A Novel dual notched 4-element MIMO (Multi-Input-Multi-Output) antenna with gap sleeves and H-slot is proposed and fabricated for UWB (ultra wide-band) applications. The proposed antenna is CPW (Co-Planar Waveguide) fed and consists of four orthogonal elements with good isolation. It has low profile and small dimensions of 80x80x1.6mm3. The proposed MIMO antenna achieved an impedance bandwidth (S11<-10dB) from 2.1GHz - 20GHz with notches from 3.3GHz - 4.1GHz and 8.2GHz - 8.6GHz frequency bands. These achieved notches can filter the interference of WiMAX(3.3GHz - 3.7GHz), and military/radar applications band (8.2GHz - 8.6GHz). Mutual coupling among the elements is also below -25dB. The performance parameters of proposed MIMO antenna are relatively good with very low ECC (Envelop Correlation Coefficient) less than 0.02 except at notches and DG (Diversity Gain) nearly 10. Peak gain of 5.8dB is achieved by the proposed antenna and the radiation efficiency is also above 80% except at notches.The computer-generated and experimental results are in accord and therefore, the proposed four element MIMO antenna can be suggested as a suitable aspirant for UWB applications with stop bands for WiMAX and military/radar applications.

This paper presents the analysis of a collinear MIMO (Multiple Input and Multiple Output) antenna and its conformal models for 5G and milli-meter wave communications. The proposed MIMO antenna contains two collinear elements, integrated with balun structure and DGS (Defected Ground Structure). The proposed antenna is of compact size with dimensions 22 x 13 x 0.254 mm³. It operates for an impedance bandwidth (S₁₁ < -10dB) of 17.5 GHz and 2.4 GHz. A peak gain of 6.72dB is achieved and the maximum efficiency obtained is 98.7%. Maximum isolation between the two elements of the proposed MIMO antenna is about 89.5dB in the operating band. To validate the proposed MIMO antenna, a prototype is fabricated and tested. The simulated and measured results: impedance bandwidth, radiation pattern, gain, isolation between the two elements, diversity gain and ECC are in good agreement.

Synthesis, characterisation and order parameter studies of p-n-alkoxy benzoic acids 11oba and 12oba have been carried out along with 1–3wt% Fe₃O₄ nanoparticle (NP) dispersion separately. These nanocompounds are characterised by spectroscopic techniques such as polarising optical microscope, differential scanning calorimetry and scanning electron microscopy. The phase transitions can be easily identified by image processing methods with Matlab tool to reduce the costly equipment’s usage in finding the heat flow with respect to temperature. Further, the refractive index measurements are carried out using modified spectrometer for the liquid crystals (LCs) with the various concentrations of NPs at various wavelengths. It is found that the values of birefringence (δn) increase with increase in concentrations of NPs, and this shows that strong Vanderwaal’s interaction takes place due to well cappingbetween the NPs and LC molecules. The orientational order parameter has been determined from well-known theoretical molecular internal field models: Kuczynski method, effective geometry method and Haller’s extrapolation method. In all these methods, the order parameter found increases like birefringence with the dispersion of NPs. The increase in the birefringence δn values results in wide-angle vision, and thereby the LC nanocomposites are much useful in many optical display devices for various display applications. Graphical abstract

The optical technique developed by [W. Kuczynski, B. Zywucki, and J. Malecki, Determination of orientational order parameter in various liquid-crystalline phases, Mol. Cryst. Liq. Cryst. 381 (2002), pp. 1–19; B.J. Zywucki and W. Kuczynski, IEEE transactions on optical phenomena – The orientational order in nematic liquid crystals from birefringence measurements, Dielectr. Electr. Insul. 8 (2001), pp. 512–515] is fabricated and used to determine the orientational order parameter in two dimeric liquid crystalline compounds nematic and SmA phases of α,ω-bis(4-alkylanilinebenzylidene-4′-oxy)alkane (m.OnO.m) homologous series. The compounds studied are 5.O8O.5 and 5.O10O.5 which exhibit nematic and SmA, and nematic phases, respectively. The orientational order parameter in both the phases of nematic and SmA phases of the compound one and the nematic phase of the compound two are obtained using the principle of Newton's rings which gives directly the birefringence, δn of the liquid crystal dimer. The merits of the technique used are presented over the conventional techniques for the determination of orientational order parameter. The results for the two compounds are compared with those values estimated from n _e, n _o and density using the two internal field models due to Vuks and Neugebauer applicable to nematic phase.

The temperature gradient of refractive indices, dn _e/dT and dn _o/dT of a number of liquid crystals of different homologous series are analysed. It was found that the materials studied possess high clearing temperatures and the cross over temperatures estimated are well above room temperature and they show an odd–even effect with the chain length in a homologous series.