dB Attenuation Research Articles

A Wavelength Tunable Multi-Section PIC as an Upstream Transmitter for TWDM Networks

In this paper, we demonstrate a novel multi-section directly modulated laser transmitter for upstream operation in the application of time wavelength division multiplexing (TWDM) architecture. The photonic integrated circuit (PIC) is fabricated using a regrowth-free process that favors simplified and fast manufacturing. The PIC is based on a master-slave configuration, with an addition of a variable optical attenuator (VOA) section between them, and a semiconductor optical amplifier (SOA) at the output. The VOA enables control of the optical injection from the master to the directly modulated slave laser improving the transmission performance. The integrated SOA section at the output is used to boost or turn off the optical output power of the transmitter, thereby enabling burst mode operation. Experimental results show that the PIC can be tuned to four wavelength channels on a 100 GHz frequency grid. We also demonstrate that each channel achieves error-free performance (bit error ratio < 10e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> ), when modulated with 10 Gbps signal and transmitted over 25 km and 50 km fiber. The SOA-based output disable feature of the PIC delivers more than 60 dB attenuation.

Tracking-Differentiator-Based Position and Acceleration Feedback Control in Active Vibration Isolation with Electromagnetic Actuator

In order to improve the performance of the active vibration isolation system (AVIS) with electromagnetic actuator, several problems of vibration control are studied. Position control is a critical component in suspension systems, and the position sensor noise can extremely affect the stability of the system, so a tracking differentiator (TD) is proposed to obtain effective differential signal from relative position sensor. In vibration control, the feedback of acceleration combined with PD position feedback is presented to suppress transmission of periodic vibrations. Then, taking the acceleration transmission as the evaluation index, the acceleration transmission under the presented control method is derived, and the influence of control parameters on vibration isolation performance is discussed in detail. The vibration isolation performance is improved from 24.47 dB to 2.4 dB at resonance frequency, and −34 dB attenuation is achieved at 100 Hz with respect to vibration isolation mount system tested on the ground. The experimental results demonstrate that the performance of active vibration isolation system are improved by the proposed acceleration feedback control.

Feature Extraction of a Non-Stationary Seismic–Acoustic Signal Using a High-Resolution Dyadic Spectrogram

Using a novel mathematical tool called the Te-gram, researchers analyzed the energy distribution of frequency components in the scale–frequency plane. Through this analysis, a frequency band of approximately 12 Hz is identified, which can be isolated without distorting its constituent frequencies. This band, along with others, remained inseparable through conventional time–frequency analysis methods. The Te-gram successfully addresses this knowledge gap, providing multi-sensitivity in the frequency domain and effectively attenuating cross-term energy. The Daubechies 45 wavelet function was employed due to its exceptional 150 dB attenuation in the rejection band. The validation process encompassed three stages: pre-, during-, and post-seismic activity. The utilized signal corresponds to the 19 September 2017 earthquake, occurring between the states of Morelos and Puebla, Mexico. The results showcased the impressive ability of the Te-gram to surpass expectations in terms of sensitivity and energy distribution within the frequency domain. The Te-gram outperformed the procedures documented in the existing literature. On the other hand, the results show a frequency band between 0.7 Hz and 1.75 Hz, which is named the planet Earth noise.

Enhanced backscatter and unsaturated blue wavelength shifts in F-doped fused silica optical fibers exposed to extreme neutron radiation damage

Amorphous fused silica (a-SiO2) optical fibers, with and without inscribed Bragg gratings, were interrogated using infrared (∼1550 nm) optical backscatter reflectometry during ∼25 days of intense neutron irradiation to a fast (energy > 0.1 MeV) neutron fluence of ∼1021 n/cm2, or ∼1.5 atomic displacements per atom. The reflected light amplitudes in Ge-doped core telecommunications fiber dropped below detection limits (>15 dB attenuation) within 3 days of irradiation (∼1020 fast n/cm2). Amplitudes from a pure silica core, F-doped silica cladding fiber reached equilibrium levels ∼1.5–2 dB higher than pre-irradiation values, whereas Bragg gratings inscribed in the same fiber using a femtosecond laser (point-by-point method) suffered > 45 dB attenuation. Blue wavelength shifts were initially consistent with previous radiation-induced compaction models but increased linearly with increasing neutron fluence (no evidence of saturation) beyond 1020 n/cm2 and exceeded 0.6%, which corresponds to >1,000 °C drift if used to measure temperature changes.

