A novel fabrication process using a laser machining is proposed, allowing for the creation of arbitrary conductor geometries on an ultrathin dielectric substrate. During the engraving process, a thin aluminum layer is removed from a Mylar substrate, leaving a periodic conductive array. This process provides several advantages over existing techniques and may open additional applications due to the ability to economically create ultra-thin, conformal, optically transparent, light weight surfaces. The proposed technique is modelled and validated through experimental measurements of fabricated simple band-stop square and circle loop frequency selective surfaces (FSSs). Good agreement is observed between the simulated and measured results with resonances 9.9 GHz and 10 GHz for the square loop and 14.2 GHz and 14.4 GHz for the circle loop.
Frequency-selective surfaces (FSSs), have various applications in microwave electromagnetics. This paper reports a solution to the current FSS challenges of flexibly, low profile, simple fabrication and polarization control using a novel structure operating across X and Ku frequency bands where a linearly polarized wave is rotated by 90°. The FSSs were fabricated by laser engraving a thin layer of 5m aluminum on a 65 m Mylar substrate with a relative permittivity of 2.7, and separated by a dielectric spacing layer of 0.9 mm polypropylene substrate, with a relative permittivity of 3. The co and cross-polarized reflection and transmission response of the structure was investigated using numerical modeling and was measured experimentally. A parametric study was also conducted focusing on key performance indicators, and specifically the bandwidth of the structure. The novelty of this polarization rotation structure lies in its ultra-thin profile (0.034 λ0), flexibility and significant transmission bandwidth. The fabricated prototypes experimental results were in good agreement with the simulated results, with a simulated -6 dB bandwidth of 61% and a measured -6dB bandwidth of 60%. Applications include antenna radomes where polarization is particularly important, as well as other polarization filtering applications which require a conformal low profile structure.INDEX TERMS flexible, frequency selective surface (FSS), microwave filters, polarizer, ultra-thin.
Student engagement continues to be a major challenge, particularly in electromagnetics courses. This is independent of whether courses are compulsory or elective. This paper presents an approach to assessing students that provides them with an opportunity for experiential learning, following Kolb's learning cycle. Final year students are required to develop and complete two experimental projects over the 12-week trimester. At the outset of each project, pairs of students choose a three-line project outline; projects are unique to each two-person group with an obscure but practical industrial outcome designed to complement the lecture material. To succeed, students must continue to discuss their project strategies, measurements and final applications with the teaching team throughout the trimester. Students have rated the course experience very highly, and in some cases, their projects have enhanced their post-graduation employment opportunities in the field directly related to one of their projects.
Frequency-selective surfaces (FSSs) are commonly employed at microwave frequencies to control free space electromagnetic interference. This paper reports the use of cascaded dual miniaturized elements for radio secure environments. Miniaturized elements have reduced size (< 0.1 wavelengths), and exceptional angular stability. Thin, flexible and optically transparent FSS samples were fabricated by laser engraving elements into a conductive aluminum layer, with a supporting Mylar substrate (relative permittivity 2.7), and thickness of 65μm. The linearly polarized transmission response was investigated numerically by exploring the scattering parameters and the surface currents at resonance. Miniaturized elements in both single and cascaded FSS structures, have been explored to create both broadband and multiband responses across the L and S frequency bands, respectively. The theoretical and experimental results were in good agreement for the fabricated dual element dual layer translated band-stop FSS, displaying a resonant frequency reduction of 70% compared to a square loop with the same dimensions, along with significantly broad operation bandwidths of 118% and 104% for simulated and measured, respectively. These improvements were due to the selection of the individual elements in the array, their geometric arrangement, and the introduction of additional layers with lateral offsets.
Frequency selective surfaces (FSSs) have applications across multiple disciplines due to their unique electromagnetic properties. This paper investigates the use of both rounded square loops, and simple loop type dual elements arranged in unique patterns, to control the transmission and reflection bandwidth and resonant frequencies over KU and K frequency bands supported by equivalent circuit models. The FSSs were fabricated using laser engraving to create conductive loop type elements on a thin, flexible and optically transparent Mylar substrate (relative permittivity of 2.7 and thickness of 65 μm). The frequency response of the surfaces are controlled through the element self-inductance and capacitive coupling with neighbouring elements. This work shows that different arrangements result in the formation of multiple distinct resonances. The theoretical and experimental results were in good agreement where rounded squares and dual element arrays were employed to create broadband and multiband band-stop FSSs. A polarization sensitive surface exhibited stop-bands at 12 and 16 GHz in transverse electric polarization and a stop-band at 14.4 GHz in transverse magnetic polarization. This technique can be applied to any periodic array through careful selection of the individual elements in the array, as well as their arrangement.
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