Mahdi M. Sadeghi

Micro-hydraulic structure for high performance bio-mimetic air flow sensor arrays

Here we introduce a novel micro-hydraulic structure that can significantly improve performance of many MEMS devices. Using this structure we fabricate and test a new type of low-power, accurate and robust flow sensor in which a hair-like appendage is used to translate flow into hydraulic pressure. This pressure is hydraulically amplified and sensed with a capacitance that is integrated with the micro-hydraulic system. The air flow sensor can detect flow speeds ranging from zero to 10 m.s−1 with a resolution of 1 cm.s−1 in the low flow regime and a predicted minimum detectable flow of 3 mm.s−1.

Electrostatically driven micro-hydraulic actuator arrays

This paper describes an all-electrical individually-addressable micro-hydraulic actuator array that produces high displacement and force by utilizing hydraulic amplification and electrostatic control, offering a considerable improvement in fabrication technique and performance over the recently-introduced micro-piston hydraulic actuator array [1,2]. The fabricated micro system consists of 3×3 and 4×4 arrays of actuator cells. A curved electrode capacitive actuator with a diameter of 2236 µm driven at 200 V produces 30.0 µm deflection on the front side at 14.4 kPa of pressure which corresponds to 11.3 mN force generated by the capacitive actuator on the back side. Actuation occurs from DC to 15 Hz.

Hair-based sensors for micro-autonomous systems

We seek to harness microelectromechanical systems (MEMS) technologies to build biomimetic devices for low-power, high-performance, robust sensors and actuators on micro-autonomous robot platforms. Hair is used abundantly in nature for a variety of functions including balance and inertial sensing, flow sensing and aerodynamic (air foil) control, tactile and touch sensing, insulation and temperature control, particle filtering, and gas/chemical sensing. Biological hairs, which are typically characterized by large surface/volume ratios and mechanical amplification of movement, can be distributed in large numbers over large areas providing unprecedented sensitivity, redundancy, and stability (robustness). Local neural transduction allows for space- and power-efficient signal processing. Moreover by varying the hair structure and transduction mechanism, the basic hair form can be used for a wide diversity of functions. In this paper, by exploiting a novel wafer-level, bubble-free liquid encapsulation technology, we make arrays of micro-hydraulic cells capable of electrostatic actuation and hydraulic amplification, which enables high force/high deflection actuation and extremely sensitive detection (sensing) at low power. By attachment of cilia (hair) to the micro-hydraulic cell, air flow sensors with excellent sensitivity (< few cm/s) and dynamic range (> 10 m/s) have been built. A second-generation design has significantly reduced the sensor response time while maintaining sensitivity of about 2 cm/s and dynamic range of more than 15 m/s. These sensors can be used for dynamic flight control of flying robots or for situational awareness in surveillance applications. The core biomimetic technologies developed are applicable to a broad range of sensors and actuators.

High-speed electrostatic micro-hydraulics for sensing and actuation

In this paper, we report a novel architecture for significant performance enhancement of previously introduced electrostatic micro-hydraulic structures. We develop a 2-D multi-physics model for analysis of our first generation electrostatic micro-hydraulic system (straight-wall architecture) used for sensing and actuation. Using this model, we design and fabricate a new sloped-wall device with a time constant 400× less than that of earlier designs, while maintaining other specification. The optimized electrostatic micro-hydraulic systems are successfully fabricated and tested. Micro-hydraulic structures of various geometries exhibit a measured bandwidth of 50 to 70 Hz, which corresponds to a sensor response time of about 18 ms.

High sensitivity, high density micro-hydraulic force sensor array utilizing stereo-lithography fabrication technique

We introduce a micro-hydraulic force sensor with the ability to maintain high sensitivity at reduced footprint size to realize an array of force sensors with capability resembling human fingertip touch sensing. This sensor utilizes a micro-hydraulic structure as an enhanced sensing mechanism along with a tactile interface fabricated with a low cost, fast prototyping stereo-lithography apparatus. The sensor is capable of delivering high average sensitivity of 87 fF/mN (maximum observed: 260 fF/mN), a minimum detectable capacitance change of 80 aF at quiescence and a spatial resolution of 1 mm. It is sensitive enough to detect the fall of a 38.5 nL water droplet. The sensor full-scale force range with a 2-μm thick parylene membrane is 15 mN. With an array using 15 μm thick parylene, the full-scale range can be expanded to 180 mN.

Electrostatic Micro-Hydraulic Systems

MEMS micro-hydraulic structures for amplification of force or deflection are introduced. These structures are integrated with capacitances to form electrostatic micro-hydraulic actuators (EMA). Hydraulic amplification and liquid permittivity are used to create stand-alone, efficient, and large deflection, and high force actuators. Force is generated using electrostatics with no need for external pressure sources. Use of integrated electrostatic force significantly reduces the device size. Utilizing this concept, a micro-valve and two types of EMA micro-piston arrays (water-based and silicone oil-based) are fabricated and tested. The micro-valve can switch fluid flows with the pressure ranging from 10 to 50 kPa at a maximum flow conductance of 20.3 sccm at 10 kPa with an actuation voltage of 340 VDC or 120 VAC. The silicone oil based micro-hydraulic micro-piston array has shown a maximum out-of-plane deflection of about 100 μm at 210 VDC, and a maximum bandwidth of about 5 Hz with a foot print size of 0.16 cm2 and a maximum power consumption of 20 μW at 1 Hz. These devices are the smallest ever reported microhydraulic systems that include the actuation source.

A Discrete Model for an Electrostatically Driven Micro-Hydraulic Actuator

High-force, large-deflection actuators are critical for devices such as valves and pumps used in micro-fluidic systems. The major technical impediment in improving the performance of the micro-actuators lies in the lack of understanding the physical phenomena and their interactions of electric, mechanical, and fluidic fields for performing their intended functions. Because of the complexity of the actuator, the fully coupled numerical analysis such as finite element analysis is extremely expensive.Here, we introduce a discrete model of an Electrostatic Micro-Hydraulic (EMH) actuator. The model considers all dynamic forces which are involved in a time operation of the hydraulic actuator cell and covers three major physics: electrostatic, mechanical and fluidic. The physics have been coupled together to investigate the dynamic of the device.The discrete dynamic model developed in this work may be used for simple yet accurate predictions of dynamic performance of such actuators, and is preferable to more complicated and very expensive coupled numerical models. The analysis relies on physics-based equations and can be modified to accommodate different chamber geometries, different material properties and different working fluids. Results from the analytical model compare favorably with experimental measurements.Copyright