Critical Frequency Range Research Articles

Acoustic Wave Generation in Nanofluids: Effect of the Kapitza Resistance on the Thermophone to Mechanophone Generation Mechanism Transition

High frequency, short wavelength acoustic wave generation in fluids, by means of immersed nanotransducers, is key to applications ranging from the biomedical to the ICT sector, all the way to investigating fundamental aspects of the mechanics of fluids. In this context, the commonly adopted generation mechanism is the thermophone, where the nanotransducer serves as a nanoheater for the surrounding fluid and the acoustic wave is launched by water thermal expansion. Its performance, however, is severely degraded when reaching up to hypersonic frequencies. We analytically investigate the thermoacoustic response in the frequency domain for the case of a gold nanofilm transducer in contact with water. We prove that another generation mechanism, the mechanophone, sets in this critical frequency range, widening the acoustic generation bandwidth. In the mechanophone, it is the nanotransducer thermal expansion that launches pressure waves in water. We find a threshold frequency discriminating between these two regimes, which can be tuned by acting on the Kapitza resistance at the solid–liquid interface. We then show how the mechanophone mechanism can be activated in the frame of photoacoustic generation with pulsed laser sources. The unveiled physics bears generality beyond the specific system and explains the acoustic generation mechanisms in nanofluids.

Measurement-Based Black-Box Harmonic Stability Analysis of Commercial Single-Phase Inverters in Public Low-Voltage Networks

This paper presents a measurement-based stability analysis of commercially available single-phase inverters in public low-voltage networks. In practice, manufacturers typically do not disclose the parameters of the inverter design, although interactions with the low-voltage network need to be assessed and predicted. State-of-the-art modeling methods require knowledge about the internal parameters. The method proposed in the paper is based on measurements in the laboratory and does not require detailed knowledge about the specific inverter design for the identification of the black-box linear time-periodic representation. The gained information is used for the black-box stability analysis in the frequency range up to 2 kHz, which covers the bandwidth of the control of the inverters. The method is validated for a commercially available photovoltaic inverter in the laboratory. An instability that leads to a shutdown of the inverter is demonstrated, while the critical frequency range is predicted accurately.

3D intra-cellular wave dynamics in a phononic plate with ultra-wide bandgap: attenuation, resonance and mode conversion

The intra-cellular wave dynamics of a water jetted phononic plate are experimentally investigated by means of high-resolution three-dimensional (3D) scanning laser Doppler vibrometry. The study is focused on the vibrational behavior around the ultra-wide bandgap of the plate (with a relative bandgap width of 0.89), as the critical frequency range of its phononic functionality. Broadband vibrational excitations are applied using a piezoelectric transducer and both in-plane and out-of-plane operational deflection shapes of the unit-cells are analyzed with respect to mode shapes calculated by finite element (FE) simulation. Attenuation and resonance of both symmetric and antisymmetric wave modes are validated, and it is shown that despite the absence of in-plane wave energy actuation, the symmetric modes are effectively excited in the phononic lattice, due to mode conversion from co-existing antisymmetric modes. Supported by FE modal analysis, this mode conversion observation is explained by the slight through-the-thickness asymmetry introduced during manufacturing of the phononic plate which leads to coupling of modes with different symmetry. The results confirm the potential of such detailed 3D inspection of phononic crystals (and in general acoustic metamaterials) in gaining full insight about their intracellular dynamics, which can also illuminate discrepancies with respect to idealized numerical models that might be due to manufacturing imperfections.

An investigation into the designing of fibrous sound absorption materials incorporated with nanofibers: a case study of a multi-layered material composed of PET nonwoven and PAN nanofibers

The present work aimed to investigate the effect of nanofiber enhancement on the sound absorption performance of fibrous materials through a brief review of the recent progress in the field and highlight the current challenges and issues for measuring and modeling the sound absorption coefficient (SAC) of such structures. Moreover, some composite samples consist of polyethylenterephthalat (PET) nonwoven fabric and polyacrylonitrile (PAN) nanofibers web were prepared to be studied as a case study. The nanofiber deposition amounts, nanofiber orientation, and nanofiber layering sequence were chosen as the main variables of samples. Various amounts of deposition were achieved through three different electrospinning (ES) time of 15, 60, and 180 min. The random and aligned orientation of the nanofiber web was obtained by using a rotating collector. The effect of the layering sequence of the nanofiber layer was studied in the form of quadruple-layered assemblies of samples. The results showed that the samples incorporated with the nanofiber layer with 60 min of ES and random orientation when it is used in the second position of the layering sequence have the best performance of sound absorption, mainly at lower critical frequency range. Furthermore, a discussion on some available empirical models and compare the results confirms that there is a need for developing a new approach for measuring and modeling the SAC and consequently designing such absorbers.

