This paper proposes and studies the characteristics of a laser-driven optothermal microactuator (OTMA) directly operated in water. A theoretical model of optothermal temperature rise and expansion is established, and simulations on a 1000 µm long OTMA are conducted, revealing that its arm is able to expand and contract in response to the laser pulses in a water environment. Microactuating experiments are further carried out using a microfabricated OTMA. The results demonstrate that the OTMA can be practically actuated in water by a 650 nm laser beam and that the OTMA’s deflection amplitude increases linearly with laser power. When irradiated by laser pulses with 9.9 mW power and 0.9–25.6 Hz frequencies, the OTMA achieves deflection amplitude ranging from 3.9 to 3.2 µm, respectively. The experimental results match well with theoretical model when taking the damping effect of water into account. This research may be conducive to developing particular micro-electromechanical systems or micro-optoelectromechanical devices such as underwater optothermal micromotors, micro-pumps, micro-robots, and other underwater microactuators.

This paper proposes a method of a symmetric optothermal microactuator (S-OTMA) directly driven by laser pulse. Based on the principle of thermal flux, a dynamic model is established describing the laser-induced optothermal temperature rise and optothermal expansion of the S-OTMA's expansion arm. The dynamic optothermal expansion and the relationship between the expansion amplitude and laser pulse frequency are simulated, indicating that the expansion arm expands and reverts periodically with the same frequency of the laser pulse, and that the expansion amplitude decreases with the increase of laser pulse frequency. Experiments have been further conducted on a micro-fabricated S-OTMA under a laser pulse of 3.3 mW power and 2-18 Hz frequency. It is shown that the S-OTMA can periodically deflect in accordance with the same frequency of the laser pulse, with a maximum response frequency of at least 18 Hz. The maximum deflection (vibration) amplitude is measured to be 13.7 µm (at 2 Hz), and the amplitude decreases as the frequency increases. Both the theoretical model and experiments prove that the S-OTMA is capable of implementing direct laser-controlled microactuation in which only ~3 mW laser power is demanded. Furthermore, bi-directional actuation of the optothermal microactuator (such as S-OTMA) can be easily achieved by alternately irradiating either arm of the microactuator. This work may broaden the applications of the S-OTMA, as well as optothermal microactuators in MEMS/MOEMS and micro/nano-technology.

This paper presents microscopic research on properties of asymmetric optothermal microactuator (OTMA) with different lever ratios. A theoretical model is established on the basis of thermal flux theorem to describe the increase in temperature induced by laser irradiation and thermal expansion of OTMAs' expansion arms. The increases in temperature of three asymmetric OTMAs with total lengths/lever ratios of 540 μm/7.2, 1,080 μm/7.2, 1,080 μm/14.4 were simulated under irradiation of 2.8 mW laser beam, which revealed that a similar increase in temperature will distribute on three expansion arms, with maximum the temperature increase of 82.73, 87.67, and 88.03 C, respectively. Due to these increases in temperature, the arms expand longitudinally and thus the OTMAs are capable of deflecting laterally with enlarged deflection amplitudes. To obtain optimized deflecting properties, three OTMAs with aforementioned lever ratios are further microfabricated and experimented using an optical microscopic observation and measuring system combined with a charge-coupled device. The experimental results show that these OTMAs can be directly actuated by laser beam and acquire maximum deflections of 6.8, 7.2, and 11.4 μm when only 2.8 mW laser power is employed. In addition, it is demonstrated that, although doubling the lever ratio of OTMA does not correspondingly generate twofold deflection, the deflection amplitude can significantly increase with the increase in the lever ratio. With their characteristic elegances, the OTMAs are expected to be practically applied in the micro-electromechanical system and the micro-opto-electromechanical system. K E Y W O R D S asymmetric optothermal microactuator, microscopic observation and measuring, dynamic modelling, lever ratio, microdeflection

This article proposes to develop a WiFi‐controlled portable atomic force microscope (AFM). The AFM consists of a horizontal probe, controlling circuits, digital to analog (D/A) and analog to digital (A/D) interfaces, a microcomputer (Raspberry Pi, RPi), and a laptop. The proposed AFM uses a pocket‐size power supply to drive the controlling circuits, the D/A and A/D interfaces, as well as the RPi that constructs network hotspots and generates scanning signals. With special design and integration of the whole system, both of the AFM probe and electronic controlling system are portable. At a distance of 50 m from the proposed AFM, experiments in the constant height mode and the constant force mode are conducted to evaluate its performance. The results show that this WiFi‐controlled AFM has a maximum scan range of 3.6 × 3.6 μm2 with nanometer order resolution. Meanwhile, it achieves satisfactory image contrast, stability, and repeatability. Compared with conventional AFMs, the AFM proposed in this paper no longer relies on commercial AC mains supply or high‐voltage DC power supply, and realizes WiFi‐controlled AFM scanning and imaging in 50 m or farther without wire or network cable connection to a laptop or a desktop computer. Given credits to these features, WiFi‐controlled AFMs are expected to own a wider range of application, especially in isolated environments, outdoor researches, or even fieldwork investigations.