Abstract Current wearable technologies strive to incorporate more medical functionalities in wearable devices for tracking health conditions and providing information for timely medical treatments. Beyond tracking of a wearer’s physical activities and basic vital signs, the advancement of wearable healthcare devices aspires to continuously monitor health parameters, such as cardiovascular indicators. To properly monitor cardiovascular health, the wearables should accurately measure blood pressure in real-time. However, current devices on the market are not validated for continuous monitoring of blood pressure at a clinical level. To develop wearable healthcare devices such applications, they must be validated by considering various parameters, such as the effects of varying skin properties. Being located between the blood vessel and the wearable device, the skin can affect the sensor readings of the device. The primary goal of this study is to investigate the effect of skin property on the radial pulse measurements. To this end, a range of artificial vein-inserted skin samples with varying properties is fabricated using Magneto-Rheological Elastomers (MRE), materials whose mechanical properties can be altered by external magnetic fields. The samples include layers to simulate the structure of skin and a silicone vein for the pulse to pass through. Note that they are not intended to represent real human skin-vein properties but created to vary a range of stiffness properties to carry out the study. Experiments are performed using a cam system capable of generating realistic human pulse waveforms to pass through the samples. During the indentation testing, the sample is compressed using a dynamic mechanical analyzer (DMA) to record experienced surface pressure, allowing the pulse patterns to be studied. Various samples are used to probe the effects of base resin hardness, iron content, and magnetic field. A pressure sensor incorporated in the cam simulator is used to benchmark the internal pulse pressure of the vein while the DMA indents the sample in order to note the pulse pressures being passed through the sample. Test results show that the properties of the skin influence the resulting pulse behaviors, particularly the ratio of the recorded pulse pressures from the sensor and the DMA.

This study aims to investigate the influence of temperature on the linear and nonlinear rheological behavior of a MR fluid, MRF 132DG, using a rotational rheometer. The experiments were designed to obtain properties of the fluid under oscillatory shear strain in the amplitude and frequency sweep modes, while maintaining different constant temperatures (−5, 0, 20 and 50 °C). The data were used to evaluate the storage and loss moduli under different levels of magnetic flux density considering the linear as well as nonlinear viscoelastic regions. The critical strain amplitudes were further obtained. Results showed enhanced linear viscoelastic region with increasing magnetic field density. Moreover, the effects of temperature and magnetic field on the frequency dependency of the fluid properties are illustrated for small and large amplitudes of shear strains.

Magnetorheological fluid is a special smart fluid which can show different rheological properties under different magnetic flux densities due to its magnetically sensitive structure. This makes the fluid able to be manipulated and semi-actively controlled for various applications such as dampers, clutches and brakes. To provide an effective damping it is necessary to create an appropriate control algorithm. In order to design a structure with magnetorheological fluid and to get an idea for a control approach, the physics of the fluid motion has to be modelled. Computational Fluid Dynamics is an effective tool to model any fluid behaviour or any fluid involved structure. For magnetorheological devices, despite number of numerical models available in the literature, a befitting model is not yet presented. In this study a mapped rheological model is proposed and used in a magnetorheological damper simulation. The results are compared with other models and experimental data. It is shown that the new mapped model is effective and better than old approaches. It also showed a good agreement with the experimental data.

Magneto-Active elastomers (MAEs) and magneto-rheological elastomers (MREs) are smart materials that consist of hard and soft magnetic particles, respectively, embedded in a flexible matrix. Their actuation capabilities are dependent on the arrangement of particles achieved during the fabrication process. Previous works have shown varying degrees of particle alignment and / or agglomeration as a function of fabrication process variable, most notably volume fraction of the particulates, their magnetic material type (hard vs soft), and the strength of the external field applied during curing. In this work, we simulated the dynamics of magnetic particles suspended in a fluid matrix to predict the evolution of microstructures resulting from these varying process conditions. The simulations accounted for the magnetic interaction of all particles using standard dipole-dipole interaction potentials along with dipole-field potentials developed from the Zeeman Energy. Additionally, the field local to each particle, on which magnetization depends, was determined by the sum of the external fields generated by each member of the ensemble and their demagnetizing fields. Fluid drag forces and short range particle-particle repulsion (non-overlapping) were also considered. These interactions determined the body forces and torques acting on each particle that drove the system of equations of motions for the ensemble of particles. The simulation was carried out over a nearest neighbor periodic unit cell using an adaptive time stepping numerical integration scheme until an equilibrium structure was reached. Structural parameters, related to the magnetic energy, spatial distribution, spatial alignment, and orientation alignments of the particle distributions were defined to characterize the simulated structures. The effect of volume fraction and intensity of the external magnetic field on the achieved particle distributions were studied. At low external field strengths, the particles formed long entangled chains that had very low alignment with the applied field. The remnant magnetic potential energy of these configurations was also significantly low. As the field is increased the length of the chains reduced and the alignment increased. The corresponding change in magnetic potential energy of the system with an increase in the applied field was found to follow a power law fit that spanned a wide range of magnetic field strengths. At low volume fractions the particles aligned rapidly with the field and formed short chains. As the volume fraction of the samples increased the chains grew longer and closer to each other, and magnetic potential of the structure became lower. Results of the simulations suggest that it is possible to tailor the microstructure and thus affect remanent magnetization and magnetization anisotropy, by judicious control of process parameters. This ability could have implications for newly emerging additive manufacturing techniques utilizing suspensions of magnetic particulates.