An Ultra Compact Microstrip Branch Line Coupler with Wide Stopband Using LCL Filter and Meandered Stubs for Microwave Applications

A branch line coupler (BLC) with ultra-compact size and harmonic suppression ability using an LCL filter and meandered stubs is proposed in this paper. There are some important factors in microstrip coupler design, including size reduction, harmonic suppression, and low insertion loss. Thus, improving each of these factors will contribute to a more efficient design. In the proposed circuit, for the first time, LCL filters, including four T-shaped circuits and four meandered line open-ended stubs, were used together to reduce the circuit size and suppress unwanted harmonics. The proposed LCL filters, incorporated in the BLC branches, resulted in superior size reduction and harmonic suppression for the presented BLC. The proposed BLC correctly worked at 900 MHz with 300 MHz operating bandwidth, which showed 33% fractional bandwidth (FBW). Additionally, a wide suppression band from 1.4 GHz to 8.8 GHz, with more than 20 dB attenuation level was obtained, which suppressed the second to ninth unwanted harmonics. The overall size of the proposed 900 MHz coupler was only 11 mm × 10.4 mm (0.044 λ × 0.042 λ) while the size of the conventional 900 MHz coupler was 61.5 mm × 62.5 mm (0.25 λ × 25 λ). The proposed BLC had a very small size and only occupied 3% of the size of the conventional coupler, which corresponded to a 97% size reduction. To the best of the authors’ knowledge, to date, the best size reduction has been obtained among the published couplers. Furthermore, the experimental results verified the simulated and analyzed results of the proposed technique and demonstrate its potential for improving the performance and miniaturizing the size of other similar BLCs.

GHz sample excitation at the ALBA-PEEM

We describe a setup that is used for high-frequency electrical sample excitation in a cathode lens electron microscope with the sample stage at high voltage as used in many synchrotron light sources. Electrical signals are transmitted by dedicated high-frequency components to the printed circuit board supporting the sample. Sub-miniature push-on connectors (SMP) are used to realize the connection in the ultra-high vacuum chamber, bypassing the standard feedthrough. A bandwidth up to 4 GHz with -6 dB attenuation was measured at the sample position, which allows to apply sub-nanosecond pulses. We describe different electronic sample excitation schemes and demonstrate a spatial resolution of 56 nm employing the new setup.

Factors influencing the electromagnetic transmission of mercury vapor discharge plasma tube arrays

Low-pressure Mercury vapor discharge plasma tubes were used to form arrays to control electromagnetic transmission. The internal and external factors influencing a discharge tube array were adjusted to expand the electromagnetic wave manipulation ability. The plasma electron density (n e) is the key parameter for electromagnetic wave manipulation. Microwave transmission was used to diagnose n e under different working conditions. Simulations and electromagnetic transmission measurements were used to investigate the behavior of the effect of internal and external factors on electromagnetic transmission. Simulation results indicated that increasing n e increased the attenuation, widened the attenuation bandwidth, and shifted the attenuation band to higher fRequencies. The experimental results showed that increasing the discharge power significantly increased n e and widened the strong attenuation frequency band. n e first increased and then decreased when the gas pressure was increased. The tube diameter affected both n e and the plasma layer thickness, and the attenuation band of the plasma tube array moved to a low frequency with an increase in tube diameter. The primary and secondary order of the influence of external factors other than power on the attenuation bandwidth obtained via an orthogonal experiment is as follows: gas composition > tube diameter > pressure. The maximum attenuation bandwidth for 10 dB attenuation was 9.85 GHz. The results show that the attenuation control ability of the plasma tube array can be significantly improved by adjusting the external factors of the plasma tube.

