Electret-based vibrational energy harvesters (E-VEHs) are promising power sources for wireless sensor nodes. However, conventional E-VEHs require a dedicated charging process for the dielectric, which complicates high-throughput manufacturing. Our precious work introduces the use of self-assembled electrets (SAEs), which are polar organic semiconductors exhibiting spontaneous orientation polarization (SOP), and demonstrates an SAE-based VEH that does not require a charging process. For this device, the effect of the surface potential of the patterned SAE (p-SAE) on the output current must be understood; however, the relationship between them remains unclear. In this study, the surface potential and output current of p-SAEs with various structures are precisely evaluated using a Kelvin probe. A linear relationship between the surface potential and output current is observed in the modeled p-SAE VEHs, indicating that the output current can be enhanced merely by increasing the average film thickness of the SAE. Furthermore, we find that the surface potential of p-SAEs originates from the SOP and can be controlled by changing the average film thickness, density, and occupancy rate of the pattern. These findings suggest that p-SAEs are suitable for the mass commercialization of E-VEHs, as they eliminate the need for a dedicated charging process and enable the deposition of SAEs after the movable electrode is fabricated.

This paper is the first to report on the surface potential trimming of self-assembled electrets (SAEs) through localized ultraviolet (UV) light exposure. We experimentally demonstrate that the surface potential of SAE thin films selectively changes in response to variations in exposure area and exposure time. These results provide new insights into the design of SAE-based micro-electro-mechanical systems (MEMS) devices, such as vibration energy harvesters (VEHs) and physical sensors, and suggest the potential to greatly enhance design flexibility and performance tunability.

Optical correlation‐domain reflectometry (OCDR) provides distributed reflectivity measurements with moderate range, high spatial resolution, and real‐time capability. Conventional systems, however, rely on bulky instruments that hinder field use. We propose and experimentally demonstrate a remote‐head OCDR, where only the fiber under test (FUT) and circulator are placed on‐site, connected to the main system via kilometer‐scale fibers. The reflectivity distribution of the FUT was clearly measured, with multiple reflection points detected and ~ 15 cm spatial resolution maintained. These results confirm the feasibility of remote‐head OCDR and its potential for practical infrastructure monitoring. © 2026 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

This paper focuses on parallel-plate electrostatic actuators, which are fundamental structures found in Micro-Electro-Mechanical Systems (MEMS) for numerous modern devices. It considers the equations used to model these actuators. In particular, we investigate the behavior of the solutions to a MEMS model that is represented by a second-order ordinary differential equation, where the spring is characterized as soft, linear, or hard. We present the mathematical structure underlying the pull-in and touchdown phenomena that characterize the behavior of systems incorporating soft and hard spring, based on the behavior of linear springs. The pull-in phenomenon corresponds to the degeneration of the solutions to the model equation. The touchdown phenomenon corresponds to the finite-time singularity of the solutions. These global dynamics and structures are systematically revealed through geometric approaches based on Poincaré-type compactification, the center manifold theorem, and blow-up technique. These methods successfully induce and resolve the dynamics at infinity.

This paper presents the first investigation into how the dry etching depth of the reinforcement layer in perfluorinated polymer optical fibers (PF-POFs) influences radial stress distribution. Using finite element method simulations, we model the PF-POF structure based on the actual dry-etched profiles achieved through reactive ion etching (RIE). The results demonstrate that increasing the etching depth leads to higher radial stress in both the core and cladding layers when strain is applied longitudinally. These findings suggest that RIE processes present a feasible method for tuning the sensitivity of PF-POF-based strain sensors. © 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

This paper is the first to report on the controllability of the surface potential of self-assembled electrets (SAEs) subjected to corona discharge. We experimentally demonstrate that the surface potential of SAE thin films changes in response to variations in needle electrode voltage (VN) and discharge time during corona discharge. These findings offer new insights for designing micro-electro-mechanical systems (MEMS) vibration energy harvesters (VEHs) and other devices utilizing SAEs.

