Pressure sensor flexible

In this chapter we review recent progress of organic transistors for sensor applications. Emphasis is put on large-area, flexible pressure sensors suitable for electronic artificial skin and for photodetectors suitable for sheet image scanners. We also describe future prospects of large-area sensors and the other issues. 

Large-area pressure sensor sheets are mechanically flexible, as shown in Fig. 16.1, and can therefore be wrapped around fine cylindrical bars, for example robot fingers. A sense of touch for humanoid robots is far behind the senses of sight and hearing. This is mainly because a flexible, large-area pressure sensor matrix has not been manufactured at reasonable cost. Flexible pressure sensors have been made from polymers or rubber. With increasing number of sensors in the matrix, however, problems associated with wiring cannot be overlooked this makes it impossible to increase the density or total number of sensors to that comparable with human skin. 

In this scheme we have overcome the above problem by introducing organic transistor integrated circuits as a flexible active matrix to read out pressure images, or distribution of pressure. As a result, we have successfully developed large-area, flexible pressure sensors with the number of pressure sensors exceeding 1,000. As shown in Fig. 16.2, the device is manufactured by laminating four different functional films ... 

Someya, T. et al., A large-area, flexible pressure sensor matrix with organic field-effect transistors for artificial skin applications, Proc. Natl. Acad. Sci. U.S.A., 101, 9966, 2004. 

The development of flexible pressure sensor films was an important step in endowing robots with skin sensitivity, but e-skins are expected to add at least two more functionalities thermal sensing and conformability. Without conformability, e-skins cannot be applied to three-dimensional surfaces. Stretchable e-skins for humans are commercially available, but they do not possess electric functionality. Indeed, various stretchable materials, like rubber, are used in daily activities, but they have poor... 

Ashruf, C.M.A., 2002. Thin flexible pressure sensors. Sens. Rev. 22 (4), 322—327. Available at http // www.emeraldinsight.com/joumals. htm issn=0260-2288 volume=22 issue=4 articleid= 876363 show=html (accessed 20.01.14). 

Wang, F., et al., 2014. Flexible pressure sensors for smart protective clothing against impact loading. Smart Mater. Struct. 23 (1), 15001. 

Figure 8.22 shows a schematic representation of the flexible pressure sensor. The electrospun web with aluminum foil was sandwiched between ITO coated polyethylene terephthalate(PET-ITO) film and plastic film. In this sample, ITO... 

At the sensor level, the solution was to use a flexible pressure sensor based on ahgned-CNTs/PDMS nanocomposites (carbon nanotubes (CNTs) embedded into polydimethyl-siloxane (PDMS) elastomer). The pressure sensor was based on the capacitive principle (Fig. 11.20). The sensor design used a close box with air trapped inside (dielectric) at a specific pressure (P ). As the outside pressure varies (P, the box deflects due to the pressure differential between the inside (reference pressure) and the outside danain. 

Wardle, B.L., Rocha, L.A., 2012. Flexible pressure sensors modeling and experimental characterization. Procedia Eng. 47, 1177-1180. Elsevier B.V. Available from http // linkinghub.elsevier.com/re trieve/pii/S1877705812044244. 

Reprinted from Sepulveda, A., 2013. Use of Nanocomposites for Flexible Pressure Sensors. University of Minho, Portugal. Available from http //hdl.handle.net/1822/34582 http // repositorium.sdum.uminho.pt/. 

Die Fabrik auf dem Chip, Spektrum der Wissenschafi, October 2002 Miniaturization and modularization of parts of future chemical apparatus general advantages of micro flow expert opinions specialty and fine chemical applications leading position of German technology flexible manufacture large-capacity micro reactors reformers for small-capacity applications compatible and automated micro-reaction systems process-control systems temperature and pressure sensors [209]. 

Fig. 15. Fiber-optic pressure sensor. As light passes into a cavity resonator formed by a glass substrate and a flexible diaphragm, it is reflected from both surfaces, forming an interference pattern that changes as the diaphragm flexes with pressure changes. (Yazbak, Foxboro, Massachusetts)...

Fig. 6.11. Capacitive pressure sensor with flexible diaphragm...

Fig. 16.1. A flexible, large-area pressure sensor. A plastic film with organic transistors (1),...

Fig. 6. Schematic design of a pressure sensor. A flexible stainless steel membrane interfaces the pressure-sensitive elements (bridged piezo-resistors) from the measuring liquid. Some products contain the amplifier electronics in the housing and are (somehow) temperature compensated. The shown 2-strand cabling mode resulting in a current signal is very convenient...

The first example is a technology originally patented by S. Suzuki et al., Hitachi Ltd., Japan [49]. Their solution for absolute pressure sensors, as well as for relative pressure sensors, is shown in a cross-sectional view in Figure 5.1.15. The piezoresistive silicon sensor element is anodically bonded to a thick glass part that constitutes the vacuum reference volume in the absolute pressure sensor or that contains a hole as a pressure inlet port for the relative pressure sensor. The pressure sensor die is typically housed in a cavity package with pressure inlet ports as part of the body. The surface of the sensor element is usually protected with a gel or other flexible material for corrosion resistance. 

Figure 1 illustrates the operational principle of hydrogel-based sensors. Pressure sensor chips with a flexible thin silicon bending plate and with an integrated piezoresistive Wheatstone bridge inside this plate have been employed as... 

In this section, we describe a solution that employs a net-shaped structure to make flexible electronic film devices conformable to three-dimensional surfaces [18]. Although the base films we presently use are of polyimide and poly(ethylenenaph-thalate) (PEN) — materials that are stiff and not inherently stretchable in a rubberlike sense — our solution includes struts of network structures that twist with the application of tension, as can be seen in Figure 6.3.7. Due to this three-dimensional strut deformation, the whole network structure functions electrically with a unidirectional extension of 25%. We have implemented the pressure sensor network on the surface of an egg and have obtained pressure images in this configuration. 

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. 

Includes specific examples of radio-frequency ID lags, chemical and pressure sensors, flexible scanners, and display technology... 

All these findings contribute to new opportunities for the fabrication of flexible and efficient devices, with small dimensions, that may have potential applications for the fabrication of all-plastic sensing devices [34]. In particular, for strain/pressure sensors, the use of conducting polymers instead of metals allows to apply a pressure on the device without risks of irreversible damage to the contacts. 

Moreover, it may also be possible in the next few years to develop electronic skin made entirely out of organic transistors. In particular the possibility of developing strain and pressure sensors that can simultaneously act as switches and as sensors, without the need of any further sensing element, will be an interesting possibility. Furthermore, flexible chemosensitive transistors, biosensors, and temperature sensors could be developed using the same technologies allowing new features for this application. 

Quartz and piezoelectric ceramic crystals have more temperature independent constants than PVDF, so they are used for force and acceleration transducers. However, PVDF films can be used for large area flexible transducers. Their sensitivity to stress or strain allows the construction of pressure sensors (using the J33 coefficient), and accelerometers by mounting a seismic mass on the film. PVDF electrets are particularly suited for large area hydrophones (Fig. 12.21) that detect underwater signals. Their... 

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