Functional plastic films:nano-engineered composite based flexible microwave antennas with near-unity relative visible transmittance

Microwave antennas are essential elements for various applications,such as telecommunication,radar,sensing,and wireless power transport.These antennas are conventionally manufactured on rigid substrates using opaque materials,such as metal strips,metallic tapes,or epoxy pastes;thus,prohibiting their use in flexible and wearable devices,and simultaneously limiting their integration into existing optoelectronic systems.Here,we demonstrate that mechanically flexible and optically transparent microwave antennas with high operational efficiencies can be readily fabricated using composite nanolayers deposited on common plastic substrates.The composite nanolayer structure consists of an ultra-thin copper-doped silver film sandwiched between two dielectric films of tantalum pentoxide and aluminum oxide.The material and thickness of each constituent layer are judiciously selected such that the whole structure exhibits an experimentally measured averaged visible transmittance as high as 98.94%compared to a bare plastic substrate,and simultaneously,a sheet resistance as low as 12.5Ω/sq.Four representative types of microwave antennas are implemented:an omnidirectional dipole antenna,unidirectional Yagi-Uda antenna,low-profile patch antenna,and Fabry-Pérot cavity antenna.These devices exhibit great mechanical flexibility with bending angle over 70°,high gain of up to 13.6 dBi,and large radiation efficiency of up to 84.5%.The proposed nano-engineered composites can be easily prepared over large areas on various types of substrates and simultaneously overcome the limitations of poor mechanical flexibility,low electrical conductivity,and reduced optical transparency usually faced by other constituent materials for flexible transparent microwave antennas.The demonstrated flexible microwave antennas have various applications ranging from fifth-generation and vehicular communication systems to bio-signal monitors and wearable electronics.

A low-cost invasive microwave ablation antenna with a directional heating pattern

Microwave ablation(MWA) is a cancer treatment method. The tumor tissue absorbs electromagnetic energy, which heats and kills it. A microwave ablation antenna plays a critical role in this process. Its radiation field must completely cover the tumor but not the healthy tissue. At present, the radiation pattern of most invasive ablation antennas is spherical.However, in the clinic, the shape of some tumors may be asymmetrical or the antenna cannot be inserted into the center of the tumor for some other reason. In order to solve these problems, a directional heating antenna for microwave ablation is proposed in this paper. The proposed antenna, operating at 2.45 GHz, consists of a monopole and a reflector. The feed is given by a substrate integrated coaxial line(SICL) and coplanar waveguide(CPW). The omnidirectional radiation field of the monopole is reflected by a reflector that is extended from the outer conductors of the SICL to form a directional radiation field. The impedance matching network is designed on SICL to match the antenna to 50 Ω. The antenna is fabricated using a mature printed circuit board(PCB). The reflection coefficient of the antenna in porcine liver tissue measured by a vector network analyzer shows good agreement with the simulations. Then, an ablation experiment in porcine liver is conducted with power of 10 W for 10 min, and the experimental results confirm the validity of the design.

Single-layer broadband planar antenna using ultrathin high-efficiency focusing metasurfaces

Phase gradient metasurfaces（PGMS） offer a fascinating ability to control the amplitude and phase of the electromagnetic（EM） waves on a subwavelength scale, resulting in new applications of designing novel microwave devices with improved performances. In this paper, a reflective symmetrical element, consisting of orthogonally I-shaped structures, has been demonstrated with an approximately parallel phase response from 15 GHz to 22 GHz, which results in an interesting wideband property. For practical design, a planar antenna is implemented by a well-optimized focusing metasurface and excited by a self-designed Vivaldi antenna at the focus. Numerical and experimental results coincide well. The planar antenna has a series of merits such as a wide 3-d B gain bandwidth of 15–22 GHz, an average gain enhancement of 16 d B, a comparable aperture efficiency of better than 45% at 18 GHz, and also a simple fabrication process. The proposed reflective metasurface opens up a new avenue to design wideband microwave devices.

Triple-Band L-Shaped Monopole Antenna with Defected Ground Plane for WLAN and WiMAX Application

This paper presents the simulation and measured results of a triple-band L-shaped monopole antenna with defected ground plane for applications in wireless local area networks（WLANs） and worldwide interoperability for microwave access（WiMAX） bands.The triple-band L-shaped monopole antenna with defected ground plane was fabricated on a FR4 substrate. The lower band is associated with the shorted parasitic strip in the protruding stub of the ground plane; the middle band is expected to be controlled by the longer strip of L-shaped monopole in the front side,while the higher band is associated with the short strip of L-shaped monopole in the front side. The proposed antenna has a good agreement between the measured and the simulation results. It has a 10 d B return loss with the bandwidth of 250 MHz（2270 MHz to 2520MHz） in the lower band, 600 MHz（3320 MHz to 3,920MHz） in the middle band, and 1110 MHz（5030 MHz to6140 MHz） in the higher band. The proposed antenna covers the ISM（industrial, scientific and medical）,HIPERLAN（high performance radio local area network）, UNII（unlicensed national information infrastructure）, and WiM AX bands.

