Electro-optical Methods Research Articles

Single ferroelectric liquid crystal compounds targeted for optical voltage sensing

Nine compounds containing fluorine or chlorine atoms in the lateral position in the rigid core with a chiral terminal octyloxy-chain were synthesized mainly using Suzuki-Miyaura coupling, Mitsunobu, hydrogenation, and esterification reactions. New compounds were investigated using polarized optical microscopy (POM), differential scanning calorimetry (DSC), spectrophotometry, and electro-optical methods. A computational analysis of the effect of lateral substitution by halogen atoms on the phenyl ring on the dipole moment of the compound was provided and discussed. The designed compounds exhibit a wide temperature range of the ferroelectric phase (>40.0 °C), a low melting point (in most cases below 50.0 °C), low melting enthalpy (around 10.0–20.0 kJ/mol), a short helical pitch (in most cases below 200 nm at room temperature) and high tilt angle that ensures a cone angle of up to 90°; all those properties make them of great potential for the deformed helix ferroelectric (DHF) mode. Revealed features allow synthesized compounds in fully integrated polarization-based photonic transducers to have excellent linearity and the highest sensitivity observed in ferroelectric liquid crystals for DHF mode. For the first time, the DHF effect was reached for the single molecule FLC material in a broad temperature range down to 38 °C. These findings pave the way for a new class of optical sensors for, among others, industrial monitoring networks and brain/machine interfaces with unprecedented performance.

Liquid crystal mixtures with the chiral benzoate dopant

ABSTRACT The results of studies conducted by means complementary methods: differential scanning calorimetry, transmitted light intensity measurements, polarized optical microscopy and electrooptical methods of two new liquid crystal mixtures are presented. The investigated mixtures consist of achiral thiosobenzoates, 7OS5 and 8OS5, and a chiral addition of benzoate, MHOBCO6. In all mixtures there is a wide low temperature range of the existence of the ferroelectric SmC* phase.

Drone and Controller Detection and Localization: Trends and Challenges

Unmanned aerial vehicles (UAVs) have emerged as a rapidly growing technology seeing unprecedented adoption in various application sectors due to their viability and low cost. However, UAVs have also been used to perform illegal and malicious actions, which have recently increased. This creates a need for technologies capable of detecting, classifying, and deactivating malicious and unauthorized drones. This paper reviews the trends and challenges of the most recent UAV detection methods, i.e., radio frequency-based (RF), radar, acoustic, and electro-optical, and localization methods. Our research covers different kinds of drones with a major focus on multirotors. The paper also highlights the features and limitations of the UAV detection systems and briefly surveys the UAV remote controller detection methods.

Electron-optical methods for tubers quality diagnosing

The tubers quality assessment and indicators are presented in the article. The world experience of electron-optical methods using for instrumental diagnostics of potatoes ripeness and commercial quality, the feature of which is to determine the tuber quality without violating its physical integrity, is described. A brief description of each group of electro-optical methods is given. The use of combined methods is proposed to increase the accuracy of tubers sensing, in particular, when creating multi-parameter sorting devices. Due to the complexity of the potato sensing process, software and hardware are required, designed on the principle of the biological neural networks organization and functioning.

Synthesis and mesomorphic properties of new organosiloxane chiral calamitic liquid crystals

A new chiral calamitic compound consisting of a phenyl core that is connected through ester linkers to a benzoate carrying a chiral (S)-2-methylbutoxy group at one side and a biphenyl carboxylate with an undecenyloxy chain at other side has been synthesized. Additionally, the siloxane substituted derivatives and a dimer with these two identical chiral calamitics linked by a disiloxane spacer have been obtained via hydrosilylation reaction to study the effect of combining the chiral moiety and siloxane segments within the same structure on liquid crystalline properties. The chiral calamitic compound and derivatives with a siloxane end-group or a siloxane spacer have been characterized using classical spectroscopic methods (1H NMR, 13C NMR, 29Si NMR and MS) and elemental analysis (EA). The liquid crystalline properties of all new compounds were investigated by differential scanning calorimetry, optical polarizing microscopy, X-ray scattering and electro-optic methods. With the introduction of a siloxane end-group to the vinyl-terminated calamitic compound exhibiting enantiotropic chiral nematic phase (N*) and chiral tilted smectic phase (SmC*), the occurrence of stable smectic phase was strongly promoted. In a similar way, the dimer with two identical calamitic mesogens connected by a disiloxane spacer exhibited a wider smectic mesophase interval in addition to the presence of N* mesophase. The new mesogens exhibit a ferroelectric switching with PS of around 200 nC cm−2 in their chiral tilted smectic (SmC*) mesophase range. The transition temperatures of organosiloxanes are considerably lower than that of olefinic precursor.

