Piezoresistive tactile sensors made using nanocomposite polymeric materials have been shown to possess good flexibility, electrical performance, and sensitivity. However, the sensing performance, especially in the low-pressure range, can be significantly improved by enabling uniform dispersion of the filler material and utilization of effective structural designs that improve the tactile sensing performance. In this study, a novel flexible piezoresistive tactile sensor with a grid-type microstructure was fabricated using polymer composites comprising multi-walled carbon nanotubes (MWCNTs) as the conductive filler and polydimethylsiloxane (PDMS) as the polymeric matrix. The research focused on improving the tactile sensor performance by enabling uniform dispersion of filler material and optimizing sensor design and structure. The doping weight ratio of MWCNTs in PDMS varied from 1 wt.% to 10 wt.% using the same grid structure-sensing layer (line width, line spacing, and thickness of 1 mm). The sensor with a 7 wt.% doping ratio had the most stable performance, with an observed sensitivity of 6.821 kPa⁻¹ in the lower pressure range of 10–20 kPa and 0.029 kPa⁻¹ in the saturation range of 30–200 kPa. Furthermore, the dimensions of the grid structure were optimized and the relationship between grid structure, sensitivity, and sensing range was correlated. The equation between pressure and resistance output was derived to validate the principle of piezoresistance. For the grid structure, dimensions with line width, line spacing, and thickness of 1, 1, and 0.5 mm were shown to have the most stable and improved response. The observed sensitivity was 0.2704 kPa⁻¹ in the lower pressure range of 50–130 kPa and 0.0968 kPa⁻¹ in the saturation range of 140–200 kPa. The piezoresistive response, which was mainly related to the quantum tunneling effect, can be optimized based on the dopant concentration and the grid microstructure. Furthermore, the tactile sensor showed a repeatable response, and the accuracy was not affected by temperature changes in the range of 10 to 40 °C and humidity variations from 50 to 80%. The maximum error fluctuation was about 5.6% with a response delay time of about 1.6 ms when cyclic loading tests were performed under a normal force of 1 N for 10,200 cycles. Consequently, the proposed tactile sensor shows practical feasibility for a wide range of wearable technologies and robotic applications such as touch detection and grasping.

Oral cancer has consistently been ranked among the top ten cancers in terms of mortality with five year survival rates being among the lowest for all major cancers. Consequently, great efforts are being made to develop new diagnostic tools that can enable early detection in a clinical setting. In this study, we report on the design and development of a novel pen-like handheld device, with a miniaturized tactile sensor mounted on the front-end and integrated with a portable back-end readout module. The device can be used for tissue palpation in the oral cavity and obtain quantitative information regarding the elasticity of oral lesions and abnormalities, thus eliminating the need for manual palpation by the clinician. The sensing mechanism of the proposed tactile sensor is based on the two-spring model and employs two components with varying stiffness values, namely a hard copper ball embedded in a soft elastomeric packaging. The differential voltage output of the piezoelectric sensing film corresponding to the two components can provide information regarding the elasticity of the tissue under contact. To simulate feasibility of the tactile sensor in differentiating tissue elasticity, we have contacted the sensor with different elastomeric silicone materials under the same applied force. The experiments confirmed that the sensor response could be used to differentiate five silicones with varying Young's moduli ranging from 0.2 to 3.1 MPa and a corresponding Shore hardness of 2 to 56 Shore A. A two-stage linear trend was observed with a sensitivity of 0.356/MPa for softer silicones (2 ~ 9 Shore A) and 0.059/MPa for harder silicones (24 ~ 56 Shore A). Furthermore, the portable readout module that we have developed can analyze the data from the tactile sensor and transmit it wirelessly via Bluetooth for cloud computing. The proposed device is easy-to-use in general clinical settings and could enable early detection and improved prognosis of oral cancer.

