Showing papers by "David McGloin published in 2021"

3-D Printed All-Dielectric Dual-Band Broadband Reflectarray With a Large Frequency Ratio

Abstract: This communication proposes a new all-dielectric broadband dual-band reflectarray with a large frequency ratio using low-cost 3-D printing. In contrast to conventional reflectarrays using metallic resonant cells or dielectric slabs as phasing elements with full metal ground, the proposed design uses air as the phasing element and a stepped dielectric mirror structure as the ground. In this way, the metal ground is removed, which makes the design an all-dielectric one. Taking advantage of the dielectric mirror that only exhibits a bandgap in the predesigned band while allowing electromagnetic (EM) waves to pass through it at the frequency out of the bandgap region, a dual-band reflectarray is obtained. By properly selecting the bandgap frequency of the dielectric mirror, the dual-band frequency ratio is scalable and can be very large. Furthermore, instead of using a metallic or dielectric resonator based on resonance, air layers with linear phase response are adopted as the phasing element. Thus, the reflectarray shows broadband and stable performance over the dual-band. Compared with the state-of-the-art works using printed circuit boards (PCBs) or microfabrication, the proposed design is low cost and lightweight, and can be rapidly prototyped. For proof-of-concept, a prototype operating at $K$ -band and $V$ -band with a frequency ratio of 2.7 is printed and measured.

Additively Manufactured Millimeter-Wave Dual-Band Single-Polarization Shared Aperture Fresnel Zone Plate Metalens Antenna

Abstract: Fresnel zone plate (FZP) lens antenna, consisting of a set of alternative transparent and opaque concentric rings arranged on curvilinear or flat surfaces, have been widely used in various fields for sensing and communications. Nevertheless, the state-of-art FZP lens antennas are limited to a single band due to the frequency-dependent feature, which hinders their use in multi-band applications. In this work, a shared aperture dual-band FZP metalens antenna is proposed by merging two single-band FZP metalens antenna operating at distinct frequency bands seamlessly into one. Instead of using conventional metallic conductors, double-screen metagrids are devised in this work to form the concentric rings. Because the metagrids show distinct transmission/reflection properties at different frequencies, the performance of one set of concentric rings operating at the one band will not be affected by the other operating at the different band. In addition, to compensate for the phase shift introduced by the metagrids, an additional dielectric ring layer is added atop the FZP taking advantage of additive manufacturing. Thus, the radiation performance of the dual-band FZP lens antenna is comparable to that of each single FZP metalens antenna. For proof-of-concept, an antenna prototype operating at the dual band, 75 and 120 GHz with a frequency ratio of 1.6, is fabricated using an integrated additively manufactured electronics (AME) technique. The measured peak gains of 20.3 and 21.9 dBi are achieved at 75 and 120 GHz, respectively.

Self-evolving ghost imaging

Abstract: Ghost imaging captures 2D images with a point detector instead of an array sensor. It could therefore solve the challenge of building cameras in wave bands where sensors are difficult and expensive to produce and could open up more routine THz, near-infrared, lifetime, and hyperspectral imaging simply by using single-pixel detectors. Traditionally, ghost imaging retrieves the image of an object offline by correlating measured light intensities with pre-designed illuminating patterns. Here we present a “self-evolving” ghost imaging (SEGI) strategy for imaging objects bypassing offline post-processing. It also offers the capability to image objects in turbid media. By inspecting the optical feedback, we evaluate the illumination patterns by a cost function and generate offspring illumination patterns that mimic the object’s image, bypassing the reconstruction process. At the initial evolving state, the object’s “genetic information” is stored in the patterns. At the following imaging stage, the object’s image (48×48pixels) can be updated at a 40 Hz imaging rate. We numerically and experimentally demonstrate this concept for static and moving objects. The frame-memory effect between the self-evolving illumination patterns provided by the genetic algorithm enables SEGI imaging through turbid media. We further demonstrate this capability by imaging an object placed in a container filled with water and sand. SEGI shows robust and superior imaging power compared with traditional computational ghost imaging. This strategy could enhance ghost imaging in applications such as remote sensing, imaging through scattering media, and low-irradiative biological imaging.

Effects of spatial confinement on migratory properties of Dictyostelium discoideum cells.

Abstract: Migratory environments of various eukaryotic cells, such as amoeba, leukocytes and cancer cells, typically involve spatial confinement. Numerous studies have recently emerged, aimed to develop expe...

Single-Pixel Diffuser Camera

Abstract: We present a compact, diffuser assisted, single-pixel computational camera. A rotating ground glass diffuser is adopted, in preference to a commonly used digital micro-mirror device (DMD), to encode a two-dimensional (2D) image into single-pixel signals. We retrieve images with an 8.8% sampling ratio after the calibration of the pseudo-random pattern of the diffuser under light-emitting diode (LED) illumination. Furthermore, we demonstrate hyperspectral imaging with line array detection by adding a diffraction grating. As the random and fixed patterns of a rotating diffuser placed in the image plane can serve as 2D modulation patterns in single-pixel imaging, we do not need further calibration for spectral imaging case since we use a parallel recovery strategy for images at all wavelengths. The implementation results in a cost-effective single-pixel camera for high-dimensional imaging, with potential for imaging in non-visible wavebands.

Sub-Terahertz 3-D Printed All-Dielectric Low-Cost Low-Profile Lens-Integrated Polarization Beam Splitter

Abstract: Polarizing beam splitters (PBSs) are essential components for polarization-multiplexed communication system. However, conventional PBS, such as Rochon prism and Wollaston prism, must be sufficiently thick to generate enough walk-off distance between two orthogonal polarizations due to the low birefringence of natural material. To reduce this requirement, we propose and demonstrate a three-dimensional printed low-cost low-profile Fresnel-Rochon prism. By adjusting the dimensions of the artificially engineered gratings that comprise the prism, the refractive index tensor along the x - and y -direction can differ, enabling the independent manipulation of the deflection angles of the orthogonal polarized components. Applying the Fresnel principle to this Rochon prism, the thickness can be greatly reduced while the polarization splitting and deflection angles remain unaltered. Meanwhile, the transmission efficiency of the prism is also improved as less energy is dissipated in the lossy printing material. In addition, in contrast to conventional Rochon prisms formed by two right triangle prisms, the proposed Rochon prism enjoys the benefit of simple fabrication without any further assembly procedure. Prototypes operating at 0.14-THz frequency were printed and measured to verify the idea.

Single-pixel diffuser camera

Abstract: We present a compact, diffuser-assisted, single-pixel computational camera. A rotating ground glass diffuser is adopted, in preference to a commonly used digital micro-mirror device (DMD), to encode a two-dimensional (2D) image into single-pixel signals. We retrieve images with an 8.8% sampling ratio after the calibration of the pseudo-random pattern of the diffuser under incoherent illumination. Furthermore, we demonstrate hyperspectral imaging with line array detection by adding a diffraction grating. The implementation results in a cost-effective single-pixel camera for high-dimensional imaging, with potential for imaging in non-visible wavebands.