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The topological simulation of acoustic waves has induced unconventional propagation characteristics, thereby offering extensive application potential in the field of acoustics. In this paper, we propose a machine learning-assisted method for the inverse design of acoustic wave topological edge states and demonstrate its practical applicability. Leveraging the predictions from a trained artificial neural network algorithm, the design of wide-bandwidth topological insulators is achieved, with simulation results indicating an approximately 2.8-fold enlargement of the single-cell topological bandgap. Further investigation into their wide-bandwidth topological transport properties is conducted. Additionally, two distinct functional acoustic routing devices are devised. Superior performance of the wide-bandwidth acoustic topological devices has been verified through simulation experiments. This approach provides an efficient and viable avenue for the design and optimization of acoustic devices, with the potential to enhance the management and control efficiency of acoustic signal propagation. [ABSTRACT FROM AUTHOR]

The study of optical topological insulators (PTIs) has revealed intriguing optical properties that diversify the ways in which light can be manipulated, offering significant potential for a wide range of applications. This paper presents a machine learning (ML)-based approach for the reverse design of optical PTIs. Using finite element methods, the paper addresses the challenge of computing the band structure of a dual-band model, enabling the construction of a dataset suitable for ML training. With the goal of maximizing dual-band bandgaps, the study employs the random forest algorithm to predict target parameters and further designs topological edge states. Leveraging these boundary state patterns, two different optical PTI beam splitters are devised, and their transmission coefficients and losses are computed. The results demonstrate that optical devices designed using topological boundary states exhibit enhanced stability and robustness. This approach offers a reliable solution for applications in fields such as optical communication and optical sensing. [ABSTRACT FROM AUTHOR]

Formaldehyde (FA) in food is harmful to human health, an effective detecting tool is highly desired especially for the on-site test. Herein, an amperometric aqueous FA sensor was fabricated by applying Pt–Ag core-shell nanoparticles as electrocatalyst. The well-characterized core-shell nanostructure exhibits high electro-catalytical activity for the detection of FA molecules in solution due to the synergistic effect of bimetallic Pt–Ag nanostructure. The proposed sensor exhibits high FA sensing performance, with a linear detection range from 1 to 100 μM and a limit of detection (LOD) down to 1.0 μM on the optimized conditions. Interferents coexisting in food samples were efficiently minimized by good selectivity. The Pt–Ag nanostructure-based FA sensor keeps catalytical activity for at least 30 d and shows good batch reproducibility. The proposed sensor was applied for the detection of FA in the food samples and satisfactory results were obtained, showing potential for the fast, simple, disposable, and cost-effective FA detecting method for food safety. [ABSTRACT FROM AUTHOR]

The fault diagnosis of rotating machinery involves revealing the possible faults in advance to reduce dispensable breakdowns; the difficulty of this lies in identifying the periodic features of rotating machines contaminated by background noise. Time-domain synchronous averaging (TSA) has been studied to eliminate random noise in signals. However, TSA sometimes cannot extract useful signals more accurately because of the accumulative phase error caused by the discrete sampling process and the difficulties in obtaining accurate prior information. Hence, the moving interpolation and Kurtosis searching criterion are used for more accurate extraction of harmonics and transient impacts. Also, an improved compensation algorithm based on moving interpolation is proposed to overcome the amplitude attenuation caused by cumulative phase error for low signal to noise ratio (SNR) signal. To determine some parameters in the algorithm such as the number of periods and the time delay of windows which depend on a priori information relevant to the fault period, a searching method for the prior information in vibration signals including transient impacts and harmonics with Kurtosis and minimum mean square error criterion is proposed to optimize the algorithm in the process of feature extraction. Finally, the improved TSA (ITSA) is applied to extracting the fault features in a real factory, and the performance of fault feature extraction in low SNR signal conditions with the ITSA has been enhanced effectively. [ABSTRACT FROM AUTHOR]

Flow measurement is an essential requirement in medical, industrial, automotive and environmental applications, Thanks to the rapid development of microelectromechanical system (MEMS) micro-fabrication techniques, silicon-based microflow sensor chips used as the key component of microfluidic control systems have attracted particular attentions due to the miniaturized chip-size, high precision, low power consumption, rapid response and low-cost batch-fabrication capability. Up to present, many different types of silicon microflow sensors have been proposed and developed. This paper provides a review on recently completed works on design, fabrication and properties of the MEMS-based silicon monolithic microflow sensors. Some technical challenges and application outlooks are also discussed in the paper. [ABSTRACT FROM AUTHOR]

