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Electrothermal actuators are highly advantageous for microelectromechanical systems (MEMS) due to their capability to generate significant force and large displacements. Despite these benefits, their application in reconfigurable conduction line switches is limited, particularly when employing commercial processes. In DC MEMS switches, electrothermal actuators require electrical insulation between the biasing voltage and the transmission line to prevent interference and maintain the integrity of the switch. This work presents a chevron-type electrothermal actuator utilizing a stack of S i O 2 / Al thin films on a silicon (Si) structural layer beam to create a DC MEMS switch. The design leverages a thin film Al heater to drive the actuator while the S i O 2 layer provides electrical insulation, suppressing crosstalk with the Si layer. The electrical contact resistance of a Si-to-Si interface was evaluated by applying a controlled current and measuring the resultant voltage. A low contact resistance of 150 Ω was achieved when an initial contact gap of 2.52 μm was closed using an actuator with an actuation voltage of 1.2 V and a current of 205 mA, with a switching speed of less than 5 ms. Factors such as the contact force, the temperature, and the residual device layer etching angle significantly impact the Si-to-Si contact resistance and the switch's longevity. The switch withstands a breakdown voltage up to 350 V at its terminal contacts. Thus, it will be robust to self-actuation caused by unwanted voltage contributions, making it suitable for high-voltage and harsh environment applications. [ABSTRACT FROM AUTHOR]

Crawling robots have great potential in some harsh environments, but there are still some limitations, such as tiny structures that can only produce small deformation and poor load-carrying capacity. A lightweight inchworm-like crawling robot made of bistable structure driven by electrothermal actuation is proposed in this paper. The robot has the characteristics of large deformation and a certain extent of load capacity. The motion of the crawling robot was realized by the common effect of the bistable structure and the designed feet with anisotropic friction. The unstable transition process between snap-through and snap-back processes of the bistable structure was utilized to provide morphological deformation. Meanwhile the feet with anisotropic friction transformed the deformation to unidirectional movement of the crawling robot. Through electric experiments, the electrothermal driving influencing factors of bistable structure are tested, including heating time, maximum temperature and curvature change, which demonstrates the possibility of driving inchworm-like crawling robot with bistable structure and large-deformation. And the structure of the inchworm-like crawling robot assembled by a bistable shell pasted with an electric heating sheet and the designed feet with anisotropic friction. In order to evaluate the motion properties and load-carrying function of the inchworm-like crawling robot, the step length test under different voltages and the experiment of the crawling robot load-carrying capacity were completed. The results show that the crawling robot performs well in load-carrying, can achieve crawling movement under the condition of carrying 10 g and 20 g objects. The inchworm-like crawling robot provides a method to achieve large-deformation and load-carrying and demonstrates it is suitable in some extreme environments. [ABSTRACT FROM AUTHOR]

Electrothermal polymer artificial muscle has drawn great attention because of its unique structure for imitating the functions of natural muscles with the external thermal stimulus. Herein, we develop a thermal responsible twisted and coiled polymer fiber-based artificial muscle. In brief, the polyethylene fibers and silver-plated nylon wire are prepared; these types of fibers are twisted causing coil nucleation and ultimately nucleation of supercoils to obtain novel parallel-stranded spiral structure of artificial muscle (PE@SPN fiber artificial muscle). The excellent electrothermal property of silver-plated nylon wire contributed to the superior performance of the actuator compared to nickel wire and copper wire. The composite yarn actuator generates contractile strokes of up to 11% under 2.5 Mpa tension and outputs 140 J/kg energy density; the composite yarn actuator can work at ambient temperature about to 50 ℃ with high contractile stroke and long-term stability. In contrast to previous fiber actuators based on PA6 fishing line and sewing thread, which are normally operated at 100 ℃, the actuator based on PE@SPN fiber artificial muscle is operated at a temperature of about 50 ℃. Meanwhile, a bionic elbow joint is designed and driven by the actuator based on polyethylene fiber. We successfully demonstrate the flexion/extension of finger by using the actuation of PE@SPN fiber artificial muscle. The results of experiments show that the promise as a soft actuator towards prosthetics, wearable robot, and power-assisted device applications. [ABSTRACT FROM AUTHOR]

Electrothermal actuators are highly advantageous for microelectromechanical systems (MEMS) due to their capability to generate significant force and large displacements. Despite these benefits, their application in reconfigurable conduction line switches is limited, particularly when employing commercial processes. In DC MEMS switches, electrothermal actuators require electrical insulation between the biasing voltage and the transmission line to prevent interference and maintain the integrity of the switch. This work presents a chevron-type electrothermal actuator utilizing a stack of SiO2/ Al thin films on a silicon (Si) structural layer beam to create a DC MEMS switch. The design leverages a thin film Al heater to drive the actuator while the SiO2 layer provides electrical insulation, suppressing crosstalk with the Si layer. The electrical contact resistance of a Si-to-Si interface was evaluated by applying a controlled current and measuring the resultant voltage. A low contact resistance of 150 Ω was achieved when an initial contact gap of 2.52 μm was closed using an actuator with an actuation voltage of 1.2 V and a current of 205 mA, with a switching speed of less than 5 ms. Factors such as the contact force, the temperature, and the residual device layer etching angle significantly impact the Si-to-Si contact resistance and the switch’s longevity. The switch withstands a breakdown voltage up to 350 V at its terminal contacts. Thus, it will be robust to self-actuation caused by unwanted voltage contributions, making it suitable for high-voltage and harsh environment applications.

