Tested Frequency Range Research Articles

Frequency-dependent material properties of copper and aluminum alloys

In this paper, the dynamic behavior of copper and aluminum alloys as used in electric drive units is investigated. Isothermal frequency sweeps are performed from 0.1 up to 50 Hz at temperatures of up to 400 °C. An evaluation of the test results at a constant frequency of 1 Hz shows a decrease in the storage modulus and an increase in the material damping. Considering all frequencies, a supplementary frequency dependency related to the material composition is detected. The lower the volume fraction of the alloying elements, the higher the impact of temperature and frequency on the material properties. The variations of the material parameters allow applying the time temperature superposition principle to estimate the dynamic behavior beyond the limited tested frequency range and temperatures by fitting the Williams–Landel–Ferry equation. Additional thermal aging of CU-ETP specimens does not affect the storage modulus, but diminishes the material damping. The findings show that each material has to be tested with regard to its respective application, material composition and manufacturing process. Furthermore, they demonstrate the relevance of considering the frequency-dependent material properties of low-alloyed copper and aluminum, especially in case of temperatures above 100 °C.

Noise control and experimental study of a highpressure oil pump enclosure

ABSTRACTThe present experimental study has been conducted to evaluate the impact of an acoustic enclosure of high-pressure oil pump, which is used to reduce the noise emission of an automobile engine. The enclosure is double-layered and made of nylon 66 (PA66) as an outer structure and polyurethane foam as the inner material. The sound signals of the engine were measured separately without an acoustic enclosure and covered by the enclosure. The signals were measured with 5 microphones around the engine under two electric loading conditions (0% and 100% load). The results revealed that the sound pressure level (SPL) of the engine increased significantly with the high-pressure oil pump installed, and the gap between SPL was larger for 100% load than 0% load. Furthermore, the enclosure of high-pressure oil pump was effective to attenuate the engine noise at almost the entire audio frequency range. The SPL reduced approximately 2 dB within nearly the entire test frequency range, supporting the remarkable noise reduction effect of the high-pressure oil pump enclosure.

Synthesis of α-cordierite based glass-ceramic from Bayan Obo tailing and fly ash through volume crystallization

The α-cordierite glass-ceramics samples were synthesized from Bayan Obo mine tailing and fly ash through volume crystallization as a result of using (NH4) H2PO4 and MgF2 as the nucleating and glass network relaxing agents, respectively. The application of some natural impurities within above wastes, i.e., CaO, Na2O, and K2O, as the flux to lower the viscosity of the base glass, also contributed to this successful synthesis. The density, bending strength, Vickers hardness, dielectric constant and loss within the 1-10 MHz testing frequency range, and the average coefficient of thermal expansion of the glass-ceramic were characterized at 2.56 g cm−3, 113.5 ± 15.87 MPa, 7.04 ± 0.26 GPa, ∼7.3, ∼10−2 and 1.86 × 10−6 °C−1 respectively. These properties make this solid waste-derived material a lucrative candidate for replacing the industrial cordierite in metallurgy and construction. The results of this study may serve as a useful example of the re-utilization of solid wastes similar to Bayan Obo tailing with high added value.

Investigation on a two-stage platform of large stroke for broadband vertical vibration isolation

For the purpose of preventing vibration-sensitive optical switches from malfunction caused by broadband vertical vibration, a novel two-stage vibration isolation platform is proposed. The primary stage is a bellows-type isolator of large stroke and low isolation frequency, and the secondary stage is a small-stroke hybrid isolator composed of bellows and voice-coil actuators. In the primary stage, two pre-compressed horizontal bellows and one vertical bellows are used to counter the weight of the switch and to reduce the total height of the isolator. The static properties of the primary stage are analyzed, and the vibration isolation of the platform is investigated. Numerical results indicate that the two-stage platform is effective in isolating vertical vibration. Experiments are also conducted to verify the performance of the platform. It is exhibited that the transmissibility is less than 0 dB over 2 Hz, and the attenuation rate reaches −35 dB/dec at high frequencies. The frequency range of test is 2–200 Hz, and the maximum displacement is 10 mm at 2 Hz. In the secondary stage, the actuators can substantially suppress the resonance peak, and promote isolation performance at low frequencies.

