Applications humidity sensors

In several cases application of various additives to the surface of a semiconductor adsorbent, specifically adsorbing or reacting with particles to be detected enables one to improve selectivity. As an example we can mention the use of hygroscopic salts to bind water in humidity sensors, the application of particles of sulfanilic acid to the surface of hhO to detect NO2 [10]. However, the high operational temperature in majority of semiconductor sensors deprives the method of specific surface additives of its general character. 

The physical and chemical properties of MgO films prepared by the sol-gel technique were the area interest of the examinations presented by Shukla75. The aim of mentioned work was to produce films with nano size particles so as to employ them for the sensor applications, as adsorption in such films increases many folds due to the increase of surface area. Infra-red spectroscopic studies indicated the presence of solvent in the precursor, which helped in decomposition to nano-particles during nucleation of the film. The MgO sol-gel films were deposited on the glass rod bend in U-shape for humidity sensor. 

Most microhotplate-based chemical sensors have been realized as multi-chip solutions with separate transducer and electronics chips. One example includes a gas sensor based on a thin metal film [16]. Another example is a hybrid sensor system comprising a tin-oxide-coated microhotplate, an alcohol sensor, a humidity sensor and a corresponding ASIC chip (Application Specific Integrated Circuit) [17]. More recent developments include an interface-circuit chip for metal oxide gas sensors and the conccept for an on-chip driving circuitry architecture of a gas sensor array [18,19]. 

Apart from the aforementioned most frequently used sensor technologies, also selective electrochemical sensor combinations have been commercialised for use in dedicated applications. The combination of electrochemical CO, H2S, SO2 and NH3 sensors was used for quality and freshness control of foods like fish [98] and meat [99]. Combinations of MOSs and MOSFETs supplemented with a selective IR absorption sensor for carbon dioxide and a humidity sensor for measuring relative humidity were also described [100]. 

Applications. The saturated salt sensor has certain advantages over other electrical humidity sensors, such as % RH instruments. Because the salt sensor operates as a current earner saturated with Li and Ci ions, addition of contaminating ions has little effect on its behavior compared to a typical RH sensor, which operates "starved" of ions and is easily contaminated. A properly designed saturated sail sensor is not easily contaminated since, from an ionic standpoint, it can be considered precontaminaied. 

Kusano, H. Kimura Shin, L Kitagawa, M. Kobayashi, H. Application of Cellulose Langmuir-Blodgett Films as Humidity Sensors, and Characteristics of the Sorption of Water Molecules into Polymer Monolayers. Thin Solid Films 1997, 295, 53-59. 

There are several applications of ZnO that are due to its excellent piezoelectric properties [28,164]. Examples are surface-acoustic wave (SAW) devices and piezoelectric sensors [28,165-167]. Typically, SAW devices are used as band pass filters in the tele-communications industry, primarily in mobile phones and base stations. Emerging field for SAW devices are sensors in automotive applications (torque and pressure sensors), medical applications (chemical sensors), and other industrial applications (vapor, humidity, temperature, and mass sensors). Advantages of acoustic wave sensors are low costs, ruggedness, and a high sensitivity. Some sensors can even be interrogated wirelessly, i.e., such sensors do not require a power source. 

Another successful application of capacitance-based sensing is in humidity and moisture monitoring. Humidity sensors have been developed for which... 

Recently the use of humidity sensors has greatly increased in a range of industries such as in the production of electronic devices, precision instruments and foodstuffs. As humidity is a permanent environmental factor, its measurement and/or control are of importance not only for human comfort but also for many industries and technologies. In recent years, major domestic applications of humidity sensors have been eg, automatic humidity control in air conditioners, automatic cooking by microwave ovens, and dew sensing on the cylinder heads of VTRs [1, 2]. 

A humidity sensor has to satisfy the following practical requirements (1) high sensitivity over a wide humidity range, (2) quick response, (3) good reproducibility and no hysteresis, (4) robustness and long life, (5) resistance to contaminants, (6) insigniHcant dependence on temperature, and (7) simple structure and low cost. For particular applications, other requirements should be satisHed, such as low power, low weight, or microprocessor compatibility. 