SiGe spheres with different diameters are successfully fabricated on a virtual SiGe template using a laser irradiation method. The results from scanning electron microscopy and micro-Raman spectroscopy reveal that the diameter and Ge composition of the SiGe spheres can be well controlled by adjusting the laser energy density. In addition, the transmission electron microscopy results show that Ge composition inside the SiGe spheres is almost uniform in a well-defined, nearly spherical outline. As a convenient method to prepare sphere-shaped SiGe micro/nanostructures with tunable Ge composition and size, this technique is expected to be useful for SiGe-based material growth and micro/optoelectronic device fabrication. [ABSTRACT FROM AUTHOR]

The absorption coefficient is usually considered as a constant for certain materials at the given wavelength. However, recent experiments demonstrated that the absorption coefficient could be enhanced a lot by the PN junction. The absorption coefficient varies with the thickness of the intrinsic layer in a PIN structure. Here, we interpret the anomalous absorption coefficient from the competition between recombination and drift for non-equilibrium carriers. Based on the Fokker–Planck theory, a non-equilibrium statistical model that describes the relationship between absorption coefficient and material thickness has been proposed. It could predict the experimental data well. Our results can give new ideas to design photoelectric devices. [ABSTRACT FROM AUTHOR]

This paper reports a silicon-chip based electromagnetic (EM) vibration energy harvester that is fabricated with a wafer-level micro-casting technique to form on-chip integrated 3D metal solenoids and magnet sliding channels. Many solenoids of 150-turn coil are simultaneously formed by filling molten ZnAlx alloy into the pre-micromachined solenoid moulds in one wafer within 7 min. After saw dicing to obtain the solenoid chips, a sliding permanent magnet for responding to environmental vibration is inserted into the pre-etched silicon channel inside the solenoid. Excited by external vibration, the magnet can slide in the channel to generate electricity. The size of the micro electro mechanical systems (MEMS) harvester chip is only 10.5 × 2.5 × 1.7 mm3. The experimental results show that the energy harvester can efficiently collect vibration energy in the environment. Under excited acceleration-amplitude of 49 m s−2 (i.e. 5 g) at the frequency of 24 Hz, the normalized power density (NPD) generated from the harvester reaches 12.38 μW cm−3 g−2. By comparing with reported non-MEMS wire-wound EM harvesters and on-chip piezoelectric/electrostatic ones, this silicon-chip based EM harvester exhibits much superior NPD. [ABSTRACT FROM AUTHOR]

Relevant experiments have shown that more than 90% of photo-generated carriers can escape from multiple quantum wells (MQWs) sandwiched between p-type and n-type layers (a PIN structure). The escape time of the photo-generated carriers is on the femtosecond scale, much less than their relaxation time. In contrast, photo-generated carriers cannot escape from MQWs sandwiched between two n-type layers (a NIN structure) with bias. We found that there is a high barrier for holes and that the electric field intensity in QWs is close to zero, resulting in holes accumulating and a low escape efficiency in a NIN structure with bias. [ABSTRACT FROM AUTHOR]

This paper presents a tiny 0.4 mm × 0.4 mm piezoresistive absolute pressure sensor chip with a fabrication cost as low as 0.01 US$/die. With the thin-film under bulk-silicon technique, a very thin but uniform poly-silicon pressure-sensing diaphragm is formed beneath a bulk-silicon beam-island structure to accommodate piezoresistors. The thin diaphragm exhibits a high sensitivity, and the beam-island-reinforced structure helps reduce deflection and improve linearity. The sensor is fabricated using a novel scar-free micro-hole inter-etch and sealing (MIS) process. In this newly developed process, seals are removed from the diaphragm area and placed on both the single-crystalline silicon island and single-crystalline silicon frame surrounding the poly-silicon diaphragm. Thus, the thin diaphragm is kept flat and smooth, thereby enhancing the sensing performance and fabrication yield. More importantly, the diaphragm-beam-island structure is small enough to fabricate sensor chips as small as 0.4 mm × 0.4 mm. With the high-yield process, a very low fabrication cost of 0.01 US$/die is realised owing to a high throughput of 90 000 die per 6 inch wafer. The ultra-small and low-cost pressure sensor exhibits sensitivity of 0.88 mV kPa−1/3.3 V, hysteresis of 0.15% full scale (FS), repeatability error of 0.04% FS, and non-linearity of 0.10% FS. Without any additional thermal compensation method, the sensor exhibits a low temperature coefficient of zero-point offset of −0.064%/°C FS and a temperature coefficient of sensitivity (TCS) of −0.22%/°C within the temperature range from −25 °C to +85 °C, at a full measurement range (i.e. full scale) of 100 kPa. With the new scar-free MIS process, the presented pressure sensor looks promising for smartphones, drones, and other consumer-electronic applications. [ABSTRACT FROM AUTHOR]

