Micromachines最新文献

Although significant strides have been made in cardiac pacing, the field is still evolving. While transvenous permanent pacing is highly effective in the management of bradyarrhythmias, it is not risk free and may result in significant morbidity and, rarely, mortality. Transvenous leads are often the weakest link in a pacing system. They may dislodge, fracture, or suffer breaches in their insulation. This review was undertaken to clarify leadless risks, benefits, and alternatives to transvenous cardiac pacing for bradyarrhythmias and heart failure management. In order to clarify the role(s) of leadless pacing, this narrative review was undertaken by searching MEDLINE to identify peer-reviewed clinical trials, randomized controlled trials, meta-analyses, and review articles, as well as other clinically relevant reports and studies. The search was limited to English-language reports published between 1932 and 2024. Leadless pacing was searched using the terms Micra™, Nanostim™, AVEIR™, single-chamber leadless pacemaker, dual-chamber leadless pacemaker, cardiac resynchronization therapy (CRT), cardiac physiological pacing (CPP) and biventricular pacing (BiV). Google and Google Scholar, as well as bibliographies of identified articles were also reviewed for additional references. The advantages and limitations of leadless pacing as well as options that are under investigation are discussed in detail.

As an innovative branch of electronics, intelligent electronic textiles (e-textiles) have broad prospects in applications such as e-skin, human-computer interaction, and smart homes. However, it is still a challenge to distinguish multiple stimuli in the same e-textile. Herein, we propose a dual-parameter smart e-textile that can detect human pulse and body temperature in real time, with high performance and no signal interference. The doping of SWCNTs in PEDOT:PSS improves the electrical conductivity and Seebeck coefficient of the prepared composites, which results in excellent pressure and temperature-sensing properties of the PEDOT:PSS/SWCNTs/CS@PET-textile (PSCP) sensor. The dual-mode sensor has high sensitivity (32.4 kPa^-1), fast response time (~21 ms), and excellent durability (>2000 times) in pressure detection. Concurrently, this sensor maintains a high Seebeck coefficient of 25 μV/K in the 0-120 K temperature range with a tremendous linear relationship. Based on impressive dual-mode sensing characteristics and independent temperature-difference- and pressure-sensing mechanisms, smart e-textile sensors realize the real-time simultaneous monitoring of weak pulse signals and human body temperature, showing great potential in medical healthcare. In addition, the potential energy is excited by the temperature gradient between the human skin and the environment, which provides a novel idea for wearable self-powered devices.

A balanced dielectric resonator filtering power divider with isolation performance is proposed. By using the coupling of the TE111y modes between three rectangle dielectric resonators, combined with balanced feed structures, the differential-mode filtering and power dividing functions, as well as the common-mode suppression were achieved effectively. Additionally, by technically utilizing the hollow structure of the stacked substrates, isolation resistor structures are introduced at the two output ports to improve the isolation level of the power divider. It can solve the problem of traditional metal-cavity dielectric resonator filter power dividers being unable to add isolation structures due to structural reasons. Compared with the reported dielectric resonator filtering power dividers, the proposed one has the characters of a lower profile and high isolation. For demonstration, one dielectric resonator filtering power divider was fabricated and measured at 11.65 GHz with the profile of 0.66 λ_g and an isolation higher than 15 dB. The simulation results are in good agreement with the measured results.

The metal bipolar plate is a critical component of the hydrogen fuel cell stack used in proton exchange membrane fuel cells. Bipolar plates must have high accuracy micro-channels with a high aspect ratio (AR) between the channel depth and the half periodic width to achieve optimal cell performance. Conventional forming methods, such as micro-stamping, hydroforming, and rubber pad forming, cannot achieve these high ARs given that in these processes, material deformation is dominated by stretch deformation. In micro-roll forming the major deformation mode is bending, and this enables production of channels with higher ARs than is currently possible. However, micro-roll forming uses multiple sets of forming roll stands to form the part and this leads to technological challenges related to tool alignment and roll tool precision that must be overcome before widespread application can be achieved. This study presents a new methodology to achieve tight tool tolerances when producing micro-roll tooling by utilizing wire-EDM and micro-turning techniques. This is combined with a new micro-roll former design that enables high-precision tool alignment across multiple roll stations. Proof of concept is provided through micro-roll forming trials performed on ultra-thin titanium sheets that show that the proposed technology can achieve tight dimensional tolerances in the sub-millimeter scale that suits bipolar plate applications.

Trench MOS Barrier Schottky (TMBS) rectifiers offer superior static and dynamic electrical characteristics when compared with planar Schottky rectifiers for a given active die size. The unique structure of TMBS devices allows for efficient manipulation of the electric field, enabling higher doping concentrations in the drift region and thus achieving a lower forward voltage drop (VF) and reduced leakage current (IR) while maintaining high breakdown voltage (BV). While the use of trenches to push electric fields away from the mesa surface is a widely employed concept for vertical power devices, a significant gap exists in the analytical modeling of this effect, with most prior studies relying heavily on computationally intensive numerical simulations. This paper introduces a new physics-based analytical model to elucidate the behavior of electric field and potential in the mesa region of a TMBS rectifier in reverse bias. Our model leverages the concept of shared charge between the Schottky and MOS junctions, capturing how electric field distribution is altered in response to trench geometry and bias conditions. This shared charge approach not only simplifies the analysis of electric field distribution but also reveals key design parameters, such as trench depth, oxide thickness, and doping concentration, that influence device performance. This model employs the concept of shared charge between the vertical Schottky and MOS junction. Additionally, it provides a detailed view of the electric field suppression mechanism in the TMBS device, highlighting the significant effects of the inversion charge on the MOS interface. By comparing our analytical results with TCAD simulations, we demonstrate strong agreement, underscoring the model's accuracy and its potential to serve as a more accessible alternative to resource-intensive simulations. This work contributes to a valuable tool for TMBS device design, offering insights into electric field management that support high-efficiency, high-voltage applications, including power supplies, automotive electronics, and renewable energy systems.