A miniaturized highly selective MTM‐inspired filter for lowpass and triple‐band bandpass performance with configurable transmission zeros and bandwidth

SummaryThis paper presents a novel, compact, and highly selective metamaterial inspired filter with low insertion loss, lowpass, and triple‐band bandpass characteristics. The presence of five transmission zeros and seven poles facilitates highly selective filtering performance. The improved impedance matching and transmission characteristics have been achieved by embedding complementary split ring resonator as defected ground structure. The filter circuit area excluding 50 Ω feed lines is merely 0.17λg × 0.05λg at 3‐dB cut‐off frequency of lowpass passband (1.11 GHz). The 3‐dB fractional bandwidths of the three bandpass regions are 39.50% (1.3–1.94 GHz), 21.20% (3.12–3.86 GHz), and 21.06% (4.04–4.99 GHz) at the center frequencies of 1.62, 3.49, and 4.51 GHz, respectively. Intended filter also offers a wide stopband extending from 2.15 to 2.96 GHz at close to 20 dB attenuation level. Further, position of transmission zeros and 3‐dB passband bandwidths can be adjusted by carefully choosing structural design parameters. The metamaterial effect of the proposed filter has been demonstrated by plotting refractive index followed by validating the performance with the help of experimental measurements. No filter shows lowpass characteristic along with three bandpass performances as found by the authors exploring literature, which presents the novelty of the proposed work.

A Tuned Microwave Resonant System for Subcutaneous Imaging

A compact and planar imaging system was developed using a flexible polymer substrate that can distinguish subcutaneous tissue abnormalities, such as breast tumors, based on electromagnetic-wave interactions in materials where permittivity variations affect wave reflection. The sensing element is a tuned loop resonator operating in the industrial, scientific, and medical (ISM) band at 2.423 GHz, providing a localized high-intensity electric field that penetrates into tissues with sufficient spatial and spectral resolutions. The resonant frequency shifts and magnitudes of the reflection coefficients indicate the boundaries of abnormal tissues under the skin due to their high contrasts to normal tissues. The sensor was tuned to the desired resonant frequency with a reflection coefficient of -68.8 dB for a radius of 5.7 mm, with a tuning pad. Quality factors of 173.1 and 34.4 were achieved in simulations and measurements in phantoms. An image-processing method was introduced to fuse raster-scanned 9 × 9 images of resonant frequencies and reflection coefficients for image-contrast enhancement. The results showed a clear indication of the tumor's location at a depth of 15 mm and the capability to identify two tumors both at the depth of 10 mm. The sensing element can be expanded to a four-element phased array for deeper field penetration. Field analysis showed the depths of -20 dB attenuation were improved from 19 to 42 mm, giving wider coverage in tissues at resonance. Results showed that a quality factor of 152.5 was achieved and a tumor could be identified at a depth of up to 50 mm. In this work, simulations and measurements were conducted to validate the concept, showing great potential for subcutaneous imaging in medical applications in a noninvasive, efficient, and lower-cost way.

LoRaWAN CubeSat with an Adaptive Data Rate: An Experimental Analysis of Path Loss Link Margin

One of the challenges of the Internet of Things (IoT) is to provide connectivity to devices around the globe. Long Range (LoRa) is one of the most practical technologies due to its low-power and long-range capabilities to be used by the Low Earth Orbit (LEO) CubeSat. This study aims to evaluate the performance of the Long Range Wide Area Network (LoRaWAN) in receiving uplink messages from ground sensor nodes at an altitude of 550 km with a maximum elevation angle of 0°. An Adaptive Data Rate (ADR) is applied for the dynamic signal reception with respect to receiving signal strength. In this study, the path loss is simulated using attenuation levels from 30–150 dB to ensure that the signal connectivity success rate is at a minimum elevation angle and to perform the link analysis under various conditions. The results show that the LoRaWAN signals are successfully received with an SNR of −21 at the 150 dB attenuation from the end nodes because of its spread-spectrum technique which allows the system to detect signals under the noise floor.

Design and Experimentation of Inductorless Low-Pass NGD Integrated Circuit in 180-nm CMOS Technology

This article introduces an innovative design of a low-pass (LP) negative group delay (NGD) integrated circuit (IC) in the 180-nm CMOS technology. The LP-NGD circuit is an inductorless topology constituted by RC-network with CMOS metal-insulator-metal (MIM) capacitor and polygate resistor. The design methodology is illustrated by considering the chip layout process. Then, the first run simulation is performed with the design rule check (DRC) and 2.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\times }$ </tex-math></inline-formula> 2.2 mm layout versus schematic (LVS) approaches. The feasibility of the CMOS LP-NGD IC circuit implementation is validated with chip-onboard (CoB). The proof of concept (PoC) of the LP-NGD miniaturized circuit was tested in both S-parameter and time domain (TD). As expected, the calculated, simulated, and experimented results of CoB showing NGD of about −10 ns over 12 MHz and −10 dB attenuation are confirmed. The active CMOS LP-NGD technology compensates the insertion loss to 2.4 dB, the GD reaches −11 ns, and the reflection loss reaches −20 dB. Moreover, TD investigations were also performed to show the feasibility of generating pulse and arbitrary waveform signal time advance through the designed and fabricated LP-NGD CoB prototypes.

