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Energy harvesting from external Ultra-low frequency vibrations is currently attracting a lot of attention. However, for the same system, it is difficult to satisfy the need for more efficient energy harvesting in a variety of external environments. Accordingly, an adjustable gearing device connected to the energy harvesting system is used herein for adapting energy harvesting to a wide range of external environments. The device uses four symmetrical inclined springs. One end of the springs is connected to a gear and the other end to a mass element. The geometrical parameters of the system can be varied by rotating the gears, thus varying the dynamic stiffness of the system. The kinetic equations of the system are derived and their nonlinear terms are Taylor-expanded. The amplitude-frequency response curve of the system is obtained by solving using the harmonic balance method. Multi-color plots of RMS values of induced voltage and electric power are obtained using the fourth-order Runge-Kutta method. The results show that the device has excellent adjustable performance. Adjusting the rotation angle of the gears can change the soft and hard characteristics of the system's dynamic stiffness and the intrinsic frequency, thus improving the system's energy harvesting performance in different environments. [Display omitted] • An energy harvesting system using a gear unit for regulation is proposed. • The natural frequency of the system is varied by changing the angle of the gears. • The nonlinear form of the system is adjusted by changing the angle of the gears. • The potential energy of the system is adjusted by changing the angle of the gears. • The RMS value of the system is used to analyze its energy harvesting efficiency. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) is a new type of self-powered equipment which can collect vibration energy in the environment. However, using traditional linear float technology is difficult to achieve the low frequency vibration energy harvesting of broadband. In order to solve the problem of the bandwidth limitation the output of TENG, dipteran flight-inspired bistable triboelectric nanogenerator (DFIB-TENG) was proposed in this paper, which was inspired by the flying mechanism of the double wing. The effects of excitation frequency, amplitude and the link length on the energy harvesting of the DFIB-TENG are studied. The results show that the DFIB-TENG has high output in the wide range of 3–7 Hz. The DFIB-TENG has the maximum energy output in the excitation frequency of 6 Hz, the excitation amplitude is 40 mm and the link length is 65.0 mm. The short circuit current of the DFIB-TENG is 12.17 μA, and the output voltage is 1108 V, the output power is 1.25 mW. The DFIB-TENG can drive 50 led lights or feed the electronic watch when working. The dynamic model of the DFIB-TENG was established by the Euler-Lagrange equation, and the dynamic response was analyzed by numerical analysis. The numerical simulation results are consistent with the experimental results, and the correctness of the completion results is verified. The DFIB-TENG can be used to harvest low frequency bridge vibration energy, providing electricity for its health monitoring and sensing network. [Display omitted] • Dipteran flight-inspired bistable triboelectric nanogenerator (DFIB-TENG) was proposed. • Broadband energy harvesting can be achieved by using dipteran flight mechanism • Experimental results show that DFIB-TENG can be used to harvest low frequency vibration energy. [ABSTRACT FROM AUTHOR]

This study aimed to compare the effect of local vibration (LV) and whole body vibration (WBV) on lower body flexibility and to assess whether vibration treatments were more effective than traditionally used static and dynamic stretching methods. Twenty-four well-trained male combat athletes (age: 22.7 ± 3.3 years) performed four exercise protocols - LV (30 Hz, 4 mm), WBV (30 Hz, 4 mm), static stretching (SS), and dynamic stretching (DS) - in four sessions of equal duration 48 hours apart in a randomized, balanced order. During a 15-minute recovery after each protocol, subjects performed the stand and reach test (S&R) at the 15th second and the 2nd, 4th, 6th, 8th, 10th and 15th minute. There was a similar change pattern in S&R scores across the 15-minute recovery after each protocol (p = 0.572), remaining significantly elevated throughout the recovery. A significant main protocol effect was found for absolute change in S&R scores relative to baseline (p = 0.015). These changes were statistically greater in LV than WBV and DS. Changes in SS were not significantly different from LV, but were consistently lower than LV with almost moderate effect sizes. After LV, a greater percentage of subjects increased flexibility above the minimum detectable change compared to other protocols. Subjects with high flexibility (n = 12) benefited more from LV compared with other methods (effect size ≥ 0.862). In conclusion, LV was an effective alternative exercise modality to acutely increase lower extremity flexibility for well-trained athletes compared with WBV and traditional stretching exercises. [ABSTRACT FROM AUTHOR]

