Divinylsiloxane-bis-benzocyclobutene (DVS-BCB) has attracted significant attention as an intermed... more Divinylsiloxane-bis-benzocyclobutene (DVS-BCB) has attracted significant attention as an intermediate bonding material, owing to its excellent properties. However, its applications are limited, due to damage to peripheral devices at high curing temperatures and unoptimized compressive pressure. Therefore, it is necessary to explore the compressive pressure condition for DVS-BCB bonding. This study demonstrates an optimization process for void-free DVS-BCB bonding. The process for obtaining void-free DVS-BCB bonding is a vacuum condition of 0.03 Torr, compressive pressure of 0.6 N/mm2, and curing temperature of 250 °C for 1 h. Herein, we define two factors affecting the DVS-BCB bonding quality through the DVS-BCB bonding mechanism. For strong DVS-BCB bonding, void-free and high-density chemical bonds are required. Therefore, we observed the DVS-BCB bonding under various compressive pressure conditions at a relatively low temperature (250 °C). The presence of voids and high-density cr...
Inkjet printing technology uses the low-cost direct deposition manufacturing technique for printi... more Inkjet printing technology uses the low-cost direct deposition manufacturing technique for printing and is applicable in various fields including optics, ceramics, three-dimensional printing in biomedicine, and conductive circuitry. This study reviews the classifications and applications of inkjet printing technologies, with a focus on recent publications. The different design approaches, applications, and research progress of several inkjet printing techniques are reviewed. Among them, the piezoelectric inkjet printing technology is the main focus owing to its reliability and handling of a diverse range of inks. A piezo-driven inkjet printhead is activated by applying a voltage waveform to a piezoelectric membrane. The waveform ensures the formation of the designed droplet and a stable jet. A survey of various drivingvoltage waveforms is conducted, which can serve as a reference to the research community that uses piezodriven inkjet printheads. The challenges of printing quality, stability, and speed and their solutions as published in recent studies are reviewed. Technologies for producing high-viscosity inkjets are explored, and the applications of inkjet printing technology in textile, displays, and wearable devices are discussed.
After a piezoelectric inkjet printhead jets the first droplet, the actuating membrane still vibra... more After a piezoelectric inkjet printhead jets the first droplet, the actuating membrane still vibrates, creating residual vibrations in the ink channel, which can degrade the inkjet printhead performance. For suppressing these vibrations, an optimized actuating voltage waveform with two pulses must be obtained, of which the first pulse is used for jetting and the second pulse is used to suppress the residual vibrations. In this study, the pressure history within the ink channel of a recirculating piezoelectric inkjet printhead was first acquired using lumped element modeling. Then, for suppressing residual vibrations, a bipolar voltage waveform was optimized via analysis of the tuning time (tt ), dwell time (td2), rising time (tr2), falling time (tf2), and voltage amplitude of the second pulse. Two voltage waveforms, Waveform 01 and Waveform 02, were optimized thereafter. In Waveform 01, tt=2 μs, td2=2 μs, and tr2 and tf2=1 μs were finalized as the optimal parameters; in the case of a...
Flexible electrodes should have a good mechanical durability and electrical properties under even... more Flexible electrodes should have a good mechanical durability and electrical properties under even extreme bending and deformation conditions. We fabricated such an electrode using an inkjet printing system. In addition, annealing was performed under curing temperatures of 150, 170, and 190 °C to improve the electrical resistance performance of the electrode. Scanning electron microscopy, X-ray diffraction, nanoindentation, and surface profile measurements were performed to measure and analyze the electrode characteristics and the change in the shape of the coffee ring. The bending deformation behavior of the electrode was predicted by simulations. To confirm the bending durability of the flexible electrode according to different curing temperatures, the bending deformation and electrical resistance were simultaneously tested. It was found that the electrode cured at a temperature of 170 °C could endure 20,185 bending cycles and had the best durability, which was consistent with the ...
