Bandwidth Enlargement Research Articles

Noise control in ducts using Herschel-Quincke acoustic metamaterial array

Acoustic resonators, like Helmholtz, side branch tubes, expansion chambers, Herschel-Quincke, and so on, are usually used to control duct noise in acoustic systems. Noise attenuation in local resonators occurs due to impedance mismatch of incident, transmitted, and reflected waves induced by the addition of resonators. The frequency band and the attenuation level generated by the resonator depend on its geometry and behave as a narrow-band filter. However, a much larger frequency band, called bandgap, is obtained if they are appropriately distributed (periodically or not) along the duct length. This paper investigates acoustic noise attenuation for an acoustic metamaterial using a Herschel-Quincke (HQ) resonator. It is modeled by the transfer matrix method and the finite element method. Also, a study about the arrangements of the HQ resonators (serial and parallel) is conducted to verify their accuracy and efficiency related to bandwidth enlargement and sound transmission loss. Simulated results are obtained for different examples and compared to those from the literature.

Large-range high-speed dynamic-mode atomic force microscope imaging: adaptive tapping towards minimal force

In this paper, a software-hardware integrated approach is proposed for high-speed, large-range tapping mode imaging of atomic force microscope (AFM). High speed AFM imaging is needed in various applications, particularly in interrogating dynamic processes at nanoscale such as polymer crystallization process. Achieving high speed in tapping-mode AFM imaging is challenging as the probe-sample interaction during the imaging process is highly nonlinear, making the tapping motion highly sensitive to the probe sample spacing, and thereby, difficult to maintain at high speed. Increasing the speed via hardware bandwidth enlargement, however, leads to a substantially reduction of the imaging area. Contrarily, the imaging speed can be increased without loss of the scan size through control (algorithm)-based approach. For example, the recently-developed adaptive multiloop mode (AMLM) technique has demonstrated its efficacy in increasing the tapping-mode imaging speed without loss of scan size. Further improvement, however, has been limited by the hardware bandwidth and the online signal processing speed and computation complexity involved. Thus, in this paper, the AMLM technique is further enhanced to optimize the probe tapping regulation, and integrated with a field programmable gate array platform to further increase the imaging speed without loss of quality and scan range. Experimental implementation of the proposed approach demonstrates that high-quality imaging can be achieved at a high-speed scanning rate of 100 Hz and higher, and over a large imaging area of over 20 μm.

Fabrication and DC-Bias Manipulation Frequency Characteristics of AlN-Based Piezoelectric Micromachined Ultrasonic Transducer.

Due to their excellent capabilities to generate and sense ultrasound signals in an efficient and well-controlled way at the microscale, piezoelectric micromechanical ultrasonic transducers (PMUTs) are being widely used in specific systems, such as medical imaging, biometric identification, and acoustic wireless communication systems. The ongoing demand for high-performance and adjustable PMUTs has inspired the idea of manipulating PMUTs by voltage. Here, PMUTs based on AlN thin films protected by a SiO2 layer of 200 nm were fabricated using a standard MEMS process with a resonant frequency of 505.94 kHz, a -6 dB bandwidth (BW) of 6.59 kHz, and an electromechanical coupling coefficient of 0.97%. A modification of 4.08 kHz for the resonant frequency and a bandwidth enlargement of 60.2% could be obtained when a DC bias voltage of -30 to 30 V was applied, corresponding to a maximum resonant frequency sensitivity of 83 Hz/V, which was attributed to the stress on the surface of the piezoelectric film induced by the external DC bias. These findings provide the possibility of receiving ultrasonic signals within a wider frequency range, which will play an important role in underwater three-dimensional imaging and nondestructive testing.