Magneto-rheological fluids (MRF) are commonly applied in MRF brakes and vibration damping. The apparent viscosity dependence with respect to the magnetic field has been addressed in detail in the state of the art. The aim of this paper is to experimentally study the vibration effects on the particle chain-like structures and, as a consequence, the shear stress variation applied to the fluid. Three vibration configurations have been applied to a ferromagnetic cylinder rotating between two magnetic poles filled with MRF a “Z-vibration” where the generated displacement is along the rotation axis of the shearing cylinder, a “θ-vibration”, tangential to the cylinder, and an “R-vibration”, normal to the cylinder surface. First we focus on the vibration mode characterisation in free air, and then when plunged in the fluid. In a second step, we measure the reactive torque generated on the clutch under different magnetic field intensities with different rotation speeds and vibration amplitudes. It appears that the “R-vibration” configuration is providing the most influence, up to 20% of torque reduction observed at moderate B field. The “Z-vibration” and the “θ-vibration” configurations respectively have less influence on the torque, nevertheless vibrations always tend to decrease the corresponding yield stress in the MRF.

Creating a multi-variance human pulsation simulator is crucial for deeper understanding of human pulsation system and developing useful medical devices. Current pulsatile systems are bulky, complex, and expensive. In order to address these disadvantages, this project intends to develop a simple and cost-effective pulsatile simulator using Magneto-Rheological fluids whose flow can be controlled by magnetic fields instantly. It also intends to evaluate its effectiveness in generating various arterial blood pulsation patterns. To this end, a test setup consisting of tubing, an electromagnet, and sensors along with MR fluids was constructed. Using Pulse Width Modulation (PWM) techniques, the electromagnet produced control signals to regulate the flow motion. The output pressure changes (perceived human pulsation) were measured using a pressure sensor installed in the tubing. Using the test setup, a series of testing was performed to measure arterial pulsations by varying the duty cycles of PWM signals. The results show that the pulsatile system was capable of replicating various human pulsation waveforms.

This study investigates the dynamic properties of Magneto-Rheological Elastomers (MRE) with hard magnetic particles used as bending actuators under an alternating magnetic field. As earlier studies demonstrated that a dispersion of hard magnetic particles in polymeric materials, aligned in a preferred orientation, cause rotational motion in the sample when a magnetic field is applied perpendicularly to the magnetization direction of the particles. They focused on static responses of MREs with hard magnetic particles. The primary goal of this study is to characterize the dynamic behavior of a flexible bending actuator based on MREs under alternating magnetic fields. In this study, samples from a previous study, consisting of barium hexaferrite particles at 30% concentrations by volume, were tested. A C-shaped electromagnet was constructed to apply alternating magnetic fields along the length of the sample. By securing only one end of the sample to the electromagnet, the sample is free to bend similar to a cantilever beam. Using this setup, the tip displacement of the sample was recorded using a precision load cell and a laser displacement sensor under various input magnetic field strengths and frequencies. The results show that increasing the voltage output or the magnetic field strength increases the displacement of the sample. The results also show that, as the frequency of the sinusoidal voltage input increases, the amplitude of the tip displacement of the sample decrease.

