Magnetic Shape Memory Actuators Research Articles

A Design Approach for a Valve Based on a Magnetic Shape Memory Actuator

With the motivation to meet the increasing requirements on fast-switching pneumatic valves, Magnetic Shape Memory alloys (MSM) are considered as a promising alternative to conventional actuators. Regarding the desired strokes, forces and actuation frequencies MSM alloys meet the requirements best among other solid-state transducers for valve applications. However, the hysteresis in the magneto-mechanical behavior is challenging during the sizing process of a component based on an MSM actuator. It has proved to be valuable to apply a system simulation including a lumped element model of the MSM element in the early design phase. In this contribution, a design approach for the valve based on an MSM actuator is shown. A system network model was used to design a functional prototype of the valve to achieve the specifications defined within a requirements analysis. These specifications were derived from characteristic features of conventional established fast-switching pneumatic valve. The analysis of the subsystems was done to exploit the deviations and their influences on the system behavior. Furthermore, the experimental research of the functional prototype of the valve was carried out to check for functionality and to evaluate whether the specifications were met. A nominal volume flow of 120 Nl/min was reached at a supply Voltage U of 48;{text{V}} and current i of 7.6;{text{A}} which exceeds the aim of 100 Nl/min. By means of an optimization of the actuators geometry the response time could be reduced to less than 1;{text{ms}}. The desired maximum modular dimension of 9 mm was not achieved by the functional prototype due to the available production process, but would be feasible with series production.

Variability of Twin Boundary Velocities in 10M Ni–Mn–Ga Measured Under $$\upmu{\text{s}}$$-Scale Force Pulses

Twin boundary motion is the basic mechanism responsible for fast actuation of magnetic shape memory (MSM) alloys. Previous studies implied on a wide diversity of twin boundary velocities measured under similar conditions. Here, a data set of more than 400 velocity values is measured under conditions that are relevant for MSM applications and represents the dynamic behavior of 73 twin boundaries. Velocities are measured using an electro-mechanical setup that applies a controllable $$\upmu{\text{s}}$$ -scale force pulse and combines force measurements with high-speed imaging. The latter allows extracting velocities of individual twin boundaries, which are then correlated to the macroscopic stress in the sample. The appearance of type I twins is more prevalent than type II, resulting a much larger data set for type I twins. Statistical analysis of velocity points of type I twins reveals an increasing trend of the velocity with the macroscopic stress, as well as useful information on the probability distribution of velocity data. Velocities of type II twins exhibit large variability over a relatively narrow stress range. This can reason the large differences in maximal velocities reported previously for this twin type. The obtained statistical data can improve the design and modeling of MSM actuators.

Next Generation Autofocus and Optical Image Stabilization System for Camera Modules Using Magnetic Shape Memory Actuators

Currently, camera modules are used in a wide range of applications ranging from micropo-sitioning actuator systems used in smartphones to larger modules used in stationary cameras, CCTV, and others. Modern camera modules are required to perform positioning functions to improve the stability and quality of captured images. These functions mainly include the autofocus (AF) and optical image stabilization (OIS) functions. Traditionally, separate actuators and sensors are used for AF and OIS, each contributing towards energy consumption, module size, and manufacturing costs. This is particularly disadvantageous in the case of smartphones owing to their inherent space and battery charge limitations. This paper presents a novel Magnetic Shape Memory (MSM) actuator system that combines the AF and OIS functions, which are performed using two actuators; thus, this system is a simple, compact, and cost-effective solution to the drawbacks of conventional technology. Furthermore, the smart properties of MSM alloys reduce the energy consumption of these systems through the utilization of their inherent holding forces and the associated shape memory effect. The realization of AF and OIS functions is discussed and verified experimentally for the proposed actuator system using data obtained from a fabricated prototype.

Giant magnetic-field-induced strain in Ni-Mn-Ga micropillars

We report on the observation of fully reversible magnetic-field-induced strain of 6% in a single-crystalline micropillar fabricated from a bulk Ni50Mn28.5Ga21.5 single crystal. Xe plasma source focused ion beam column milling technology was used to machine 50 × 50 × 100 μm3 cuboid pillars. The removal of about 2 μm of ion-beam-damaged surface layer enabled magnetic field actuation in pillars. Our results demonstrate the feasibility of manufacturing of micrometre-sized magnetic shape memory actuators by focused ion beam technique.

