Dynamic metamaterial aperture for microwave imaging

Abstract

We present a dynamic metamaterial aperture for use in computational imaging schemes at microwave frequencies. The aperture consists of an array of complementary, resonant metamaterial elements patterned into the upper conductor of a microstrip line. Each metamaterial element contains two diodes connected to an external control circuit such that the resonance of the metamaterial element can be damped by application of a bias voltage. Through applying different voltages to the control circuit, select subsets of the elements can be switched on to create unique radiation patterns that illuminate the scene. Spatial information of an imaging domain can thus be encoded onto this set of radiation patterns, or measurements, which can be processed to reconstruct the targets in the scene using compressive sensing algorithms. We discuss the design and operation of a metamaterial imaging system and demonstrate reconstructed images with a 10:1 compression ratio. Dynamic metamaterial apertures can potentially be of benefit in microwave or millimeter wave systems such as those used in security screening and through-wall imaging. In addition, feature-specific or adaptive imaging can be facilitated through the use of the dynamic aperture.

Polarizability extraction of complementary metamaterial elements in waveguides for aperture modeling

“…To address this problem, we outline an alternative method based on the mode expansion of cylindrical waves propagating through the waveguide. This framework is particularly advantageous for modeling and designing planar structures [48,76]. We also demonstrate that the extracted polarizability of a metamaterial element depends on the geometry of the waveguide in which it is embedded.…”

Experimental Synthetic Aperture Radar With Dynamic Metasurfaces

“…While it seems fair that the diverse pattern case uses a similar number of measurements (i.e. 11 masks), we know that the aperture can image with fewer measurements in this modality [25], [31]. As such, we use a new set of 3 masks at each z position.…”

“…The overall radiation pattern generated by this aperture is thus the superposition of the radiation from each single radiator. By integrating a tuning mechanism into each independent resonator, further control over the radiated waveforms can be achieved [25]. The flexibility offered by dynamic metasurfaces may be used to steer directive beams for enhanced signal strength [22], create nulls in the pattern to avoid jamming [26], [27], probe a large region of interest with a wide beam, or even interrogate multiple positions at once with a collection of beams [28].…”

“…More recently, a dynamic metasurface aperture was utilized in nearfield computational imaging. In this case, uncorrelated patterns were employed to perform microwave imaging in a similar vein to the frequency-diverse approach pioneered in [25], [31].…”

Measurement Matrix Analysis and Radiation Improvement of a Metamaterial Aperture Antenna for Coherent Computational Imaging

“…Hence, to obtain a metamaterial aperture that generates the frequency-agile far-field patterns that are as orthogonal as possible, elements distributed on the aperture must have a strong resonance with a high Q-value. Other approaches to frequency-diverse imaging have also been pursued, including multiply scattering structures, such as mode-mixing cavities and dynamic metamaterial apertures [8][9][10]. Fractal models have been used to design fractal antennas with very special properties: about one-tenth of a wavelength and a pre-fractal geometrical configuration [11] could be used in metamaterial miniaturized technology, which is needed for coherent imaging.…”