Narrow Bandpass Response Research Articles

Dual-frequency switchable bandpass filter in the terahertz range based on enhanced trapped-mode resonances

We propose a high-quality and mechanically tunable dual-band narrow bandpass filter working in the THz range. Its high transmittance and modulation depth are verified both by simulations and experiments. The proposed design consists of two metasurfaces with concentric fabricated meta-atoms back-to-back on the two sides of a thin polyimide layer. When the polarization of the incident THz waves changes from y to × direction, the modulation depth of transmittance monotonically changes from 95.46% to a few percent at the resonance frequencies of 0.481 THz and inversely varies from a few percent to 97.62% at the resonance frequency of 0.931 THz. The analysis of in-plane and inter-planar distributions of induced surface current reveals that the narrow bandpass response is attributed to the excitation of “trapped mode”. The induced antiphase current excitation between the two metasurfaces not only lower the dipole moment but also weakly couple to external electromagnetic fields, consequently, leading to the high transmittance and narrow bandwidth. These features of such a simple device potentially can contribute to the design of much more advanced THz modulators and other THz applications in the future.

IoT-Sodar Network for Airshed Management Planning

Airshed management planning is imperative across the world for better air-quality management. It is a major concern for the research community to develop an effective, fast, and continuous monitoring system for planning and decision making for Airshed Management. SODAR is a crucial instrument for the continuous determination of atmospheric boundary layer (ABL) height for Airshed management planning in a defined area. The Internet of Things can play an important role in the real-time determination of ABL height from multiple locations. In this study, the Internet of Things-based Sodar Network (IoT-SN) has been proposed to connect six Sodar sites of Northern India. The proposed IoT-SN attributes a high gain and narrow bandpass response analog signal conditioning stage. The experimental performance shows the advantage of 10 dB gain in comparative analysis. The data validation of the ABL structure and ABL height has proved the reliable interconnectivity of the proposed IoT-SN. The experimental results illustrate the data transmission accuracy of 99.74% for the ABL structure; data estimation accuracy of 95.57% for ABL height with a variation of less than ±13% in the error value has been obtained from IoT-SN. Therefore, the proposed IoT-SN is important for improved Airshed management planning.

High Responsivity and High Rejection Ratio of Self-Powered Solar-Blind Ultraviolet Photodetector Based on PEDOT:PSS/β-Ga2O3 Organic/Inorganic p-n Junction.

A high responsivity self-powered solar-blind deep UV (DUV) photodetector with high rejection ratio was proposed based on inorganic/organic hybrid p-n junction. Owing to the high crystallized β-Ga2O3 and excellent transparent conductive polymer PEDOT:PSS, the device exhibited ultrahigh responsivity of 2.6 A/W at 245 nm with a sharp cutoff wavelength at 255 nm without any power supply. The responsivity is much larger than that of previous solar-blind DUV photodetectors. Moreover, the device exhibited an ultrahigh solar-blind/UV rejection ratio (R245nm/R280nm) of 103, which is two orders of magnitude larger than the average value reported in Ga2O3-based solar-blind photodetectors. In addition, the photodetector shows a narrow bandpass response of only 17 nm in width. This work might be of great value in developing a high wavelength selective DUV photodetector with respect to low cost for future energy-efficient photoelectric devices.

2.4-GHz $Q$ -Enhanced Lumped Ring Filter With Two Transmission Zeros Using 0.18- $\mu$ m SiGe BiCMOS Process

A 2.4-GHz Q-enhanced lumped ring filter with a narrow bandpass response and two stopband-rejection transmission zeros using 0.18- $\mu \text{m}$ SiGe BiCMOS technology is demonstrated in this letter. A transformer-based Q-enhanced technique is employed to boost the Q-factor of on-chip inductors for low passband insertion loss. The measured results show zero dB insertion loss, 120-MHz 3-dB bandwidth for the passband centered at 2.45 GHz and with two transmission zeros at 2.35 and 2.65 GHz, respectively. The noise figure is about 14.5 dB, IP1dB is about −15.2 dBm and IIP3 is about −4.5 dBm, respectively. The total current consumption is 9.9 mA at 1.8 V supply voltage.

High-Selectivity Bandpass Frequency-Selective Surface in Terahertz Band

A terahertz (THz) bandpass frequency-selective surface (FSS) with high selectivity is proposed in this work. The three-layered FSS filter consists of identical tripole resonators located on the top and bottom layers and rectangular coupling apertures etched on a conducting plane in between. Multiple signal paths exist between the top and bottom resonators through the coupling apertures. Therefore, this aperture-coupled resonator (ACR) structure exhibits a narrow bandpass response, and two transmission zeros appear near the skirts of the passband. These zero points considerably improve the frequency selectivity and suppress the sidebands of the FSS. For demonstration, a microfabrication process was used to realize an ACR FSS at 850 GHz. The frequency performance of the ACR FSS in terms of insertion loss is investigated numerically and experimentally. The measured transmission responses at normal incidence based on time-domain as well as frequency-domain measurements agree well with the simulated one, thus verifying the proposed design. Furthermore, the frequency-domain measurement reveals that the FSS response remains stable at various incident angles for both TE and TM polarizations.