Graphene/polypyrrole nanocomposites with high negative permittivity and low dielectric loss tangent

Graphene (GNs)/ polypyrrole (PPy) nanocomposites with different content of GNs prepared by in-situ polymerization possess negative permittivity in the range of test frequency. Importantly, the GNs/PPy nanocomposites also have low dielectric loss tangent. ATR and XRD tests showed that no significant change in chemical bond and crystallization is found in GNs/PPy nanocomposites. SEM analysis indicated that GNs/PPy nanocomposites form different morphologies with the increase of GNs content. The negative permittivity of GNs/PPy nanocomposites is mainly caused by the plasmon resonance of the free electrons. The variation of resistivity and negative permittivity are basically consistent, which reflects that the good conductivity of the nanocomposites is attribute to the plasmon resonance of free electrons. The moderate addition of GNs is beneficial to the development of permittivity to a great negative value and decrease the dielectric loss tangent. The negative permittivity is up to −1.226 × 105 and the dielectric loss tangent is reduce to 0.32 in GNs/PPy nanocomposites with 10 wt% GNs content. The negative permittivity and the low dielectric loss tangent in GNs/PPy nanocomposites is achieved in a wider frequency range 1–1000 MHz.

Low loading carbon nanotubes supported polypyrrole nano metacomposites with tailorable negative permittivity in radio frequency range

Abstract Metacomposites with conductive polymer matrix toward negative permittivity have promising applications in energy storage devices and electromagnetic shielding. In this paper, carbon nanotubes (CNTs)/polypyrrole (PPy) nanocomposites with different loadings of CNTs have been synthesized using a surface-initiated polymerization (SIP) method. Scanning electron microscopy (SEM) results indicate that conductive networks have constructed inside the nanocomposites by CNTs and PPy granules. A frequency switch of permittivity from positive to negative in pure PPy and CNTs/PPy nanocomposites with low CNTs loading (1 wt%) is observed, which can be analyzed by the Lorentz model. Besides, all negative permittivity behavior in the test frequency range (10–1000 MHz) is found in CNTs/PPy nanocomposites with higher CNTs content which can be easily tuned by adjusting the CNTs loading. Negative permittivity is considered arising from the plasma oscillation of delocalized electrons in conductive networks and could be fitted by Drude model. Furthermore, the equivalent circuit models, ac conductivity and dielectric loss are discussed.

Acute motor and vocal response of humpback whales (Megaptera novaeangliae) to playback of amplitude-modulated noise: A method to test frequency range of hearing

The frequency hearing range of mysticete cetaceans remains elusive despite a growing concern about the negative impacts of anthropogenic noise. A playback study was conducted in the Maui Nui region of Hawaii during March 2018. Stationary humpback whales (i.e., single singers or silent dyads) were targeted due to their predictable behavior that allowed for observations pre, during, and post-playback. Playback consisted of amplitude-modulated noise that was broadband, high-pass filtered, or 1/3 octave bandpass filtered. The animal’s motor behavior was recorded by video from a swimmer positioned above the animal. Acoustic playback and acquisition was performed from a small vessel approximately 41 m to 56 m from a targeted animal. A total of 16 playbacks were conducted with estimated received levels between 116 dB–138 dB RMS (re 1 μPa). Motor responses ranged from abruptly swimming away to subtle fluke movements with a median response latency of 1.7 sec (n = 7). Vocal responses ranged from abrupt song termination to unexpected changes in song unit pattern, with a median response latency of 2.94 sec (n = 8). This novel playback methodology was effective at producing and measuring motor and vocal responses to sound and may be useful in measuring the hearing range of mysticetes.

