Measured Frequency Spectrum Research Articles

Functional Carbon Springs Enabled Dynamic Tunable Microwave Absorption and Thermal Insulation.

Electromagnetic (EM) wave pollution and thermal damage pose serious hazards to delicate instruments. Functional aerogels offer a promising solution by mitigating EM interference and isolating heat. However, most of these materials struggle to balance thermal protection with microwave absorption (MA) efficiency due to a previously unidentified conflict between the optimizing strategies of the two properties. Herein, this study reports a solution involving the design of a carbon-based aerogel called functional carbon spring (FCS). Its unique long-range lamellar multi-arch microstructure enables tunable MA performance and excellent thermal insulation capability. Adjusting compression strain from 0% to 50%, the adjustable effective absorption bandwidth (EAB) spans up to 13.4GHz, covering 84% of the measured frequency spectrum. Notably, at 75% strain, the EAB drops to 0GHz, demonstrating a novel "on-off" switchability for MA performance. Its ultralow vertical thermal conductivity (12.7mW m-1 K-1) and unique anisotropic heat transfer mechanism endow FCS with superior thermal protection effectiveness. Numerical simulations demonstrate that FCS outperforms common honeycomb structures and isotropic porous aerogels in thermal management. Furthermore, an "electromagnetic-thermal" dual-protection material database is established, which intuitively demonstrates the superiority of the solution. This work contributes to the advancement of multifunctional MA materials with significant potential for practical applications.

Broadband target strength of arabesque greenling, Pacific sand lance, and pointhead flounder

Abstract Measurement of target strength (TS) is important for estimating the abundance of species using fisheries acoustics. However, most researchers have only used a limited number of representative frequencies for acoustic measurements of fish without a swim bladder (bladderless fish). Here, we measured the broadband TS of three bladderless fish species, arabesque greenling (Pleurogrammus azonus), Pacific sand lance (Ammodytes personatus), and pointhead flounder (Cleisthenes pinetorum), using two broadband echosounders. TS measurements were conducted in a seawater tank over frequency ranges of 45–90 and 80–120 kHz using a tether method. Higher TS and directivity were observed at higher frequencies than at lower frequencies for pointhead flounder and arabesque greenling. However, the TS for Pacific sand lance was relatively flat over the measured frequency spectra. Additionally, the TS of pointhead flounder and Pacific sand lance could be expressed as a function of body length and the TS of arabesque greenling could be expressed as a function of body length and frequency, which could be used in fish species discriminations and size estimations.

Analysis of the roll imprint on the cross-sectional area of hot rolled wire rod by frequency spectroscopy

This work presents an approach for analysing the sensor data of an eddy-current based cross-sectional area measurement for hot rod and wire steel in an innovative manner and for approximating the influence on the forward slip by longitudinal tensile forces between the mill stands. The method is based on frequency spectroscopy of the cross-sectional area of the rolled stock. The measurement data of three sensors already implemented in two hot rolling mills is used in order to obtain information out of the roll imprint on the cross-sectional area. Since measurement data from two measuring sites and from three sensors are evaluated, this allows statements to be made about the reliability and reproducibility of the measurement and shows that the method can be used for different rolling blocks such as 3-roll and 2-roll blocks. In addition, a mathematical model is presented which allows conclusions to be drawn about possible causes for certain characteristics in the measured frequency spectrum of the cross-sectional area.

