Search

This paper presents a planar architecture implementing dual-nonlinearity mechanism for broadening bandwidth of a two-degree-of-freedom MEMS energy harvester. The proposed device consists of an electromagnetic-based inner resonator for power generation, and an outer resonator for accessory frequency tuning. In comparison with conventional 2DOF configuration, different high-order nonlinearity is subjected to the first two resonances by nonlinear springs incorporated into the inner and outer resonator, respectively, achieving double hardening responses with increased bandwidth at elevated excitation. Moreover, independent tuning of the resonant frequency and working bandwidth of both resonances could be achieved through concordant control of inner and outer nonlinear resonator, and with further adjust of mass and frequency ratio, the low-efficiency power generation range separating adjacent resonances could be effectively reduced. It’s numerically shown that with proper nonlinearity at both oscillation stages, the approximate convergence of two nonlinear resonances with broadband and narrow low-efficiency range could be achieved following the mass ratio of $\mu and linear frequency ratio of $0.7 between inner and outer stage. At acceleration of 1 g, test result further confirms that under dual-nonlinearity with nonlinearity ratio of 0.5, a continuous energy harvesting spectrum covering two nonlinear responses is realized with mass ratio of 0.02 and frequency ratio of 1, showing 3-dB bandwidth of 65 Hz. Power output of $127.7~\mu \text{W}$ and normalized power density of $1064~\mu $ Wcm $^{-3}\text{g}^{-2}$ are achieved with the optimum load resistance of $37.5~\Omega $ . This mechanism could be further applied to multi-DOF VEH for ultra-wide bandwidth of energy harvesting. [2020-0231]

This letter presents a highly efficient microsolenoid integrated with a closed magnetic circuit to enhance the power density of microelectromechanical systems (MEMS) electromagnetic energy harvesters. Compared with most MEMS electromagnetic energy harvesters adopting an air-cored planar coil, a high permeability closed magnetic circuit is specifically designed and integrated inside the microsolenoid with multiple wire turns for higher electromechanical coupling, which contributes to the effective increased power density of the MEMS energy harvester. Moreover, the wafer-level microsolenoid is compatible with nonlinear springs, which bring higher power output over a wideband frequency range. At an acceleration of 1 g , the prototype shows a load power of 265.2 µW and normalized power density of 5.9 mW·cm-3·g-2 with a load resistance of 40.1 Ω, accompanied with a half-power bandwidth of 30 Hz. The fully integrated solenoid is compatible with other soft magnetic-material and frequency-broadening mechanisms, providing adequate potential for comprehensive performance enhancement of MEMS electromagnetic energy harvesters.

The stable travel range of parallel-plate electrostatic actuator with a linear suspension flexure is limited to a third of the nominal gap due to the pull-in instability resulting from the inherent nonlinear behavior of electrostatic force. To overcome this problem, the nonlinear suspension flexure that can counteract the nonlinearity of electrostatic force is widely adopted. Based on this concept, we present a novel method for designing a customized nonlinear micro-flexure with monotonically increasing stiffness. The mechanism is characterized that an ejector rod consisting of the double clamped-guided beams slides along a geometrically customized trajectory patterned on the slider, and thus, a prescribed force-displacement relationship in horizontal direction is generated. To validate this design concept, two specific flexures, a mimic-electrostatic-nonlinearity flexure, whose restoring force varies with the electrostatic force, and a seventh-order nonlinear flexure, whose flexure force is proportional to the eighth power of the deflection, were designed and fabricated on the silicon-on-insulator wafer. The experimental results show that the measured force-displacement curves for two nonlinear flexures are in good agreement with the theoretical predictions. In addition, the proposed method can be also introduced to other systems, in which the prescribed nonlinearity is needed. [2018-0240]

A novel planar architecture with dual-nonlinearity mechanism is proposed for broadening bandwidth of a two-degree-of-freedom (2DOF) MEMS energy harvester. Two micro springs with different inherent nonlinearity are incorporated into the inner and outer oscillation stage of a 2DOF planar spring-mass resonator, helping to generate double hardening nonlinear responses with increased bandwidth, and for the first time, overcoming the deep valley separating neighboring resonances in multi-modal system. This characteristic leads to an ultra-wide operation bandwidth covering two adjacent nonlinear responses. Test results show that at the acceleration of 1g, a continuous energy spectrum with half power bandwidth over 100Hz and high normalized power density of $952\ \mu \mathrm{Wcm}^{-3}\mathrm{g}^{-2}$ are achieved.

