Humidity sensors materials polymers

Fundamental concepts of the molecular layering method have been developed and applied by the team headed by Professor Valentine Aleskovsky in Russia. This method, similar to atomic layer epitaxy and atomic layer deposition, has been used to create monolayers on oxides and polymers as humidity sensors, flame retardants, and agents to enhance sintering in ceramic materials. 

Nieuwenhuizen and Harteveld [92] have realized a nerve agent dosimeter gas sensor based on the strong interaction between certain metal ions and organophosphorus compounds. In this case, the sensor material contains La(III) 2-bis(carboxymethyl)amino hexadecanoic acid and different factors such as humidity, concentration and layer thickness have been studied and optimized. Using a combination of a metallic complex with a molecular-imprinted polymer, a very sensitive sensor was developed for the detection of soman, a chemical warfare agent (the detection limit was 7 ppt) [93]. The biosensing material is based on a polymer coated onto a fiber-optic probe modified with a luminescent europium detection complex. This complex was... 

The fabrication of humidity sensors on silicon chips has recently become possible using 1C. production technology [37, 49], This realizes a small, low cost humidity sensor, and makes it possible to integrate the humidity sensor with other sensors or signal-handling circuitry on the same chip. A new integrated temperature and humidity sensor developed by Yamamoto et al., consists of a polymer capacitor on the p-n diode of a temperature sensor [50] as illustrated in Figure 20-33. A thin film of polyimide is used as the moisture-sensitive material... 

Since protection of individuals and the environment has become more important, improved sensors to measure chemical and physical changes such as chemical spedes, temperature, pressure, or humidity are required. Much research has been carried out to apply conducting polymers as sensor materials. 

The absorption of water by polymers is especially suited to the development of a capacitive humidity sensor based on the high dielectric constant of water, since capacitance depends on the area, the thickness, and the dielectric constant of a dielectric. Uptake of water causes an increase in the dielectric constant followed by an increase in capacitance. Polyimide is a suitable sensitive material, but so are certain inorganic ceramics such as AI2O3 [142] and low-density Ta205, which change their capacitance with the formation of water dipoles. Low-density Ta20s layers can be formed by anodic oxidation of sputtered tantalum films, whereas polyimide films are deposited by spin coating and subsequent polymerization. 

Chatzandroulis S, Tegou E, Goustouridis D, Polymenakos S, Tsoukalas D (2004) Capadtive-type chemical sensors using thin sUicon-polymer bimorph membranes. Sens Actuators B 103 392-396 Chen Z, Jin M-C (1992) An alpha-alumina moisture sensor for relative and absolute humidity measurement In Proceedings of the 27th annual conference of IEEE Industry Application Society, Houston, TX, vol 2, pp 1668-1675 Chen Z, Lu C (2005) Humidity sensors a review of materials and mechanisms. Sens Lett 3(4) 274—295 Chen Z, Jin M-C, Zhen C (1990) Humidity sensors with reactively evaporated Al Oj films as porous dielectrics. Sens Actuators B 2 167-171... 

Sakai Y (1993) Humidity sensors using chemically modified polymeric materials. Sens Actuators B 13(14) 82-85 Sakai Y, Sadaoka Y, Ikeuchi K (1986) Humidity sensors composed of grafted copolymers. Sens Actuators 9 125-131 Sakai Y, Sadaoka Y, Matsuguchi M (1996) Humidity sensors based on polymer thin films. Sens Actuators B 35-36 85-90... 

Capacitive humidity sensors commonly contain layers of hydrophilic inorganic oxides which act as a dielectric. Absorption of polar water molecules has a strong effect on the dielectric constant of the material. The magnitude of this effect increases with a large inner surface which can accept large amounts of water. An example of this type of dielectric is porous j8-alumina. Colloidal ferric oxide, certain semiconductors, perowskites and certain polymers have also been used. /1-alumina is characterized by ionic conductance. Materials of this type can be characterized by a complex resistance composed of real (ohmic) as well as capacitive terms. The behaviour of such solids can be symbolized by a model and an associated equivalent circuit as given in Fig. 5.8. 

Raw material comonomer for ion exchange resin, comonomer for functional polymer, humidity sensor. 

Conductometric relies on the measurement of either conductivity or resistivity. This type of sensor comprises a capacitor that changes its capacitance when exposed to the desired analyte. The capacitance of the sensor changes due to a selectively absorbing material such as polymers or other insulators. These absorbing materials serve as the dielectric layer of the capacitor and their permittivity changes with exposure to the analyte. These sensors are commonly used to detect humidity as well as carbon dioxide and volatile organic compounds (Patel et al., 2003). In the humidity sensor case, the dielectric layer comprises a water-sensitive polymer (Lazarus and Fedder, 2011). 

Humidity - [SIMULTANEOUS HEAT AND MASS TRANSFER] (Vol 22) -ceramic sensors for [CERAMICS - ELECTRONIC PROPERTIES AND MATERIAL STRUCTURE] (Vol 5) -effect on barrier properties [BARRIER POLYMERS] (Vol 3) -sensors for [SENSORS] (Vol 21)... 

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