Kiron Mateti

Piezoelectric MEMS sensors: state-of-the-art and perspectives

Over the past two decades, several advances have been made in micromachined sensors and actuators. As the field of microelectromechanical systems (MEMS) has advanced, a clear need for the integration of materials other than silicon and its compounds into micromachined transducers has emerged. Piezoelectric materials are high energy density materials that scale very favorably upon miniaturization and that has led to an ever-growing interest in piezoelectric films for MEMS applications. At this time, piezoelectric aluminum-nitride-based film bulk acoustic resonators (FBAR) have already been successfully commercialized. Future innovations and improvements in inertial sensors for navigation, high-frequency crystal oscillators and filters for wireless applications, microactuators for RF applications, chip-scale chemical analysis systems and countless other applications hinge upon the successful miniaturization of components and integration of piezoelectrics and metals into these systems. In this article, a comprehensive review of micromachined piezoelectric transducer technology will be presented. Piezoelectric materials in bulk and thin film forms will be reviewed and fabrication techniques for the integration of these materials for microsensor applications will be presented. Recent advances in various piezoelectric microsensors will be presented through specific examples. This review will conclude with a critical assessment of the future trends and promise of this technology.

Monolithic SUEX Flapping Wing Mechanisms for Pico Air Vehicle Applications

This paper develops a simple flapping wing mechanism fabricated monolithically from an epoxy-based negative photoresist (SUEX) dry film. The developed fabrication process has fewer steps compared to other methods, does not use precious metals, and greatly reduces processing time and cost. It simultaneously defines the pico air vehicle (PAV) airframe, compliant flapping mechanism, and artificial insect wing using photolithography. Using this process, we designed and fabricated the LionFly, a flapping wing mechanism actuated by a PZT-5H bimorph actuator. Rapid prototypes were fabricated with precisely defined features and material properties and geometry that are similar to insects. We present the fabrication process and characterization of SUEX and show that flexure thickness can be controlled by 310 nm UV dose. Static and dynamic modeling of the LionFly have excellent agreement with experimental data. Performance from multiple prototypes shows devices with resonance frequency of 49.13 ± 1.43 Hz and up to 75° peak to peak flapping angle demonstrating applicability of the fabrication process for flapping wing PAV applications.

Wing rotation and lift in SUEX flapping wing mechanisms

This research presents detailed modeling and experimental testing of wing rotation and lift in the LionFly, a low cost and mass producible flapping wing mechanism fabricated monolithically from SUEX dry film and powered by piezoelectric bimorph actuators. A flexure hinge along the span of the wing allows the wing to rotate in addition to flapping. A dynamic model including aerodynamics is developed and validated using experimental testing with a laser vibrometer in air and vacuum, stroboscopic photography and high definition image processing, and lift measurement. The 112?mg LionFly produces 46? flap and 44? rotation peak to peak with 12? phase lag, which generates a maximum average lift of 71??N in response to an applied sinusoidal voltage of 75?V AC and 75?V DC at 37?Hz. Simulated wing trajectories accurately predict measured wing trajectories at small voltage amplitudes, but slightly underpredict amplitude and lift at high voltage amplitudes. By reducing the length of the actuator, reducing the mechanism amplification and tuning the rotational hinge stiffness, a redesigned device is simulated to produce a lift to weight ratio of 1.5.

SUEX Flapping Wing Mechanisms for Pico Air Vehicles

This paper introduces a simple and low cost flapping wing mechanism fabricated monolithically from SUEX dry film, an epoxy based negative photoresist similar to SU-8. The developed process has fewer steps compared to other methods, does not use precious metals, and greatly reduces processing time and cost. It simultaneously defines the PAV airframe, compliant flapping mechanism, and artificial insect wing using photolithography. Rapid prototypes were fabricated with precisely defined features and material properties and geometry that are similar to insects. A linear model with simplified aerodynamics is developed with amplitude dependent damping and validated using experimental results in air and in vacuum. Angles up to 45° at a resonant frequency of 47 Hz are observed that demonstrate applicability of the developed fabrication process for flapping wing air vehicle applications.© 2012 ASME

Piezoelectric T-Beam Actuators

This paper develops models, fabricates, experimentally tests, and optimizes a novel piezoelectric T-beam actuator. With a T-shaped cross-section, and bottom and top flanges and web electrodes, a cantilevered beam can bend in both in-plane and out-of-plane directions upon actuation. Analytical models predict the tip displacement and blocking force in both directions. Six mesoscale T-beam prototypes are monolithically fabricated by machining and microfabrication techniques and experimentally tested for in-plane and out-of-plane displacements and out-of-plane blocking force. The analytical models closely predict the T-beam displacement and blocking force performance. A nondimensional analytical model predicts that all T-beam designs for both in-plane and out-of-plane actuations, regardless of scale, have nondimensional displacement and blocking force equal to nondimensional voltage. Another form of nondimensional model optimizes the T-beam cross-section for maximum performance. Optimization study shows that a cross-section with width ratio, b * , and thickness ratio, t * , approaching zero produces maximum displacement, b * = t * = 0.381 produces maximum blocking force, and b* ≈ 0.25, t * ≈ 0.33 produces maximum mechanical energy.