The “soft-landing” effect during the closure of RF-MEMS switches is crucial for improving their reliability. However, the rebound suppression effectiveness has rather poor robustness against the dimension deviations and waveform distortions resulting from micro-fabrication tolerance, wear and tear, and circuit aging in the device’s life-cycle. In contrast to the traditional constant stiffness system, this letter proposes a novel self-adaptive stiffness approach, whereby the system’s stiffness increases markedly with increasing displacement so that its elastic potential energy against the electrostatic energy is mainly concentrated in the region near the closing position for a better rebound suppression. Our experiments show that, for an ensemble of fabricated devices subjected to the unified dual-pulse actuation waveform, the reliable working gap range of the new approach ( $1.4~\mu \text{m}$ ) in which the switches can be closed completely, is 4.6 times larger than that of the constant stiffness scheme ( $0.3~\mu \text{m}$ ). In addition, for the actuation voltage and pulse time with variations of up to ±10%, this new approach shows significantly reduced closure time and bounce.

A novel electromagnetic energy harvester structure with a highly efficient closed magnetic circuit is presented. An opposite polarity arrangement of a permanent magnet pair results in the maximum change of magnetic flux linkage in the solenoid when the energy harvester is in vibration. The strong coupling between the stator iron cores and the vibrating permanent magnets leads to significantly enhanced output voltage and power and a broadened operation bandwidth. Compared to open magnetic circuits, a closed magnetic circuit can effectively improve the output voltage and power. A maximum root mean square output voltage of 67 mV, a working bandwidth of 7.3 Hz, and a load power of 3.04 µW are obtained from the prototype at an acceleration of 5 m/s2.

This paper reports a novel nonlinearity tuning method through sophisticated geometrical design for wideband energy harvesting application. By carefully controlling the thickness to length ratio of the planar spring beams, the nonlinear stiffness coefficient can be intentionally and precisely adjusted, while the linear stiffness coefficient can be kept unchanged. Thanks to the different effects on the linear and nonlinear parts, both the resonant frequency of the linear part and the bandwidth range of nonlinear vibration can be designed separately. As a proof of concept, MEMS-based electromagnetic vibrational energy harvesters employing the independent nonlinearity tuning method have been designed and fabricated. Both simulation and experiment were conducted to validate our method. At the acceleration of 0.5 g, the micro-fabricated device is able to tune the operating bandwidth of the output voltage from 37 Hz to as wide as 75 Hz. This design can easily tune the length and thickness of the spring beams without changing the volume of the whole energy harvester device, which is compatible with MEMS batch fabrication process.

This paper presents the first MEMS-based bi-stable electromagnetic energy harvester with polarity-reversible integrated closed magnetic circuit. The mechanism of polarity reversal in micro-scale closed magnetic circuit is utilized to maximize the flux variation rate, and the overall size and fabrication tolerance of the proposed device are effectively reduced with integrating closed magnetic circuit and resonant structure. Bi-stable configuration with shallow potential barrier less than 3.6μJ is achieved to trigger and sustain inter-well oscillation in micro-scale. It’s experimentally and numerically shown that at the acceleration of 1g, a large bandwidth of 75.2Hz with power output of 146.3μW is obtained, and significant normalized power density (NPD) of 203.2μWcm-3g-2 is simultaneously achieved.

In this paper, we designed and fabricated a highly nonlinear suspension flexure with geometrically predetermined eighth order force-displacement relation for extension of the stable travel range of electrostatic actuator. Its strong nonlinearity is obtained by a rolling slide between a customized curved trajectory and a ball at the tip of the mandril. The customized nonlinear behavior can be adjusted and dominated by a geometrically predetermined trajectory. The experimental result illustrates that the restoring force of the fabricated nonlinear flexure is proportional to the eighth power of the electrode displacement approximately, and the stable travel of the electrostatic actuator with this flexure is extended to at least 63% of the nominal gap. The proposed scheme can also be implemented to other systems where the nonlinearity is needed, such as energy harvesting and the damper in the micro-scale.

