Jayant Sirohi

Piezoelectric wind energy harvester for low-power sensors

There has been increasing interest in wireless sensor networks for a variety of outdoor applications including structural health monitoring and environmental monitoring. Replacement of batteries that power the nodes in these networks is maintenance intensive. A wind energy–harvesting device is proposed as an alternate power source for these wireless sensor nodes. The device is based on the galloping of a bar with triangular cross section attached to a cantilever beam. Piezoelectric sheets bonded to the beam convert the mechanical energy into electrical energy. A prototype device of size approximately 160 × 250 mm was fabricated and tested over a range of operating conditions in a wind tunnel, and the power dissipated across a load resistance was measured. A maximum power output of 53 mW was measured at a wind velocity of 11.6 mph. An analytical model incorporating the coupled electromechanical behavior of the piezoelectric sheets and quasi-steady aerodynamics was developed. The model showed good correlation with measurements, and it was concluded that a refined aerodynamic model may need to include apparent mass effects for more accurate predictions. The galloping piezoelectric energy-harvesting device has been shown to be a viable option for powering wireless sensor nodes in outdoor applications.

Design and Development of a High Pumping Frequency Piezoelectric-Hydraulic Hybrid Actuator

This paper describes the design and development of a piezoelectric-hydraulic hybrid actuator operating at a high pumping frequency. The actuator is envisaged as a potential actuator for a trailing edge flap on a full scale smart rotor system. While recent research efforts based on the same concept have investigated actuators with large piezoelectric stacks operating at a relatively low pumping frequency, the goal of the present work is to investigate the behavior of the actuator at a low volumetric displacement and high pumping frequency. Preliminary design of the actuator system is carried out, and the dependence of the performance of the actuator on various system parameters is identified. This enables the optimum selection of geometric parameters and piezostack characteristics for a given external load. Challenges to achieving high pumping frequencies were identified and solutions were implemented. The actuator was driven by two piezostacks, of a total length of 36 mm and cross-sectional area 100 mm 2 . The actuator was tested up to a pumping frequency of 1 kHz, developing a maximum no-load velocity of 1.2 in/s and a blocked force of 35 lb in the unidirectional output mode. Bidirectional output performance was also measured, by incorporating a 4-way valve in the hydraulic circuit. At a frequency of 5 Hz, a no-load output displacement with an amplitude 32 mils was measured.

Fundamental Behavior of Piezoceramic Sheet Actuators

This paper investigates the behavior of piezoceramic sheet actuators under different types of excitation and mechanical loading. The research especially focuses on the application of these actuators to the development of smart rotor systems. The free strain response of the actuators under DC excitation is experimentally investigated along with the associated drift of the strain over time. Effect of tensile stress on the free strain response is examined. The magnitude and phase of the free strain response of the actuator under different excitation voltages and frequencies is measured, and a phenomenological model to predict this behavior is developed and validated. The power consumption of the free actuator and a pair of actuators surface bonded to a host structure is calculated by the impedance method and validated by measurement. Additionally, depoling of the actuators is discussed, along with the feasibility of recovering performance by repoling in the event of accidental depoling.

An improved Shape Memory Alloy actuator for rotor blade tracking

The design, analysis, and testing of an improved Shape Memory Alloy (SMA)-based tracking tab actuator is described in this paper. The goal of the actuator is to provide in-flight tracking capability for a helicopter rotor in order to minimize 1/rev vibrations due to rotor dissimilarities. Previous SMA-based actuator designs demonstrated the potential for in-flight rotor tracking but admitted drawbacks that led to inconsistent operation under air-loads. The current research builds upon the existing knowledge base and addresses the challenges encountered in previous designs. The objective is to achieve a deflection of 58 with an accuracy of 0:18 under realistic aerodynamic loading conditions. The present actuation concept is based on the bidirectional motion of a pair of antagonistic SMA wires, with a passive friction brake to lock the tab position. A theoretical model of the actuator was developed based on Brinson’s thermomechanical model. The model was used to predict the behavior of the actuator under external loading and applied as a design tool to identify optimal actuator parameters. The actuator was integrated into a NACA 0012 12 in. chord blade section and tested in an open-jet wind tunnel at speeds of up to 120 ft/s (0.107 M) and at angles of attack up to 158. Closed-loop tracking was implemented using a PID controller with gains selected by Ziegler-Nichols tuning. The improved SMA actuator meets the project goals by achieving repeatable tab deflection of up to 58with an average accuracy of 0.058. Position hold under power-off conditions and a duty cycle of 20 cycles/h were also demonstrated.

Comparison of Piezoelectric, Magnetostrictive, and Electrostrictive Hybrid Hydraulic Actuators

In recent years, active material driven actuators have been widely researched for potential applications in the fields of aerospace, automotive, and civil engineering. While most of these active materials, such as piezoelectric, magnetostrictive, and electrostrictive materials, have high force and bandwidth capabilities, they are limited in stroke. In combination with hydraulic systems, the field-dependent motion of these materials can be amplified to produce high force, high stroke actuators. In a hybrid hydraulic pump, the motion of an active material is used to pressurize a hydraulic fluid. Since the properties of active materials vary greatly in terms of free strain and block force, there is a need to identify the optimum active material for a particular application. This study compares four active materials, Lead—Zirconate—Titanate (PZT), Lead—Magnesium—Niobate (PMN), Terfenol-D and Galfenol, as the drivers of a hybrid hydraulic actuation system. The performance of each of these active materials has been evaluated in the same hydraulic actuator through systematic testing of the actuator while maintaining the same length and volume for each active material. In each case, the active material has a length of around 54 mm and a cross-sectional area of 25 mm2. Commonly used metrics such as output power and electromechanical efficiency are used for comparison. Of the four materials tested in this study, PMN presented the largest free strain (2000 με), while Galfenol presented the least (300 με). The highest no-load velocity is also exhibited by the PMN-based actuator (270 mm/s). The maximum output power obtained is 2.5 W for both PMN and Terfenol-D-based actuators while the highest electromechanical efficiency obtained is 7% for the PMN-based actuator.

