SmA Transition Research Articles

Mechanical and Fatigue Properties of Welded Fe-Mn-Si Shape Memory Alloys.

This paper presents the experimental results of a study evaluating the mechanical and fatigue performance of welded Fe-Mn-Si SMA. For the experimental study, welded and welded-and-heat-treated Fe-Mn-Si SMA specimens were fabricated, and fatigue tests were performed at various stress amplitudes. In addition, direct tensile tests and recovery stress tests were also performed to evaluate the material properties of Fe-Mn-Si SMAs. The elastic modulus, yield strength, and tensile strength of the welded specimens were reduced by 35.4%, 12.1%, and 8.6%, respectively, compared to the values of the non-welded specimens. On the other hand, the elastic modulus, yield strength, and tensile strength of the welded-and-heat-treated Fe-Mn-Si SMA specimens were increased by 18.6%, 4.9%, and 1.3%, respectively, compared to the values of the welded specimens. Both welded and welded-and-heat-treated Fe-Mn-Si SMAs failed at lower cycles than the conventional Fe-Mn-Si SMAs at the same stress amplitude. High-cycle fatigue failure, characterized by cycles exceeding 104, typically occurs at relatively low stress levels within the elastic region, whereas low-cycle fatigue failure, generally occurring within cycles below 104, involves high stress levels that encompass both elastic and plastic deformation. Regardless of the welding condition, the stress amplitude at which Fe-Mn-Si SMA transitions from high-cycle to low-cycle failure exceeded the yield strength.

Probing the mesophase formation in thermotropic liquid crystal HBDBA using temperature-dependent Raman spectroscopy and DFT method

Liquid crystalline properties of the synthesized liquid crystal (LC) N-(o-hydroxybenzylidene)-N′-(4-n-alkoxybenzylidene) azines (HBDBA) are probed thoroughly using the comprehensive array of techniques e.g. differential scanning calorimetry (DSC), differential thermal analysis (DTA), polarizing optical microscopy (POM), temperature-dependent Raman spectroscopy and density functional theory (DFT) method. In this study, intricate molecular interactions crucial for mesophase formation of liquid crystalline system HBDBA and molecular rearrangement that occurs during LC transitions are unravelled comprehensively. Remarkably, at the Cr → SmA phase transition, the peak position, linewidth, and intensity of signature Raman bands are prominently changed. A thorough analysis of Raman marker bands and DFT calculation confirm the disruption of intramolecular hydrogen bonds in HBDBA at the Cr → SmA transition. The conclusion of the present study enriches the understanding of the underlying mechanisms of mesophase formation and intricate molecular interactions and arrangement at the molecular level of the thermotropic LC.

Effect of disubstitution pattern of the terminal alkyl chains on the mesophase of liquid crystals based on lanthanide(III) complexes: A study of the thermal, emission and dielectric behavior

In the present work, new luminescent lanthanide complexes with extended mesomorphic range were prepared by coordination to lanthanide ions (Eu3+, Sm3+ and Tb3+) of the new 4-pyridone based organic ligands (L) with 3,4- (7-n) and 3,5-di(alkyloxy)benzyl (8-n) mesogenic groups and variable length (n = 12 or 14 carbon atoms) onto the benzyl unit. The cumulative results of the elemental analyses as well as the 1H, 13C NMR and IR spectroscopies support the structure of the organic derivatives and their lanthanide complexes [LnL3(NO3)3] (9-n/Ln and 10-n/Ln) described in this work. These complexes show characteristic lanthanide solid state emission, both at room and elevated temperatures corresponding to crystalline, glassy or liquid crystal states. The long range SmA phases displayed by all complexes were supported by a combination of characterization methods, including: differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and variable-temperature powder X-ray diffraction (XRD). This work shows that the number, substitution pattern and length of flexible alkoxy chains are important parameters to control the phase-transition characteristics of the lanthanide complexes. Complexes with 3,4-disubstituted pattern (9-n/Ln) show higher clearing temperatures (nearly 60 °C for Eu3+, 70 °C for Sm3+ and 85 °C for Tb3+ complexes) compared to their counterparts with 3,5-disubstituted pattern (10-n/Ln). Moreover, complexes 9-n/Ln crystallize when cooling their LC phase while complexes 10-n/Ln are stable in glassy state at room temperature as a consequence of the different close interdigitated molecular packing evidenced by XRD measurements. Dielectric spectroscopy was employed to detect the changes of order degree specific to each phases (crystalline, LC or isotropic). The variation of dielectric constant and the electrical conductivity versus temperature shows three transition intervals for selected complexes 10-14/Sm and 10-14/Tb, which delimit the main intervals: 45–60 °C, 90–110 °C; 140–160 °C corresponding to the Cr1-Cr2, Cr2 – SmA and SmA-Iso transitions, and agree very well with the DSC results. The change of characteristic time, obtained by Havriliak-Negami fit function, with temperature also provides a very good correlation with the DSC and POM results.

