Narrow-band Input Research Articles

Automated operational modal analysis of bell towers subjected to narrowband input

Vibration-based Structural Health Monitoring (SHM) systems are very attractive to remotely assess the health state of structures of the historical urban landscape, such as bell towers, in operational conditions or after hazardous events, because of their limited invasiveness and the opportunity to enhance the knowledge about their mechanical behavior. The present study focuses on towers because, in spite of their relatively simple structural scheme, aging of materials as well as earthquake-induced damage resulted in a number of structural collapses occurred worldwide over the years. In this context, automated Operational Modal Analysis (OMA) techniques are key elements for the development of vibration-based SHM systems.After recognizing the critical aspects in the development of effective automated OMA procedures able to deal with the operational vibration response of bell towers, the present paper describes a strategy for automated OMA based on power spectral density transmissibility (PSDT) functions. The validation of the procedure is documented with reference to the dynamic response of a bell tower located in a minor center of the Italian Inner Areas, highlighting its effectiveness in identifying the fundamental modes from operational vibrations, and its robustness to the narrowband input associated with swinging bells.

A 320 μW Multi-Band Receiver with N-Path Switched-Capacitor Networks

This paper presents a multi-band ultra-low power (ULP) receiver with N-Path Switched-Capacitor (NPSC) networks in 90 nm CMOS process. The NPSC is integrated into the feedback loop of the low noise amplifier (LNA) to flexibly provide narrowband input matching at multiple sub-GHz Industrial, Scientific, and Medical (ISM) bands by adjusting the switching frequency. Moreover, the LNA with an NPSC network is utilized to suppress the out-of-band signal at the input and output of the LNA, simultaneously. In order to achieve an ultra-low power consumption, a sub-threshold LNA and four passive NPSC mixers are implemented in this receiver. The ULP receiver achieves a measured gain of 40±2 dB in ISM bands (430/860/915/960 MHz). The measured noise figure and out-of-band IIP3 are 10±0.5 dB and −0.3±2 dBm, respectively. The ULP receiver chip consumes 320 μW at 0.4 V power supply and occupies a chip area of 0.31 mm2.

High parametric efficiency in laser cavity-soliton microcombs.

Laser cavity-soliton microcombs are robust optical pulsed sources, usually implemented with a microresonator-filtered fibre laser. In such a configuration, a nonlinear microcavity converts the narrowband pulse resulting from bandwidth-limited amplification to a background-free broadband microcomb. Here, we theoretically and experimentally study the soliton conversion efficiency between the narrowband input pulse and the two outputs of a four-port integrated microcavity, namely the 'Drop' and 'Through' ports. We simultaneously measure on-chip, single-soliton conversion efficiencies of 45% and 25% for the two broadband comb outputs at the 'Drop' and 'Through' ports of a 48.9 GHz free-spectral range micro-ring resonator, obtaining a total conversion efficiency of 72%.

An efficient Lamb wave-based virtual refined time-reversal method for damage localization in plates using broadband measurements

This study proposes a modified virtual time-reversal (VTR) algorithm for baseline signal-free damage detection in plate-like structures. The physical actuation and sensing of Lamb waves are performed using a broadband Gaussian excitation instead of the conventional narrowband modulated tone burst excitations. The forward response and the reconstructed signal due to the time-reversal process for a narrowband input signal are then constructed virtually using the broadband transfer function. The method eliminates the possibility of numerical errors encountered in the conventional VTR method based on narrowband excitations. It is also more efficient than the traditional VTR algorithm because it can probe at multiple excitation frequencies using a single measurement for each sensing path. This modified VTR algorithm is employed in the recently developed refined time-reversal method (RTRM), which uses an extended signal length of the reconstructed signal for computing damage index (DI) and probes the structure at the best reconstruction frequency. The new method is termed the virtual refined time-reversal method (VRTRM). The DIs based on the VRTRM are used in the reconstruction algorithm for probabilistic inspection of defects to achieve baseline signal-free localization of damages. The efficacy of the proposed VRTRM for damage localization is experimentally verified with the established technique RTRM. Experiments are performed in an aluminium plate equipped with a network of surface-bonded piezoelectric patch transducers to illustrate the conventional VTR’s pitfalls and the modified VTR’s accuracy for a single mass damage scenario. The results show that the proposed VRTRM is as accurate as the established technique RTRM in estimating the reconstructed signals and localizing a block mass damage. Finally, the VRTRM is shown to localize in a dual damage scenario with excellent accuracy. In contrast, the conventional main mode-based VTR method fails to localize the damages with or without single-mode tuning.