Diamagnetic anisotropy and rotational viscosity of 6CHBT nematic liquid crystal

Nematic liquid crystal with polar terminal NCS group was studied by using acoustic and electro-optical methods. Experimental results on rotational viscosity have been obtained by two methods. The anisotropy of diamagnetic susceptibility of the studied LC with temperature variation was determined based on the comparison of these methods. The present results may be useful for testing physical models of the orientation dynamics of nematic liquid crystals in alternating electric and magnetic fields.

Electro-Optical Diagnostics at KARA and FLUTE – Results and Prospects

Electro-optical (EO) methods are nowadays well-proven diagnostic tools, which are utilized to detect THz fields in countless experiments. The world’s first near-field EO sampling monitor at an electron storage ring was developed and installed at the KIT storage ring KARA (Karlsruhe Research Accelerator) and optimized to detect longitudinal bunch profiles. This experiment with other diagnostic techniques builds a distributed, synchronized sensor network to gain comprehensive data about the phase-space of electron bunches as well as the produced coherent synchrotron radiation (CSR). These measurements facilitate studies of physical conditions to provide, at the end, intense and stable CSR in the THz range. At KIT, we also operate FLUTE (Ferninfrarot Linac- und Test-Experiment), a new compact versatile linear accelerator as a test facility for novel techniques and diagnostics. There, EO diagnostics will be implemented to open up possibilities to evaluate and compare new techniques for longitudinal bunch diagnostics. In this contribution, we will give an overview of results achieved, the current status of the EO diagnostic setups at KARA and FLUTE and discuss future prospects.

Review of surface transient charge measurement on solid insulating materials via the Pockels technique

Surface charges accumulated on solid insulating materials in electrical apparatuses and electronic devices could distort the initial electric field and severely damage the insulation performance. Accurate transient surface charge measurement is critical to determine the mechanisms of charge transport and flashover occurrence, and estimate surface insulation strength under high voltage. The measurement technique based on the Pockels electro-optic effect is considered as the only approach for 2-D dynamic charge distribution behaviour so far, and it has good capability to avoid original electric field distortion caused by conventional methods featured by metal probes. This paper reviews recent progress of the non-invasive dynamic surface charge measurement systems on the Pockels technique. We focus especially on typical systems with transmitting and reflecting configurations and the frequently used fast inversion algorithms. It can be inferred that higher spatial-temporal resolution, higher signal-to-noise ratio, and better compatibility for both transparent and opaque materials are the future development trends, which greatly depend on multiple technological breakthroughs at impact-resistant electro-optic crystals, advanced high-speed photography and high-performance inversion algorithms. In addition, the recent studies on transient behaviour of surface discharge, together with the present limitation and future prospects are discussed. It is expected that more ideas will be inspired in transient surface charge measurement by the Pockels technique and other relevant electro-optic methods.

Characterization and applications of a newly formulated ferroelectric liquid crystal mixture W315

In this article, we present the formulation, characterization, and application of a newly prepared ferroelectric liquid crystal (FLC) mixture namely W315 composed of pyrimidine compounds. The characterization of FLC material under investigation has been performed through polarizing optical microscopic, dielectric spectroscopic, differential scanning calorimetric and other electro-optical methods. The temperature dependence of the dielectric loss factor of the homogeneously aligned FLC sample shows a phase change from Smectic C* to Smectic A that further confirms the transition temperature of FLC material. From electro-optical observations, the values of spontaneous polarization, rotational viscosity, and response time of W315 were found to be 8.03 nC/cm2, 86.56 mPa s, and 890 µs respectively. The material constants of FLC material under investigation can be utilized in various FLC based faster displays and non-display devices.

Theoretical Modelling of Liquid Crystal Electro-Optical Material Display Elements to Achieve Optimal Low Power Consumption Ship Stealth

Advanced optical stealth techniques are of growing importance in the role of manned and unmanned aircraft or ship platforms. We consider here the concept of using passive reflective display elements rather than high power active light projection to achieve a low observable camouflaged ship platform. This paper presents practical consideration towards minimal radiated power user-driven requirements using adaptive liquid crystal electro-optical methods. Optical reflectivity for a multi-layer liquid crystal cell structure composed of a glass/ ITO/ aligning layer/ liquid crystal/ aligning layer/ ITO/ glass will support optical guided modes. Reflectivity as a function of angle and voltage are compared with theory generated from a Fresnel matrix formalism. Voltage device modulated reflectivities are then simulated across a ship platform to evaluate this method for low power consumption, with minimal radiated optical radiation.

