Bent-beam Actuators Research Articles

Performance evaluation simulation of the optical splitters integrated with unidirectional fiber elements

Abstract This study has clarified the performance evaluation simulation of the optical splitters integrated with unidirectional fiber elements. The simulative performance evaluation of electrostatic, thermal, and piezoelectric actuation based micro electro mechanical systems. The force against the displacement based electrostatic and elastic forces for parallel plate actuator is simulated by MEMSover simulation software. The voltage with angular displacement for a torsion bar actuator is clarified. Besides the lateral displacement against voltage for a comb drive actuator is reported. The dependence of the film thickness on the deflection of a bimetallic cantilever, the dependence of passive beam length on deflection of a bimorph actuator and the transient response of a bent beam actuator are demonstrated. Moreover the piezoelectric actuator force against applied voltage and the piezoelectric actuator displacement against applied voltage variations are reported.

Tough Al-alginate/poly(N-isopropylacrylamide) hydrogel with tunable LCST for soft robotics.

Tough Al-alginate/poly(N-isopropylacrylamide) (PNIPAM) hydrogel has been synthesized by introducing an interpenetrating network with hybrid physically cross-linked alginate and chemically cross-linked PNIPAM. Varying the concentration of AlCl3 regulates the mechanical properties of the tough hydrogel and tunes its lower critical solution temperature (LCST) as well. The tough Al-alginate/PNIPAM exhibits 6.3 ± 0.3 MPa of compressive stress and 9.95 of uniaxial stretch. Tunability of LCST is also achieved in a wide range within 22.5-32 °C. A bending beam actuator and a four-arm gripper made of bilayer (Na-alginate/PNIPAM)/(Al-alginate/PNIPAM) hydrogel as prototype of all-hydrogel soft robotics are demonstrated. A finite element (FE) simulation model is developed to simulate the deformation of the soft robotics. The FE simulation not only reproduces the deformation process of performed experiments but also predicts more complicated devices that can be explored in the future. This work broadens the application of temperature-responsive PNIPAM-based hydrogels.

Exceptionally tough and notch-insensitive magnetic hydrogels.

Most existing magnetic hydrogels are weak and brittle. The development of strong and tough magnetic hydrogels would extend their applications into uncultivated areas, such as in actuators for soft machines and guided catheters for magnetic navigation systems, which is still a big challenge. Here a facile and versatile approach to fabricating highly stretchable, exceptionally tough and notch-insensitive magnetic hydrogels, Fe(3)O(4)@Fe-alginate/polyacrylamide (PAAm), is developed, by dispersing alginate-coated Fe(3)O(4) nanoparticles into the interpenetrating polymer networks of alginate and PAAm, with hybrid physical and chemical crosslinks. A cantilever bending beam actuator as well as a proof-of-concept magnetically guided hydrogel catheter is demonstrated. The method proposed in this work can be integrated into other strong and tough magnetic hydrogels for the development of novel hydrogel nanocomposites with both desirable functionality and superior mechanical properties.

Three-dimensional micro assembly of a hinged nickel micro device by magnetic lifting and micro resistance welding

The three-dimensional micro assembly of hinged nickel micro devices by magnetic lifting and micro resistance welding is proposed here. By an electroplating-based surface machining process, the released nickel structure with the hinge mechanism can be fabricated. Lifting of the released micro structure to different tilted angles is accomplished by controlling the positions of a magnet beneath the device. An in situ electro-thermal actuator is used here to provide the pressing force in micro resistance welding for immobilizing the tilted structure. The proposed technique is shown to immobilize micro devices at controlled angles ranging from 14° to 90° with respect to the substrate. Design parameters such as the electro-thermal actuator and welding beam width are also investigated. It is found that there is a trade-off in beam width design between large contact pressure and low thermal deformation. Different dominated effects from resistivity enhancement and contact area enlargement during the welding process are also observed in the dynamic resistance curves. Finally, a lifted and immobilized electro-thermal bent-beam actuator is shown to displace upward about 27.7 µm with 0.56 W power input to demonstrate the capability of electrical transmission at welded joints by the proposed 3D micro assembly technique.

An active micro joining mechanism for 3D assembly

An active joining mechanism for the construction of microstructures, comprising detethered microparts and locking actuators fabricated on a wafer, has been implemented. An active locking mechanism is a system on chip (SOC) type of actuator which is designed to control the socket's opening to allow insertion of a micropart with zero force. This allows the delicate micropart to be secured without the need of substantial forces that could cause damage to the micropart or the socket. Moreover, it enhances the assembly throughput, tolerance and yield due to the frictionless self-alignment of the micropart. The design concept, assembly and extensive characterization have been illustrated for 100 µm thick microstructures made of SOI wafers and patterned by deep reactive ion etching. Single-sided and double-sided electrothermal bent beam actuators are utilized for the socket to actively open during assembly and close to lock the micropart against the locking mechanism. Finally, the mechanical and electrical characteristics of the joints can be further enhanced by reflow of the deposited layers of the 80Au–20Sn solder alloy at the contact areas.