Elucidation of microwave absorption mechanisms in Co–Ga substituted Ba–Sr hexaferrites in X-band

The tunable microwave absorbers are used to combat the electromagnetic pollution created by the development of high speed electronic devices. In the present paper, we report microwave absorption characteristics of M-type Ba0.5Sr0.5CoxGaxFe12−2xO19 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) hexagonal ferrite compositions prepared by using double sintering ceramic method. X-ray diffraction analysis of the prepared compositions revealed the formation of M-phase along with the minor traces of hematite in substituted compositions. The microwave absorption has been elucidated substantially through various mechanisms in the test frequency range from 8.2 to 12.4 GHz, which is still partially explored in literature. The substitution of Co2+ and Ga3+ ions enhances microwave absorption, bandwidth, decreases thickness and improves impedance matching. The hysteresis parameters also comply with the microwave absorption. The optimal reflection loss of − 29.74 dB is observed in the composition x = 0.2 at 8.28 GHz with 2.0 mm thickness. The investigated mechanisms of microwave absorption can be incorporated to optimize the absorption and design of the microwave absorbers.

Improved Triboelectric Nanogenerator Output Performance through Polymer Nanocomposites Filled with Core-shell-Structured Particles.

Core-shell-structured BaTiO3-poly( tert-butyl acrylate) (P tBA) nanoparticles are successfully prepared by in situ atom transfer radical polymerization of tert-butyl acrylate ( tBA) on BaTiO3 nanoparticle surface. The thickness of the P tBA shell layer could be controlled by adjusting the feed ratio of tBA to BaTiO3. The BaTiO3-P tBA nanoparticles are introduced into poly(vinylidene fluoride) (PVDF) matrix to form a BaTiO3-P tBA/PVDF nanocomposite. The nanocomposites keep the flexibility of the PVDF matrix with enhanced dielectric constant (∼15@100 Hz) because of the high permittivity of inorganic particles and the ester functional groups in the P tBA. Furthermore, the BaTiO3-P tBA/PVDF nanocomposites demonstrate the inherent small dielectric loss of the PVDF matrix in the tested frequency range. The high electric field dielectric constant of the nanocomposite film was investigated by polarization hysteresis loops. The high electric field effective dielectric constant of the nanocomposite is 26.5 at 150 MV/m. The output current density of the nanocomposite-based triboelectric nanogenerator (TENG) is 2.1 μA/cm2, which is above 2.5 times higher than the corresponding pure PVDF-based TENG.

Partial discharge behavior and ground insulation life expectancy under different voltage frequencies

Power electronic transformers, namely solid state transformers, have aroused a widespread attention due to the integration issue of large scale renewable energy in modern power system. High frequency power transformer (HFPT) is one of its key components operating at several to tens of kHz. Under such high frequency voltage, accelerated insulation aging and premature insulation failure occur frequently. Partial discharge (PD) is considered as the main cause of electrical performance deterioration in HV systems or LV ones where overvoltage or surge may occur. Therefore, it is necessary to study the PD behavior and insulation life under different voltage frequencies, in order to have a better understanding of premature failure mechanism. In this paper frequency dependence of space charge and PD properties is firstly analyzed theoretically and mathematically, followed by the results of electrical aging tests conducted on polyimide (PI) films that were subjected to surface PDs under 5-30 kHz sinusoidal voltage. Discharge characteristics and lifetime of PI film under different frequencies have been discussed, along with the correlation between lifetime and PD. Both theoretical analyses and experimental results show that average PD amplitude and total PD number per cycle increase first and then decrease afterwards with voltage frequency, which means that the frequency induced inflection phenomenon exists in the tested frequency range. Synergistic action of high frequency induced thermal effect and reduced space charge dissipation time under high frequency is the reason for this novel phenomenon. Besides, strong linear correlation has been found between lifetime and PD characteristic-total PD amplitude per second, which reveals the accelerated aging mechanism under high frequency electrical stress.

