Piezoresistive pressure sensors with high sensitivity and linearity are critical for aerospace and other industries, however, attempts to improve sensitivity often reduce linearity. Therefore a diaphragm secondary stress utilization method (DSSUM) is proposed, which can significantly increase sensor sensitivity without sacrificing the linearity. The DSSUM realizes the detection of primary and secondary stresses on the diaphragm through the eight-piezoresistor Wheatstone bridge without changing the structure of the diaphragm. A differential pressure sensor with a measurement range of -15 similar to 15 kPa has been designed and fabricated based on DSSUM. Comparative test results show that DSSUM can increase the sensitivity of the sensor by 50.32 % to 32.35 mV/kPa while maintaining the linearity at 0.031 %F.S. The repeatability of the sensor is 0.02 %FS, the hysteresis is 0.01 %FS, and the zero drift is 0.052 %FS. By using DSSUM, both wide-range and small-range pressure sensors can increase their sensitivity by more than 50 % without impacting linearity. The DSSUM offers a new method for achieving high-performance pressure sensors and holds potential for wide application.

High-temperature thin-film sensors (HTTSs) offer promising solutions for in situ monitoring of various thermal and mechanical parameters in extreme environments. However, maintaining their stable operation at high temperatures exceeding 1000 °C for extended durations remains challenging due to severe material degradation. This study first demonstrates a microstructural engineering strategy to enhance the thermal endurance of metal oxide thin films through integrating high-melting-point metal oxide nanophases. Using standard Micro-Electro-Mechanical System (MEMS) technologies, alumina (Al2O3) is atomically integrated into indium tin oxide (ITO) thin films. The influence of Al2O3 doping on the ITO matrix under various high-temperature conditions, with emphasis on the variations of chemical composition, crystal structure, morphology, recrystallization, and sensing behavior, is systematically investigated. An optimized film, characterized by an Al/In ratio of 1.57 wt.%, exhibits a record-low resistance drift of 0.002% h-1 during a 10 h exposure at 1200 °C.

Wall shear stress is one of the key parameters in turbulent boundary layers, playing a pivotal role in aerodynamic optimization and fuel efficiency enhancement. Although MEMS-based direct measurement stands as the most promising approach for wall shear stress quantification, the inherent limitations of floating sensing structures under harsh environments lead to mechanical failure, representing persistent technical barriers in practical applications. This work presents a novel MEMS sensor equipped with a protective floating cover plate, achieving high-robustness measurement through coordinated structural-process innovations. Based on the Dual Silicon-On-Insulator (DSOI) fabrication process, a protective floating configuration is developed. The critical process techniques, including deep silicon etching, wet etching of glass through vias, and silicon-glass anodic bonding synergistically establish protection for the sensing structures. The established electromechanical coupling mathematical model elucidates quantitative mapping relationships between critical structural parameters and sensing performance. Experimental characterization reveals a linear sensitivity of 28.3 mV Pa−1 and a resonance frequency of 2.9 kHz. In supersonic tunnel experiments at Mach 2.0, the sensor achieves unprecedented full-cycle dynamic capture from establishment through stabilization to dissipation with millisecond-level transient response characteristics. This work provides a robust, high-precision solution for aerodynamic and fluid dynamics applications, paving the way for improving energy efficiency and flow control strategies.

Piezoelectric micromachined ultrasonic transducers (p-MUTs) have been extensively utilized in medical imaging, range-finding, gesture recognition, and so on. However, the piezoelectric layer is dominated by the toxic Pb(Zr, Ti)O3, other materials possess inferior piezoelectric coefficients, and the traditional clamped diaphragm restricts the p-MUT response. In this work, lead-free ZnO films are doped by the vanadium nanostructures and are implemented to beam-island structure membranes, which are aimed to achieve non-toxic and high-performance p-MUTs. Firstly, the doping mechanism of ZnO is analyzed and the p-MUT structure is designed. Secondly, simulation based on the finite element method is conducted to evaluate the dynamic displacement of p-MUTs, after which prototypes are fabricated by the standard micromachined process. The effects of key fabrication parameters including O2 flow rates, sputtering targets, and annealing temperatures on V-doped ZnO films are investigated in detail. By using atomic force microscopy (AFM) and X-ray diffraction (XRD), the surface morphology and crystal structure of the films are analyzed respectively. Moreover, the piezoelectric properties are measured by piezo response force microscopy (PFM). The results indicate a piezoelectric coefficient as high as 194.5 p.m./V, which is superior to most doped ZnO films. Finally, an experimental testing system is established to examine the p-MUT performance. Compared with the clamped diaphragm, the beam-island structure can acquire better electromechanical coupling and achieve range-finding successfully. This work provides a fine application prospect for enhancing the performance of lead-free p-MUTs.