in the area of FP lens and, for the deep-subwavelength imaging capability of such lens to facilit... more in the area of FP lens and, for the deep-subwavelength imaging capability of such lens to facilitate applications in medical imaging, biometrics, and non-destructive testing. Methods Lens fabrication. Three lenses were fabricated with an array of square-shaped parallelepiped apertures using a 3D printer. The lenses with thicknesses h = 40 and 80 mm were fabricated using an Object 30 Pro 3D printer (Stratasys Company) and transparent VeroClear material, which consisted of transparent thermoplastic polymethyl methacrylate (PMMA). Owing to its larger thickness, the lens with h = 212 mm was fabricated using a stereolithographyapparatus (SLA) with a Kings 3D laser printer and a photocurable resin material. All three lenses consisted of a 2D array of 30 × 10 holes in the y-and z-directions, respectively. The length of the side of the square hole (a) and the periodicity (Λ) were 1.0 and 1.5 mm, respectively. Simulation. The numerical data were obtained via the FEM-based commercial software COMSOL Multiphysics. Simulations were performed by applying Acoustic Pressure, Frequency Domain (.acpr) physics. To reduce the model size, the perfectly matched layer (PML) was employed surrounding the model with a 20 mm thickness. Parallelepiped air holes with side length a = 1.0 mm and thicknesses h = 40, 80, or 212 mm were placed individually between two air blocks with periodicity Λ = 1.5 mm in a 2D array of 20 × 7 blocks in the y-and z-directions, respectively (Fig. 4). The array of hole blocks acts as a lens to perform subwavelength imaging. Monopole point sources used to generate the sound pressure were placed in front of the lens. To reduce the computational time and complexity, only the air part was meshed. A 1D array of data points along the y-direction behind the lens was created to scan the SPL. The separation between two adjacent points was 0.5 mm. Experimental setup. As shown in Fig. 6a, two micro-speakers (DTEC-30008-000, diameter of speaker opening = 1.5 mm) placed in front of the metalens were excited by a function generator (Tektronix, AFG 31000) with a 1 V p-p sinusoidal wave. Behind the lens, a microphone (G.R.A.S. 26 CB, diameter = ¼ʺ) was placed that could be moved along the y-axis by a stepper motor to scan the SPL. The maximum resolution of the motor was 1 µm and the sensitivity of the microphone was 4 mV/Pa. As shown in Fig. 6a,b, the analogue data received from the microphone were converted to digital data by a four-channel National Instrument (NI) data acquisition (DAQ) card (Model NI 9234). Finally, to derive the SPLs, the digital data were manipulated using the LabVIEWbased software NI Signal Express 2013. Note that the reference pressure was fixed to 20 µPa to represent the data in decibels.
Performance Study of Impact-Point Estimation Systems Using Two Types of Acoustic Sensor Arrangement Methods
Journal of Sensors
In this study, a shooting experiment is carried out with an acoustic sensor array that can detect... more In this study, a shooting experiment is carried out with an acoustic sensor array that can detect shock wave at high-sound pressures and withstand the shock wave of the bullet. Delta- and H-type of acoustic sensor units are constructed. The measured values of the temporal arrival differences estimated based on the distance between the acoustic sensors are then compared with the theoretical calculations according to the types of bullets and shooting distance. In addition, an impact-point estimation system (IPES) is fabricated, which comprises delta- and H-type sensor units, a target, signal processing device, and an impact point estimation algorithm. The impact points on the target caused by the shooting experiment are compared with those calculated using the impact point estimation algorithm. Finally, the mean absolute error MAE between the actual and the calculated impact-point coordinates is calculated, and the performances of the delta- and H-type IPES are evaluated.
