A five-band absorber based on graphene metamaterial for terahertz ultrasensing

We design and propose a five-band absorber based on graphene metamaterial for the terahertz (THz) sensing field. The localized surface plasmon resonances (LSPR) of patterned graphene are excited, contributing to five tunable ultra-narrow absorption peaks, which are specified by the electric field distributions. Moreover, the absorber is insensitive to different polarization modes and incident angles. When increasing the Fermi level of the patterned graphene, which is composed of a round ring and a square ring connected by four thin wires, the resonant frequencies exhibit distinct blue shifts. For refractive index sensing, due to the addition of a continuous dielectric groove, the theoretical results show that the maximum averaged normalized sensitivity, Q factor, and FOM can reach 0.647 RIU-1 (refractive index unit, RIU), 355.94, and 215.25 RIU-1, indicating that the sensing performances are further enhanced compared with previous works. As a result, the proposed structure may provide a new method to realize ultrasensing in the THz region.

An ultrathin acoustic metasurface composed of an anisotropic three-component resonator

An ultrathin acoustic metasurface consisting of an anisotropic three-component resonator is proposed. The resonator can induce nondegenerate dipole resonances at the same resonant frequencies. A large phase delay can be obtained based on the resonance, which can be modulated by the direction of polarization. The anisotropic resonator can be regarded as an effective homogenous medium with an anisotropic mass density, and the phase change can also be attributed to the change of the effective material parameters. A good comparison between the results for the metasurface and its effective slab is obtained.

Piezoelectric MEMS Acoustic Transducer with Electrically-Tunable Resonant Frequency

The paper presents a technique to obtain an electrically-tunable matching between the series and parallel resonant frequencies of a piezoelectric MEMS acoustic transducer to increase the effectiveness of acoustic emission/detection in voltage-mode driving and sensing. The piezoelectric MEMS transducer has been fabricated using the PiezoMUMPs technology, and it operates in a plate flexural mode exploiting a 6 × 6 mm doped silicon diaphragm with an aluminum nitride (AlN) piezoelectric layer deposited on top. The piezoelectric layer can be actuated by means of electrodes placed at the edges of the diaphragm above the AlN film. By applying an adjustable bias voltage Vb between two properly-connected electrodes and the doped silicon, the d31 mode in the AlN film has been exploited to electrically induce a planar static compressive or tensile stress in the diaphragm, depending on the sign of Vb, thus shifting its resonant frequency. The working principle has been first validated through an eigenfrequency analysis with an electrically induced prestress by means of 3D finite element modelling in COMSOL Multiphysics®. The first flexural mode of the unstressed diaphragm results at around 5.1 kHz. Then, the piezoelectric MEMS transducer has been experimentally tested in both receiver and transmitter modes. Experimental results have shown that the resonance can be electrically tuned in the range Vb = ±8 V with estimated tuning sensitivities of 8.7 ± 0.5 Hz/V and 7.8 ± 0.9 Hz/V in transmitter and receiver modes, respectively. A matching of the series and parallel resonant frequencies has been experimentally demonstrated in voltage-mode driving and sensing by applying Vb = 0 in transmission and Vb = −1.9 V in receiving, respectively, thereby obtaining the optimal acoustic emission and detection effectiveness at the same operating frequency.

Design and Analysis of Reconfigurable Antenna for Wide Band Applications

The relevance of reconfiguration in a dynamic environment is to improve an antenna’s performance by allowing it to transition between multiple frequencies. In this paper, we designed a reconfigurable patch antenna and fed it by strip line feeding by placing 2 slots to obtain different resonant frequencies. The feature of reconfigurability is attained by using Pin Diodes. In our design, we take a 2 pin diode. The proposed Antenna can operate on different frequencies i.e. 2.88GHz, 5.5GHz, 10.8GHz and 11.1GHz with the efficiency of 90% and more at different conditions of the diodes. This analysis is done by using HFSS Software.

Design of multi-band millimeter wave antenna for 5G smartphones

The design of a millimeter wave (mmW) antenna for the 5G mobile applications is presented in this paper. The designed antenna has dimensions of 10×10×0.245 mm³. This includes the copper ground plane. The resonance of the proposed mmW antenna lies within the range of 33 GHz and 43 GHz. These frequency bands are covering the 5G proposed band in terms of the signal speed, data transmission, and high spectral efficiencies. Computer simulation technology (CST) software is used to simulate the proposed 5G antenna including the characteristics of S-parameters, gain, and radiation pattern. Simulation results show that the return loss at resonant frequencies goes -22 dB, which satisfies the requirements of 5G mobile technology.

Using additive technologies to create broadband antennas with fractal geometry

The paper presents the results of a study of the frequency dependence of the S11 parameters of antenna samples with fractal geometry, created using 3D printing technology, followed by the deposition of a conductive copper coating by galvanization. It is shown that changing the dimension of the fractal at different iterations, shifting and dividing the resonant frequencies, it is possible to flexibly form the working bands of antennas in any frequency range and any width. The developed designs can be used to create broadband rectennas.

Effects of the Vibration Amplitude in Vibratory Stress Relief on the Fatigue Life of Structures

This research aims to investigate the effects of vibration amplitude in vibratory stress relief (VSR) on the fatigue strength of structures with residual stress. Experiments are carried out on specimens with residual stress generated by local heating. Flat specimens made of A36 steel are prepared to be suitable for setting up fatigue bending tests on a vibrating table. Several groups of samples are subjected to VSR at resonant frequencies with different acceleration amplitudes. The results show that VSR has an important influence on the residual stress and fatigue limit of steel specimens. The maximum residual stress in the samples is reduced about 73% when the amplitude of vibration acceleration is 57 m/s2. The VSR method can also improve the fatigue limit by up to 14% for steel samples with residual stress.

Broadband tunable acoustic metasurface based on piezoelectric composite structure with two resonant modes

In this letter, we propose a deep-wavelength tunable acoustic metasurface composed of a fixed piezoelectric composite structure with a broad operating frequency range. The metasurface unit has two tunable resonant frequencies determined by specific external inductors and can continuously modulate the phase of transmitted wave. The influence of the inductors on the resonant frequencies are studied by simulation and experiment. Moreover, the functions of acoustic beam steering and focusing by the designed metasurface at three arbitrarily chosen frequencies are verified in simulation. This work may have good potential in design of acoustic metasurfaces with broadband operating frequencies.