Hongjie Zhao

Magnetotunable left-handed material consisting of yttrium iron garnet slab and metallic wires

A magnetotunable left-handed material (LHM) consisting of yttrium iron garnet (YIG) slab and metallic wires has been demonstrated by experiments and simulations. The left-handed passband through the LHM can be dynamically and continuously tuned in a wide frequency region by an applied magnetic field. The tunability of the passband is attributed to that of the negative permeability induced by ferromagnetic resonance in the YIG slab. The authors proposed a convenient means to design tunable LHM based on the ferromagnetic materials as an alternative to tunable split ring resonators.A magnetotunable left-handed material (LHM) consisting of yttrium iron garnet (YIG) slab and metallic wires has been demonstrated by experiments and simulations. The left-handed passband through the LHM can be dynamically and continuously tuned in a wide frequency region by an applied magnetic field. The tunability of the passband is attributed to that of the negative permeability induced by ferromagnetic resonance in the YIG slab. The authors proposed a convenient means to design tunable LHM based on the ferromagnetic materials as an alternative to tunable split ring resonators.

Magnetically tunable negative permeability metamaterial composed by split ring resonators and ferrite rods

We experimentally demonstrate a tunable negative permeability metamaterial (NPM) at microwave frequencies by introducing yttrium iron garnet (YIG) rods into a periodic array of split ring resonators (SRRs). Different from those tuned by controlling the capacitance of equivalent LC circuit of SRR, this metamaterial is based on a mechanism of magnetically tuning the inductance via the active ambient effective permeability. For magnetic fields from 0 to 2000 Oe and from 3200 to 6000 Oe, the resonance frequencies of the metamaterial can blueshift about 350 MHz and redshift about 315 MHz, respectively. Both shifts are completely continuous and reversible. Correspondingly, the tunable negative permeabilities are widened by about 360 MHz and 200 MHz compared to that without YIG rods.

Tunable negative permeability in an isotropic dielectric composite

A tunable isotropic negative effective permeability is experimentally demonstrated in a three-dimensional (3D) dielectric composite consisting of dielectric ceramic cube arrays by temperature changing. It shows that a strong subwavelength magnetic resonance can be excited in dielectric cubes corresponding to the first Mie resonance mode and can be continuously and reversibly adjusted from 13.65to19.28GHz with the temperature changing from −15to35°C. Accordingly, negative permeability can be performed in the frequency range of about 6GHz by adjusting the temperature. It provides a convenient route to design adaptive metamaterials and 3D invisible cloak.

Tunable two-dimensional left-handed material consisting of ferrite rods and metallic wires.

We demonstrate a magnetically tunable and two-dimensional (2D) left-handed material (LHM) consisting of an array of ferrite rods and metallic wires by experiments and simulations. It shows that the ferrite rod has a 2D isotropic negative permeability. By combining the ferrite rods with metallic wires, we observe experimentally a 2D LH passband that can be tuned dynamically, continuously and reversibly by an external magnetic field within in a wide frequency range with a response of 3.5 GHz/kOe. Retrieved effective parameters based on simulated scattering parameters show that operating frequency and value of negative refraction index can be conveniently tuned by changing the external magnetic field.

Ferrite-based magnetically tunable left-handed metamaterial composed of SRRs and wires.

We experimentally demonstrate a magnetically tunable left-handed metamaterial by introducing yttrium iron garnet rods into SRRs/wires array. It shows that the left-handed passband of the metamaterial can be continuously and reversibly adjusted by external dc applied magnetic fields. Retrieved effective parameters based on simulated scattering parameters show that tunable effective refraction index can be conveniently realized in a broad frequency range by changing the applied magnetic field. Different from those tuned by controlling the capacitance of equivalent LC circuit of SRR, this metamaterial is based on a mechanism of magnetically tuning the inductance via the active ambient effective permeability.

Experimental demonstration of tunable negative phase velocity and negative refraction in a ferromagnetic/ferroelectric composite metamaterial

A tunable left-handed transmission is demonstrated experimentally in a ferromagnetic/ferroelectric composite metamaterial (CMM) consisting of an array of yttrium iron garnet (YIG) rods combined with barium strontium titanate (BST) rods. We observed a passband in the CMM within the overlap of the stop bands of YIG rods alone and BST rods alone. Both measured phase velocity and refractive index of the CMM are shown to be negative at the relevant frequency range. The frequency showing left handedness can be adjusted continuously, dynamically, and reversibly by an applied magnetic field with a sensitive response of 3.5 GHz/kOe.

Realization of negative permittivity of Co2Z hexagonal ferrite and left-handed property of ferrite composite material

The complex permeability and complex permittivity of Co2Z hexagonal ferrite and the microwave properties of ferrite composite material consisting of Co2Z and yttrium iron garnet (YIG) slabs have been discussed in this paper. Negative permittivity is obtained in the semiconductive Co2Z, and Zn doping can further enhance the dielectric resonance. However, the high conductivity prevents Co2Z from producing negative permeability that originates from ferromagnetic resonance, i.e. double negative properties cannot be obtained in semiconductive or metallic ferromagnet. When Co2Z is combined with YIG, the composite structure shows magneto-tunable left-handed properties where Co2Z provides negative permittivity and YIG provides negative permeability.

Magnetic tuning of electrically resonant metamaterial with inclusion of ferrite

We experimentally demonstrate a magnetic tuning of electrically resonant metamaterial (EMM) at microwave frequencies by introducing microwave ferrite rods into the periodic array of electrically resonant element. Different from those based on controlling the capacitance of equivalent LC circuit, this tunability arises from a mechanism of magnetically tuning the inductance of resonant element via the active ambient effective permeability. For magnetic fields from 0 to 5000 Oe, resonance frequency of the EMM can be continuously and reversibly tuned in a range of about 800 MHz. The active effective permittivity has also been investigated through the simulated scattering parameters.

Realization and modulation of negative permeability using an array of hexaferrite rods

The realization of negative permeability of an array of ferrite rods and the influencing factors are presented. The negative permeability is realized around the ferromagnetic resonance frequency of ferrite, and a tunable electromagnetic band gap is observed in the array of ferrite rods. The electromagnetic property of the array of ferrite rods is dominated by the units characteristics, including the dimension of the rods, but is insensitive to the structure parameters, such as spacing distance and duty ratio, which indicates that the array is a metamaterial, not a photonic crystal. Metamaterials with multi-band gaps are made using an array with different ferrite rods.

Abnormal refraction of microwave in ferrite/wire metamaterials

We report the experimentally observed abnormal refraction in metamaterials (MMs) consisting of ferrite rods and metallic wires with two kinds of configurations. Negative refraction (NR) and positive refraction (PR) are demonstrated in an MM constructed with parallel-arranged rods and wires. The frequencies of both NR and PR can be adjusted dynamically and together by an applied magnetic field and the PR occurs at frequencies slightly lower than that of the NR. The NR is attributed to simultaneously negative effective permittivity and permeability, and the PR is resulted from positive effective permittivity and permeability with the positive effective permittivity originating from electromagnetic coupling between the closest rod and wire. By making the rod cross the wire to reduce the coupling, we observed sole NR in an MM consisting of the cross-arranged rods and wires. Theoretical analysis explained qualitatively the abnormal refraction behaviors of microwave for the two kinds of MMs and it is supported by the retrieved effective parameters and field distributions.