WAVEGUIDE FILTER USING FREQUENCY SELECTIVE SURFACE WITH MINIATURIZED ELEMENT

In this paper, a waveguide fllter using miniaturized- element frequency selective surface (FSS) is presented. The proposed FSS is composed of periodic array of metallic patches separated by small gaps and metallic lines. The array of patches constitutes a capacitive surface and the lines a coupled inductive surface, which together act as a resonant structure. At about 5.0GHz, a narrow bandpass response is designed. Dimensions of the FSS element are much smaller than the operating wavelength, which is less than 1=13‚. For this miniaturized element, grating lobes are restrained and do not appear event to 25GHz. Moreover, the FSS has stable performances for various incident angles. Design procedure and measurement results of the FSS are presented and discussed.

A simple microwave photonic notch filter based on a semiconductor optical amplifier

A novel microwave photonic notch filter structure is proposed and experimentally demonstrated. The structure is based on a recirculating delay line loop consisting of an optical variable delay line, a semiconductor optical amplifier (SOA) and a tunable narrowband optical filter. Negative tap is generated using wavelength conversion based on cross-gain modulation of an amplified spontaneous emission spectrum in the SOA. A narrow bandpass response with negative coefficients and a broadband all-pass response are combined to achieve a narrow notch response with flat passband which can eliminate interference with minimal impact on the expected signal. Experimental results show good agreement with theoretical analysis.

Design and Simulation of a Miniature Thick-Screen Frequency Selective Surface Radome

In this letter, we present a miniature conical thick-screen frequency-selective surface (FSS) radome at C-band and investigate the effect of the miniature FSS radome located in close proximity of a monopole antenna. The unit cell of the thick-screen FSS radome is designed according to the concept of artificial puck plate (APP), and its strict periodic array mounted on sharp conical surface is indicated in detail. The FSS radome, together with a monopole antenna, is simulated using the software HFSS both at the pass- and stopbands. Simulated results show that the miniature thick-screen FSS radome has a narrow band-pass response and could be useful for out-of-band radar cross-section (RCS) control.

A Simple Red: Far-Red Sensor Using Gallium Arsenide Phosphide Detectors

1. A low-cost portable instrument was designed to measure the red :far-red ratio (660 :730 nm) and photosynthetically active radiation (PAR, 400-700 nm). The sensor head comprises three gallium arsenide phosphide photodiodes associated with tinted-glass filters. 2. Such detection takes advantage of the spectral response curves of these diodes, which provide a narrow bandpass response when combined with an appropriate filter. No interference filtering and no amplification is required. The output is displayed on a battery-powered unit enclosing two digital voltmeters for both PAR and red :far-red ratio readings. 3. The unit is easy to produce and requires no knowledge of electronics. The instrument was tested under field conditions against a spectroradiometer. 4. This approach may provide a basis to assess other spectral vegetation indices such as NDVI.

A frequency-selective surface using aperture-coupled microstrip patches

A frequency-selective surface based on the aperture coupled microstrip is presented. This surface has a narrow bandpass response useful for building radomes with low out-of-band radar cross section (RCS). The analysis employs the spectral domain moment method. The design criteria and a simple lumped element model are derived and presented. Experimental data from a waveguide simulator are presented which confirm the theory.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Development of the water window imaging x-ray microscope utilizing normal incidence multilayer optics

We describe the development of the water window imaging x-ray microscope based on normal-incidence multilayer x-ray mirrors. The narrow bandpass response inherent in multilayer x-ray optics is accurately tuned to wavelengths within the "water window." Similar doubly-reflecting multilayer optical systems have been fabricated for our astronomical rocket-borne x-ray/EUV telescopes. Previous theoretical studies performed during the MSFC X-Ray Microscope Development Program established that high-resolution multilayer x-ray imaging microscopes are possible by using either spherical (Schwarzschild configuration) optics or aspherical configu rations. These microscopes require ultrasmooth mirror substrates, which have been fabricated using advanced flow polishing methods. Hemlite-grade sapphire microscope optic substrates have been accurately figured and polished to a smoothness of 0.5-&angst; rms, as measured by the Zygo profilometer. We describe the current status of fabrication and testing of the optical and mechanical subsystems for the water window imaging x-ray microscope. This new instrument should yield images of carbon-based microstructures within living cells of unprecedented spatial resolution and contrast, without need for fixatives, dyes, and chemical additives.