Showing papers on "Bimorph published in 2021"

Light-driven bimorph soft actuators: design, fabrication, and properties

Abstract: Soft robots that can move like living organisms and adapt to their surroundings are currently in the limelight from fundamental studies to technological applications, due to their advances in material flexibility, human-friendly interaction, and biological adaptation that surpass conventional rigid machines. Light-fueled smart actuators based on responsive soft materials are considered to be one of the most promising candidates to promote the field of untethered soft robotics, thereby attracting considerable attention amongst materials scientists and microroboticists to investigate photomechanics, photoswitch, bioinspired design, and actuation realization. In this review, we discuss the recent state-of-the-art advances in light-driven bimorph soft actuators, with the focus on bilayer strategy, i.e., integration between photoactive and passive layers within a single material system. Bilayer structures can endow soft actuators with unprecedented features such as ultrasensitivity, programmability, superior compatibility, robustness, and sophistication in controllability. We begin with an explanation about the working principle of bimorph soft actuators and introduction of a synthesis pathway toward light-responsive materials for soft robotics. Then, photothermal and photochemical bimorph soft actuators are sequentially introduced, with an emphasis on the design strategy, actuation performance, underlying mechanism, and emerging applications. Finally, this review is concluded with a perspective on the existing challenges and future opportunities in this nascent research Frontier.

Self-Locomotive Soft Actuator Based on Asymmetric Microstructural Ti3C2Tx MXene Film Driven by Natural Sunlight Fluctuation.

Abstract: Soft actuators and microrobots that can move spontaneously and continuously without artificial energy supply and intervention have great potential in industrial, environmental, and military applications, but still remain a challenge. Here, a bioinspired MXene-based bimorph actuator with an asymmetric layered microstructure is reported, which can harness natural sunlight to achieve directional self-locomotion. We fabricate a freestanding MXene film with an increased and asymmetric layered microstructure through the graft of coupling agents into the MXene nanosheets. Owing to the excellent photothermal effect of MXene nanosheets, increased interlayer spacing favoring intercalation/deintercalation of water molecules and its caused reversible volume change, and the asymmetric microstructure, this film exhibits light-driven deformation with a macroscopic and fast response. Based on it, a soft bimorph actuator with ultrahigh response to solar energy is fabricated, showing natural sunlight-driven actuation with ultralarge amplitude and fast response (346° in 1 s). By utilizing continuous bending deformation of the bimorph actuator in response to the change of natural sunlight intensity and biomimetic design of an inchworm to rectify the repeated bending deformation, an inchwormlike soft robot is constructed, achieving directional self-locomotion without any artificial energy and control. Moreover, soft arms for lifting objects driven by natural sunlight and wearable smart ornaments that are combined with clothing and produce three-dimensional deformation under natural sunlight are also developed. These results provide a strategy for developing natural sunlight-driven soft actuators and reveal great application prospects of this photoactuator in sunlight-driven soft biomimetic robots, intelligent solar-energy-driven devices in space, and wearable clothing.

Wirelessly Actuated Thermo- and Magneto-Responsive Soft Bimorph Materials with Programmable Shape-Morphing

Abstract: Soft materials that respond to wireless external stimuli are referred to as "smart" materials due to their promising potential in real-world actuation and sensing applications in robotics, microfluidics, and bioengineering. Recent years have witnessed a burst of these stimuli-responsive materials and their preliminary applications. However, their further advancement demands more versatility, configurability, and adaptability to deliver their promised benefits. Here, a dual-stimuli-responsive soft bimorph material with three configurations that enable complex programmable 3D shape-morphing is presented. The material consists of liquid crystal elastomers (LCEs) and magnetic-responsive elastomers (MREs) via facile fabrication that orthogonally integrates their respective stimuli-responsiveness without detrimentally altering their properties. The material offers an unprecedented wide design space and abundant degree-of-freedoms (DoFs) due to the LCE's programmable director field, the MRE's programmable magnetization profile, and diverse geometric configurations. It responds to wireless stimuli of the controlled magnetic field and environmental temperature. Its dual-responsiveness allows the independent control of different DoFs for complex shape-morphing behaviors with anisotropic material properties. A diverse set of in situ reconfigurable shape-morphing and an environment-aware untethered miniature 12-legged robot capable of locomotion and self-gripping are demonstrated. Such material can provide solutions for the development of future soft robotic and other functional devices.

Polarization-Modulated Multidirectional Photothermal Actuators.

