Uwe Marschner

Passive Wireless Resonant Galfenol Sensor for Osteosynthesis Plate Bending Measurement

The healing process of bone fractures can be monitored by a measurement of the osteosynthesis plate bending. For this purpose a wireless magnetostrictive bending sensor is proposed. A planar rectangular coil on top of a magnetostrictive Galfenol ( alloy) layer forms an electrical resonant circuit. The sensor is manufactured in thin film technology. Coil turns were electrodeposited by pattern plating. Sensors with overall dimensions of (13 2 0.5) mm were manufactured with varied turn numbers showing self-resonance frequencies from 5 to 50 MHz. Examined sensors possess linear frequency-force characteristic up to 6 N with frequency shifts of 6 kHz . In order to obtain the sensor resonance frequency wirelessly, several measurement techniques were employed using inductively coupled coils. Frequency domain measurements have been carried out by employing a network analyzer with a single detection coil and a lock-in amplifier with separate coils for excitation and detection. In time domain measurements, two coils for transmission and reception are used. In the transmit case a short sine pulse excites the sensor and afterwards its decaying response signal is received. To determine the resonance frequency, a frequency counting, Fourier or wavelet technique can be used. By integrating additional cores of high permeability into sensor and detection coil, measurement ranges can be increased.

Indirect Measurement of a Bar Magnet Position Using a Hall Sensor Array

The measured magnetic induction field of a bar magnet can be used to compute or measure indirectly the position of the magnet. A model-based parameter estimation approach requires a precise induction field model and knowledge of the model error. In this paper, different analytic models describing the axial component of the induction field in front of a small cylindrical bar magnet are compared with Hall sensor array measurements and finite-element simulations. The used solenoid model matched the finite-element method simulations but requires a high numerical effort. The approximate dipole model is suitable when a proposed correction function for the estimated distance is applied and current and position are estimated simultaneously

Local Parameter Estimation Performed by Tailor-Made Microsystems

Abstract In this paper practical investigations are presented toward a microsystem which is able to store a static nonlinear process model and to perform nonlinear parameter estimation. The implementation of a gradient-free and a gradient and Hessian calculating nonlinear multidimensional minimization algorithm are compared based on an example process and criteria like processing time needed for one iteration, number of iterations and robustness

Combining network models and FE-models for the simulation of electromechanical systems

The combination of Network Methods and Finite Element Methods on user level is a time-efficient method for the simulation of dynamic behavior of electromechanical systems. Combined simulation can be structured into five areas of application: determination of network structures with FE-simulations, determination of network parameters with FEsimulations, inclusion of network elements in FE-models, inclusion of equivalent network structures in FE-models and simulation of models incorporating different model levels. The capabilities of the combined simulation are demonstrated by sample applications. Combined Simulation is suited for a better system insight and fast simulation-based optimization.

Preliminary Galfenol vibratory gyro-sensor design

This paper presents a prototype micro-gyro sensor design that employs the new magnetostrictive alloy GalFeNOL for transduction of Coriolis induced forces into an electrical output. The concept takes advantage of the principles employed in vibratory gyro sensors and the ductile attributes of GalFeNOL to target high sensitivity and shock tolerance in a miniature gyro sensor. In this study, preliminary test results are presented as concept verification with a meso-scale tuning fork vibratory gyro sensor.

Detection coil independent frequency domain measurements for an inductively coupled resonant magnetoelastic bending sensor

Inductively coupled resonant sensors (ICR) are a class of wireless, passive sensors which can be used to monitor environmental parameters. Thereby a measurand alters the sensor resonance frequency through an inductance, capacitance and/or resistance change. When performing frequency domain measurements with a detection coil its parasitic capacitance and coupling factor influence onto the evaluated sensor resonance frequency are usually neglected, which leads to an additional measurement uncertainty. Analytical circuit analysis shows, that the transformed sensor impedance can be extracted from the detection coil frequency response function by a calibration scheme, which removes this influence and provides the true sensor resonance frequency. This technique allows a detection coil to be tuned to the sensor resonance frequency, increasing the detection range. By evaluating multiple frequency response characteristics additional sensor parameters can be estimated, such as its resistance, mutual inductance and either inductance or capacitance by providing one a priori known static quantity.