Fabrication-tolerant and CMOS-compatible polarization splitter and rotator based on a compact bent-tapered directional coupler

In this paper, we demonstrate a broadband, low-loss, compact, and fabrication-tolerant polarization splitter and rotator (PSR) on a silicon-on-insulator platform. The PSR is based on an asymmetric directional coupler (ADC), which is covered with SiO2 from the top to make it compatible with the standard metal back end of line (BEOL) process. Conventional ADC-based PSRs suffer from stringent fabrication requirements and relatively low bandwidth, while the proposed bent-tapered design is highly insensitive to the fabrication errors (＞70 nm tolerance on the coupling gap) with an enlarged bandwidth and a compact footprint of 53 µm × 7 µm. It yields a polarization conversion loss less than 0.7 dB, a transverse electric (TE) insertion loss better than 0.3 dB, an ultra-low crosstalk with the TE extinction better than 30 dB, and the transverse magnetic extinction better than 25 dB, over a 200 nm wavelength range (1.5 µm–1.7 µm), in both ports. At the 1.55 µm wavelength, the calculated ultra-low polarization conversion loss and TE insertion loss are 0.27 dB and 0.08 dB, respectively.

Resistor Inductor Capacitor Impedance Optimization of Violet Laser Diodes for Free-Space Quadrature Amplitude Modulation Orthogonal Frequency Division Multiplexing Data Link

To optimize the high-speed modulation package of the TO-can mounted violet laser diode (VLD) for optical wireless communication, three different impedance matching methods with adding or removing resistor/inductor/capacitor (R/L/C) elements are employed to discuss their effects on the direct encoding bandwidth of the VLD. With reducing the parasitic inductance by shortening the cathode/anode pin length of the TO-can VLD, the 2.5-mm-long pin acts as a series inductance to 1.74 nH to enormously improve the modulation bandwidth of the VLD for encoding the 16 quadrature amplitude modulation orthogonal frequency division multiplexing data as high as 20.4 GB/s. Neither the surface mounted device (SMD) resistor nor the SMD inductor in series connection can further improve the modulation bandwidth of the VLD. In contrast, a parallel connection of the VLD with Teflon ring capacitor can somewhat broaden its encodable bandwidth at low biased conditions, whereas the allowable bandwidth still degrades when increasing the VLD bias to enlarge its modulation throughput. Numerical simulations also verify that the shortening pin length (with reducing the inductance) of TO-can VLD is the best selection for bandwidth enlargement. With optimized impedance matching design, the comparison on data transmission characteristics for several 2.5-mm-pin VLDs with different rated powers is presented.

Equivalent impedance and power analysis of monostable piezoelectric energy harvesters

Nonlinearity has been successfully introduced into piezoelectric energy harvesting for power performance enhancement and bandwidth enlargement. While a great deal of emphasis has been placed by researchers on the structural design and broadband effect, this article is motivated to investigate the maximum power of a representative type of nonlinear piezoelectric energy harvesters, that is, monostable piezoelectric energy harvester. An equivalent circuit is proposed to analytically study and explain system behaviors. The effect of nonlinearity is modeled as a nonlinear stiffness element mechanically and a nonlinear capacitive element electrically. Facilitated by the equivalent circuit, closed-form solutions of power limit and critical electromechanical coupling, that is, minimum coupling to reach the power limit, of monostable piezoelectric energy harvesters are obtained, which are used for a clear explanation of the system behavior. Several important conclusions have been drawn from the analytical analysis and validated by numerical simulations. First, given the same level of external excitation, the monostable piezoelectric energy harvester and its linear counterpart are subjected to the same power limit. Second, while the critical coupling of linear piezoelectric energy harvesters depends on the mechanical damping ratio only, it also depends on the vibration excitation and magnetic field for monostable piezoelectric energy harvesters, which can be used to adjust the power performance of the system.

The evolution of FWI and its perceived benefits

Despite the mathematics behind full waveform inversion (FWI) being published in the early 1980s, it was 30 years before the method could be efficiently implemented on the scale of conventional 3D marine seismic volumes. FWI has evolved from using only transmitted waves and being constrained because towed streamer data lacked the very long offsets and ultra-low frequencies necessary to derive stable velocity updates beyond shallow depths. FWI now uses the full seismic wavefield (both transmitted and scattered wavefields), recovers deep velocity updates for standard offsets and frequencies and increasingly uses a wider range of frequencies that contribute to seismic imaging. We use several case examples to consider the benefits and caveats for robust FWI application: for resolving near-surface features and reducing seismic imaging uncertainty in areas with complex overburden heterogeneities; for resolving near-surface features and improving volumetric estimates; for using an enlarged bandwidth to resolve small model features; for updating the velocity in high contrast regimes; and for the creation of survey-wide, high-resolution models to reduce imaging uncertainty, complement attribute analysis, estimate elastic properties and prospect derisking. Collectively, we demonstrate how to produce high-resolution velocity models when conventional methods cannot and how to generate earth models in an accelerated fashion to reduce project turnaround. We describe pragmatic limits to what maximum FWI frequencies are reasonable and suggest ways that may soon by-pass signal processing and obtain direct earth attributes.

