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This paper presents the design and development of a low cost and reliable maximal voluntary bite force sensor which can be manufactured in-house by using an acrylic laser cutting machine. The sensor has been designed for ease of fabrication, assembly, calibration, and safe use. The sensor is capable of use within an hour of commencing production, allowing for rapid prototyping/modifications and practical implementation. The measured data shows a good linear relationship between the applied force and the electrical resistance of the sensor. The output signal has low drift, excellent repeatability, and a large measurable range of 0 to 700 N. A high signal-to-noise response to human bite forces was observed, indicating the high potential of the proposed sensor for human bite force measurement.

We report the effect of stress or strain on the electronic characteristics of a normally off AlGaN/GaN high electron mobility transistor (HEMT) and demonstrate its role as a highly sensitive pressure sensor. We observe that the HEMT drain current exhibits a linear change of 2.5%/bar upon the application of pressure, which is translated to a strain sensitivity of 1250 ppm−1. This is the highest strain sensitivity ever reported on HEMTs and many other conventional strain sensing configurations. The relative change of drain current is largest when the gate bias is near-threshold and drain bias is slightly larger than the saturation bias. The electron sheet density and mobility changes in the AlGaN/GaN heterointerface under the applied pressure or mechanical strain are explained qualitatively. The spontaneous and piezoelectric-polarization-induced surface and interface charges in the AlGaN/GaN heterojunction can be used to develop very sensitive and robust pressure sensors. The results demonstrate a considerable potential of normally off AlGaN/GaN HEMTs for highly sensitive and reliable mechanical sensing applications with low energy consumption.

The single-jet mode in an electrohydrodynamic (EHD) system is the most desirable mode for generating uniform droplets and fibers and has many applications in numerous fields. Several studies have been carried out to enhance the performance of the EHD process focusing on this mode. In this paper, we introduce the use of a chamfered nozzle in an EHD system to greatly extend the single-jet mode's voltage range, and generally, to enhance the EHD process in terms of control capability and product quality. We carried out simulations and experiments to compare the performance of a chamfered nozzle and conventional flat-end nozzle. Both theoretical analysis and experiments demonstrate that the chamfered nozzle in an EHD system reduces the critical voltage, broadens the voltage range for the single-jet mode, and enhances homogeneity in particle and fiber generation. Furthermore, the chamfered nozzle's advantages were demonstrated in fabricating highly uniform poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) fibers for piezoelectric sensor development. Owing to the fibers' excellent quality, the sensor shows high sensitivity that can detect and differentiate between the drops of a metal bead, a water droplet, and an oil droplet. The use of a chamfered nozzle with its advantages shows potential for development of better EHD-based devices.

This paper reports on the impact of compressive pressure on the electrical properties of carbon nanotube (CNT) yarns fabricated by dry web-spinning and heat-treatment processes. Under increasing applied compressive pressure in the radial direction of the yarn, the electrical resistance of CNT yarns gradually decreased by 2.8% at a threshold applied pressure of 60 kPa where the resistance change is saturated. The decrease of CNT resistance with increasing pressure is attributed to the increase in the volume fraction of CNT, resulting in the increase of the effective junctions between adjacent CNTs, and the reduction of the tunneling distance between single CNTs. CNT yarns embedded in elastomers show high potential as an advanced functional element for a wide range of mechanical sensing applications including flexible pressure and tactile sensing.