Electromyography (EMG) signal is the electrical potential generated by contracting muscle cells. Long-term and accurate EMG monitoring is desirable for neuromuscular function assessment in clinical and the human–computer interfaces. Herein, we report a skin-integrated, biocompatible, and stretchable silicon microneedle electrode (SSME) inspired by the plant thorns. The silicon microneedles are half encapsulated by the polyimide (PI) to enhance the adaptability to deformation and resistance to fatigue. Thorn-like SSME is realized by the semi-additive method with a stretchability of not less than 36%. The biocompatibility of SSME has been verified using cytotoxicity tests. EMG monitoring in motion and long-term has been conducted to demonstrate the feasibility and performance of the SSME, which is compared with a commercial wet electrode. Hopefully, the strategies reported here can lead to accurate and long-term EMG monitoring, facilitating an effective and reliable human–computer interface.

The hysteresis characteristic of piezoelectric micro-positioning platforms seriously affects its positioning accuracy in precision positioning. It is important to design an effective hysteresis model and control scheme. Based on the analysis of the Duhem model, this paper proposes to divide the hysteresis curve into two parts, the step-up section and the step-down section, to identify the model parameters, respectively, and a hybrid intelligent optimization algorithm based on the artificial fish swarm algorithm and the bat algorithm is proposed. The simulation experiment verified that the error of the improved model was reduced by 48.97%, which greatly improved the identification accuracy of the Duhem model. Finally, an inverse model of the Duhem model for the segmental identification of the improved artificial fish swarm algorithm is established, and a composite controller integrating feedforward, feedback and decoupling control is designed on the basis of the inverse model, and an experimental verification is carried out. The results show that the displacement errors of the composite controller under different voltage signals are all within 0.25%. Therefore, the established model can accurately express the hysteresis characteristics of the platform, and the use of the composite controller can effectively reduce the accuracy error caused by the hysteresis characteristics.

Energy conversion efficiency and operation bandwidth are two main concerns in piezoelectric energy harvesting in low-frequency vibration environments. This paper presents a compact two-degree-of-freedom nonlinear piezoelectric energy harvester (2DOF NPEH) with a stopper. The proposed harvester consists of an elastic beam, a piezoelectric beam with tip mass, a pair of repulsive magnets, and a mechanical stopper. A bistable configuration is established through magnetic interaction. This study investigates the generating characteristics of the 2DOF NPEH under frequency-sweep excitation, utilizing a rigid stopper (RS) and different elastic stoppers (ESs). The experimental results indicate that the implementation of a mechanical stopper in a NPEH contributes to widening the operation bandwidth and enhancing the peak voltage. As the stiffness of the stopper increases, the bandwidth gradually shrinks while the peak voltage increases. The optimal energy conversion efficiency depends on the stiffness of the ES, and it occurs when the wire diameter of the spring is 1.2 mm. Compared with the 2DOF NPEH without a stopper, the utilization of a RS results in a 13.85-fold increase in the bandwidth of the generator at the first resonance. Moreover, the maximum absolute voltage is 12.82 times and 3.47 times the output voltage of the 2DOF NPEH at the first and second resonance, respectively. This work offers valuable insights into the design and optimization of piezoelectric energy harvesters in practical applications.

To realize the frequency tuning of phononic crystals (PCs) and the functional design of tunable PCs, acoustic components with more flexible working frequencies are manufactured to meet the various requirements of engineering applications. We proposed a combined tuning method that combines the change of the Young’s modulus of the shape memory alloy and the rotation of the scatterer. The tunable band structure and transmission spectra of the method were calculated using the finite element method. We analyzed the effect of fill rate and viscosity of matrix on the band structure and studied the regulation law of the dual regulation mode. The numerical results show that the double tuning method makes up for the shortcomings of the single tuning method and has the characteristics of widely tuning range, continuous adjustment, and more tuning modes. In addition, a PC waveguide is constructed by using this combined tuning method, which realizes the flexible construction of waveguide channels and the continuous tuning of wide frequency range. It is an important guideline for the research of tunable waveguides, the design of acoustic components, and the application of practical engineering.

Human cerebral oxygenation and hemodynamics can be estimated by cerebral oxygenation parameters. Functional near-infrared spectroscopy (fNIRS) can be used to measure the hemoglobin concentration index of brain tissue noninvasively and in real time. However, limited by cumbersome equipment, high price and uncomfortable wear, conventional fNIRS monitoring systems still cannot achieve continuous and long-term monitoring. In this work, a flexible and wearable long-term monitoring system is developed featured with cost efficiency, simple preparation and light weight (only 1.6 g), which consists of a pair of light-emitting diodes (LEDs) and a photodetector (PD). Triangular serpentine interconnectors are introduced to connect the functional elements, enabling the device to be stretched in multiple directions. The device can continuously work for 7 h and be subjected to 2000 cycles of bending loading, with less than 3% change in voltage value, 1.89% and 1.9% change in LED luminous power and 0.9% change in voltage value. Furthermore, the hand-gripping and breath-holding experiments show that the system can accurately measure the changes in hemoglobin concentration in accordance with the commercial device. The flexible fNIRS system presented here not only provides a simple preparation process but also offers new ideas for daily cerebral state monitoring and prolonged clinical monitoring.