Sensors, sensing systems, and their architectures for sports sciences and related applications are reviewed and summarized. The sports science was considered the core of the focus, which was linked to the innermost shell (characteristics) of the complete article framework. Different sensors were included in the intermediate shell of the framework, which translate quantify and qualify activities and results. The outermost shell of the framework was the application, in which various sports were given as examples. To support this structure, widely-used detection systems (such as inertial measurement units, force sensors, physiological sensors, global positioning systems, and local positioning systems) are concluded for various sports activities. Not only publicly-acceptable sports (for example, swimming, badminton, basketball, and soccer) but also those with professional teams and played in limited regions (for example, American football, cricket, and hockey) are scientifically quantified with sports science-supportive sensors here. Additionally, mild (such as running and yoga) and extensive activities (such as boxing and rugby) are both included in this summary for comprehensive comparison on the sensing systems. Different evaluation aspects from the user (player), coaching team, and audience are mentioned when the smart sensors are able to provide immersive experience. Practical considerations of comfort feeling, cost for production, and material supportiveness are sequentially concluded in this manuscript with extensive demonstration from 160 references.

This paper reports the first implementation of long-period gratings (LPGs) on perfluorinated plastic optical fibers (PF-POFs) using a micro dry etching technology, which is more controllable and potentially mass-processable than conventional laser irradiation techniques. Micrometer-scale periodic structures were fabricated on PF-POFs by a reactive ion etching processing with a silicon shadow mask, and the frequency characteristics specific to LPGs are experimentally confirmed by inducing refractive index modulation due to internal stress distribution. These findings highlight the potential for further precise control of the properties of LPG-based PF-POF sensors, as well as their wide use in applications.

High‐spatial‐resolution Brillouin optical correlation‐domain reflectometry (BOCDR) in perfluorinated graded‐index polymer optical fibers (PFGI‐POFs) is gaining attention for structural health monitoring. A major challenge has been accurately predicting Rayleigh noise behavior, which constrains the modulation amplitude and spatial resolution. However, prior models did not consider differences in optical path lengths caused by the refractive indices of silica fibers (used in circulators) and PFGI‐POFs. We refine the noise model to incorporate these differences. Experiments with varying fiber lengths show that the revised model more accurately predicts Rayleigh noise bandwidth, especially with longer circulator fibers. Errors of up to 120 MHz in the conventional model are reduced to within 25 MHz, showing the importance of proper optical path modeling in BOCDR. © 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

SAEs (self-assembled electrets) are recently reported electrets that can be deposited in semiconductor manufacturing processes and, unlike conventional electrets, do not require any charging process. We have developed an integration technology of SAEs with MEMS (micro-electro-mechanical systems) for the first time and successfully demonstrated SAE-based MEMS vibrational energy harvesters. This presentation introduces the integration technology of MEMS and SAEs, the characterization of SAE films formed in MEMS devices, and SAE-MEMS co-design technologies, including future prospects.

Polymer optical fibers (POFs) are promising candidates for sensor applications due to their high strain resistance, flexibility, and cost-effectiveness. The performance of POF-based sensors can be enhanced through precise micro-processing of the fibers. However, conventional methods for observing POF cross-sections often fail to capture the detailed profiles of micro-processed POFs, leading to inaccuracies in sensor design and analysis. In this work, we developed a new protection layer-assisted cross-sectional observation method to preserve the surface profiles of POFs during cutting and polishing. As a proof of concept, we applied this method to perfluorinated (PF)-POFs dry-etched by reactive ion etching (RIE). Epoxy resin was used as a protection layer to maintain the structural integrity of the fibers during the cutting process. The cross-sectional profiles of the micro-processed PF-POFs were successfully captured using a laser microscope. These profiles, previously difficult to predict, were found to be crucial for analyzing the strain sensor performance. Finite element method simulations further demonstrated the impact of these geometric features on the strain characteristics of the PF-POFs. Our results confirm that the proposed method is effective for constructing accurate design and analysis models of micro-processed POFs, paving the way for improved sensor technologies.