Abstract: Photothermal actuators have attracted increasing attention due to their ability to convert light energy into mechanical deformation and locomotion. This work reports a freestanding, multidirectional photothermal robot that can walk along a predesigned pathway by modulating laser polarization and on-off switching. Magnetic-plasmonic hybrid Fe3 O4 /Ag nanorods are synthesized using an unconventional templating approach. The coupled magnetic and plasmonic anisotropy allows control of the rod orientation, plasmonic excitation, and photothermal conversion by simply applying a magnetic field. Once the rods are fixed with desirable orientations in a bimorph actuator by magnetic-field-assisted lithography, the bending of the actuator can be controlled by switching the laser polarization. A bipedal robot is created by coupling the rod orientation with the alternating actuation of its two legs. Irradiating the robot by a laser with alternating or fixed polarization synergistically results in basic movement (backward and forward) and turning (including left-, right-, and U-turn), respectively. A complex walk along predesigned pathways can be potentially programmed by combining the movement and turning modes of the robots. This strategy provides an alternative driving mechanism for preparing functional soft robots, thus breaking through the limitations in the existing systems in terms of light sources and actuation manners.

Wearable Sunlight-Triggered Bimorph Textile Actuators.

Abstract: Photothermal bimorph actuators have attracted considerable attention in intelligent devices because of their cordless control and lightweight and easy preparation. However, current photothermal bimorph actuators are mostly based on films or papers driven by near-infrared sources, which are deficient in flexibility and adaptability, restricting their potential in wearable applications. Herein, a bimorph textile actuator that can be scalably fabricated with a traditional textile route and autonomously triggered by sunlight is reported. The active layer and passive layer of the bimorph are constructed by polypropylene tape and a MXene-modified polyamide filament. Because of the opposite thermal expansion and MXene-enhanced photothermal efficiency (>260%) of the bimorph, the textile actuator presents effective deformation (1.38 cm-1) under low sunlight power (100 mW/cm2). This work provides a new pathway for wearable sunlight-triggered actuators and finds attractive applications for smart textiles.

Light-driven autonomous self-oscillation of a liquid-crystalline polymer bimorph actuator

Abstract: Oscillation, widely existing in nature, is of vital importance for human society (e.g., energy utilization, signal transmission and communication), but preparing soft self-oscillators with facile accessibility, fatigue resistance, precise and noncontact control in multi-way tunable approaches is still desirable and challenging. Here, we report the fabrication of a light-driven tunable self-oscillator based on bimorph films of commercial Kapton and photoactive liquid-crystalline polymers with physical crosslinking sites, which can be remotely powered under constant irradiation of UV/visible light. The photomechanical behaviors of the bimorph actuators are acquired from the photoinduced changes in the volume of the photoactive polymer, and both the cis-azobenzene content and the trans–cis dynamic isomerization process are determinant factors. By combining the self-shadowing effect and inertia effect of the actuator, self-sustained oscillation is obtained. In nature, only leaves with particular size and weight could sway as appropriate strong wind blows from a specific direction, which inspires us to tune the oscillating frequency and amplitude with multiple approaches, like light intensity/wavelength (from UV to visible light), irradiated position, and size/weight of the oscillator for regulating the inertia effect. Such autonomously light-fueled self-oscillators are found to have potential applications in detecting charges and signal transmission.

Near-Zero Drift and High Electromechanical Coupling Acoustic Resonators at > 3.5 GHz

Abstract: In this article, near-zero drift and high electromechanical coupling acoustic resonators have been designed and demonstrated. The acoustic resonator is based on Lamb acoustic waves in a bimorph composed of lithium niobate on silicon dioxide. Our approach breaks through a performance boundary in conventional Lamb-wave resonators by introducing the bimorph while operating at higher order resonant modes. This enables the resonator to achieve frequency scalability, a low-temperature coefficient of frequency, and high electromechanical coupling altogether. The electromechanical coupling and temperature coefficient of the resonator were analytically optimized for the A3 mode through adjusting the thicknesses of different materials in the bimorph. Resonators with different dimensions and stack thickness were fabricated and measured, resulting in a temperature coefficient of frequency ranging from −17.6 to −1.1 ppm/°C, high electromechanical coupling ranging from 13.4% to 18%, and quality factors up to 800 at 3.5 GHz. The achieved specifications are adequate for fifth-generation (5G) sub-6-GHz frequency bands n77 and n78.

Self-Sensing and Control of Soft Electrothermal Actuator

Abstract: 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.