This study aims to obtain safe working condition of the electrothermal U-shaped actuator (EUA). The finite difference method is applied for modeling and solving the steady electric-thermal state and maximum temperature of the microactuator. The critical voltages causing beam buckling and overheating phenomena are determined to avoid the axial instability as well as melting deformation of the actuator. The relationships between temperature and the frequency or amplitude of the AC are analyzed. The results showed that the structure and the applied voltage levels have significant influence on the temperature distributions and the value of the stress. It is confirmed that the temperature between 300 to 600 °C is comparatively suitable for microactuator according to theoretical and experimental analysis, and the microactuator is able to provide accurate and stable number of cycles for tens of millions. [ABSTRACT FROM AUTHOR]

Microgrippers are miniature tools that have the capability to handle and manipulate micro- and nano-scale objects. The present work demonstrates the potential impact of the incorporation of perforations on a 'hot and cold arm' electrothermal actuation mechanism in order to improve the operation of microgrippers in terms of arm opening and operating temperature. By applying a voltage to one arm and setting the other as a ground, the current passes through the electrothermal actuator and induces its displacement along the in-plane direction. The difference in the geometry of the two arms causes one arm to expand more than the other and this results in transverse bending. A computational model was developed using a finite element analysis tool to simulate the response of the thermal actuators with varying geometries and investigate the impact of incorporating perforations on the arms of the thermal actuators to enhance its performance in terms of deflection and operating temperature. The simulation results were compared to their experimental counterparts reported in the literature. A good agreement between the numerical and experimental data was obtained. A novel design of a microgripper, made of perforated electrothermal actuators, was introduced. Its main characteristics, including the tip opening of the gripper arms, the applied voltage, and the stress and temperature distributions, were analyzed using the developed computational model. Different perforation shape and distribution were investigated. The present study demonstrates the capability of perforations to enhance the operation of microgrippers as manifested by the obtained higher tip displacement and lower tip temperature in comparison to conventional microgripper designs made of non-perforated thermal actuators. Furthermore, the highest stress generated on the microgripper elements was found to be much lower than the yield strength of the constituent material, which indicates proper functioning without any mechanical failure. [ABSTRACT FROM AUTHOR]

Optical devices are frequently being used in medical applications to image lesions and malignancies, and to assist with surgical procedures. The advances in micro-electro-mechanical systems (MEMSs) and optics led to the fabrication of flexible endoscopes as small as a few millimeters in diameter. The design of a sub-millimeter sized optical fiber scanner is presented in this paper. The proposed scanner consisted of a vibrating optical fiber that carried the laser light to the targeted imaging sample. The desired vibratory motion of the scanning device was obtained using a U-shaped electrothermal actuator where the asymmetry in the actuator’s arm length caused the free end of the actuating device to bend allowing a bidirectional motion at its free end. The periodic square current wave passing through the actuator caused it to bend in a timely manner. By matching the signal frequency to the resonant frequency of the cantilever fiber and placing the cantilever appropriately relative to the actuator, the distal end of the fiber was allowed to follow a Lissajous scan. In optical scanners, the Lissajous scan pattern is normally obtained using a pair of actuators. This paper presents the design of a scanner providing a 2D Lissajous scan using a single actuator. Such a technique can provide basis for the development of sub-millimeter sized forward-viewing endoscopic catheters, whereas the smallest single fiber endoscope has a diameter of 1.2 mm. In the medical field, such a device has the potential to image small cavities of the body increasing the diagnostic yield of the medical procedures.

A safety and arming device with a condition feedback function has been designed in this article to improve the intelligence and safety of ignition devices. The device achieves active control and recoverability by virtue of four groups of bistable mechanisms which consist of two electrothermal actuators to drive a semi-circular barrier and a pawl. According to a specific operation sequence, the barrier is engaged by the pawl at the safety or the arming position. The four groups of bistable mechanisms are connected in parallel, and the device detects the contact resistance generated by the engagement of the barrier and pawl by the voltage division of an external resistor to determine the parallel number of the mechanism and give feedback on the device's condition. The pawl as a safety lock can restrain the in-plane deformation of the barrier in the safety condition to improve the safety function of the device. An igniter (a NiCr bridge foil covered with different thicknesses of Al/CuO films) and boron/potassium nitrate (B/KNO3, BPN) are assembled on both sides of the S&A device to verify the safety of the barrier. The test results show that the S&A device with a safety lock can realize the safety and arming functions when the thickness of the Al/CuO film is set to 80 μm and 100 μm. [ABSTRACT FROM AUTHOR]