The magnetorheological Brake (MRB) is an electromechanical brake in which smart magnetorheological (MR) fluids have been utilized to generate the required braking torque. The purpose of this study is to design optimize a real-size MRB for automobile applications considering geometrical, material and magnetic circuit parameters. The mathematical equations governing the system’s braking torques are derived. The dynamic range of a disk-type MRB expressing the ratio of generated toque at on and off states has been formulated as a function of the rotational speed, geometrical and material properties, and applied electrical current. The magnetic circuit analysis of the proposed MRB is performed to find the relation between magnetic field intensity and the applied electrical current as a function of the MRB geometrical and material properties. Finally, a multidisciplinary design optimization problem has been formulated to identify the optimal brake geometrical parameters to maximize the dynamic range of the MRB under weight, size and magnetic flux density constraints. The optimization problem has been solved using combined Genetic Algorithm and Sequential Quadratic Programming techniques. The optimal design is then compared with those available in the literature.

Magnetoactive elastomers (MAEs) are composites made of an elastomeric matrix and a magnetizable filler material. The combination of their properties enables a MAE to undergo a change of its rheological respective damping behavior. Furthermore, it is expected that such a magnetic field can lead to an actuation of a MAE. This actuation causes actuation forces perceptible on the surfaces of MAEs. For the investigation of the induced actuation forces different MAE-probes are characterized in a first step. The resulting forces of these MAE-probes are measured by generating a variable external magnetic field in a suitable test setup. Subsequently, a finite element analysis (FEA) is carried out to investigate the behavior from a theoretical point of view by introducing an appropriate continuum mechanical model approach based on the Kelvin force. Therefore, a coupling of magnetism and structural-mechanics domain is developed and implemented using the FEA-tool Comsol Multiphyisics. Finally, the experimental and numerical results of the actuation forces are compared showing a good accordance.

This paper presents a novel Magentorheological (MR) brake with permanent magnets. The proposed MR brake can generate a braking torque at a critical rotation speed without an external power source, sensors, or controllers, making it simple and cost-effective device. The brake system consists of a rotary disk, permanent magnets, springs and MR fluid. Permanent magnets are attached to the rotary disk via springs, and they move outward through grooves with two different gap distances along the radial direction of the stator due to centrifugal force. Thus, the position of the magnets is dependent on the spin speed, and it can determine the magnetic fields applied to MR fluids. Proper design of the stator geometry gives the system unique torque characteristics. To show the performance of an MR brake system, the electromagnetic characteristics of the system are analyzed, and the torques generated by the brake are calculated using the result of the electromagnetic analysis. After the simulation study, a prototype brake system is constructed and its performance is experimentally evaluated. The results demonstrate the feasibility of the proposed MR brake as a speed regulator in rotating systems.

This contribution deals with the theoretical and experimental investigation of the giant MR-effect. The giant MR-effect can be utilized to increase the yield stress of magnetorheological fluids (MRF). To obtain a boost of the yield stress the MRF has to be normally compressed while it is exposed to a magnetic field in order to create stronger particle structures. For the experimental investigation a MRF test actuator with an conical shear gap is designed, enabling an adjustment of the shear gap’s height by applying a compressing normal force. The experimental investigation points out that a potentially increase of the yield stress can be achieved on the one hand. On the other hand it is dependent on the magnetic field strength during the compression as well as on the shear rate and shear strain. The results are used to motivate a modeling approach which combines the rheological behavior with tribological effects. The validation of the modeling approach shows a good accordance to the behavior of the physical investigated giant MR-effect.

Results are reported from an ongoing experimental investigation of the effects of thermo-oxidative aging on the mechanical behavior of an epoxy shape memory polymer (SMP). Chemo-rheological degradation due to macromolecular scission and cross-linking is one of the main factors contributing to the chemical aging of thermo-responsive SMPs. This aging may manifest as residual strain or irreversible material property changes, which can affect the performance and limit the useful life of a SMP. A relatively new epoxy SMP based on the diglycidyl ether of bisphenol A is synthesized, and specimens are tested under uni-axial tension using a dynamic mechanical analyzer. Fundamental viscoelastic behavior and thermal expansion coefficients are first characterized, showing a glass transition near 60 °C. Shape memory cycle experiments are performed at shape fixing temperatures of 80, 125, 150 and 175 °C, and the effect of fixing time at each temperature is examined upon subsequent strain recovery at 80 °C. Performance parameters such as recovery ratio, speed of recovery and residual strain are quantified as a function of shape fixing time and temperature. No effect of chemical aging was seen at a fixing temperature of 80 °C, although the recovery ratio decreases initially with increasing fixing time and stabilizes near 92 %. Only minor effects of chemical aging are seen in the mechanical responses for fixing temperatures of 125 and 150 °C, but specimens exhibit progressively more noticeable color changes that indicate oxidation. Significant effects are observed at the highest fixing temperature of 175 °C, where chemical aging at longer fixing times results in a reduction in recovery rate across the rubber-glass transition temperature, progressively larger residual strains, lack of complete strain recovery at 80 °C, and higher temperatures to achieve 90 % strain recovery.