In this paper, we propose an inherent variable stiffness approach to suppress bounce of electrostatic actuator caused by the gap deviation which is unavoidable because of the micro-fabrication deviation, the tear and wear in the device life-cycle. The variable stiffness is realized through simple clamped-guided beam with large deformations. It have been demonstrated that for the 0.3 μm gap variation, the fluctuation of collision speed (from zero to 2.7cm/s) for the variable stiffness actuator is 62% less than that of constant stiffness counterpart (from zero to 7.18cm/s) under the dual pulse voltage actuation. Meanwhile, the driving voltage based on the variable stiffness spring is only 19.5% lower than that of the constant stiffness spring. The proposed variable stiffness approach may find ample application for extending the life-cycle.

An inherent variable stiffness approach was proposed to suppress the rebound and impact of the electrostatic switch due to waveform deviations. A simple clamped-guided beam spring with large deflection, which generated inherent cubic nonlinear restoring force, was adopted for implementation of the approach. The initial stiffness is very small but increases significantly with the displacement. In this way, the spring restoring force is mostly concentrated in the second half of the operation stroke during closing switch, which weakens the sensitivity of the device performance to the actuation voltage waveform and achieves better robustness. A dual-pulse actuation voltage method for soft-landing (near zero closing speed) was studied to evaluate the effectiveness of the approach. According to the experimental results, even the pulse width varied 10%, no rebound was observed for the electrostatic switch with the new configuration. At the same time, the actuation voltage of the new actuator was 19.5% lower than that of the constant stiffness spring counterpart.

This paper presents a nonlinear electrostatic actuator which utilizes the nonlinear mechanical properties of the classical clamped-guided beam springs with large deform­ation to slow impact velocity of the movable plates. The initial stiffness of the spring is very small but increases significantly with the displacement. In this way, the increased kinetic energy would be limited. At the same time, because of the small initial stiffness, a lower driving voltage can generate enough kinetic energy to overcome the restoration force to reach a dynamical pull-in stage. The experiments indicated that the impact velocity was 0.67cm/s. The driving voltage is 49% lower than the linear spring counterpart. The static stable travel is extended to about 56.5% of the initial gap in theory.

This paper proposed the segmented magnetic circuit method to simulate the large displacement planar micro-coil (PMC) microactuator for micro-magnetic relay applications, which adopted enclosed miniaturized magnetic yokes. The segmented magnetic circuit model has been established to describe the magnetic flux variation and the redistribution effects of the magneto motive force (MMF) induced by the large air gap and large ratio between the radical and vertical size. Based on the optimized parameters, the PMC microactuator was fabricated through UV-LIGA technology and tested to verify the model under scrutiny. The large displacement was realized by using laminated photoresist sacrificial layer process. After comparing the measurement and simulation results, it is concluded that the modified model can describe the influence of key parameters over the output electromagnetic force. The proposed methodology is demonstrated to be efficient in the analysis and optimization of the magnetic MEMS devices of PMC structures with embedded magnetic yoke.

A micro-compression test method was presented to evaluate the mechanical property of the TSV-Cu micropillar in this paper. Firstly, the test sample containing TSV-Cu micropillar was prepared by MEMS micromachining technology. Then, the mechanical property of TSV-Cu micropillar was measured by a self-made micro-compression system. Finally, the effect of thermal treatment on the mechanical property of TSV-Cu micropillar was studied. The experimental results showed that the average yield strength (σ0.2) of the TSV-Cu micropillar was 167 MPa. But it decreased to 137 MPa after being thermally treated at 400°C for 1 hour, which was probably due to the increased grain size of Cu.

This letter provides an investigation on the combined influence of the potential barrier (ΔE) and separation gap of a double well (Δx) to maximize the performance of an electromagnetic bistable energy harvester (BEH). A concise method based on a high-fidelity orthogonal array sampling technique is further developed to facilitate the searching of the parameter-set corresponding to the desired potential well. According to numerical and experimental results, a barrier depth slightly lower than the threshold of interwell oscillation cooperating with a properly large separation gap is preferred for improving the power output, and enlarging the redundancy of the excitation intensity for inducing the well escape behavior. Compared to the potential well with the same barrier depth but a narrow separation gap of 1.7 mm, the optimal well with a larger Δx of 2.3 mm not only demonstrates a 60% higher output power at an acceleration of 1 g, but the intensity threshold for interwell oscillation is also reduced to 0.7 g. This work presents an insight and a method into shaping the potential well for the optimized performance and increased redundancy of a bistable configuration.