Experimental Study on the Sound Absorption Properties of Finger Millet Straw, Darbha, and Ripe Bulrush Fibers

Nowadays, emerging noise pollution by external factors causes harmful diseases in human beings. The development of a bio‐based filler or panel will help to eliminate some unwanted noise in working places and living rooms. This work aimed to develop an ecowaste fiber (leftover after harvesting)‐based sound absorber and analyze its capabilities for sound absorption. The ecowaste fibers are collected by the gleaning process, i.e., the process of collecting leftovers from fields. The sound absorption capabilities of three natural fibers extracted from Eleusine coracana (Finger millet) straw, Desmostachya bipinnata (Darbha), and Typha domingensis (Ripe bulrush) plants are investigated in this study, both individually and in hybrid combinations. The sound absorption property mainly depends on factors such as porosity, flow resistivity, thickness, density, and tortuosity. Fiber length and fiber type play a significant role when fibers are arranged individually or in hybrid combinations. The stacking effect on the sound absorption coefficient of hybridized fiber arrangement was experimentally analyzed. The sound absorption coefficient (α) was found to be lower in the range of 1000 Hz–2500 Hz for all the combinations. As a homogenous fiber arrangement, the darbha fiber exhibited the better NRC (noise reduction coefficient) of 0.86 for 50 mm thickness among three different fibers and as a hybrid composition, ripe bulrush and darbha fibers exhibited NRC of 0.90 which is more capable of absorbing sound in the critical frequency range of 500 to 2000 Hz. These types of natural fiber fillers are highly capable of better sound absorbing and used in the applications such as classrooms, sound recording rooms, and theatres.

All-GFRP footbridge under human-induced excitation

The dynamic behavior of lively footbridge is a complex problem. Recently there were numerous publications and recommendations related to the dynamic nature of footbridge. The complicated procedure which was set in a number of instructions and standards says nothing about actions aimed at avoiding critical frequency range in structure. In the paper, results of dynamic in-situ tests of cable-stayed all-GFRP (Glass Fiber Reinforced Polymer) footbridge are presented. Fiberline Footbridge, located in Kolding city in Denmark, was constructed in 1997 using 12 different pultruded profiles all made of GFRP material. The dynamic characteristics as well as vertical response of the tested footbridge under human excitation are given and discussed. Firstly, in order to estimate the dynamic properties of the footbridge, a series of free-decay responses under human jumping were conducted. The fundamental frequency of the analyzed structure was within a critical range. A methodology for footbridge classification with regard to their dynamic sensitivity was worked out and the correlation between the structure's properties and its dynamic response under pedestrian excitation was formulated. It was found that the analyzed footbridge fulfilled vibration comfort criteria elaborated by technical guide Sétra, however, more restricted acceleration limits suggested by Eurocode were not met.

Deadly Intraslab Mexico Earthquake of 19 September 2017 (Mw 7.1): Ground Motion and Damage Pattern in Mexico City

