Broadband Characteristics Research Articles

Advances in CODE V design in terahertz imaging system

The band of terahertz (THz) spans from microwave to infrared bands, which belongs to the transition band from macro-electronics to micro-photonics, possessing peculiarities different from electromagnetic waves in other bands. THz technology with the characteristics of high penetration, broadband, high resolution and transient are employed in various fields, such as space remote sensing, nondestructive detection biomedical imaging and near-field microscopy. These broad applications, in turn, provide incentive to further improve the basic performance of THz technology. Aiming at the application of terahertz technology in the imaging field, this novel mainly discussed the basic principle, key devices, system composition, technical advantages and future development trend of terahertz imaging system. The application status of CODE V optical design software in designing scanning lens systems for terahertz imaging, such as free-form surfaces, non-free surfaces and multi-lens groups are further discussed in this paper.

A liquid column resonance transducer driven by Class IV flextensional transducer.

A liquid column resonance (LCR) transducer, also referred to as an organ pipe transducer, is a type of transducer that utilizes the liquid column resonance mode to produce acoustic energy underwater. Traditional transducers, such as piezoelectric rings or Janus transducers, are commonly used as the driving source in LCR transducers. A flextensional transducer (FT) is introduced into the LCR transducer as the driving source because of the relatively larger volume velocity at low frequencies. Moreover, the eigen-mode of the Class IV FT is easier to couple with the LCR mode to broaden the bandwidth of a LCR transducer. To overcome the problems associated with the low stiffness of elliptical metal pipes, an improved aluminum pipe, which has a cross-beam to increase the stiffness, was proposed and utilized in a LCR transducer driven by a Class IV FT. The fabricated LCR transducer prototype driven by the Class IV FT has two resonance peaks from 700-2000 Hz, and the transmitting voltage response values of these peaks are 132.1 and 137.8 dB (re 1 μPa/V @1 m). Comparing with an LCR transducer driven by a 33-mode ring, the results show that the LCR transducer driven by a Class IV FT provides good efficiency and broadband characteristics.

New low-frequency broadband metamaterials based on inerter and novel large-linear negative stiffness mechanism

Elastic metamaterials are recently emerging structural–functional materials, which provide a new way for the control of elastic waves. However, the current low-frequency broadband performance is yet to be further improved. Herein, a novel large-linear negative stiffness mechanism is first proposed, which is capable of generating constant negative stiffness; the influences of the relevant structural parameters are discussed, and a design method for this mechanism is also given. Subsequently, a new type of elastic metamaterial is designed by combining the inerter and the proposed negative stiffness mechanism; a parametric programming method with general characteristics is proposed to guide the selection of unit-cell parameters, and it is revealed that only at most one negative stiffness spring is allowed to exist in the system. Finally, the low-frequency broadband characteristics of the metamaterial are investigated. It is found that the proposed metamaterial can produce a basin-like attenuation band, i.e., the attenuation curve at the bottom of the attenuation band is a stable flat line; in a given frequency range, the introduction of negative stiffness can further increase the attenuation strength of the metamaterial basin-like band.

A Broadband Butterfly-Shaped 90° Waveguide Twist for Rapid Design

A broadband 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> waveguide twist operating in millimeter wave (mm-wave) is proposed and verified in this letter. Excellent performance is obtained by a novel butterfly-shaped waveguide, which has the advantage of simple construction and can be designed rapidly for different frequencies when compared with conventional ones. Two waveguide twists used for WR10 and WR4.3 rectangular waveguides are fabricated by CNC manufacturing. The proposed design exists broadband characteristics, with 37% and 42% relative bandwidth by the measured results in WR10 and WR4.3 frequency bands. The measured results also show that the return loss is better than 20 and 15 dB from the frequency range of 75–110 and 170–260 GHz, respectively, and the in-band insertion loss is around 0.1–0.2 and 1 dB.