Study of magnetic field distribution in anisotropic single twin-boundary magnetic shape memory (MSM) element in actuators

Magnetic shape memory effect exhibited by certain alloys at room temperature is known for almost 20 years. The most studied MSM alloys are Ni-Mn-Ga alloys which exhibit up to 12% magnetic field-induced strain (change in shape) depending on microstructure. A multibillion cycle operation without malfunction along with their “smart” properties make them very promising for application in electromagnetic (EM) actuators and sensors. However, considerable twinning stress of MSM crystals resulting in magneto-mechanical hysteresis decreases the efficiency and output force of MSM actuators. Whereas twinning stress of conventional MSM crystals has been significantly decreased over the years, novel crystals with Type II twin boundaries (TBs) possess even lower twinning stress. Unfortunately, the microstructure of MSM crystals with very low twinning stress tends to be unstable leading to their rapid crack growth. Whilst this phenomenon has been studied experimentally, the magnetic field distribution in anisotropic single twin-boundary MSM elements has not been considered yet. This paper analyses the magnetic field distribution in two-variant single twin-boundary MSM elements and discusses its effects on magnetic field-induced stress acting on the twin boundary.

Electromagnetic and Thermal Analyses of High-Performance Magnetic Shape Memory Actuators for Valve Applications

Magnetic shape memory (MSM) alloys are relatively new smart alloys, which have enormous potential to be used in actuators, sensors, and other electrical devices. Their large strain and considerable stress output can be controlled by magnetic fields or mechanical stresses. Maximum magnetic field-induced strain varies from 6% to 12% of the MSM element’s length depending on its microstructure. However, very low operational temperature limit is one of the main drawbacks of conventional MSM alloys. This makes their application in high-performance actuators challenging due to considerable power losses. This paper discusses different MSM actuator designs, optimized particularly for large force output for pneumatic electromagnetic valve applications. The thermal problem is addressed through analyzing the heat transfer conditions of each particular design and the effects of different cooling systems. An energy-efficient operating cycle for varying actuator loads that takes advantage of the shape memory effect is also proposed. This allows the minimization of energy losses, resulting in an acceptable increase in the temperature ensuring stable continuous actuation.

Tracking Control of a Magnetic Shape Memory Actuator Using an Inverse Preisach Model with Modified Fuzzy Sliding Mode Control.

Magnetic shape memory (MSM) alloys are a new class of smart materials with extraordinary strains up to 12% and frequencies in the range of 1 to 2 kHz. The MSM actuator is a potential device which can achieve high performance electromagnetic actuation by using the properties of MSM alloys. However, significant non-linear hysteresis behavior is a significant barrier to control the MSM actuator. In this paper, the Preisach model was used, by capturing experiments from different input signals and output responses, to model the hysteresis of MSM actuator, and the inverse Preisach model, as a feedforward control, provided compensational signals to the MSM actuator to linearize the hysteresis non-linearity. The control strategy for path tracking combined the hysteresis compensator and the modified fuzzy sliding mode control (MFSMC) which served as a path controller. Based on the experimental results, it was verified that a tracking error in the order of micrometers was achieved.

Review of properties of magnetic shape memory (MSM) alloys and MSM actuator designs

Magnetic shape memory alloys are a new group of "smart" materials that exhibit large strain of 6-12% when subjected to magnetic fields. This indicates their enormous potential to be used in different electromagnetic (EM) devices such as actuators, sensors, energy harvesters and dampers. Shape change in MSM materials is controlled by magnetic field and doesn't involve phase transformation, allowing it to overcome a number of disadvantages of conventional shape memory alloys (SMAs). MSM devices are capable of producing large force and stroke output in considerably small dimensions. At the same time they can have fast response and potentially very long lifetime. This paper discusses different modern designs and approaches to MSM actuator design with their advantages and disadvantages. An overview on characteristics of MSM alloys is also presented in order to highlight how different properties of the material influence the total output of a device.

