The main purpose of this study is to investigate dynamic characteristics of semi-active Tuned Vibration Absorbers (TVAs) using an adjustable damper, such as a Magneto-Rheological (MR) damper. Based on on-off and continuous control polices, closed-form groundhook equivalent models are developed for analytical studies of semi-active TVA models. In addition, the transmissibilities of groundhook equivalent models are compared with passive TVAs. The results indicate that semi-active TVAs, with off-state damping levels within a critical value, are capable of lowering the magnitude of resonant peaks without increasing vibration. In contrast, increasing damping in passive TVAs results in reducing the amplitude of resonant peaks at the expense of increasing vibrations at the tuned frequency. A parametric study of the groundhook TVAs shows that the effectiveness of semi-active TVAs increases with larger on-state damping, larger mass ratio, and smaller off-state damping.

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.

Over the past two decades, induction heating technology has begun to replace conventional heating methods in manufacturing due to its ability to rapidly and uniformly heat conductive materials. This advancement has made induction heating very attractive to a wide range of industries, including applications in which thin sheet geometries are used (sheet thickness < 10 mm). According to preliminary testing, conventional coil geometries cannot efficiently heat thin sheet samples. Thus, the primary goal of this study is to investigate a suitable coil design for thin sheet materials and to evaluate the effects of varying coil design parameters. To this end, this project has developed a 3D Multiphysics model that includes a longitudinal induction coil and a thin sheet workpiece. Using the model, a series of parametric studies have been performed to identify the best induction coil geometry for heating of thin sheets along with suitable excitation parameters for the coil and workpiece. It was found that uniform heating is produced when the space between coils is tight. Additionally, insignificant variance in temperature uniformity was found when vertically displacing the workpiece within the coil. Parametric studies resulted in finding a cross-section geometry that reduced temperature deviation to within 1.1% across the workpiece width. The model can be used as a design tool for developing a (full-scale) prototype induction heating system.

Artificial and synthetic skins are widely used in the medical field; used in applications ranging from skin grafts to suture training pads. There is a growing need for artificial skins with tunable properties. However, current artificial skins do not take into account the variability of mechanical properties between individual humans as well as the age-dependent properties of human skin. Furthermore, there has been little development in artificial skins based on these properties. Thus, the primary purpose of this research is to develop variable stiffness artificial skin samples using magnetorheological elastomers (MREs) whose properties that can be controlled using external magnetic fields. In this study, multiple MRE skin samples were fabricated with varying filler particle volume contents. Using a precision dynamic mechanical analyzer, a series of indenting experiments were performed on the samples to characterize their mechanical properties. The samples were tested using a spherical indenter that indented a total depth of 1 mm with a speed of 0.01 mm/s and unloaded at the same rate. The results show that the modulus or stiffness increases significantly as the iron percent (w/w) in the sample increases. Additionally, the stiffness of the sample increases proportional to the intensity of the applied external magnetic field. To assess the MRE samples’ variability of properties, the testing results were compared with in vivo human skin testing data. The results show the MRE samples are feasible to represent the age-dependent stiffness demonstrated in in vivo human skin testing. The MRE materials studied will be further studied as a variable-stiffness skin model in medical devices, such as radial pulse simulators.

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.

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.

To provide a realistic haptic sensation, cutaneous, thermal, and kinaesthetic sensation should be simultaneously conveyed to a user. While many research efforts have been conducted to develop separate haptic modules, it is quite challenging to construct an integrated haptic device which is sufficiently small to be incorporated into a computer mouse interface. In an effort to achieve this goal, this study proposes the new design of a compact combined haptic device with cutaneous, thermal, and kinaesthetic modules. To convey realistic tactile sensations despite the limited size of the interface, the cutaneous module includes a 3 × 3 miniature pin-array display and an amplitude-modulated (AM) vibration generator. The pin-array display is intended to mimic both small-scale shapes and rough surfaces. The AM vibration generator creates a variety of amplitude-modulated vibrations to replicate the continuous texture of a virtual object. To further convey the temperature and thermophysical properties of an object, the thermal module including a peltier element and a cooling jacket is integrated to the cutaneous module. Since the kinaesthetic information is equally important while perceiving objects, two kinaesthetic actuators operated by MR fluids are located on the control circuit board while supporting the cutaneous and thermal modules. The integrated haptic device can be used to enhance the sense of reality with combined haptic feedbacks while users interact with virtual graphic environments.