High-precision piezoresistive pressure sensors play a significant role in aerospace, automotive, and other fields. Nonlinear error is the key factor that restricts the improvement of the sensor precision. A mathematical model for evaluating the sensor’s nonlinear error is established, based on which a piezoresistor sensitivity matching method is proposed to suppress the nonlinear error. By adjusting the piezoresistors' structure and position on the sensing membrane, four piezoresistors with equal sensitivity are obtained, and theoretical quasi-zero nonlinear error is achieved. To verify the design, sensor prototypes are fabricated utilizing the MEMS technology. After sensor packaging, a cylindrical absolute pressure sensor featuring a 4 mm diameter with a range from 0 to 100 kPa is acquired. The experimental results demonstrate the excellent performance of the proposed sensor, which indicates a nonlinear error as low as ±0.004

In this work, we designed and built two types of calibration devices to study the dynamic characteristics of the indium tin oxide (ITO) thin-film thermocouples (TFTCs) under different conditions. The first device, based on a nanosecond laser, generates a 150-mW heat pulse within 25 ns, and the experimental analysis of the cooling process reveals the dynamic characteristics of the ITO TFTCs under natural convection conditions. The second device uses a detonation wave that generates a 270 C-degrees airflow environment in 400 ns at 4.86 Mach, representing forced convection conditions. Experimental results show that in the nanosecond laser experiment, the time constant of the ITO TFTC is 122.08 mu s, corresponding to a frequency response of 1.30 kHz. In contrast, in the detonation wave experiment, the time constant of the ITO TFTCs decreases to 15.65 mu s and the frequency response increase to 10.17 kHz. These results demonstrate that the dynamic characteristics of the ITO TFTCs are not constant and can be significantly influenced by the measurement environment.

The thermal effect of human skin was a concern in this article, and here, we reported a flexible artificial skin for the detection of air temperature and flow shear stress. The flexible artificial skin consisted of two overlapped functional devices. The bottom layer heater detected the flow shear stress and air temperature through the force convection heat transfer process, while the upper layer temperature sensor sensed a coupling temperature. This coupled working mode simulated the perception system of human skin. The neural network algorithm was used to train the relationship model of coupled multiphysical parameters, and the flow shear stress and air temperature were decoupled. The flexible artificial skin achieved resolutions of 0.915 Pa to flow shear stress and 0.068 degrees C to air temperature. Moreover, the temperature compensation of the heater could be omitted by this coupling measurement method. This kind of flexible artificial skin opened new avenues for intelligent robots, artificial skin, and multilayer composite flexible electronics.

Wall shear stress and flow direction provide a basis for analyzing the boundary layer conditions, investigating drag reduction mechanisms, and enhancing environmental perception. This work presents novel single-loop and dual-loop hot-film sensors driven by the constant temperature, which are capable of simultaneously measuring wall shear stress and flow direction. Based on the heat transfer and fluid dynamics theory, a mathematical model is developed to analyze the flow directions. The sensors feature multi-layer structures, where the numerous leads are concealed and embedded in the insulation layer to enhance their robustness and integration. Utilizing the microelectromechanical system technology, sensor prototypes with single-loop and double-loop are fabricated. In particular, a new process method for accomplishing junction holes in the polyimide insulation layer is proposed. The sidewall-to-bottom angle of junction holes fabricated through wet etching is ~29.4°. After metal lays are deposited in the junction holes, the upper and bottom surfaces of the insulation layer are able to conduct electricity. Moreover, a testing system consisting of a microchannel and a turbulence generator is established to carry out the experimental verification. Then, the hot-film sensors are tested in the microchannel with a maximum Reynolds number of Re d = 8600. Low-frequency turbulence as well as natural transition signals are detected by the hot-film sensors successfully. In the range of wall shear stress from 0 to 14.2 Pa, the accuracies of the dual-loop and single-loop hot-film sensors in perceiving flow directions are better than ± 3° and ± 6.5°, respectively. This work assists to analyze the boundary layer states, investigate drag reduction mechanisms, and enhance environmental perception in flow field.

