Jiangtao Huangfu

Experimental confirmation of negative refractive index of a metamaterial composed of Ω-like metallic patterns

A one-dimensional metamaterial is realized using three connected Ω rings printed back-to-back and reversed on two sides of a dielectric substrate. Both transmission and prism experiments are reported, yielding concordant results of the presence of a left-handed frequency band. Experiments show reduced losses and an enlarged left-handed frequency band.

Planar focusing antenna design by using coordinate transformation technology

The coordinate transformation by using form-invariant transformations of Maxwell equations has led to an approach for designing devices with anisotropic metamaterial. In this paper, we present the design methodology for a low profile planar focusing antenna based on the transformation of a parabolic antenna. The electromagnetic behavior of the planar antenna is simulated by a two-dimensional finite element method and the results show that the planar antenna has the same performances as the parabolic antenna. The coordinate transformation technology provides an alternative design method to the conventional antennas.

Experimental Study on Several Left-Handed Matamaterials

Left-handed materials (LHM) are engineered structures that exhibit electromagnetic properties not found in nature. Real applications of LHM need substrates with low loss, wide bandwidth as well as stable mechanical characteristics. In this paper, we summarize some experimental as well as numerical results of lefthanded materials with different configurations of rods and splitring resonators (SRRs). Hot-press technics utilized in PC board manufacture are used to produce solid-state multi-layer left-handed materials. Either mechanical or electromagnetic characteristics of LH samples are notably improved.

Metamaterial exhibiting left-handed properties over multiple frequency bands

We present experimental measurements at microwave frequencies of a double band left-handed metamaterial. The sample of metamaterial is composed of an extended version of the S-shaped resonators that exhibit simultaneously a negative permittivity and a negative permeability response at comparable frequencies. The experimental results clearly show that there exist two frequency bands where the refraction index is negative. The double left-handed passbands are due to the multiple capacitances and inductances induced in the structure, which can be further tuned to realize a metamaterial with multiple (more than two) left-handed frequency bands.

Negative refraction of a combined double S-shaped metamaterial

We present a combined double S-shaped metamaterial structure that exhibits a left-handed property over a wide frequency band of 6GHz. The transmission experiment, phase measurement, and prism refraction experiment from the structure confirm the presence of the negative index of refraction.

Application of coordinate transformation in bent waveguides

We apply coordinate transformations in the design of waveguides with bent geometry to reduce reflection at the incident port. It was found that in the case of metallic waveguides, by applying the transformation to the medium inside a right-angle bent waveguide, low reflection can be obtained. For the case of dielectric waveguides, this can also be done by applying the same transformation to the bent region containing both the dielectric core and its claddings. Our proposed technique provides an alternative method for designing bent waveguides with low insertion loss.

High-directivity antenna with small antenna aperture

We show in this letter that, by using an inhomogeneous metamaterial shell, it is possible to achieve highly directive emission with a small antenna aperture. The material parameters of the metamaterial substrate are obtained by a nonmonotonic optical transformation. Therefore, a large antenna can be effectively transformed to an equivalent one with much smaller aperture. Full-wave finite-element modeling has been performed to confirm this point. The concept proposed here provides a possible solution to reduce the size of antenna without disturbing the radiation characteristics.

Equivalent circuit model for left-handed metamaterials

A general equivalent circuit model to calculate the effective permeability of various configurations of split-ring resonators (SRRs) is presented. In the proposed model, each column of the SRR units along the axis of the rings is modeled as a quasisolenoid under magnetic induction. The inductance per ring of the infinite column of these rings is calculated, assuming all the rings in this column support the same current. The electromagnetic coupling between these individual columns of the rings is integrated into this circuit model, which is then applied to a two dimensional cross embedded split-ring resonator. The agreement between the predicted results and numerical simulations shows the efficiency of the model in predicting the frequency band of negative permeability.

Noncontact Distance and Amplitude-Independent Vibration Measurement Based on an Extended DACM Algorithm

Utilizing microwave continuous-wave Doppler radars to wirelessly detect mechanical vibrations have been attracting more and more interests in recent years. In this paper, aiming to solve the null point and nonlinear issues in small-angle approximation-based Doppler radar sensors and eliminate the codomain restriction in the arctangent demodulation approach, we propose and investigate an extended differentiate and cross-multiply (DACM) algorithm. With an additional accumulator, the noise performance of the original DACM algorithm is improved. Moreover, the amplitude information of the vibration can be directly retrieved from accumulation without involving any distance-dependent issue. Experimental validations show that the proposed algorithm can fully recover the vibration patterns with the measured noncalibrated amplitude agreeing well with the known precalibrated data. Application examples of mechanical fault detection and human vital sign detection are demonstrated, showing a wide range of potential applications of this algorithm.

A Tunable Microstrip Bandpass Filter With Two Independently Adjustable Transmission Zeros

In this letter, a tunable microstrip bandpass filter (BPF) with two independently adjustable transmission zeros (TZs) is reported. By introducing two microwave varactors to tune the TZs, the center frequency and the bandwidth of the BPF can be separately adjusted within a broad tuning range by varying the dc bias voltages applied to the varactors. Theoretical analysis and design approach are described. The experimental result of a demonstrative BPF shows that a less than 4 dB insertion loss, a relative bandwidth of 9% and a center frequency tunable from 1.4 to 2 GHz are obtained. The measured performance of the fabricated filter shows good agreement with the proposed theory.