Gallium nitride (GaN) exhibits distinctive physical and chemical properties that render it indispensable in a multitude of electronic and optoelectronic devices. Given that GaN is a typical hard and brittle material that is difficult to machine, femtosecond laser technology provides an effective and convenient tool for processing such materials. However, GaN undergoes complex physical and chemical changes during high-power ablation, which poses a challenge to high-precision processing with controllable geometry. In this study, the quantitative relationship between the parameters of a single-pulse femtosecond laser and GaN ablation morphology was investigated using isotherm distribution. A multiphysics model using COMSOL Multiphysics^® was developed to generate the isothermal distributions. Experiments were conducted on the femtosecond laser ablation of GaN at various single-pulse energies, and the resulting ablation morphologies were compared with the predictions from the multiphysics model. The comparison demonstrated that the calculated isotherm distribution accurately predicted not only the ablation diameter and depth but also the crater shape across a broad range of laser fluences. The predicted errors of the ablation diameters and depths were within 4.71% and 10.9%, respectively. The root mean square error (RMSE) and coefficient of determination (R²) were employed to evaluate the prediction errors associated with the crater shapes, which fell within the range of 0.018-0.032 μm and 0.77-0.91, respectively. This study can provide an important reference for utilizing femtosecond lasers in the precise ablation of GaN to achieve desired geometries.

This paper presents an X-band high-power GaN MMIC power amplifier (PA). To balance efficiency, output power, and saturated power flatness, the load-line theory is employed to analyze and validate the power variation trends within an extended continuous Class B/J (CCBJ) impedance space. Theoretical constant power contours are plotted within this space. An L-C impedance matching network is used to match the amplifier's output impedance to the overlapping region of the 0.5 dB constant power contour and the CCBJ impedance space, significantly improving the in-band power flatness of the PA based on the CCBJ design approach. Additionally, an RC parallel structure is integrated into the interstage matching network to maximize gain while ensuring stability. The proposed PA, implemented using a 0.25 µm commercial GaN process, achieves a saturated output power of 47-47.6 dBm with in-band fluctuations within ± 0.3 dB, a power gain of 27.0-27.8 dB, and an efficiency of 40-45.5% across the X-band.

Inertial microfluidics, as an efficient method for the manipulation of micro-/nanoparticles, has garnered significant attention due to its advantages of high throughput, structural simplicity, no need for external fields, and sheathless operation. Common structures include straight channels, contraction-expansion array (CEA) channels, spiral channels, and serpentine channels. In this study, we developed a CEA channel embedded with hook-shaped microstructures to modify the characteristics of vortices. Through experimental studies, we investigated the particles' migration mechanisms within the proposed structure. The findings indicated that, in comparison to conventional rectangular microstructures, the particles within the hook-shaped microstructured CEA channels experienced a more pronounced influence from inertial lift forces. Moreover, the magnitude of the second flow within the novel configuration was directly proportional to the channel width, the length of the expansion segment, and the embedding depth of the microstructure. The innovative structure was subsequently employed for particle trapping, focusing, and separation. The experimental outcomes revealed focusing efficiency of up to 99.1% and sorting efficiency of up to 97%. This research holds the potential to enhance the foundational theory of Dean flows and broaden the application spectrum of inertial contraction-expansion microfluidic chips.

Observing the intricate microstructure changes in abrasive flow machining with traditional experimental methods is difficult. Molecular dynamics simulations are used to look at the process of abrasive flow processing from a microscopic scale in this work. A molecular dynamics model for micro-cutting a single crystal γ-TiAl alloy with a rough surface in a fluid medium environment is constructed, which is more realistic. The evolution of material removal, cutting force, temperature, energy, and dislocation during micro-cutting are analyzed. The impact of cutting depth, abrasive particle sizes, and abrasive material on the micro-cutting process are analyzed. The analysis shows that the smaller cutting depth and abrasive particle sizes are beneficial to obtain a better machining surface, and the cubic boron nitride (CBN) abrasive is an effective substitute material for diamonds. The purpose of this study is to provide unique insights for improving the material removal rate and subsurface quality by adjusting machining parameters in actual abrasive flow precision machining.

The electrochemical cutting technique, utilizing electrolyte flushing through micro-hole arrays in the radial direction of a tube electrode, offers the potential for cost-effective and high-surface-integrity machining of large-thickness, straight-surface structures of difficult-to-cut materials. However, fabricating the array of jet micro-holes on the tube electrode sidewall remains a significant challenge, limiting the broader application of this technology. To enhance the efficiency and quality of machining these jet micro-holes on the tube sidewall, a helical electrode electrochemical drilling method assisted by anode vibration has been proposed. The influence of parameters, such as the rotational direction and speed of the helical electrode, as well as the vibration amplitude and frequency of the workpiece, on the machining results was investigated using fluid field simulation and machining experiments. It was found that these auxiliary movements could facilitate the renewal of electrolytes within the machining gap, thereby enhancing the efficiency and quality of electrochemical drilling. Using the optimized machining parameters, an array of 10 jet micro-holes with a diameter of 200 μm was machined on the metal tube sidewall. Electrochemical cutting with radial electrolyte flushing tests were then performed through these micro-holes.