Negative group delay experimentation with tee connector and cable structures

The unfamiliar negative group-delay (NGD) phenomenon is experimented with structure constituted by tee-connectors and coaxial cables. The topology of the NGD generator is described. It consists of two parallel 50-Ω characteristic impedance cables. The S-parameter model in function of the cable physical lengths is established. The existence condition enabling to understand the NGD phenomenon is defined. A proof of concept simply is constituted by two three-port SMA connectors, three SMA transitions and 13-cm length cables. The NGD experimentation is performed from 1.5 GHz to 3.5 GHz. Tri-band NGD aspects in good agreement with the theory and simulation is observed experimentally. Particularly, high figure-of-merit NGD circuit with −3 ns NGD level, less than 2 dB insertion loss and 12 dB return loss around 3 GHz centre frequency is measured.

High-resolution birefringence investigation on the effect of surface-functionalized CdSe nanoparticles on the phase transitions of a smectic — A liquid crystal

The high-resolution optical birefringence study was carried out to experimentally study the impact of surface functionalized CdSe nanoparticles on the phase transitions of a smectic A liquid crystal 8CB (octylcyanobiphenyl). The birefringence data have then been used to probe the temperature variation of the nematic order parameter across both the nematic-isotropic (N − I) and the nematic-smectic A (N − SmA) phase transitions of 8CB + CdSe colloidal mixtures. With the inclusion of CdSe nanoparticles, both the N − I and the N − SmA phase transition temperatures have been observed to shift to lower temperatures as compared to the 8CB host, signalling the stabilization of the SmA phase. For 8CB + CdSe colloidal mixtures, the N − I transition is identified as weakly first order while the N − SmA transition remains continuous within the experimental resolution. From the detailed inspection of the optical birefringence data in close vicinity of the N − SmA transition, the upper limits for a possible latent heat for all colloidal mixtures have been derived. Also, the specific heat capacity critical exponent α values near the N − SmA transition for all compositions have been produced. it has been well established that the incorporation of CdSe nanoparticles to 8CB host leaves the N − SmA transition essentially bulk-like. A Landau-de Gennes type mean-field approach has also been used to describe our experimental data.

Design of Output‐Input Inversed Polarity Pulse Power Divider for Ultra‐Wideband Communications

The implementation of a output‐input inverse polarity pulse power divider based on the use of a SMA directly feed asymmetric coplanar stripline phase inverter for ultra‐wideband communication is proposed. The novelty of the proposed power divider can be demonstrated that the electromagnetic energy guided by the CPW divides naturally into the slots of two asymmetric coplanar striplines and the polarity of the input pulse be reversed by asymmetric coplanar stripline to SMA transition. SMA connectors are mounted directly to the output asymmetric coplanar striplines and seven pairs of metal rods are soldered vertically to the substrate with seven resistors on top for improving the isolation and matching performance. The simulated and measured result in frequency domain agree well showing equal power division with less than 2 dB of additional insertion loss and in‐phase for the outputs ports across the desired band of 0.4 GHz to 4.0 GHz (one decade) which indicates an ultra‐wideband feature. The return loss for all the ports and the isolation between the two output ports are better than 10 dB which demonstrates good matching and isolation performance. To illustrate the short pulse performance of the proposed power divider, Inverse Fourier Transformation is used to calculate the input and output signals. The Gaussian pulse with a −10 dB bandwidth is utilized as the stimulus signal and the port signals in time domain are derived from the measured scattering parameters and discussed. Time domain results show that the same magnitude of the pulse is obtained between the two outputs and the polarity of the output pulse has been inversed compared to the input one. Simulated and measured results in both frequency and time domain agree well and show the feasibility and validity of the proposed power dividers.

DESIGN of a 3‐DB directional coupler based on groove gap waveguide technology

AbstractIn this letter, a groove gap waveguide (GGW) based 3‐dB directional coupler is proposed. The designed component is composed of three parts: GGW structure, extra matching pins and GGW to standard SMA transition. The designed quadrature 3‐dB coupler is optimized to work in the Ku‐band covering 13–15 GHz. Measured results show that over 14.3% bandwidth, 20 dB isolation and 1.2 VSWR is achieved. The main advantage of GGW‐based components is that it does not require good electrical contact among different metallic parts of the structure which considerably simplifies the manufacturing processes and hence reduces cost especially for millimeter‐waves applications.