Optical scanners are used frequently in medical imaging units to examine and diagnose cancers, assist with surgeries, and detect lesions and malignancies. The continuous growth in optics along with the use of optical fibers enables fabrication of imaging devices as small as a few millimeters in diameter. Most forward viewing endoscopic scanners contain an optical fiber acting as cantilever which is vibrated at resonance. In many cases, more than one actuating element is used to vibrate the optical fiber in two directions giving a 2D scan. In this paper, it is proposed to excite the cantilever fiber using a single actuator and scan a 2D region from its vibrating tip. An electrothermal actuator is optimized to provide a bidirectional (horizontal and vertical) displacement to the cantilever fiber placed on it. A periodic current, having a frequency equal to the resonant frequency of cantilever fiber, was passed through the actuator. The continuous expansion and contraction of the actuator enabled the free end of fiber to vibrate in a circle like pattern. A small change in the actuation frequency permitted the scanning of the area inside the circle. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To study the dynamic performance of the V-shaped electrothermal actuator, electrothermal and thermoelastic coupling models are established based on the heat transfer theory and the forced vibration equation, respectively. A one dimensional multi-physical field coupling theoretical model of the V-shaped electrothermal actuator is proposed. The electrothermal coupling model is solved by the method in which the sine transformation and the implicit difference are combined together. Then, a convergence test is performed. The number of discrete points in the sine transformation has less influence on the temperature stability. The transient and static temperature distributions of the model coincide with that of the finite element method (FEM) at different voltages. The static displacements gained by the experiment and the edge detection algorithm also match well with that gained by the thermoelastic coupling model at different voltages. Based on the proposed model, the dynamic performances of the actuator at step and sine voltages are analyzed. The research results indicate that changes of temperature and displacement in the middle of the V-shaped electrothermal actuator are larger with the amplitude of sine voltage increasing. When the loading time of sine voltage is larger than 5 periods (50 ms), the average temperature and displacement in the middle of the actuator are equal to those with equivalent direct voltage. When applied to a periodic voltage, the motion of the actuator is also gradually cyclical and has the same time period with the voltage cycle.

Microgrippers are miniature tools that have the capability to handle and manipulate micro- and nano-scale objects. The present work demonstrates the potential impact of the incorporation of perforations on a ‘hot and cold arm’ electrothermal actuation mechanism in order to improve the operation of microgrippers in terms of arm opening and operating temperature. By applying a voltage to one arm and setting the other as a ground, the current passes through the electrothermal actuator and induces its displacement along the in-plane direction. The difference in the geometry of the two arms causes one arm to expand more than the other and this results in transverse bending. A computational model was developed using a finite element analysis tool to simulate the response of the thermal actuators with varying geometries and investigate the impact of incorporating perforations on the arms of the thermal actuators to enhance its performance in terms of deflection and operating temperature. The simulation results were compared to their experimental counterparts reported in the literature. A good agreement between the numerical and experimental data was obtained. A novel design of a microgripper, made of perforated electrothermal actuators, was introduced. Its main characteristics, including the tip opening of the gripper arms, the applied voltage, and the stress and temperature distributions, were analyzed using the developed computational model. Different perforation shape and distribution were investigated. The present study demonstrates the capability of perforations to enhance the operation of microgrippers as manifested by the obtained higher tip displacement and lower tip temperature in comparison to conventional microgripper designs made of non-perforated thermal actuators. Furthermore, the highest stress generated on the microgripper elements was found to be much lower than the yield strength of the constituent material, which indicates proper functioning without any mechanical failure.

A safety and arming device with a condition feedback function has been designed in this article to improve the intelligence and safety of ignition devices. The device achieves active control and recoverability by virtue of four groups of bistable mechanisms which consist of two electrothermal actuators to drive a semi-circular barrier and a pawl. According to a specific operation sequence, the barrier is engaged by the pawl at the safety or the arming position. The four groups of bistable mechanisms are connected in parallel, and the device detects the contact resistance generated by the engagement of the barrier and pawl by the voltage division of an external resistor to determine the parallel number of the mechanism and give feedback on the device’s condition. The pawl as a safety lock can restrain the in-plane deformation of the barrier in the safety condition to improve the safety function of the device. An igniter (a NiCr bridge foil covered with different thicknesses of Al/CuO films) and boron/potassium nitrate (B/KNO3, BPN) are assembled on both sides of the S&A device to verify the safety of the barrier. The test results show that the S&A device with a safety lock can realize the safety and arming functions when the thickness of the Al/CuO film is set to 80 μm and 100 μm.

Herein, we present an affordable, a highly size- and shape-diverse high-resolution microheater for efficiently and position-selectively heating soft electrothermal actuators. The microheater was readily manufactured in large quantities by photolithographically etching a copper layer laminated with a polyimide (PI) sheet. Electrothermal actuators were fabricated by spin coating thermally expandable polydimethylsiloxane (PDMS) onto the surface of a patterned Cu (p -Cu) heater. The line-pattern dimensions of the p -Cu heater were optimized for uniform heating, after which it was used to prepare PDMS/ p -Cu/PI devices. A 20 × 5 mm standard actuator typically exhibited a large bending curvature of 1.4 cm−1 at a low voltage of 2.25 V with a response time of approximately 10 s. Furthermore, we verified the feasibility of fabricating a scaled-down actuator with a critical dimension of 50 μm and a complicated device with multiple independent deformation locations on a single substrate. The miniaturized actuator exhibited a lower bending curvature than the standard device at a higher input electrical power density when heated to the same temperature. This behavior was quantitatively interpreted using the coefficient of natural convection through simulations using finite element analysis. Biomimetic demonstration devices, such as a flower-like actuator and a biomimetic hand, were successfully prepared using a p -Cu heater designed to heat multiple user-defined positions, and their normal operations were experimentally confirmed. [Display omitted] • Affordable strategy for fabricating an electrothermal microheater based on the photolithographic etch of commercial FCCL. • An electrothermal actuator exhibited a bending curvature of 1.4 cm-1 at a voltage of 2.25 V with a response time of 10 s. • Dependence of heating and bending behavior on size and shape of the heater was interpreted by using finite element analysis. • Successful demonstration of a flower-like actuator and a biomimetic hand with multiple position-defined heaters. [ABSTRACT FROM AUTHOR]

