The advent of negative index materials has spawned extensive research into metamaterials over the past decade. Metamaterials are attractive not only for their exotic electromagnetic properties, but also their promise for applications. A particular branch–the metamaterial perfect absorber (MPA)–has garnered interest due to the fact that it can achieve unity absorptivity of electromagnetic waves. Since its first experimental demonstration in 2008, the MPA has progressed significantly with designs shown across the electromagnetic spectrum, from microwave to optical. In this Progress Report we give an overview of the field and discuss a selection of examples and related applications. The ability of the MPA to exhibit extreme performance flexibility will be discussed and the theory underlying their operation and limitations will be established. Insight is given into what we can expect from this rapidly expanding field and future challenges will be addressed.

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We present a single pixel terahertz (THz) imaging technique using optical photoexcitation of semiconductors to dynamically and spatially control the electromagnetic properties of a semiconductor mask to collectively form a THz spatial light modulator (SLM). By co-propagating a THz and collimated optical laser beam through a high-resistivity silicon wafer, we are able to modify the THz transmission in real-time. By further encoding a spatial pattern on the optical beam with a digital micro-mirror device (DMD), we may write masks for THz radiation. We use masks of varying complexities ranging from 63 to 1023 pixels and are able to acquire images at speeds up to 1/2 Hz. Our results demonstrate the viability of obtaining real-time and high-fidelity THz images using an optically controlled SLM with a single pixel detector.

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Introduction: Young-onset dementia affects about 1 in 1500 people aged under 65 years in the United Kingdom (UK). It is associated with loss of employment, independence and an increase in psychological distress. This project set out to identify the benefits of a 2 hours per week structured activity programme of gardening for people with young-onset dementia. Method: A mixed methods (qualitative and quantitative) study of therapeutic gardening for people with young-onset dementia, measuring outcomes for both participants with young-onset dementia and their carers, was used. Twelve participants were recruited from a county-wide mental health service for older adults, based on onset of dementia being before the age of 65 years (range 43–65 years). Of these, two participants dropped out and one died during the project. Measures included the Mini Mental State Examination (MMSE), Bradford Well-Being Profile, Large Allen Cognitive Level Screen (LACLS) and Pool Activity Level (PAL). Findings: Over a 1-year period the carers of the people with young-onset dementia found that the project had given participants a renewed sense of purpose and increased well-being, despite cognitive functioning continuing to decline during this period. Conclusion: This study suggests that a meaningful guided activity programme can maintain or improve well-being in the presence of cognitive deterioration.

We investigate the application of dynamic metasurface antennas (DMAs) to synthetic aperture radar (SAR) systems. Metasurface antennas can generate a multitude of tailored electromagnetic waveforms from a physical platform that is low-cost, lightweight, and planar; these characteristics are not readily available with traditional SAR technologies, such as phased arrays and mechanically steered systems. We show that electronically tuned DMAs can generate steerable, directive beams for traditional stripmap and spotlight SAR imaging modes. This capability eliminates the need for mechanical gimbals and phase shifters, simplifying the hardware architecture of a SAR system. Additionally, we discuss alternative imaging modalities, including enhanced resolution stripmap and diverse pattern stripmap, which can achieve resolution on par with spotlight, while maintaining a large region-of-interest, as possible with stripmap. Further consideration is given to strategies for integrating metasurfaces with chirped pulse RF sources. DMAs are poised to propel SAR systems forward by offering a vast range of capabilities from a significantly improved physical platform.

In this letter, we discuss the design, fabrication, and experimental characterization of a bi-layer fully functional near-perfect metamaterial absorber (MMA) in the long-wavelength infrared (LWIR), which is broadband and generally insensitive to polarization up to a 60 incidence angle. A spectral absorptance of !99% was attained simultaneously at multiple LWIR wavelengths, with a bandwidth of 2 lm where the absorptance is !90%. This remarkable behavior is attributed to the strong mixing of coupling modes between the two resonators and the ground plane in the presence of a lossy dielectric, in which single layer structures do not exhibit. Furthermore, we show, by comparing two different MMA structures, how the absorption can be tailored by design within and across several IR subdivisions through a slight change in geometrical parameters. The bi-layer MMA has the immediate application of a functionally versatile, low-profile thermal sensor or emitter. Perfect absorbers in the infrared (IR) are particularly exciting due to their applicability as thermal emission control surfaces, among other applications. Efforts have been made to tailor the thermal emission of structures through the use of 1-D and 2-D gratings, 1,2 photonic crystals, 3,4 and microstrip patch arrays.5 However, many of these solutions are narrowband and lack functionality at certain polarizations or incidence angles, all of which are critical to practical thermal applications where maximum absorption of light is desired. 6 Since the experimental demonstration of a near-unity metamaterial absorber (MMA) in the microwave spectrum in 2008, 7 a great deal of research has been invested into establishing the utility of a perfect absorber for real-world application. Work rapidly expanded into the terahertz, 8 short-wave IR, 9 mid-wave IR, 10 near-infrared, 11,12 and visible range; 13 and with it came a flood of attempts to increase bandwidth and insensitivities to polarization and incidence angles (see Ref.6 for a comprehensive review). Initially, most of these designs suffered in one area or another: multi-band and wideangle designs were still narrow-band 14-17 or polarization-dependent, 7,8 while these wholly insensitive broadband designs did not attain a consistent absorptance over 90%. 18,19 However, significant advancements have been made in creating "fully functional" near-perfect absorbers: those which exhibit strong broadband responses while being simultaneously angle and polarization insensitive. In the past year alone, fully functional MMAs have been demonstrated in the microwave, 20-25 terahertz, 26-28 and optical 29 regimes. Despite this advancement, we found a lack in development of fully functional IR MMAs. [30][31][32][33][34][35][36][37][38] In this letter, we demonstrate, both computationally and experimentally, a fully functional near-perfect MMA in the long wavelength IR (LWIR) range. We used a bi-layer pattern to achieve a wide-angle, polarization-insensitive, broadband performance which is superior overall to many single layer 30,31,33...

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