Concentric Hexagonal Array Research Articles

Vibrational studies of 2,3,5,6-tetrachloro-1,4-benzoquinone and its reactivity: An ab-initio computational method

The IR spectrum of 2,3,5,6-Tetrachloro-1,4-benzoquinone (p-chloranil) has been recorded in the solid phase in the range 4000 – 400 cm-1. ab initio calculations have been performed using Gaussian 03 program to compute optimized geometry, harmonic vibrational frequencies along with intensities in IR and Raman spectra and atomic charges at RHF/6–31+G*, B3LYP/6-31+G*, B3LYP/6-31++G** and B3LYP/6-311++G** levels for p-chloranil and parent molecule p-benzoquinone. The optimized molecular structures are found to be planar and possess D2h point group symmetry for both the molecules. The C=C bond lengths are larger whereas the C=O bond lengths are shorter in p-chloranil as compared to p-benzoquinone which is also reflected in the corresponding vibrational frequencies. The atomic arrangements in p-benzoquinone and p-chloranil possess two concentric hexagonal arrays and both the arrays of p-benzoquinone contain mixed charges. In the case of the p-chloranil molecule, the outer array is negatively charged and the inner array is positively charged which leads to increased susceptibility at the sites to which chlorine atoms are attached in p-chloranil towards the nucleophile. Consequently, p-chloranil is a good candidate for synthesis of many derivatives of 1,4-benzoquinone. The optimized geometrical structures along with the atomic charges on the atomic sites of p-benzoquinone and p-chloranil reveal the reactivity of p-chloranil molecules towards nucleophilic substitution reactions as compared to p-benzoquinone.

Multi-Angle Fusion for Low-Cost Near-Field Ultrasonic in-Air Gesture Recognition

With the growing interest in Human-Machine interface (HMI), an increasing amount of effort is made to provide always-on low-cost touchless control solutions for Internet-of-Things (IoT) edge devices. In this study, we explore near-audio ultrasound for in-air ultrasonic gesture design and recognition. We propose to use beamforming followed by stages of feature extraction and a Temporal Convolution Network (TCN) for classification. The study is applied to a small form factor concentric hexagonal array of 7 microphones where a beamforming stage is leveraged for spatial feature extraction and ultrasonic gesture features fusion from different angles. In case of such limited number of microphones, we show that a customized Filter-and-Sum (FaS) beamformer is well suited for this application with a set of 5-tap filters. We optimize the beamformer by fitting a fixed beam in the ultrasonic frequency domain, to make the ultrasonic band of interest (18 kHz - 24 kHz) available for use. The beamformer generates parallel readings in time of Doppler shifts from a set of assigned angles as a hand gesture is performed near the array. A TCN of only 10k parameters is used to classify these parallel readings into predefined symbols to build a gesture alphabet. The TCN operates on two modes sharing the same TCN structure with the option to switch between them by loading different set of coefficients. Features from concatenated beamformed frequency points are learned with a per symbol classification accuracy in the range 92%-100% computed on a test set and visualized in the form of normalized confusion matrix. The proposed system gives users a degree of flexibility where gesture diversity can be obtained by grouping the trained symbols from the built alphabet in a post-training design stage. This paves the way for flexible, intuitive and easy to remember gestures.

Design of time modulated concentric circular and concentric hexagonal antenna array using hybrid enhanced particle swarm optimisation and differential evolution algorithm

Design of circular arrays (CAs) and hexagonal arrays (HAs) with low sidelobe level (SLL) and high directivity is usually achieved by increasing the number of array elements, which leads to a high undesired mutual coupling. Therefore this study presents an efficient optimisation method and a framework to show how to design multi-ring concentric CAs (CCA) and concentric HAs (CHAs) configurations using a hybrid enhanced particle swarm optimisation and differential evolution (hybrid EPSO/DE) optimisation technique. The presented optimum CCA and CHA have perfect invariant SLL and high directivity with low mutual coupling by keeping the inter-element spacing not less than half a wavelength which is not possible to be achieved in CA and HA arrangements. Different configurations with two-rings, three-rings and four-rings are presented. The rotation angle of outer rings and the complex excitations of array elements are first optimised. Then, this design is further optimised using a time modulation technique by controlling the switch-on times and the phases of elements excitations of the best CCA and CHA array designs. The presented time modulated (TM) concentric CA and TM concentric HA designs attain ultra-low SLL, reduced sideband level and maximised directivity besides reducing the dynamic range of the array excitations.