The rapid and responsive capabilities of soft robots in perceiving, assessing, and reacting to environmental stimuli are highly valuable. However, many existing soft robots, designed to mimic humans and other higher animals, often rely on data centers for the modulation of mechanoelectrical transduction and electromechanical actuation. This reliance significantly increases system complexity and time delays. Herein, drawing inspiration from Venus flytraps, a soft robot employing a power modulation strategy is presented for active stimulus reaction, eliminating the need for a data center. This robot achieves mechanoelectrical transduction through Ni 3 (2,3,6,7,10,11-hexaiminotriphenylene) 2 (Ni 3 (HITP) 2 ) metal-organic framework (MOF) with an ultralow time delay (256 ns) and electromechanical actuation via graphite. The Joule heating effect in graphite is effectively modulated by Ni 3 (HITP) 2 before and after the presence of pressure, thus enabling the stimulus reaction of soft robots. As demonstrated, three soft robots are created: low-level edge tongue robots, Venus flytrap robots, and high-level nerve-center-controlled dragonfly robots. This power modulation strategy inspires designs of edge soft robots and high-level robots with a human-like effective fusion of conditioned and unconditioned reflexes., (© 2024 Wiley‐VCH GmbH.)

Optical scanners are used frequently in medical imaging units to examine and diagnose cancers, assist with surgeries, and detect lesions and malignancies. The continuous growth in optics along with the use of optical fibers enables fabrication of imaging devices as small as a few millimeters in diameter. Most forward viewing endoscopic scanners contain an optical fiber acting as cantilever which is vibrated at resonance. In many cases, more than one actuating element is used to vibrate the optical fiber in two directions giving a 2D scan. In this paper, it is proposed to excite the cantilever fiber using a single actuator and scan a 2D region from its vibrating tip. An electrothermal actuator is optimized to provide a bidirectional (horizontal and vertical) displacement to the cantilever fiber placed on it. A periodic current, having a frequency equal to the resonant frequency of cantilever fiber, was passed through the actuator. The continuous expansion and contraction of the actuator enabled the free end of fiber to vibrate in a circle like pattern. A small change in the actuation frequency permitted the scanning of the area inside the circle.

Soft electrothermal actuators have been of particular interest to researchers in soft mechatronic/robotic systems due to their large deformation, lightweight, and low power actuation. Closed-loop control of soft actuators is critical for high-precision applications, due to the nonlinear relationship between actuation voltage and output bending motion. In this article, a resistive self-sensing approach was developed for the soft electrothermal actuator, which enables the closed-loop control of the actuator without external sensors. The self-sensing of the actuator's deformation is achieved by measuring the resistance change of the embedded microfilament heater of the soft electrothermal actuator. When the bimorph electrothermal actuator deflects under the temperature change, its deflection can be detected by the temperature-incurred resistance change of the embedded heater. A closed-loop controller was designed using the self-sensed deflection signal. To handle the different responses of the actuator in the heating and cooling stages, a switching proportional-integral-derivative control algorithm was designed. Specifically, two sets of control parameters were tuned and used for the heating and cooling stages, respectively. The performance of the designed control algorithm was evaluated for step response, tracking of complex wave signals, and disturbance rejection. Compared with the open-loop operation, the closed-loop controlled actuator demonstrated a much more rapid and accurate response (the rising time and settling time were reduced over 80%) and excellent tracking and disturbance rejection capabilities. [ABSTRACT FROM AUTHOR]

Microgrippers can be effectively applied for handling, positioning and assembling of the micro components. In the present study, a new design of a U-shape electrothermal microgripper was fabricated and developed with the voltages correspond between 1 to 10 volts. The microgripper was made of silicone with thickness of 25 microns, and pieces between 460 to 480 microns. The proposed microgripper has a simpler design and more facile fabrication comparing to most reported electrothermal microgripper. The behavior of the microgripper was simulated in COMSOL software to measure the displacement of the arms which hold and heat generations during the voltage changes. The present microgripper has more thermal and voltage tolerance comparing to other electrothermal microgripper. Furthermore, the obtained amount of tip displacement for voltage changes is acceptable. Another simulation method based on a three layer artificial neural network model (ANN) was carried out. Feed forward back propagation algorithm was employed as training algorithm to predict the displacement. The obtained results from both models proved that ANN model had better estimation due to the mean absolute percentage error of 1.024% and determination coefficient of 0.9995. Moreover, they confirm higher capability and accuracy of ANN in prediction of arms displacement compared to FEM.

