Thermal sensor network

A flexible thermal sensor network has been developed employing organic semiconductor diodes in a manner suitable for integration with the pressure sensor network. The possible implementation of both pressure and thermal sensors on the surfaces is presented. By means of laminated sensor networks, the distributions of pressure and temperature are simultaneously obtained. 

In the present design, the thermal sensor network contains its own organic transistor active matrix for data readout. This arrangement provides for a self-contained thermal sensor when combined with a pressure sensor, yielding two electrically independent networks. The design of the active matrices is exactly the same for both networks. 

The process for the thennal sensor network is as follows. Organic diodes, to be used as sheet-type thermal sensors, are manufactured on an ITO-coated PEN film. A 30-mn thick p-type semiconductor of copper phthalocyanine (CuPc) and a 50-nm thick n-type semiconductor of 3,4,9,10-perylene-tetracarboxylic-diimide (PTCDI) are deposited by vacuum sublimation. A 150-mn thick gold film is then deposited to form cathode electrodes having an area of 0.19 mm. The film with the organic diodes is coated with a 2-pm thick parylene layer and the electronic interconnections are made by the method similar to that mentioned before. The diode film is also mechanically processed to form net-shaped structures. Finally, to complete the thermal sensor network, we laminated the transistor and diode net films together with silver paste patterned by a microdispenser. This is shown in Figure 6.3.11. 

FIGURE 6.3.11 Cross-sectional illustration of the thermal sensor network, which contains both the diode and organic transistor. 

FIGURE 6.3.12 Thermal sensor network. Temperature dependence of current is measured under voltage bias of 2 V and data normalized by current at room temperature is plotted as a function of 1000/T for three samples stand-alone thermal sensors, denoted by solid circles, consisting of double organic semiconductors (30-nm thick CuPc and 50-nm thick PTCDl), and single organic semiconductors (80-nm thick CuPc or 80-nm thick PTCDl, denoted by solid squares and open circles, respectively) sandwiching between ITO and Au electrodes. 

FIGURE 6.3.14 Integration of pressure and thermal sensor networks, (a) A possible implementation of thermal and pressure sensor films. The pressure and thermal sensors are represented by P and T, respectively. Scale is 4 mm. (b) The spatial distribution of temperature that is converted from the temperature-dependent current in the thermal sensor network. A copper block (15 x 37 mm ), whose temperature is maintained at 50°C, is positioned diagonally, as is indicated by the dotted line. The sensing area is 44 X 44 mm. (c) Simultaneously, the spatial distribution of pressure is measured with the pressure sensor network. 

FIGURE 6.3.13 One ceU of the thennal sensor network devices consisting of the diode-based thermal sensors and transistors is characterized at varions temperatures from 30 to 80°C. 

Someya, T., Kato, Y., Sekitani, T., Iba, S., Noguchi, Y, Murase, Y, Kawaguchi, H., and Sakurai, T., Conformable, flexible, large-area networks of pressure and thermal sensors with organic transistor active matrixes, Proc. Natl. Acad. Sci. U.S.A., 102, 12321, 2005. 

A highly complex network of arteries, arterioles, and capillaries penetrates the dermis from below and extends up to the surface of, but not actually into, the epidermis. A matching venous system siphons the blood and returns it to the central circulation. Blood flow through the vasculature is linked to the production and movement of lymph through a complementary dermal lymphatic system. The dermis is laced with tactile, thermal, and pain sensors. 

These measure the change in thermal conductivity of a gas due to variations in pressure—usually in the range 0.75 torr (100 N/m2) to 7.5 x 10"4 torr (0.1 N/m2). At low pressures the relation between pressure and thermal conductivity of a gas is linear and can be predicted from the kinetic theory of gases. A coiled wire filament is heated by a current and forms one arm of a Wheatstone bridge network (Fig. 6.21). Any increase in vacuum will reduce the conduction of heat away from the filament and thus the temperature of the filament will rise so altering its electrical resistance. Temperature variations in the filament are monitored by means of a thermocouple placed at the centre of the coil. A similar filament which is maintained at standard conditions is inserted in another arm of the bridge as a reference. This type of sensor is often termed a Pirani gauge. 

A katharometer is employed to determine the concentration of H2 in a H2/CH4 mixture. The proportion of H2 can vary from 0 to 60 mole per cent. The katharometer is constructed as shown in Fig. 6.54 from four identical tungsten hot-wire sensors for which the temperature coefficient of resistance ft, is 0.005 K. The gas mixture is passed over sensors R, and R whilst the reference gas (pure CH4) is passed over sensors R2 and R,. The total current supplied to the bridge is 220 mA and it is known that the resistance at 25°C and surface area of each sensor are 8 Q and 10 mm2 respectively. Assuming the heat transfer coefficient h between gas and sensor filaments to be a function of gas thermal conductivity k only under the conditions existing in the katharometer and that in this case h = k x 10 (h in W/m2K and k in W/mK), draw a graph of the output voltage V0 of the bridge network as a function of mole per cent H2. 

Foy, B.R. and Theiler, J., Scene analysis and detection in thermal infrared remote sensing using independent component analysis. Independent Component Analyses, Wavelets, Unsupervised Smart Sensors, and Neural Networks 11, Proceedings of SPIE vol. 5439, 131-139(2004)... 

Single wall carbon nanotube (SWNT) network sensors were prepared as previously described (7-9). The carbon nanotube network (CNN) sensors were spray coated with a 0.1% by weight solution of polymer to a thickness of approximately 100 nm. These CNN sensors can be monitored simultaneously in capacitive and resistive mode. The capacitance was measured by applying a 0.1 V, 30 kHz, AC voltage between a conducting Si substrate and a S T network deposited on a thermal SiOa layer. The induced AC current was measured using a Stanford Research Systems SR830 lock-in amplifier. 

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