Development of a single-ended magnetic alloy loaded cavity in the Japan Proton Accelerator Research Complex rapid cycling synchrotron

Abstract The Japan Proton Accelerator Research Complex (J-PARC) Rapid Cycling Synchrotron (RCS) employs magnetic alloy (MA) loaded cavities. We realize multi-harmonic rf driving and beam-loading compensation owing to the broadband characteristics of the MA. The currently installed cavity is the conventional type, which is designed to be driven by tube amplifiers in a push–pull operation. The push–pull operation has some advantages, i.e., suppressing a higher harmonic distortion without the beam acceleration and shortening the cavity length. However, a disadvantage arises at the high intensity beam acceleration where the multi-harmonic rf driving causes a severe imbalance of the anode voltage swing and restricts the tube operation. Although we have achieved an acceleration for the design beam power of 1 MW, the imbalance becomes an issue in increasing the beam power further. We have developed a single-ended MA cavity to avoid such difficulty. The cavity has no tube imbalance intrinsically and it is found that the power consumption to drive the cavity can be reduced compared with the conventional one.

RF-SOI Low-Noise Amplifier Using RC Feedback and Series Inductive-Peaking Techniques for 5G New Radio Application.

This paper presents a low-noise amplifier (LNA) with an integrated input and output matching network designed using RF-SOI technology. This LNA was designed with a resistive feedback topology and an inductive peaking technology to provide 600 MHz of bandwidth in the N79 band (4.4 GHz to 5.0 GHz). Generally, the resistive feedback structure used in broadband applications allows the input and output impedance to be made to satisfy the broadband conditions through low-impedance feedback. However, feedback impedance for excessive broadband characteristics can degrade the noise performance as a consequence. To achieve a better noise performance for a bandwidth of 600 MHz, the paper provided an optimized noise performance by selecting the feedback resistor value optimized for the N79 band. Additionally, an inductive peaking technique was applied to the designed low-noise amplifier to achieve a better optimized output matching network. The designed low-noise amplifier simulated a gain of 20.68 dB and 19.94 dB from 4.4 to 5.0 GHz, with noise figures of 1.57 dB and 1.73 dB, respectively. The input and output matching networks were also integrated, and the power consumption was designed to be 9.95 mA at a supply voltage of 1.2 V.

Parallel photonic acceleration processor for matrix-matrix multiplication.

We propose and experimentally demonstrate a highly parallel photonic acceleration processor based on a wavelength division multiplexing (WDM) system and a non-coherent Mach-Zehnder interferometer (MZI) array for matrix-matrix multiplication. The dimensional expansion is achieved by WDM devices, which play a crucial role in realizing matrix-matrix multiplication together with the broadband characteristics of an MZI. We implemented a 2 × 2 arbitrary nonnegative valued matrix using a reconfigurable 8 × 8 MZI array structure. Through experimentation, we verified that this structure could achieve 90.5% inference accuracy in a classification task for the Modified National Institute of Standards and Technology (MNIST) handwritten dataset. This provides a new effective solution for large-scale integrated optical computing systems based on convolution acceleration processors.

Chiral Metasurface Enabled Circularly Polarized OAM-Generating Folded Transmitarray Antenna With High-Gain Low-Profile and Broadband Characteristics

A broadband low-profile high-gain folded transmitarray antenna (FTA) is proposed to generate orbital angular momentum (OAM) with circular polarization. A chiral metasurface is employed as the top layer with the function of reflecting anticipant circularly polarized (CP) incident waves while transmitting the orthogonal ones. The geometric phase is then introduced to achieve 360° coverage of the transmission phase without affecting the reflection one. To obtain a high-gain and compact planar source, a 2 × 2 patch antenna array, integrated with the bottom metallic ground, is selected as the feed. Two proof-of-concept prototypes for vortex beam generation are constructed and experimentally measured. Both simulated and measured results demonstrate that <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> =–1 and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> =+1 OAM mode beams can be generated from 8.7 GHz to 9.5 GHz, and the measured maximum gains for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> =–1 and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> =+1 reach 18.1 dBi and 18.3 dBi with the corresponding peak aperture efficiencies of 6.1% and 6.4%, respectively. Meanwhile, the axial ratios (ARs) of the peak of far-field patterns are less than 3 dB over the entire operating frequency range, providing broadband CP vortex beams. The proposed high-gain low-profile broadband FTA antenna shows a promising perspective in OAM-based wireless communication.

