Effects of initial charge on triboelectrification of plastics.

Plastic recycling is one of the most economical and environment-friendly solutions for effective plastic waste management. Triboelectric separation is one of beneficial methods to accomplish this. A method and device capable of analyzing the triboelectrification of materials with specific initial charges are proposed in this study. The process of triboelectrification is experimentally analyzed for various initial-charge conditions using the proposed method and device. The triboelectrification process can be divided into two groups depending on the initial-charge conditions. For the specific initial conditions, termed Group 2 in this work, it is observed that the initial charge of one material is first released into the control volume, following which the two materials exchange charges, unlike in the conventional triboelectrification process. This study is expected to provide valuable insights into triboelectrification analysis, thereby advancing the multistage plastic-separation processes.

Test bed for rotation-based triboelectric nanogenerators.

The triboelectric nanogenerator (TENG) has been attracting attention for electronic devices and sensors consuming low power. Among the few operating modes of the TENG, the rotation-based TENG provides a more continuous and smoother output than the linear-motion-based TENG. To evaluate the output performance of the rotation-based TENG precisely and quantitatively, a test bed that adjusts the eccentricity error, tilt angle error, contact force, and rotational speed is proposed. The test bed includes a motor, torque sensor, 2-axis planar stage, 2-axis tilting stage, 1-axis vertical stage, 3-degree-of-freedom force/torque (3-DOF F/T) sensor, and voice coil actuator. With the proposed test bed, the effects of the eccentricity error, tilt angle error, contact force, and rotational speed on the electrical output performance of the rotation-based TENG are analyzed. The test bed is expected to be used for quantitative performance analysis and comparative study of various rotation-based TENGs, and it can help improve the performance and reliability of rotation-based TENGs.

Test bed for contact-mode triboelectric nanogenerator.

The triboelectric nanogenerator (TENG) has become one of the strongest candidates for sustainable power sources. The power of a TENG depends on factors such as contact area, contact parallelism, contact force, and contact speed. In order to evaluate the performance of the TENG precisely and quantitatively, it is necessary to apply consistent experimental conditions and measurement processes. In this paper, we propose a test bed capable of adjusting the contact area and contact parallelism and measuring the contact force, contact speed, current, and voltage in real time. The test bed consists of a 2-axis planar stage, a 2-axis tilting stage, a 1-axis vertical stage, a 3-degree-of-freedom (DOF) force/torque sensor, a capacitive displacement sensor, and a voice coil actuator. The 3-DOF force/torque sensor can provide feedback on the degree of parallelism and contact area alignment as well as contact force. With the proposed test bed, the effects of parallelism error, contact area, contact force, and contact speed on the performance of contact-mode TENGs are quantitatively analyzed. This test bed is expected to be used for the quantitative analysis of contact-mode TENGs with various new structures and for comparison among different devices.

Design of a four-degree-of-freedom nano positioner utilizing electromagnetic actuators and flexure mechanisms.

Positioning devices are widely used in industrial applications. High precision is a key performance of the positioner and recently high precision positioners for advanced applications are required to satisfy other performances such as larger motion range, nanometer level precision, and multiple degree-of-freedom (DOF) motion within compact size. We propose a new 4-DOF high-precision positioner employing voice coil motors and flexure guides. Millimeter motion range and nano level resolution were achieved simultaneously, utilizing the frictionless characteristic of the voice coil motors and the flexures. The mathematical model describing static and dynamic behaviors of the positioner was developed and the design parameters were optimized to achieve the best performances. The proposed positioner was manufactured with the size of 180 × 180 × 30.7 mm(3) which was very compact. The experiment of feedback control showed the motion range more than 1.80 × 1.80 mm(2) in-plane and 0.3 mm vertically and the minimum resolution of 10 nm in-plane and 14 nm vertically.

Design and fabrication of vibration based energy harvester using microelectromechanical system piezoelectric cantilever for low power applications.

We fabricated dual-beam cantilevers on the microelectromechanical system (MEMS) scale with an integrated Si proof mass. A Pb(Zr,Ti)O3 (PZT) cantilever was designed as a mechanical vibration energy-harvesting system for low power applications. The resonant frequency of the multilayer composition cantilevers were simulated using the finite element method (FEM) with parametric analysis carried out in the design process. According to simulations, the resonant frequency, voltage, and average power of a dual-beam cantilever was 69.1 Hz, 113.9 mV, and 0.303 microW, respectively, at optimal resistance and 0.5 g (gravitational acceleration, m/s2). Based on these data, we subsequently fabricated cantilever devices using dual-beam cantilevers. The harvested power density of the dual-beam cantilever compared favorably with the simulation. Experiments revealed the resonant frequency, voltage, and average power density to be 78.7 Hz, 118.5 mV, and 0.34 microW, respectively. The error between the measured and simulated results was about 10%. The maximum average power and power density of the fabricated dual-beam cantilever at 1 g were 0.803 microW and 1322.80 microW cm(-3), respectively. Furthermore, the possibility of a MEMS-scale power source for energy conversion experiments was also tested.