Investigations on laser actuation and life cycle characteristics of NiTi shape memory alloy bimorph for non-contact functional applications

Abstract: A laser source was used as non-contact mode of heating to actuate NiTi/kapton polyimide shape memory alloy (SMA) bimorph. The bimorph was fabricated by depositing NiTi thin film over Kapton polyimide sheet of dimension 5 × 2 cm2 using thermal evaporation. The laser parameters such as laser power, scanning speed and number of passes were optimized to ensure actuation without damaging the bimorph. The actuation was carried out at laser powers and scanning speeds of 14 to 16 W and 13–16 mm/s respectively. The displacement of SMA bimorph was found to increase with increase in laser power whereas it decreases with increase in scanning speeds. At lower laser power, the scanning speeds have influenced the actuation behavior to larger extent. Notably at the laser power of 14 W, the influence of scanning speed was significant and registered 53 % reduction in displacement with increase in scanning speeds from 13 mm/s to 16 mm/s. A minimum and maximum displacement of 0.35 mm and 3.8 mm was obtained during laser actuation of bimorph. The temperature experienced during laser actuation has been simulated using COMSOL Multiphysics and corroborated with the actuation behavior of the SMA bimorph. The displacement range and the actuation speed of laser actuation were found to be higher than the conventional electrical actuation. Furthermore, the life cycle analysis has been performed up to 100 laser passes and the phenomenon for reduction in displacement has been discussed in detail. Laser actuation of SMA bimorph could be utilized in thermal switches, adaptive optics and remote actuation of SMA elements etc.

A Light-Driven Vibrotactile Actuator with a Polymer Bimorph Film for Localized Haptic Rendering.

Abstract: A vibrotactile actuator driven by light energy is developed to produce dynamic stimulations for haptic rendering on a thin-film structure. The actuator is constructed by adopting a thermal bimorph membrane structure of poly(3,4-ethylenedioxythiophene) doped with p-toluenesulfonate (PEDOT-Tos) coated onto a polyethylene terephthalate (PET) film. Upon irradiation of near-infrared (NIR) light, the light energy absorbed at the PEDOT-Tos layer is converted into thermoelastic bending deformation due to the mismatch in coefficient of thermal expansion between PEDOT-Tos and PET. Since the light-induced deformation is reversible, spatially localized, and rapidly controllable with designed light signals, the proposed actuator can produce vibrotactile stimulation over 10 dB at arbitrary areas in the human-sensitive frequency range from 125 to 300 Hz using a low input power of ∼2.6 mW mm-2, as compared with a complex electrical circuit and high input power needed to achieve such actuation performance. Together with its simple structure based on light-driven actuation, the advent of this actuator could open up new ways to achieve substantial advances in rendering textures at a flexible touch interface.

Bimorph Pinned Piezoelectric Micromachined Ultrasonic Transducers for Space Imaging Applications

Abstract: This paper reports a bimorph pinned piezoelectric micromachined ultrasonic transducer (PMUT) for enhanced sound pressure output and electromechanical coupling factor for space imaging applications. An equivalent circuit model has been built to analyze the dynamic behavior of PMUTs and prototype devices have been designed, fabricated. Experimental results show a 58% measured increase in the electromechanical coupling factor and pulse-echo measurements show a 4-meter traveling distance in air under a 133 kHz driving frequency. As a demonstration example, a relatively long-distance (>1.5 meters) ultrasound imaging test in air is conducted using a $4\times 4$ bimorph, pinned dual-electrode PMUTs array based on the transmission beamforming scheme. As such, this work enhances and extends the PMUT performances and capabilities for potential broad applications. [2021-0102]

Nonlinear dynamic modeling of bimorph piezoelectric actuators using modified constitutive equations caused by material nonlinearity

Abstract: Commonly, linear constitutive equations have been utilized for describing the electromechanical behavior of piezoelectric actuators. These equations are valid for low excitation amplitudes and smal...

3D Ultrasonic Object Detections with >1 Meter Range

Abstract: This paper reports an ultrasonic 3D object detector with > 1 meter range based on an AlN piezoelectric micromachined ultrasonic transducers (pMUTs) chip. Compared with the state-of-art technologies, three distinctive advancements have been achieved: (1) more than 1-meter in sensing distance enabled by a bimorph dual electrode pMUT design; (2) small form factor (6×6 mm2) and a more than 135° field of view; (3) capability of real time 3D object detection with up to 125 fps (frames per second) based on the scheme of ultrasound beamforming. As such, this work could open up a new class of miniaturized, low-power, real-time 3D object detections for applications such as drone navigation, machine vision and so on.

A 1×20 MEMS mirror array with large scan angle and low driving voltage for optical wavelength-selective switches

Abstract: Wavelength-selective switches (WSSs) are the core devices for reconfigurable optical add-drop multiplexers (ROADMs) that are essential in all-optical networks. WSSs based on microelectromechanical (MEMS) mirror arrays exhibit high potential due to their high switching speed and large port counts, but there still exist challenges to achieve large optical scanning angle at low voltage. This paper presents a 1×20 MEMS mirror array (MMA) design that can scan over 10° in both axes at less than 5 V. The MMA is based on an unique electrothermal bimorph actuator design that can perform 2D scanning and its fill factor reaches 96 %. The 1×20 MMA design has been successfully fabricated using a combined bulk- and surface- micromachining process. The size of each mirror plate is 240 μm by 500 μm. The measured maximum optical scan angles in the x-axis and y-axis are 29.3° and 11.8°, respectively, at 3 V. The measured response time is about 3.7 ms. The thermal crosstalks between adjacent electrothermal actuators are about 10 %. Long-term stability tests show that the angular drifts of the individual mirrors are about 0.002°/h.