Over 7% magnetic field-induced strain in a Ni-Mn-Ga five-layered martensite

A Ni-Mn-Ga single crystal with a modulated five-layered martensite structure is reported, demonstrating giant magnetic field induced strain (MFIS) of 7.1% at room temperature and of 6% at temperatures close to the austenite transformation (TA = 71 °C). The room temperature MFIS clearly exceeds the best results of around 6% measured earlier in 10M martensites. The larger MFIS is connected to the huge (>1%) change in the lattice distortion of the 10M structure, obtained within a narrow temperature interval of 47 K, which has been previously observed only during intermartensitic transformation. The present material shall effectively reduce the size of magnetic shape memory actuators.

Magnetomechanical properties of a high-temperature Ni–Mn–Ga magnetic shape memory actuator material

A Ni–Mn–Ga single crystal with a phase transformation temperature above 350 K is investigated. The material demonstrates a magnetic field-induced strain (MFIS) of 7% at room temperature and of 4.2% at 350 K. The temperature dependence of the magnetic anisotropy and of the saturation magnetization has been studied in detail. At 350 K a maximum magnetic stress of 1.6 MPa and a twinning stress of 0.6 MPa were measured, explaining the MFIS obtained at elevated temperatures.

Control of Magnetic Shape Memory Actuators Using Observer-Based Inverse Hysteresis Approach

Magnetic shape memory (MSM) actuators belong to active material technologies with a high energy density and outstanding field-strain relation. Large-scale multivariate field-stress-strain hysteresis effects, however, antagonize their broad use because of the inherent difficulties with control. In this brief, we describe and compare experimentally several MSM control strategies, including the observer-based inverse hysteresis approach proposed in the previous works and combined here with a linear feedback controller by connecting both in parallel. For a prototypic MSM actuator with return spring, it is shown that the actuator plant can be approximated by an appropriate hysteresis operator and a linear transfer function of residual dynamics. The positioning profiles with a bandwidth 0.1-10 Hz and amplitudes between 0.01 and 0.1 mm have been evaluated by the experiments.

Development of a miniaturized clamping device driven by magnetic shape memory alloys

This article deals with the potential of magnetic shape memory actuators for the use in micro applications and in particular in clamping devices. The most common actuator concepts are introduced briefly, including the so-called push–push concept. Subsequently, an overview of clamping technology is given and the advantages of mechanical clamping are pointed out. It is proposed to use the push–push actuation concept for the development of an energy-efficient clamping device driven by magnetic shape memory alloys. Hence, the design of the magnetic shape memory clamping device and the dimensioning of its magnetic circuits are presented. Finally, the characteristics of the device are experimentally examined and the results are summarized.

A magnetic shape memory foil actuator loaded by a spring

This paper presents experimental and simulation results on the performance of a novel linear actuator that uses the magnetic shape memory (MSM) effect in a Ni–Mn–Ga foil device loaded by a mechanical spring. The linear MSM actuator shows reversible actuation cycles with maximum magnetic field induced strain change of 5.6% for optimized spring constant and prestress. The experimental results are compared with simulations based on a thermodynamics-based Gibbs free energy model. The model has been implemented in a finite element program, which uses beam elements and an integral magnetic solver. The simulations qualitatively describe the observed tensile stress dependence of the magnetostrain of the MSM foil actuator. We demonstrate that the effects of material inhomogeneity need to be taken into account to further improve the agreement with the experiment.

Why Magnetic Shape Memory Alloys?

Why Magnetic Shape Memory Alloys?

Magneto-Mechanical Energy Conversion in Magnetic Shape Memory Alloys

Magnetic Shape Memory (MSM) alloys present a novel means of transforming electric energy into mechanical work via the intermediate generation of magnetic field from electric current. They thereby follow a similar path of energy conversion as classical electromagnets. In this paper we will compare known designs of MSM actuators and electromagnets and discuss their characteristics based on properties of available MSM materials.

