We propose a design strategy to fabricate a flexible bend sensor (BS) with ultrasensitivity towards airflow using all PVDF nanofiber web based sensing element and electrode to monitor human respiration. The unique electrospinning (rotational speed of collector of 2000 rpm and tip-to-collector distance of 4 cm) with silver nanoparticles interfacing was introduced to prepare an Ag-doped oriented PVDF nanofiber web with high β-phase content as sensing element (AgOriPVDF, β-phase crystallinity ~ 44.5 %). After that, a portion of the prepared AgOriPVDF was processed into flexible and electrically conductive electrode through electroless silver plating technique (SP-AgOriPVDF). Interestingly, the encapsulated AgOriPVDF BS with SP-AgOriPVDF electrode exhibited superior piezoelectric bending response (open-circuit peak-to-peak output voltage, Vp-p ≈ 4.6 V) to injected airflow, which is more than 200 times higher than that of the unpackaged randomly aligned PVDF nanofiber web BS with conductive tape electrode (Vp-p ≈ 0.02 V). In addition, the factors influencing the 2 bend sensitivity of BS such as β-phase content, nanofiber orientation, flexibility of electrode and so forth were thoroughly analyzed and then discussed. We also demonstrated that the AgOriPVDF BS has sufficient capability to detect and identify various respiratory signal, presenting a great potential for wearable applications, e.g. smart respiratory protective equipment.
This paper presents new proposals in the evaluation and determination of the optimum materials suitable for use in the design and development of firefighter protective clothing by simultaneously addressing the conflicting factors of thermal protection [heat transfer index (HTI), radiant heat transfer index (RHTI) and thermal threshold index (TTI)] and anti-heat stress [water vapor resistance (WVR) and total heat loss (THL)]. To achieve this, this paper proposes new indices for the materials, two types of ''total performance'' indices, which are defined as the sum and the product of the competing factors of thermal protection and anti-heat stress. The results showed that the candidate materials of firefighter protective clothing were easily rated when the new indices were applied. Of five candidate materials viz. A, B, B 1 , B 2 and C, the B sample, with values for HTI 24 = 13.2 ± 0.2 s, RHTI 24 = 18.0 ± 0.8 s, TTI = 1132 ± 33 J/m 2 , WVR = 17.5 ± 0.3 m 2 Pa/W and THL = 266.2 ± 4.1 W/m 2 , was found to exhibit the best total performance. However, the methods proposed to the scientific community in this paper have so far been validated on a limited data set only, and will require further validation by a wider group of researchers and with more samples. Lastly, comments on ISO 11999-3:2015 were also made for the further improvement and development of technical standards.
Multiple strain sensors are required to identify individual forces/stresses on human joints and recognize how they work together in order to determine the motion’s direction and trajectory. However, current sensors cannot detect and differentiate the individual forces/stresses and their contributions to the motion from the sensors’ electrical signals. To address this critical issue, we propose a concept of unimodal tension, bend, shear, and twist strain sensors with piezoelectric poly L-lactic acid films. We then construct an integrated unimodal sensor (i-US) using the unimodal sensors and prove that the i-US can detect and differentiate individual strain modes, such as tensioning, bending, shearing, and twisting in complex motion. To demonstrate the potential impact of unimodal sensors, we design a sleeve and a glove with the i-US that can capture wrist motions and finger movements. Therefore, we expect unimodal strain sensors to provide a turning point in developing motion recognition and control systems.
Despite the importance of respiration and metabolism measurement in daily life, they are not widely available to ordinary people because of sophisticated and expensive equipment. Here, we first report a straightforward and economical approach to monitoring respiratory function and metabolic rate using a wearable piezoelectric airflow transducer (WPAT). A self-shielded bend sensor is designed by sticking two uniaxially drawn piezoelectric poly l -lactic acid films with different cutting angles, and then the bend sensor is mounted on one end of a plastic tube to engineer the WPAT. The airflow sensing principle of the WPAT is theoretically determined through finite element simulation, and the WPAT is calibrated with a pulse calibration method. We prove that the WPAT has similar accuracy (correlation coefficient >0.99) to a pneumotachometer in respiratory flow and lung volume assessment. We demonstrate metabolism measurement using the WPAT and the relationship between minute volume and metabolic rates via human wear trials. The mean difference of measured metabolic rates between the WPAT and a Biopac indirect calorimeter is 0.015 kcal/min, which shows comparable performance. Significantly, unlike the Biopac indirect calorimeter with an airflow sensor, an oxygen gas sensor, and a carbon dioxide gas sensor, we merely use the simple-structured WPAT to measure metabolism. Thus, we expect the WPAT technology to provide a precise, convenient, and cost-effective respiratory and metabolic monitoring solution for next-generation medical home care applications and wearable healthcare systems.
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