Qingmin Wang

Magnetically tunable metamaterial perfect absorber

A magnetically tunable metamaterial perfect absorber (MPA) based on ferromagnetic resonance is experimentally and numerically demonstrated. The ferrite-based MPA is composed of an array of ferrite rods and a metallic ground plane. Frequency dependent absorption of the ferrite-based MPA under a series of applied magnetic fields is discussed. An absorption peak induced by ferromagnetic resonance appears in the range of 8–12 GHz under a certain magnetic field. Both the simulated and experimental results demonstrate that the absorption frequency of the ferrite-based MPA can be tuned by the applied magnetic field. This work provides an effective way to fabricate the magnetically tunable metamaterial perfect absorber.

Multi-band terahertz metasurface absorber

A terahertz metasurface perfect absorber with multi-band performance is demonstrated. The absorber is composed of a ground plane and four split-ring resonators (SRRs) with different dimensions, separated by a dielectric spacer. The numerical simulation results illustrate that the proposed absorber has four distinct absorption peaks at resonance frequencies of 4.24, 5.66, 7.22, and 8.97 THz, with absorption rates of 96.8%, 99.3%, 97.3%, and 99.9%, respectively. Moreover, the corresponding full width at half-maximum (FWHM) values are about 0.27, 0.35, 0.32, and 0.42 THz, respectively, which are much broader than those of previously reported absorbers. Besides, the calculated magnetic field distributions allow us to understand the absorption mechanism in detail. The effects of incident angle and azimuthal angle on the absorber are also investigated. The results show that the proposed absorber is partially sensitive to the incident angle, which makes this design promising for practical applications in terahertz imagers and detectors.

Tunable Dielectric Properties of Ferrite-Dielectric Based Metamaterial

A ferrite-dielectric metamaterial composed of dielectric and ferrite cuboids has been investigated by experiments and simulations. By interacting with the electromagnetic wave, the Mie resonance can take place in the dielectric cuboids and the ferromagnetic precession will appear in the ferrite cuboids. The magnetic field distributions show the electric Mie resonance of the dielectric cuboids can be influenced by the ferromagnetic precession of ferrite cuboids when a certain magnetic field is applied. The effective permittivity of the metamaterial can be tuned by modifying the applied magnetic field. A good agreement between experimental and simulated results is demonstrated, which confirms that these metamaterials can be used for tunable microwave devices.

Magnetically tunable dual-band transmission through a single subwavelength aperture

By placing two pairs of dielectric cubes and ferrite cuboids symmetrically on both sides of a single subwavelength aperture, we realize a magnetically tunable dual-band transmission. One transmission peak is induced by the Mie resonance of dielectric cubes, and the other one is induced by the ferromagnetic resonance of ferrite cuboids. The enhancement transmission controlled by the ferromagnetic resonance can be tuned by adjusting the applied magnetic field, which is confirmed by the experimental and simulated results. This work provides a way to realize tunable enhanced transmission through a single subwavelength aperture, which has greater potential for the tunable filters.

Tunable metamaterial bandstop filter based on ferromagnetic resonance

Tunable wideband microwave bandstop filters have been investigated by experiments and simulations. The negative permeability is realized around the ferromagnetic resonance frequency which can be influenced by the demagnetization factor of the ferrite rods. For the filter composed of two ferrite rods with different size, it exhibits a -3 db stop bandwidth as large as 500 MHz, peak absorption of -40 db and an out-of-stopband insertion loss of -1.5 db. This work provides a new way to fabricate the microwave bandstop filters.

Enhanced photoluminescence properties of SrTiO3:Pr3+ nanocrystals by the “TEG-sol” method

SrTiO3(STO):Pr3+ nanopowders are synthesized because of their excellent photoluminescence (PL) performance. The PL intensity is enhanced by morphological control and oxygen vacancy. The “TEG-sol” method is used to prepare STO:Pr3+ nanopowders with a size lower than 10 nm. Abundant oxygen vacancies are formed in the nanopowders without any further processing. The effect of annealing temperature on the PL properties is systematically studied. Bright green-white emission is achieved from pristine STO:Pr3+. Red emission is obtained after annealing at a temperature higher than 400 °C. A flexible and translucent STO:Pr3+/polyvinylidene fluoride nanocomposite film is fabricated, which shows outstanding PL and dielectric properties.SrTiO3(STO):Pr3+ nanopowders are synthesized because of their excellent photoluminescence (PL) performance. The PL intensity is enhanced by morphological control and oxygen vacancy. The “TEG-sol” method is used to prepare STO:Pr3+ nanopowders with a size lower than 10 nm. Abundant oxygen vacancies are formed in the nanopowders without any further processing. The effect of annealing temperature on the PL properties is systematically studied. Bright green-white emission is achieved from pristine STO:Pr3+. Red emission is obtained after annealing at a temperature higher than 400 °C. A flexible and translucent STO:Pr3+/polyvinylidene fluoride nanocomposite film is fabricated, which shows outstanding PL and dielectric properties.

High-efficiency polarization conversion phase gradient metasurface for wideband anomalous reflection

An ultra-wideband polarization conversion metasurface based on S-shaped metallic structure is designed and prepared. The simulation results show that the polarization conversion bandwidth is 14 GHz for linearly polarized normally incident electromagnetic waves and the cross-polarized reflectance is more than 99% in the range of 10.3 GHz–20.5 GHz. On the premise of high reflection efficiency, the reflective phase can be regulated by changing the geometrical parameter of the S-shaped metallic structure. A phase gradient metasurface composed of six periodically arrayed S-shaped unit cells is proposed and further demonstrated both numerically and experimentally. The specular cross-polarization reflection of the phase gradient metasurface is below −10 dB, which shows a good performance on manipulating the direction of the reflected electromagnetic waves.

Wideband terahertz absorber based on Mie resonance metasurface

Terahertz absorber has attracted much attention. However, most of them have complex structures and narrow bandwidth. Here, a wideband terahertz metasurface absorber based on Mie resonance is demonstrated. The metasurface absorber is prepared by combining four dielectric resonators with different permittivity values into a single unit cell. The absorption of the wideband metasurface absorber goes beyond 80% from 8.37 to 8.60 THz, showing wideband absorption performance. In addition, the center frequency of the wideband metasurface absorber can be tuned by the size and permittivity of the dielectric resonators, which makes the proposed absorber suitable for applications in wideband terahertz devices.

Wideband metasurface filter based on complementary split-ring resonators

A wideband metasurface filter based on complementary split-ring resonators (CSRR) has been prepared. The frequency and transmission bandwidth of the metasurface filters with different split widths are discussed. After analyzing the mechanism of the metasurface, the proposed metasurface filters are fabricated. The electromagnetic properties of the metasurface are measured by a designed test system. The measured results are in good agreement with the simulated ones, which shows that the metasurface filter has a wideband property. As the split width of the CSRR increases, the frequency of the passband shifts to higher frequency regions and the transmission bandwidth decreases.

Thermally tunable slot-coupled dielectric resonator antenna

A thermally tunable slot-coupled dielectric resonator antenna (DRA) has been designed and prepared by placing a thermosensitive ceramic resonator onto the slot. Typical magnetic resonance occurs in the resonator, which is closely related to its dielectric constant. Because the dielectric constant of the ceramic resonator decreases as the temperature increases, the resonance frequency of the proposed DRA increases as the temperature increases. The simulated results are in good agreement with the measured ones, which confirms the thermally tunable behavior. This approach provides a way for designing the frequency tunable antennas.