This paper reports an active catheter-tip device functionalized by integrating a temperature-responsive smart polymer onto a microfabricated flexible heater strip, targeting at enabling the controlled steering of catheters through complex vascular networks. A bimorph-like strip structure is enabled by photo-polymerizing a layer of poly(N-isopropylacrylamide) hydrogel (PNIPAM), on top of a 20 × 3.5 mm2 flexible polyimide film that embeds a micropatterned heater fabricated using a low-cost flex-circuit manufacturing process. The heater activation stimulates the PNIPAM layer to shrink and bend the tip structure. The bending angle is shown to be adjustable with the amount of power fed to the device, proving the device’s feasibility to provide the integrated catheter with a controlled steering ability for a wide range of navigation angles. The powered device exhibits uniform heat distribution across the entire PNIPAM layer, with a temperature variation of

In this paper, the actuation behavior of a two-axis electrothermal MEMS (Microelectromechanical Systems) mirror typically used in miniature optical scanning probes and optical switches is investigated. The MEMS mirror consists of four thermal bimorph actuators symmetrically located at the four sides of a central mirror plate. Experiments show that an actuation characteristics difference of as much as 4.0% exists among the four actuators due to process variations, which leads to an average angular scan error of 0.03°. A mathematical model between the actuator input voltage and the mirror-plate position has been developed to predict the actuation behavior of the mirror. It is a four-input, four-output model that takes into account the thermal-mechanical coupling and the differences among the four actuators; the vertical positions of the ends of the four actuators are also monitored. Based on this model, an open-loop control method is established to achieve accurate angular scanning. This model-based open loop control has been experimentally verified and is useful for the accurate control of the mirror. With this control method, the precise actuation of the mirror solely depends on the model prediction and does not need the real-time mirror position monitoring and feedback, greatly simplifying the MEMS control system.

Rotational rheometers are used to measure paste properties, but the test would take too long to be useful for quality control (QC) on the job site. In this paper, a new type of rheometer is proposed based on a one degree of freedom (DOF) micro-electro-mechanical systems (MEMS)-based motion stage. Preliminary data will be presented to show the capability of the system to measure the viscoelastic properties of a paste. The parallel plate geometry rheometer consists of two plates, which move relative to each other to apply a strain to the material to be tested. From the stress measured and the strain applied, the rheological characteristics of the material can be calculated. The new device consists of an electrothermal actuator and a motion plate. For the rheological measurements, the device is designed to generate the shear stress up to 60 Pa and maintain its stiffness to less than 44 N/m. With these features, the device uses a square plate of 1.5 mm x 1.5 mm to provide enough area for a few microliter level volumes. The motion of the square plate is monitored by a capacitive sensor at the end of the oscillating plate which has a resolution of 1.06 µm. When a reference cementitious paste, Standard Reference Material (SRM)-2492, is placed between the oscillating plate of the presented motion stage and a fixed plate, the reduction in the displacement of the oscillating plate is monitored showing that the presented motion stage is reasonably designed to detect the response of the reference cementitious paste.

Micro-electrical-mechanical mirrors based on electrothermal bimorph actuators have unparalleled advantages of large scan range, low driving voltage, and high fill factor, but their reliability issues are not well understood. One of the main failure phenomena is the burnout of the refractory metal resistor embedded in electrothermal bimorph actuator structures. In this paper, the burnout process was thoroughly studied via both electrical and optical testing. In particular, the current passing through the embedded resistor was monitored throughout the entire burnout process. It was found that the burnout was caused by multiple steps of anomalies, including electrical breakdown at poor step coverage, short circuit, overheating, and electromigration. Electrical models and lumped-element thermal models were established and electrothermomechanical finite-element method simulations were performed. The modeling and simulation results are all in good agreement with the experimental results. These findings will help greatly improve future design for better reliability. [ABSTRACT FROM AUTHOR]

In this paper we examine the suitability of SU-8 2000 as a construction material for electrothermal actuators and the actuator stability for long-term operation. The fabrication of SU-8 was optimized for mechanical and thermal stability. Samples with different softbake duration, exposure dose and postbake temperature were evaluated using Fourier-Transform IR-spectroscopy and dynamic-mechanical analysis. The exposure dose and postbake temperature proved to have a strong influence on the cross-linking and the glass transition temperature. A final hardbake levels the effects of the process history. A high degree of crosslinking, a low drop of the dynamic modulus over temperature (30%) up to the glass transition temperature 100–140 °C were achieved for SU-8 with an exposure dose of 1500 mJ/cm², a postbake temperature of 95 °C and hardbake of 240 °C. Electrothermal actuators proved to be stable until the end of the experiment after 2400 duty cycles. Actuator deflections up to 55 μm were measured (actuator length: 4 mm) for input powers up to 160 mW and a maximum operating temperature of 120 °C. Higher temperatures led to permanent deformations and failure. An offset drift of up to 20% occurs during actuation, but converges after a burn-in phase of about two hours.

