Dragan Avirovik

Remote light energy harvesting and actuation using shape memory alloy—piezoelectric hybrid transducer

Shape memory alloys (SMAs) exhibit a memory effect which causes the alloy to return to its original shape when heated beyond the transformation temperature. In this study, we show that SMA can be heated remotely by laser and the resulting deformation can be converted into electricity through a piezoelectric bimorph. In addition, the laser actuated SMA deformation can also be used to provide controlled actuation. We provide experimental results demonstrating both the power harvesting and actuation behavior as a function of laser pulse rate. SMA used in this study exhibited higher absorption in the ultraviolet region which progressively decreased as the absorption wavelength increased. Raman analysis revealed TiO2 formation on the surface of SMA, whose concentration increased irreversibly with temperature. Negligible changes in the surface oxidation were detected in the working temperature range (<150 °C).

Tunable magnetoelectric response of dimensionally gradient laminate composites

A magnetoelectric (ME) sensor exhibiting wideband behavior as a function of applied magnetic DC bias and frequency was designed by combining the dimensionally gradient piezoelectric layer with Metglas magnetostrictive layers in laminate configuration. The ME coefficient of the band in the DC magnetic range of 52–242 Oe was measured to be 3000 mV/cm Oe under the resonant condition of f = 107 kHz. The wideband in the AC magnetic field frequency range of 41–110 kHz had the ME coefficient in the vicinity of 260 mV/cm Oe under the conditions of HAC = 1 Oe and HDC = 70 Oe. This frequency-dependent ME behavior clearly showed two different states on each side of the resonance peak which could open the possibility of developing new applications such as magnetic field-controlled switches.

Theoretical and experimental correlation of mechanical wave formation on beams

Mechanical waves can be broadly categorized into traveling waves and standing waves. In this study, the nature of the waves in a finite solid medium is investigated to reveal the excitation parameters that influence their behavior. Theoretical and experimental analysis is conducted to find the conditions for generating traveling waves using piezoelectric ceramics as the actuation agent in piezo-structural-coupled systems. A continuous electromechanical model is developed in order to predict the structural dynamics and is validated through experiments. The results from this study provide the fundamental physics behind the generation of mechanical waves and their propagation through finite mediums.

Characterization and representation of mechanical waves generated in piezo-electric augmented beams

Mechanical waves are induced in solids due to the systems coupling with an external excitation. Depending upon the nature of the resulting displacement and phase difference between the vibrating particles at a particular frequency, the mechanical waves can be classified as standing waves, traveling waves or a combination of the two. This study focuses on the identification of these different forms of mechanical waves and discusses methods that can be suitably used for their classification. The Hilbert and Fourier methods of classification were validated using experimental results and then compared against each other. The experimental and theoretical analysis of mechanical waves was conducted on a beam with free-free boundary conditions excited by piezoelectric elements.

Low-frequency nanotesla sensitivity in Metglas/piezoelectric/carbon fiber/piezoelectric composites with active tip mass

We report nanotesla sensitivity in Metglas/piezoelectric/carbon fiber/piezoelectric laminates with active tip mass operating in the vicinity of second bending mode. The peak magnetoelectric response for the laminate with an active tip mass (1 g) in longitudinal-transversal mode under Hdc=8 Oe and Hac=1 Oe was found to be ∼1.08 V/cm Oe at 43 Hz (first bending mode) and ∼19 V/cm Oe at 511 Hz (second bending mode). At the standard 1 kHz frequency, the maximum resolution of 5 nT was measured under Hac=0.5 Oe.