Contact bounce, high driving voltage, and poor robustness to process deviations are the main bottlenecks that limit the reliability of MEMS electrostatic switches. In this study, a variable stiffness strategy offers an optimized path to reach the closure position for the movable electrode. In the proposed method, the switching system's stiffness is low enough to reduce the driving voltage at the initial stage but increases rapidly as the movable electrode approaches the closure position for braking. Our experimental results prove that this strategy can suppress contact bounce, reduce pull-in voltage without compromising pull-in time, and also enhance robustness to process deviations, improving the overall reliability of the MEMS switches.Contact bounce, high driving voltage, and poor robustness to process deviations are the main bottlenecks that limit the reliability of MEMS electrostatic switches. In this study, a variable stiffness strategy offers an optimized path to reach the closure position for the movable electrode. In the proposed method, the switching system's stiffness is low enough to reduce the driving voltage at the initial stage but increases rapidly as the movable electrode approaches the closure position for braking. Our experimental results prove that this strategy can suppress contact bounce, reduce pull-in voltage without compromising pull-in time, and also enhance robustness to process deviations, improving the overall reliability of the MEMS switches.

A new fabrication technology utilizing the nickel foil as the flexible mask for the non-planar surface patterning is presented. Compared with the traditional patterning on the planar substrates, the versatile micro-fabrication method based on the re-usable nickel membrane mask, has patterned on the curve surface. We shape the pattern in the nickel foil by the laser cutting. It allow for fabrication on a wide range of substrates, enabling feature line widths down to 50 μm. The nickel foil masks, gaining reconversion as force is removed, can be wrapped precisely on the targeted curve substrate.

This paper describes a new fabrication technology for high aspect ratio magnetic microstructures. These microstructures are made of composite magnetic materials. In this new technology, a master mold was made using photolithography and the mixture of magnetic particles and polymer was used in micro-molding process. The microstructures were then thermally cured at a temperature lower than 80 °C. To demonstrate the feasibility of using the technology in making magnetic microstructures, both hard magnetic and soft magnetic particles were tried in our experiments. The magnetic particle sizes ranged from 2.3 to 44 μm, which sets the limitations in feature sizes achievable for the magnetic microstructures. Different weight ratios were tried, the maximum weight ratio between the magnetic particle and the polymer was over 2:1. For both wall and trench microstructures, the maximum aspect ratio was found to be over 10, which demonstrates its great potential for micro-fabrication applications.

This article proposes a bistable electromagnetic micro-actuator consisting of a planar suspended platform and an integrated micro-coil, which was fabricated by micro-electromechanical systems technology. Its operational principle is based on the equilibrium between the magnetic force and elastic force. The elastic force of the suspended platform is analyzed by Castigliano's theorem, and the magnetic force is analyzed by the magnetic circuit method. Both the mechanical and magnetic characteristics were simulated by the finite-element method and verified by testing. Test results showed that the bistable electromagnetic micro-actuator could be realized at a voltage pulse of 5 V with 380 μm of large displacement, and the response time is about 4.96 ms.

This paper presents the design, simulation, fabrication and characterization of a novel electromagnetic vibration energy harvester with sandwiched structure and air channel. It mainly consists of a top coil, a bottom coil, an NdFeB permanent magnet and a nickel planar spring integrated with silicon frame. The prototype is fabricated mainly using silicon micromachining and microelectroplating techniques. The tested natural frequency of the magnet-spring system is 228.2Hz. The comparison between the simulation and the tested results of the natural frequency shows that the Young's modulus of microelectroplated Ni film is about 163GPa rather than 210GPa of bulk Ni material. Experimental results indicate that the sandwiched structure and the air channel in the silicon frame of the prototype can make the induced voltage increase to 42%. The resonant frequency of the prototype at 8m/s^2 acceleration is 280.1Hz, which results from the nonlinear behavior of the magnet-spring system. The load voltage generated by the prototype is 162.5mV when the prototype is at resonance and the input vibration acceleration is 8m/s^2 and the maximal load power obtained is about [email protected] when the load resistance is [email protected]

This paper reports the design, fabrication and characterization of a bistable electromagnetic microrelay based on non-silicon surface micromachining technology. It mainly consists of an integrated microcoil at bottom with a spacer, and a suspension spring with a permanent magnet on top. Bistable mechanism is realized by the adoption of the SmCo permanent magnet to hold the microrelay at latching position without current. Switching between two stable states is completed by the variation of current direction in the microcoil. The corresponding power consumption is 25mJ. The fabrication processes of related components are presented. The test result shows that the bistable electromagnetic microrelay can work with low operation voltage pulse of 5V. The output displacement is about 380@mm while the response time is about 4.96ms. Besides, the test insertion loss is -0.02dB and the isolation is -39.91dB at 30MHz.