Non-Wovens as Sound Reducers

Abstract Within the present study, the effect of hemp (40 wt%) and polyactide (60 wt%), non-woven surface density, thickness and number of fibre web layers on the sound absorption coefficient and the sound transmission loss in the frequency range from 50 to 5000 Hz is analysed. The sound insulation properties of the experimental samples have been determined, compared to the ones in practical use, and the possible use of material has been defined. Non-woven materials are ideally suited for use in acoustic insulation products because the arrangement of fibres produces a porous material structure, which leads to a greater interaction between sound waves and fibre structure. Of all the tested samples (A, B and D), the non-woven variant B exceeded the surface density of sample A by 1.22 times and 1.15 times that of sample D. By placing non-wovens one above the other in 2 layers, it is possible to increase the absorption coefficient of the material, which depending on the frequency corresponds to C, D, and E sound absorption classes. Sample A demonstrates the best sound absorption of all the three samples in the frequency range from 250 to 2000 Hz. In the test frequency range from 50 to 5000 Hz, the sound transmission loss varies from 0.76 (Sample D at 63 Hz) to 3.90 (Sample B at 5000 Hz).

Determination of the permittivity of n‐hexane/oil sands mixtures over the frequency range of 200 MHz to 10 GHz

AbstractCombined electromagnetic (EM) heating and solvent injection has been recently proposed to recover bitumen from oil sands due to its great environmental friendliness. The permittivity of oil sands with the presence of solvent is a crucial property for the design, evaluation, and optimization of this process. In this study, we use the open‐ended coaxial probe method to measure the permittivity of oil sands over the frequency range of 200 MHz to 10 GHz. Results of the permittivity of the constituents of oil sands reveal that water is a major dielectric contributor; no relaxation phenomenon has been found for bitumen, sand, and n‐hexane over the tested frequency range. Also, the results for the oil sands mixtures show that water content is crucial for the permittivity of oil sands; both the dielectric constant and loss factor are enhanced with an increasing water content. With the addition of n‐hexane, the permittivity of bitumen slightly changes and fluctuates between the dielectric values of pure bitumen and n‐hexane. As for the n‐hexane/oil sands mixtures, the added n‐hexane induces the asphaltene aggregation/flocculation, affecting the interaction between water and asphaltene and leading to an enhanced free water content in the oil sands. Consequently, the permittivity of oil sands significantly increases after n‐hexane addition. Based on the experimental data, we evaluate the prediction accuracy of commonly used mixing models. A modified Lichtenecker‐Rother model considering effective water saturation is proposed to accurately characterize the permittivity of n‐hexane/oil sands mixtures. The obtained data and correlations can be useful when experimental data are missing.

Printed flexible electrochemical pH sensors based on CuO nanorods

Nanostructured metal oxides have attracted significant interest in a range of areas in electrochemical applications such as sensors, supercapacitors, and battery electrodes etc. Printing of these materials on flexible substrates will open new applications for the fabrication of sensors for monitoring the biological-food-medicine-agricultural systems. This paper presents the printed CuO based flexible electrochemical pH sensors. The sensors with interdigitated electrodes, screen printed on flexible substrates, are based on CuO nanostructures having nanorods (NR) morphology. The morphology influences the charge transfer phenomena and hence the sensor performance, as confirmed by the electrochemical studies. The NR based sensors have better stability with respect to conventional nanoflowers (NF). The structural analysis shows NRs exhibit high crystallinity and low surface roughness (130 nm) with respect to NF (192 nm). The sensor capacitance in the test frequency range (20 Hz–10 MHz) decreases exponentially with increase in pH. The CuO NR based sensor exhibits a sensitivity of 0.64 μF/pH in the range pH 5–8.5. The sensor performance towards interfrence to other ions and analytes such as Na+, K+, glucose, and urea was found to have negligible influence (±1.5 nF) on the sensing electrode. The capacitance of sensors is also found to vary with different bending conditions.