Phase transitions in three-component mixtures containing alkoxybenzoic acids with a chiral material

ABSTRACTThe paper contains results of investigation into phase polymorphism and electro-optical properties of ternary mixtures composed of two mesogenic 4-n-alkoxybenzoic acids: dodecyloxybenzoic acid (12OB) and tetradecyloxybenzoic acid (14OB) with a molar ratio of 1:1 and chiral liquid crystal (S)-4-(1 methylheptyloxy)biphenyl-4'-(heptyloxyphenyl)-4-carboxylate (MHOBOPO7). Mixtures with the following contents of the mole fraction of the chiral compound in relation to the content of acids OB: were prepared; A–0.50; B–0.33; C–0.20; D–0.10; E–0.05; F–0.025. The polymorphism of the mixtures was determined by three complementary methods: Differential Scanning Calorimetry (DSC), Transmitted Light Intensity (TLI) and Polarizing Optical Microscope (POM). The extent of the smectic phase C and the nematic phase were increased. The smectic C phases in mixtures A, B, C, D showed a clear ferroelectric character. Ferroelectric properties of mixtures were determined by electro-optical methods.

ZnO/FLC nanocomposites with low driving voltage and non-volatile memory for information storage applications

Nanocomposites comprises of nano sized zinc oxide (ZnO, size ~10 nm) particles and ferroelectric liquid crystal (FLC) material have been prepared and studied. The concentration of the dopant (ZnO nanoparticles) in FLC matrix varied from 0.0 to 1 wt%. Distinct nanocomposites have been used to fabricate memory device and studied through dielectric spectroscopy, optical microscopy and electro-optical methods to explore electro-optic and memory parameters. Experimental results reveal that doping of ZnO nanoparticles in FLC leads to long lasting memory and low deriving voltage in nanocomposites. The achieved prolonged memory effect in nanocomposites may attribute to the charge transfer at the interfaces. Another reason, application of applied field may lead to ion trapping effect at ZnO surface which in turn minimize the depolarized field and enhance the memory effect in nanocomposites.

Enhancement of dielectric and electro-optical parameters of a newly prepared ferroelectric liquid crystal mixture by dispersing nano-sized copper oxide

ABSTRACT Here, we present the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared ferroelectric liquid crystal (FLC) mixture, namely W302. The FLC mixture, comprising of pyrimidine compounds, was characterised through dielectric spectroscopy, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and other electro-optical methods. The material parameters such as spontaneous polarisation, rotational viscosity, response time and tilt angle of W302 were found to be 14 nC/cm2, 240 mPa.s, 150 µs and 28ᴼ, respectively. The phase transition temperatures of W302 were observed through DSC and further confirmed by the dependence of dielectric loss factor in homogeneously aligned FLC sample with temperature. We also demonstrate the observance of a low-frequency dielectric relaxation mode due to the unwinding of the helix, called as partially unwound helical mode (p-UHM) along with Goldstone mode. The behaviour of p-UHM has been systematically studied with temperature and applied bias field. Further, dispersion of nCuO into host W302 has shown a significant increase in dielectric permittivity. Also, the p-UHM relaxation peak in the dielectric regime has disappeared with the incorporation of nCuO. These studies would be useful to fabricate better electro-optical devices for display, switching and beam steering applications. The formulation and characterization of a ferroelectric liquid crystal (FLC) mixture W302 composed of pyrimidine compounds is presented. Then, we observed the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared and characterized FLC mixture.

Systematic study of the chiral smectic phases of a fluorinated compound

ABSTRACTPhysical properties of the partially fluorinated compound 3F5FPhF, with hockey stick-like molecules, were studied by complementary methods. Apart from the already reported paraelectric SmA*, ferroelectric SmC* and antiferroelectric SmC*A phases, the presence of the smectic C*α subphase in the phase sequence was proved by differential scanning calorimetry, polarising optical microscopy, electro-optic and dielectric spectroscopy methods. The temperature dependence of the smectic layer thickness and correlation length of the lateral short-range order was determined by X-ray diffraction. Based on dielectric measurements three relaxation processes were revealed in the antiferroelectric SmC*A phase (two collective: PL, PH and one molecular: s-process), two collective ones (Goldstone and soft modes) were found both in the ferroelectric SmC* phase and SmC*α subphase while one relaxation process (soft mode) in the paraelectric SmA* phase. The results were compared with that obtained for other structurally similar compounds, and it was shown that even addition of one methylene group to the side chain influences much on the physical properties.

Nonvolatile waveguide transmission tuning with electrically-driven ultra-small GST phase-change material

Low-power reconfigurable optical circuits are highly demanded to satisfy a variety of different applications. Conventional electro-optic and thermo-optic refractive index tuning methods in silicon photonics are not suitable for reconfiguration of optical circuits due to their high static power consumption and volatility. We propose and demonstrate a nonvolatile tuning method by utilizing the reversible phase change property of GST integrated on top of the silicon waveguide. The phase change is enabled by applying electrical pulses to the μm-sized GST active region in a sandwich structure. The experimental results show that the optical transmission of the silicon waveguide can be tuned by controlling the phase state of GST.