This paper presents a new method of wet releasing SU-8 structures using very thin Omnicoat^(TM) as sacrificial layer and NMD-3 developer as releasing solution. Four-inch sized SU-8 structures with different pattern and thickness of [email protected] have been successfully released from silicon substrate by this method. Experiments show that Omnicoat^(TM) layer is very helpful to strip SU-8 molds in which metal structures are electroplated. SU-8 can be removed directly using remover if there is an Omnicoat^(TM) layer between the substrate and SU-8 and the electroplated structures is with large dimension. In the case of electroplated structures with small feature size, SU-8 can be removed by combining wet stripping and plasma etching. Nickel micro coils with linewidth of [email protected] and aspect ratio of 4.1 have been fabricated. The analysis about the influence of Omnicoat^(TM) layer's thickness on integrity of SU-8 micro coils is also given in our work.

This paper presents a micro electromagnetic energy harvester which can convert low level vibration energy to electrical power. It mainly consists of an electroplated copper planar spring, a permanent magnet and a copper planar coil with high aspect ratio. Mechanical simulation shows that the natural frequency of the magnet-spring system is 94.5 Hz. The resonant vibration amplitude of the magnet is 259.1 μm when the input vibration amplitude is 14 μm and the magnet-spring system is at resonance. Electromagnetic simulation shows that the linewidth and the turns of the coil influence the induced voltage greatly. The optimized electromagnetic vibration energy harvester can generate 0.7 μW of maximal output power with peak–peak voltage of 42.6 mV in an input vibration frequency of 94.5 Hz and input acceleration of 4.94 m/s2 (this vibration is a kind of low level ambient vibration). A prototype (not optimized) has been fabricated using MEMS micromachining technology. The testing results show that the prototype can generate induced voltage (peak–peak) of 18 mV and output power of 0.61 μW for 14.9 m/s2 external acceleration at its resonant frequency of 55 Hz (this vibration is not in a low ambient vibration level).

This paper presents a new vibration-based electromagnetic micro power generator fabricated using microelectromechanical systems (MEMS) technology, which can convert ambient vibration energy into electric power. The microgenerator consists of a permanent magnet of NdFeB, a copper planar spring and a two-layer copper coil. ANSYS modal analysis was used to predict the resonant frequencies and resonant vibration modes of the spring-mass system. The detailed fabrication processes of the microgenerator are given. Experimental results show that the prototype microgenerator can generate open-circuit voltage of 60mV ac peak-peak with 121.25Hz input frequency and the acceleration of 1.5g (g=9.8m/s^2). The experimental and simulated results were compared and discussed.

This paper discusses fabrication and performance of novel circular spiral inductors on silicon. The substrate materials underneath the inductor coil are removed by wet etching process. In the fabrication process, fine polishing of the photoresist is used to simplify the processes and ensure perfect contact between the seed layer and the top of pillars. Dry etching technique is used to remove the seed layer. The results show that Q-factor of the inductor is greatly unproved by removing silicon underneath the inductor coil. The spiral inductor with line width of 50 fan has a peak Q-factor of 10 for the inductance of 2.5 nH at frequency of 1 GHz, and the resonance frequency of the inductor is about 8.5 GHz. For the inductor of conductor width of 80 µm, the peak Q-factor increases to about 17 for inductance of 1.5 nH in the frequency range of 0.05–3.00 GHz.

Three electromagnetic vibration energy scavengers with electroplated Ni springs have been designed, fabricated and characterised. Prototype I consists of a coil, an Ni spring on a silicon frame and a permanent magnet. Prototypes II and III are with a sandwich structure and consist of two coils, an Ni spring and a permanent magnet. There are air channels in the silicon frame in prototype III. These prototypes were fabricated using microelectromechanical systems microfabricating techniques. The experimental results show the electroplated Ni spring is a nonlinear and hardened one, so the spring–magnet system has a different resonant frequency under different excited vibration. The tested results show that prototype III has the highest output voltage and output power. The maximal load voltage is 157.5 mV and the maximal load power is 21.7 µW for prototype III when it is excited by vibration with 280.9 Hz frequency and 0.8 g acceleration.

