Absorption Notch Research Articles

Wood's anomaly beyond the Meixner-Schäfke theorem: Analytical and experimental investigation of sinusoidally modulated metasurfaces with normal susceptibilities

We present a rigorous analysis of plane-wave-illuminated sinusoidally modulated metasurfaces (MSs) with normal susceptibility components, without limiting the modulation-index values. In contrast to tangentially polarizable scenarios, which are treated within the conventional continued-fraction framework of Meixner and Sch\"afke, the unconventional structure of the generalized sheet transition conditions with regard to normal components manifests exotic stability conditions, which were not addressed by this framework. By introducing small losses into the constituents of such MSs (inevitable in practice), we resolve these stability issues and establish a valid solution for the scattered fields. Such solutions reveal that for a certain range of modulations these surfaces feature a resonant absorptive notch at an angle related to the period, associated with strong coupling to the weakly evanescent first-order Floquet-Bloch harmonic. Based on our observations, we identify this phenomenon as Wood's anomaly for MSs with normal susceptibilities. We verify these observations numerically and experimentally using suitable, systematically designed, printed-circuit-board prototypes. This work highlights the fundamental intricacies involving theoretical analyses of inhomogeneous normally polarizable MSs and constitutes a firm ground for further exploration and utilization of nonuniform configurations with these mostly ignored degrees of freedom.

Bandpass Filter With Tunable/Switchable In-Band Interference Rejection

This letter presents a wideband bandpass filter (BPF) with a tunable and switchable in-band notch. This allows the RF front end to pass the signal of interest uninterrupted in the absence of an in-band interferer and reject part of the passband in case a narrowband interferer exists. The BPF is based on a two-path architecture, loaded with resonators on one of the paths to deliver an absorptive notch. The resonators are tuned with varactor diodes and are deactivated when the diodes are in forward bias. The implemented proof-of-concept hardware operates in the 4.8–7.8-GHz frequency range, with an in-band notch tunable between 5 and 6.25 GHz, when activated. The transmission lines were implemented as striplines, resulting in a measured insertion loss of 0.6 dB.

Combination of absorptive notch filter and tunable dual‐band conventional notch filter

AbstractIn this paper, a new kind of absorptive bandstop filter composing three series‐coupled lines is designed, investigated, and fabricated. The proposed circuit is indeed a combination of a dual‐band conventional notch filter and a single‐band absorptive filter generating two conventional and an absorptive notch. More precisely, the circuit introduces a fixed absorptive notch at 4.22 GHz and two electronically tunable (approximately 20%) conventional notches at 1.62–2 and 4.71–5.75 GHz, respectively. Besides, the FBWs of the first conventional notch, the second one, and the absorptive notch are 5.5 ± 1, 3.5 ± 1, and 3 ± 1%, respectively. The instantaneous surface current density of the circuit is depicted to investigate the generation of notches. The circuit has a compact size of 44.7 × 11.85 mm2 equaling to 0.489 × 0.129 ; moreover, it can successfully absorb more than 98% of the input power at its absorptive notch.

Dual-Band Dual-Mode Filter-Enhanced Linearity Measurement

This letter presents, for the first time, a new filter-enhanced linearity measurement technique using a dual-band and dual-mode filter. While traditional two-tone linearity tests are simple and effective, their ultimate performance is determined by the quality (dynamic range and noise floor) and cost of the employed equipment. On the other hand, the proposed method consists of a simple conventional single-tone test facilitated by a low-cost appropriately designed bandstop filter (BSF). In particular, the employed dual-band/dual-mode absorptive BSF suppresses the fundamental frequency by over 35 dB (absorptive notch) and the second harmonic by over 25 dB (reflective notch), allowing for accurate measurement of the third harmonic, and hence, IP3. The proof-of-concept system is demonstrated at 2 GHz. The filter absorbs with better than 20 dB of reflection the excitation signal at f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =2 GHz and reflects the signal at 2f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =4 GHz. With just the insertion of the presented filter and without improving the measurement equipment, we demonstrate an improvement of over 12.7 dB in the IP3 characterization to a maximum of 81 dBm. We also demonstrate the ability to conduct this test with just a low-cost power detector in lieu of a spectrum analyzer leading to a simple scalable measurement technique.