A Magnetorheological Piezohydraulic Actuator

Magnetorheological (MR) fluids can be used in a variety of smart semiactive systems. The MR damper shows an especially great potential to mitigate environmentally induced vibration and shocks. Another aspect of MR fluids is the construction of MR valve networks in conjunction with a hydraulic pump resulting in a fully active actuator. These devices are simple, have few moving parts, and can be easily miniaturized to provide a compact, high energy density pressure source. The present study describes a prototype MR-piezo hybrid actuator that combines the piezopump and MR valve actuator concepts, resulting in a self-contained hydraulic actuation device without active electromechanical valves. Durability and miniaturization of the hybrid device are major advantages due to its low part count and few moving parts. An additional advantage is the ability to use the MR valve network in the actuator to achieve controllable damping. The design, construction, and testing of a prototype MR-piezo hybrid actuator is described. The performance and efficiency of the device is derived using ideal, Bingham plastic and biviscous representations of MR valve behavior, and is evaluated with experimental measurements. This study seeks to provide a design tool to develop an actuator for a specific application.

Investigation of the Dynamic Characteristics of a Piezohydraulic Actuator

A piezohydraulic actuator is a hybrid device consisting of a hydraulic pump driven by piezo stacks, that is coupled to a conventional hydraulic cylinder via a set of fast-acting valves. Because the performance of the actuator is strongly related to the pumping frequency, a good understanding of the dynamics of the system is essential for designing a high-efficiency actuator. This article describes the development of a frequency domain model to quantify the dynamics of a piezohydraulic hybrid actuator. The analysis treats the hydraulic circuit as a series of fluid transmission lines, each represented by a transfer matrix that determines the relationship between the pressure and velocity at the inlet and at the outlet. The model includes the effects of fluid compressibility, inertia and viscosity. An experimental procedure to measure the frequency response of the device is described, and is used to validate the analysis. The effect of tubing length and fluid viscosity on the dynamic characteristics of the system is investigated. Longer tubing lengths result in lower resonant frequencies of the system, while increasing fluid viscosity results in a decrease in the magnitude of the resonant peak.

Hover Performance of a Cycloidal Rotor for a Micro Air Vehicle

In recent years, interest has been growing in a new class of very small flight vehicles called micro air vehicles (MAVs). Hover capability is highly desirable with respect to the mission requirements of these vehicles. Due to the small size of MAVs and the low Reynolds number regime in which they operate, scaling down conventional rotorcraft configurations to the MAV scale may not yield optimum performance. Unconventional vehicle configurations can be explored to realize high endurance hover capable MAVs. This paper investigates the hover performance of a small-scale cycloidal rotor to determine its viability for use in a micro air vehicle. A 6 inch diameter prototype rotor was constructed and tested to determine the effects of number of blades, blade pitch angle, and rotational speed on thrust output and power requirements. Pressure distribution was measured to obtain insight into the downwash and flow through the rotor. An analytical model, using a combination of vertical axis wind turbine theory and an indicial solution for the aerodynamic response was developed to predict rotor performance, and was validated with the experiments. The performance of the cycloidal rotor was compared to that of a conventional rotor of the same diameter in terms of power loading. Based on the analytical model and the experimental results, a conceptual design of an MAV utilizing cycloidal propulsion was developed. The conceptual cyclo-MAV utilizes two cycloidal rotors, providing thrust, propulsion, and control. Complete vehicle weight is envisaged to be 240 g, with two three-bladed rotors of six inches diameter.

Development of a compact piezoelectric-hydraulic hybrid actuator

This paper describes the development of a compact hybrid hydraulic actuation system as a potentially high-authority compact actuator for various applications including actuation of the trailing edge flap of a smart rotor system. The actuation system is divided into two parts, a pump driven by piezostack actuators and an output hydraulic actuator. The present work focuses on the design, analysis and testing of the pump. Analytical models are developed for various elements of the system. Operating the piezostacks at a frequency of up to 250 Hz over a period of five minutes, the pump generated a maximum pressure rise of 180 psi, displacing approximately 100 ml of hydraulic fluid in the process. A maximum temperature of 55 degree(s)C was measured on the piezostack.

Fundamental Understanding of Piezoelectric Strain Sensors

This paper investigates the behavior of piezoelectric elements as strain sensors. Strain is measured in terms of the charge generated by the element as a result of the direct piezoelectric effect. Strains from piezoceramic and piezofilm sensors are compared with strains from a conventional foil strain gage and the advantages of each type of sensor are discussed, along with their limitations. The sensors are surface bonded and are calibrated by means of a dynamic beam bending setup over a frequency range of 5 - 500 Hz. Correction factors to account for transverse strain and shear lag effects due to the bond layer are analytically derived and validated experimentally. Additionally, design of signal conditioning electronics to collect the signals from the piezoelectric sensors is addressed. The superior performance of piezoelectric sensors compared to conventional strain gages in terms of sensitivity and signal to noise ratio is demonstrated.