The goal of this study was to measure the mechanical stiffness of individual cells and to observe changes due to the application of repeated cell mechanical loads. 28 single baker's yeast cells ( Saccharomyces cerevisiae) were fatigue tested and had their stiffness measured during repetitive loading cycles performed by a MEMS squeezer in aqueous media. Electrothermal micro-actuators compressed individual cells against a reference back spring; cell and spring motions were measured using a FFT image analysis technique with ~10 nm resolution. Cell stiffness was calculated based on measurements of cell elongation vs. applied force which resulted in stiffness values in the 2-10 N/m range. The effect of increased force was studied for cells mechanically cycled 37 times. Cell stiffness decreased as the force and the cycle number increased. After 37 loading cycles (~4 min), forces of 0.24, 0.29, 0.31, and 0.33 μN caused stiffness drops of 5%, 13%, 31% and 41% respectively. Cells force was then set to 0.29 μN and cells were tested over longer runs of 118 and 268 cycles. After 118 cycles (~12 min) cells experienced an average stiffness drop of 68%. After 268 cycles (~25 min) cells had a stiffness drop of 77%, and appeared to reach a stiffness plateau of 20-25% of the initial stiffness after approximately 200 cycles. [ABSTRACT FROM AUTHOR]

This paper reports a microelectromechanical systems (MEMS)-based microgripper, integrating two-axis actuators and force sensors, for microscale compression and shear testing of soft materials. The device employs V-beam electrothermal actuators to drive an active gripping arm and compress or shear a microscale sample grasped at the gripping tips, and two triplate differential capacitive sensors to measure the compression and shear forces applied to the sample with nanonewton resolution (compressive force resolution: 7.7 nN, and shear force resolution: 57.5 nN). Using the microgripper, we demonstrate, for the first time, on-chip compression and shear testing of polydimethylsiloxane (PDMS) microstructures prepared at different crosslinking levels. We believe that this device will be useful for accurately characterizing mechanical properties of a variety of microscale soft materials. [ABSTRACT FROM AUTHOR]

The design and fabrication of an electrothermal MEMS actuation structure which is capable of producing large out-of-plane deflection is presented. The actuators are used to move a 1 mm2 mirror structure, where the large deflection allows one to achieve large beam steering angles. The electrothermal actuators are designed to operate via joule heating with a monolithically integrated heater. The proposed design was analyzed using finite element method simulation software (COMSOL 5.3a), to determine the thickness of each material layer, the initial out-of-plane upward deflections, the configuration of the heating element to achieve the desired actuation deformations, and the overall steady-state temperature distribution through the actuation structure due to Joule heating. Finally, the actuation assemblies were fabricated, released, tested and compared with our simulation results.

Photonic packaging, which includes high-precision assembly of photonic sub-systems, is currently a bottleneck in the development of commercially-available integrated photonic products. In the pursuit of a fully-automated, high-precision, and cost-effective photonic alignment scheme for two multi-channel photonic chips, this paper explores different designs of the on-chip electrothermal actuators for positioning mechanically-flexible waveguide structures. The final alignment goal is ∼100 nm waveguide to waveguide. The on-chip actuators, particularly for out-of-plane actuation, are built in a 16 μm-thick SiO 2 photonic-material stack with 5 μm-thick poly-Si as an electrothermal element. A major challenge of out-of-plane positioning is a 6 μm height difference of the waveguides to be aligned, due to different built-up material stacks, together with a misalignment tolerance of 1 μm–2 μm from the pre-assembly (flip-chip) process. Therefore, the bimorph-actuator design needs to compensate this height difference, and provide sufficient motion to align the waveguides. We propose to exploit the post-release deformation of so-called short-loop bimorph actuator designs to meet these joint demands. We explore different design variants based on the heater location and the integration of actuator beams with waveguide beams. The actuator design (with 30 μm poly-Si and 900 μm SiO 2 in length) has ∼8 μm out-of-plane deflection and is able to generate ∼4 μm motion, which meets the design goal.

This article presents the conceptual design of a novel compliant microelectromechanical systems (MEMS)-based gripper with integrated electrothermal actuator and electrothermal force sensor. By this design solution, the device possesses some unique characteristics including a small and compact footprint size, and a large driving force by the thermal actuator. Owing to the use of a compliant rotational bearing, a large gripping range is obtained. The sensing arm has a capability of detecting the force transmitted from the left arm so as to prevent the damage of the grasped object. Analytical models are developed to evaluate the statics and dynamics performance of the gripper. Simulation results show that the thermal actuator produces sufficient gripping force to execute the gripping operation with a range of 80 mm under a low input voltage of 6 V. Moreover, the results of the established theoretical models match well with the finite element analysis (FEA) simulation results, which verifies the feasibility of the proposed gripper design. [ABSTRACT FROM AUTHOR]

An amplitude-division Fourier transform spectroscopy system has been constructed. The system design hinges on an electrothermally actuated micromirror with large piston motion. The micromirror is composed of electrothermal mesh actuators and can generate up to 95~\mu \textm usable linear optical path difference of the system at only 0.8~Vdc . A custom electrical system is developed to control the micromirror and data processing is implemented to extract the spectrum from interferograms. The system can achieve a spectral resolution of 5 nm at 532 nm. [ABSTRACT FROM PUBLISHER]

A microcantilever system with new actuation principle is developed for enhancing the range of tip deflection. Differing from conventional springboard-like actuation principle, the proposed microcantilever system is based on a slider-crank mechanism. In this system, out-of-plane deflection of the microcantilever can be translated and amplified from in-plane motion of high-powered thermal actuators, which is located away from cantilever body to ensure both energetic driving force and good thermal isolation. Analytical models of both the microcantilever system and the electrothermal actuator are studied concerning the optimized geometry for desired amplification ratio and balanced force/displacement outputs. The prototype is fabricated by standard lithographic process, and an integrated sharp tip is easily machined by a hybrid wet/dry etching method. The fabricated cantilever is experimentally tested and shows that a 22 μm in-plane motion from actuators at an input electrical power of 1026 mW can drive the microcantilever to deflect up to 230 μm, demonstrating the expected actuation principle. The developed microcantilever system with integrated sharp tip shows the promise to work as a microprobe in the multifunctional analysis instrument. [ABSTRACT FROM AUTHOR]