Micromachining of a bimorph Pb(Zr,Ti)O3 (PZT) cantilever using a micro-electromechanical systems (MEMS) process for energy harvesting application.

We designed and fabricated a bimorph Pb(Zr,Ti)O3 (PZT) cantilever with an integrated Si proof mass to obtain a low resonant frequency for an energy harvesting application. The cantilevers were fabricated on the micro-electromechanical systems (MEMS) scale. A mode of piezoelectric conversions were d31 and d33 mode in cantilever vibration Therefore, we designed and fabricated a single cantilever with d31 unimorph, d31 bimorph, d33 unimorph, and d33 bimorph modes. Finally, we fabricated a device with beam dimensions of about 5,400 microm x 480 microm x 14 microm (< +/- 5%), and an integrated Si proof mass with dimensions of about 1,481 microm x 988 microm x 450 microm (< +/- 5%). In order to measure the d31 and d33 modes, we fabricated top and bottom electrodes. The distance between the top electrodes was 50 microm and the resonant frequency was 89.4 Hz. The average powers of the d31 unimorph, d31 bimorph, d33 unimorph, and d33 bimorph modes were 3.90, 9.60, 21.42, and 22.47 nW at 0.8 g (g = 9.8 m/s2) and optimal resistance, respectively.

Design and fabrication of a PZT cantilever for low frequency vibration energy harvesting.

In this study, a PZT cantilever with a Si proof mass is designed and fabricated for a low frequency energy harvesting application. A mathematical model of a multi-layer composite beam was derived and applied in a parametric analysis of the piezoelectric cantilever. Finally, the dimensions of the cantilever were determined for the resonant frequency of the cantilever. Our cantilever design was based on MATLAB and ANSYS simulations. For this simulation, the proof mass volumes were varied from 0 to 0.5 mm3 and resonant frequencies were calculated from 833.5 Hz to 125.5 Hz, respectively. Based on simulation, we fabricated a device with beam dimensions of about 4.10 mm x 0.48 mm x 0.012 mm, and an integrated Si proof mass with dimensions of about 0.481 mm x 0.48 mm x 0.45 mm. The resonant frequency, maximum peak voltage, and highest average power of the cantilever device were 224.8 Hz, 4.8 mV, and 2.24 nW, respectively.

Note: Design of a novel ultraprecision in-plane XYθ positioning stage.

This paper presents the design, fabrication, and experimental results of a novel ultraprecision in-plane XYθ positioning stage with kinematic decoupling between translational motion and rotational motion components. Two translational motions are guided by four cymbal mechanisms that have both motion guide and motion amplifier. Four leaf springs guide a rotational motion amplified by a Scott-Russell linkage mechanism. The proposed stage has advantages such as an in-plane symmetrical configuration as well as ease of design and control by serial kinematics. The experimental results demonstrate that the stage has a translational full motion range of 58 µm and a rotational full motion range of 1.05 mrad. The crosstalk experimental results show good agreement with the theoretical prediction of the decoupling between translational motion and rotational motion.

Vomer-palatal flap, reconstruction of the palatal defect after maxillectomy.

Rotational palatal flaps are frequently used to repair defects after partial or total maxillectomy procedures. However, their use is determined by the availability of sound tissues for defect closure. In an attempt to increase the amount of tissues available, we developed a vomer-palatal flap to include a part of vomer mucoperiosteum. The technique proved efficiency in a series of patients treated at Seoul National University Dental Hospital.

A new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage.

Next-generation lithography requires a high precision stage, which is compatible with a high vacuum condition. A magnetic levitation stage with six degrees-of-freedom is considered state-of-the-art technology for a high vacuum condition. The noncontact characteristic of magnetic levitation enables high precision positioning as well as no particle generation. To position the stage against gravity, z-directional electromagnetic levitation mechanisms are widely used. However, if electromagnetic actuators for levitation are used, heat is inevitably generated, which deforms the structures and degrades accuracy of the stage. Thus, a gravity compensator is required. In this paper, we propose a new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage. The novel Halbach magnetic bearing exerts a force four times larger than a conventional magnetic bearing with the same volume. We also discuss the complementary characteristics of the two magnetic bearings. By modifying the height of the center magnet in a Halbach magnetic bearing, a performance compromise between levitating force density and force uniformity is obtained. The Halbach linear active magnetic bearing can be a good solution for magnetic levitation stages because of its large and uniform levitation force.