Directional sound beam forming is an area of interest in practical acoustic applications where le... more Directional sound beam forming is an area of interest in practical acoustic applications where leakywave principles and techniques may provide efficient solutions. Here, we present a type of high-gain acoustic leaky antenna used for acoustic beamforming using an admittance-modulation metasurface which consists of periodic subwavelength grooves with sinusoidal depth profiles. The acoustic metasurface converts the surface waves into far-field radiating waves forming a high-gain surface wave antenna. We numerically and experimentally demonstrate far-field propagation angles of −30 o , 0 o , and 30°at 19 300, 22 000, and 23 900 Hz, respectively, and show that the radiation angle and beamwidth can be independently controlled by modulating the sinusoidal profile. Also, we use a Laser Doppler Vibrometer to directly measure the surface wave damping along a circular sinusoidally modulated admittance surface (SMAS).
This paper reports a review about microelectromechanical system (MEMS) microphones. The focus of ... more This paper reports a review about microelectromechanical system (MEMS) microphones. The focus of this review is to identify the issues in MEMS microphone designs and thoroughly discuss the state-of-the-art solutions that have been presented by the researchers to improve performance. Considerable research work has been carried out in capacitive MEMS microphones, and this field has attracted the research community because these designs have high sensitivity, flat frequency response, and low noise level. A detailed overview of the omnidirectional microphones used in the applications of an audio frequency range has been presented. Since the microphone membrane is made of a thin film, it has residual stress that degrades the microphone performance. An in-depth detailed review of research articles containing solutions to relieve these stresses has been presented. The comparative analysis of fabrication processes of single- and dual-chip omnidirectional microphones, in which the membranes ...
This paper presents the fabrication of Si3N4-based artificial basilar membrane (ABM) with ZnO nan... more This paper presents the fabrication of Si3N4-based artificial basilar membrane (ABM) with ZnO nanopillar array. Structure of ABMs is composed of the logarithmically varying membrane fabricated by MEMS process and piezonanopillar array grown on the Si3N4-based membrane by hydrothermal method. We fabricate the bottom substrate containing Si3N4-based membrane for inducing the resonant motions from the sound wave and the top substrates of electrodes for acquiring electric signals. In addition, the bonding process of the top and bottom substrate is performed to build ABM device. Depending on sound wave input of the specific frequency, specific location of the ABM produces a resonant behavior. Then a local deformation of the piezonanopillar array produces an electric signal between top and bottom electrode. As experimental results of the fabricated ABM, the measured resonant frequencies are 2.34 kHz, 3.97 kHz, and 8.80 kHz and the produced electrical voltages on each resonant frequency ar...
In this study, a MEMS microphone that uses Si 3 N 4 as the vibration membrane was produced for ap... more In this study, a MEMS microphone that uses Si 3 N 4 as the vibration membrane was produced for application as an auditory device using a sound visualization technique (sound visualization) for the hearing impaired. Two sheets of 6-inch silicon wafer were each fabricated into a vibration membrane and back plate, after which, wafer bonding was performed. A certain amount of charge was created between the bonded vibration membrane and the back plate electrodes, and a MEMS microphone that functioned through the capacitive method that uses change in such charge was fabricated. In order to evaluate the characteristics of the prepared MEMS microphone, the frequency flatness, frequency response, properties of phase between samples, and directivity according to the direction of sound source were analyzed. The MEMS microphone showed excellent flatness per frequency in the audio frequency (100 Hz-10 kHz) and a high response of at least −42 dB (sound pressure level). Further, a stable differential phase between the samples of within −3 dB was observed between 100 Hz-6 kHz. In particular, excellent omnidirectional properties were demonstrated in the frequency range of 125 Hz-4 kHz.
The purpose of this study is to get optimum design and operation conditions of the heating rubber... more The purpose of this study is to get optimum design and operation conditions of the heating rubber roller for laminating process. The cause of performance degradation of heating rubber roller is delamination of rubber on metal tube, rubber aging due to high temperature. We measured the material properties of thermal expansion, thermal conductivity, specific heat and density and analyzed thermal distributions of rubber layer using finite element method. As a result of heat/flow analysis, the density distribution of heating coil must shorten the stabilization time by reducing the temperature deviation on the length direction at the temperature rising section after increasing the density of the area contacting with the laminate film at the center part which is an opposite of the current composition while enabling to maintain the temperature of heater to be consistent while maintaining the temperature deviation to be low when heat loss is created. Finally, we determined optimum heating method of heating rubber roller.