The Impact of Fireworks Noise on the Acoustic Climate in Urban Areas

New Year’s Eve is an example of a situation in which urban residents are exposed to an almost continuous and increased noise level from the impulsive sounds sources – fireworks. This custom has become a source of many controversies related to the protection of human and animal health or environmental pollution. However, current legal regulations only slightly affect the subject of noise of fireworks and its harmfulness. Currently, it does not seem possible to completely prohibit the use of fireworks in urban areas, but this does not mean that it is not possible to decrease the degree of their annoyance. The paper consists the issues of identification, analysis and assessment of impulsive noise of fireworks and acoustic climate during New Year’s Eve. Material presented refers to measurements of time series, frequency spectrum and values of noise parameters of selected fireworks. It was presented, among others, that the measured values exceed the criteria for occupational noise (LCpeak), due to the direct hazard of hearing loss, from 1.8 dB at a distance of 25 m and 6.2 dB at a distance of 15 m. Also this work discusses results of impulsive noise measurements of fireworks recorded during New Year’s Eve in years 2016–2017. Material refers to measurements at three measurement points spread over the city of Krakow. Obtained results were compared with typical noise levels for night time in urban area, indicating also the main sources of annoyance and hazard from this type of noise.

A review on different regulation for the measurement of transport noise and vibration

Transport noise and vibration have a negative influence on the environment, human health, and quality of life. The measurement and analysis of transport noise and vibration are required by the regulations and guidelines that various countries have set in order to manage and mitigate these effects. This review paper provides an overview of the requirements for the measurement and analysis of vibration and noise in transportation in different countries. The paper examines the measurement and analysis parameters, methods, and standards used in the United States, Europe, Australia and Japan. The review finds that although the requirements for measurement and analysis vary between countries, there are common parameters and methods used worldwide, such as sound pressure level and frequency spectrum measurements, noise and vibration impact assessment, prediction, and control measures. A comprehensive understanding of the measurement and analysis requirements for transport noise and vibration in different countries is essential for ensuring compliance with regulations, mitigating adverse impacts, and promoting sustainable transport development.

An injection-locking diode laser at 671 nm with a wide tuning range up to 6 GHz

We present a compact injection-locking diode laser module to generate 671 nm laser light with a high output power up to 150 mW. The module adopts a master–slave injection-locking scheme, and the injection-locking state is monitored using the transmission spectrum from a Fabry–Pérot interferometer. Beat frequency spectrum measurement shows that the injection-locked slave laser has no other frequency components within the 150-MHz detection bandwidth. It is found that without additional electronic feedback, the slave laser can follow the master laser over a wide range of 6 GHz. All the elements of the module are commercially available, which favors fast construction of a complete 671-nm laser system for the preparation of cold 6Li atoms with only one research-grade diode laser as the seeding source.

Frequency-Dependent Dielectric Spectroscopy of Insulating Nanofluids Based on GTL Oil during Accelerated Thermal Aging

Improving the dielectric properties of liquid-insulating materials is a current problem in research into the insulation system of a power transformer. Modern optimization of insulating liquids involves the potential use of unique synthetic esters enriched with nanoparticles. This study presents the results of the dielectric response of liquefied gas-based (GTL) insulating liquids during accelerated thermal aging. The dielectric relaxation spectroscopy method was used in the frequency domain to point out power losses as an imaginary part of a complex electric modulus. The relaxation spectra express the validity of applying this complex dielectric parameter. The polarization processes of the base oil alternately change position in the low-frequency band during thermal aging. Fullerene nanofluid undergoes three phases of dielectric loss changes during thermal aging. In the case of magnetic nanofluid, the effect of electric double-layer polarization disappeared after 500 h of thermal aging. It was found that with the gradual increase in the thermal aging time, there is no gradual increase in the dielectric losses investigated in the measured frequency spectrum. This study shows that the concentration of the two types of nanoparticles independently causes a different dielectric response to an applied AC electric field in the GTL base fluid.

