Huygens’ principle is a well-known concept in electromagnetics that dates back to 1690. Here, it is applied to develop designer surfaces that provide extreme control of electromagnetic wave fronts across electrically thin layers. These reflectionless surfaces, referred to as metamaterial Huygens’ surfaces, provide new beam shaping, steering, and focusing capabilities. The metamaterial Huygens’ surfaces are realized with two-dimensional arrays of polarizable particles that provide both electric and magnetic polarization currents to generate prescribed wave fronts. A straightforward design methodology is demonstrated and applied to develop a beam-refracting surface and a Gaussian-to-Bessel beam transformer. Metamaterial Huygens’ surfaces could find a wide range of applications over the entire electromagnetic spectrum including single-surface lenses, polarization controlling devices, stealth technologies, and perfect absorbers.

Methods to analyze and synthesize two-dimensional, bianisotropic metamaterials (metasurfaces) are presented. First, a general bianisotropic metasurface is analyzed by using closed-form expressions that relate the reflection and transmission coefficients to its constituent surface parameters. Next, a systematic method to synthesize bianisotropic metasurfaces is outlined. It is analytically shown that bianisotropic metasurfaces can be realized by cascading anisotropic, patterned metallic sheets (electric sheet admittances). This geometry allows for straightforward design and fabrication from microwave to optical wavelengths. To demonstrate the utility of the proposed method, four devices exhibiting exotic polarization transformations are presented: a polarization rotator, an asymmetric circular polarizer, an asymmetric linear polarizer, and a symmetric circular polarizer. The optimal performance at centimeter, millimeter, and micrometer wavelengths highlights the versatility of the design process.

It is experimentally shown that bianisotropic metasurfaces allow for extreme polarization control of light with high performance. A metasurface providing asymmetric transmission (i.e., polarization conversion) of circularly polarized light is reported at a wavelength of $1.5\text{ }\text{ }$\mu${}\mathrm{m}$. The experimental transmittance and extinction ratio are 50% and $20:1$, which represents an order of magnitude improvement over previous optical structures exhibiting asymmetric transmission. The metasurface consists of patterned gold sheets that are spaced at a subwavelength distance from each other. The same design and fabrication processes can be used in the future to completely control the phase, amplitude, and polarization of light.

Using a patterned, grating-like plate to control the electromagnetic near field, we demonstrate focusing well beyond the diffraction limit at ∼ 1 gigahertz. The near-field plate consists of only capacitive elements and focuses microwaves emanating from a cylindrical source to a spot of size ≈ λ/20 (half-power beamwidth), where λ is the free-space wavelength. These plates will find application in antennas, beam-shaping devices, nonradiative wireless power-transfer systems, microscopy, and lithography.

Unprecedented control of an electromagnetic wave front is demonstrated with reflectionless metasurfaces that can manipulate vector Bessel beams: cylindrical vector beams with a Bessel profile. First, two metasurfaces are developed to convert linearly and circularly polarized Gaussian beams into vector Bessel beams. Each unit cell of the metasurfaces provides polarization and phase control with high efficiency. Next, the reciprocal process is demonstrated: an incident radially polarized Bessel beam is transformed into collimated, linearly and circularly polarized beams. In this configuration, a planar Bessel beam launcher is integrated with a collimating metasurface lens to realize a low-profile lens-antenna. The lens-antenna achieves a high directivity (exceeding 20 dB) with a subwavelength overall thickness. Finally, a metasurface providing isotropic polarization rotation is used to transform a radially polarized Bessel beam into an azimuthally polarized Bessel beam. This work demonstrates that metasurfaces can be used to generate arbitrary combinations of radial and azimuthal polarizations for applications such as focus shaping or generating tractor beams.

Temporally modulated metamaterials have attracted significant attention recently due to their non-reciprocal and frequency converting properties. Here, a transparent, time-modulated metasurface, that functions as a serrodyne frequency translator, is reported at X-band frequencies. With a simple biasing architecture, the metasurface provides electrically-tunable transmission phase that covers 360°. A sawtooth waveform is used to modulate the metasurface, allowing Doppler-like frequency translation. Modal analysis of an analogous time-modulated medium is performed to gain insight into the operation of the metasurface-based serrodyne frequency translator. Two such metasurfaces can be cascaded together to achieve magnetless devices that perform either phase or amplitude non-reciprocity.