Effects of layer order on the mobility of mesogenic molecules in SmA liquid-crystalline emulsions

We fabricate smectic-A liquid-crystalline emulsions (SmA-LCEs) in which monodisperse 8CB-swollen micelles are dispersed in water. Synchrotron X-ray measurements reveal that the correlation length of the layer order in LCEs cannot diverge at the nematic (N)-SmA transition, and the saturated length linearly increases with the increase in the diameter of LC-swollen micelles. Moreover, we investigate the permeation of 7CB N molecules into 8CB SmA-LCEs by measuring the enhancement of the depolarized light scattering intensity due to the shift of the SmA-N phase transition, and confirm that the layer order suppresses the mobility of LC molecules in LCEs similar to the bulk state of SmA LCs. The mobility drastically accelerates near the SmA-N transition temperature due to the continuous extinction of the smectic layer order. The slow permeation process of 7CB is also confirmed via synchrotron X-ray diffraction examining the shrinkage of the smectic layer repeat distance, caused by intercalation of 7CB.

Dielectric behaviour and dechiralization lines dynamics of a pure Smectic-C* in confined geometry: onset of mesoscopic ferrielectricity

ABSTRACTDielectric behaviour of a new ferroelectric liquid crystal (CLF08) having large spontaneous polarisation (120 nC/cm2 at 110 Hz), short pitch and high purity, is studied in the frequency range 5 Hz to 1 MHz, in the smectic C* and smectic A phases using a 7-micron-thick cell in planar alignment. Dielectric permittivity, polarisation and optical measurements are investigated that shows complex ferroelectric behaviour. These experiments evidence the Goldstone and Soft mode relaxations far from the SmC*to SmA transition. The density of dechiralization lines is observed under polarised light microscope. Its behaviour under electric field exhibits a remarkable accordance with the dielectric response. These results are discussed in connection with a possible onset of ferrielectricity in the dechiralization lines system.

SHAPEMOL: a 3D code for calculating CO line emission in planetary and protoplanetary nebulae

Modern instrumentation in radioastronomy constitutes a valuable tool for studying the Universe: ALMA has reached unprecedented sensitivities and spatial resolution, while Herschel/HIFI has opened a new window for probing molecular warm gas (~50-1000 K). On the other hand, the software SHAPE has emerged in the past few years as a standard tool for determining the morphology and velocity field of different kinds of gaseous emission nebulae via spatio-kinematical modelling. SHAPE implements radiative transfer solving, but it is only available for atomic species and not for molecules. Being aware of the growing importance of the development of tools for simplifying the analyses of molecular data, we introduce shapemol, a complement to SHAPE, with which we intend to fill the so-far under-developed molecular niche. shapemol enables user-friendly, spatio-kinematic modelling with accurate non-LTE calculations of excitation and radiative transfer in CO lines. It allows radiative transfer solving in the 12CO and 13CO J=1-0 to J=17-16 lines, but its implementation permits easily extending the code to different molecular species. shapemol allows easily generating synthetic maps and line profiles to match against interferometric or single-dish observations. We fully describe shapemol and discuss its limitations and the sources of uncertainty to be expected in the final synthetic profiles or maps. As an example of the power and versatility of shapemol, we build a model of the molecular envelope of the planetary nebula NGC 6302 and compare it with 12CO and 13CO J=2-1 interferometric maps from SMA and high-J transitions from Herschel/HIFI. We find the molecular envelope to have a complex, broken ring-like structure with an inner, hotter region and several 'fingers' and high-velocity blobs, emerging outwards from the plane of the ring. We derive a mass of 0.11 Msun for the molecular envelope.

Design and characterisation model for a linearly polarised patch array fed by serial rectangular waveguide network

A novel method for considering radiating structures independently to their feeding networks is presented. The integration of both parts separately designed suffers a critical misalignment with the theoretical behaviour caused by the mutual coupling effects between adjacent elements. This method analyses radiated near E-field monitors to adjust the whole antenna after joining both independently designed parts. A linearly polarised patch array fed by a rectangular waveguide with internal coupling patches for X band (11–12 GHz) has been designed to validate the method performance. A double stacked microstrip patch structure with an integrated phase compensation microstrip line has been used as radiating element. The coupling patches inside the waveguide are connected to the external radiating patches by means of metallic probes. The presented method requires changes in the feeding structure as in the radiating elements. Several prototypes have been manufactured and measured: the feeding waveguide structure connectorised, the radiating patches connectorised, the union of both with SMA transitions and the final integration into the complete antenna. 18.5 dBi gain and 85% efficiency peak values, as well as 6% usable bandwidth have been experimentally achieved.

