Key Engineering Materials Vols. 609-610

Abstract: In this paper, the crosstalk in potential measurements caused by the topographic feedback and the resonance frequency in Kelvin probe force microscopy (KPFM) was investigated in frequency modulation (FM), amplitude modulation (AM) and heterodyne amplitude modulation (heterodyne AM) modes. We showed theoretically that the distance-dependence of the modulated electrostatic force in AM-KPFM is significantly weaker than in FM-and heterodyne AM-KPFMs. We experimentally confirmed that the crosstalk in FM-KPFM and heterodyne AM-KPFM is weak than that in AM-KPFM due to the bigger difference of the modulated frequencies in topographic and potential measurements in FM and heterodyne AM-KPFMs. We also compared the corrugations in the local contact potential difference (LCPD) on the surface of Si (001) show that difference on topographic (potential) images is approximately 15 pm (10 mV) between the faulted and unfaulted parts using heterodyne AM-KPFM, on the other hand, this difference cannot be observed using AM-KPFM mode. Original of this was attributed to the low crosstalk between the topographic and the LCPD measurements in heterodyne AM-KPFM.

Abstract: A new concept of using four meander suspensions as a constraint is proposed to construct planar spring-like energy harvester actuators with larger displacement. Meander suspensions with multi-folded beams having three vibrating directions. This paper introduce a new structure of “-type” to calculate modulus of elasticity of one meander suspensions. Based upon the micro deformation theory and the displacement superposition theory, the expression on the displacement for the movement end of the meander beams by outer forces and force moments are deduced. Since the energy harvester is geometric symmetry, elasticity coefficient and natural frequency of the energy harvester will be deduce by above given information. The finite-element analysis was used to model the performances and verified the above mentioned mechanic analysis method.

Abstract: Deep reactive ion etching (DRIE) process is specially invented for bulk micromachining fabrication with the objective of realizing high aspect ratio microstructures. However, various tolerances, such as slanted etched profile, uneven deep beams and undercut, cannot be avoided during the fabrication process. In this paper, the slanted etched profile fabrication tolerance with its effect on the performances of lateral comb-driving resonator, in terms of electrostatic force, mechanical stiffness, and resonance frequency, are discussed. It shows that comb finger with positive slope generates larger electrostatic force. The mechanical stiffness along lateral direction increases when the suspended beam slants negatively. The resonance frequency is 1.116 times larger if the comb finger and beam are tapered to -2⁰ and + 2⁰, respectively. These analytical results can be used to compensate the fabrication tolerances at design stage and allow the resonator to provide more predictable performance.

Abstract: This paper presents an analysis about the variation of quality factor (Q-factor) aiming at the complex micro resonator to explore the mechanism of the energy loss under different pressures. To demonstrate the work, a series of resonators are designed, which mainly differs in the squeeze-damping and scale of the beam. According to corresponding structure, the Q-factor is measured at different pressures while the theoretical air damping model combined with Christians model is also proposed. The air damping models of three types are proved to have 10%~30% relative error compared to experimental results in low vacuum, respectively. And, for the high vacuum, the structural energy loss plays an important role on the Q-factor, which increases with the decrement of comb quantity and the beam width.

Abstract: The heat and mass transfer process between gas and micron water droplets is complicated. During the process, the collision of droplets can affect the evaporation rate of droplets, and the heat and mass transfer between two phases as well. Unsteady numerical simulation was done in this paper to investigate the effect of droplets collision on the heat and mass transfer. The results show that after the water droplets collide and combine together, the total heat transfer area decreases, thus the accelerated rate of droplet temperature drops. As a result, the unsteady time of droplet temperature rising with considering droplets collision in calculation is longer than that of without considering droplets collision. After droplets collide and combine together, the evaporation rate drops, thus the droplets survival time and time for evaporating completely are extended. The steady gas temperature with droplets collision is higher slightly than that without droplets collision, which indicates that the droplets collision affect the results by using numerical prediction. Against the experimental data, the predicted results with droplets collision are more believable than that without collision. Considering the droplets collision and combination, the change rate of the droplets diameter drops, thus the gas velocity picks up slowly.

Abstract: The atomic spin interaction is very important for understanding the superficially magnetic feature of nanostructure at atomic level. Magnetic exchange force microscopy (MExFM) is an innovative means of measuring surface spin force. But it is difficult to separate the surface topography and spin information. We develop the magnetic exchange force microscopy using ferromagnetic resonance (FMR-MExFM). The theoretical and experimental results demonstrate that this method can separate the two kinds of information effectively. Here, in order to obtain the high sensitivity in detecting the ferromagnetic resonance, we fabricate the microwave irradiation device to optimize the position between the device and the cantilever. We have succeeded in observing the ferromagnetic resonance effect and determining its resonant frequency using the homemade microwave irradiation device and the network analyzer. This research is very important for developing FMR-MExFM and novel magnetic sensor, detecting the magnetic information, etc.

Abstract: Based on the traditional piezoelectric effect theory, the process of multi-piezoelectric effects generation is analyzed and the theory of the secondary and tertiary piezoelectric effect is deduced by four kinds of piezoelectric equations. Experimental research is performed through the PZT-5 piezoelectric ceramics stack, the existence of multi-piezoelectric effects is verified and experimental data is obtained under certain boundary conditions. The experimental data results show that if an external force which is applied to the positive piezoelectric effect is 400, the displacement generated by the secondary converse piezoelectric effect is 0.16. Therefore, starting from the first positive piezoelectric effect of the piezoelectric ceramics under applied force, the displacement generated by the secondary converse piezoelectric effect and the voltage generated by the tertiary positive piezoelectric effect are all linear with the applied force.

Abstract: The novel solid MEMS switch can improve the performance of the MEMS initiator, which will be more secure and reliable.While the leads of its package are weak under launch environment. Therefore, this paper aims to carry out multi-physical field reliability analysis, by using FEM simulation analysis, which can simulate the real launch environment better and obtain the reliability and potential failure modes of leads in impact, temperature, current coupling field, thus providing theory reference for the design and application of the novel solid MEMS switch.

Abstract: In the paper, the PV power supply control system is proposed to realize the uninterrupted power supply, including DC and AC supply. By the method of combining software with hardware, through the solar panel to the configured two pieces of battery could realize the function of fast and slow charging, and the supply battery is changed by testing the battery power to the load uninterrupted power supply. Moreover, when the output voltage of the solar panel is lower than the battery, the output voltage of solar panel is boosted by DC/DC circuit to make the solar panel at low pressures also to charge the battery, effectively solving the difficult solar energy in the weak power supply problem.

Abstract: The paper do some research on the positive piezoelectric effect of piezoelectric ceramic stack. Piezoelectric energy generator is laid on the highway surface, and using the stress which is generated by piezoelectric device to generate electric energy when the vehicle is passing. The generated electric energy is stored in the lithium battery package for street lighting at night after the circuit adjustment. The experimental demonstration and theoretical analysis show that the electric energy generated in piezoelectric stack can be stored in 12V-12Ah lithium battery package within 12h by the circuit of 3F ultracapacitor and LM2575HVT-12V regulator when the output voltage of LM2575HVT-12V is 12V. 12V-12Ah lithium battery package supply energy to the 12V, 12W high power LED lighting for 12h, and meeting the street lighting standards.