Slow-Wave Half-Mode Substrate Integrated Waveguide 3-dB Wilkinson Power Divider/Combiner Incorporating Nonperiodic Patterning

A half-mode substrate integrated waveguide (HMSIW) with developed microstrip polyline unit cells etched on the waveguide surface is investigated in this letter. Modified analysis of the effective electrical parameters analysis is proposed. By applying the modified retrieval method, effective permittivity and permeability are extracted accurately to further describe the influence of the proposed structure, as well as slow-wave effect. Then, a compact 3-dB Wilkinson power divider/combiner based on polyline-patterned slow-wave HMSIW is developed for broadband microwave applications. The prototype achieves a fractional bandwidth of 91.7%, with the amplitude and phase variations less than 0.5 dB and ±4°, respectively. Compared with some reported SIW and HMSIW power divider, this letter achieves a size reduction of 40% and a bandwidth enlargement over 50%, illustrating its suitability for practical broadband applications.

A unified N-SECE strategy for highly coupled piezoelectric energy scavengers

This paper proposes a novel vibration energy harvesting strategy based on an extension of the synchronous electric charge extraction (SECE) approach, enabling both the maximization of the harvested power and a consequent bandwidth enlargement in the case of highly coupled/lightly damped piezoelectric energy harvesters. The proposed strategy relies on the tuning of the frequency of the energy extraction events, which is either N times greater than the vibration frequency (Multiple SECE case, ) or times smaller (Regenerative SECE, ). We first prove analytically than increasing or decreasing both lead to a damping reduction. While has no impact on the system’s resonance frequency in the Regenerative case we show that this resonant frequency becomes a function of in the Multiple SECE case (). Experimental results on a highly coupled/lowly damped piezoelectric harvester demonstrates the potential of this strategy, leading to 257% harvested power improvement compared to SECE (). and the possibility to tune the resonant frequency on a range as large as 35% of the short-circuit resonant frequency of the harvester.

A Broadband Impedance-Matching Method for Microstrip Patch Antennas Based on the Bode-Fano Theory

Abstract Considering the narrow bandwidth of microstrip antennas, but also their applicability in upcoming technologies, this paper addresses the problem of wide-band matching, the theoretical bounds on the matching bandwidth and low-cost and low-complexity matching strategies. In this context the Bode-Fano bounds of single mode, linearly polarized aperture-coupled microstrip antennas is evaluated, optimized and compared to the theoretical bounds on matching bandwidth of other common feeding technologies. A detailed study of the input impedance of aperture-coupled patch antennas shows how to widen the Fano bounds. Based on this, a straight-forward and effective method to optimize the Fano bound is given. After optimization of the antennas input impedance, basic matching techniques can be applied, to exploit the enlarged bandwidth potential. As an example a $\lambda/4$-transformer as matching element is proposed. Design equations and simulation and measurement results of X-band prototypes are given as verification.

Issues in vibration energy harvesting

In this study, fundamental issues related to bandwidth and nonlinear resonance in vibrational energy harvesting devices are investigated. The results show that using bandwidth as a criterion to measure device performance can be misleading. For a linear device, an enlarged bandwidth is achieved at the cost of sacrificing device performance near resonance, and thus widening the bandwidth may offer benefits only when the natural frequency of the linear device cannot match the dominant excitation frequency. For a nonlinear device, since the principle of superposition does not apply, the ‘‘broadband” performance improvements achieved for single-frequency excitations may not be achievable for multi-frequency excitations. It is also shown that a large-amplitude response based on the traditional ‘‘nonlinear resonance” does not always result in the optimal performance for a nonlinear device because of the negative work done by the excitation, which indicates energy is returned back to the excitation. Such undesired negative work is eliminated at global resonance, a generalized resonant condition for both linear and nonlinear systems. While the linear resonance is a special case of global resonance for a single-frequency excitation, the maximum potential of nonlinear energy harvesting can be reached for multi-frequency excitations by using global resonance to simultaneously harvest energy distributed over multiple frequencies.

