In the paper the SPICE model of functionally dependent voltage and current sources is proposed, which is used in the process of schematic simulation of impedance signal converters. This simulation allows analyzing the signal conversion parameters, functional analysis of circuit decisions, optimization of operating modes, etc. The results of model research give an opportunity to calculate the influence of interferences of harmonic signals of activating sources used in signal converters of impedance
In this paper, the results of the development and modeling measurement of impedance converters are presented. The main nodes, the parameters of which are decisive in terms of operation accuracy of the impedance measuring converters, are quadrature synchronous detectors and integrators of the detected signal.
For nowadays the main goal for using the sensors are the investigations the new gas sensitive materials. Optical gas sensors are characterized by most of the high response. Such sensors distinguished by the high sensitivity, selectivity and stability and have long-term operation1. The principle of operation is based on the absorption of NH3 gas by sensitive element of primary transducer and changing the spectral characteristics. Principle of gas sensor operation is based on the registration of shift of the wavelength minimum in spectral characteristics of cholesteric-nematic mixture (CNM). In paper as sensitive material used the CNM on the basis of BLO-61 cholesteric liquid crystal (CLC) with 5CB nematic liquid crystal (NLC) doped by single and multiwall carbon nanotubes. The optimal nanocomposite structure composition to obtain the maximum value of spectral sensitivity coefficient was determined. In paper was found the increasing the nanotubes concentration in CNM leads to increasing the spectral sensitivity coefficient independently of 5CB concentration in CNM, but the maximum nanotubes concentration was chosen to take in to account the optical transparency of experimental samples. Gas sensitive material on the basis of cholesteric-nematic mixture doped carbon nanotubes for optoelectronic NH3 gas sensor.
In paper the concept of interaction of cholesteric liquid crystals (CLC) with creatinine and urea to designing the active medium material for optical sensor of biological substances are presented. It is shown that there is a general tendency to reduce the pitch of supramolecular helical structure versus of increasing of concentrations of aqueous solutions for all investigated substances. A decision to designing the scheme of signal converter of optical sensors with frequency selection is proposed. In basis of the proposed decision is impedance converter provided the inductive nature of the impedance circle of load photodiode and therefore suppressing of direct component of the photocurrent.
It has been studied the spectral characteristics of the porous silicon dioxide and cholesteric liquid crystal. It has been shown that doping of the EE1 cholesteric liquid crystal with Fe3O4 magnetite nanoparticles doesn’t shift significantly the position of the transmittance minimum of the material. It has been found that the deformation of chiral pitch of cholesteric liquid crystal with magnetite is observed in case of doping of porous nanocomposite host with following shifting of minimum of transmittance into short wavelength direction. It has been shown that influence of carbon monoxide on optical characteristics of the cholesteric liquid crystal with magnetite can be explained by the interaction of CARBON MONOXIDE molecules with magnetite nanodopants.
The temperature-concentration dependence of the field hysteresis loop ((delta) U) in nematic- cholesteric mixtures was researched. The matrices were the mixtures of cianobipheniles in which helical structure was created by the addition of optically active dopants (0.4 ... 2.5 weight%) or addition of non-liquid crystal material BIXH-3. It was shown that the magnitude of (delta) U decreases with the increasing of a temperature. The maximum of the (delta) U can be attained by the change of the concentration of the dopant in mixtures.
The field hysteresis of the cholesteric-nematic transition (CNT) in mixtures with small (up to 2 weight%) maintenance of optically active material is being researched. It is shown that the relative magnitude of the loop of the hysteresis and (delta) U depends on the ratio d/P, (gamma) equals (root)K22/K33 and surface free energy. In the case of fixed magnitude of the surface free energy the ratio of constants of the elasticity and of the liquid crystal material gives a substantial magnitude of the constructive parameters of the display d/Po, which gives us a maximum of the (delta) U. The influence of the temperature dependence of the constants of the elasticity and step of the induced spiral on the temperature dependence (delta) U takes place.
Correlation of structure of nematic-cholesteric mixtures and physical constants such as dielectric anisotropy (Delta) (epsilon) , microscopic force of twist (Beta) , coefficients of twist elasticity K22 is investigated.
Hysteresic properties of cholesteric-nematic phase transition in liquid crystals is investigated. It is established that the surface orientation influences the relative value of the hysteresis loop. The strongest dependence of the relative value of the hysteresis loop from the concentration of cholesteric admixture was observed for the orientation coating on the basis of SiO
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.