Application of vibration diagnostics methods in the creating of elements of personal electric transport

The study of vibration loading of the main elements of personal electric vehicles and the search for ways to reduce vibration characteristics was conducted. The issues of measuring vibration arising on a bicycle, which is driven by human muscle power and an electric drive, are considered. Measurements of vibration acceleration and frequency spectra in a certain area of motion were carried out using the “Octave-101VM” spectrum analyzer in three stages. At the first stage, the electric bike was driven by a pedal drive, at the second – by an electric drive, at the third – the pedals and the electric drive worked in parallel. As a result of the tests carried out, it was found that the greatest vibration occurred in the “Motor” mode during the use of an electric bicycle, the least vibration occurred when driving with the electric motor turned off. It was found that the electric drive increases the vibration level (at the same time, the electric bike does not exceed the maximum permissible values of vibration levels on all axes). In order to reduce the vibration arising from the electric motor on a personal electric vehicle, a 3D computer model has been developed and an airless wheel mover has been manufactured using this model on a 3D printer (a wheel for an electric scooter with internal damping has been manufactured). Bench tests have shown that the developed wheel, in comparison with a pneumatic tire, has a smaller (up to 45 %) contact spot. The results obtained can be used in the development of competitive products, in particular personal electric vehicles.

The angle dependent ΔE effect in TiN/AlN/Ni micro cantilevers

In this work, magnetoelectric MEMS sensors based on a TiN/AlN/Ni laminate are investigated for the first time in regards of the anisotropic elastic properties when using hard magnetic Nickel as magnetostrictive layer. The implications of crystalline, uniaxial and shape anisotropy are analysed arising from the anisotropic Δ E effect in differently oriented cantilevers with 25 µm length and 15° spacing. The Δ E effect is derived analytically to consider the angular dependency of the different anisotropies within the sensors. In the measured frequency spectra complex profiles are observable consisting of contributions from neighbouring structures which are connected by a common electrode. The crosstalk effect is strongly depending on the cantilever orientation and reflects the anisotropic mechanical properties of the material stack. The intensity of the crosstalk effect is increasing for shortened cantilevers and narrowing distance between structures. The Δ E effect is investigated based on cantilevers of different angular spacing and of a single cantilever that is rotated in the magnetic field. The derived peak sensitivities are reaching values of 1.15 and 1.31 T −1 . The angular dependency of the sensitivity is found to be approximately constant for differently oriented cantilevers. In contrast, for a singly rotated cantilever an angular dependency of the 4th order is observed. • Δ E effect related eigenfrequency change can be described by uniaxial magnetic anisotropy. • sensitivity differs for single rotated cantilever compared to differently oriented ones. • observed crosstalk effect is depending on structure length, orientation and spacing.

The effect of hearing protection worn by talker and/or target listener on speech production in quiet and noise.

Speech production while wearing hearing protectors poses significant challenges due to their occlusion effect and disruption of the Lombard effect. An experiment was conducted with 24 individuals as they read a list of 12 sentences in open ears and while wearing an earmuff in quiet and in four different noises [pink, International Female Fluctuating Masker (IFFM), speech-spectrum noise (SSnoise), and helicopter] at two levels (70 and 85 dBA). An acoustic manikin, fitted or not with an identical protector, served as the target listener. In noise, speech levels decreased when the talkers wore the earmuff but increased when the target listener was fitted with the earmuff. When the earmuff was used by both the talkers and target listener, speech levels were lower by 3-6 dB at the higher noise level compared to when they were both open ears. Speech levels were typically lower, but extended speech intelligibility index estimates were consistently higher, in fluctuating (IFFM, helicopter) than in continuous noises (pink, SSnoise). Talkers' pitch frequency and voice spectrum measurements followed very closely the changes in speech levels, showing no evidence of compensatory voice modifications. Implications of the lower talker speech levels when wearing hearing protectors are discussed in terms of protector selection, training, and individuals with hearing loss.