Polydimethylglutarimide (PMGI) as a sacrificial material for SU-8 surface-micromachining

SU-8 is finding increased use as a structural polymer MEMS material due to its biocompatibility, mechanical properties and low cost. The goal of this work is to expand the use of SU-8 through the creation of SU-8-based surface-micromachining processes that use polydimethylglutarimide (PMGI) as a sacrificial layer. PMGI is a deep-UV positive resist, used mainly for bilayer lift-off processes. PMGI is a good sacrificial layer candidate, as it is spinable at a wide variety of thicknesses, is photopatternable and has a glass transition temperature greater than the processing temperatures required for SU-8. PMGI is shown to be useful as a sacrificial layer for SU-8 surface micromachining processes with one freestanding layer with patterned metal, single-layer devices with more than one thickness, and two layer devices. Two classes of devices were fabricated with the developed processes. The first class of devices are compliant mechanisms, including bent-beam actuators, thermal isolation platforms and out-of-plane grippers. The second class of devices fabricated are freely moving devices such as hinged plates and gears, which require the use of true kinematic joints, such as scissor hinges, staple hinges and pin joints.

Design and analysis of a polymeric photo-thermal microactuator

This paper presents the modeling, simulation and characterization of a photo-thermally actuated bent-beam microactuator. The microactuator consists of a single polymeric layer (SU-8) fabricated with conventional photolithography techniques. The principle of operation is based on the thermal expansion of the bent-beams that absorb the required heat by laser illumination. This provides an effective non-contact actuation mechanism by laser beam focusing. A theoretical model of the microactuator is derived and verified by finite element simulations and experiments. The experiments show that a bent-beam actuator with 800 μ m long, 40 μ m wide, 100 μ m thick and 6 ° bent arms achieves a tip displacement of 16 μ m with an incident laser beam of 50 mW power while keeping the maximum temperature less than 125 ° C. This study merges the advantages of photo-thermal actuation with practicality of polymeric materials. To verify the effectiveness of the proposed microactuator mechanism, a microgripper with bent-beam actuator was fabricated and characterized. It has been demonstrated that the opening of the gripping fingers can be increased from 20 to 50 μ m for a microgripper with 1000 μ m long fingers with an incident laser power of 50 mW. This polymeric microgripper with photo-thermal actuation provides a way of gentle grasping with electrical isolation, high repeatability and low temperature operation that is particularly crucial for biomanipulation applications. The polymeric photo-thermal actuator described in this study expands the practical applications of microactuators/microgrippers which are critical tools in bioMEMS devices.

Polydimethylglutarimide (PMGI) as a structural material for surface micromachining

This work investigates the use of polydimethylglutarimide, or PMGI, as a structural material for surface micromachining. PMGI is a commercially available, positive-toned deep-UV resist designed for use in bi-layer lift-off techniques. This paper presents a technique for the microfabrication of free-standing PMGI structures, and uses those structures to extract the coefficient of thermal expansion and Young's modulus for PMGI. Our study found PMGI's coefficient of thermal expansion to be 56 ± 6 ppm °C−1 and Young's modulus to be 5.0 ± 0.5 GPa. Active structures were also fabricated by including a patterned metal layer. This allows the fabrication of active devices, such as bent-beam actuators. PMGI is a commercially available polymer being used in micromachining, and this paper provides the first report of its thermo-mechanical properties.

A silicon electrothermal rotational micro motor measuring one cubic millimeter

A micro machined single crystal silicon micro motor has been developed that uses electrothermal actuators and micro assembly. The entire motor system occupies one cubic millimeter and can be integrated into a variety of packages. Four electrothermal bent-beam actuators in the stator drive the 290 µm diameter 50 µm thick rotor through friction-based contact. Flexures between the actuators and contact points step the rotor less than one degree with each driving waveform cycle; the motor can achieve 7.3 rpm. Since the micro motor is assembled it resists rotation in a power-off state and drives with 0.14 µN m of torque. Details on the design, assembly and operation of the device are included. Finite element analysis has been applied to model the electrothermal transient response and achieve an 81% improvement in efficiency with 24 V pulse driving signals. The 1.2 mm by 1.2 mm by 0.7 mm device has been shown to rotate a 100 µm diameter tungsten probe within the confines of a SEM.

Macro-modeling for polysilicon cascaded bent beam electrothermal microactuators

A comprehensively thermal-electro-mechanical analytical model which can precisely predict the performance of polysilicon cascaded bent beam electrothermal actuators has been presented in this paper. This model has taken into account various modes of heat dissipations such as heat loss to circumstance by convection and radiation and to substrate by conduction through trapped air volumes with a temperature range from 300 to 800 K. Furthermore, the influences result from temperature dependent physical parameters of polysilicon are also considered. The model is validated by both 3D-FEA model simulations and available experimental data. With this model, the tip displacement as a function of geometrical dimension as well as many other physical parameters of polysilicon cascade bent beam actuator can be accurately simulated. Moreover, optimization means for achieving high performance of cascaded bent beam actuators are provided based on the theoretical model.

A new electrical residual stress characterization using bent beam actuators

In this paper we propose a new class of sensitive and compact passive stress measurement pattern that uses the piezoresistivity of polysilicon. The proposed measurement pattern utilizes the resistance change of the beam that connects the structures moving in opposite directions. The unit structure is composed of a pair of bent beam actuators with apexes at their mid-points connected by a link beam. The bent beam actuators are 15 μm wide and 200 μm long, and are bent by 0.1 rad (0.7°). The link beam is 5 μm wide and 264 μm long. The unit structure composed of bent beam actuators amplifies and transforms deformations caused by residual stress into elongation or contraction of the linking beam. Hence, the residual stress can be evaluated by measuring the resistance change of the proposed pattern. It is shown that tensile and compressive residual stress levels of about 10 MPa, corresponding to strains below 6 × 10−5, can be measured by using a 40 μm thick test pattern of polysilicon. The sensitivity of the proposed test pattern is 0.83% for the stress of 10 MPa. Additionally, electrical measurements allow this pattern to be suitable for post-packaging stress monitoring.