High Frequency Excitation Signals Research Articles

Dynamic modeling of stack giant magnetostrictive actuator with magnetic equivalent network considering eddy current effect

Stack giant magnetostrictive actuators (SGMAs) are widely used in various fields for its merits such as saving the space and improving the evenness of the bias magnetic field provided for the giant magnetostrictive material (GMM). In this paper, based on the flow path of the magnetic flux in SGMA, a magnetic equivalent network corresponding to quasistatic conditions is proposed taking flux leakage and fringing effect into account. Meanwhile, complex reluctances of the GMM rods are introduced to describe the decrease and phase shift of magnetic field intensities caused by eddy current under high-frequency excitation signals. Furthermore, the magnetic equivalent network, determining the relationship between excitation signals and magnetic field intensities, is combined with the Jiles–Atherton model, nonlinear constitutive theory of GMM concerning multi-field coupling, and structural dynamics of SGMA so as to derive a multi-field coupling model predicting the tracking behaviors of SGMA to the excitation signals. Moreover, a finite element method is conducted, an SGMA prototype is fabricated, and an experimental platform is set up to verify the proposed model. Comparison between results derived from the magnetic equivalent network and those calculated by the finite element method indicates that the proposed network is able to predict the magnetic field distribution inside the SGMA prototype in quasistatic conditions; further comparison between results obtained from the proposed multi-field coupling model and those from experiments indicates that the model can accurately predict tracking behaviors of the SGMA prototype to the excitation signals.

A DSP-Based EIT System With Adaptive Boundary Voltage Acquisition

Electrical Impedance Tomography (EIT), a valuable technique modality for estimating electrical properties of an object by electrode measurements. During the measurement process, high-frequency excitation signal and the large dynamic range of boundary voltage both cause negative effects on system detection accuracy. Focusing on the induced signal detection, we proposed an adaptive boundary voltage acquisition method, which thoroughly modeled the EIT system by LTSPICE and MATLAB, dynamically adjusted the boundary voltage amplitude gain according to the induced signal voltage range, and changed sampling period for high frequency component of excitation signal. A DSP-based EIT hardware experimental platform under development was constructed, including a current source integrated direct digital synthesis and data acquisition circuit. The data acquisition circuit composed of programmable differential amplifier, low-pass filter and offset adjustment circuit is used for signal acquisition. Comparative experiments are systematically implemented for evaluating the proposed method. Quantitatively, the SNR difference of each measurement channel is reduced from 26.42dB to 6.33dB. The maximum SNR of the system can reach 60.67dB. The maximum image error (IE) is reduced from 28.17% to 15.60%. Accordingly, the proposed adaptive boundary voltage acquisition method is proved to be great beneficial to improve EIT system accuracy.

Experimental modelling and analysis of compact hydro-pneumatic interconnected suspension strut considering pneumatic thermodynamics and hydraulic inertial properties

Hysteresis properties exist in the Hydro-pneumatic interconnected suspension (HIS) system, which are mainly related to the gas state, inertial of hydraulic fluid in the long connection pipes and friction properties. The available model is normally simplified based on the ideal gas state equation and no hydraulic inertial assumption, and then cannot describe the dynamic properties of HIS strut accurately, which restricts the better application of HIS in different areas. In this study, the mathematical model of one kind of compact HIS strut integrating the gas chamber within the strut piston rod are proposed. The proposed model considers the gas state model described by ideal gas law with Energy Equation and the fluid inertial properties combined with laminar flow model across the connection pipes and seal frictions described by hyperbolic tangential hysteresis friction model, in which all the model parameters are identified through extensive experimental data. The validity of the proposed model has been verified through experimental under in-phase and out-of-phase harmonic excitations with different amplitudes and frequencies. The results show that the established model can not only describe the fundamental properties (force–displacement/velocity) with good accuracy, but predict the hysteresis phenomenon and frequency dependency property associated with both the gas pressure–displacement characteristic related to the heat transfer and the pressure-flow rate property between connection pipes related to the inertial of fluid flow reasonably well. The result also reveals that the effect of fluid inertial to the dynamic properties of the HIS strut is significant, which may make the stiffness performance worse under both in-phase and out-of-phase excitations especially high frequency excitation signals.

New Schemes for GPS-Denied Source Localization Using a Nonholonomic Unicycle

Inspired by the extremum seeking (ES) algorithm, new approaches for source localization in global positioning system denied environments are presented using a nonholonomic unicycle. Existing ES-based schemes apply an excitation signal that causes difficulties in the analysis and performance of the unicycle. The aim of this brief is to develop schemes without employing any excitation signal. To this end, two control schemes are developed for tuning the forward and angular velocities of the unicycle. The first scheme only tunes the forward velocity and is based on the conventional form of ES. In this form, a high-frequency excitation signal (dither) is employed to find the gradient of an unknown function that is optimized. The proposed scheme benefits from the fact that the dither part already exists in the unicycle model. The second scheme only tunes the angular velocity and is based on the recently developed form of ES. In this form, the function that is optimized appears as the argument of a sine/cosine function. The presented scheme takes the advantage from the fact that the sine/cosine function of this form of ES already exists in the vehicle model. Both schemes are structurally simple and significantly improve the unicycle motion. A stability analysis of the schemes is carried out using the averaging theory and their performances are illustrated through carefully studied simulation examples.