Power spectral density analysis for nonlinear systems based on Volterra series

A consequence of nonlinearities is a multi-harmonic response via a mono-harmonic excitation. A similar phenomenon also exists in random vibration. The power spectral density (PSD) analysis of random vibration for nonlinear systems is studied in this paper. The analytical formulation of output PSD subject to the zero-mean Gaussian random load is deduced by using the Volterra series expansion and the conception of generalized frequency response function (GFRF). For a class of nonlinear systems, the growing exponential method is used to determine the first 3rd-order GFRFs. The proposed approach is used to achieve the nonlinear system’s output PSD under a narrow-band stationary random input. The relationship between the peak of PSD and the parameters of the nonlinear system is discussed. By using the proposed method, the nonlinear characteristics of multi-band output via single-band input can be well predicted. The results reveal that changing nonlinear system parameters gives a one-of-a-kind change of the system’s output PSD. This paper provides a method for the research of random vibration prediction and control in real-world nonlinear systems.

Reflective coupled microring resonators for reconfigurable photonic systems: Performance analysis

We propose reflective type triple coupled microring resonators (TCMMRs) for reconfigurable photonic based systems. We have developed an analytical model and analyzed its useful performance characteristics. The TCMMRs based device exhibits a wide range of performance characteristics such as multi-band filtering, optical logical operations, and optical true-time delay lines. Reconfigurable multiple resonances and their splitting features associated with the device provide useful filtering performance characteristics such as high out-of-band rejection, flat-top bandwidth, and near to ideal shape factor. The device can perform multiple functions such as bandpass, bandstop, and notch filtering with a good performance. Unlike two input narrowband logical operations demonstrated in the literature, our proposed device can perform as three-input optical logical operator, and it can switch wideband microwave frequency signals optically. Moreover, the device exhibits wideband flat top group delay response. It carries out delay tuning using a single variable coupling coefficient which simplifies the complexity of the tuning encountered in binary tree-structured optical beamforming networks based on conventional microring resonators.

A 4.4-mA ESD-Safe 900-MHz LNA With 0.9-dB Noise Figure

A 900-MHz 1.2-V 4.36-mA low-noise amplifier (LNA) with a minimum of 0.92-dB noise figure (NF) at 868 MHz, -12-dBm IIP3, with one inductor (external) is demonstrated. The circuit achieves narrowband input matching on a wideband LNA without inductive degeneration. A new half-cascoding technique is used to improve the input matching (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ) while simultaneously achieving sub-1-dB NF performance. The 0.13-μm CMOS LNA is fabricated with embedded electrostatic discharge (ESD) protection diodes that add 60 and 80-fF loads at the RF input and output ports. At 868 MHz, the packaged LNA has a measured input return loss (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ) of -18 dB and the transmission gain (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> ) of 14.2 dB. At 900 MHz, the LNA has a measured NF of 0.98 dB. The LNA (excluding the buffer) occupies an area of 0.047 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The chip passes the human body model (HBM) test with an ESD zap of 2.5 kV within 10% margin of its prezap I-V characteristics, under JEDEC standards. Multiple packaged chips were characterized with no perceptible difference in performance, indicating a robust design.

