Multilayer microhydraulic actuators with speed and force configurations

Microsystems & Nanoengineering volume  7, Article number: 22 (2021 ) Cite this article

Electrostatic motors have traditionally required high voltage and provided low torque, leaving them with a vanishingly small portion of the motor application space. The lack of robust electrostatic motors is of particular concern in microsystems because inductive motors do not scale well to small dimensions. Often, microsystem designers have to choose from a host of imperfect actuation solutions, leading to high voltage requirements or low efficiency and thus straining the power budget of the entire system. In this work, we describe a scalable three-dimensional actuator technology that is based on the stacking of thin microhydraulic layers. This technology offers an actuation solution at 50 volts, with high force, high efficiency, fine stepping precision, layering, low abrasion, and resistance to pull-in instability. Actuator layers can also be stacked in different configurations trading off speed for force, and the actuator improves quadratically in power density when its internal dimensions are scaled-down.

The invention of electrostatic motors, pioneered by Benjamin Franklin and Andrew Gordon in 1740, significantly predates Michael Faraday’s demonstration of the first inductive motor in 1821, yet electrostatic motors have never gained a significant technological foothold. Historically, electrostatic motors have required high voltage and had low output power. In the last few decades, microelectromechanical (MEMS) motors1 have improved the outlook for capacitively driven rotational actuation. At the microscale, a higher driving frequency can increase the power density, and smaller electrode gaps can reduce the driving voltage. Some high-frequency piezoelectrically driven ultrasonic motors2,3 have gained commercial acceptance; however, most MEMS motors still suffer from an unacceptably low torque and the inability to scale in three dimensions due to their inherently thin nature4. To address these challenges a desirable electrostatic motor technology should offer a low operating voltage, high torque, high efficiency, and the ability to scale up in thickness. It is known how to achieve these characteristics individually. A low-voltage operation can be obtained by using a thin dielectric5,6. A high torque can be obtained by having a large capacitance change in a small displacement, either by using planar capacitive coupling5,7 or by using a small stepping distance5,8,9. Extendibility in thickness, without increasing voltage, can be obtained with a layered structure design10,11. Finally, high efficiency can be obtained by using a dielectric with low loss5,8,12. All these characteristics have been individually demonstrated, but to our knowledge, they have never been combined into a single actuator technology.

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