Research Article| October 10, 2018 Deadly Intraslab Mexico Earthquake of 19 September 2017 (⁠Mw 7.1): Ground Motion and Damage Pattern in Mexico City S. K. Singh; S. K. Singh aInstituto de Geofísica, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacan, 04510 Mexico City, Mexico, krishnamex@yahoo.com Search for other works by this author on: GSW Google Scholar E. Reinoso; E. Reinoso bInstituto de Ingeniería , Universidad Nacional Autónoma de México, Circuito Interior s/n, Ciudad Universitaria, Coyoacan, 04510 Mexico City, Mexico Search for other works by this author on: GSW Google Scholar D. Arroyo; D. Arroyo cDepartamento de Materiales, Universidad Autónoma Metropolitana, Avenida San Pablo 180, Reynosa Tamaulipas, Azcapotzalco, 02200 Mexico City, Mexico Search for other works by this author on: GSW Google Scholar M. Ordaz; M. Ordaz bInstituto de Ingeniería , Universidad Nacional Autónoma de México, Circuito Interior s/n, Ciudad Universitaria, Coyoacan, 04510 Mexico City, Mexico Search for other works by this author on: GSW Google Scholar V. Cruz‐Atienza; V. Cruz‐Atienza aInstituto de Geofísica, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacan, 04510 Mexico City, Mexico, krishnamex@yahoo.com Search for other works by this author on: GSW Google Scholar X. Pérez‐Campos; X. Pérez‐Campos aInstituto de Geofísica, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacan, 04510 Mexico City, Mexico, krishnamex@yahoo.com Search for other works by this author on: GSW Google Scholar A. Iglesias; A. Iglesias aInstituto de Geofísica, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacan, 04510 Mexico City, Mexico, krishnamex@yahoo.com Search for other works by this author on: GSW Google Scholar V. Hjörleifsdóttir V. Hjörleifsdóttir aInstituto de Geofísica, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacan, 04510 Mexico City, Mexico, krishnamex@yahoo.com Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2018) 89 (6): 2193–2203. https://doi.org/10.1785/0220180159 Article history first online: 10 Oct 2018 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation S. K. Singh, E. Reinoso, D. Arroyo, M. Ordaz, V. Cruz‐Atienza, X. Pérez‐Campos, A. Iglesias, V. Hjörleifsdóttir; Deadly Intraslab Mexico Earthquake of 19 September 2017 (⁠Mw 7.1): Ground Motion and Damage Pattern in Mexico City. Seismological Research Letters 2018;; 89 (6): 2193–2203. doi: https://doi.org/10.1785/0220180159 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search ABSTRACT In the wake of death and destruction left by the 2017 earthquake in Mexico City, it is natural to ask whether the event was unexpected and anomalous. Although such an intraslab earthquake (⁠Mw 7.1; depth=57 km⁠; epicentral distance = 114 km from the city) was considered likely, the recordings in the city during the last 54 yrs reveal that the ground motion during the 2017 earthquake was anomalously large in the critical frequency range to the city (0.4–1 Hz). The intraslab earthquakes occur closer to Mexico City, at greater depth, and involve higher stress drop than their interplate counterparts. Consequently, the ground motion is relatively enriched at high frequencies as compared with that during interplate earthquakes, which is dominated by lower frequency waves (⁠f<0.5 Hz⁠). This explains the observed difference in the damage pattern during the 2017 and the disastrous interplate earthquake of 1985 (⁠Mw 8.0). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Numerical and experimental assessment of a typical brazilian footbridge

Abstract For the range of medium spans, around 30 to 40m, composite footbridges are getting popular in Brazil. This kind of structure consists on longitudinal steel truss beams providing support for a concrete deck usually made of precast elements. Typical examples of these structures may be found in many cities in Brazil, especially in Brasilia where a large number of highways demanded a significant set of footbridges. Due to the amount of this kind of composite footbridges in Brazil, studies concerning their mechanical behavior are required in order to ensure pedestrian’s safety. For this end, in this paper, a typical Brazilian composite footbridge located in Brasilia is analyzed by means of experimental tests and computational modeling. The focus is the determination of natural frequencies and mode shapes. Strategies to correctly obtain the vertical modes are also discussed since vertical vibration is the main vibration problem expected for the tested footbridge. The obtained results showed that structural balance between stiffness and mass leads to natural frequencies out of the critical frequency range excited by pedestrians in normal use, although the idea was not to measure how these parameters, mass or stiffness, could influence the model. Moreover, Finite Element models were evaluated comparing complexity versus accuracy to predict modal parameters.

Evaluation and Improvement of the Reproducibility of CISPR 25 ALSE Test Method

The reproducibility of the absorber lined shielded enclosure radiated emission test method, defined in the standard CISPR 25, is evaluated through an interlaboratory comparison (ILC). The ILC started on September 2016 and concluded on February 2017. Nineteen data sets have been received and analyzed. The investigated frequency range is from 1 to 1000 MHz. The most critical (worst reproducibility) frequency range is the one from 10 to 50 MHz where the robust (outlier-resistant) standard deviation of the measured values is comprised between 5 and 8 dB. In the frequency range from 50 to 1000 MHz, the robust standard deviation is comprised between 2 and 3 dB. The main causes of nonreproducibility are identified and test setup adjustments aimed at improving the reproducibility are proposed.