Existence of time lag in crystalline to smectic A (K–SmA) phase transition of 4-decyl-4-biphenylcarbonitrile (10CB) liquid crystal

This study explores the presence of time lag in crystalline to smectic A (K–SmA) phase transition of 4-decyl-4-biphenylcarbonitrile (10CB) liquid crystal. A non-isothermal heating and cooling study were performed for 10CB liquid crystal using calorimetric technique where heating scan was performed from 250 to 350 K, and cooling scan was performed from 350 to 250 K. A clear difference in K–SmA phase transition was observed between heating and cooling scans. An attracting inclination effect in K–SmA transition was observed on cooling which is completely absent on heating. The inclination of the K–SmA transition peak increases and shows an existence of time lag during cooling, whereas other family member shows no effect i.e., 8CB. K–SmA peak shows a lower enthalpy with higher activation when compared with 8CB. The presence of time lag and increase in activation can be explained in terms of the density and nature of the material.

4-[4-(Heptyloxy)benzoyloxy]phenyl 2-oxo-7-trifluoromethyl-2H-chromene-3-carboxylate

The title compound, C31H27F3O7, is a liquid crystal and exhibits enanti­otropic SmA and nematic phase transitions. In the crystal, the the 2H-chromene ring system makes dihedral angles of 54.46 (17) and 7.79 (16)°, respectively, with the central benzene ring and 4-(hept­yloxy)benzene ring. The three F atoms of the –CF3 group are disordered over two sets of sites, with an occupancy ratio of 0.62 (3):0.38 (3). The crystal structre features two pairs of C—H⋯O hydrogen bonds, which form inversion dimers and generate R 2 2(10) and R 2 2(30) ring patterns. C—H⋯O inter­actions along [100] and C—H⋯π inter­actions futher consolidate the packing, leading to a three-dimensional network.

Reorientation mechanisms in smectic A liquid crystals

The reorientation mechanism of smectic A (SmA) layers in a field is non-trivial; at least two different mechanisms have been reported. In thin samples reorientation is achieved through complete disordering and reordering of the smectic layers, while in thick samples layers can also appear to rotate continuously as a monodomain. We explore the transition between these regimes, showing qualitatively that the mechanism adopted depends on the relative importance of the sample–cell wall interaction. We observe reorientation of the smectic layers of 4′-n-octyl-4-cyanobiphenyl (8CB) in a magnetic field of flux density 4 T within 4 K of the nematic to Sm-A transition. Using time-resolved small angle X-ray scattering on samples of thickness 170 μm, 270 μm or 340 μm, we determine the transition between the thickness regimes, demonstrating a new multi-step process that is adopted in specific cases. Importantly, the time-resolved experiments allow the dynamics of the reorientation to be probed, and we measure temperature-independent angular speeds of 0.038 ± 0.002° s−1 for the continuous rotation process. Finally, we report evidence of apparent random changes in layer spacing (∼0.5 Å) as a precursor to the rotation of the Sm-A layers in some cases and discuss the possible origin of this phenomenon.

Phase transition studies in symmetric dimeric liquid crystals

As a part of the systematic studies on symmetric liquid crystal dimer homologous series, α,ω-bis-(4-n-alkylaniline benzylidene-4′-oxy) alkanes, (referred to as m.OnO.m with m = 3, 4, and 5; and n = 8, 9, and 10), we present in this article the nature of phase transitions across isotropic–nematic and nematic–smectic-A (N–SmA) phases exhibited by the just mentioned compounds. The methods employed are differential scanning calorimetry and dilatometry. The compounds studied were 3.O8O.3, 4.O8O.4, and 5.O8O.5; and 3.O9.03, 5.O9O.5, 3.O10O.3, 4.O10O.4, and 5.O10O.5. Different from the case of their corresponding monomers, all these compounds exhibit a nematic phase only with the exception of 5.O8O.5 which exhibits a SA phase in addition to the nematic phase. The phase transitions viz., isotropic–nematic transitions studied in all these compounds were confirmed to be of first-order nature, whereas the N–SmA transition exhibited by the compound 5.O8O.5 only was found to be of second-order nature. We also report in this article the calculated density jumps, thermal expansion coefficient maxima, and pressure dependence of transition temperatures which are analyzed in the light of the available literature data.