Speech Enhancement Based on Array-Processing-Assisted Distributed Fiber Acoustic Sensing

Distributed Fiber acoustic sensing (DAS) based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) has attracted lots of attention due to unique advantages. In security monitoring, speech recognition and other relevant fields, DAS’s ability to acquire speech signals is a key indicator for the practical application. However, the speech signal has broadband and non-stationary characteristics, so the conventional filtering is not sufficient, and the speech enhancement algorithm based on the characteristics of the speech signal is needed; on the other hand, the acoustic sensitivity of conventional fiber layout is not high enough, resulting in poor signal quality. In this paper, speech enhancement based on array-processing-assisted DAS system is proposed to recover speech signal with high-fidelity. Pulse compression Φ-OTDR, combined with multichannel speech enhancement algorithm based on optimally modified log-spectral amplitude (OM-LSA) is used. As far as we know, this is the first time that the multichannel OM-LSA speech enhancement is proposed for DAS. Compared with the signal before processing, the speech signal processed by this method has a great improvement in the signal distortion, background noise intrusiveness and signal overall quality. In addition, other signal enhancement methods, such as wavelet denoising and beamforming are also analyzed and compared. Our scheme outperforms in above three aspects. This scheme does not need to obtain a large number of data sets in advance, and can be transplanted to other DAS systems, which has great significance for realizing high performance speech acquisition.

Multiband polarization insensitive metamaterial absorber for radar cross-section reduction

In this paper, a polarization-insensitive, metamaterial absorber with more than 91 % absorptivity is investigated numerically and experimentally for radar cross-section reduction at X, Ku, and K bands. The unit cell structure of the absorber is comprised of a symmetrically arranged defective L-shaped patch made of copper metal, which is imprinted on a metal-backed FR-4 lossy dielectric substrate. The proposed absorber yields multiband absorption response at distinct absorption peaks at 11.1, 15.5, and 16.3 GHz along with the broadband response of 4.8 GHz from 18.6 to 23.4 GHz (absorption peaks at 18.9, 20, 21.9, and 23 GHz) in the absorption spectra. The Characteristic mode analysis has been carried out and presented to verify the modes and resonance in the structure. The physical absorption phenomenon is clarified by presenting the induced electric field, top and bottom surface current distribution, and various retrieved constitutive electromagnetic parameters. The structure is studied for various polarization angles for both transverse electric (TE) and transverse magnetic (TM) waves at normal incidence which shows strict insensitivity to the direction of arrival of electromagnetic(EM) signal. The structure is also investigated under oblique incidence for both TE and TM waves where the response holds good up to 50° incident angles in both cases. The novelty of the proposed absorber lies in its multiband response at X, Ku, and K bands through a unique metallic pattern on a thin FR-4 substrate along with characteristics of broadband, polarization insensitiveness, wide incidence angle independence, and compactness incorporated in a single and simple design without using external components. A prototype of the absorber has been fabricated and simulated results are validated with measured results. All the above-mentioned attributes in a simple design make it commercially suitable for radar cross-section (RCS) reduction and energy harvesting applications at X, Ku, and K bands.