This paper presents design and testing of a haptic keypad system using an array of haptic actuators. The research goals are to construct a prototype haptic keypad system using haptic actuators and to evaluate the performance of the prototype keypad for haptic rendering. To this end, an MR haptic actuator was designed and fabricated such that it can convey realistic force feedback to users. To demonstrate haptic applications of the MR actuator, a haptic keypad system was constructed, which consists of following components: (1) 3 × 3 array of haptic actuators, (2) 3 × 3 array of force sensing resistors (FSR), (3) a controller including a micro-processor, a current amplifier and a wireless communication module, (4) a graphic display unit with PC. After constructing a prototype keypad system, a haptic rendering technology was employed to interface the hardware keypad system with test software (virtual environment). The prototype system enabled human operators to interact with the target contents in a virtual environment more intuitively. The evaluation results show a feasibility of applications of MR fluids-based haptic actuators in real-world mobile applications.

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.

The primary purpose of this paper is to provide a comprehensive review on the time delay of impact MR buffer system. The phenomenon of time delay which occurs in most of the MR buffer systems has been given little attentions especially in the applications where little time delay is demanded. Furthermore, the methods of reducing time delay have not been discussed in detail. So, in this study, several efforts have been made to decrease or even eliminate the phenomenon of time delay. Firstly, we analyzed two kinds of power supply sources and coil winding patterns. Next, an advanced correcting circuit was designed and the parameters of transfer function were determined by experimental data. The results show that, compared with the original circuit, it only takes 5ms to achieve 95% of the final state after correction, which increases 75% immediately. Furthermore, to evaluate the effect of compensation control strategy on time delay, the adaptive Smith compensation control was adopted and tested. Using the open on-off control strategy, four operating start times of current were applied, ranging from 0 to 300ms in increments of 100ms. The results show that the original maximum time delay is more than 150ms and it can be reduced to less than 50ms by adaptive smith compensation. Further analysis illustrates that decreasing time delay improves the dynamic performance of MRD in the buffer process, such as decreased overshoot, less fluctuation etc.

This paper presents a miniature haptic actuator based on MR fluids, which is designed to convey realistic haptic sensations to users in small electronic devices. The proposed MR actuator can create various kinaesthetic sensations. The haptic sensation, which is generated in the form of resistive force, should vary according to the stroke of the actuator (or the pressed depth of the plunger). Thus, a sensing method for gauging the pressed depth should be integrated into the proposed actuator for demonstrating its real-world haptic application. To determine the pressed depth of the MR actuator, this study proposes an impedance sensing mechanism. The proposed sensing method measures the impedance change of the solenoid coil embedded in the actuator in the form of voltages to estimate the pressed depth. Using a prototype actuator, the sensing performance of the proposed sensing method, was evaluated. The results show that the sensitivity of the proposed impedance sensing method is sufficient to regulate the output resistive force over a small stroke range of the actuator.

The focuses of this study are to design an adaptive tuned vibration absorber based on a smart material known as magnetorheological elastomers (MRE) and to test its dynamic performance. A primary system replicating a cryogenic cooler was designed and fabricated in order to test the effectiveness of the vibration absorber. A hybrid magnetic system (electromagnet and permanent magnets) was also designed and fabricated in order to actuate the MRE as an adaptive stiffness element in the vibration absorber. Vibration testing was conducted on both the primary system and vibration absorber individually in order to characterize the behavior and verify the design constraints. Further testing was performed on the two degree of freedom system to measure and assess the feasibility of the MRE material for use in an application requiring an adaptive vibration absorber. The results show that by using a hybrid design for the electromagnet within the vibration absorber, the stiffness of the MRE material can be both increased and decreased above its nominal value; therefore demonstrating the feasibility of this design as an alternative adaptive vibration absorber.

This paper presents a numerical investigation of a smart base isolation system employing magneto-rheological (MR) elastomers or an MR elastomer-based base isolation system. MR elastomers are a new class of smart materials whose elastic modulus or stiffness can be adjusted depending on the magnitude of the applied magnetic field. Hence, they can be used as controllable stiffness elements in engineering systems. The primary goal of this study is to investigate the dynamic performance of the smart base-isolation in mitigating excessive vibrations of a building structure under earthquake loadings. To this end, a five-story shear building model coupled with a smart base-isolation is developed. Using this model, a series of numerical simulations is performed to evaluate the effectiveness of the MR elastomer-based base isolation system under several historic seismic excitations. The results show that the proposed base isolation system outperform the conventional passive-type base isolation system in reducing the responses of the building structure for all seismic excitations considered in this study.