Metal-polymer films are widely used for flexible sensors and actuators, enduring various mechanical loads and facing the risk of structural damage. In this work, a method of manipulating the metal-polymer interface characteristics by metal nanoparticles in the transition layer is presented to prevent film fracture and restrain electrical failures. A transition layer with nickel (Ni) nanoparticles is grown on the surface of polyimide (PI) film through the stages of ring cleavage, ion exchange, and reduction. Further, the research investigates the influence of three parameters - the concentration of ring cleavage solution, the time of ring cleavage, and the concentration of reductant - on the thickness and particle morphology of the transition layer. After depositing similar to 200 nm Ni film by magnetron sputtering, the film with a transition layer can withstand twice more than the maximum tensile force of untreated Ni-PI films when the resistance change reaches 10 %. The transition layer featuring metal nanoparticles increases the shear strength between Ni and PI by over 50 %. This method has been proposed for the first time, which considerably improves the adhesion properties of these two widely used materials, which provides a fine application prospect in flexible electronics.

Hot-film sensors measure wall-shear stress based on the forced convective heat transfer. Variations of ambient temperatures lead to significant measurement errors for such thermal sensors and must be corrected for sometimes. Although methods for correcting the temperature shifts of hot-film sensors driven in constant temperature or constant voltage mode have been suggested over the years, the temperature dependence and relevant correction schemes of constant current mode of operation are still open questions. In this study, temperature dependence characteristics of constant current hot-film sensors are investigated within relatively large temperature changes in air and water channel flows (28 °C and 16 °C, respectively). The specific property of constant overheat ratios under varying temperatures for constant current driving mode is found and a quite simple temperature correction function is derived on that basis to eliminate the temperature dependence without any assumed heat transfer correlation. With the correction function, the data at different ambient temperatures are collapsed to single curves with high R2 factors over 0.99, typically. Furthermore, after correction, the relative errors of the measured wall-shear stress are reduced to within ± 6 %. It will then enable the constant current hot-film sensors to calibrate at only one ambient temperature instead of a multiple range of temperatures as with many other schemes, which is more practical and convenient.

A Tandem Wheatstone Bridge Low-Pressure (TWBLP) sensor with high sensitivity which can be widely used in medical and industrial fields has been designed and fabrication. Compared with the Conventional Low-Pressure (CLP) sensor, the TWBLP sensor membrane is arranged with eight piezoresistors, which are formed into two Wheatstone Bridges. They achieved the detection of membrane stress with different positions and different directions. The output ports of the two Wheatstone Bridges are connected in tandem to realize the on-interference superposition of the output electric potential, thus improving the sensitivity of the sensor. The structure of the sensor membrane and the position of the piezoresistors are calculated by the Finite Element Analysis (FEA). The TWBL sensor is simple in structure and easy to produce in large quantities, with the advantage of high sensitivity, it can provide tiny pressure measurement results for pressure measurement in related fields. In the laboratory environment, the local atmospheric pressure is used as the reference zero point to calibrate the sensor. The test results show that the sensitivity of the TWBLP sensor is 28.2% higher than that of the CLP sensor. When the sensitivity is in the range from -10kPa to 10kPa, the sensitivity reaches 23.07mV /kPa, and the measurement accuracy is 0.19%F.S.

In this paper, a novel and practical double-sided comb-liked misaligned electrode structure based on spatial polarization field design was proposed. Simulation results indicated that a voltage of 7.66 mV was produced under the friction force of 100 Pa, whereas output voltage closed to zero at normal force up to 1000 Pa when the polarization electric field is set at 60°. Additionally, tests at different polarization electric field angles showed the sensor to maintain minimal response to normal force and to have a maximum response to friction force when polarization electric field was 60°, which proved good agreement with the simulations. When the polarization electric field is 60°, the sensor exhibited a large friction force perception range of 1 N~16 N and a sensitivity of 2.95 mV/N. And at normal force up to 80 N, the sensor output voltage was close to zero. It indicated that the polyvinylidene fluoride film sensor based on double-sided comb-liked misaligned electrode structure with ability to generate output voltage under friction force and low interference by normal force. Additionally, the friction force sensor exhibited good stability at low temperatures. Furthermore, under 2000 cycle tests, the sensor still maintained a stable output voltage under friction force and the underwater characterization of the sensor was also investigated. Thus, the sensor prepared with potential applications value for precise ship-ice friction force measurements and reduced the crosstalk of normal force.