Broadband dual‐podal multilayer Vivaldi antenna array for remote sensing applications

AbstractA novel wideband multilayer dual‐podal Vivaldi antenna with broadband characteristics from 5.5 to 20.82 GHz, is presented. Contrary to traditional Vivaldi antennas that are antipodal‐based, this design is realised by placing a pair of podal Vivaldi antennas with corrugated slots on the top and bottom of a substrate stack (consisting of two dielectric layers) using a Bondply. The pair is fed in‐phase with the help of a Strip‐Line (SL) transmission section that is terminated on a radial stub to couple capacitively to the antenna elements. With this technique of electrically coupling a podal Vivaldi pair, improved performance parameters are achieved, specifically: a measured maximum gain of 9.33 dBi, Half Power Beam Width of 126.5° in the H‐plane, and a maximum Front‐to‐Back (F/B) ratio of 14.36 dB with an overall antenna size of 29 × 21 × 1.63 mm. The in‐depth understanding of the working mechanism is supported by a detailed parametric analysis, current distribution, and a clear physical insight into the operating principles. Moreover, a 1 × 4 Vivaldi antenna array is also designed and analysed. A measured maximum gain of the 13 dBi at 15 GHz in the array is achieved along with the wide bandwidth of 6.3 GHz from 10.78 to 17.07 GHz. The array is fed through an SL corporate feed network that ensures in‐phase excitation of all four Vivaldi pairs. A Grounded Co‐planar Waveguide to SL transition is adopted for connecting the 2.92 mm Radio Frequency launcher on the top layer. The very compact geometry of the proposed structure enables its integration into the systems for remote sensing applications.

Designing hybrid-guidance large mode area fiber for high-power lasers

All-solid large-mode-area antiresonant fibers possess unique characteristics of broadband, low-loss transmission of fundamental mode with effective single mode operation. Hinging on the principle, we propose a unique hybrid guidance mechanism, combining antiresonant guidance with total internal reflection-based guidance to design bend-tolerant, ultra large mode field area (>3000 µm2) fibers for high-power laser applications. Low-index rods are strategically interspersed into the antiresonant cladding to enhance the modal confinement in the fiber, resulting in lower confinement loss of the fundamental mode and its increased tolerance to bending and to the refractive index dip caused by non-uniform doping of active ions in the fiber core. We show that total internal reflection guidance greatly helps confine the fundamental mode without masking the characteristic features of antiresonant guidance, like effective single mode operation over broad spectral bandwidth. We present a detailed theoretical analysis to design a bendable, effectively single-moded passive and active hybrid-guidance antiresonant fibers, optimized to work in the 1 µm wavelength band. The design principles are universal and can be extended to shift the operating wavelength to the 2 µm range as well.

An L-shaped and bending-torsion coupled beam for self-adaptive vibration energy harvesting

Vibration energy harvesting is promising for powering wireless sensor networks for mechanical equipment monitoring. Considering the broadband feature of ambient vibrations, a novel L-shaped self-adaptive piezoelectric energy harvester (LSA-PEH) with a slider is proposed. A linearized mathematical model of the LSA-PEH is established to obtain the relationship between its resonant frequency and the slider position. The maximum resonant frequency that can be achieved by the LSA-PEH is predicted based on the linearized model. The corresponding condition is to fix the slider at around 0.08 m, which is a nodal point. Moreover, the theoretical model explains why the slider moves back and forth when the excitation frequency is 40 Hz. Experimental results show that the slider of the proposed LSA-PEH can passively relocate its position to adjust its resonant frequency and maintain resonance. By the same criteria, the bandwidth of the proposed LSA-PEH is increased by 350% compared to a conventional L-shaped beam harvester.

A fusion bandwidth extension technique for broadband low‐noise amplifier

SummaryWideband low‐noise amplifiers (LNAs) are widely used in 5G and 6G communication systems. This paper first analyzes two common bandwidth extension technologies: the stagger tuning technique and the magnetically coupled resonators (MCR) technique. Then, a four‐stage LNA based on double‐tuned transformer combined with stagger tuning idea and MCR idea was proposed. In order to improve the broadband characteristics of the LNA, the loose coupling double‐tuned transformer is carefully designed. Compared with the traditional stagger tuning LNA, it has better broadband characteristics, lower element error sensitivity, and lower design complexity. This designs a gain bandwidth product of 1.48 T with a −3‐dB bandwidth in 9.11 GHz and the noise factor is lower than 3 dB, which covers more than 45% −3‐dB fractional bandwidth. The LNA consumes 37‐mW power with a 1.1‐V supply and occupies 1.22 × 0.4 mm2.