A novel suspended radio frequency (RF) spiral inductor was fabricated on glass substrate by using the microelectromechanical systems (MEMS) technology. The suspended spiral inductor is sustained with the T-shaped pillars. Great improvements in Q-factor have been achieved because of the separation between the substrate and the inductor. In the fabrication process, fine polishing of the photoresist is used to simplify the processes and ensure the seed layer and the pillars contact perfectly, and dry etching technique is used to remove the seed layer. The inductance and Q-factor are measured using the HP 8722D network analyzer in the frequency range of 0.05-10 GHz. The maximum quality factor of this inductor is 37 for the inductance of 4.2 nH with a suspended height of 60 /spl mu/m. Also, the relationship between the maximum quality factor and the suspended height were studied; the maximum quality factor grows gradually with the increase of the suspended height.

This paper presents a bistable microswitch fully batch-fabricated on a single glass wafer, comprising of a microactuator, a signal transformer, a microspring and a permanent magnet. The bistable mechanism of the microswitch with large displacement of 160 μm depends on the balance of the magnetic force and elastic force. Both the magnetic force and elastic force were optimized by finite-element simulation to predict the reliable of the device. The prototype was fabricated and characterized. By utilizing thick laminated photoresist sacrificial layer, the large displacement was obtained to ensure the insulation of the microswitch. The testing results show that the microswitch realized the bistable mechanism at a 3–5 V input voltage and closed in 0.96 ms, which verified the simulation.

This paper presents non-silicon MEMS technology for fabrication of Optical communication components. Both pure non-silicon and combined micromachining technologies were realized. For the pure non-silicon surface micromachining technology, the Ni and permalloy were chosen as the structure layer; the photo resist and copper were chosen as the sacrificial layer. Based on the technology, the micro-hinge was realized. It may find ample application in the out-of-plane microstructure, which is common in free-space optical transmission. As an example, a MEMS variable optical attenuator is introduced. It consisted of a hinged shutter to adjust the optical power transmission between the input and output optical fibers. For the combined micromachining fabrication, the electroplating was combined with the traditional bulk silicon technology to realize some unique structure for passive alignment. For example, we had developed the micro-fabricated nickel clamps for packaging of optical fibers in photonics devices. Compared with the all silicon scheme, this approach only involves one additional sputtering, photolithography, and electroplating process.. The presented non-silicon micromachining process offered more choice of material and facilitated the implementation of structure innovation.

Optical power equalization between wavelength-path slots in wavelength division multiplexing (WDM) networks is an increasingly concerning issue in all-optical networks, and this made variable optical attenuators (VOAs) play an increasingly important role in fiber optic transmission systems. Various types of optical attenuators have been realized, but conventional available mechanical VOAs are bulky, costly, and slow. MOEMS technology provides new approaches to improve the characteristic mentioned above. Previous attempts to realize MEMS variable optical attenuators include the use of a micro-driven shutter, a mechanical antireflection switch (MARS) modulator, a micro-machined tilted mirror, and a micro-machined membrane-type waveguide. In this paper, we report the design and fabrication of two types of electromagnetically actuated variable optical attenuator (VOA). They are both driven by a similar construction containing of a plane coil and a FeNi armature. The first one adjusts the attenuation by moving a shutter between the two fibers, the second one by moving one of the fibers directly. The first one is fabricated by nonsilicon surface micromachining technology. In which a copper layer was used as the sacrificial layer, and the electroplated FeNi as the structure layer. This scheme provides another way to fabricate the optical microstructure. According to the experiment results, it has insertion loss less than 3 dB at 1550-nm wavelength, dynamic range greater than 40 dB, 0.2-dB repeatability, and return loss better than 40 dB, driving voltage less than 20 V. For the second one, it included the silicon platform for adjustment of optical coupling between two optical fibers. The main fabrication process of the silicon platform is was the KOH antistrophic wet chemical etching of silicon wafers. The silicon wafer is further selectively etched from the bottom side to subtract the thickness of the silicon elastic platform. In addition, two V grooves were fabricated for alignment of the input and output optical fibers. One of the V grooves is on the mobile elastic platform; the other is on the fixed framework. When the platform is attracted downward by the electromagnetic force, the central axes of the two fibers are mismatched to adjust the attenuation. The insertion loss is less than 1 dB, the polarization dependent loss is less than 0.1 dB, dynamic range is larger than 50 dB, and the driving voltage is less than 5 V. The design, fabrication, and test of the two devices are all introduced detailedly below. The first device is suitable for fast adjustment. The second one may be adopted in applications where, the fabrication cost and polarization-dependent loss is of more concern.