Magneto-rheological elastomer (MRE) is known as class of smart materials whose elastic property can be varied by the applied external magnetic field. For the use of semi-active vibration control, any kind of external sensor such as accelerometer or displacement sensor is usually used to monitor the real-time response of structures while leaving cost, proper installation and maintenance problems for real applications. In addition to the field-dependent stiffness change property of MRE, the electrical resistance of the composite is also changed by the induced strain within the elastomer providing a new self-sensing feature as a multifunctional material. In the present study, a novel dynamic vibration absorber having self-sensing function and adaptability using Magneto-rheological elastomer is developed. The natural frequency of the absorber is instantaneously tuned to a dominant frequency extracted from the strain signal. The damping performance of the absorber is investigated by applying the absorber to a fundamental base-excited 1-dof vibration system. Investigations show that the vibration of the target structure exposed to a non-stationary disturbance can be satisfactorily reduced by the proposed frequency-tunable dynamic absorber without the use of an external sensor, at the exceeding performance in comparison to conventional passive-type dynamic absorber.

Shape memory polymers (SMPs) are known to change their elastic stiffness as they respond to change in induced stimulus such as temperature. Under appropriate loading and pre-deformation, a shape memory effect can be captured as the stimulus change. From the nature of polymers, the pre-deformation can tend to be large and can in turn be memorized by SMPs. Due to this characteristic of SMPs, it makes a great candidate for morphing structures. To analyze complex structures a simple but yet practical constitutive model needs to be developed for commercial engineering application. In this paper, a thermomechanical constitutive model is proposed making use of the standard linear viscoelastic model. The total strain during the shape memorization process is defined by mechanical, thermal and storage strains. The rheological model defined is an elastic element in parallel with a Maxwell element, which in turn are both in series with storage and thermal element. Inclusion of a storage strain within the model reveals the internal strain storage mechanism as the temperature of the material drops. Similar work done in the past requires material parameters that can be arduous to determine in the laboratory. This model proposes a simplified approximate material parameter called a binding factor which accounts for the polymer’s molecular architecture and morphology as the temperature changes. Finally, the model is applied to a four step shape memorization and stress-free recovery process. For this study, the four steps considered are a) Pre-loading of the material at high temperature b) Constant strain fixity c) unconstrained relaxation at low temperature d) unconstrained free strain recovery. The developed model is validated by comparing the predictions to experimental results in literature.

This paper proposes a new bed stage for patients in ambulance vehicle in order to improve ride quality in term of vibration control. The vibration of patient compartment in ambulance can cause a secondary damage to a patient and a difficulty for a doctor to perform emergency care. The bed stage is to solve vertical, rolling, and pitching vibration in patient compartment of ambulance. Four MR (magneto-rheological) dampers are equipped for vibration isolation of the stage. Firstly, a mathematical model of stage is derived followed by the measurement of vibration level of patient compartment of real ambulance vehicle. Then, the design parameters of bed stage is undertaken via computer simulation. Skyhook, PID and LQR controllers are used for vibration control and their control performances are compared.