Imine based chiral liquid crystals: Effect of varying the terminal substituent and orientation of ester linking unit

New liquid crystalline compounds composed of three-benzene-ring molecular core comprising both the imine and ester linkage units, (S)-3,7-dimethyloctyloxy chiral unit at one of terminals and n-dodecyl/dodecyloxy group as other side chain have been synthesized and characterized to study the effect of varying terminal chains, the orientation of polar ester linking group and the presence of molecular chirality on mesophase properties of imine based calamitic compounds. The liquid crystalline properties of the compounds were investigated by differential scanning calorimetry, optical polarizing microscopy and electro-optic methods. As a result of the strong effect of chirality of (S)-3,7-dimethyloctyloxy chain, all Schiff bases (imines) exhibit enantiotropic chiral smectic C (SmC*), chiral nematic (N*) as well as SmX phase just below the SmC* phase and blue phase (BP) appearing monotropically. The SmC* phase shows ferroelectric switching behaviour with PS values in the range 70–130 nC cm−2. The alteration of the n-alkyl tail with an alkoxy chain gives rise to a significant increase up to 30 °C in mesomorphic transitions. The change in the orientation of polar ester linking group has no effect on the type and sequence of observed LC phase. As compared with (S)-4-(3,7-dimethyloctyloxy)phenol based imine derivatives (7a, 7b), the chiral nematic (N*) mesophase temperature range of (S)-4-(3,7-dimethyloctyloxy)benzoate based compounds (8a, 8b) significantly broadened. Additionally, a decrease on the phase transition temperatures occurred with regardless of introducing n-dodecyl/dodecyloxy group as side chains.

Degradation behavior of deep UV-LEDs studied by electro-optical methods and transmission electron microscopy

Degradation mechanism of 265-nm deep ultraviolet light emitting diodes (UV-LEDs) has been investigated by means of electroluminescence, current-voltage measurement, capacitance-voltage measurement, and transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectrometer (EDAX). It is revealed that a major degradation mode of UV-LEDs may be the leakage current induced optical degradation. The current pathway is demonstrated by TEM with EDAX, indicating that the contact metals can partially interact with p-type materials, which accelerate the degradation of LEDs. The presented results can help to understand the degradation mechanisms and improve the reliability of deep UV-LEDs.

Manifestation of strong magneto-electric dipolar coupling in ferromagnetic nanoparticles−FLC composite: evaluation of time-dependent memory effect

ABSTRACTRod-shaped 5 wt.% copper-doped ZnO (ZnO:Cu2+) ferromagnetic nanoparticles (NPs), prepared by hydrothermal method, were dispersed in ferroelectric liquid crystal (FLC) named Felix 17/100. The effect of ferromagnetic NPs on the physical properties of FLC material (Felix 17/100) has been investigated by dielectric, electro-optical and polarising optical microscopic methods. A noteworthy time-dependent memory has been observed in the NPs-dispersed FLC composite attributed to the coupling of magnetic field associated to NPs with the director orientation of FLC. Improvement in spontaneous polarisation and dielectric susceptibility of FLC material has been ensued with the addition of ferromagnetic NPs. Faster electro-optic response, at lower applied voltage, has also been observed in NPs-dispersed FLC composite. These changes are accredited to the magneto-electric dipolar coupling existing due to the interactions between magnetic-dipole and electric-dipole moments of magnetic NPs and FLC material, respectively. The formation of periodic domains capable to show memory effect has been observed in composite. The observed time-dependent memory was confirmed by dielectric and electro-optical methods. FLC material enriched with the properties of ferromagnetic NPs can be utilised in advanced multifunctional optical devices, time-dependent memory-based security devices and computational purposes.

Dynamic Kerr effect in a strong uniform AC electric field for interacting polar and polarizable molecules in the mean field approximation.

Analytical formulas for the electric birefringence response of interacting polar and anisotropically polarizable molecules due to a uniform alternating electric field are derived using Berne's forced rotational diffusion model [B. J. Berne, J. Chem. Phys. 62, 1154 (1975)] in the nonlinear version described by Warchol and Vaughan [J. Chem. Phys. 71, 502 (1979)]. It is found for noninteracting molecules that the signal consists of a frequency-dependent DC component superimposed on an oscillatory part with a frequency twice that of the AC driving field. However, unlike noninteracting molecules, the AC part strongly deviates from its dilute counterpart. This suggests a possible way of motivating new experimental studies of intermolecular interactions involving electro-optical methods and complementary nonlinear dielectric relaxation experiments.

Study of the kinetics of space charge formation in colloidal magnetic nanoparticles in liquid dielectrics

The relaxation time of a near-electrode space charge in magnetic colloids based on dielectric liquids is experimentally established via electrooptical methods as being in the range of 0.05–0.3 s depending on the conductivity of the sample. The results agree with the data of the electrosurface effect in magnetic colloids.