This paper proposes the system design of a weighted-pendulum-type electromagnetic generator for harvesting energy from a rotating wheel. Different from the traditional energy-harvesting device, the natural frequency of the suitable weighted pendulum, which oscillates due to periodic change of the tangential component of gravitational force, can match up with the rotational frequency of the wheel at any speed. In addition, the pendulum oscillates at a large angle and angular velocity so as to generate a large amount of power. The physical model of the pendulum was first constructed and the equation of motion was then derived via the Lagrange method. Then, the models of power generation were derived by using Faraday's law of induction and the Lorentz force law. The nonlinear dynamic behaviors were discussed considering the characteristic length, variable electromagnetic damping, and wheel rotation speed. Finally, an experimental rig was constructed to verify the correctness of numerical results. The suitable weighted pendulum combined with coils and magnets has demonstrated the power generation of several hundred micro-Watts in the experiment.

Blood pressure (BP) is a crucial indicator of cardiac health and vascular status. This study explores the relationship between radial artery BP and wrist skin strain. A BP estimation method based on the physical model of wrist skin tissues and pulse wave velocity (PWV) is proposed. A photoplethysmography (PPG) sensor and strain gauge are used in this method. The developed strain-based pulse wave sensor consists of a pressing force sensor, which ensures consistent pressing force, and a strain gauge, which measures the cardiac pulsation on the wrist skin. These features enable long-term BP monitoring without incurring the limb compression caused by a cuff. Thus, this method is useful for individuals requiring continuous BP monitoring. In this study, the BP of each participant was measured in three modes (before, during, and after exercise), and the data were compared using a clinically validated sphygmomanometer. The percentage errors of diastolic and systolic BP readings were, respectively, 4.74% and 4.49% before exercise, 6.38% and 6.10% during exercise, and 5.98% and 4.81% after a rest. The errors were compared with a clinically validated sphygmomanometer.

A novel natural frequency self-tuning energy harvester is presented, which utilizes the presence of the nonlinearity model and the well-weighted swing disk to maximize the power output and the frequency bandwidth for a wheel rotating at any speed. Kinetic energy harvesters are frequency selective, meaning that they have high power transmission efficiency only when they are excited at their natural frequency. The well-weighted swing disk with nonlinear effects can render the energy harvester more broadband, that is, it has a more steady power generation at various wheel speeds than the ill-weighted swing disk has. We integrate magnets in a novel circular Halbach array and coils into the design to augment the magnetic strength on one side of the array where the coils are placed. Therefore, the gradient of the average magnetic flux density for the circular Halbach array disk is larger than that of the multipolar magnetic disk. The dynamic models with electromechanical couplings have been established and are analyzed. In the experiments, the power output of the prototype at an optimum external resistance was approximately 300–550 µW at about 200–500 rpm and precisely matches the numerical results.