Broadband spectrum characteristics and radiative effects of primary brown carbon from wood pyrolysis

Brown carbon (BrC), known as light-absorbing organic aerosol in the near-ultraviolet (UV) and short visible region, plays a significant role in the global and regional climate change. A detailed understanding of the spectral optical properties of BrC is beneficial for reducing the uncertainty in radiative forcing calculation. In this work, the spectral properties of primary BrC were investigated by using a four-wavelength broadband cavity-enhanced albedometer with central wavelengths at 365, 405, 532 and 660 nm. The BrC samples were generated by the pyrolysis of three types of wood. During the pyrolysis process, the measured average single scattering albedo (SSA) at 365 nm was about 0.66 to 0.86, where the average absorption Ångström exponent (AAE) was between 5.8 and 7.8, and the average extinction Ångström exponent (EAE) was within 2.1 to 3.5. The full spectral measurement of SSA (300–700 nm) was realized by an optical retrieval method and the retrieved SSA spectrum was directly applied to evaluate aerosol direct radiative forcing (DRF) efficiency. The DRF efficiency over ground of various primary BrC emissions increased from 5.3 % to 68 % as compared to the non-absorbing organic aerosol assumption. A decrease of about 35 % in SSA would cause the DRF efficiency over ground to change from cooling effect to warming effect (from −0.33 W/m2 to +0.15 W/m2) in the near-UV band (365–405 nm). The DRF efficiency over ground of strongly absorptive primary BrC (lower SSA) contributed 66 % more than weakly absorptive primary BrC (higher SSA). These findings proved the importance of broadband spectral properties of BrC, which are substantial for radiative forcing evaluation of BrC and should be considered in global climate models.

Laboratory demonstration of the wrapped staircase scalar vortex coronagraph

Of the over 5000 exoplanets that have been detected, only about a dozen have ever been directly imaged. Earth-like exoplanets are on the order of 10 billion times fainter than their host star in visible and near-infrared, requiring a coronagraph instrument to block primary starlight and allow for the imaging of nearby orbiting planets. In the pursuit of direct imaging of exoplanets, scalar vortex coronagraphs (SVCs) are an attractive alternative to vector vortex coronagraphs (VVCs). VVCs have demonstrated 2 × 10 − 9 raw contrast in broadband light but have several limitations due to their polarization properties. SVCs imprint the same phase ramp as VVCs on the incoming light and do not require polarization splitting, but they are inherently chromatic. Discretized phase ramp patterns such as a wrapped staircase help reduce SVC chromaticity and simulations show it outperforms a chromatic classical vortex in broadband light. We designed, fabricated, and tested a wrapped staircase SVC, and here we present the broadband characterization on the high contrast spectroscopy testbed. We also performed wavefront correction on the in-air coronagraph testbed at NASA’s Jet Propulsion Laboratory and achieved an average raw contrasts of 3.2 × 10 − 8 in monochromatic light and 2.2 × 10 − 7 across a 10% bandwidth.