Influence of light source on the strain sensitivity of a polarisation maintaining fibre loop mirror based on voltage demodulation

The sensitivity is an important performance for a polarisation maintaining fibre (PMF) loop mirror (PM-FLM) sensor based on voltage demodulation. This paper investigates the method of improving the strain sensitivity of a PM-FLM based on voltage demodulation, including the demodulation principle, the derivation of the output light power equation, and experimentally studies on the strain sensitivity of a PM-FLM with different narrow-band input light source. The results show that the PM-FLM using a high-power light source as input has a high strain sensitivity but a small linear range of strain measurement, and the PM-FLM using a low-power light source as input has a low strain sensitivity but a large linear range of strain measurement. Hence, a high-power narrow-band light source as input can be chosen to improve the strain sensitivity, and the authors can also reduce the input light source power to enlarge the linear range of strain measurement.

Correlation-Based Calibration for Nonlinearity Mismatches in Dual-Channel TIADCs

Mismatches affect the dynamic performance of time-interleaved analog-to-digital converters (TIADCs). Linear mismatches can be calibrated by many mature methods, but if higher performance is required, nonlinearity mismatches have to be suppressed. The background calibration method based on input-free band (IFB) functions poorly for narrow-band signals. This brief proposes a correlation-based calibration method for nonlinearity mismatches in dual-channel TIADCs which behaves well for both wide-band and narrow-band signals. The output samples are calibrated by reducing the residual distortions which are approximated by multiplying the pseudo distortions and the estimated mismatch coefficients. The pseudo distortions are acquired by using a frequency-shifter, a differentiator, and multipliers. The coefficients which indicate the mismatch strength are estimated by eliminating the cross-correlation of the calibrated output samples and the calibrated pseudo distortions at zero lag. Simulations show that the proposed method can improve the SFDR by dozens of dBc for narrow-band input signals, compared with the IFB method. For the 16-QAM signal, the error vector magnitude improvement over the IFB method is 35.48 dB.

Fatigue crack detection using dual laser induced nonlinear ultrasonic modulation

In this study, a nonlinear ultrasonic modulation technique based on dual laser excitation is proposed for fatigue crack detection. Two pulse lasers are shot on the target specimen for ultrasonic generation. The corresponding ultrasonic responses are measured by a laser Doppler vibrometer (LDV) and analyzed to extract the crack induced nonlinear ultrasonic modulation. First, the effect of the pulse laser beam size on the frequency content of the generated ultrasonic waves is numerically and experimentally investigated. Then, this finding of the laser beam size effect is utilized to generate wideband (WB) and narrowband (NB) ultrasonic waves by adjusting the laser beam sizes of the two pulsed excitation lasers. Nonlinear ultrasonic modulation results from the interaction of WB and NB ultrasonic waves when a fatigue crack exists in the target specimen. The fatigue crack is then detected by comparing the spectral responses obtained under a single WB input and both WB and NB inputs. In the end, a fully noncontact dual laser ultrasonic system is developed and used to detect micro fatigue cracks in aluminum and steel plate specimens.

Waveform Modeling and Generation Using Hierarchical Recurrent Neural Networks for Speech Bandwidth Extension

This paper presents a waveform modeling and generation method using hierarchical recurrent neural networks (HRNN) for speech bandwidth extension (BWE). Different from conventional BWE methods which predict spectral parameters for reconstructing wideband speech waveforms, this BWE method models and predicts waveform samples directly without using vocoders. Inspired by SampleRNN which is an unconditional neural audio generator, the HRNN model represents the distribution of each wideband or high-frequency waveform sample conditioned on the input narrowband waveform samples using a neural network composed of long short-term memory (LSTM) layers and feed-forward (FF) layers. The LSTM layers form a hierarchical structure and each layer operates at a specific temporal resolution to efficiently capture long-span dependencies between temporal sequences. Furthermore, additional conditions, such as the bottleneck (BN) features derived from narrowband speech using a deep neural network (DNN)-based state classifier, are employed as auxiliary input to further improve the quality of generated wideband speech. The experimental results of comparing several waveform modeling methods show that the HRNN-based method can achieve better speech quality and run-time efficiency than the dilated convolutional neural network (DCNN)-based method and the plain sample-level recurrent neural network (SRNN)-based method. Our proposed method also outperforms the conventional vocoder-based BWE method using LSTM-RNNs in terms of the subjective quality of the reconstructed wideband speech.

