Brian B. Tierney

Design of Self-Matched Planar Loop Resonators for Wireless Nonradiative Power Transfer

An impedance-matching technique for magnetically coupled planar-loop resonators employing transmission lines and capacitive stubs is presented for application in wireless nonradiative power transfer (WNPT). These distributed components can be incorporated into the planar resonator itself, thereby eliminating external matching networks. The theory behind the impedance-matching technique is given in detail. Parameter tradeoffs are explored and a design procedure is provided. Two different planar loop designs are presented. The first design yields a loop-to-loop power transfer efficiency of 91% at a coupling distance of 15 cm (1.67 loop radii). The second design yields 85% efficiency at a coupling distance of 20 cm (2.22 loop radii). These results show that planar self-matched loop resonators enable compact efficient WNPT.

Planar Shielded-Loop Resonators

The design and analysis of planar shielded-loop resonators for use in wireless nonradiative power transfer systems is presented. The difficulties associated with coaxial shielded-loop resonators for wireless power transfer are discussed and planar alternatives are proposed. The currents along these planar structures are analyzed and first-order design equations are presented in the form of a circuit model. In addition, the planar structures are simulated and fabricated. Planar shielded-loop resonators are compact and simple to fabricate. Moreover, they are well-suited for printed circuit board designs or integrated circuits.

Arbitrary Beam Shaping Using 1-D Impedance Surfaces Supporting Leaky Waves

A technique for generating an arbitrary, prescribed radiation pattern from a 1-D leaky-wave antenna is presented. The technique is applied to leaky-wave impedance surfaces. A homogenized model for an impedance surface is used so that the work is not limited to particular geometries. The model consists of a grounded, uniaxial dielectric substrate topped by a reactance sheet. To synthesize prescribed aperture fields, the leakage constant α|| and phase constant β|| along the antenna are tailored. The aperture field is determined by adapting the Orchard-Elliott method used in array synthesis to continuous line sources. The aperture field is related to α|| and β|| using a well-known approach, then the transverse resonance technique is employed to analytically relate α|| and β|| to the electrical parameters of the impedance surface. Specifically, the extraordinary index and sheet reactance are used to control α|| and β||. The designs presented demonstrate the synthesis of a variety of far-field patterns. Full-wave simulations show an improvement over previous beam synthesis techniques based on geometrical optics. Moreover, the numerical techniques demonstrate an efficient, gradient search method as an alternative to the iterative FFT methods explored previously, which have not generated radiation patterns with such high accuracy.

Planar shielded-loop resonators for wireless non-radiative power transfer

A planar analog to the conventional coaxial shielded-loop resonator used for wireless non-radiative power transfer (WNPT) is introduced. Simulation and experimental results show that the inner conductor need not be completely shielded by the outer conductor to achieve resonance and efficient power transfer. The prototypes also demonstrate the ease and consistency of fabrication compared to conventional coaxial shielded loops.

Synthesis of Tensor Impedance Surfaces to Control Phase and Power Flow of Guided Waves

A synthesis method for printed-circuit tensor impedance surfaces (PCTISs) is presented that allows arbitrary control of phase progression and power flow of guided waves. PCTISs consist of a subwavelength-patterned metallic cladding atop a grounded dielectric substrate. The cladding is modeled by an anisotropic tensor sheet admittance. The synthesis method employs field analysis to determine the required tensor sheet admittance values for a prescribed phase progression and power-flow direction. An inhomogeneous distribution of PCTIS unit cells can be used to design a 2-D metasurface capable of spatial control of surface waves. A collimator is designed to verify the proposed synthesis procedure and demonstrate its utility.

A compact, metamaterial beamformer designed through optimization

A compact, metamaterial-based antenna beam-former is presented. The design employs a new optimization technique that couples a custom finite-element method (FEM) electromagnetic solver to a constrained minimization algorithm. The optimization operates on a surrogate model of the beam-former composed of an inhomogeneous, anisotropic material. This technique is an alternative to transformation electromagnetics that offers improved flexibility and physical realizability. In particular, the technique offers device designs which transform stipulated input (incident) fields to prescribed output fields (with desired amplitude and phase distribution), while constraining the material parameters to realizable values.

Controlling Leaky Waves With 1-D Cascaded Metasurfaces

A simple metasurface topology is presented which can spatially control the amplitude, phase, and polarization of leaky-wave modes. Using this technique, the tailoring of radiation patterns, including polarization, is demonstrated. The metasurfaces are modeled as full-tensor electric sheet admittances separated by dielectric layers, backed by a ground plane. These structures can be fabricated simply by stacking patterned metallic sheets. Such metasurfaces have been previously designed to control electromagnetic wavefronts incident from free space. In contrast, this communication presents a theoretical study on their application in synthesizing leaky-wave radiation patterns.

Arbitrary leaky-wave antenna patterns with stacked metasurfaces

Complete control of the magnitude, phase, and polarization of an antenna aperture using leaky waves supported by cascaded metasurfaces is discussed. The proposed structure consists of cascaded, tensor electric sheet admittances separated by dielectric substrates atop a ground plane. The design methodology is briefly discussed.

Radiation pattern synthesis using impedance surfaces supporting leaky waves

We report impedance surfaces that offer subwavelength control of the leakage constant ax and propagation constant ßx. This enhanced control allows tailoring of the aperture field at the impedance surface and therefore the synthesis of arbitrary far-field patterns. The transverse resonance technique is used to analytically relate the complex wavenumber kx to the electrical parameters of the proposed impedance surface. Two design examples are reported: a constant amplitude aperture distribution for increased directivity, and a Hamming window amplitude distribution for reduced sidelobe levels.

Tailoring leaky-wave radiation with impedance surfaces

A method for designing TM leaky-wave antennas with prescribed far-field patterns using impedance surfaces is presented. The impedance surface amounts to a grounded, anisotropic substrate topped by a reactance sheet. The transverse resonance technique is employed to analytically solve for the propagation and leakage constants along the structure. Two design examples are reported: a constant amplitude aperture field with increased directivity, and a modified Hamming window aperture field with reduced sidelobe levels.