This paper compares four nonlinear springs for the micro power generator (MPG) application which convert low level vibration energy into electrical power. The magnet-spring system decides the generator's resonant frequency, and this work proves that the spring's nonlinearity level influences the width of the operating frequency. The four different planar springs have the same outer/inner dimensions and the same linear stiffness calculated by ANSYS. The minimum nonlinear deflection of the springs is 0.372mm at the load of 15mN, while the maxim result is 0.693mm and the linear result is supposed to be 0.870mm. The spring samples were fabricated with lithography, etching, and microelectroplating technology and were tested to compare their nonlinearity in both static elasticity coefficient and dynamic response including amplitude-frequency curve, peak-peak output voltage and the bandwidth for above 30mV output voltage, which demonstrated that the energy harvester output bandwidth could be improved by careful consideration of the nonlinearity of the spring and the largest bandwidth frequency was 33 Hz.

In this paper, a new electroplating mask regarding deep etching on glass was revealed. It consisted of sputtered Chromium and Copper layer with electroplated Chromium and Gold layer, in combination with hard baked thick photoresist AZ4620 mask layer. After more than 3 hours' immerging in the HF etching solution, the etching depth attained more than 500μm. By using hard baking photoresist, the smoother surface was achieved. In addition, increasing the pattern width may help to reduce the undercut etching level and to accelerate the etching process. Compared with other masks in the literature, this new electroplating mask was simple, low cost and compatible with lithography technology, it can be widely used in MEMS applications.

An electromagnetically actuated MEMS variable fiberoptic attenuator was designed and fabricated. The device consists of an electromagnetic microactuator, a fiber alignment component, a ferronickel shutter, and two single mode fibers. The shutter actuated by the microactuator was interposed in the gap between input and output fiber, which can regulate the optical output. Non-silicon surface micromachining technology, which uses copper layer as the sacrificial layer and the electroplated ferronickel as the structure layer, was used to fabricate the shutter. The magnetic and mechanical behaviour of the device was investigated by using analytical methods and ANSYS FEM, and some its geometric structural parameters were then optimized. The attenuator has less than 3dB-insertion loss at 1550nm, greater than 45dB dynamic range, and better than 40dB return loss.

An eight-channel variable optical attenuator (VOA) array fabricated by MEMS technology is presented. Based on micro electromagnetic actuation, the attenuation level is adjusted by changing the radial offset between the input/output optical fiber. The relationship between the attenuation and the offset was analyzed based on wave-guide transmission theory. The structure parameter was determined through mechanics and magnetic circuit analysis. The device was fabricated and packaged by micromachining technology. The packaged volume of the device is 80×40×12mm 3 . According to the experiment results, the insertion loss is less than 1dB, the polarization dependent loss is less than 0.1dB, dynamic range is above 35dB and the driving voltage is less than 5V. It is proved to be a low cost, high performance passive device for future all-optical-networks.

For Dynamic Power Equalization in all optical networks, a magnetically actuated, surface micromachined micro shutter in variable optical attenuator (VOA) has been fabricated and characterized. The fabrication of the micro shutter is based on the nonsilicon surface micromachine technology. The electroplated FeNi are used as the structure layer, the photoresist and Cu is adopted as the sacrificial layer. In addition, the theoretical analysis of the diffraction optical propagation through the micro shutter in the VOA has also been carried out. The analysis is based on a gaussian beam approximation to the fiber mode, a calculation of the free space diffraction past a square aperture based on the Fresnel-Kirkhoff diffraction integral, and the mode-overlap integral between the diffracted beam and the fiber mode. The theoretical calculation result is in good agreement with the experimental data. Based on the model set up, the performance of the VOA can be optimized for better adjustment characteristics.

Power management is an increasingly concerned issue in all-optical network, where the continuous adjustment of the transmitted power is required. In this paper, the diffractive optical propagation inside a magnetic actuated, surface micromachined variable optical attenuator has been modeled and characterized. The modeling of the diffractive optical propagation is based on a gaussian beam approximation to the fiber mode, a calculation of the free space diffraction past a square aperture based on the Fresnel-Kirkhoff diffraction integral, and the mode-overlap integral between the diffracted beam and the fiber mode. The fabrication of the attenuator is based on the nonsilicon surface micromachine technology. The experimental data is in good agreement with the theoretical calculation result. Based on the work, a variable optical attenuator (VOA) has been successfully developed.