Bimorph-based electrothermal micromirrors can generate large lateral-shift-free (LSF) vertical displacement by employing electrothermal bimorph actuators with multiple segments of bimorphs. The vertical displacement of an LSF bimorph actuator is maximized when all the bimorph segments have equal temperature change. However, due to the distributed heat conduction and convection, the temperature changes on different bimorph segments are different. We report a new LSF bimorph actuator design with non-uniform width bimorph segments to achieve a uniform temperature distribution among multiple bimorph segments. A model is developed to optimize the new LSF bimorph design with three biomorph segments with the widths of 25 µm, 110 µm and 75 µm, which reaches the same average temperature of 316 K on the three bimorphs with incentive current of 5 mA and convection coefficient of 500 W/m2K. [Display omitted] • Establish the 1D model for analysis the thermal distribution on electrothermal micromirror. • The 1D model have a good agreement with the result of model in COMSOL. • The 1D model gives a guidance for realization of uniform average temperature distribution on different bimorphs. • It provides a method to further decrease the lateral shift of LSF actuators. [ABSTRACT FROM AUTHOR]

Liquid microlens (LML) has attracted wide attention due to their miniaturization, uniformities and easy integration in adaptive optical systems. However, optical aberration and simple varifocal imaging are still critical challenges for the broader application of LML. Inspired by the easy deformation of droplets trapped by micropillars, LML in scaffold microstructures are proposed. In this paper, we present a simple, low-cost and effective approach to fabricate LML in scaffold microstructures. Our LML consists of glycerol droplets trapped in hydrophobic NOA71 scaffold microstructures, which are imprinted onto an ITO glass substrate to enable electrothermal control of the LML imaging characteristics. The electrothermal control allows changing the shape of the LML spherical surface, thus making it possible to tune their focus, decrease their imaging aberration, and improve their imaging definition. The electrothermal actuator is obtained by applying a DC power with a voltage of 8.4 V and a current of 0.39 A onto the ITO glass. It is found that the imaging aberration of LML reduced by 6 times of initial state and the imaging definition of LML increased by 2.8 times of initial state on the DC power for 2 min. Thus, the LML in scaffold microstructures demonstrates the potential of the adjustable imaging performance in the development of integrated dynamical tunable optical devices. [Display omitted] • A new liquid microlens (LML) in scaffold microstructures was design and constructed by liquid self-assembly technology. • A simple electrothermal actuator was developed to change the imaging properties of LML in scaffold microstructures. • LML in scaffold microstructures has a smaller response time under electrothermal actuator than LML in microhole. • Imaging aberration of LML reduced by 6 times and imaging definition of LML increased by 2.8 times on DC power for 2 s. [ABSTRACT FROM AUTHOR]

In this paper we examine the suitability of SU-8 2000 as a construction material for electrothermal actuators and the actuator stability for long-term operation. The fabrication of SU-8 was optimized for mechanical and thermal stability. Samples with different softbake duration, exposure dose and postbake temperature were evaluated using Fourier-Transform IR-spectroscopy and dynamic-mechanical analysis. The exposure dose and postbake temperature proved to have a strong influence on the cross-linking and the glass transition temperature. A final hardbake levels the effects of the process history. A high degree of crosslinking, a low drop of the dynamic modulus over temperature (30%) up to the glass transition temperature 100-140 °C were achieved for SU-8 with an exposure dose of 1500 mJ/cm2, a postbake temperature of 95 °C and hardbake of 240 °C. Electrothermal actuators proved to be stable until the end of the experiment after 2400 duty cycles. Actuator deflections up to 55 μm were measured (actuator length: 4 mm) for input powers up to 160 mW and a maximum operating temperature of 120 °C. Higher temperatures led to permanent deformations and failure. An offset drift of up to 20% occurs during actuation, but converges after a burn-in phase of about two hours. [ABSTRACT FROM AUTHOR]

In this paper, we present an electrothermal actuator with two degrees of freedom that can achieve independent in-plane and out-of-plane motions. The device is fabricated with the MetalMUMPs, which offers silicon nitride, polysilicon, and nickel as the major structural materials. The electrothermal actuator achieves large movement. The in-plane tip displacement is 82 \mu\m at 0.039 W. The out-of-plane swing of the tip is 18 \mu\m as the applied voltage varies from 0 to 90 V (0 to 0.36 W) and vice versa. A versatile microelectromechanical systems gripper that is capable of 2-D manipulation can be constructed with two such actuators, each of which serves as the gripper arm. [ABSTRACT FROM PUBLISHER]

Highlights: [•] A new MEMS-based 3D confocal scanning microendoscope has been designed, constructed and experimentally verified. [•] The compact fiber-optic endoscopic probe integrates the MEMS scanners, fiber and high-quality micro-optics. [•] Both lateral scan and axial scan are performed by MEMS devices with large scan ranges and low drive voltages. [•] Polarization sensitive components have been employed to suppress unwanted reflections. [•] 2D and 3D confocal reflectance images of various samples have been obtained with high resolutions. [ABSTRACT FROM AUTHOR]