Structural Dynamics Modification of Vibration-Test Fixture

Abstract Vibration tests are designed and executed for verifying the qualification of aerospace hardware. To accomplish this, a test fixture is required, to transmit mechanical energy from the shaker to the test specimen. This paper presents the experimental testing and finite element model correlation of an available vibration test fixture. The objective was to design an optimized fixture in which the first natural frequency was out of the test frequency range (5–2000 Hz). Many iterations of the test were performed, but the results are presented for only the few that contributed to the optimized design of the vibration test fixture. The final optimized design is presented and discussed.

Effect of Moisture Content and Particle Size on Extinction Coefficients of Soils Using Terahertz Time-Domain Spectroscopy

Use of ultrafast terahertz (THz) laser spectroscopy as a nondestructive way to characterize the physicochemical properties of natural soils is still immature because how and to what extent the soil type, particle size, porosity, and moisture contents affect the THz spectroscopic responses of natural soils remains poorly identified. Herein, we explored the effect of moisture content and particle size on extinction coefficients of soils at a frequency range of 0.2–2 THz using ultrafast THz time-domain spectroscopy (THz-TDS) for three representative natural soils at different moisture contents. In the absence of water, the porosity and particle size distribution were found to mainly affect the THz transmission and scattering. Particularly, the Mie scattering appeared to have a pronounced effect on extinction coefficients of sand. In the presence of water, the moisture content played the governing role in absorption over the other factors. It was found that the effective medium modeling using Lambert–Beer model well predicted the extinction coefficients of silt and clay for a frequency range of 0.1–1 THz. Whereas, the experimentally determined extinction coefficients of sand were significantly greater than our model over the tested frequency range, owing to severe Mie scattering. These results provide complied test data that support the feasibility of using THz-TDS to remotely identify the physical characteristics of soils.

Development of a method for determining binaural sensitivity to temporal fine structure

Objective: To develop and evaluate a test of the ability to process binaural temporal-fine-structure (TFS) information. The test was intended to provide a graded measure of TFS sensitivity for all listeners. Design: Sensitivity to TFS was assessed at a sensation level of 30 dB using the established TFS-LF test at centre frequencies of 250, 500 and 750 Hz, and using the new TFS-AF test, in which the interaural phase difference (IPD) was fixed and the frequency was adaptively varied. IPDs varied from 30 to 180°. Study Sample: Nine young (19–25 years) and 23 older (47–84 years) listeners with normal hearing over the tested frequency range. Results: For the young listeners, thresholds on the TFS-AF test did not improve significantly with repeated testing. The rank-ordering of performance across listeners was independent of the size of the IPD, and moderate-to-strong correlations were observed between scores for the TFS-LF and TFS-AF tests. Older listeners who were unable to complete the TFS-LF test were all able to complete the TFS-AF test. Conclusions: No practice effects and strong correlations with an established test of binaural TFS sensitivity make the TFS-AF test a good candidate for the assessment of supra-threshold binaural processing.

A mixed-effects model approach for the statistical analysis of vocal fold viscoelastic shear properties.

A mixed-effects model approach was introduced in this study for the statistical analysis of rheological data of vocal fold tissues, in order to account for the data correlation caused by multiple measurements of each tissue sample across the test frequency range. Such data correlation had often been overlooked in previous studies in the past decades. The viscoelastic shear properties of the vocal fold lamina propria of two commonly used laryngeal research animal species (i.e. rabbit, porcine) were measured by a linear, controlled-strain simple-shear rheometer. Along with published canine and human rheological data, the vocal fold viscoelastic shear moduli of these animal species were compared to those of human over a frequency range of 1-250Hz using the mixed-effects models. Our results indicated that tissues of the rabbit, canine and porcine vocal fold lamina propria were significantly stiffer and more viscous than those of human. Mixed-effects models were shown to be able to more accurately analyze rheological data generated from repeated measurements.