Considering the radius difference among layers and nonlinear temperature distribution inside the fiber coil, a simple, accurate model for the quantitative analysis of the thermal induced nonreciprocity in sagnac interferometer has been put forward and confirmed by experimental results. Based on the model, a novel approach to reduce the Shupe effect by 60% has been figured out.

A novel electro-thermal and mechanical latching micro-switch is proposed in this study. Theoretical calculations were carried out to determine the geometric parameters of the micro-switch. An electrophoretic polymer film was introduced as the actuation layer to sustain the nickel resistance heater of the electro-thermal actuator. Compared to SU-8, the electrophoretic polymer film had a large thermal expansion coefficient as well as a high adhesive force between the polymer film and Ni. By optimizing the processes, the micro-switch was finally fabricated using a MEMS process. In order to demonstrate the dynamic performance of the micro-switch, a sequential double-pulsed power was used to actuate the fabricated micro-switch, which was connected with an external circuit. The testing results indicated that the electro-thermal latching micro-switch could control the ON/OFF state of the external circuit.This demonstrated the bistable behaviour of the electro-thermal micro-switch.

Power management is an increasingly concerned issue in Dense Wavelength Division Multiplexed (DWDM) network. It poses strict comprehensive requirements, such as electronic controllability, cost and volume, etc, on the Variable Optical Attenuator (VOA). The characteristics of MEMS technology make it to be one of the most prospective candidates to meet these requirements. This paper consists of three parts. The first part is a description of VOA application in all-optic network. In the light of these aspects, the main requirements for VOA devices are quantitatively identified. In the second part, the current situation of research on MEMS based VOA is presented extensively. Finally, several novel applications of MEMS based VOA in all optic networks are illustrated. It illustrates the premise that MEMS VOA can bring added capability or new functionality to optical designs and increase the incentive to explore their potential in lightwave subsystems. Considering the attractive market volume in 2008, MEMS based VOA seems to be one of the most prospective candidates for the commercialization of optical MEMS technology.

A topology variation method for the tuning of nonlinear vibration of planar spring was proposed and experimentally validated, which exhibited great potential for the application of energy harvesting by broadening the response bandwidth of the device. According to the numerical simulation and experimental results of all the three typical topological configurations, the topological scheme with inclined straight shape could provide the best nonlinearity. When this method was applied to the energy harvesting, the prototype device demonstrated a bandwidth of 28 Hz @180 Hz. It is concluded that the topological variation methodology could be efficient for the performance optimization of the energy harvester.

An electromagnetic bistable microactuator fabricated on a single wafer is presented. Its overall size is 3×3×1 mm. Tested results show that the bistable state of the device is realised by 5 V voltage pulse and held by the permanent magnet without current. The response time is 0.96 ms with a large displacement of 160 µm.

Different electrolytes are used to fabricate nickel structures in MEMS devices by the LIGA or UV-LIGA process to meet different requirements. In order to investigate the microstructure and mechanical properties of nickel thin films electroplated in different electrolytes, four sets of nickel specimens were fabricated in different electrolytes: sulfamate bath with both saccharine and butynediol added (type A-I); sulfamate bath with saccharine added (type A-II); watts bath with saccharine added (type B); and chloride bath with saccharine added (type C). The function of these additives was to obtain the stress-free nickel films. The specimens were measured in our uniaxial tensile test system; their surface morphology and fractography, microstructure and texture were studied by SEM, TEM and XRD, respectively. The results show that the four sets of specimens have different mechanical properties and microstructures. The tensile strength of type A-II, type C and type A-I specimens increases with decreasing grain size, which is in accordance with the Hall?Petch law. In contrast, type B specimens have the highest value of ultimate tensile strength and elongation, but with the largest grain size among all the specimens. The XRD results show that there is no preferred orientation in type B while others have a preferred orientation in (2?0?0) along the growth direction. This might be the reason for the difference between type B and other types.

A long throw bi-stable electromagnetic micro-actuator is presented. Its configuration was easy to be batch fabricated. According to the experiment results, when the actuator was applied with a 5 V voltage pulse, the bi-stable switch was realised and the output displacement was larger than 150 m. Its overall size is 6 × 6 × 3 mm. The device structure, principle and fabrication method are also presented.