Equivalent Circuit of a Piezomagnetic Unimorph Incorporating Single-Crystal Galfenol

In this paper, the reversible transducer properties of a piezomagnetic unimorph are investigated experimentally and aggregated in a linear equivalent circuit. The unimorph consists of a single-crystal Galfenol plate, which is mounted to an aluminum plate. Such two-layer piezomagnetic elements are used in bending actuators or sensors. The completed two-port model of the transducer describes the dynamic behavior in sensing, as well as actuation direction, and includes the magnetomechanical interaction. The coupling of the transducer with a solenoid and demagnetization are considered. A circuit simulator can be used to investigate efficiently the dynamic behavior of the system, and circuit theory can be applied to analyze and simplify the equivalent circuit model.

Electromagnetic Network Models of Planar Coils on a Thin or Thick Magnetic Layer

A method is presented to determine the magnetic reluctance of a thin or a thick magnetic layer of permeability ¿ underneath a planar coil based on inductance measurements. The procedure is substantiated on the basis of the linear electromagnetic network model. The influence of the involved magnetic reluctances on the inductance is analyzed by a transformation into the electrical domain applying linear network theory. From inductance measurements the individual contributing inductances can be calculated and from the back transformation into the magnetic domain the reluctances and further parameters, such as the magnetic field strength for a given electrical current or the permeability. Analytical results are compared with FEM simulations and with measurements obtained from a magnetostrictive bending sensor.

A new imaging approach for in situ and ex situ inspections of conductive fiber–reinforced composites by magnetic induction tomography

Fiber-reinforced plastics for industrial applications face constantly increasing demands regarding efficiency, reliability, and economy. Furthermore, it was shown that fiber-reinforced plastics with tailored reinforcements are superior to metallic or monolithic materials. However, a trustworthy description of the load-specific failure behavior and damage evolution of composite structures can hardly be given, because these processes are very complex and are still not entirely understood. Among other things, several research groups have shown that material damages like fiber fracture, delamination, matrix cracking, or flaws can be discovered by analyzing the electrical properties of conductive composites, for example, carbon fiber–reinforced plastics. Furthermore, it was shown that this method could be used for structural health monitoring or nondestructive evaluation. Within this study, magnetic induction tomography, which is a new imaging approach, is introduced in the topic of nondestructive evaluation of carbon fiber–reinforced plastics. This non-contacting imaging method gains the inner spatial distribution of conductivity of a specimen and depicts material inhomogeneity, like damages, not only in two-dimensional images but also in three-dimensional images. Numerical and experimental investigations are presented, which give a first impression of the performance of this technique. It is demonstrated that magnetic induction tomography is a promising approach for nondestructive evaluation. Potentially, it can be used for fabrication quality control of conductive fiber–reinforced plastics and as a structural health monitoring system using an integrated or superficially applied magnetic induction tomography setup.

Galfenol resonant sensor for indirect wireless osteosynthesis plate bending measurements

The healing process of bone fractures can be monitored by a measurement of the osteosynthesis plate bending. An electrical resonant circuit consisting of a coil with a magnetostrictive Galfenol core and a capacitance enables an indirect wireless measurement of the plate bending. The Galfenol core is manufactured with a thin film technology using a Galfenol Fe83Ga17 alloy. The sensor has a quit good linear resonant frequency-force characteristic. Both, time and frequency domain measurement techniques for the sensor, use an external measurement coil. In the frequency domain the transformed sensor impedance is evaluated and the resonance frequency is determined by a local extremum. In the time domain a short energizing sinus pulse is transmitted, the sensor response is received and a frequency counting, Fourier or Wavelet technique is used for resonance frequency detection.