Vibration control of a rotor by magnetic shape memory actuators—an experimentalwork

Deficiencies in practical applications for magnetic shape memory actuators motivated theauthors to start experimental and theoretical research in the field of multifunctionalmaterials. The authors present the concept of using magnetic shape memory actuatorsfor controlling, altering and tuning the forced vibration of a rotor. The maingoal of their experimental research is to show how the activation of magneticshape memory actuators can influence the forced vibration responses of a rotorin terms of altering and tuning selected rotor natural frequencies and modes ofvibrations. Experimental results show that magnetic shape memory actuators can besuccessfully applied for vibration reduction and vibration control in the case of rotorsystems.

Magnetic shape memory alloys for forced vibration control of beam-like structures

In this paper the use of actuators utilizing the magnetic shape memory effect for forcevibration control of beam-like structures is discussed. In order to model the shape memoryeffect in magnetic shape memory alloys, a modified phenomenological one-dimensionalmodel based on the Liang and Rogers classical shape memory alloy behaviour model isdeveloped and presented. The model developed has been implemented for use by the finiteelement method. Then the effectiveness of the use of magnetic shape memory actuators forthe case of a beam with two actuators has been investigated. The influence ofvarious actuation parameters for the magnetic shape memory actuators for controland tuning of transverse vibration of the beam has also been successfully shown.

Voltage generation induced by mechanical straining in magnetic shape memory materials

Magnetic shape memory (MSM) materials change their shape with the magnetic field. They can also be used in the reverse operation as sensors or voltage generators. The present paper demonstrates that large voltages are induced when the MSM material is mechanically compressed inside a MSM actuator. The experimental results reveal that voltages of close to 100 V were generated with a Ni–Mn–Ga MSM material subjected to short mechanical impulses, because of a change in its magnetization. The induced voltage depends on the geometrical and material parameters of the MSM actuator, as well as on the speed by which the MSM material changes its shape. A magnetic model for calculating the induced voltage is proposed and the measurement results from a MSM-type actuator are presented. The magnetic model demonstrates good accordance with the experimental results. The physical reason for the voltage signal is discussed and potential applications are proposed.

Magnetic shape memory actuator performance

Magnetic shape memory (MSM) is a newly developed actuator material. The MSM material changes its shape when exposed to an external magnetic field. Accordingly, motion generation applications such as actuators can be made. Coupling factor, temperature range, acceleration, speed, rise time, stroke and force of different MSM actuators are presented in this paper. Different types of dependencies of MSM actuators performance on their structure are also discussed.

Magnetic shape memory effect progress from idea to first actuators and sensors

The report will review the recent progress in studies of Magnetic Shape Memory (MSM) materials and latest developments of their applications. Magnetically controlled shape memory (MSM) materials are a new class of actuators and sensory materials. MSM materials can change their shape in a magnetic field applied due to the rearrangement of different martensite variant fractions. Inversely, magnetic field around the materials alters when proportions of the variants are changed by mechanical loading. The first effect can be utilized in actuators and the last one in sensors. Effect of high magnetic field on the ferrous-based shape memory alloys has been observed by Kakeshita et al. (1985) and Sadovsky (1986). A new method based on redistribution of twin martensite variants by low magnetic field as well as early models of magnetic-field-induced strains were suggested by Ullakko (1995, 1996) and James and Wuttig (1996). Magnetic-field-induced strains of about 0.2% in non-stoichiometric NiMnGa alloy was measured by Ullakko et al. (1996). NiMnGa was selected for that research, because it is a ferromagnetic shape memory alloy and low energy is required to drive twin boundaries by stress (Martynov and Kokorin, 1992). Magnetic-field-induced motion of a twinning dislocation that results in a shear strain was modeled by Muellner and Ullakko (1998). MSM effect was modeled by James and Wuttig (1998), O'Handley (1998) and Likhachev and Ullakko (1999, 2000). Field-induced strains of 4.5% after mechanical pre-loading were measured by James et al. (1999). Shear strains of 5% were observed by Murrey et al. (1999). The reversible elongation and contraction effect of over 5% in the rotating magnetic field was found by Ullakko, Sozinov and Yakovenko (1999). In this report recent experimental results including reversible linear and bending strains, magnetization measurements, twin band microstructure change, fatigue and frequency response of non-stoichiometric Ni-Mn-Ga alloys as well as a new MSM model will be discussed. Presentation of functioning MSM actuators and sensors with extension-compression and also bending actuating modes will be made.