A Hybrid Master-Slave Genetic Algorithm-Neural Network Approach for Modeling a Piezoelectric Actuator

This work presents an approach for developing the model of a smart fin dynamics that is activated by a fully-enclosed piezoelectric (PZT) bimorph actuator, which is created by bonding two Macro Fiber Composites (MFCs). Observing the dynamics of the fin indicates that the use of a linear dynamic model does not adequately describe its behavior. An earlier work proposed incorporating a proportional damping matrix as well as Bouc-Wen hysteresis model and backlash operators to create a more accurate model. However, the number of parameters describing the expanded model is large, which limits its use. Therefore, there is a need for a different approach for developing an alternative model of the fin. In this work, a hybrid master-slave Genetic Algorithm (GA)-Neural Network (NN) model is proposed to identify the optimal set of parameters for the damping matrix constants, the Bouc-Wen hysteresis model and the backlash operators. A total of nine sinusoidal input voltage cases that resemble a grid of three different amplitudes excited at three different frequencies are used to train and validate the model. Three input cases are considered for training the NN architecture, connection weights, bias weights and learning rules using GA. The NN consists of three layers: an input layer that has two nodes for the amplitude and the frequency of the input voltage, an output layer that has seven nodes for the backlash, hysteresis, and damping operators, and a hidden layer that is free to have any number of nodes between two and nine. The GA constantly performs natural selection of chromosomes that propagate best compilation of NN parameters. Simulation results show that the proposed model can predict the damping, hysteresis and backlash of the smart fin–actuator system under various operational conditions.

Piezoelectric Two Layer Plate for Position Stabilization

Numerous vibrating electromechanical systems miss a rigid connection to the inertial frame. An artificial inertial frame can be generated by a shaker which compensates for vibrations. In this paper we present an encapsulated and perforated unimorph bending plate for this purpose. As basis for system simulation and optimization a new 3-port multi domain network model was derived. An extension of the network allows the simulation of the acoustical behavior inside the capsule. Network parameters are determined using Finite Element simulations. The dynamic behavior of the network model agrees with the Finite Element simulation results up to the first resonance of the system. The network model was verified by measurements on a laboratory setup, too.

Analytical and Numerical Modelling of Shape Memory Alloy Negator Springs for Long-Stroke Constant-Force Actuators

This paper explores the merits of shape memory Negator springs as powering elements for solid state actuators. A Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbour. The unique characteristic of Negator springs is the nearly-constant force needed to unwind the strip for very large, theoretically infinite deflections. Moreover the flat shape, having a high area over volume ratio, grants improved bandwidth compared to any solution with solid wires or helical springs. The SMA material is modelled as elastic in austenitic range while an exponential continuum law is used to describe the martensitic behaviour. The mathematical model of the mechanical behaviour of SMA Negator springs is provided and their performances as active elements in constant-force, long-stroke actuators are assessed. The SMA Negator spring is also simulated in a commercial finite element software, ABAQUS, and its mechanical behaviour is estimated through FE analyses. The analytical and the numerical prediction are in good agreement, both in martensitic and in austenitic range.

Modelling of Mechanical Nonlinearity in an Electromagnetic Vibration Energy Harvester Using a Forced Duffing Equation

This work reports on the modelling and experimental validation of a bi-axial vibration energy harvesting approach that uses a permanent-magnet/ball-bearing arrangement and a wire-coil transducer. The harvester’s behaviour is modelled using a forced Duffing oscillator, and the primary first order steady state resonant solutions are found using the homotopy analysis method (or HAM). Solutions found are shown to compare well with measured bearing displacements and harvested output power, and are used to predict the wideband frequency response of this type of vibration energy harvester. A prototype harvesting arrangement produced a maximum output power of 12.9 mW from a 12 Hz, 500 milli-g (or 4.9 m/s2) rms excitation.

Load Monitoring of Aerospace Structures Using Micro-Electro-Mechanical Systems (MEMS)

The National Research Council of Canada has developed Structural Health Monitoring (SHM) test platforms for load and damage monitoring, sensor system testing and validation. One of the SHM platform consists of two 2.25 meter long, simple cantilever aluminium beams that provide a perfect scenario for evaluating the capability of a load monitoring system to measure bending, torsion and shear loads. In addition to static and quasi-static loading procedures, these structures can be fatigue loaded using a realistic aircraft usage spectrum while SHM and load monitoring systems are assessed for their performance and accuracy. In this study, Micro-Electro-Mechanical Systems (MEMS), consisting of triads of gyroscopes, accelerometers and magnetometers, were used to compute changes in angles at discrete stations along the structure. A Least Squares based algorithm was developed for polynomial fitting of the different data obtained from the MEMS installed in several spatial locations of the structure. The angles obtained from the MEMS sensors were fitted with a second, third and/or fourth order degree polynomial surface, enabling the calculation of displacements at every point. The use of a novel Kalman filter architecture was evaluated for an accurate angle and subsequent displacement estimation. The outputs of the newly developed algorithms were then compared to the displacements obtained from the Linear Variable Displacement Transducers (LVDT) connected to the structures. The determination of the best Least Squares based polynomial fit order enabled the application of derivative operators with enough accuracy to permit the calculation of strains along the structure. The calculated strain values were subsequently compared to the measurements obtained from reference strain gauges installed at different locations on the structure. This new approach for load monitoring was able to provide accurate estimates of applied strains and loads.

