RESUMEN

Low-cost and portable electromagnetic (EM) stroke diagnostic systems are of great interest due to the increasing demand for early on-site detection or long-term bedside monitoring of stroke patients. Biosensor antennas serve as crucial hardware components for EM diagnostic systems. This article presents a detect capability enhanced biosensor antenna with a planar and compact configuration for portable EM stroke detection systems, overcoming the problem of limited detection capability in existing designs for this application. The proposed antenna is developed based on multiple dipoles, exhibiting multi-mode resonances and complementary interaction. In the frequency domain, the simulated and measured results with the presence of head phantoms show that this compact planar antenna achieves improved performance in both impedance bandwidth and near-field radiation inside the head tissues, which all contribute to enhancing its stroke detection capability in radar-based EM diagnosis. An array of 12 elements is numerically and experimentally tested in a lab-setting EM stroke diagnostic system to validate the detection capability of the proposed antenna. The reconstructed 2-D images inside the head demonstrate successful detection of different stroke-affected areas, even as small as 3 mm in radius, significantly smaller than those of reported relevant works under the same validation setting, confirming the enhanced detection capability of the proposed antenna.

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RESUMEN

Orbital angular momentum (OAM) modes of electromagnetic (EM) waves have been extensively studied to obtain more than two independent channels at a single frequency. Thus far, however, multiple radiators have been used to achieve this goal in wireless communications. For the first time, a single radiator was designed to simultaneously transmit three OAM waves in free space at the same frequency. Our design makes use of the radiating resonant modes of a dielectric resonator antenna (DRA). For demonstration, a wireless communication system consisting of a pair of transmitting and receiving OAM DRAs was setup and measured. Three EM waves carrying three different signals were transmitted and received successfully, increasing the system throughput without requiring any complex signal processing algorithms. It confirms that a single radiator can wirelessly transmit more than two independent EM waves at a single frequency by using multi-OAM modes. The work is useful for the future high-speed wireless communication systems.

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We report on an apodization scheme for terahertz fiber Bragg gratings. The grating consists of only 90 ablated notches on two opposite sides of a subwavelength polymer fiber. The grating strength can be effectively tuned by controlling the longitudinal shift between the two-sided notches, and apodization can be achieved by applying an envelope profile. Side lobe suppression of 14 dB was experimentally observed when compared with an unapodized grating.

RESUMEN

Transmission filters for the terahertz domain having a shaped bandpass have been modeled and demonstrated. The filter designs were based on the desired filter type and bandwidth, and implemented by cascading quarter wave phase shifted fiber Bragg gratings written in Topas polymer subwavelength fiber. As an example, a 5-pole Chebyshev filter with <3 GHz bandwidth was designed and fabricated. Experimental and simulated results are in good agreement.

RESUMEN

We demonstrate fiber Bragg gratings written in polymer fiber for use in the THz window for the first time. A KrF excimer laser operating at 248 nm was used to inscribe notch-type gratings in single component Topas subwavelength fiber. A transmission loss at the centre wavelength of the grating of 60 dB is observed in short gratings containing only 192 notches. Experimental results and modeling are presented. The gratings are expected to find use in THz signal filtering and chemical or biosensing applications.

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