The tactile pressure sensor is of great significance in flexible electronics, but sensitivity customization over the required working range with high linearity still remains a critical challenge. Despite numerous efforts to achieve high sensitivity and a wide working range, most sensitive microstructures tend to be obtained only by inverting naturally existing templates without rational design based on fundamental contact principles or models for piezoresistive pressure sensors. Here, a positive design strategy with a hyperelastic model and a Hertzian contact model for comparison was proposed to develop a flexible pressure sensor with highly customizable linear sensitivity and linearity, in which the microstructure distribution was precalculated according to the desired requirement prior to fabrication. As a proof of concept, three flexible pressure sensors exhibited sensitivities of 0.7, 1.0, and 1.3 kPa⁻¹ over a linear region of up to 200 kPa, with a low sensitivity error (<5%) and high linearity (~0.99), as expected. Based on the superior electromechanical performance of these sensors, potential applications in physiological signal recognition are demonstrated as well, and such a strategy could shed more light on demand-oriented scenarios, including designable working ranges and linear sensitivity for next-generation wearable devices.

Effective transformation from paraelectric to a high fraction of ferroelectric phase is crucial to produce piezoelectric materials with a high piezoelectric constant for broad applications. In polyvinylidene fluoride (PVDF) thin films, both mechanical stretching and electric poling processes have been found to be critical in the α → β phase transformation. However, in PVDF fibers fabricated by the electrospinning process, the roles of mechanical stretching and electric poling have not been well explored. Here, the properties of PVDF fibers from electrospinning and forcespinning, a mechanical spinning process without electric poling, have been characterized and analyzed by FTIR and XRD spectroscopic techniques. The results show that pure mechanical stretching in the forcespun fibers can result in a high fraction of the all-trans β-phase, at 95%. Electrospun fibers from the same material system, on the other hand, can also reach a high fraction of β-phase, at approximately 99%. These results preliminarily demonstrate that mechanical stretching is the main reason for β-phase induction in PVDF fibers. Further experiments performed in this work show that higher wt% of PVDF, lower polymer solution supply rate, and more uniformly mixed solvent systems facilitate achieving a higher level of ferroelectric β-phase in electrospun PVDF fibers.

Ammonia gas sensors are very essential in many industries and everyday life. However, their complicated fabrication process, severe environmental fabrication requirements and desorption of residual ammonia molecules result in high cost and hinder their market acceptance. Here, laser direct writing is used to fabricate three parallel porous 3D graphene lines on a polyimide (PI) tape to simply construct an ammonia gas sensor. The middle one works as an ammonia sensing element and the other two on both sides work as heaters to improve the desorption performance of the sensing element to ammonia gas molecules. The graphene lines were characterized by scanning electron microscopy and Raman spectroscopy. The response and recovery time of the sensor without heating are 214 s and 222 s with a sensitivity of 0.087% ppm⁻¹ for sensing 75 ppm ammonia gas, respectively. The experimental results prove that under the optimized heating temperature of about 70 °C the heaters successfully help implement complete desorption of residual NH₃ showing a good sensitivity and cyclic stability.

The in situ strain/stress monitoring of hot components in harsh environments remains a challenging task. In this study, TiB ₂ /SiCN thin-film strain gauges were fabricated on nickel base alloy substrates via direct writing. The static and dynamic strain responses were investigated from 25 °C up to 800 °C. The results show that this thin-film strain gauge fabricated by ceramic-based materials exhibits excellent thermal stability and strain response. Without any anti-oxidative protective layer deposited, its operating temperature is as high as $700^{\circ }\text{C}$ , which is 200 °C higher than that of the high-temperature piezoresistive thin-film strain gauges that have been developed and comparable to thin-film strain gauges with protective layers. The gauge factor of theTiB ₂ /SiCN high-temperature thin-film strain gauge is 7.12, which is higher than that of most high-temperature thin-film strain gauges. In addition, the strain gauge exhibits excellent resistance stability with a mechanical hysteresis of $3~\mu \varepsilon $ and a resistance drift of 0.0008/h at room temperature. Therefore, TiB ₂ /SiCN thin-film strain gauges provide an effective approach for the measurement of in-situ static and dynamic strain of hot components in harsh environments.

Heat flux is key parameter for evaluating the heat dissipation of turbine blade. The accurate measurement of heat flux is vital for the optimizing cooling system and fabrication of turbine blade. The thin film heat flux gauge is usually fabricated on insulated substrate and located away from the measured area of turbine blade. As a result, the changes of heat flux on the surface of turbine blade cannot be reflected quickly and accurately. This paper innovatively designs membrane structure of thin film heat flux gauge on nickel alloys. The sensor is fabricated on the surface of the nickel alloys by thin-film depositing technology to realize in-situ surface heat flux measurement, and ITO/In ₂ O ₃ thermopile is used to replace precious thermopile to improve sensitivity. The results show that the sensitivity and response frequency of the sensor respectively are measured to be $61.93~\mu \text{V}$ /(kW/m ² ) and over 14400Hz respectively, which can measure heat flux of 236.4kW/m ² at $888^\circ \text{C}$ . Besides, the thin film heat flux gauge is fabricated on the surface of turbine blade to verify functional feasibility with same preparation process of that on nickel alloys, and can obtain reproducible results. This work suggest that the thin film sensor based on ITO/In ₂ O ₃ thermopile has great potential in applications used as optimizing cooling system of components in aeronautics and astronautics.