On Differentiation Among Pilot Signals of Multiple Mobile Targets in Retro-Reflective Beamforming for Wireless Power Transmission

An experimental study is conducted on several retro-reflective beamforming schemes for wireless power transmission to multiple wireless power receivers(referred to herein as“targets”).The experimental results demonstrate that,when multiple targets broadcast continuous-wave pilot signals at respective frequencies,a retro-reflective wireless power transmitter is capable of generating multiple wireless power beams aiming at the respective targets as long as the multiple pilot signals are explicitly separated from one another by the wireless power transmitter.However,various practical complications are identified when the pilot signals of multiple targets are not appropriately differentiated from each other by the wireless power transmitter.Specifically,when multiple pilot signals are considered to be carried by the same frequency,the wireless power transmission performance becomes heavily dependent on the interaction among the pilot signals,which is highly undesirable in practice.In conclusion,it is essential for a retro-reflective wireless power transmitter to explicitly discriminate multiple targets’pilot signals among each other.

Nonlinear three-magnon scattering in low-damping La_(0.67)Sr_(0.33)MnO_(3)thin films

Three-magnon scattering,a nonlinear process in which a high-energy magnon splits into two low-energy magnons with energy and momentum conservation,has been widely studied in the magnonics community.Here,we report experimental observation of nonlinear three-magnon scattering in La_(0.67)Sr_(0.33)MnO_(3)thin films with low magnetic damping(~10^(-4))by all-electric and angle-resolved spin wave spectroscopy.The reflection spectra of the spin wave resonance with high-power excitation at Damon–Eshbach configuration demonstrate a scattering regime with gradual signal disappearance,where a magnon of Damon–Eshbach mode decays into two magnons of volume mode above the threshold power(-10 dBm)of the injected microwave.The nonlinear scattering is only allowed at low-field regime and the calculated dispersions of dipole-exchange spin wave claim the mechanism of allowed and forbidden three-magnon scattering.The films and heterostructures of La_(0.67)Sr_(0.33)MnO_(3)have been already demonstrated with rich physical phenomena and great versatility,in this work the nonlinear magnetic dynamics of La_(0.67)Sr_(0.33)MnO_(3)thin films is revealed,which offer more possibility for applications to oxide magnonics and nonlinear magnonic devices.

Effect of the antenna slot numbers and position on the performance of microwave ablation

Microwave ablation(MWA)is a type of thermal ablation used for cancer treatment in interventional radiology.To induce localized tissue heating MWA employs electromagnetic waves within the microwave energy spectrum,which is done by the precisely designed antenna.This study substantially emphasizes the design and performance ameliorating of slot(both single and double)antennae and compares the results with conventional monopole antennae in terms of temperature distribution,specific absorption ratio(SAR),and thermal tissue damage rate.The simulation has been done in COMSOL by solving the Bioheat equation along with Maxwell electromagnetic equations using the finite element method.The simulation results reveal that the double-slot antenna has the most accurate and directional heat dissipation for liver tumors as well as the highest tissue damage rate and SAR.The highest SAR was found to be 3500 W/kg and 3350 W/kg at the implant depth of 61 mm and 63 mm for double and single-slot antennae,respectively.In addition,the fastest tissue damage occurred near the upper slot of the double-slot antenna.This study helps to understand the basic design parameters for enhancing single and doubleslot antennae performance.

Photonic microwave true time delays for phased array antennas using a 49 GHz FSR integrated optical micro-comb source[Invited]

We demonstrate significantly improved performance of a microwave true time delay line based on an integrated optical frequency comb source. The broadband micro-comb(over 100 nm wide) features a record low free spectral range(FSR) of 49 GHz, resulting in an unprecedented record high channel number(81 over the C band)—the highest number of channels for an integrated comb source used for microwave signal processing. We theoretically analyze the performance of a phased array antenna and show that this large channel count results in a high angular resolution and wide beam-steering tunable range. This demonstrates the feasibility of our approach as a competitive solution toward implementing integrated photonic true time delays in radar and communications systems.

Low-profile microwave lens antenna based on isotropic Huygens＇ metasurfaces

An isotropic electromagnetic （EM） lens based on Huygens＇ metasurface is proposed for 28.0 GHz lens antenna design. The lens consists of a series of non-resonant and subwavelength metallic patterns etched on both sides of an ultrathin dielectric substrate. Both electric and magnetic responses are introduced to realize desired abrupt phase change and high-efficiency transmission for the secondary wavelets in the incident wavefront. Then, a substrate-integrated waveguide （SIW） fed patch antenna is combined with the lens as the primary feed to form a low-profile lens antenna system. The simulated and measured results coincide with each other, and demonstrate that the prototype realizes 8.8 dB-12.6 dB gain increment and low side-lobe levels over the bandwidth of 26.7 GHz-30.0 GHz. The novel design leads to a low-profile, light weight, and low-cost antenna solution in a wireless communication system.

Broadband terahertz spectroscopy

An overview of the major techniques to generate and detect THz radiation so far,especially the major approaches to generate and detect coherent ultra-short THz pulses using ultra-short pulsed laser,has been presented.And also,this paper,in particularly,focuses on broadband THz spectroscopy and addresses on a number of issues relevant to generation and detection of broadband pulsed THz radiation as well as broadband time-domain THz spectroscopy （THz-TDS） with the help of ultra-short pulsed laser.The time-domain waveforms of coherent ultra-short THz pulses from photoconductive antenna excited by femtosecond laser with different pulse durations and their corresponding Fourier-transformed spectra have been obtained via the numerical simulation of ultrafast dynamics between femtosecond laser pulse and photoconductive material.The origins of fringes modulated on the top of broadband amplitude spectrum,which is measured by electric-optic detector based on thin nonlinear crystal and extracted by fast Fourier transformation,have been analyzed and the major solutions to get rid of these fringes are discussed.