Effect of carbon nanotubes on the isotropic to nematic and the nematic to smectic- A phase transitions in liquid crystal and carbon nanotubes composites

A high-resolution ac-calorimetric study on the weakly first-order isotropic to nematic (I -N) and the continuous nematic to smectic-A (N -SmA) phase transitions of the liquid crystal octyl-cyanobiphenyl (8CB) doped with well-dispersed multiwall carbon nanotubes (CNTs) as a function of CNT concentrations is reported. Thermal scans were performed for all samples having CNT weight fraction from Φ(w) = 0.0005 to 0.0060 over a wide temperature range well above and below the two transitions in pure 8CB. Both the I -N and the N -SmA transitions evolve in character and have their transition temperatures qualitatively offset by ∼ 1.10 K lower as compared to that in pure 8CB for all 8CB+CNTs samples. The enthalpy change associated with each phase transition is essentially the same as that of pure 8CB and remains unchanged with increasing Φ(w). However, there is an evidence that the thermal transport properties of the composites differ from the pure LC upon cooling below a Φ(w)-dependent temperature within the nematic phase. In addition, a new C(p) feature is resolved for intermediate Φ(w) samples that appears to be correlated to this onset temperature.

Evidence of pressure dependence tricritical point at the nematic–smectic-A transition

We examine the effect of pressure on the nematic to smectic-A N–SmA) transition within the Landau phenomenological theory. The influence of pressure on the N–SmA transition is discussed by varying the coupling between the orientational and translational order parameters. The possibility of the tricritical point at the N–SmA transition is discussed in a phenomenological way. The theoretical predictions are found to be in good qualitative agreement with experimental results.

Splay-bend elasticity of a nematic liquid crystal with T-shaped molecules

We measured the splay (K11) and bend (K33) elastic constants in the nematic phase of a liquid crystal with T-shaped molecules. We find that the ratio, K33/K11 ≃1 in the entire nematic range except very close to the nematic to Sm-A (SN) transition. Both K33 and K11 show pretransitional divergence as the SN transition is approached from higher temperature. The ratio, K33/K11 suggests that the length (L) to effective width (D) ratio (i.e., L/D ) is significantly smaller due to the presence of long and flexible lateral group, compared to that of rigid rodlike molecules. It is argued that apart from the extra contribution to the elasticity the long and flexible lateral group also has a significant contribution to the suppression of the splay fluctuations in the onset of smectic short-range fluctuation. The structure of the Sm-A phase is investigated by using small angle x-ray diffraction, and a possible arrangement of the molecules in the Sm-A layer is proposed.

Banana-calamitic dimers: unexpected mesophase behaviour by variation of the direction of ester linking groups in the bent-core unit

A five-ring bent-core unit and a phenyl benzoate moiety are linked together by means of a flexible spacer. Starting from dimers having different length of the aliphatic parts, that is the terminal alkyloxy chains and the spacer, the direction of each of the four ester connecting groups in the bent-core unit is reversed step by step. In this way thermodynamically stable polar and non-polar mesophases in unusual sequences could be obtained. For instance, a SmCsPAF–SmCs´PAF transition and the existence of two nematic phases (N, NX) have been observed. The nematic phases of the banana-calamitic dimers exhibit unusual properties comparable to those of the nematic phases reported for some monomeric bent-core mesogens. The electric field-induced enhancement of the SmCP–SmA transition temperature of one compound proves the existence of polar clusters already in the non-polar SmA phase.

COMPACT, BROAD-STOPBAND LOWPASS FILTERS USING SIRS-LOADED CIRCULAR HAIRPIN RESONATORS

A novel compact resonator for LPF is proposed in this paper. It is composed of a circular hairpin resonator and a pair of coupled parallel stepped impedance resonators (SIRs) inside. With the loaded SIRs, additional two transmission zeros can be introduced and adjusted easily to cancel the spurious responses for stopband extending, while do not change the fllter size. Filters using one and two of the new cells were designed and measured. The two-cell LPF has an insertion loss less than 0.6dB from DC to 1.6GHz, including attenuation of double SMA transitions at both sides of the circuit which is about 0.3dB and a wide i10dB stopband from 2.5 to 13GHz (corresponding to 146% normalized 10dB stopband), but has a size of only 0:129‚g £ 0:073‚g.