Terahertz metamaterial devices: from thickness and material dependence to perfect absorption

Metamaterials consist of subwavelength unit cells periodically patterned to exhibit extraordinary electromagnetic properties that do not exist in naturally occurring materials. The far-infrared, or terahertz frequency region of the electromagnetic spectrum is ripe with potential with metamaterials providing a promising technological route towards developing application. Metamaterial “perfect absorbers”, typically configured with three layers as metamaterials-dielectric-ground, have attracted tremendous interest due to near unity absorption of incident electromagnetic radiation over a designed frequency range, with the device having subwavelength thickness. Several theories have been developed to understand the physics of perfect absorption. However, it is important to develop alternative numerical and analytical strategies that transparently connect with the electromagnetic and dielectric properties of the constituent materials to better understand how experimentally accessible parameters ultimately determine the absorption. First, this dissertation introduces a metamaterial absorber with air as spacer layer instead of dielectric materials. In the absence of dielectric material loss, the design can achieve three times higher quality factor compared to traditional designs. Additionally, the absence of the spacer material yields the possibility to access the space between the metamaterial layer and the ground plane inspiring a microfluidic channel integrated sensing device with sensitivity more than three times of the reported results. Second, this dissertation investigates the dependence of the metamaterial absorption maxima on the spacer layer thickness and the reflection coefficient of the metamaterial layer obtained in the absence of the ground plane layer. We observed that the absorption peaks redshift as the spacer thickness is increased, in excellent agreement with the analysis. Third, this dissertation presents a detailed analysis of the conditions that result in unity absorption in metamaterial absorbers. These simple expressions reveal a redshift of the unity absorption frequency with increasing loss that, in turn, necessitates an increase in the thickness of the dielectric spacer. Our findings can be widely applied to guide the design and optimization of the metamaterial absorbers and sensors

The diploid genome sequence of an Asian individual

Here we present the first diploid genome sequence of an Asian individual. The genome was sequenced to 36-fold average coverage using massively parallel sequencing technology. We aligned the short reads onto the NCBI human reference genome to 99.97% coverage, and guided by the reference genome, we used uniquely mapped reads to assemble a high-quality consensus sequence for 92% of the Asian individual's genome. We identified approximately 3 million single-nucleotide polymorphisms (SNPs) inside this region, of which 13.6% were not in the dbSNP database. Genotyping analysis showed that SNP identification had high accuracy and consistency, indicating the high sequence quality of this assembly. We also carried out heterozygote phasing and haplotype prediction against HapMap CHB and JPT haplotypes (Chinese and Japanese, respectively), sequence comparison with the two available individual genomes (J. D. Watson and J. C. Venter), and structural variation identification. These variations were considered for their potential biological impact. Our sequence data and analyses demonstrate the potential usefulness of next-generation sequencing technologies for personal genomics

Integrating microsystems with metamaterials towards metadevices

Optics: Dynamically tuning how materials respond to light Specially engineered materials known as metamaterials have led to a boost in the performance of optical and photonic devices, with yet further improvements within reach by finding ways to dynamically tune their properties. Metamaterials consist of arrays of structures smaller than the wavelength of light, offering an unprecedented opportunity to tune their interaction with electromagnetic waves. Xin Zhang’s team at Boston University has reviewed approaches to integrate microelectromechanical systems and nanoelectromechanical systems (MEMS and NEMS) with metamaterials to create metadevices. By using MEMS and NEMS to adjust how the array in a metamaterial is arranged, metadevices can be rapidly and reversibly reconfigured to detect, modulate, or respond to specific electromagnetic frequencies. The authors conclude by highlighting avenues for the improvement of metadevices, which have applications from LIDAR to 5G communication

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The document provides supplemental information to “Electromechanically Tunable Metasurface Transmission Waveplate at Terahertz Frequencies”