A Single-Sideband Time-Modulated Phased Array With Low Sideband Level Suitable for Wide-Bandwidth Signals

Single-sideband time-modulated phased arrays (STMPAs) are able to generate a scanned beam at the first sideband while suppressing undesired sidebands. In this article, an STMPA with very low sideband level (SBL) suitable for wide-bandwidth signals is proposed. The design utilizes time-modulated pulses with stepped waveforms, which are realized by digital attenuators. This provides more degrees of freedom to improve the performance of STMPAs compared with previous techniques. Optimization of waveforms to achieve low SBLs as a function of the number of steps is discussed. This optimization is subject to some practical restrictions stemming from the characteristics and limitations of digital attenuators. Compared with previous STMPAs designed to eliminate undesired sidebands, the proposed design results in very low SBLs while reducing the impact of aliasing for wideband signals. Quantitative analysis of hardware complexity and aliasing effects is presented to demonstrate it. To validate the analysis presented, STMPAs with four-step and eight-step waveforms were designed and fabricated. Their measured SBLs are −28.72 and −33.57 dB, respectively. Measured frequency spectrum, waveform of modulating pulse, and radiation pattern of scanned beams are all presented.

Analytical prediction of tensile stress of photomask protective membranes based on measured frequency spectrum

The quality of photomask protective membranes is generally quantified in terms of its internal tensile stress. However, the tensile stress is not easily measured directly using experimental methods. Hence, the present research derives an theoretical model based on large deflection assumption for predicting the frequency spectrum of a pellicle. Using this model, the tensile stress of any membrane can be inversely derived by comparing the predicted frequency spectrum obtained using different tensile stress estimates with that determined experimentally using confocal microscopy and fast Fourier transform. The feasibility of the proposed approach is demonstrated by comparing the calculated frequencies of the main vibration modes of three commercial pellicles with the experimental results. The validated model is then used to investigate the effects of the membrane initial displacement, membrane width, and membrane thickness on the frequency response of a typical pellicle membrane.

Monitoring growing cracks in aircraft lugs by means of the electro-mechanical impedance method

Lugs are common connecting elements in many fields of engineering, e.g., aircraft and automotive. High stress concentrations at the inner edge of the bolt hole lead to early crack initiation and rapid fatigue crack growth under cyclic loading. However, a complete failure of such components is in most cases not acceptable. This contribution presents a model-based methodology to monitor the crack propagation in aircraft lugs by means of the electro-mechanical impedance method. For this purpose, piezoelectric sensors are permanently attached to the monitored structure. The evaluated structural components are necked, straight and tapered lugs. Crack propagation is analyzed numerically by coupled-field finite element models and experimentally using an impedance analyzer. Simulated and measured frequency spectra of pristine (no crack present) and damaged (a crack of various lengths is present) structures show significant deviations in resonance frequencies which are considered as clear indicators of the present crack. Furthermore, the length of artificially introduced cracks is determined by specific resonance frequency shifts for each lug shape. Crack length estimation based on resonance frequency shifts has already been shown in a recent study for necked double shear lugs, which is now extended for straight and tapered lug shapes. Finally, a discussion on the applicability of the presented crack analysis methodology for structural health monitoring of aircraft lugs under fatigue loading is presented.

Dynamic Susceptibility of Ferrofluids: The Numerical Algorithm for the Inverse Problem of Magnetic Granulometry

The size-dependent properties of magnetic nanoparticles (MNP) are the major characteristics, determining MNP application in modern technologies and bio-medical techniques. Direct measurements of the nanosized particles, involved in intensive Brownian motion, are very complicated; so the correct mathematical methods for the experimental data processing enable to successfully predict the properties of MNP suspensions. In the present paper, we describe the fast numerical algorithm allowing to get the distribution over the relaxation time of MNP magnetic moments in ferrofluids. The algorithm is based on numerical fitting of the experimentally measured frequency spectra of the initial dynamic magnetic susceptibility. The efficiency of the algorithm in the solution of the inverse problem of magnetic granulometry is substantiated by the computer experiments for mono- and bi-fractional ferrofluids.

