Here we introduce the electromagnetic shielding effectiveness (SE) of reduced graphene oxide (RGO) sheets interleaved between polyetherimide (PEI) films fabricated by electrophoretic deposition (EPD). Incorporating only 0.66 vol % of RGO, the developed PEI/RGO composite films exhibited an electromagnetic interference shielding effectiveness (EMI SE) at 6.37 dB corresponding to ∼50% shielding of incident waves. Excellent flexibility and optical transparency up to 62% of visible light was demonstrated. It was achieved by placing the RGO sheets in the localized area as a thin film (ca. 20 nm in thickness) between the PEI films (ca. 2 μm) to be an interleaved and alternating structure. This unique interleaved structure without any delamination areas was fabricated by a successive application of cathodic and anodic EPD of both RGO and PEI layers. The EPD fabrication process was ensured by an alternating deposition of the quarternized-PEI drops and RGO, each taking positive and negative charges, respectively, in the water medium. We believe that the developed facile fabrication method of RGO interleaved structure with such low volume fraction has great potential to be used as a transparent EMI shielding material.
Portable energy storage devices have gained special attention due to the growing demand for portable electronics. Herein, an all-solid-state supercapacitor is successfully fabricated based on a poly(vinyl alcohol)-H3PO4 (PVA-H3PO4) polymer electrolyte and a reduced graphene oxide (RGO) membrane electrode prepared by electrophoretic deposition (EPD). The RGO electrode fabricated by EPD contains an in-plane layer-by-layer alignment and a moderate porosity that accommodate the electrolyte ions. The all-solid-state RGO supercapacitor is thoroughly tested to give high specific volumetric capacitance (108 F cm(-3)) and excellent energy and power densities (7.5 Wh cm(-3) and 2.9 W cm(-3), respectively). In addition, the all-solid-state RGO supercapacitor exhibits an ultralong lifetime for as long as 180 days (335 000 cycles), which is an ultrahigh cycling capability for a solid-state supercapacitor. The RGO is also tested for being used as a transparent supercapacitor electrode demonstrating its possible use in various transparent optoelectronic devices. Due to the facile scale-up capability of the EPD process and RGO dispersion, the developed all-solid-state supercapacitor is highly applicable to large-area portable energy storage devices.
RuO2/carbon powder electrodes have been designed to be enclosed in a supercapacitor cell and compressed under a constant pressure (4.84 kgf cm−2), which could overcome binder failure under repeated volumetric changes.
In the fabrication of InAlAs/InGaAs metamorphic high-electron-mobility transistor (mHEMT), the determination of whether etching has been completed to the desired gate recess depth is made by measuring whether the drain current through the channel layer has reached the target current. Non-uniformity of the etching rate occurs during wet etching with citric acid. In this study, the cause of that non-uniformity was investigated. We confirmed that an electrochemical potential caused by the electrolyte of the etching solution was induced between the ohmic electrode and the epitaxial layer of the recess region, resulting in a non-uniform etching rate. In particular, the case where the Au of an ohmic electrode is exposed by the monitor window for the measuring channel current was considered. The gate recess etch rate was changed by the presence, location and size of the photoresist openings on the ohmic electrodes.
In this study, an inertial measurement unit (IMU) sensor module and software algorithm were developed to identify anomalous kicks that should not be given scores in Taekwondo competitions. The IMU sensor module was manufactured with dimensions of 3 cm × 3 cm × 1.5 cm and consists of a high-g sensor for high acceleration measurement, a 9-DOF sensor, and a Wi-Fi module for wireless communication. In the experiment, anomalous kicks and normal kicks were collected by the IMU sensor module, and an AI model was trained. The anomalous kick determination accuracy of the trained AI model was found to be 97.5%. In addition, in order to check whether the strength of a blow can be distinguished using the IMU sensor module, an impact test was performed with a pendulum under the same test conditions as the impact sensor installed in the impact test setup, and the correlation coefficient was 0.99. This study is expected to contribute to improving scoring reliability by suggesting the possibility of discriminating anomalous kicks, which were difficult to judge in Taekwondo competitions, through the analysis of Taekwondo kicks using inertial data and impulses.
Based on the results of computational fluid dynamics simulations, this study designed and fabricated a flexible thermal-type micro flow sensor comprising one microheater and two thermistors using a micro-electromechanical system (MEMS) process on a flexible polyimide film. The thermistors were connected to a Wheatstone bridge circuit, and the resistance difference between the thermistors resulting from the generation of a flow was converted into an output voltage signal using LabVIEW software. A mini tube flow test was conducted to demonstrate the sensor’s detection of fluid velocity in gas and liquid flows. A good correlation was found between the experimental results and the simulation data. However, the results for the gas and liquid flows differed in that for gas, the output voltage increased with the fluid’s velocity and decreased against the liquid’s flow velocity. This study’s MEMS-based flexible microthermal flow sensor achieved a resolution of 1.1 cm/s in a liquid flow and 0.64 cm/s in a gas flow, respectively, within a fluid flow velocity range of 0–40 cm/s. The sensor is suitable for many applications; however, with some adaptations to its electrical packaging, it will be particularly suitable for detecting biosignals in healthcare applications, including measuring respiration and body fluids.
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