Ferric metal-organic framework for microwave absorption

In this study, we have shown for the first time that ferric metal-organic framework (Fe-MOF) has the ability to attenuate gigahertz-range electromagnetic radiation through means of a novel interference mechanism. A large reflection loss value of −54.2 dB can be obtained, equivalent to over 99.999% absorption efficiency. The microwave absorption performance is largely dependent on the dielectric permittivity and magnetic permeability properties. The electrical loss ratio tgδε increases with the frequency from 0.13 at 1.0 GHz to 0.69 at 18.0 GHz, while the magnetic loss ratio tgδμ is only between 0.05 and 0.14. The conductivity σ increases with the frequency from 0.08 S/m at 1.0 GHz to 5.24 S/m at 18.0 GHz, while the skin-depth δ decreases with the frequency. The thickness (d) of the absorber is inversely proportional to the reflection loss peak value (RLpeak), the reflection loss peak frequency (fpeak), and the critical reflection loss peak width (Δf10). The non-zero magnetic susceptibility (χ) accelerates the shift of fpeak to lower values as d grows bigger; however, it improves the RLpeak value and larger microwave absorption efficiency and reduces the quick narrowing of the critical frequency range. The microwave performance of Fe-MOF is likely related to its microwave conductivity, which may originate from the polar rotations in the interface or defects. A new mechanism is proposed for the large reflection loss based on the interference of the reflected microwave from the front and back surface of the microwave absorber, especially when the thickness matches with the odd integer values of the wavelength.

Delay Compensation for Real Time Disturbance Estimation at Extremely Large Telescopes

In ground-based astronomy, aberrations due to structural vibrations, such as piston, limit the achievable resolution and cannot be corrected using adaptive optics (AO) for large telescopes. We present a model-free strategy to estimate and compensate piston aberrations due to the vibrations of optical components using accelerometer disturbance feed forward, eventually allowing the use of fainter guide stars both for the fringe detector and in the AO loop. Because the correction performance is very sensitive to signal delays, we present a strategy to add a delay compensation to the developed disturbance estimator, which can, in principle, be applied to many other applications outside of astronomy that lack observer performance due to a measurement delay or need a prediction to compensate for input delays. The ability to estimate vibration disturbances in the critical frequency range of 8–60 Hz is demonstrated with on sky data from the Large Binocular Telescope (LBT) Interferometer, an interferometer at the LBT. The experimental results are promising, indicating the ability to suppress differential piston induced by telescope vibrations by a factor of about 3 (rms), which is significantly better than any currently commissioned system.

Numerical analysis of two experiments related to thermal fatigue

Abstract Jets in cross flow are of fundamental industrial importance and play an important role in validating turbulence models. Two jet configurations related to thermal fatigue phenomena are investigated: • T-junction of circular tubes where a heated jet discharges into a cold main flow and • Rectangular jet marked by a scalar discharging into a main flow in a rectangular channel. The T-junction configuration is a classical test case for thermal fatigue phenomena. The Vattenfall T-junction experiment was already subject of an OECD/NEA benchmark. A LES modelling and calculation strategy is developed and validated on this data. The rectangular-jet configuration is important for basic physical understanding and modelling and has been analyzed experimentally at CEA. The experimental work was focused on turbulent mixing between a slightly heated rectangular jet which is injected perpendicularly into the cold main flow of a rectangular channel. These experiments are analyzed for the first time with LES. The overall results show a good agreement between the experimental data and the CFD calculation. Mean values of velocity and temperature are well captured by both RANS calculation and LES. The range of critical frequencies and their amplitudes, however, are only captured by LES.

A One-Dimensional Lumped-Mass Model for a Rubber Bushing and Its Application to the Calculation of Dissipation Energy

Modal analysis is employed in this paper using hammer impact testing to characterize the dynamic response of rubber bushing. Based on multi‐body dynamic analysis and acceleration transfer function, the rubber core is decomposed into three pieces, which are joined by spring and dashpot considering the large deformation and damping properties. Parameters of mass, stiffness and damping coefficients are identified through fitting against the Bode plot of the transfer function. With those parameters, the stability of this structure can be evaluated by exploring the critical excitation frequency range, which attributes the failure mechanism of rubber to thermal effect. The dissipation energy in each piece of the rubber core is calculated to demonstrate the accumulation of energy in rubber bushing. This paper successfully employs multi‐body analysis to predict the dissipation energy of rubber components.