Fast microwave calibration system for cryogenic device characterization

We designed a calibration system to characterize the performance of microwave devices at low temperatures. This system comprises an in-situ calibration circuit and an adapted thru-reflect-line calibration algorithm, with which we can transfer the reference ports from room temperature to cryogenic temperature with high precision. We validated the circuit and the algorithm at room temperature with better than 0.9 dB accuracy. In addition, we demonstrated how we can extract the actual S 21 of a 20 dB attenuator and a high pass filter at 20 mK using this calibration system. The calibration bandwidth of this system covers from 4.1 GHz to 18 GHz. The requirement that the phase difference between line and thru be greater than 20°determines the lower frequency limit, and the maximum operational frequency of the microwave switch determines the upper frequency limit. This system can be used for fast and accurate analysis of various cryogenic devices such as filters and amplifiers.

A new configuration of a compact printed coplanar low pass filter with high rejection

The aim of this contribution is a new study on the achievement, fabrication and the test of a new low pass filter (LPF) coplanar structure based on periodic resonators. The proposed structure can be easly integrated with microwave devices, the validated LPF circuit has a wide band pass and high band stop. The design was done by two electromagnetic (EM) solvers one is based on moment method and the other one on finite integration technique. In order to reach a final LPF structure with good characteristics concerning the insertion loss of−0.8 dB and high attenuation until 15 GHz, the cut-off frequency of this filter is equal to 6,77 GHz. Many series of optimization were conducted using multiple algorithms. The whole area of the validated LPF is16×40 mm2.

Varactor-tuned wideband band-pass filter for 5G NR frequency bands n77, n79 and 5G Wi-Fi

A wide-band band-pass filter (BPF) using coupled lines, rectangular stubs and Stepped-Impedance Resonators (SIRs) is presented in this paper. The proposed BPF operates over a large pass-band from 3.15 to 6.05 GHz covering 5G New Radio (NR) frequency Bands n77, n79 and 5G Wi-Fi, which includes the G band of US (3.3 to 4.2 GHz), 5G band of Japan (4.4 to 5 GHz) and 5G Wi-Fi (5.15 to 5.85 GHz). The presented filter has a maximum pass-band Insertion-Loss (IL) of 2 dB, a sharp roll-off rate and suppresses all the unwanted harmonics from 4.2 GHz up to 12 GHz with a 15 dB attenuation level. The performance of each section can be analyzed based on lumped-element circuit models. The electrical size of the BPF is 0.258 λg × 0.255 λg, where λg is the guided wavelength at the central frequency. The design accuracy is verified through implementing and testing the final BPF. The pass-band band-width can be controlled by adding the varactor diodes. A good relationship between the band-width and the varactor diodes are extracted by the curve fitting technique.

Effectively Optimized Dual-band Frequency Selective Surface Design for GSM Shielding Applications

Nowadays, global system for mobile communication (GSM) systems are widely used. Therefore, the impact of mobile GSM signals on human health is one of the current research topics. Furthermore, electromagnetic interference caused by GSM signals can be a significant threat to electronic devices today. To overcome these problems, the surfaces of electronic equipment and exterior or interior walls of buildings can be covered with frequency selective surface (FSS) that stops unwanted GSM signals and passing the other signal. This work presents a novel dual-band FSS that attenuates the 900 MHz and 1800–2170 MHz GSM bands by at least 10 dB in the transmission direction. At the design stage, nested geometries are used to achieve multi-stop band frequency response. The proposed design is effectively optimized by utilizing the equivalent circuit geometries and current and electric field distribution diagrams. So, minimum of 10 dB attenuation is achieved in targeted GSM bands for all polarizations and up to 60 degrees (except TM 60 degrees) of incidence angles.