Bandwidth enlargement of CMOS TIA using on-chip T-network for patient diagnosis in biomedical application

This work concerns on CMOS based trans-impedance amplifier (TIA) where enhancing the bandwidth by using optimized on-chip T-network for biomedical diagnosis applications.The proposed TIA consists of inductive peaking components as an input stage, distributed amplifier with feedback loop as middle stage while output as T-network. The proposed TIA with T-network achieves much wide band operation within range of 4.8–19.6GHz. As compared to conventional TIA, additional trans-impedance bandwidth of 1.4GHz in the lower band while 9.1GHz in higher band are able to achieve for the proposed design.The proposed architectures are implemented into ADS platform using commercial 65nm TSMC process.With this proposed technique, TIA also succeeds lower bit error rate (BER) for high speed data transmission in optical receiver i.e. beneficial towards the biomedical diagnosis. Chip fabrication of proposed TIA consuming less power of 10.8mW from the power supply of 1.6V. Measured and simulated data exhibits a wide bandwidth operation with trans-impedance gain of 55dBΩand made good correlation with each other. Moreover, experimental BER demonstrates less than 10–11 by providing pseudorandom bit sequence at 6–11Gb/s within desired band of operation in TIA. The optimized on-chip T-network occupies only 10% of the whole chip area of 0.4mm2.

Electrical constant envelope signals for nonlinearity mitigation in coherent-detection orthogonal frequency-division multiplexing systems

A theoretical analysis and a numerical investigation of 3-dB peak-to-average power ratio electrical constant envelope over orthogonal frequency-division multiplexing (OFDM) signals in coherent-detection optical (CO) systems are proposed. A 100-Gb/s optical system is studied to increase the nonlinear tolerance (NLT) to both Mach–Zehnder modulation and optical propagation impairments. Simulation results show that, with 16- and 64-QAM subcarrier modulations, the proposed system outperforms a conventional CO-OFDM system, if an optical modulation index OMI=2.5 and an electrical phase modulation index 2πh=3 are simultaneously adopted. The achieved NLT denoted by a performance gain of 24 dB is attractive after propagation through 1200 km of dispersion-uncompensated standard single-mode fiber, especially for 10-dBm fiber input power and despite the intrinsic bandwidth enlargement of PMs.

A novel fully planar quad band Wilkinson power divider

In this paper, by using extended composite right and left handed transmission line (E-CRLH-TL), the fully planar quad band Wilkinson power divider (WPD) proposed exhibits the benefits of bandwidth enlargement, excellent isolation and equal power split between output ports in the four pass-bands. The proposed divider is designed and fabricated on a low cost substrate with dielectric constant of 4.4 and a thickness of 0.8mm as work at four arbitrary frequency bands of 2.4GHz (ISM), 3.5GHz (WiMax), 5.2GHz (WiFi) and 5.8GHz (WiFi). The results of the measured and simulated designs are in good agreement with each other which verifies the proposed design methodology. The design concept of this paper can be easily extended to various multi-band microwave devices.

Bandwidth-Enlargement of a Low-Profile Open-Ring Slot Antenna Based on SIW Structure

In this letter, a compact proximity-fed open-ring slot antenna loaded substrate-integrated waveguide (SIW) structure for bandwidth enlargement is proposed and experimentally validated. The antenna was initially designed for ultrawideband operation and covers the frequency band from 3.8 to 11 GHz with reflection coefficient lower than -10 dB. With the use of stub along with the microstrip feedline, the lower band matching performance is improved. A novel technique for bandwidth enlargement at higher band based on SIW structure is presented. Metallic via-holes through substrate connecting the top and bottom metal plates are strategically aligned to extra widen the antenna bandwidth up to 20 GHz to resonate in the Ku-band. Details of the design methodology and results are presented and discussed.

