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.

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.

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.