Split Cantilever Multi-Resonant Piezoelectric Energy Harvester for Low-Frequency Application

Abstract: This paper presents a new way to design a broadband harvester for harvesting high energy over a low-frequency range of 10–15 Hz. The design comprises a cantilever beam with two parallel grooves to form three dissimilar length parallel branches, each with an unequal concentrated tip mass. The piezoelectric material covers the whole length on both sides of the beam to form a bimorph. Appropriate geometry and mass magnitudes are obtained by a parametric study using the Finite Element Method. The design was simulated in COMSOL Multiphysics to study its response. The first three bending modes were utilized in energy harvesting, resulting in three power peaks at their respective fundamental frequencies. The adequate load resistance determined was 5.62 kΩ, at which maximum power can be harvested. The proposed harvester was compared to two other harvesters presented in the literature for validation: First, an optimized conventional harvester while the proposed harvester is operating at adequate load resistance. Second, a multimodal harvester, while the proposed harvester is operating at a 10 kΩ load. The suggested harvester proved to be more efficient by harvesting sufficiently higher broadband energy and is applicable in a wide range of vibration environments because of its adaptability in design.

Evaluating Energy Generation Capacity of PVDF Sensors: Effects of Sensor Geometry and Loading

Abstract: This paper focuses on the energy generating capacity of polyvinylidene difluoride (PVDF) piezoelectric material through a number of prototype sensors with different geometric and loading characteristics. The effect of sensor configuration, surface area, dielectric thickness, aspect ratio, loading frequency and strain on electrical power output was investigated systematically. Results showed that parallel bimorph sensor was found to be the best energy harvester, with measured capacitance being reasonably acceptable. Power output increased with the increase of sensor’s surface area, loading frequency, and mechanical strain, but decreased with the increase of the sensor thickness. For all scenarios, sensors under flicking loading exhibited higher power output than that under bending. A widely used energy harvesting circuit had been utilized successfully to convert the AC signal to DC, but at the sacrifice of some losses in power output. This study provided a useful insight and experimental validation into the optimization process for an energy harvester based on human movement for future development.

Ultrasond-Induced Haptic Sensations Via PMUTS

Abstract: This work presents the sense of touch via non-contact ultrasonic waves by a dual-electrode bimorph piezoelectric micromachined transducer (pMUT) array. The prototype device has 12×12 elements with circular diaphragms of 415μm in radius made of 2 μm-thick AlN. They are fabricated by a CMOS compatible micromachining process resulting a resonant frequency at 109.4 kHz. Experimentally, a best haptic sensation on human fingers is found when emitting high frequency ultrasonic waves to emulate 100 Hz signals by means of pulse width modulation with a 50% duty cycle. Strong haptic sensations are reported by volunteers under an AC peak-to-peak amplitude of 12 V up to 10 cm away from the transducers. Applications as the human-machine interfaces in biomedical, gaming, and AR/VR are a few of the MEMS uses; we present results by transmitting a series of Morse codes remotely to the skins of volunteers.

Large deformation mechanical modeling with bilinear stiffness for Macro-Fiber Composite bimorph based on extending mixing rules:

Abstract: Macro-Fiber Composite bimorph is a kind of piezoelectric actuator that allow large bending deformation. However, macro-fiber composites exhibit strong stiffness nonlinearity in their operation rang...

Piezoelectric vibration energy harvester with tapered substrate thickness for uniform stress

Abstract: This paper presents modification in the thickness profile of bimorph cantilever type piezoelectric vibration energy harvester (PVEH) to achieve uniform stress along the beam length. The thickness profile is obtained by varying the thickness of substrate layer and keeping the thickness of piezoelectric layers constant. Analytical expressions for the cantilever beam displacement, stress on the beam and generated voltage are derived and solved for sinusoidal input excitations. The results from the analytical expressions are validated with that of the finite element (FE) analysis of an identical PVEH. The generated power and stress distribution in the proposed PVEH are compared with that of an equivalent conventional PVEH of uniform thickness. Compared to the conventional PVEH, in the proposed PVEH the generated power is 20% higher for an input acceleration of 0.2g, and the stress on the proposed device is found to be uniformly distributed with the peak stress value reduced significantly by 46%.