Analysis of Miniature Metamaterial and Magnetodielectric Arbitrary-Shaped Patch Antennas Using Characteristic Modes: Evaluation of the <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math> </inline-formula> Factor

Evaluating the $Q$ factor of antennas using metamaterial substrates is a challenge and requires new analysis techniques. This challenge is even more important for arbitrary-shaped antennas. In this paper, we address the problem of analysis and evaluation of metamaterial-based antennas through the use of characteristic modes. We propose a new expression for the total $Q$ factor, which is independent of the excitation and based on the eigenvalues of the structure. The proposed expression is used to compute the $Q$ factor of an arbitrary-shaped resonant antenna and shows excellent agreement with other expressions in the literature such as the ones proposed by Yaghjian, Best, and Gustafsson. The approach is then used to analyze small patch antennas over metamaterial and magnetodielectric substrates. It is shown using the defined $Q$ factor expression that a magnetic substrate offers a significant bandwidth enlargement for the first active modes, and a dielectric substrate presents the opposite effect. This agrees with other works based on analytical approaches. Furthermore, we demonstrate that a reactive impedance metamaterial substrate presents identical modal significances that are identical to a conventional magnetodielectric substrate when associated with a patch antenna. This analysis is suitable for structures presenting noncanonical geometries and arbitrary shapes such as metamaterial inclusions.

Control Power Reduction and Frequency Bandwidth Enlargement of Robotic Legs by Nonlinear Resonance

Legged robots are regarded as a new means for transportation at uneven terrains and dangerous situations. In particular, quadruped robots that are capable of high-speed running are receiving great attention due to their superior mobility. The legs of such high-speed running robots rapidly repeat the swing and stance motions. Therefore, the legs of high-speed running robots should exhibit low impedance and friction for fast swing motions, while it is required to produce a significantly large actuation force for propulsion of the robot body in a stance phase. For this purpose, a direct-driven actuation mechanism was proposed for the Cheetaroid robot in our previous work. In this paper, in order to further enlarge the frequency bandwidth of the leg module and to reduce the required control (i.e., actuation) power, a dual-stage spring is designed to introduce a motion-adaptive resonance into the system. The structure and parameters of the dual-stage spring are determined in an optimal manner to minimize the control power. The resonance due to the dual-stage spring occurs only during high-speed locomotion, since the overall mechanism is designed such that the spring force is applied to the leg for high-speed locomotion only. The proposed system is verified by simulation studies and experimental results in this paper.

Spatial bandwidth enlargement and field enhancement of shear horizontal waves in finite graded piezoelectric layered media

Shear horizontal (SH) wave propagation in finite graded piezoelectric layered media is investigated by transfer matrix method. Different from the previous studies on SH wave propagation in completely periodic layered media, calculations on band structure and transmission in this paper show that the graded layered media possess very large band gaps. Harmonic wave simulation by finite element method (FEM) confirms that the reason of bandwidth enlargement is that waves within the band gap ranges are spatially enhanced and stopped by the corresponding graded units. The study suggests that the graded structure possesses the property of manipulating elastic waves spatially, which shows potential applications in strengthening energy trapping and harvesting.

The Doherty Power Amplifier: Review of Recent Solutions and Trends

In this paper, an extensive review of the most up-to-date papers on microwave Doherty power amplifiers is presented. The main applications are discussed, together with the employed semiconductor technologies. The different research trends, all aimed to improve the advantages of the Doherty scheme and to solve its inherent drawbacks, are presented. The first considered topic is the maximization of efficiency and/or linearity, where analog and digital techniques are exploited. Another important trend is the bandwidth enlargement of the Doherty architecture, that involves a large number of papers. Multi-band, multi-mode solutions are also considered, using either fixed or reconfigurable solutions. The final section is dedicated to the most significant Doherty integrated implementations.

Accurate Linearization with Low-Complexity Models Using Cascaded Digital Predistortion Systems

Power efficiency is one of the main concerns in modern radio frequency (RF) power amplifier (PA) design. However, efficiency-driven designs typically impose operation of these devices in a compressed mode [1]. When operating in this region, the amplifiers will behave nonlinearly and produce a distorted output signal [1]. This distortion produces new spectral components at the PAs' output that are outside the bandwidth of the input signal, so the distorted output signal has a wider bandwidth than the input signal. This bandwidth enlargement effect, called "spectral regrowth," is undesired in RF transmitters due to wireless systems' spectral mask regulations [2].