Design of a Filtering Power Divider with Simple Symmetric Structure Using Stubs

A power divider (PD) with a wide stopband and simple symmetric structure using open- and short-ended stubs is analyzed and implemented in this paper. In the proposed power divider, for the first time, the output resistor is divided into two sections and open- and short-ended stubs are used between the resistors. The incorporated open- and short-ended stubs have resulted in a controllable bandwidth for the proposed PD, which resulted in 40% of the fractional bandwidth considering 3 dB attenuation of insertion loss. The proposed PD operates at 2 GHz, which shows more than 20 dB attenuation for the return and isolation losses. In addition, the obtained insertion loss at the operating frequency is approximately 0.3 dB, which shows a minor loss, and also, high isolation is achieved in the device. Moreover, 20 dB and 30 dB attenuation levels have been achieved for second and third harmonics. The results show high performance for the proposed power divider.

Design of miniaturize flexible wideband frequency selective surface for electromagnetic shielding application

In this paper, a flexible, ultra-thin, miniaturized broadband frequency selective surface (FSS) is demonstrated for wideband electromagnetic shielding application. The unit cell of the proposed FSS structure consists of cross dipoles loaded with the metallic circular strip. The proposed miniaturized FSS structure has an extremely low profile with a thickness of and a unit cell size of . This FSS structure provides wideband shielding of more than 20 dB from 1.1 to 2.6 GHz frequency region. Besides this wide stopband, the FSS structure acts as a transparent window in the frequency band which can be used for the 5G communication purpose. Moreover, by comprehending the interaction between the incident electromagnetic wave and unit cell, a conceptual equivalent circuit model is developed that helps to interpret the mechanism of the miniaturization as well as the broadband response of FSS structure. We also compared the proposed FSS with other recently reported structures and observed more than 55% improvement in size reduction with several other miniaturized flexible FSS structure. Furthermore, this FSS structure exhibits 20 dB attenuation over a wide frequency region with a fractional bandwidth of 111%. Moreover, excellent resonant stability is achieved in regards to different polarization and incident angle up to .

Surrounding line sources optimally reproduce diffuse envelopment at off-center listening positions.

Listener envelopment has previously been studied in the fields of room acoustics and multichannel sound reproduction. However, the potentially detrimental effect of a directional imbalance remains uninvestigated. This paper presents a listening experiment under anechoic conditions using a ring of 24 loudspeakers. Participants rated perceived envelopment for various loudspeaker subsets fed by incoherent noise signals. Off-center listening positions were simulated for different acoustic source models: -6 dB (point source), -3 dB (line source), or 0 dB attenuation for every doubling of distance. Only the line-source model preserved envelopment off-center, providing a low interaural level difference and a low interaural coherence as perceptual cues.

A Novel S-Band High Power Tunable Attenuator With a Magnetron for RF Conditioning of Linac

An S-band high-power tunable attenuator (HPTA) is proposed to adjust the output power of a 2.5 MW magnetron to the range of 40–2400 kW, which is equal to 0.17–17.78 dB attenuation. Additionally, the attenuation control accuracy is better than 0.9 dB/mm. The output power of the magnetron tube is changed by its current, which leads to the output frequency. Thus, the magnetron tube is not suitable for applications that require RF signals with a constant frequency and variable power. By using the proposed HPTA, which is connected to the output port of the magnetron, a signal with a constant frequency and variable power can be produced. In this new setup, the magnetron current is set to a maximum value, and then, the desired output power is realized by adjusting the attenuation of HPTA. This idea prevents the magnetron variation frequency while changing the output power. It should be noted that this system is low cost and lightweight when compared with other technologies, such as Klystron and traveling wave tubes (TWT) for RF conditioning of the linear accelerator.

Amplitude-Phase Variation in a Graphene-Based Microstrip Line.

A graphene-based transmission line with independent amplitude and phase variation capability is proposed. Variation of graphene’s tunable conductivity by an applied DC bias is exploited in designing an attenuator and a phase shifter. The attenuator and phase shifter are separated from each other by an interdigitated capacitor to ensure independent control of each section through an applied DC bias. The phase shifter is designed by optimizing lengths of a tapered line and an open stub for a maximum variation of input reactance with a change in graphene resistance. The attenuator is designed by two pairs of grounded vias connected to the transmission line through graphene. Variation of graphene resistance controls the signal passing through graphene pads into the ground causing attenuation. An independent variation of 5 dB of attenuation is measured along with an independent phase variation of 23 degrees in the frequency range of 4 GHz to 4.5 GHz.