Spectrometric analysis of silicon nitride films deposited by low-temperature liquid-source CVD

Silicon nitride (SiN) films formed by liquid-source chemical vapor deposition (LSCVD) were analyzed for photonic applications. While this deposition technique for SiN has strengths in its low reaction temperature (&amp;gt;80 °C) and fast deposition rate (&amp;gt;50 nm/min), the material properties, such as its composition, chemical bond, and optical absorption bands in waveguides, have not been studied quantitatively. Hence, we probed SiN films to understand the material characteristics by ultraviolet-to-midinfrared ellipsometry, on-chip waveguide absorption spectrometry, Rutherford backscattering/hydrogen forward-scattering spectrometry, and Fourier-transform infrared spectrometry. As interpreted by a combination of the series of analyses, the N–H bond concentration of higher than 1021 cm−3 leaves an absorption notch (&amp;gt;6.5 dB/cm) at a wavelength of 1550 nm, which cannot be avoided even by systematically varying the deposition conditions. However, except for that absorption range, a low-loss SiN waveguide (0.5–1.0 dB/cm) with a practically applicable high refractive index (∼1.85) can be formed at the deposition temperature of 100 °C. This basic materials research, which combines multiple spectrometric analyses, will help to improve our understanding of a LSCVD SiN film for photonics circuit integration.

Second‐order reflective‐type, absorptive notch filter with lumped elements

ABSTRACTIn this article, a design methodology and equations necessary for a second‐order absorptive, reflective‐type, transmission zero notch filter are introduced, derived, and described in detail. Initially, a single (first order), absorptive, reflective‐type transmission zero notch filter is described. Based on this, improvements to the first‐order reflective‐type notch filter are discussed and a novel circuit that achieves a second‐order absorptive, reflective‐type, transmission zero notch response is proposed. The necessary conditions for the achievement of the second‐order absorptive, reflective‐type, transmission zero from the proposed circuit are derived. As an experimental verification, first‐ and second‐order absorptive, reflective‐type, transmission zero circuits are fabricated and their performance measured. It is shown that the first‐order notch circuit introduces a zero into the response of a main filter with a depth of over 12 dB in the frequency range 2.19–2.27 GHz, while the second‐order notch circuit introduces a transmission zero with a depth of over 20 dB GHz, in the same frequency range as its first‐order counterpart. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2542–2545, 2014

High attenuation tunable microwave notch filters utilizing ferromagnetic resonance

We have constructed a series of microstrips for transmission of microwaves. These microstrips incorporate ferromagnetic and dielectric layers and therefore absorb microwave energy at the ferromagnetic resonance (FMR) frequency. The absorption notch in transmission can be tuned to various frequencies by varying an external applied magnetic field. For our devices, which incorporate Fe as the ferromagnetic material, the resultant FMR frequencies range from 10–20 GHz for applied fields up to only 1000 Oe. This frequency range is substantially higher than those found in devices utilizing a dielectric ferrimagnet such as YIG. We constructed devices using monocrystalline Fe films grown in a molecular beam epitaxy system. Our devices are of different construction than other Fe dielectric microstrips and show much improvement in terms of notch width and depth. We observed maximum attenuation on the order of 100 dB/cm, much larger than previously reported values of 4 dB/cm.

Temperature Measurements by Ultraviolet Filtered Rayleigh Scattering Using a Mercury Filter

We report the development of Ultraviolet Filtered Rayleigh Scattering (UV FRS) as a diagnostic tool for measurements of gas properties. A frequency tripled, narrow linewidth, Ti:sapphire laser illuminates a sample, and Rayleigh scattered light is imaged through a mercury vapor absorption e lter. The strong absorption of the e lter may be used to suppress elastic background. Tuning the laser through the absorption notch of the e lter is a means of probing the scattering line shape, which contains temperature information. Temperature measurements of air are shown to have uncertainties of less than 3%, whereas measurements of a weakly ionized discharge have uncertainties of less than 4%. An enhanced scattering cross section as well as nearly ideal e lter properties lead to temperature sensitivities for the mercury e lter in the ultraviolet which are comparable to those available with an iodine e lter in the visible. The absorption for the mercury e lter is modeled to be at least 5 orders of magnitude higher than for the iodine e lter, meaning that stronger background suppression may be achieved.

Ultraviolet filtered Rayleigh scattering temperature measurements with a mercury filter

We report the development of ultraviolet filtered Rayleigh scattering as a diagnostic tool for measurements of gas properties. A frequency-tripled narrow-linewidth Ti:sapphire laser illuminates a sample, and Rayleigh scattered light is imaged through a mercury-vapor absorption filter. Working in the ultraviolet improves the signal-to-noise ratio compared with that previously obtained in the visible as the result of an enhanced scattering cross section as well as the nearly ideal properties of the mercury filter. Tuning the laser through the absorption notch of the filter is a means of probing the scattering line shape, which contains temperature information. Temperature measurements of air are shown to have uncertainties of less than 3%.

Absorption notch in the spectrum of a transform limited pulse of small area

We consider the frequency distribution of the absorption when a short uncertainty broadened light pulse interacts with an atomic resonance sharp with respect to the spectral width of the pulse. We demonstrate theoretically that a sharp absorption notch within the frequency profile of an uncertainty broadened incident light pulse originates from destructive interference between the original pulse and the free induction tail of radiation of excited atoms. The notch is unambiguously observed for nanosecond pulses interacting with an atomic beam of sodium.