Shaohua Niu

An analysis of the coupling effect for a hybrid piezoelectric and electromagnetic energy harvester

This paper investigates the influence of the electromechanical coupling effect on the performances of a hybrid piezoelectric and electromagnetic energy harvester. For a common hybrid energy harvester, we derive an accurate analytical solution and get expressions for the resonant frequency shift, output power, amplitude and conversion efficiency. Then, based on various degrees of coupling effect, the performance of the harvester is studied with different load and excitation frequency, and compared with piezoelectric-only and electromagnetic-only energy harvesters. The results show that the bigger the coupling coefficient, the greater the resonant frequency shift, output power and conversion efficiency. In the weak coupling and medium coupling, the performances of the hybrid energy harvester are better than those of the two separate energy harvesting techniques; however, the hybrid energy harvester does not increase the power and conversion efficiency in contrast with the piezoelectric-only and electromagnetic-only energy harvester in strong coupling. In addition, the optimal load resistance of the hybrid energy harvester is related to the strength of the coupling effect; moreover, the optimal load resistance of the electromagnetic harvesting element for the hybrid harvester is bigger than that of the electromagnetic-only harvester in the medium and strong coupling. Through analysis of the results, ways of boosting the performances of the hybrid energy harvester are found.

Design and Vibration Sensitivity Analysis of a MEMS Tuning Fork Gyroscope with an Anchored Diamond Coupling Mechanism

In this paper, a new micromachined tuning fork gyroscope (TFG) with an anchored diamond coupling mechanism is proposed while the mode ordering and the vibration sensitivity are also investigated. The sense-mode of the proposed TFG was optimized through use of an anchored diamond coupling spring, which enables the in-phase mode frequency to be 108.3% higher than the anti-phase one. The frequencies of the in- and anti-phase modes in the sense direction are 9799.6 Hz and 4705.3 Hz, respectively. The analytical solutions illustrate that the stiffness difference ratio of the in- and anti-phase modes is inversely proportional to the output induced by the vibration from the sense direction. Additionally, FEM simulations demonstrate that the stiffness difference ratio of the anchored diamond coupling TFG is 16.08 times larger than the direct coupling one while the vibration output is reduced by 94.1%. Consequently, the proposed new anchored diamond coupling TFG can structurally increase the stiffness difference ratio to improve the mode ordering and considerably reduce the vibration sensitivity without sacrificing the scale factor.

Analysis of Nonlinearities in Force-to-Voltage Conversion in Vibratory Microgyroscope

At present, the MEMS vibratory gyroscope is an extensively researched MEMS sensor. The vibratory gyroscope is used to measure the angular velocity of object, which is based on Coriolis effect. According to the working principle of this kind of gyroscope, the force to voltage is an important part conversion for realizing the role of the gyro. In the paper, we analyze the nonlinearities in force-to-voltage conversion, and conclude that the mechanical quadrature signal can form the limiting factor for the overall accuracy of the system.

Modeling and Analysis of an Up-conversion Electret Electrostatic Energy Harvester

In order to reduce the environmental sensitive frequency of electret-based vibration electrostatic energy harvester (E-VEH), an up-conversion structure is designed. This harvester is a double cantilever structure includes a low frequency beam and high frequency beam. Electret is bounded to the high frequency beam, the low frequency beam vibrates excited by environment, and impacts the high frequency beam. The model of this structure is established and analyzed firstly. Then a prototype is made and tested. According to the measurement result, this kind of structure can convert part of the vibration energy within the vibration frequency between 1Hz and 70Hz into electrical energy under the action of the excitation load with the amplitude is 8m/s. This indicates that the up-conversion structure can validly reduce the sense frequency of E-VEH, and can expand the harvester work bands. Introduction With the rapid development of MEMS, COMS sensors and data processing, the times of internet of things is coming. As an important part of internet of things, wireless sensor networks are rapidly growing. At present, chemical batteries are used for suppling power to wireless sensor networks. However, it hampers the development of wireless sensor networks because chemical batteries have maintenance, environmental and size issues. In recent years, it is concerned and studied how to harvest environment energy and convert it into electric power [1-3]. The vibration harvester has been paid more attention because vibration happens in anywhere and anytime. For vibration harvester, three mechanisms have been proposed: piezoelectric, electromagnetic and electrostatic Compared with piezoelectric and electromagnetic energy harvesters, electrostatic systems have advantages of compatibility with MEMS processes and small size. Electret-based vibration energy harvesters (E-VEHs) can be divided into two types, in-plane and out-of-plane. Compared with the in-plan E-VEHs, Out-of-plane E-VEHs have lower production costs because the device structure and process are relatively simple. Driven by the merit of low production costs, more and more researchers have focused on out-of-plane E-VEHs and attempted to improve their performance. When designing structure of out-of-plane E-VEHs, cantilever or double-end fixed beam is commonly employed. The size of these harvesters is usually small as their employers are always small. Therefor the natural frequency of most harvester structures is relatively high, always at the level of KHz. However, in natural environment, vibration frequency is always at the level of Hz. In order to increasing the harvest efficiency, it is an important point to decrease the structure natural frequency. In this paper, an up-conversion structure is introduced to reduce the environmental sensitive frequency of the E-VEHs. The model of this structure is established, and its characteristics are analyzed. By test, this up-conversion structure can effectively decrease the sensitive frequency of cantilever E-VEHS. Work Mechanism of E-VEHs The core of E-VEHs is a kind of dielectric function material called electret which can keep space charge or dipole charge for a long time. With the space electret method promotion, more and more space charge electret, as shown in Fig.1 (a), has been used, especially for vibration energy harvester. 93 Copyright