This study explores the impact of a micro dry-etching technique on strain sensing based on multimode interference in a perfluorinated polymer optical fiber (POF). We demonstrate a drastic shift in strain sensitivity, from +34 nm/% in a non-etched POF to -981 nm/% in the etched POF. This notable change may be attributed to the excitation of the axially asymmetrical modes in the etched POF, which is confirmed through simulation on the stress distribution across the core. In addition, a critical wavelength for multimode interference is observed in a POF.

This paper reports a design methodology for micro-electro-mechanical systems (MEMS) vibrational energy harvesters (VEHs) using micro-cavity (MC) structures with self-assembled electrets (SAEs). Unlike the previous micro-patterned SAE design [1], we propose a SAE-filled MC structure. With this structure, the air gap and SAE film thickness in SAE-MEMS VEHs can be designed without interfering with each other. The SAE film thickness and surface potential have a proportional relationship. Thus, when a high surface potential is required, this methodology is highly effective in increasing the SAE film thickness without being restricted by the air gap.

Ni–W alloys have received considerable interest as a promising structural material for microelectromechanical systems (MEMS) due to their exceptional properties, including hardness, ductility, corrosion resistance, and thermal stability. However, the electrodeposition of Ni–W alloys in the MEMS fabrication process to achieve intact structures with a thickness of several tens of micrometers is challenging due to the occurrence of cracking caused by side reactions and internal stresses during the electrodeposition process. To address this issue, our focus was on pulsed reverse electrodeposition (PRE) as a potential solution. The utilization of the PRE technique allows for a high concentration of reactive species on the electrode surface, thereby mitigating side reactions such as hydrogen generation. In this study, we examined the effects of the PRE method on the morphological characteristics, average crystal grain size, Vickers hardness, and micro-mechanical properties of Ni–W alloys.

This paper reports an equivalent circuit model of self-assembled electret (SAE) micro-electro-mechanical systems (MEMS) vibrational energy harvesters (VEHs). For the first time, a detailed equivalent circuit model of the SAE-MEMS VEH has been implemented on a circuit simulator, considering the device energy diagram. The implemented equivalent circuit model allows analysis of the relationship between output current and SAE properties, device structures, and electrode materials. The validity of the model is confirmed by comparing the measurement and simulation results. Thus, the proposed model would be useful for the design of SAE-MEMS VEHs. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

This paper reports for the first time the relationship between surface potential and film thickness of micro-patterned self-assembled electrets (SAEs). We experimentally confirm a trend of increasing surface potential in proportion to the average film thickness $t_{\text{avg}}$ per repeated pattern of the micro-patterned SAEs. The evaluation results could be useful for the design of micro-electro-mechanical systems (MEMS) vibrational energy harvesters (VEHs) and other devices using SAEs.

This paper reports demonstration results of non-contact out-of-plane vibration energy harvesting using an electric-double-layer electret (EDLE). Unlike contact types or non-contact in-plane types, the proposed operation type can be useful in terms of expanding the operating frequency range and simplifying the device structures. A demonstration system is developed, and power generation is confirmed using an EDLE with a surface potential of −1 V under an atmospheric condition. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

This paper reports the first direct measurement results of the surface potential of micro-patterned self-assembled electrets (SAEs) for microelectromechanical systems vibrational energy harvester applications. We have developed an evaluation chip that utilizes a removable shadow mask with through-holes to realize SAE micro-patterning during SAE evaporation. A Kelvin probe is used to measure the surface potential of the micro-patterned SAEs. The surface potential of the micro-patterned SAEs with the average thickness of 65 nm was found to be 2099 mV, which is in the same order of magnitude as the surface potential estimated from the average thickness of the SAEs.

Nickel-boron alloys are prepared by an electrodeposition method. The as-deposited nickel-boron alloy is then annealed at 250 & DEG;C and 400 & DEG;C for 4 h. Their mechanical strengths and specimen size effects on the strength are evaluated by micro-compression test using pillar-type micro-specimens fabricated by focused ion beam system. In all as-deposited and annealed specimens, a smaller-is-stronger specimen size effect is confirmed. The compressive strength of the nickel-boron alloys reaches a maximum of 5.79 GPa with the smallest specimen size in this work.