Comparing one-step full-spectrum inversion with two-step splitting function inversion in normal mode tomography

SUMMARY Earth’s normal modes, or whole Earth oscillations, provide important constraints on Earth’s large-scale 3-D structure. In addition to constraining shear and compressional wave velocities, they are the only seismic data sensitive to density perturbations. Density is particularly difficult to determine, and previous studies have found contradicting results, hence the method chosen to invert normal mode data for 3-D structure becomes important. In the problem of inverting the measured frequency spectra for an earth model, we can take two approaches: (i) a one-step full-spectrum inversion, where normal mode spectra are directly inverted for a mantle model and (ii) a two-step splitting function inversion, where first the spectra are inverted for splitting functions, which are then inverted for a mantle model. Here we compare the methodology and results of both approaches, continuing the work done by Li et al. and Durek & Romanowicz, and extending it to higher spherical harmonic degrees. Using exactly the same normal mode data set, we use both inversion approaches to make 3-D shear wave velocity mantle models. Both approaches give models consistent with previous tomographic studies, although spectral misfits are consistently lower for the one-step full-spectrum inversion. We also show that we cannot draw any conclusions on odd-degree structure in the lower mantle with the currently available normal mode data sets.

Applicability of Taylor’s hypothesis during Parker Solar Probe perihelia

We investigate the validity of Taylor’s hypothesis (TH) in the analysis of velocity and magnetic field fluctuations in Alfvénic solar wind streams measured by Parker Solar Probe (PSP) during the first four encounters. The analysis is based on a recent model of the spacetime correlation of magnetohydrodynamic (MHD) turbulence, which has been validated in high-resolution numerical simulations of strong reduced MHD turbulence. We use PSP velocity and magnetic field measurements from 24 h intervals selected from each of the first four encounters. The applicability of TH is investigated by measuring the parameterϵ = δu0/√2V⊥, which quantifies the ratio between the typical speed of large-scale fluctuations,δu0, and the local perpendicular PSP speed in the solar wind frame,V⊥. TH is expected to be applicable forϵ≲ 0.5 when PSP is moving nearly perpendicular to the local magnetic field in the plasma frame, irrespective of the Alfvén Mach numberMA=VSW∕VA, whereVSWandVAare the local solar wind and Alfvén speed, respectively. For the four selected solar wind intervals, we find that between 10 and 60% of the time, the parameterϵis below 0.2 and the sampling angle (between the spacecraft velocity in the plasma frame and the local magnetic field) is greater than 30°. For angles above 30°, the sampling direction is sufficiently oblique to allow one to reconstruct the reduced energy spectrumE(k⊥) of magnetic fluctuations from its measured frequency spectra. The spectral indices determined from power-law fits of the measured frequency spectrum accurately represent the spectral indices associated with the underlying spatial spectrum of turbulent fluctuations in the plasma frame. Aside from a frequency broadening due to large-scale sweeping that requires careful consideration, the spatial spectrum can be recovered to obtain the distribution of fluctuation’s energy across scales in the plasma frame.

Nanoscale Ferroelectric Characterization with Heterodyne Megasonic Piezoresponse Force Microscopy.

Piezoresponse force microscopy (PFM), as a powerful nanoscale characterization technique, has been extensively utilized to elucidate diverse underlying physics of ferroelectricity. However, intensive studies of conventional PFM have revealed a growing number of concerns and limitations which are largely challenging its validity and applications. In this study, an advanced PFM technique is reported, namely heterodyne megasonic piezoresponse force microscopy (HM‐PFM), which uses 106 to 108 Hz high‐frequency excitation and heterodyne method to measure the piezoelectric strain at nanoscale. It is found that HM‐PFM can unambiguously provide standard ferroelectric domain and hysteresis loop measurements, and an effective domain characterization with excitation frequency up to ≈110 MHz is demonstrated. Most importantly, owing to the high‐frequency and heterodyne scheme, the contributions from both electrostatic force and electrochemical strain can be significantly minimized in HM‐PFM. Furthermore, a special measurement of difference‐frequency piezoresponse frequency spectrum (DFPFS) is developed on HM‐PFM and a distinct DFPFS characteristic is observed on the materials with piezoelectricity. By performing DFPFS measurement, a truly existed but very weak electromechanical coupling in CH3NH3PbI3 perovskite is revealed. It is believed that HM‐PFM can be an excellent candidate for the ferroelectric or piezoelectric studies where conventional PFM results are highly controversial.