Scanning magnetic tunnel junction microscope for high-resolution imaging of remanent magnetization fields

Scanning magnetic microscopy is a new methodology for mapping magnetic fields with high spatial resolution and field sensitivity. An important goal has been to develop high-performance instruments that do not require cryogenic technology due to its high cost, complexity, and limitation on sensor-to-sample distance. Here we report the development of a low-cost scanning magnetic microscope based on commercial room-temperature magnetic tunnel junction (MTJ) sensors that typically achieves spatial resolution better than 7 µm. By comparing different bias and detection schemes, optimal performance was obtained when biasing the MTJ sensor with a modulated current at 1.0 kHz in a Wheatstone bridge configuration while using a lock-in amplifier in conjunction with a low-noise custom-made preamplifier. A precision horizontal (x–y) scanning stage comprising two coupled nanopositioners controls the position of the sample and a linear actuator adjusts the sensor-to-sample distance. We obtained magnetic field sensitivities better than 150 nT/Hz1/2 between 0.1 and 10 Hz, which is a critical frequency range for scanning magnetic microscopy. This corresponds to a magnetic moment sensitivity of 10–14 A m2, a factor of 100 better than achievable with typical commercial superconducting moment magnetometers. It also represents an improvement in sensitivity by a factor between 10 and 30 compared to similar scanning MTJ microscopes based on conventional bias-detection schemes. To demonstrate the capabilities of the instrument, two polished thin sections of representative geological samples were scanned along with a synthetic sample containing magnetic microparticles. The instrument is usable for a diversity of applications that require mapping of samples at room temperature to preserve magnetic properties or viability, including paleomagnetism and rock magnetism, nondestructive evaluation of materials, and biological assays.

Optimization of the machine foundation using frequency constraints

Faced with the constantly increasing requirements for machine efficiency and reliability, designers have to pay attention to every detail, including machine foundation. Possible outage costs due to foundation damage can easily exceed the costs of design and construction of the foundation. This paper presents a novel and systematic procedure for finding an optimal design of reinforced concrete columns of the spring mounted machine foundation subjected to dynamic loads. The proposed approach assumes considerably decoupled natural modes of the critical structural members which can be optimized as simplified analytical models. It includes the following steps: FE modal analysis of the complete structure, identification of expected dynamic excitation, determination of the critical structural members, optimization of the corresponding analytical models and verification by FE modal analysis of the complete optimized structure. Turbine-generator-foundation structure was employed as an illustrative example. Operating speeds of the turbine and the generator and their higher order harmonics are taken as a critical dynamic excitation. Therefore, avoiding possible resonance region became the design objective, while the design variables were dimensions of the foundation columns cross-section. Lower and upper bounds of the design variables are determined on the basis of structural stability and space limitations regarding condenser and other auxiliary components of the turbine-generator system. The results of the analyzed example confirm that the optimization was successfully performed, since the optimized dimensions of the columns yielded natural frequencies outside the critical frequency range.

Scientific Review on the Ionospheric Absorption and Research Prospects of a Complex Eikonal Model for One-Layer Ionosphere

The present paper conducts a scientific review on ionospheric absorption, extrapolating the research prospects of a complex eikonal model for one-layer ionosphere. As regards the scientific review, here a quasi-longitudinal (QL) approximation for nondeviative absorption is deduced which is more refined than the corresponding equation reported by Davies (1990). As regards the research prospects, a complex eikonal model for one-layer ionosphere is analyzed in depth here, already discussed by Settimi et al. (2013). A simple formula is deduced for a simplified problem. A flat, layered ionospheric medium is considered, without any horizontal gradient. The authors prove that the QL nondeviative amplitude absorption according to the complex eikonal model is more accurate than Rawer’s theory (1976) in the range of middle critical frequencies.

The COMPLEIK subroutine of the IONORT-ISP system for calculating the non-deviative absorption: A comparison with the ICEPAC formula