In this paper, a virtual GeSi template has been successfully fabricated by Ge filling the porous silicon (PSi) prepared by electrochemical etching (EC etching). The microstructure quality measured with cross-sectional scanning electron microscopy and photoluminescence spectra reveal that the PSi structure is fully filled with uniformly distributed Ge. Furthermore, Raman and X-ray diffraction results also show that the template has a typical GeSi feature, which originates from Ge interdiffusion with PSi during the Ge deposition. This design and structure can be expected to be useful as a template for Ge-related materials growth and device fabrication. [ABSTRACT FROM AUTHOR]

This paper presents a micromechanical resonant gas sensor, which is operated in extensional bulk mode, for high-accuracy sensing of ultra-low concentration chemical vapors. The designed and fabricated gravimetric resonant microsensor has exhibited both high Q-factor of 11157 in air and high mass sensitivity of 10.16 Hz pg−1. Much more importantly, both theoretical analysis and sensing experiment have verified that such an extensional resonance mode is technically advantageous in sensing accuracy (e.g., output signal linearity in terms of gas concentration and reproducibility of sensitivity), which can be attributed to the uniform vibration amplitude at each point of the gas-adsorbing area. Loaded with –COOH functionalized mesoporous-silica nanopaticles as sensing material, which features an ultra-large surface area, the chemical sensing micro-resonator experimentally performs precise detection performance to ppm-level ammonia vapor. The limit of detection is as low as 1 ppm and the response time of the sensor is as short as 10 s. [ABSTRACT FROM AUTHOR]

This paper reports novel single-wafer-based piezoresistive micro flow sensors, which are bulk micromachined only from the front side of the silicon wafer to facilitate the sensor-bare chips directly packaged into micro-fluidic systems with low-cost surface mounting technology (SMT). With neither double-sided micromachining nor multiwafer bonding needed, two structural types of the piezoresistive flow sensors are designed and fabricated in (1 1 1) wafers, where 'type A' sensor has a smaller channel cross section area compared to 'type B' sensor. After the bare sensor chip directly attached on a printed circuit board (PCB), wire bonded between the pads and the PCB for electric interconnection and the inlet/outlet front side connected, deionized water is flowed into the both types of flow sensors to characterize piezoresistive output of the differential pressure sensing elements in terms of the flow rate. For 'type A' and 'type B' sensors that are both power supplied with DC 5 V, the sensitivities are sequentially measured as 766.80 mV (µL s-1)-1 and 19.12 mV (µL s-1)-1, with the nonlinearities as 0.4% FS and 0.9% FS, respectively. Compared with traditionally fabricated micro flow sensors, the single-chip fabricated differential-pressure flow sensors can be low-cost volume manufactured. Moreover, the bare sensor chips can be simply SMT packaged for low-cost micro-system applications. [ABSTRACT FROM AUTHOR]

A novel dual-unit piezoresistive pressure sensor, consisting of a sensing unit and a dummy unit, is proposed and developed for on-chip self-compensation for zero-point temperature drift. With an MIS (microholes inter-etch and sealing) process implemented only from the front side of single (1 1 1) silicon wafers, a pressure sensitive unit and another identically structured pressure insensitive dummy unit are compactly integrated on-chip to eliminate unbalance factors induced zero-point temperature-drift by mutual compensation between the two units. Besides, both units are physically suspended from silicon substrate to further suppress packaging-stress induced temperature drift. A simultaneously processes ventilation hole-channel structure is connected with the pressure reference cavity of the dummy unit to make it insensitive to detected pressure. In spite of the additional dummy unit, the sensor chip dimensions are still as small as 1.2 mm × 1.2 mm × 0.4 mm. The proposed dual-unit sensor is fabricated and tested, with the tested sensitivity being 0.104 mV kPa−1 3.3 V−1, nonlinearity of less than 0.08% · FSO and overall accuracy error of ± 0.18% · FSO. Without using any extra compensation method, the sensor features an ultra-low temperature coefficient of offset (TCO) of 0.002% °C−1 · FSO that is much better than the performance of conventional pressure sensors. The highly stable and small-sized sensors are promising for low cost production and applications. [ABSTRACT FROM AUTHOR]

The local structures in the normal and undercooled liquid eutectic Ga-In alloy are investigated by using X-ray absorption spectroscope (XAS), X-ray diffractometer (XRD) and the ab initio molecular dynamics (AIMD) simulations. The results from these three techniques all indicate that the nearest-neighbor coordination number decreases with decreasing temperature in the liquid eutectic Ga-In alloy. Moreover, the nearest-neighbor interatomic distance increases and the local atomic packing density decreases with decreasing temperature. The X-ray absorption near edge structure (XANES) measurement shows that the atomic rearrangement at the undercooled temperature results in the formation of low-coordinated polyhedron clusters with high symmetries. This finding provides a new perspective for understanding the liquid-solid transition in undercooled conditions. [ABSTRACT FROM AUTHOR]