Generation of Ultrasound Pulses in Water Using Granular Chains with a Finite Matching Layer

Wave propagation in granular chains is subject to dispersive effects as well as nonlinear effects arising from the Hertzian contact law. This enables the formation of wideband pulses, which is a desirable feature in the context of diagnostic and therapeutic ultrasound applications. However, coupling of the ultrasonic energy from a chain of spheres into biological tissue is a big challenge. In order to improve the energy transfer efficiency into biological materials, a matching layer is required. A prototype device is designed to address this by using six aluminum spheres and a vitreous carbon matching layer. The matching layer and the precompression force are selected specifically to maximize the acoustic pressure in water and its bandwidth. The designed device generates a train of wideband ultrasonic pulses from a narrow-band input with a center frequency of 73 kHz. An analytical model is created to simulate the behavior of a matching layer as a flexible thin plate clamped from the edges. This model is then verified using free-field hydrophone measurements in water, which successfully predict the increased bandwidth by generation of harmonics. The shapes of the measured and predicted waveforms are compared by calculating the normalized cross-correlation, which shows 83% similarity between both. Since the generation of harmonics is of interest in this study, the total harmonic distortion (THD) and the − 6 -dB bandwidth of the signals are used to analyze signal fidelity between the hydrophone measurements and the model predictions. The acoustic signals in water have a root-mean-square THD of 73%, and the model predicts a root-mean-square THD of 78%. The − 6 -dB bandwidths of individual pulses measured by a hydrophone and predicted with the model are 280 and 252 kHz, respectively. At these high ultrasonic frequencies, it is an experimental demonstration of resonant chains operating in water with a matching layer.

Quantum-Dot-Based Telecommunication-Wavelength Quantum Relay

The development of quantum relays for long haul and attack-proof quantum communication networks operating with weak coherent laser pulses requires entangled photon sources at telecommunication wavelengths with intrinsic single-photon emission for most practical implementations. Using a semiconductor quantum dot emitting entangled photon pairs in the telecom O-band, we demonstrate for the first time a quantum relay fulfilling both of these conditions. The system achieves a maximum fidelity of 94.5 % for implementation of a standard 4-state protocol with input states generated by a laser. We further investigate robustness against frequency detuning of the narrow-band input and perform process tomography of the teleporter, revealing operation for arbitrary pure input states, with an average gate fidelity of 83.6 %. The results highlight the potential of semiconductor light sources for compact and robust quantum relay technology, compatible with existing communication infrastructures.

An improved response spectrum method for non-classically damped systems

A complex modal truncation augmentation method is proposed in the present study for the non-classically damped systems. Compared to the traditional mode displacement superposition approach, this method considers the contributions from the high vibration modes and can therefore increase the prediction accuracy of the structural responses. It can be regarded as an improvement of the traditional method. Based on this method, the conventional CCQC (Complex Complete Quadratic Combination) modal combination rule for the non-classically damped systems is extended to take into account the contributions of the truncated high vibration modes and the effects of narrow-band inputs on the modal cross-correlation coefficients. Moreover, a practical method is developed to estimate the velocity response spectrum that is required in the CCQC rule utilizing the commonly used displacement response spectrum based on the random vibration theory. Numerical results show that the extended CCQC rule can result in more accurate structural response estimations especially when the contributions from the high vibration modes to the structural responses cannot be neglected or when the structure is subjected to the seismic inputs with narrow band widths.

Optical parametric amplification by incoherent conical pump beam

Optical parametric amplification of an input narrowband signal beam in the field of a spatially incoherent conical pump is investigated. Two amplification regimes – onset and exponential – are distinguished. The possibility to amplify the signal beam significantly and obtain a smooth intensity profile at the output is revealed. It is shown that the incoherent conical beam may act on the signal beam as a plane wave. Good agreement of theoretical and experimental data is obtained.

