Thermally Tunable Acoustic Beam Splitter Based on Poly(vinyl alcohol) Poly(N-isopropylacrylamide) Hydrogel

In this study, we demonstrated a thermally tunable acoustic beam splitter using a poly(vinyl alcohol) poly(N-isopropylacrylamide) hydrogel (PVA-pNIPAM). The nature of PVA-pNIPAM hydrogel offers exceptional temperature-dependent physical properties due to its phase transition around its lower critical solution temperature. The acoustic impedance of the hydrogel can be tuned below, above, or matched to that of water by changing the environmental temperature. An acoustic wave propagating in water can be split into transmitted and reflected components by the PVA-pNIPAM hydrogel slab on varying its angle of incidence. The intensity ratio between the reflected and the transmitted componence can be adjusted by tuning the temperature of the medium. The acoustic beam can be entirely reflected at a temperature corresponding to the matched impedance between hydrogel and water. The beam-splitting behavior was observed for acoustic waves from both a monochromatic wave and broadband pulse source. In addition, the phase of beam split pulses can be reversed by selecting the hydrogel’s operating temperature.

A Facile Synthesis of Novel Amorphous TiO2 Nanorods Decorated rGO Hybrid Composites with Wide Band Microwave Absorption

Amorphous structures may play important roles in achieving highly efficient microwave absorption performance due to the polarization losses induced by the disorders, vacancies and other functional groups existed in them. Herein, a kind of amorphous TiO2/rGO composite (a-TiO2/rGO) was successfully fabricated via a facile one-step solvothermal method. The complex permittivity of the composites can be regulated by adjusting the addition of precursor solution. The minimum reflection loss of a-TiO2/rGO composites reached −42.8 dB at 8.72 GHz with a thickness of 3.25 mm, and the widest efficient absorption bandwidth (EAB) was up to 6.2 GHz (11.8 to 18 GHz) with a thickness of only 2.15 mm, which achieved the full absorption in Ku band (12 to 18 GHz). Furthermore, the EAB was achieved ranging from 3.97 to 18 GHz by adjusting the thickness of the absorber, covering 87.7% of the whole radar frequency band. It is considered that the well-matched impedance, various polarization processes, capacitor-like structure and conductive networks all contributed to the excellent microwave absorption of a-TiO2/rGO. This study provides reference on constructing amorphous structures for future microwave absorber researches and the as-prepared a-TiO2/rGO composites also have great potential owing to its facile synthesis and highly efficient microwave absorption.

An Easy Method of Synthesis CoxOy@C Composite with Enhanced Microwave Absorption Performance

Design of interface-controllable magnetic composite towards the wideband microwave absorber is greatly significance, however, it still remains challenging. Herein, we designed a spherical-like hybrids, using the Co3O4 and amorphous carbon as the core and shell, respectively. Then, the existed Co3O4 core could be totally reduced by the carbon shell, thus in CoxOy core (composed by Co and Co3O4). Of particular note, the ratios of Co and Co3O4 can be linearly tuned, suggesting the controlled interfaces, which greatly influences the interface loss behavior and electromagnetic absorption performance. The results revealed that the minimum reflection loss value (RLmin) of −39.4 dB could be achieved for the optimal CoxOy@C sample under a thin thickness of 1.4 mm. More importantly, the frequency region with RL < −10 dB was estimated to be 4.3 GHz, ranging from 13.7 to 18.0 GHz. The superior wideband microwave absorption performance was primarily attributed to the multiple interfacial polarization and matched impedance matching ability.

Synergistic engineering of dielectric and magnetic losses in M-Co/RGO nanocomposites for use in high-performance microwave absorption

M-Co/RGO nanocomposites with well-matched impedance matching and high attenuation constant are developed and enhanced microwave absorption was obtained through the strategy of synergistic engineering of dielectric and magnetic losses.

Design of an Elliptical Patch Antenna for RF Energy Harvesting Application in 2.4 GHz Frequency band

In this paper, the design and prototype of an elliptical patch antenna is presented, which operates at the frequency of 2.4 GHz frequency band. It harvests energy from ‘Radio Frequency’ waves. The elliptical antenna has an antenna substrate made with FR4 board with dielectric constant of 3.95. The paper presents the simulation results of the basic parameters of the antenna such as: return loss, input impedance, bandwidth, gain, directivity and efficiency. The experimental results for return loss, band width and input impedance was also presented in the paper. The antenna has a gain of 5.84 dB, directivity of 6.25 dBi, return loss of -43.35 dB, bandwidth of 373 MHz, input impedance of 50.35 Ω and efficiency of 90%. The high gain, properly matched impedance for minimum return loss and high efficiency of the antenna make it eligible for energy harvesting application.

In situ synthesis of hierarchical rose-like porous Fe@C with enhanced electromagnetic wave absorption

The excellent microwave absorption performance of the rose-like porous Fe@C is due to the enhancement of matched impedance and collective multiple loss mechanism.

A General Method to Parameter Optimization for Highly Efficient Wireless Power Transfer

<pre>This paper proposes a new and general method to optimize a working <br />frequency and a load resistance in order to realize highly efficient wireless <br />power transfer. It should be noticed that neither resonant frequency nor <br />matched impedance maximizes efficiency of wireless power transfer circuit, <br />in general. This paper establishes a mathematical model of a commonly <br />used wireless power transfer circuit, and derives a mathematical expression <br />of circuit efficiency which involves a working frequency, a load resistance and <br />the other parameters as symbols. This enables us to find the optimal working<br />frequency and load resistance. The result of this paper is compared with <br />results by a method based on resonance and impedance matching, and then <br />clarified by a numerical example.</pre>