Contact-less Wind Turbine Utilizing Piezoelectric Bimorphs with Magnetic Actuation

The demand for efficient small-scale wind harvester is continually increasing in order to meet the local power needs for applications ranging from wireless sensor networks to charging of mobile devices. The efficiency of wind turbines is dependent upon several structural variables including frictional contacts. In order to overcome the problem of gearing and losses in mechanical contacts, we propose here a novel small-scale windmill design that utilizes magnetic attractive and repulsive force to create mechanical oscillation in piezoelectric bimorphs which is then converted into electric charge through direct piezoelectric effect. This contact-less wind turbine has several advantages including operation at much lower wind speeds and longer life span. The prototype was fabricated as a vertical-axis wind turbine featuring a modular Sarvonius rotor. Characterization was performed by utilizing several configurations for this modular rotor. Output power magnitude for steady-state operation in wind speeds of 2 – 10 mph was used to compare the performance of various configurations.

Millipede-inspired locomotion through novel U-shaped piezoelectric motors

We report a novel piezoelectric motor that operates at a resonance frequency of 144 Hz, much lower than that of conventional ultrasonic motors, and meets the displacement and gait requirements for designing the locomotion mechanism of a millipede-inspired robot (millibot). The motor structure consists of two piezoelectric bimorphs arranged in a U-shaped configuration. Using the first bending mode for both the piezoelectric bimorphs an elliptical motion was obtained at the tip which led to the successful implementation of millipede inspired locomotion. At an input voltage of 70.7 Vrms, the piezoelectric motor operating at resonance frequency was able to generate torque of 0.03 mN m, mechanical power of 0.84 mW and maximum velocity of 62 rad s−1. Detailed discussion is provided about the principle of operation of the millibot.

Thermal management of thermoacoustic sound projectors using a free-standing carbon nanotube aerogel sheet as a heat source

Carbon nanotube (CNT) aerogel sheets produce smooth-spectra sound over a wide frequency range (1-10(5) Hz) by means of thermoacoustic (TA) sound generation. Protective encapsulation of CNT sheets in inert gases between rigid vibrating plates provides resonant features for the TA sound projector and attractive performance at needed low frequencies. Energy conversion efficiencies in air of 2% and 10% underwater, which can be enhanced by further increasing the modulation temperature. Using a developed method for accurate temperature measurements for the thin aerogel CNT sheets, heat dissipation processes, failure mechanisms, and associated power densities are investigated for encapsulated multilayered CNT TA heaters and related to the thermal diffusivity distance when sheet layers are separated. Resulting thermal management methods for high applied power are discussed and deployed to construct efficient and tunable underwater sound projector for operation at relatively low frequencies, 10 Hz-10 kHz. The optimal design of these TA projectors for high-power SONAR arrays is discussed.

L-shaped piezoelectric motor-Part I: Design and experimental analysis

This paper proposes an L-shaped piezoelectric motor consisting of two piezoelectric bimorphs of different lengths arranged perpendicularly to each other. The coupling of the bending vibration mode of the bimorphs results in an elliptical motion at the tip. A detailed finite element model was developed to optimize the dimensions of bimorph to achieve an effective coupling at the resonance frequency of 246 Hz. The motor was characterized by developing rotational and linear stages. The linear stage was tested with different friction contact surfaces and the maximum velocity was measured to be 12 mm/s. The rotational stage was used to obtain additional performance characteristics from the motor: maximum velocity of 120 rad/s, mechanical torque of 4.7 × 10-5 N·m, and efficiency of 8.55%.

Miniature Shape Memory Alloy Heat Engine for Powering Wireless Sensor Nodes

Abstract Shape Memory Alloys (SMAs) exhibit temperature-dependent cyclic deformation. SMAs undergo reversible phase transformation with heating that generates strain which can be used to develop heat engine. In this study, we build upon the concept where environmental heat is first converted into mechanical energy through SMA deformation and then into electrical energy using a microturbine. This SMA heat engine was tailored to function as a miniature energy harvesting device for wireless sensor nodes applications. The results showed that 0.12 g of SMA wire produced 2.6 mW of mechanical power which was then used to drive a miniature electromagnetic generator that produced 1.7 mW of electrical power. The generated electrical energy was sufficient to power a wireless sensor node. Potential design concepts are discussed for further improvements of the SMA heat engine for the wireless sensing platform.