Flexible strain sensors have important applications in wearable devices, electronic skin, robotics, and virtual reality. However, simple and effective methods to adjust the sensing performance for various applications are still the key to their commercialization. Here, a flexible strain sensor with a magnetic self-assembled pearl necklace-like microstructure is proposed, named PNS-C, which effectively improves its strain sensing performance by utilizing the curing magnetic induction intensity to adjust the arrangement of nanoparticles and multiwalled carbon nanotubes. It exhibited high sensitivity (GF = 361.02, 125–150% strain), nearly 40.16 times that of the corresponding randomly distributed structural composites, fast response (loading delay time was 132 ms), and high durability (1050 cycles). The sensing properties of PNS-C enable wearable health monitoring including facial micro-motion and knee movements. Finally, a manipulator grasping motion detection system is designed to demonstrate the potential practical value of the sensor in the field of robot control.

Although the quasi-static model is widely employed in various engineering fields to guide the design of magnetorheological (MR) dampers, it is not accurate enough to describe the dynamic behaviors of MR dampers. In this study, an unsteady Bingham plastic (US-BP) model that considers fluid inertia is established. The proposed model can realize flexible switching between flow mode and mixed mode by introducing a mode parameter. To employ the US-BP model for MR dampers under different excitations, a technique combining the Fourier series method and Laplace transform is developed to deduce the velocity profiles of MR fluids. Based on the US-BP model, the damping characteristics of an MR damper under different excitation frequencies, yield stresses, and mode parameters are theoretically investigated. Furthermore, an unsteady hysteretic Bingham plastic (USHY-BP) model that incorporates particle chain deflection theory is developed to characterize the hysteretic behavior and inertia effect of the damping force. Comparisons between the simulation results and the experimental data reveal that the US-BP model can predict the unsteady behaviors of damping forces caused by fluid inertia but fails to capture the hysteresis characteristic. The USHY-BP model achieves good performance and accuracy in characterizing the dynamic properties of MR dampers.

Despite several salient benefits of numerous control systems utilizing magnetorheological (MR) fluid, practical realization of commercial products is limited due to the particles sedimentation. To overcome this problem, several measures have been proposed to optimize MR fluid settling through the viewpoints of dispersing medium viscosity, suspension force of dispersed phase and additives innovation, but the settling of MR fluid can be alleviated to an extent only. An active dispersing mechanism (ADM) proposed in the previous work is one of attractive ways to resolve the sedimentation problem in a level of device and it is promising to fulfil good serviceability for MR dampers even if the settling remains. In this work, attributive to the investigations in stirring devices, rotary blades are employed to fulfil the redispersing of settled MR fluid under the theory of solid-liquid two phase flow. The parameters and working conditions of the rotary blades are optimized to guide experimental verification in a damper-sized vessel. The vessel can be seen as a prototype for real MR damper. An immersed induction method (IIM) for the characterization of the localized MR fluid concentration is proposed to designate the dispersing process when ADM is started. With the experiments of different MR fluid volume fractions and rotating speeds of the rotary blades, it is fully testified that the faster the blades rotate, the shorter the mixing time, and the more the inclination angle of blades close to 45°, the better the dispersion capability. In addition, it is also identified that the ADM is effective to disperse the settled MR fluid and promising to the sedimentation immunity of MR damper.