Control of Oscillations of a Wing Subjected to 3D Unsteady Subsonic Aerodynamic Loads Using Piezoelectric Actuators

In the recent years, using piezoelectric material as sensors and actuators has drawn significant attention in vibration analysis and control of structures. In the present paper, bonded piezoelectric sensors and actuators have been used to control the aeroelastic oscillations of a cantilever wing under the effects of three-dimensional unsteady subsonic aerodynamic loading. An aerodynamic model using a numerical panel method is developed and validated to calculate the three-dimensional unsteady aerodynamic loading and finite element formulation is applied to model the wing structure as a cantilever plate undergoing small transverse oscillations. The structural and aerodynamic models are combined to simulate the aeroelastic oscillations and interchange the data simultaneously. An active feedback control method to suppress the oscillations is presented and investigated. Finally, an analysis is performed to examine the effects of actuator placement on the wing surface in suppression of oscillations.

Investigations on the Amplitude-Dependent Damping Behavior of Superelastic Shape Memory Alloys

The nonlinear, hysteretic stress-strain characteristic of superelastic shape memory alloys (SMA) results in energy dissipation and therefore in high damping capacities. Due to the nonlinearity the damping capacity strongly depends on the amplitude of the applied excitation. In this work, a rheological non-smooth model is used to describe the principle behavior of superelastic SMA undergoing harmonic displacements. The equivalent mechanical model consists of a spring representing the elastic deformation of the superelastic SMA in austenitic and detwinned martensitic state. A friction element represents the stress plateaus for forward and backward transformation between austenitic and martensitic state. A constant force is applied to the system to generate an offset which shifts the hysteresis to positive force values. Two mechanical stops are implemented to describe the end of the stress plateaus and therefore correspond to the strain differences of the stress levels for forward and backward transformation. Thus, the system behavior is highly amplitude-dependent. A harmonic approximation of the force generated by the superelastic SMA element during one excitation period is calculated by applying the Harmonic Balance Method to the nonlinear force signal of the rheological model. In this context the Fourier coefficients are calculated by performing a piecewise integration of the force signal. The Integrals are being calculated for each steady interval. The equivalent stiffness and damping coefficients are given for this approximation as functions of excitation amplitude and the system parameters. Based on these results, the damping capacity of a superelastic shape memory element undergoing harmonic displacements is presented using an analytical expression for the damping ratio.

Solvent Induced Shape Memory Behaviour of Sulfonated Poly Ether Ether Ketone (SPEEK)

Shape memory polymers (SMPs) are a widely studied class of materials due to their numerous applications in various fields of engineering. They find applications in deployable structures, biomedical devices, adaptive optical devices, sensors and actuators, in textiles etc. Recent studies have shown shape memory behavior in many polymers. Sulfonated poly ether ether ketone (SPEEK) is an ionic polymer which is being extensively studied for its application in fuel cells as a Proton Exchange Membrane (PEM) polymer due to its relatively higher thermal and mechanical stability over other PEMs in addition to proton transport. Recent studies on a sulfonated ionomer, Nafion® which has only one broad reversible phase transition, can show tunable, multiple shape memory effects by deforming the polymer at different temperatures without compromising the shape fixity (Rf). This paper reports, for the first time, the swelling (in solvents) induced shape memory behavior observed in SPEEK. The study was motivated by the preliminary observations of the response of SPEEK to solvent stimulus. SPEEK samples of varying degrees of sulfonation (DS) were prepared by the sulfonation of poly ether ether ketone (PEEK). The shape fixation and recovery rates (Rr) of the polymer under different temperatures and solvent conditions are reported. A comparative study of the shape memory response of the material with varying DS was also carried out. We also report for the first time the potential use of the parallel plate geometry of a rheometer for estimating the force during the shape recovery process. Visual demonstration of the shape memory effect is carried out using solvents at different temperatures.

Wireless Vibration Sensing Without a Battery

This paper presents the implementation and characterization of a low power wireless vibration sensor that can be powered by a flash light. The wireless system consists of two components, namely the wireless sensor node and the wireless interrogation unit. The wireless sensor node includes a wireless strain gauge that consumes around 6 mW, a signal modulation circuit, and a light energy harvesting unit. To achieve ultra-low power consumption, the signal modulation circuit was implemented using a voltage-controlled oscillator (VCO) to convert the strain gauge output to an intermediate frequency (IF) signal, which is then used to alter the impedance of the sensor antenna and thus achieves amplitude modulation of the backscattered antenna signal. A generic solar panel with energy harvesting circuit is used to power the strain sensor node continuously. The wireless interrogation unit transmits the interrogation signal and receives the amplitude modulated antenna backscattering, which can be down-converted to recover the IF signal. In order to measure the strains dynamically, a Phase Lock Loop (PLL) circuit was implemented at the interrogator to track the frequency of the IF signal and provide a signal that is directly proportional to the measured strain. The system features ultra-low power consumption, complete wireless sensing, solar powering, and portability. The application of this low power wireless strain system for vibration measurement is demonstrated and characterized.

Tunable Band-Pass Filters Employing Stretchable Electronic Components

This paper describes some of the recent results of an ongoing U.S. Army research program examining the electronic behavior of hyperelastic stretchable capacitor, resistor, and inductor networks for which the conductor material employed is stretchable. As with traditional rigid analog components, stretchable electronic components exhibit frequency-dependant behavior. Unlike their rigid counterparts, stretchable electronic components may also exhibit dramatic strain-dependent behavior. In this way stretchable circuit networks may be viewed as controllable spatio-temporal filters. Resistance, capacitance, and inductance all change to varying degrees depending on the specific set of spatio-temporal inputs. These variations may be harnessed to create an adaptive circuit element that is controllable. This paper describes the results of integrating stretchable components into a tunable band-pass filter. Center frequency, bandwidth, and gain can be varied in a controllable way by varying the capacitance or resistance of specific circuit elements by stretching them. Biaxially stretchable components are described that are subjected to equibiaxial strain-states as high as 100% area strain. We examine the influence that the type of compliant conductor has on tunable circuit properties and on control authority.