Frederick T. Calkins

Bio: Frederick T. Calkins is an academic researcher from Iowa State University. The author has contributed to research in topics: Transducer & Terfenol-D. The author has an hindex of 10, co-authored 10 publications receiving 412 citations. Previous affiliations of Frederick T. Calkins include Boeing Phantom Works.

Overview of Magnetostrictive Sensor Technology

Abstract: As sensors become integrated in more applications, interest in magnetostrictive sensor technology has blossomed. Magnetostrictive sensors take advantage of the efficient coupling between the elastic and magnetic states of a material to facilitate sensing a quantity of interest. Magnetic and magnetostrictive theory pertinent to magnetostrictive sensor technology is provided. Sensing configurations are based on the utilization of a magnetostrictive element in a passive, active, or combined mode. Magnetostrictive sensor configurations that measure motion, stress or force, torque, magnetic fields, target characteristics, and miscellaneous effects are discussed. The configurations are compared and contrasted in terms of application, sensitivity, and implementation issues. Comparisons are made to other common sensor configurations as appropriate. Experimental and modeling results are described when available and schematics of the configurations are presented.

Effect of prestress on the dynamic performace of a Terfenol-D transducer

Abstract: The performance of magnetostrictive Terfenol-D is highly dependent on the state of the material and in particular on the mechanical prestress. This paper presents an experimental investigation of the effect of prestress on the dynamic performance of a Terfenol-D transducer. The effects of both prestress and magnetic bias on the near dc transducer performance are also presented. Experimental results demonstrate the sensitivity of the transducer performance in terms of strain, strain rate with applied field, and material properties to relatively small changes in initial mechanical prestress. Trends in material properties, Young's Modulus, magnetomechanical coupling factor, permeability, dynamic strain coefficient, and mechanical quality factor with prestress and drive level are developed. In addition, the effect of magnetic bias and frequency of operation on the strain at different applied fields are examined and shown to significantly influence transducer output at a given prestress level. For the transducer as operated in this study, including the appropriate magnetic bias, both the magnetomechanical coupling and the strain coefficient are optimized with a prestress of 1.0 to 1.25 ksi.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Statistical Analysis of Terfenol-D Material Properties:

Abstract: This article focuses on the characterization of Terfenol-D material properties under magnetic bias, mechanical preloads, AC drive fields, frequencies of operation, and mechanical loads typical of many dynamic transducer applications. These are test conditions unlike those in most Terfenol-D characterization studies. The article also provides an explanation for prior experimental studies which suggest that significant variation in material properties are expected in Terfenol-D elements subjected to repeated tests under fixed operating conditions. Through a statistical framework for the design of experiments and data analysis, we conducted repeatability tests which demonstrate that such variations are likely to be due to imperfect control of the magnetic bias and mechanical preload from test to test, and not to intrinsic material behavior. Frequency response measurements from near DC to past the test transducer's fundamental frequency were combined with classical electroacoustics theory to determine the fun...

Overview of magnetostrictive sensor technology

Abstract: As sensors become integrated in more applications, interest in magnetostrictive sensor technology has blossomed. Magnetostrictive sensors take advantage of the efficient coupling between the elastic and magnetic states of a material to facilitate sensing a quantity of interest. Magnetic and magnetostrictive theory pertinent to magnetostrictive sensor technology is provided. Sensing configurations are based on the utilization of a magnetostrictive element in a passive, active, or combined mode. Magnetostrictive sensor configurations that measure motion, stress or force, torque, magnetic fields, target characteristics, and miscellaneous effects are discussed. The configurations are compared and contrasted in terms of application, sensitivity, and implementation issues. Comparisons are made to other common sensor configurations as appropriate. Experimental and modeling results are described when available and schematics of the configurations are presented.