Fabrication and Characterization of Micromachined Piezoelectric T-Beam Actuators

This paper presents a monolithically fabricated microelectromechanical piezoelectric cantilever beam with a T-shaped cross section capable of in-plane and out-of-plane displacements and sensing. High-aspect-ratio T-beams are achieved by direct micromachining of bulk lead zirconate titanate (PZT-4) via reactive ion etching of 65- μm-deep features. Electrodes deposited on the top and bottom web and flange regions of the T-shaped structure allow in-plane and out-of-plane motion actuation and sensing. The T-beam structures were tested for in-plane and out-of-plane tip displacements, out-of-plane blocking force, and impedance response. These results are explained using analytical models that predict static deflection, blocking force, and resonance frequency. Nine prototype micromachined T-beams are fabricated that achieve up to 129 μm of out-of-plane displacement, 11.6 μm of in-plane displacement, and 700 μN of out-of-plane blocking force.

Displacement and Blocking Force Performance of Piezoelectric T-Beam Actuators

In this paper, we present the experimental validation of the detailed models developed for the flexural motion of piezoelectric T-beam actuators. With a T-shaped cross-section, and bottom and top flange and web electrodes, a cantilevered beam can bend in both in-plane and out-of-plane directions upon actuation. Analytical models predict the tip displacement and blocking force in both directions. Mechanical dicing and flange electrode deposition was used to fabricate six meso-scale T-beam prototypes. The T-beams were experimentally tested for in-plane and out-of-plane displacements, and out-of-plane blocking force. The analytical models closely predict the T-beam displacement and blocking force performance. A nondimensional analytical model predict that all T-beam designs for both in-plane and out-of-plane actuation, regardless of scale, have nondimensional displacement and blocking force equal to nondimensional voltage. The results from experiments are favorably compared with this theoretical prediction.Copyright

Wing Rotation and Lift Modeling and Measurement in SUEX Flapping Wing Mechanisms

This paper presents detailed modeling and experimental testing of wing rotation and lift in the LionFly, a flapping wing mechanism powered by piezoelectric bimorph actuators fabricated using SUEX dry film. The goal of this paper is to understand the flapping and rotation dynamics and the lift-producing mechanisms in this device. A linear vibrational model is developed and augmented with nonlinear aerodynamic forces using the blade element method. Experimental testing using a laser vibrometer in air and in vacuum characterizes small amplitude flapping and rotation. Strobe photography and high definition image processing measures high amplitude wing trajectories. A lift measurement system using a force transducer is designed and used to measure average lift in the LionFly. The LionFly produces 46° peak flapping and 44° peak rotation resulting in lift of 71 μN at 37 Hz.Copyright

Thrust Modeling and Measurement for Clapping Wing Nano Air Vehicles Actuated by Piezoelectric T-Beams

Insects that use a Weis-Fogh clap and fling mechanism, where their wings clap together and fling apart, show an increase in thrust per unit muscle mass compared to conventional flapping insects. This has motivated the development of macroscale clapping winged ornithopters with four wings. Most clapping wing ornithopters use electric motors with gears and linkages that are inefficient at the sub-millimeter (meso)scale. Piezoelectric actuators are attractive for Nano Air Vehicles (NAVs) because they have high power density, high efficiency, and new fabrication processes have been developed at this scale. Recently developed piezoelectric T-beam actuators are monolithically fabricated from bulk PZT and function like unimorph actuators without the need to bond passive layers. These bending actuators drive a novel four-winged clapping NAV that produces thrust. This paper studies thrust force generation of a clapping wing NAV using a model-based approach. A three degree of freedom dynamic model of the clapping wing nano air vehicle is derived including unsteady aerodynamic forces and torques. The model is validated using experimental data from a NAV prototype.Copyright

Clapping Wing Nano Air Vehicle Using Piezoelectric T-Beam Actuators

Clapping wing air vehicles are inspired by the Weis-Fogh clap and fling mechanism used by certain insects, where opposing wings almost touch during part of the flap cycle, spawning vortex structures that increase thrust. Current vehicles cannot be scaled to Nano Air Vehicle (NAV) dimensions because they use electromagnetic motors, gears, and linkages that are difficult to fabricate and have poor efficiency at the sub-millimeter scale. This paper develops a novel NAV that uses piezoelectric T-beam actuators that are monolithically fabricated and exhibit unimorph behavior. A hinge and lever wing mechanism amplifies the small actuator displacements to produce large wing motions. A four wing, clapping NAV is designed, fabricated, and experimentally shown to provide a wing stroke angle of approximately 35° at 1 Hz.Copyright