To solve the instability problem of the magnetic suspension rotor caused by the low frequency vibration during high speed operation, the improved disturbance observer is utilized to observe the low frequency vibration of the magnetic suspension rotor, making a provision for the suppression of the vibration in the controller. The improved disturbance observer can not only correctly observe the low frequency vibration of the magnetic suspension rotor in high speed, but also effectively overcome the effect of the deformation of the magnetic suspension rotor in high speed. Related experiments were performed at 24 000 r/min for a 100kW magnetic suspension motor. The results of the experiments show that the low-frequency gain of the magnetic suspension motor decreased by 20 dB, and the vibration is reduced by 36. 8 μm. The control precision increases by 63. 89% after adding the improved disturbance observer into the active magnetic bearing system, compared with the original system. The results show that adding the improved disturbance observer into the system can effectively suppress the low frequency vibration and improve the stability of the magnetic suspension motor in high speed. [ABSTRACT FROM AUTHOR]

In this study, the effect of posture, vibration magnitude and frequency on seat-to-head (STH) and back support-to-head (BTH) transfer functions has been studied under vertical sinusoidal vibration. Twelve healthy male subjects participated in experimental work to measure vertical vibration transmitted to the occupants' heads in three representative postures (erect, vertical backrest and forward lean on table) under three magnitudes of vibration (0.4, 0.8 and 1.2 m/s² r.m.s.) in frequency range 1 to 20 Hz. From collected data sets, the effects of vibration magnitude, vibration frequency and postures on STH and BTH transmissibility and phase were measured over the prescribed frequency range. The result suggested that inclusion of all possible variables in optimal design of vehicle seat, suspension and comfort analysis would improve the design and analysis. The comparison of experimental and model response reveals that both models matched with mean experimental data sets most closely and the models provide the best description of the biodynamic response of seated human subjects under vertical whole body vibration. [ABSTRACT FROM AUTHOR]

The article discusses the comparison of random vibration responses between coupled model for a road-rail fire fighting vehicle and traditional model. It notes that some field measurements are carried out to validate the two models. The result shows that the traditional model is suited only to study the vibration performances of car body and low vibration features of wheel rail while the coupled model is more suitable in the study of random vibration features within the whole frequency domain.

A hybridized blue energy harvester based on triboelectric-electromagnetic hybridized generator is developed to extract the abundant energy from water waves. Within the pendulum design of the blue energy harvester, an interdigital electrodes based triboelectric nanogenerator (I-TENG), a switches based triboelectric nanogenerator (S-TENG) and an electromagnetic generator (EMG) are complementarily integrated, to more effectively scavenge the water wave energy after packaged in a waterproof enclosed box. The outputs of both TENGs are enhanced by an optimized flexible circular ring supporting a rolling magnet due to soft contact and induced larger contact area. With a novel designed hybridized circuit, output power can reach to 95.4 mW at load of 100Ω. After the management circuit, a lithium battery of 200 mAh can be charged from 3.07 V to 3.35 V by this blue energy harvester with six hours of water wave impaction. Besides using the hybridized blue energy harvester to power a digital temperature sensor directly and continuously, an all-weather IoT platform is also established with the blue energy harvester, a solar cell panel and a Bluetooth sensor module. The ambient information of humidity and temperature can be detected and sent to user-end by the Bluetooth sensor module under various conditions with or without daylight and water waves. Image 1 • A hybridized blue energy harvester based on triboelectric-electromagnetic hybridized generator is developed to extract energy from water waves. • The outputs of TENGs are enhanced by an optimized flexible circular ring supporting a rolling magnet. • With a novel designed hybridized circuit designed for hybridized generator, output power can reach to 95.4 mW at load of 100 Ω. • An all-weather IoT platform is also established with the blue energy harvester, a solar cell panel and a Bluetooth sensor module. • The ambient information of humidity and temperature can be detected and sent to user-end by the Bluetooth sensor module under various conditions with or without daylight and water waves. [ABSTRACT FROM AUTHOR]