective microscope and an optical profiler. Previous demonstrated designs had a limited vertical displacement due to the mechanical limitation imposed by the flexural lengths of the actuator arms. We proposed a new design allowing an increase of the maximum displacement by 85% with the same input voltage of 7V. The flexure arm is incorporated in the top silicon layer such that the torsion forces on the flexural arms are minimized. This enables larger deflection of the actuator arm without significant increase in the temperature. Different device configurations have been designed and tested. The temperature distributions on the actuator arms and displacements of the actuators at various conditions were analyzed using finiteelement analysis and verified experimentally. We will discuss the design configuration, testing techniques and practical issues. The potential applications of the out-of-plane actuators include flow sensors, variable capacitors, resistive sensors, optical switches and RF switches.
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