Thin film resistance temperature detectors (TFRTDs) are ideal for in-situ temperature measurements due to their non-intrusiveness and quick thermal response. Indium tin oxide (ITO) is a promising material for TFRTDs used in harsh environments due to its high melting point and large temperature coefficient of resistance (TCR). However, the performance of ITO TFRTDs at elevated temperatures has attracted little attention and needs further investigation. In this paper, ITO TFRTDs were fabricated on Al2O3 substrates by using magnetron sputtering technology. Their key indicators, including TCR, repeatability, and thermal stability, were systematically investigated from room temperature to 1000 degrees C. Results show that ITO TFRTDs possess a large TCR but poor repeatability and thermal stability. Herein, a novel Al/Al2O3 heterogeneous protective coating was employed to improve the high-temperature performance of the ITO TFRTDs. By using this method, the repeatability and resistance drift were successfully reduced by an order of magnitude: from 23.3% to 4.2% and from 0.015%/h to 0.0077%/h, respectively. The prior performance of the enhanced ITO TFRTDs makes them attractive for in-situ temperature measurement, especially in harsh environments.

Terfenol-D (Tb0.3Dy0.7Fe2) film with low coercivity and high magnetization in weak magnetic fields is essential for its application as a weak magnetic sensor. In this article, an annealing method is proposed to optimize the coercivity and magnetization of the deposited Terfenol-D film. The magnetization could be improved by releasing compressive stress and increasing saturation magnetization. The coercivity decreases and then increases sharply due to partial crystallization with the annealing temperature increasing. The low coercivity of 12.6 Oe and high magnetization at 100 Oe of 0.29 emu/g are obtained with the annealing temperature at 525 °C. Further increment in annealing temperature does not contribute to coercivity and magnetization. The annealed film could promote the application of Terfenol-D in weak magnetic sensors.

The present study introduces a weak magnetic field sensor that utilizes a laminated cantilever structure, consisting of a magnetostrictive layer, a piezoelectric layer, and a substrate layer. Consequently, the transformation from the magnetic signal to the electrical signal is accomplished through the consistent mechanical stress in both layers. A comprehensive theoretical model has been developed to evaluate the impact of key structural parameters on the magnetoelectric (ME) sensing performance, enabling the optimization of the device design. By incorporating vanadium (V) as a dopant element, a Zn-V-O film with a piezoelectric coefficient as high as 35 pm/V is fulfilled. Furthermore, the high piezomagnetic properties of Galfenol make it a suitable candidate as a magnetostrictive layer. Sensor prototypes were fabricated for experimental verification through the utilization of MEMS technology. The film was characterized using techniques, such as X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and piezoelectric force microscopy (PFM). The ME testing experiments indicated that the magnetostrictive coefficient could achieve about 9.32 kV/(cm $\cdot $ Oe) at resonant frequencies for sensors with varying lengths and a 20- $\mu \text{m}$ -thick Si substrate. The proposed sensor exhibits promising potential for improving weak magnetic field detection performance.

Langasite (LGS, La3Ga5SiO14) is a promising material in high-temperature piezoelectric devices due to its excellent thermal stability, piezoelectricity, and electrical property. A major challenge in the development of LGS-based devices is to form high-strength bonding of the brittle LGS. Here, we report that the single crystal-single crystal (dual-SC) bonding of LGS is realized through thermal activation under a low compression of 50 kPa for the first time. A record bonding strength of 23.28 MPa is achieved within the dual-SC bonded LGS/LGS structure (with a high bonding ratio exceeding 93%), which is 5 times higher than that of the recent reported LGS/LGS bonding structure (in which a relatively fragile amorphous interface layer is formed between the two LGS samples). The smooth and void-free dual-SC bonding interface of LGS is verified via the cross-sectional transmission electron microscopy (TEM) observations.