MEMS scanners are useful for medical applications as optical coherence tomography and laser microsurgery. Although widespread design of MEMS scanners have been presented, their behavior is not well known, and thus, their motions are not easily and efficiently controlled. This deficiency induces several difficulties (limited resolution, accuracy, cycle time, etc.), and to tackle this problem, this article presents the modeling of an ISC electrothermally actuated MEMS mirror and the experimental characterization for the piston motion. Modeling and characterization are important to implement the control. A multiphysic model is proposed, and an experimental validation is performed with a good correspondence for a voltage range from 0 V to 3.5 V with a maximum displacement up to 200 µm and with a relative tilting difference of 0.1°. The article also presents a simple and efficient experimental setup to measure a displacement in dynamic and static mode, or a mirror plane tilting in static mode. [ABSTRACT FROM AUTHOR]

Optical scanners are used frequently in medical imaging units to examine and diagnose cancers, assist with surgeries, and detect lesions and malignancies. The continuous growth in optics along with the use of optical fibers enables fabrication of imaging devices as small as a few millimeters in diameter. Most forward viewing endoscopic scanners contain an optical fiber acting as cantilever which is vibrated at resonance. In many cases, more than one actuating element is used to vibrate the optical fiber in two directions giving a 2D scan. In this paper, it is proposed to excite the cantilever fiber using a single actuator and scan a 2D region from its vibrating tip. An electrothermal actuator is optimized to provide a bidirectional (horizontal and vertical) displacement to the cantilever fiber placed on it. A periodic current, having a frequency equal to the resonant frequency of cantilever fiber, was passed through the actuator. The continuous expansion and contraction of the actuator enabled the free end of fiber to vibrate in a circle like pattern. A small change in the actuation frequency permitted the scanning of the area inside the circle.

Abstract: A curved concentric electrothermal actuator has been designed and developed to actuate circular micromirrors with improved area efficiency, while at the same time achieving large scan range at low voltage. This actuator consists of three curved concentric Aluminum/Tungsten bimorphs for fast thermal response and high responsivity, and two rigid frames connected in between for scan range amplification. A tip–tilt–piston micromirror with a circular mirror plate based on this actuator design has been proposed and fabricated. The mirror is capable of scanning ±11° at 0.6V, and generating a 227μm piston displacement at only 0.8V. The measured lateral shift and tilt angle of the mirror plate are less than 7μm and 0.7°, respectively, through the entire piston displacement. A piston-only micromirror has also been demonstrated, and it has even smaller lateral shift of less than 3μm and tilt of less than 0.4° through the piston scan range. This mirror generates large vertical displacement of about 200μm at only 0.9V. [Copyright &y& Elsevier]

The design, fabrication, and characterization of an electrothermally actuated lens scanner with bistable mechanical brakes, for the application of free-space board-to-board optical interconnects, are presented. An electrothermally actuated stepper motor is used to scan a 2.8-mm-diameter lens shuttle by a maximum of \pm 170\ \mu\m (\pm 1.57^\circ scanning angle). Bistable mechanical brakes, toggled with U-shaped thermal actuators, will grip and hold the lens shuttle in place while dissipating zero power. The minimum frictional braking force and maximum actuator force are both measured to be 0.75 mN. A position sensing detector is used to accurately measure the dynamics of the stepper motor and lens system, from which we verify our analytical model. Long-term testing results and solutions are also presented. We demonstrate a robust 10-Gb/s optical link capable of maintaining connection despite a board tilting of 0.45^\circ while dissipating zero power.\hfill[2012-0013] [ABSTRACT FROM AUTHOR]

Abstract: We report on the development of a low power thermally actuated bi-axis SOI micromirror that is capable of performing angular and vertical scans for optical coherence tomography (OCT) applications. The device consists of a mirror with an aluminum coating over a 3μm thick single crystal silicon base, aluminum/polysilicon electrothermal actuators with embedded heaters and polysilicon flexural connectors. In scanning mode, this mirror can satisfy our target specification of 5° angle at the low power of 1.7mW with a temperature increase of 16.5°C±7°C from ambient in the actuator. Furthermore, a maximum angle of 32° has been achieved at 12mW. In piston mode, it can reach vertical displacements of up to 131μm at 12mW with the temperature increase of 16.5°C±7°C from ambient in the actuator. The scanning speed for the mirror has been measured and the time response of the mirror is found to be 100ms. The curvature of the mirror is found to be 2.4mm±0.26mm with a roughness of 100nm±20nm. Due to low driving power and moderate temperatures developed during its operation, this device can potentially be integrated with broadband light source, photodetector and interferometery system, to form a fully integrated OCT system on GaAs substrate. [Copyright &y& Elsevier]

Abstract: In this paper we describe for the first time the design, fabrication and initial characterization results of a novel gimbal-less, thermally actuated micromirror developed for optical coherence tomography (OCT) application. We report large deflection angle of up to 30° that has been achieved at low input power of less than 17mW and voltage of less than 1V. Moreover, this device has a potential of integration with GaAs/Si substrate due to moderate temperatures developed during its operation-less than 100°C increase with respect to ambient at angular deflection of 30°. [Copyright &y& Elsevier]