Ultrafast single-shot optical vector network analyzer based on coherent time-stretch

Ever-increasing demands for a higher bandwidth of data in the optical communications augment the operating frequency of components and systems. To accelerate the development of these large-bandwidth technologies, there is a growing demand to characterize the frequency response of optical devices in real time. In this work, we report a method to significantly improve the measurement speed of an optical vector network analyzer (OVNA) with coherent time-stretch (CTS). Single-shot frequency spectrum measurements are enabled by time-stretch technology that maps the spectrum of an optical pulse to the time domain. Compared to single-ended detection, the implementation of coherent detection enables the acquiring of accurate phase information of the signal and also provides the digital processed cancellation of dispersion-induced impairments. By utilizing dispersive time-stretch and digital coherent detection techniques, we demonstrate an ultrafast and wide bandwidth OVNA. We successfully characterize its performance by measuring the frequency response of a micro-ring cavity and a silicon Mach–Zehnder interferometer with 0.07-nm spectral resolution and 0.156-rad phase accuracy over 10-nm bandwidth. Meanwhile, the dynamic responses of the magnitude and phase, and the drift of the resonance wavelength of the micro-ring modulator under thermal tuning, were fully recorded by the CTS-OVNA at a 20-MHz frame rate.

Defect detection of FRP-bonded civil structures under vehicle-induced airborne noise

Fiber-reinforced polymer (FRP)-bonded civil structures have been increasingly used in various construction fields, such as building, bridge, and tunnel. To maintain their designed mechanical performance, the integrity of interfacial bonding should be detected on a regular basis. From many recent laboratory studies, acoustic-laser technique is promising to be applied for identifying the presence of delamination or debonding in FRP-bonded civil structures. However, the defect detection performance of this technique towards real infrastructure encounters a challenging problem related to airborne vehicle noise as the number of cars circulating in urban area increases rapidly. In this study, we deal with the effect of vehicle noise on acoustic-laser technique when applying it in defect detection of FRP-bonded structures. Vehicle sound is found to not only raise the noise floor in measured frequency spectrum but also induce noise-related peaks (below 2000 Hz). Noise from a single passing vehicle causes greater reduction in signal-to-noise (SNR) ratio than that from a platoon of vehicle stream. Additionally, detecting large defect is more vulnerable to acoustic interference of vehicle noise than the small one. A quantitative function between the SNR and the noise level is set up to estimate the performance for defect detection in a construction area near the traffic flow. To handle the vehicle noise issue, a de-noising scheme is proposed and demonstrated for practical defect detection in the field.

Characterization of sound scattering layers in the Bay of Biscay using broadband acoustics, nets and video.

Sound scattering layers (SSLs) are observed over a broad range of spatio-temporal scales and geographical areas. SSLs represent a large biomass, likely involved in the biological carbon pump and the structure of marine trophic webs. Yet, the taxonomic composition remains largely unknown for many SSLs. To investigate the challenges of SSL sampling, we performed a survey in a small study area in the Northern Bay of Biscay (France) by combining broadband and narrowband acoustics, net sampling, imagery and video recordings. In order to identify organisms contributing to the observed SSLs, we compared measured frequency spectra to forward predicted spectra derived from biological data. Furthermore, to assess the confidence in SSL characterization, we evaluated uncertainties in modeling, acoustical and biological samplings. Here, we demonstrate for the first time that SSL backscattering intensity in the Bay of Biscay can be dominated in springtime by resonant gas bearing organisms below 100 kHz, namely siphonophores and juvenile fishes and by pteropods at higher frequencies. Thus, we demonstrate the importance of broadband acoustics combined to nets, imagery and video to characterize resonant backscatterers and mixed mesozooplankton assemblages.