G. Wang, Q. Wang, W. Lu, J. Li, Photoelectrochemical study on charge transfer properties of Ti02-B nano wires with an application as humidity sensors . Journal of Physical Chemistry B, 110, 22029-22034, (2006). 

The range of sample characteristics and manner of their detection, is much larger than can be realistically addressed in the space of a single chapter. We will confine this chapter mainly to the chemical sensor research areas discussed in other chapters in this volume, dividing them into electrical, optical, and mass and thermal measurements. Our focus will furthermore be on the generic chemical and physical phenomena upon which such measurements can be based, as opposed to the alternative organization that would address chemical sensors in the context of their application (i.e, auto exhaust sensor, clinical diagnostic sensor, environmental sensor) or of the kinds of samples detected (i.e, CO sensors, humidity sensor, biosensor, etc.), as used in a previous ACS Symposium Series volume on Chemical Sensors (D. Schuetzle, R. Hammerle, Eds., ACS Sympos. Ser. 309, 1986). 

Besides the applications for lighting and domes, transparent nanostructured Y-AI2O3 ceramics have various other applications, such as a humidity sensor of Y-AI2O3 [75]. Nanostructured Y AlaOs ceramics were prepared from Al-Sec-Butoxide (C12H27AIO3) by using a sol-gel process. The sensors had a long term stability of up to two years. 

Moneyron, J.E., de Roy, A., and Besse, J. P. 1991c. Protonic conductivity of hydrotdcite-type compound thick films Application to a humidity sensor. Solid State Ionics 46 175-81. 

Among the various categories of smart textiles and flexible materials, which include optically, mechanically, chemically, electrically, and thermally activated substances/ stmctures (Tao, 2001), several have shown large opportunities of applications in PPE. This includes wearable electronics, for example, physiological condition, temperature, and humidity sensors, power and data transmitters, and end-of-life indicators, which are the subject of the next chapter of this book. Various types of smart flexible materials have also found their way into PPE, for instance, as responsive barriers, self-decontaminating membranes, thermoregulating layers, and shock-absorbing patches. 

Rittersma ZM, Splinter A, Bodecker A, Benecke W (2000) A novel surface-micromachined capacitive porous silicon humidity sensor. Sens Actuators B 68 210-217 Sim J-H, Cho C-S, Kim J-S, Lee J-H, Lee J-H (1998) Eight beam piezoresistive accelerometer fabricated by using a selective porous silicon etching method. Sens Actuators A 66 273-278 Steiner P, Lang W (1995) Micromachining applications of porous silicon. Thin Solid Films 255 52-58... 

Foucaran A, Pascal-Delaimoy F, Giani A, Sackda A, Combette P, Boyer A (1997) Porous silicon layers used for gas sensor applications. Thin Solid Films 297 317-320 Foucaran A, Sorli B, Garcia M, Pascal-Delannoy F, Giani A, Boyer A (2000) Porous silicon layer coupled with thermoelectric cooler a humidity sensor. Sens Actuator A 79 189-193 Gabouze N, Belhousse S, Cheraga H (2005) CHx - Porous silicon structures for gas sensing applications. Phys Stat Solid C 2(9) 3449-3452... 

Buriak JM, Stewart MP, Geders TW, Allen MJ, Choi HC, Smith J, Raftery D, Canham LT (1999) Lewis acid mediated hydrosilylation on porous silicon surfaces. J Am Chem Soc 121 11491-11502 Connolly EJ, O Halloran GM, Pham HTM, Sarro PM, French PJ (2002) Comparison of porous silicon, porous polysilicon and porous silicon carbide as materials for humidity sensing applications. Sens Actuators B 99 25-30 Ftirjes P, Kovdcs A, Cs D, Addm M, Muller B, Mescheder U (2003) Porous silicon-based humidity sensor with interdigital electrodes and internal heaters. Sens Actuators B 95 140-144 Hedrich F, BiUat S, Lang W (2000) Structuring of membrane sensors using sacrificial porous silicon. Sens Actuators A 84 315-323... 

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