3D bioprinting is recognized as a promising biomanufacturing technology that enables the reproducible and high-throughput production of tissues and organs through the deposition of different bioinks. Especially, bioinks based on loaded cells allow for immediate cellularity upon printing, providing opportunities for enhanced cell differentiation for organ manufacturing and regeneration. Thus, extensive applications have been found in the field of tissue engineering. The performance of the bioinks determines the functionality of the entire printed construct throughout the bioprinting process. It is generally expected that bioinks should support the encapsulated cells to achieve their respective cellular functions and withstand normal physiological pressure exerted on the printed constructs. The bioinks should also exhibit a suitable printability for precise deposition of the constructs. These characteristics are essential for the functional development of tissues and organs in bioprinting and are often achieved through the combination of different biomaterials. In this review, we have discussed the cutting-edge outstanding performance of different bioinks for printing various human tissues and organs in recent years. We have also examined the current status of 3D bioprinting and discussed its future prospects in relieving or curing human health problems.

The wall shear stress and pressure are important for analyzing boundary layer flow and evaluating the aerodynamic performance of the aircraft. In this study, a flexible skin consisting of dual layer hot-film sensors and pressure belts was developed to measure the distribution of wall shear stress and pressure on an unmanned aerial vehicle during increase of angle of attack (AOA), tail spin, and decreases of AOA. The sensitivity of the dual layer hot-film sensor is improved by about 150% due to heat conduction reduced. The relative error of pressure belt is less than 1% at 10 °C–65 °C. The boundary layer separation and reattachment time, separation AOA and time-shift of the flow field changes in flight conditions are determined. The separated AOA of the left and right wing boundary layers are 26.41° and 17.58° respectively. There is a delay about 4 s between the separation of the boundary layer and the entry of the tail spin, which can provide early warning to prevent abnormal flight conditions such as post stall and tail spin.

Flexible superomniphobic doubly re-entrant (Dual-T) microstructures inspired by springtails have attracted growing attention due to their excellent liquid-repellent properties. However, the simple and practical manufacturing processes of the flexible Dual-T microstructures are urgently needed. Here, we proposed a one-step molding process coupled with the lithography technique to fabricate the elastomeric polydimethylsiloxane (PDMS) Dual-T microstructure surfaces with high uniformity. The angle between the downward overhang and the horizontal direction could reach 90° (vertical overhang). The flexible superomniphobic Dual-T microstructure surfaces, without fluorination treatment and physical treatments, could repel liquids with a surface tension lower than 20 mN m-1 in the Cassie-Baxter state. Owing to the excellent robustness of the one-step molding downward overhanging, the max breakthrough pressure of this surface could reach up to 164.3 Pa for ethanol droplets. Furthermore, the flexible superomniphobic Dual-T surface allowed impinging ethanol droplets to completely rebound at the Weber number up to 7.1 with an impact velocity of ∼0.32 m s-1. The Dual-T microstructure surface maintained excellent superomniphobicity even after surface oxygen plasma treatment and exhibited excellent structural robustness and recoverability to various large mechanical deformations.

Doubly re-entrant surfaces inspired by springtails exhibit excellent repellency to low-surface-tension liquid. However, the flexible doubly re-entrant surfaces are difficult to fabricate, especially for the overhang of the structure. Herein, we demonstrate a simple Fresnel aperture diffraction modulation strategy in microscale lithography coupled with a molding process to obtain the flexible doubly re-entrant superomniphobic surfaces with nanoscale overhangs. The negative nanoscale overhang features were formed in a single-layer photoresist due to the fine-modulation of the optical intensity fluctuation of the Fresnel aperture diffraction. The as-prepared flexible non-fluorinated polydimethylsiloxane (PDMS) doubly re-entrant microstructure based on the Fresnel aperture diffraction (D-BF) surface (without any additional treatments) could repel ethanol droplets (21.8 mN m-1) in the Cassie-Baxter state. The robust nanoscale overhangs obtained by the molding process enable the maximum breakthrough pressure for the low-surface-tension ethanol droplets on the D-BF surfaces up to about 230 Pa, allowing ethanol liquids with Weber numbers up to 8.7 to fully bounce off. The fabricated non-fluorinated D-BF superomniphobic surface maintains outstanding liquid repellency after the surface wettability modification and deformation test.