We propose watch-type sweat rate sensors capable of automatic natural ventilation by integrating miniaturized thermo-pneumatic actuators, and experimentally verify their performances and ...applicability. Previous sensors using natural ventilation require manual ventilation process or high-power bulky thermo-pneumatic actuators to lift sweat rate detection chambers above skin for continuous measurement. The proposed watch-type sweat rate sensors reduce operation power by minimizing expansion fluid volume to 0.4 ml through heat circuit modeling. The proposed sensors reduce operation power to 12.8% and weight to 47.6% compared to previous portable sensors, operating for 4 hours at 6 V batteries. Human experiment for thermal comfort monitoring is performed by using the proposed sensors having sensitivity of 0.039 (pF/s)/(g/m
h) and linearity of 97.9% in human sweat rate range. Average sweat rate difference for each thermal status measured in three subjects shows (32.06 ± 27.19) g/m
h in thermal statuses including 'comfortable', 'slightly warm', 'warm', and 'hot'. The proposed sensors thereby can discriminate and compare four stages of thermal status. Sweat rate measurement error of the proposed sensors is less than 10% under air velocity of 1.5 m/s corresponding to human walking speed. The proposed sensors are applicable for wearable and portable use, having potentials for daily thermal comfort monitoring applications.
A human stress monitoring patch integrates three sensors of skin temperature, skin conductance, and pulsewave in the size of stamp (25 mm × 15 mm × 72 μm) in order to enhance wearing comfort with ...small skin contact area and high flexibility. The skin contact area is minimized through the invention of an integrated multi-layer structure and the associated microfabrication process; thus being reduced to 1/125 of that of the conventional single-layer multiple sensors. The patch flexibility is increased mainly by the development of flexible pulsewave sensor, made of a flexible piezoelectric membrane supported by a perforated polyimide membrane. In the human physiological range, the fabricated stress patch measures skin temperature with the sensitivity of 0.31 Ω/°C, skin conductance with the sensitivity of 0.28 μV/0.02 μS, and pulse wave with the response time of 70 msec. The skin-attachable stress patch, capable to detect multimodal bio-signals, shows potential for application to wearable emotion monitoring.
Simultaneous measurement of skin physiological and physical properties are important for the diagnosis of skin diseases and monitoring of human performance, since it provides more comprehensive ...understanding on the skin conditions. Current skin analysis devices, however, require each of probes and unique protocols for the measurement of individual skin properties, resulting in inconvenience and increase of measurement uncertainty. This paper presents a pen-type skin analyzing device capable tomeasure three key skin properties at the same time: transepidermal water loss (TEWL), skin conductance, and skin hardness. It uses a single truncated hollow cone (THC) probe integrated with a humidity sensor, paired electrodes, and a load cell for the multimodal assessment of the skin properties. The present device measured TEWL with a sensitivity of 0.0068 (%/s)/(g/m
/h) and a linearity of 99.63%, conductance with a sensitivity of 1.02 µS/µS and a linearity of 99.36%, and hardness with a sensitivity of 0.98 Shore 00/Shore 00 and a linearity of 99.85%, within the appropriate ranges for the human skin. The present pen-type device has a high potential for the skin health diagnosis as well as the human performance monitoring applications.
This is the first ever proposal to use skin hardness as a physiological sign by which to estimate human thermal status and to verify its effectiveness and independence in relation to the two ...conventional signs: skin temperature and skin conductance. We propose a novel TSV model adding skin hardness to the conventional TSV model for better estimation of human thermal status with higher accuracy and lower error. We survey individual thermal sensation from 30 subjects under four different thermal conditions (normal, warm, hot, and cold); while measuring skin hardness along with the two conventional physiological signs. The novel model for estimation of thermal status from all three signs increases R
by 17.4% and decreases error by 23.5%, compared to the conventional model using two signs. The novel TSV model has potential for applications to human-machine interaction systems for better estimation of human thermal status.
A photoplethysmography (PPG) platform integrated with a miniaturized force-regulator is proposed in this study. Because a thermo-pneumatic type regulator maintains a consistent contact-force between ...the PPG probe and the measuring site, a consistent and stable PPG signal can be obtained. We designed and fabricated a watch-type PPG platform with an overall size of 35 mm × 19 mm. In the PPG measurement on the radial artery wrist while posture of the wrist is changed to extension, neutral, or flexion, regulation of the contact-force provides consistent PPG measurements for which the variations in the PPG amplitude (PPGA) was 7.2 %. The proposed PPG platform can be applied to biosignal measurements in various fields such as PPG-based ANS monitoring to estimate nociception, sleep apnea syndrome, and psychological stress.