In this study, we fabricated and evaluated the performance of film speaker using PVDF/ZnO NP comp... more In this study, we fabricated and evaluated the performance of film speaker using PVDF/ZnO NP composite structure. PVDF piezoelectric films were fabricated and characterized by XRD and SEM. ZnO nanopillars were prepared by hydrothermal synthesis on prepared PVDF piezoelectric films. We analyzed and tested the acoustic signal characteristics of the piezoelectric film. In order to fabricate an acoustic structure with a wide frequency range from low to high frequency, we have fabricated various types of film speakers and investigated the frequency characteristics. As a result, the fundamental piezoelectric properties of PVDF show that the piezoelectric constant due to ZnO NP increases. And the overall acoustic signal level is also increased by 10% or more. We investigated frequency generation from 500 Hz to 10 KHz using different sizes with PVDF/ZnO NP composite film speaker.
In this paper, we present a pH measurement method that uses a microcantilever-array-based biosens... more In this paper, we present a pH measurement method that uses a microcantilever-array-based biosensor system. It is composed of microcantilever array, liquid cell, micro syringe pump, laser diode array, position sensitive detector, data acquisition device, and data processing software. Four microcantilevers are functionalized with pH-sensitive MHA(mercaptohexadecanoic acid) as a probe, while three microcantilevers are functionalized with HDT(hexadecane thiol) as reference. We prepare PBS(phosphate buffered saline) solutions of different pH and inject them into the liquid cell with a predefined volumetric speed at regular time intervals. The functionalized mircocantilevers in the liquid cell deflect as a self-assembled monolayer on the microcantilever binds with probe molecules in the solution. The difference in deflection between the MHA-covered probe microcantilever and the HDT-covered reference microcantilever was used to compensate for thermal drift. The deflection difference clearly increases with increasing pH in the solution. It was shown that when the pH values of the PBS solutions are high, there were large variations in the deflection of microcantilevers, whereas there were small variations for low pH value. The experimental results show that the microcantilever array functionalized with MHA and HDT can detect pH value with good repeatability.
The rubber seal is a part inserted into servo cylinder to keep the air pressure constant. In orde... more The rubber seal is a part inserted into servo cylinder to keep the air pressure constant. In order for efficient movements of the servo cylinder, the frictional coefficient of the rubber seal needs to be minimized while the sealing is maintained. In this work the friction characteristics of rubber seal specimen are tested on metal plate at various conditions. The experimental conditions include roughness level, applied pressure, lubrication, and rubbing speed. The design of experiment approach is taken to assess the effect of each parameter. The nonlinear frictional response of the rubber is applied to the FEM model simulating the servo cylinder movement. The result demonstrates that precise optimization of the servo cylinder movement must be preceded by preliminary experiments coupled with the theory and FEM model.
Biomimetic artificial basilar membrane being a core part of artificial cochlear requires performa... more Biomimetic artificial basilar membrane being a core part of artificial cochlear requires performance evaluation through aging test. To evaluate the aging properties of PVDF piezoelectric membrane used for artificial basilar membrane, its mechanical properties such as tensile strength and elastic modulus and piezoelectric property such as piezoelectric constant were measured. The aging test conditions and acceleration constants were calculated based on Arrhenius model. The changes in tensile strengths and elastic moduli measured were less than 10~20% after aging test equivalent for 10 years. The piezoelectric constants were decreased drastically to 80% of its initial value in the early stage of the aging test and expected to decrease slowly down to 65% over 10 years. The experimental results show the reliability of totally implantable novel artificial cochlear and will contribute its commercialization.
Uploads
Papers by shin hur