The low frequency of the foot strike motion and the cushioning requirements of the shoe heel pose a significant challenge in the development of energy-harvesting footwear. In this study, we propose an internally threaded sleeve structure to address these challenges through the implementation of a high-performance shoe-heel-mounted energy harvester. Our design tactfully uses a two-stage frequency-up conversion mechanism to capture foot strike energy while enhancing cushioning to improve overall wearing comfort. Additionally, we analyze the acceleration amplitude during the moment of touchdown in walking, examine its frequency response, and create a predictive model to estimate the power output of the energy harvester. Finally, we validate the cushioning functionality of the fabricated prototype and evaluate its power output through testing on treadmill walking conditions. The results demonstrate a 15.6% reduction in acceleration amplitude during heel touchdown in comparison to walking without the device. In terms of power output, the prototype achieves an average peak power of 3.7 W at a stride speed of 6 km/h, exceeding the performance of the previously reported footwear energy harvester.

Invisible orthodontics, commonly known as clear alignment treatment, offers a more comfortable and aesthetically pleasing alternative in orthodontic care, attracting considerable attention in the dental community in recent years. It replaces conventional metal braces with a series of removable, and transparent aligners. Each aligner is crafted to facilitate a gradual adjustment of the teeth, ensuring progressive stages of dental correction. This necessitates the design for teeth motion. Here we present an automatic method and a system for generating collision-free teeth motion planning while avoiding gaps between adjacent teeth, which is unacceptable in clinical practice. To tackle this task, we formulate it as a constrained optimization problem and utilize the interior point method for its solution. We also developed an interactive system that enables dentists to easily visualize and edit the paths. Our method significantly speeds up the clear aligner planning process, creating the desired motion paths for a full set of teeth in under five minutes-a task that typically requires several hours of manual work. Our experiments and user studies confirm the effectiveness of this method in planning teeth movement, showcasing its potential to streamline orthodontic procedures.

Conventional dynamic torque measurement usually requires wires and slip rings for supply and data transmission, which shows many drawbacks in terms of device installation, maintenance, durability, and reliability. We, here, present a wireless torque measurement sensor without a battery, which can achieve a long-term and real-time torque monitoring on either static or dynamic rotation systems. The proposed battery-free wireless torque sensor (BWTS) is nondestructive and low cost. The BWTS is equipped with a Koch–Meander hybrid dipole antenna to receive the radiofrequency (RF) energy emitted from a customized reader. The BWTS can be activated at an input power of −15 dBm ($32 \mu \text{W}$), and the maximum operational distance in the open air is 3 m. We also study the sampling rate of the BWTS on a dynamic shaft and demonstrate it on the road, which to our best knowledge, is the first successful demonstration of fully self-powered and wireless torque monitoring in a real running car. This work indicates the feasibility of wirelessly powering torque sensors using far-field RF energy, introducing a new power solution to wireless and battery-less automotive sensors.

The very recent concept of metaverse highlights the importance of virtual reality (VR) and augmented reality (AR), which associates with a wide variety of applications in entertainment, medical treatment, and human–machine interfaces. The current VR/AR technologies mainly rely on visual interaction, while immersive experience in VR and AR highly demands sensational feedback, such as haptic and temperature with noticeable quality in wearable or even skin-integrated formarts. In this article, we report a wearable and flexible haptic interface based on electromagnetic vibrotactile actuators with high wearability and stability. By adopting double layers of copper (Cu) coils at the top and bottom of the magnetic disc, an enhanced electromagnetic field can be generated. Additionally, the intensity of the haptic feedback can be modulated according to sensed pressure in the virtual world by adjusting the value of power input and frequency. The actuator exhibits high stability and tolerance upon environmental, cyclic, and impact resistance tests. Finally, the actuators are developed into the soft VR interfaces for mounting on forearms, fingers, and hands to verify their superiority over conventional haptic actuators in the aspects of performance and applications.

Wrist-worn smart wearable devices, such as smartwatches and wristbands, are showing a high growth trajectory for decades in the wearable technology market. However, most wrist-worn generators are confined into watch bodies, which undermines the functionality of the wearables. In this study, we first characterize the dynamic properties of wrist motions and propose four rules for the design of wrist-worn energy harvesters. Based on the design rules, we then present a bionic piezoelectric energy harvester, composed of an inner band, an outer band with a piezoelectric array, and a watch body. The two-layer band structure mimics two branches of a Y-shaped hyoid bone of the woodpecker’s head. A finite element model is built to study the mechanical and electrical responses of the design. The model is validated by an experiment and is utilized to find the optimal thickness and positions of piezoelectric elements. Based on the optimizations, we fabricate a prototype with a piezoelectric array as the energy harvesting unit. With an ac–dc rectifier, the prototype is tested to characterize the electrical responses in four wrist motions. The result shows that the average power output of a bionic harvester is 2.10 mW in shaking arm motion, higher than previously reported wrist-worn generators. Finally, we demonstrate that the prototype enables to sustainably power a screen of a smartwatch, a wireless temperature monitoring system, and a commercial electronic thermohygrometer, respectively.

Current railway track condition monitoring relies on inefficient human inspectors and expensive inspection vehicles, where high-frequency inspection is unreachable since these methods occupy the tracks. This article proposes a batteryless railway monitoring system based on radio-frequency (RF) energy harvesting to detect early defects on rail tracks. The key part of the system is a batteryless wireless sensor tag (BLWST) installed on railway tracks. The BLWST can harvest RF energy from a reader installed on the train, and precisely measure and wirelessly transmit the vibration condition of tracks back to the reader. The proposed system eliminates the demands for cables and battery replacement, thus achieving low installation and maintenance costs. The high-frequency monitoring also provides a more reliable inspection than the existing methods. The BLWST is based on the 3-stage Dickson voltage multiplier (DVM) and can be activated by a dedicated RF power source at a maximum distance of 2.3 m. Experiments show that a maximum energy conversion efficiency of 25% and 500 working cycles per second are achieved. For demonstration, we construct a miniaturized railway system with the batteryless prototype and exhibit a reliable wireless power transfer and data communication.