Shape Memory Alloys (SMAs) are active metallic materials classified as “smart” or “intelligent” materials along with piezoelectric ceramic and polymers, electro-active plastics, electro-rheological and magneto-rheological fluids and others. SMAs show a multitude of different and dependent properties interesting for technological applications. These properties depend on the peculiar deformation mechanisms, accounting for the so-called shape memory effect. SMAs are nowadays used in quite different fields, like thermo-mechanical devices, anti-loosening systems, biomedical applications, mechanical damping systems, in some cases employed for large scale civil engineering structures. These multifunctional materials can be naturally considered as sensor-actuator elements demonstrating large possibilities for applications in high-tech smart systems. The use of SMAs in actuators offers an excellent technological opportunity to develop reliable, robust, simple and lightweight elements within structures or as stand-alone components that can represent an alternative to electro-magnetic actuators commonly used in several fields of industrial applications, such as automotive, appliances, consumer electronics and aerospace. NiTi-based SMAs demonstrated to have the best combination of properties, especially in terms of the amount of work output per material volume and the large amount of recoverable stress and strain. However, there are several limiting factors to a widespread diffusion of SMAs to technological fields. For instance, SMAs display a critical dependence of the shape-memory related properties, like transition temperatures, on their actual composition. For this reason, a great care in the production steps, mainly based on casting processes, is required. Another critical aspect, that is to be considered when dealing with SMAs, is the strong influence of their thermo-mechanical history on their properties. This may disclose interesting perspectives of application to smart devices in which different aspects of the shape memory phenomenology, like one and two way shape memory effect, pseudoelasticity, damping capacity, etc., are used. Last, but not least, one of the most debated aspects around NiTi alloys is microcleanliness. This concept is becoming increasingly important as the industrial market moves to smaller, lower profile devices with thinner structures. In this work a general overview about the peculiar behavior of NiTi alloys along with their main issues, the shape memory components under development, and the main efforts and directions for materials improvement will be presented and discussed. A bird’s-eye view on the future opportunities of NiTi-based shape memory actuators for industrial applications will also be given.

Magneto-rheological composites with magnetic particles are prepared. The magnetic particle is Fe-Si-B-Cr system and the average diameter is 10μm. Matrix of the composite is silicon gel. We characterized dynamic response of the material by shear test in magnetic field where intensities are 0 mT, 105 mT and 211 mT. The stiffness and damping capacity of the composite increase with increasing of the magnetic field. To understand mechanism of behavior of magneto-rheological composites, we make a model of the composite with periodical micro structure. The magneto-rheological composite undergoes magnetically induced internal stress field by applied magnetic field. The analysis model involved effect of the applied magnetic field as initial stress in the material. Particles and the magnetically induced stress make locally large strain field in the gel material. A large deformation analysis with the Ogden model using finite element method is made to demonstrate behavior of magneto-rheological composites. The simulation results are compared with experiment results and verified the effectiveness of the model.

This study presents a novel design of a miniature haptic actuator based on Magneto-Rheological (MR) fluids for mobile applications, and it evaluates the performance of a haptic actuator using a simulation model. The primary design goal for a haptic actuator for mobile applications is to miniaturize its size while generating realistic haptic sensations. To this end, this study proposes to design the MR actuator’s piston head (or plunger) in cone-shape and activate multiple modes of MR fluids (direct shear, flow and squeeze modes). Using a simulation model developed by integrating magnetic and force equations, the performance of a haptic actuator was evaluated in terms of the force (resistive force) produced by the actuator. The results show that a small actuator model, dimension of 10 mm (L) × 10 mm (W) × 6.5 mm (H), produced a maximum resistive force of about 5 N at 0.3 Watts, which is sufficient to provide force feedback to users.

This study investigates the evolution of filler particle networks using electrical and rheological property measurements. Polyvinylediene Flouride (PVDF) was used as the matrix thermoplastic polymer which was reinforced with multiwall carbon nanotubes (MWNT) as the filler phase using high shear twin screw extrusion mixing. Electrical conductivity and dielectric constant measurements were done using impedance spectroscopy. Viscosity and storage modulus measurements were performed using a dynamic rheometer. Morphologies of the composites were observed using scanning electron microscopy. The percolation behavior in electrical conductivity was determined to be 1.3 wt% MWNT content in PVDF. This is in contrast to the nanocomposite viscosity percolation threshold which occurred at 1.9 wt%.

A passive type dynamic vibration absorber offers advantages in reliability and simple constitution, however, the use of the absorber with fixed property is usually limited to harmonically excited case, where the damper is only effective for pre-determined narrow frequency range. Design of the damper following well-known optimal tuning theory could extend the effective frequency range, yet the damping performance remains at a certain amount. In this paper, the stiffness controllable elastomer composite known as Magnetorheological elastomer (MRE) is applied to the dynamic absorber whose natural frequency is tunable by the external magnetic field. MREs are first fabricated and their field-dependent properties are investigated. The MRE is then applied to a dynamic absorber along with stiffness switching scheme so that the vibration of 1-DOF structure is damped more effectively. Investigations show that the vibration of the structure can be fully reduced by the proposed dynamic absorber with variable stiffness functionality.