High Bandwidth Tunability in a Smart Vibration Absorber

Abstract: An electrically tunable vibration absorber based on the strong ΔE effect of Terfenol-D has been developed. A general description of tuned vibration absorbers is presented along with a description of the magnetostrictive effects that make an electrically tunable Terfenol-D vibration aborber function. It is emphasized that the large modulus changes achievable with the proposed magnetostrictive vibration absorber arise as a consequence of the stiffening of the crystal lattice as the magnetic field is increased from the demagnetized state to magnetic saturation. This is in contrast to the small modulus changes often reported in the literature which are achieved by operating smart materials between their open- and short-circuit states. Experimental results are presented that show agreement with prior art and demonstrate control of a magnetostrictive actuator resonant frequency between 1375 Hz and 2010 Hz by electrically varying the elastic modulus of a magnetostrictive material. This operating principle is then implemented to obtain high bandwidth tunability in a Terfenol-D vibration absorber.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Design and application of magnetostrictive materials

Abstract: Magnetostriction is the change in shape of materials under the influence of an external magnetic field. The cause of magnetostriction change in length is the result of the rotation of small magnetic domains. This rotation and re-orientation causes internal strains in the material structure. The strains in the structure lead to the stretching (in the case of positive magnetostriction) of the material in the direction of the magnetic field. During this stretching process the cross-section is reduced in a way that the volume is kept nearly constant. The size of the volume change is so small that it can be neglected under normal operating conditions. Applying a stronger field leads to stronger and more definite re-orientation of more and more domains in the direction of magnetic field. When all the magnetic domains have become aligned with the magnetic field the saturation point has been achieved. This paper presents the state of the art of the magnetostrictive materials and their applications such as: Reaction Mass Actuator, A standard Terfenol-D Actuator, Linear Motor Based on Terfenol-D (Worm Motor), Terfenol-D in Sonar Transducers, Terfenol-D Wireless Rotational Motor, Terfenol-D Electro-Hydraulic Actuator, Wireless Linear Micro-Motor, Magnetostrictive Film Applications, Magnetostrictive Contactless Torque Sensors and many other applications. The study shows that excellent features can be obtained by Magnetostrictive materials for many advanced applications.

Development of an adaptive tuned vibration absorber with magnetorheological elastomer

Abstract: In this technical note we develop an adaptive tuned vibration absorber (ATVA) based on the unique characteristics of magnetorheological elastomers (MREs), whose modulus can be controlled by an applied magnetic field. The MRE used in the developed ATVA was prepared by curing a mixture of 704 silicon rubber, carbonyl iron particles and a small amount of silicone oil under a magnetic field. The ATVA works in shear mode and consists of an oscillator, smart spring elements with MREs, a magnet conductor and two coils. Natural frequencies of the ATVA under different magnetic fields were both theoretically analyzed and experimentally evaluated by employing a beam structure with two ends supported. The experimental results demonstrated that the natural frequency of the ATVA can be tuned from 55 to 82 Hz. The relative frequency change is as high as 147%. Furthermore, the absorption capacity of the developed ATVA can achieve as high as 60 dB, which was also experimentally justified.

Magnetorheological elastomers in tunable vibration absorbers

Abstract: Filling an elastomeric material with magnetizable particles leads to mechanical properties -shear moduli, tensile moduli, and magnetostriction coefficients - that are reversibly and rapidly controllable by an applied magnetic field. The origin of the field dependence of these properties is the existence of field-induced dipole magnetic forces between the particles. These 'smart' composites, which are sometimes termed magnetorheological (MR) elastomers, have been explored for use in a number of components, including automotive suspension bushings. In these and other applications, the tunability of the stiffness can enhance the compliance-control or vibration-transfer performance of the complex mechanical systems in which they are used. In the present study, we have constructed a simple one-degree-of-freedom mass-spring system - an adaptive tuned vibration absorber - that utilizes MR elastomers as variable-spring-rate elements. This device was used not only to explore the performance of such tunable components, but also to extend measurements of the shear moduli of these materials to higher frequencies than has previously been reported. We find that the field-induced increase in moduli of these materials is effective to mechanical frequencies well above 1 kHz, and that the moduli are consistent with the behavior expected for filled elastomers.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.