Real-time numerical calculation for penetration depth of projectiles into concrete targets

ABSTRACT Based on the acceleration data measured by penetration experiments with ogive-nose projectiles into semi-infinite concrete targets, a fuzzy method which can calculate the real-time penetration depth was developed. In the proposed method, the whole process of penetration was divided into three stages according to the instantaneous velocity, and each stage was described by different models. By judging the calculation error, threshold velocities between stages were automatically determined. Meanwhile, the striking velocity of the penetration process was calculated using the acceleration in whole trajectory. The calculated values by model are in reasonably good agreement with the measured data from experiments.

Study of Intrinsic Dissipation Due to Thermoelastic Coupling in Gyroscope Resonators

This paper presents analytical models, as well as numerical and experimental verification of intrinsic dissipation due to thermoelastic loss in tuning-fork resonator. The thermoelastic analytical governing equations are created for resonator vibrating at drive-mode and sense-mode, and thermoelastic vibration field quantities are deduced. Moreover, the theoretical values are verified that coincided well with finite element analysis (FEM) simulation results. Also, the comparison of vibration field quantities is made to investigate the effect of different conditions on resonator thermoelastic vibration behavior. The significant parameters of thermoelastic damping and quality factor are subsequently deduced to analyze the energy dissipation situation in the vibration process. Meanwhile, the corresponding conclusions from other studies are used to verify our theoretical model and numerical results. By comparing with the experimental quality factor, the numerical values are validated. The combination of the theoretical expressions, numerical results and experimental data leads to an important insight into the achievable quality factor value of tuning-fork resonator, namely, that the thermoelastic damping is the main loss mechanism in the micro-comb finger structure and the quality factor varies under different vibration modes. The results demonstrate that the critical geometry dimensions of tuning-fork resonator can be well designed with the assistance of this study.

Analysis and Design of Stiffness of the Elastic Beam in Linear Vibration MEMS Gyroscope

At present, the linear vibration gyroscope is a major research of micro-mechanical gyroscopes. According to the working principle of the linear vibration gyro, in order to enhance its sensitivity, it is demanded that its driven model natural frequency and detection model natural frequency should be close. Thus, according to the gyroscope structure, it is required that the stiffness coefficients of the two models should be into a certain proportion. The stiffness coefficients of the models are mainly decided by the rigidity of the elastic beam, therefore, the design of stiffness of the elastic beam will directly affect the gyro performance. In this paper, the analytical formula for calculating the stiffness of the elastic beam, which is commonly used in linear vibration MEMS gyro, is derived by using the energy method. Then the elastic beams are designed based on the formula, and the design is reasonable verified by simulation and experimental comparison.

Measurements on mechanical properties of boron-doped silicon materials for micro inertia sensor

The capacitive structure of comb capacitive micromachined gyroscope is a kind of important structure. The mechanical properties of micro inertia sensor material had changed when the structures experienced high temperature boron diffusion, lithography and etching et.al. micromachined process. Therefore, it is necessary to measure the basic mechanical properties of boron-doped material in order to supply exact material parameters for design and fabrication of micro inertia sensor. With the rapid development of measurement technologies, the nano indentation technology had become an ideal method to obtain the mechanical properties of MEMS structures material accurately. We obtained the elastic modulus and hardness of heavy boron-doped silicon material using nano indenter. The experimental results showed that the elastic modulus and hardness of heavy boron-doped silicon material had increased comparing with the silicon material.

The micro mechanical environment on the comb capacitive micro-machined gyroscope

With the in-depth researches on MEMS sensors, a lot of mechanical problems are encountered inevitably. Especially for the comb capacitive micro-machined gyroscope, a typical MEMS inertia sensor, the speciality of its structure and micro size determines the characteristics of the mechanical environment. With the reduction of structural size, the ratio of surface force and body force has increased clearly. Comparing with the roles of body force, the roles of surface force in MEMS sensors become more and more important. The micro forces, such as electrostatic force, Van de Waals force, capillary force and air-damping force were analyzed, and the action extent of these micro forces were obtained.