The present paper proposes to discuss the ionospheric absorption, assuming a quasi-flat layered ionospheric medium, with small horizontal gradients. A recent complex eikonal model (Settimi et al., 2013b) is applied, useful to calculate the absorption due to the ionospheric D-layer, which can be approximately characterized by a linearized analytical profile of complex refractive index, covering a short range of heights between h1=50km and h2=90km. Moreover, Settimi et al. (2013c) have already compared the complex eikonal model for the D-layer with the analytical Chapman’s profile of ionospheric electron density; the corresponding absorption coefficient is more accurate than Rawer’s theory (1976) in the range of middle critical frequencies. Finally, in this paper, the simple complex eikonal equations, in quasi-longitudinal (QL) approximation, for calculating the non-deviative absorption coefficient due to the propagation across the D-layer are encoded into a so called COMPLEIK (COMPLex EIKonal) subroutine of the IONORT (IONOspheric Ray-Tracing) program (Azzarone et al., 2012). The IONORT program, which simulates the three-dimensional (3-D) ray-tracing for high frequencies (HF) waves in the ionosphere, runs on the assimilative ISP (IRI-SIRMUP-P) discrete model over the Mediterranean area (Pezzopane et al., 2011). As main outcome of the paper, the simple COMPLEIK algorithm is compared to the more elaborate semi-empirical ICEPAC formula (Stewart, undated), which refers to various phenomenological parameters such as the critical frequency of E-layer. COMPLEIK is reliable just like the ICEPAC, with the advantage of being implemented more directly. Indeed, the complex eikonal model depends just on some parameters of the electron density profile, which are numerically calculable, such as the maximum height.

A Phase Noise Analysis Method for Millimeter-Wave Passive Imager BHU-2D-U Frequency Synthesizer

A nontrivial phase noise analysis method is proposed for frequency synthesizer of a passive millimeter-wave synthetic aperture interferometric radiometer (SAIR) imager for concealed weapon detections on human bodies with high imaging rates. The frequency synthesizer provides local oscillator signals for both millimeter-wave front ends and intermediate frequency IQ demodulators for the SAIR system. The influence of synthesizer phase noise in different offset frequency ranges on the visibility phase errors has been systematically investigated with noise requirements drawn, and the integrated RMS phase error could represent uncorrelated phase noise effects in the most critical offset frequency range for visibility error control. An analytical phase noise simulation method is proposed to guide synthesizer design. To conclude, the phase noise effects on SAIR visibility errors have been concretized to noise design requirements, and good agreements have been observed between simulation and measurement results. The frequency synthesizer designed has been successfully in operation in BHU-2D-U system.

LOCAL OSCILLATOR UNCORRELATED PHASE NOISE ANALYSIS FOR MILLIMETER-WAVE PASSIVE IMAGER BHU-2D FREQUENCY SYNTHESIZER

In this paper, a nontrivial local oscillator uncorrelated phase noise analysis is proposed for frequency synthesizer of a pas- sive millimeter-wave Synthetic Aperture Interferometric Radiometer (SAIR) imager BHU-2D designed for concealed weapon detections on human bodies with high imaging rates. The frequency synthesizer pro- vides local oscillator signals for both millimeter-wave front-ends and intermediate frequency I/Q demodulators for the receivers. The in- ∞uence of local oscillator uncorrelated phase noise in difierent ofiset frequency ranges on the visibility phase errors have been systemati- cally investigated, and the corresponding system-level visibility speci- flcations are drawn. The integrated RMS phase error has been applied to set uncorrelated phase noise requirements in the most critical ofiset frequency range for visibility error control. The synthesizer design is given, and measurement results have proved that the visibility phase error requirement is achieved by the PN analysis method proposed with system-level visibility error tests performed. To conclude, the phase noise efiects on SAIR visibility phase errors are investigated by the- ory, and are properly limited by the PN requirement analysis method to ensure that the system-level visibility phase error speciflcation is satisfled.

Analysis of sound transmission through sandwich panels.

Due to their advantages over the conventional metal structure, sandwich structures have become used increasingly in transportation vehicles in recent years. However, they have some less favorable properties. In this paper, sound transmission through foam-filled honeycomb sandwich panels was studied using the statistical energy analysis (SEA). Modal density, critical frequency, and the radiation efficiency of sandwich panels were analyzed. The sound transmission loss and radiation efficiency of sandwich panels were predicted theoretically and measured experimentally. The measured results agree with the theoretical predictions quite well. An important observation is that, for foam-filled honeycomb sandwich panels, the radiation efficiency does not decrease to a plateau value at frequencies beyond the critical frequency. Although the high damping helps to improve the sound transmission loss in the critical frequency range, the overall transmission loss of sandwich panels is lower than their heavy metal counterparts. Therefore, the foam-filled honeycomb design must be modified to obtain good noise isolation capability, and a trade-off between the overall stiffness and the sound transmission properties should be considered in the design stage.