Nonlinear Observability Analysis of Micro-machined Electrostatic Actuators Using Self-Sensing

Micro-machined electrostatic actuators (MEA) like parallel plate actuators (PPAs) and comb drive actuators (GCAs) are commonly used in many applications, including gyroscopes, resonators and RF switches. The detection of an actuators' mechanical motion is desired when they are combined with feedback control techniques, especially when the application requires high performance or is affected by disturbances. The motion can be detected by a variety of sensing techniques, including capacitive, piezoresistive and optical. Electrostatic parallel plate actuators can be modeled as a type of variable capacitor, which depends on the gap between a fixed electrode and a movable electrode. Thus, the displacement of the actuator can be obtained by measuring the capacitance. However, this practical method often requires high frequency excitation signal sources or additional sensing structures. The excitation power source not only affects the performance in the actuator's steady state, but it may also generate harmonics that distort the measurement signals due to the nonlinear characteristics of the actuator. In addition, the information about velocity may not be obtained without specific sensing structures. The additional structures occupy more space in each die, which could increase the cost and size, or decrease the performance. In this study, an estimator with a series resistor configuration is proposed. The estimator can estimate the displacement and velocity by measuring the voltage of the power supply and the voltage across the actuator itself. To evaluate the feasibility, a nonlinear observability analysis is applied. The analysis shows the observability index among different system states. A simulation study verified the proposed theories.

Research on Mechanical Design with Design and Implement of High-Frequency Excitation Signal Source in Eddy Current Testing

How to control the stability of the electrical and mechanical system is the most important content in the study of mechanical and electrical design. This paper studies the design and implement of high-frequency eddy current testing excitation source system. Design of a high-frequency signal generating equipment based on MCU, DDS technology and transistor power amplifier technology. The equipment can be used to generate a stable signal with the frequency below 10MHz. It has some characteristics included adjustable frequency, stable output of frequency and amplitude. It can greatly improve the accuracy and efficiency of detection of the eddy current testing system.

Robust Piezo Impedance Magnitude Measurement Method

Piezo impedance spectroscopy is widely used in structural health monitoring (SHM) applications. Purpose of the research was tofind most robust and cheap method for impedance magnitude measurement. Proposed system consists of analog front end (AFE), signalsynthesizer and microcontroller unit. AFE enables to use low sampling rate, while using high frequency excitation signal. Proposedsystem uses chirp excitation signal in 20kHz- 600kHz frequency range. Results were compared against measurements made withcommercial impedance analyzer. Results show great potential for this method in SHM applications. Ill. 6, bibl. 10 (in English; abstractsin English and Lithuanian). http://dx.doi.org/10.5755/j01.eee.113.7.623

Spectral Element Modelling of Wave Propagation and Impedance Based SHM Systems

In recent years many SHM approaches based on elastic waves that are generated and sensed by surface-bonded piezoelectric patches have been developed. Some of those utilize wave propagation phenomena; others use changes in the electromechanical impedance to detect structural damage. The capability of most approaches strongly depends on adequate choice of SHM system parameters like excitation signals and actuator/sensor types and positions. For this reason there is a growing interest in efficient and accurate simulation tools to shorten time and cost of the necessary tedious pretests. To detect small damage generally high frequency excitation signals have to be used. Because of this a very dense finite element mesh is required for an accurate simulation. As a consequence a conventional finite element simulation becomes computationally inefficient. A new approach that seems to be more promising is the time domain spectral element method. This contribution presents the theoretical background and some results of numerical calculations of the propagation of waves. The simulation is performed using the spectral element method (SEM), which leads to a diagonal mass matrix. Besides a significant saving of memory this leads to a crucial reduction of complexity of the time integration algorithm for the wave propagation calculation. A new approach to simulate the E/M impedance using time domain spectral elements is shown. An example demonstrates a good correlation of simulation and measurement data, so that the proposed simulation methodology seems to be a promising tool to make impedance based SHM systems more efficient, especially regarding the necessary parameter studies.

An LVDT-based self-actuating displacement transducer

A novel linear actuator with inherent sensing capabilities is developed from a linear variable differential transformer (LVDT). By superposition of dc currents upon high-frequency excitation signals, the coils of the LVDT are capable of exerting a push/pull force on the armature while retaining the original displacement-sensing function. LC resonant circuits and active bandpass filters are designed to effectively isolate the sensing signals from the dc energizing sources. Linearity and sensitivity of the device are largely preserved compared to the original LVDT. For actuation, it is found that the magnetic force on the armature can be maximized by energizing a specific combination of the three coils according to armature positions. A simple control algorithm is developed for closed-loop control. It is implemented with an 8-bit microcomputer. Real-time testing shows that rest-to-rest control can be achieved with positioning errors of 0.02–0.04 mm and settling time below 0.2 s.