SBS reduction in nanosecond fiber amplifiers by frequency chirping.

We demonstrate a technique for SBS reduction in a nanosecond Yb-fiber amplifier by imposing 1.19 GHz/ns frequency chirp on the seed pulses with a pulse-driven phase modulator. A nearly 9-fold increase in the SBS threshold was observed for 8.4 ns pulses. SBS threshold data and transient SBS gain for various degrees of chirp are reported and compared with theoretical calculations. We further demonstrate the recovery of the input narrowband spectrum by applying an opposite chirp with a second phase modulator after the amplification.

Bandwidth-efficient calibration method for nonlinear errors in M-channel time-interleaved ADCs

In order to enhance the effective resolution of time-interleaved analog-to-digital converters (TI-ADCs), both linear and nonlinear channel mismatches should be carefully calibrated. This paper concentrates on a bandwidth-efficient background calibration method for nonlinear errors in M-channel TI-ADCs. It utilizes the least-mean square algorithm as well as a certain degree of oversampling to achieve adaptive mismatch tracking. The calibration performance and computational complexity are investigated and evaluated through behavioral-level simulations. Furthermore, a calibration strategy for narrow-band input signals is proposed and verified as an improvement of the basic calibration structure for such signals.

On time reversal-based signal enhancement for active lamb wave-based damage identification

Lamb waves have been a promising candidate for quantitative damage identification for various engineering structures, taking advantage of their superb capabilities of traveling for long distances with fast propagation and low attenuation. However, the application of Lamb waves in damage identification so far has been hampered by the fact that the characteristic signals associated with defects are generally weaker compared with those arising from boundary reflections, mode conversions and environmental noises, making it a tough task to achieve satisfactory damage identification from the time series. With awareness of this challenge, this paper proposes a time reversal-based technique to enhance the strength of damage-scattered signals, which has been previously applied to bulk wave-based damage detection successfully. The investigation includes (i) an analysis of Lamb wave propagation in a plate, generated by PZT patches mounted on the structure; (ii) an introduction of the time reversal theory dedicated for waveform reconstruction with a narrow-band input; (iii) a process of enhancing damage-scattered signals based on time reversal focalization; and (iv) the experimental investigation of the proposed approach to enhance the damage identification on a composite plate. The results have demonstrated that signals scattered by delamination in the composite plate can be enhanced remarkably with the assistance of the proposed process, benefiting from which the damage in the plate is identified with ease and high precision.

Low-noise amplifier with narrow-band and wide-band input impedance matching design

A low-noise amplifier (LNA) with cascode structure and shunt-peaking load is presented in this article. Both Narrow-band input impedance and wide-band input impedance LNAs were implemented in 0.18 μm CMOS process. Maximum power gain of the narrow-band input impedance LNA is 19.3 dB; maximum power gain of the wide-band input impedance LNA is 15.3 dB. Minimum noise figure of the narrow-band input impedance LNA is 3.1 dB; minimum noise figure of the wide-band input impedance LNA is 3.0 dB. Power consumptions including buffers are 24.5 and 25.6 mW, respectively.

Subword Partition based Data Driven Clock Gating Scheme for Low Power VLSI Design

low power optimization has been major concern in VLSI design from last two decades. The work presented here analyzes various clock gating based power optimization techniques in the context of digital signal processing applications. The clock gating based techniques with architecture level optimization possibilities are discussed. A novel method for data specific clock gating based on subword partition is developed and same is verified on Transposed FIR filter structure. The generic VHDL models of subword datapath based FIR architectures are used along with Xilinx Vivado power and performance analysis tools for validation. The results show power optimization upto 47% for narrowband input signal conditions on Virtex-6 Lx240T FPGA. The research shows a promising direction of power optimization technique, which can be used for wide range of signal processing applications.