This paper investigates the effectiveness of a smart damping system consisting of a magnetorheological (MR) damper and an electromagnetic induction (EMI) device in reducing cable vibrations. The smart damping system incorporates an EMI device to reduce complexity of conventional MR damper based semi-active control system by eliminating external power sources. This is because the EMI part in the system generates electrical energy (i.e., induced voltage) from mechanical energy (i.e., reciprocal motions of an MR damper), which can be used as a power source for the MR damper. The primary goal of this experimental study is to evaluate the performance of the proposed smart damping system using a full-scale, 44.7 meters long, high-tension cable. To this end, free vibration responses and damping of the proposed smart damping system were compared with those of an equivalent passive control system. The experimental results show that the smart damping system shows better control performance than all the passive control cases.

This study presents the dynamic numerical model of magneto-rheological elastomers (MREs) along with the dynamic testing of the material under various loading conditions. Primarily the loading in shear mode is considered in this study because many civil engineering structures are subjected to shear loading. Experimental tests were carried out in order to characterize the dynamic behavior of MREs. A test setup was designed and fabricated to load the MRE samples in shear mode with varying magnetic fields. A series of shear tests of MRE samples were performed under various magnetic field values, amplitudes and frequencies of loading. The test results show that the material stiffness is increased with increasing magnetic field and loading frequency within the ranges of the magnetic field and exciting frequency considered in this work. Based on the experimental results, a dynamic model was developed to capture the dynamic behavior of the MRE.

The primary purpose of this study is to experimentally evaluate the dynamics of a Magneto-Rheological Tuned Vibration Absorber (MR TVA) with several semi-active control schemes. A test rig was built to represent a two-degree of freedom primary structure model coupled with an MR TVA, and four semi-active control policies were considered. The four control policies include: velocity-based, on-off groundhook control (on-off VBG); velocity-based, continuous groundhook control (continuous VBG); displacement-based, on-off groundhook control (on-off DBG); and displacement-based, continuous groundhook control (continuous DBG). Using the test apparatus, a series of tests were conducted to investigate the dynamics of the MR TVA with each control policy. The performances of each of the cases were then analyzed along with the equivalent passive TVA. The performance index was the transmissibility between the input and the output displacement of the structure. The experimental results indicated that the MR TVA with all of the semi-active control policies, outperformed the passive TVA in reducing structural vibrations. Furthermore, the displacement-based groundhook control policies perform better in reducing the resonant vibrations of the primary structure than the velocity-based groundhook control schemes.

This paper offers a method and an experimental example of determining the response time of Magneto-Rheological (MR) dampers. The response time of MR dampers for automotive suspension applications is valuable information because it is one of the key factors that determine the practical effectiveness of the use of MR dampers in vehicles. However, a detailed description of the response time of MR dampers is seldom given in the literature. Furthermore, the methods of computing the response time are not discussed in detail. Therefore, this study intends to develop a method for experimental determination of the response time of MR dampers for automotive suspensions. A triangle wave that maintains a constant velocity across the damper is proposed as the input to use in experiments. This triangle wave ensures a constant velocity across the damper in order to accurately evaluate the response time of the MR damper. The response time was defined as the time required to make the transition from the initial state to 63.2% of the final state, or one time constant. The time constant is a measure of how long it takes a system to respond to a given input. In other words, the response time is the time necessary for the damper to achieve the desired force upon activation. To demonstrate the method, the response time was found for an MR damper particularly designed and fabricated for vehicle applications. Two cases were considered: activation response time of the damper and deactivation response time of the damper. Both cases were studied during the rebound stroke of the damper. It was found that the response time of the MR damper under activation and deactivation was 15.4 ms and 13.9 ms respectively. The results are comparable to those found in the literature.

A passive TVA is only effective when it is tuned properly; otherwise, it can magnify the vibration levels. Often, inevitable off-tuning of a TVA occurs due to changes in the primary structure mass and stiffness for force-excited structural systems such as a floor. The main purpose of this study is to evaluate the robustness of semi-active groundhook TVAs to structure mass and stiffness off-tuning. In the case of floor systems, adding external mass to an existing floor, such as people and furniture, will increase the floor mass, and reduce the mass ratio. Theses changes result in off-tuning of the frequency ratio, which is defined by the ratio of the natural frequency of the TVA to the primary structure natural frequency. In order to study the effect of off-tuning, a force-excited equivalent model of a groundhook TVA is developed and its closed-form solutions are obtained for dynamic analysis of such systems. Moreover, the optimal design parameters of both passive and groundhook equivalent semiactive TVA models are obtained based on minimization of peak transmissibility. The two optimally tuned models are compared as the primary mass and primary structure stiffness changes. The results indicate that the peak transmissibility of the groundhook TVA is lower than that of passive, implying that the groundhook TVA is more effective in reducing vibration levels. The results further indicate that the groundhook TVA is more robust to changes in primary structure mass and stiffness.