A piezoelectric pulsewave energy harvester composed of flexible three-layers generates electrical power from human arterial pulsewaves. We present the simple structure and novel fabrication process ...of the flexible three-layers, having a silver inter-electrode layer between a P(VDF-TrFE) piezoelectric layer and a polyimide support layer. The triple functions and the purposes of the silver inter-electrode layer are designed, acting as an electrode for piezoelectric poling, an electrode for piezoelectric energy harvesting, as well as an etch stop barrier for window patterning on the polyimide support layer. We also developed special processes for the window patterning on the polyimide support layer with the polyimide residue removal on the silver electrode, thereby increasing the piezoelectric energy generation efficiency and support flexibility, as well as achieving an electric contact to the silver electrode through the patterned window. The fabricated energy harvester generates 0.2~1.9 μW from the human pulsewave in the range of 50~220 BPM, where the effect of window formation is demonstrated to increase energy efficiency and flexibility in the amount of 45% and 8%, respectively. The flexible energy harvester is capable to integrate additional physiological sensors for the applications to the multi-functional self-powered skin patches.
This paper presents a thermal peripheral blood flowmeter where a force sensor is integrated to compensate the blood flow measurement. Since blood flow is highly sensitive to the contact force between ...the sensor and skin, previous blood flowmeters needed to be fixed on the skin with a constant contact force. We integrate a force sensor with a thermal blood flowmeter to measure both blood flow and contact force simultaneously for force-compensated blood flow measurement. The blood flowmeter presented here is composed of a resistance temperature detector and a piezoresistive force sensor and was fabricated by surface and bulk micromachining techniques. In the experimental measurement, the blood flow linearly decreased with the contact force at the rate of 31.7% N-1. By using the measured compensation coefficient, the device showed a constant blood flow with the maximum difference of 6.4% over the contact force variation of 1-3 N, and otherwise showed the maximum difference of 75.0%. The present device is suitable for applications with portable biomedical instrumentation or air-conditioning systems for the estimation of human thermoregulation status.
We present a flexible multimodal stress sensor, where a skin temperature sensor, a skin conductance sensor, and a pulse wave sensor are integrated; thereby minimizing skin contact area as well as ...increasing device flexibility for applications to human stress monitoring in daily life. We design and fabricate the multilayered stress sensor, and experimentally verify the sensor performance for the simultaneous measurement of skin temperature, skin conductance and arterial pulse wave. The skin contact area of the flexible multimodal stress sensor has been reduced the 0.8% of the conventional stress measurement device; thus, demonstrating sensor's potential for multimodal Human bio-signal monitoring applications, such as mobile electronics and wearable devices with improved wearing comfort.
A portable sweat rate sensor integrated with a thermo-pneumatic actuator for automatic ventilation has been proposed and experimentally verified its performance. The previous forced ventilation sweat ...rate sensors using external ventilating devices had the problem of the bulky size with the lack of portability. The previous natural ventilation sweat rate sensors with portable sizes meanwhile required a manual ventilation per each measurement. The total weight of the present portable sweat rate sensor is 6.2% of that of the previous forced ventilation sweat rate sensors. The integrated thermo-pneumatic actuator lifts the humidity measuring chamber above the skin for automatic natural ventilation. The portable sweat rate sensor, having a size of 38±0.5mm×41±0.5mm×29±0.5mm with a total weight of 63±1g, is capable of lifting the humidity chamber 1.91±0.27mm above the skin in a movement cycle period of 3min. The portable sweat rate sensor measures the sweat rate with a sensitivity of 0.056 (pF/s)/(g/m2h) and a linearity of 99.1% in a sweat rate range of 3.76–137.68g/m2h. The portable sweat rate sensor is insensitive to the environmental air flow, and thus demonstrates high potential for mobile human thermoregulatory status monitoring applications, such as human monitoring jackets and cognitive air-conditioning systems based on human sweat.
Physiologically relevant phantoms with high reliability are essential for extending the therapeutic applications of high-intensity therapeutic ultrasound. Here we describe a tissue-mimicking phantom ...capable of quantifying temperature changes and observing non-thermal phenomena by high-intensity therapeutic ultrasound. Using polydiacetylene liposomes, we fabricated agar-based polydiacetylene hydrogel phantoms (PHPs) that not only respond to temperature, but also have acoustic properties similar to those of human liver tissue. The color of PHPs changed from blue to red depending on the temperature in the range 40°C-70°C, where the red/blue ratio of PHP had a good linearity of 99.06% for the temperature changes. Furthermore, repeated high-intensity focused ultrasound led to histotripsy on the PHP with liquefied and damaged areas measuring 0.7 and 4.0 cm
, respectively, at the signal generator amplitude setting voltage of 80 mV. Our results indicate not only the usability of the thermochromic phantom, but also its potential for evaluating non-thermal phenomena in various high-intensity focused ultrasound therapies.
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