Tunable Broadband Acoustic Vortex Generator with Multiple Orders Based on Mie Resonances Structure

AbstractAcoustic vortices are intensely researched in metasurfaces for their potential application in acoustic communication and particle manipulation. By elaborately designing acoustic metasurfaces with phase profiles, an acoustic vortex is obtained. However, most existing studies are limited to the single working frequency and the specific topological charge. To address these limitations, a tunable broadband acoustic vortex generator is designed to generate acoustic vortices with multiple orders. For this purpose, an annulus subwavelength Mie resonator is theoretically proposed first. In the Mie resonator, the multipole mode is excited by coupling eccentric monopole sources at related resonance frequencies. Then coupling the Mie resonance structure and two eccentric monopole sources can realize the multipole crossing, thus generating acoustic vortices with topological charge m of ±1, ±2, ±3, ±4, and ±5. Numerical simulations and an experiment further confirm the theory. In addition, frequency tunability, broadband characteristics, and system robustness are quantitatively studied. The designed vortex generator performs well on these characteristics, which may have potential applications in acoustic communication for multiplexing and demultiplexing.

Leading edge erosion detection for a wind turbine blade using far-field aerodynamic noise

In this paper, the feasibility of using far-field acoustic measurements as a non-contact monitoring technique for wind turbine blade leading edge erosion is assessed. For this purpose, a DU96 W180 airfoil with several eroded leading edge configurations of different severities is experimentally investigated. The eroded leading edges are designed with pits, gouges and coating delamination scaled from a real eroded blade. To assess the feasibility of the technique in quasi-realistic configurations, experiments are carried out under clean and turbulent inflow conditions. Acoustic measurements are performed with a phased microphone array. In the absence of inflow turbulence, because of the low Reynolds number at which the experiments are carried out, the case with minor erosion severity shows similar far-field noise spectra as the clean leading-edge cases, i.e., the presence of tonal peaks caused by laminar boundary layer instability noise through a self-sustained feedback loop but with higher tonal amplitudes. Increasing the damage level (considered as moderate erosion), the spectra of the noise scattered from the suction side show that the tonal peaks shift to higher frequencies and have lower amplitudes, thus suggesting that the damage alters the flow features responsible for the acoustic feedback loop; whereas, the spectra from the pressure side show a broadband noise distribution. For heavy erosion, the far-field noise spectra show broadband features from both airfoil sides, thus suggesting that the damage has fully forced the transition to turbulent flow; in which case, an increase in the low-frequency content is observed. Conversely, in the presence of turbulent inflow, when comparing the noise scattered at the trailing edge, no difference is found. However, leading edge impingement noise decreases at medium–high frequency compared with the baseline case at a chord-length-based Strouhal number StC∼10. The experimental results also suggest that the delamination feature is the one which is the most easily detectable and the approach is valid for a wide range of angles of attack and inflow velocity.

Enhanced acoustic black hole energy harvesters with multipiezoelectric array designs

This study theoretically and numerically proposes vibroacoustic energy harvesting concepts based on acoustic black holes (ABHs) and piezoelectric materials. Various ABH configurations in planar structures have been explored and investigated from the perspective of flexural wave localization and energy confinement. Different piezoelectric energy transducers, attached to the center region of ABHs with loading circuits are designed. Energy harvester with arrayed two ABHs shows higher energy production density than a harvester with single ABH under the same driving conditions. The energy harvester with the combination of the arrayed ABHs and the multipiezoelectric arrays shows high output electrical power density and broadband features.

Synthesis of Broadband Oversized Miter Bend for High-Power Millimeter Wave System

An optimum approach for designing a TE01 mode broadband oversized miter bend is proposed by synthesizing a mixture beam with the characteristics of conical Gaussian beam. With the analysis of the characteristics realized by the simple mixture modes based on the gap theory, the optimized mixture mode under different waveguide dimensions for high transmission efficiency miter bend is deduced. According to the analysis results and the broadband mode synthesis technology, a Ka -band oversized waveguide miter bend propagating circular TE01 mode is designed, fabricated, and measured. According to the transmission measurement results, the miter bend can achieve the transmission efficiency up to 95% in the frequency range of 32–38 GHz, which verifies the broadband and high-efficient characteristic of the component. The near-field test results further demonstrate the high output vector purity of the TE01 mode over 95.5% and the scalar purity over 98% is acquired in the working frequency band.