Q-factors of CVD monolayer graphene and graphite inductors

A carbon-based inductor may serve as an important passive component in a carbon-based radio-frequency (RF) integrated circuit (IC). In this work, chemical vapor deposition (CVD) synthesized monolayer graphene and graphite inductors are fabricated and their Q-factors are investigated. We find that the large series resistance of signal path (including coil resistance and contact resistance) in monolayer graphene inductors causes negative Q-factors at the whole frequency range in measurement. Comparatively, some of the graphite inductors have all of their Q-factors above zero, due to their small signal path resistance. We also note that some other graphite inductors have negative Q-factor values at low frequency regions, but positive Q-factor values at high frequency regions. With an equivalent circuit model, we confirm that the negative Q-factors of some graphite inductors at low frequency regions are related to their relatively large contact resistances, and we are able to eliminate these negative Q-factors by improving the graphite-metal contact. Furthermore, the peak Q-factor (Qp) can be enhanced by lowering down the resistance of graphite coil. For an optimized 3/4-turn graphite inductor, the measured maximum Q-factor (Qm) can reach 2.36 and the peak Q-factor is theoretically predicted by the equivalent circuit to be as high as 6.46 at a high resonant frequency, which is beyond the testing frequency range. This research indicates that CVD synthesized graphite thin film is more suitable than graphene for fabricating inductors in carbon-based RF IC in the future.

Effects of Sm addition on electromagnetic interference shielding property of Mg–Zn–Zr alloys

The electromagnetic interference (EMI) shielding of Sm-containing magnesium alloys in the 30–1500 MHz testing frequency range was investigated by coaxial cable method. The results demonstrated that Mg–3Zn alloys displayed the best electromagnetic shielding property. When 0.5 wt% of Zr was added for crystal grain refinement, the shielding effectiveness (SE) was apparently reduced. The addition of the rare earth element Sm in ZK magnesium alloys can improve the electromagnetic interference shielding of magnesium alloys. The main reason for the differences in electromagnetic interference shielding of magnesium alloys was the change in conductivity. The addition of Zr in Mg–Zn alloys can refine the grains and consequently improve the grain boundary area significantly. Therefore, the number of irregularly arranged atoms at the grain boundaries increased, decreasing the conductivity of magnesium alloys and leading to a decrease in the electromagnetic interference shielding. Following the Sm addition, the Mg–Zn–Sm phase was precipitated at the grain boundaries and in cores. The precipitation of Sm-containing rare earth phases could consume the solid-soluted Zn atoms within the Mg, resulting in an increase in electrical conductivity and electromagnetic interference shielding improvement.

Structural, magnetic and electrical properties of Zr-substitued NiZnCo ferrite nanopowders

Zr-substituted NiZnCo ferrite nanopowders, Ni0.4−xZn0.5ZrxCo0.1Fe2.0O4 (0≤x≤0.20), were synthesized by the sol-gel auto-combustion method. The effects of Zr substitution on the structural, magnetic and electrical properties have been investigated. The DTA and TG results indicate that there are three steps of combustion process. The X-ray diffraction patterns show that the lattice parameter and the average crystallite size increase with the increase of Zr substitution. The saturation magnetization increases with the increase of Zr substitution when x≤0.05, and then decreases when x>0.05. Meanwhile, the coercivity initially decreases with the increase of Zr substitution when x≤0.05, and then increases when x>0.05. The polarization behavior for all the samples in the test frequency range from100Hz to10MHz obeys the charge polarization mechanism, which happens since the frequency of the hopping of electron exchange between Fe2+ and Fe3+ ions are far from the frequency of alternating-current field. And the dielectric constant increases with the increase of Zr substitution. The relaxation peak of the frequency dependence of dielectric loss is observed for x≥0.10, which is due to the frequency of charge hopping between the Fe2+ and Fe3+ exactly matches with the frequency of the external applied field. Electrical transport behavior of the ferrite nanopowders is found to follow the impurity semiconductor, and the effect of Zr substitution on the temperature dependence of dc resistivity is observed.