This paper presents the design and implementation of fuzzy logic control for human walking using lab-developed sensors and the second lower limb robotic exoskeleton (LLRE-II) to detect gait phases. A piezoresistive tactile sensor (PRTS) was developed and used to measure the foot pressure to predict human walking behavior. The proposed sensor with grid structures was then fabricated using polymer composites of multi-walled carbon nanotubes (MWCNTs) combined with polydimethylsiloxane (PDMS). The doping ratio and design of the grid structure of the sensors were optimized to achieve a good sensing range. The foot reactive forces measured by the four sensors were calculated and converted to force ratio factors to improve the performance of gait phase detection by the fuzzy logic control. Based on the sensor tests, the most stable doping ratio was fixed as 7 wt%, and the ratio of the grid structure (line width:line spacing:thickness) was 1:1:1. Sensors were set in the soles of the shoes on the foot pads of the exoskeleton, and the foot reactive forces were captured for analysis. The performance of the proposed algorithm for gait phase detection was verified experimentally. The results indicated that both regular and irregular walking could be detected by the proposed method.

By the conventional solid state reaction method, a small amount of lithium fluoride (LiF) was used as the sintering promoter to improve the sintering and piezoelectric characteristics of (Ba_0.95Ca_0.05)(Ti_0.93Sn_0.07)O₃ (BCTS) lead-free piezoceramic sheets. Using X-ray diffraction (XRD) and a scanning electron microscope (SEM), the inferences of the crystalline and surface microstructures were obtained and analyzed. Then, the impedance analyzer and d₃₃-meter were used to measure the dielectric and piezoelectric characteristics. In this study, the optimum sintering temperature of the BCTS sheets decreased from 1450 °C to 1390 °C due to LiF doping. For the 0.07 wt % LiF-doped BCTS sheets sintered at 1390 °C, the piezoelectric constant (d₃₃) is 413 pC/N, the electric–mechanical coupling coefficient (k_p) is 47.5%, the dielectric loss (tan δ) is 3.9%, and the dielectric constant (ε_r) is 8100, which are all close to or even better than that of the pure undoped BCTS ceramics. The Curie temperature also improved, from 85 °C for pure BCTS to 140 °C for BCTS–0.07 LiF sheets. Furthermore, by using the vibration system and fixing 1.5 g tip mass at the end of the sheets, as the vibration frequency is 20 Hz, the proposed piezoelectric ceramic sheets also reveal a good energy harvesting performance at the maximum output peak voltage of 4.6 V, which is large enough and can be applied in modern low-power electronic products.

In recent years, smart beehive monitoring has attracted attention due to its highly profitable industry. However, colony collapse disorder (CCD) syndrome, which is described by the sudden disappearance of the bee colony, severely affects the honey bee industry in most countries of the world. The causes of CCD are not verified, but electromagnetic interference (EMI) is the possible one that appears in most beehive monitoring systems. Based on this motivation, this paper presents a new paradigm for beehive monitoring utilizing the proposed system consisting of a host module, multiple sensor modules, and relay modules. Each sensor module is responsible for collecting the in-hive parameters of each beehive such as temperature, humidity, hive weight, carbon dioxide, oxygen, and entrance counts. The collected sensor data are then transmitted to the relay module by infrared (IR) communication to avoid EMI. The relay module integrates the IR receiver and power line communication (PLC) transmitter technologies, where the former is used to receive optical signals with in-hive parameters, and the latter is used to transform the abovementioned signals into PLC interface. Moreover, a host module is introduced to aim at receiving the signals from multiple relay modules by the PLC interface. The distances of IR communication and PLC are determined through simulation results under the target bit error rate of $10^{-3}$ to provide accurate in-hive parameters with negligible interference from multiple beehives. Experimental results also show that the proposed system could meet the requirements of real-time and long-term data collection and transmission.

This letter presents the design and implementation of a LoRa-based wireless communication system aimed at monitoring of driver’s biomedical signals in the car environments. The proposed system is composed of a sensor node, a LoRa gateway, and a cloud server. Each sensor node includes four parts as microcontroller unit, data collection unit, wireless communication unit, and supplied power unit. The microcontroller unit is mainly designed as the signal processing module to deal with the detection of abnormal ECG symptom such as left bundle branch block (LBBB), which is the most common symptoms of myocardial infarction. The data collection unit contains a sequential stage of the instrumentation amplifier and the filter blocks. The notification of LBBB detection is then transmitted to the LoRa gateway by wireless communication unit. The LoRa gateway with multiple wireless interfaces is designed to collect the information from the sensor node to transmit to cloud server. The experimental results are conducted to evaluate the detection performance of LBBB by means of MIT-BIH arrhythmia database.