Effect of frequency bandwidth on interaural cross-correlation in relation to sound image width of reproduced sounds of a violin

This article discusses the effect of frequency bandwidth on the maximum absolute value of interaural cross-correlation coefficient (IACC) in relation to sound image width (also known as auditory source width, ASW). Subjective experiments concerning sound image width were performed using reproduced sounds of a violin. This article shows that separation into 1/24 and more octave bands and averaging IACC values of these frequency bands leads to a higher correlation to sound image width than IACC in broader frequency bands. Moreover the average of 1/n octave bands of the temporal deviation of interaural time differences and interaural level differences could be confirmed as measures correlating with sound image width.     

热疗用聚焦脉冲声场的时域和频域特性研究

本文用传递函数的概念导出了凹球面聚焦脉冲声扬的简洁表达式,从数值计算上和实验上研究了这种声场和中轴线上不同位置处声压信号的持续时间和频谱特征,分析了它们对热疗的影响。     

Demonstration of high conversion efficiency to second harmonic in a wide tuning range

This article discusses the second-harmonic generation (SHG) of tightly focused fs laser pulses in a BBO crystal. It was found theoretically and demonstrated experimentally that the spatial walk-off (SWO) and group-velocity dispersion (GVD) effects can suppress the pulse distortion and gain depression of SHG due to group-velocity mismatch (GVMM), thus keeping a reasonable pulse waveform and conversion efficiency simultaneously in a relatively wide tuning range. Using this approach, the SHG efficiency of a 2 mm long BBO crystal in a reflecting focusing geometry was enhanced significantly.     

Air-ground interaction in long range propagation of low frequency sound and vibration—field tests and model verification

An extensive program of intermediate and long range impulsive sound propagation field tests have been conducted. The test program and the performed measurements are presented. Particular focus is given on the air-ground interaction and its effect on low frequency sound and vibration propagation. It is found that the pressure wave interaction with the viscoelastic Rayleigh wave in the ground may have a significant effect on the ground impedance and the sound and vibration propagation. This introduces an important mechanism not covered in commonly used ground impedance models. Numerical simulation models have been developed and verified against the test data. The ground impedance does not only effect the sound pressure propagation. If either acoustically induced ground vibration, or ground to building transmitted vibration, is to be considered, the acousto-seismic impedance has a dramatic effect on the level of ground vibration induced by a given sound pressure. For a site where Rayleigh wave interaction appears at the dominant frequencies of the sound pressure, the ground vibration may be greater than a factor 100 (40 dB) than at a site with ground conditions not making the interaction happen.     

甚高频激发容性耦合氩等离子体的电子能量分布函数的演变

甚高频激发的容性耦合等离子体由于离子通量和能量的相对独立可控而受到人们的关注. 本文采用朗缪尔探针诊断技术测量了40.68 MHz激发的容性耦合Ar等离子体的特性(如电子能量概率分布、电子温度和密度等)随宏观参量的演变情况. 实验结果表明, 电子能量概率分布随着气压的增加从双麦克斯韦分布逐步转变为单麦克斯韦分布并最终演变为Druyvesteyn分布, 而射频激发功率的增加促进了低能电子布居数的增强; 在从等离子体放电中心移向边界的过程中, 低能电子的布居数显著下降, 而高能电子的布居则有所上升; 放电极板间距的变化直接导致了等离子体中电子加热模式的转变. 另外, 我们也对等离子体中的高低能电子密度和温度的分配情况进行了讨论.     

Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range

The perylene(C20H12) layer effect on the electrical and dielectric properties of Al/p-Si(MS) and Al/perylene/p-Si(MPS) diodes have been investigated and compared in the frequency range of 0.7 kHz–2 MHz. Experimental results show that C–V characteristics give an anomalous peak for two structures at low frequencies due to interface states(Nss) and series resistance(Rs). The increases in C and G/ω at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant(ε) and dielectric loss(ε) are subtracted using C and G/ω data at 1.5 V. The ε and ε values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln(σac)–ln(ω) for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2–V characteristics, the doping acceptor atom concentration(NA) and barrier height(ΦB) for Schottky barrier diodes(SBDs) of MS and MPS types are also obtained to be 1.484 × 1015 and 1.303 × 1015cm 3, and 1.10 and 1.13 eV, respectively.     

Prediction of NVH behaviour of trimmed body components in the frequency range 100-500 Hz

The work within this paper focuses on the application and validation of numerical methods for predicting the acoustic and structural NVH behaviour of trimmed body components in an automotive context. In particular, the level of modelling refinement and accuracy necessary to establish a reliable finite element analysis model for comparative purposes in the development of alternative designs is investigated.Specifically, the roof structure of a passenger car was investigated from various performance aspects, using both structural and acoustic excitation. The roof was initially tested in situ, with and without interior lining, to provide a reference for subsequent component tests. It was then detached from the car, mounted in a stiff frame and tested in a transmission window using both acoustic and structural excitation.A finite element model of the detached component was developed using shell and solid elements for the structure and solid elements for the interior lining. Predictions were carried out to evaluate the STL as well as the vibrational frequency response due to a force applied to the structure. Special attention was given to the modelling of the headliner as well as the air gap separating the headliner from the outer sheet metal. A sensitivity study of various headliner properties was performed in addition to a comparison between solutions calculated using standard Nastran elements and augmented poro-elastic elements via the software package CDH/EXEL.The main objective of the current work has been to establish a datum reference for alternative designs. From this aspect, the validation of the numerical modelling methodology, in particular the level of detail and accuracy used, was a crucial step. It was found that the predictions agreed very well with the measured data. As an additional, very interesting result, it was also found that the in situ testing correlated well with the transmission suite testing.     

High permeability and low power loss of Ti and Zn substitution lithium ferrite in high frequency range

The effect of Zn and Ti on the magnetic, power loss and structural properties of Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ ferrites (x=0.0 to 0.30 in step of 0.05)+0.5 wt% Bi₂O_3, prepared by standard ceramic technique, has been investigated. Complex permeability (μ*=μ′−jμ″) has been analyzed at room temperature in frequency range from 1 to 10³ MHz. It was found an enhancement in permeability with Ti and Zn concentration in Li_0.5Zn_xTi_xMn_0.05Fe_2.45−2xO₄ and exhibits the maximum value 106 for x=0.20 sample. Complex permeability of these ferrites exhibits stable frequency response up to 7 MHz beyond which the real part decreases sharply and imaginary part increases to have a peak at the relaxation frequency. Power loss measurements have been carried out in induction condition (B=10 mT) in frequency range of 50 kHz to 3 MHz. Power loss has been found to be quite low with the substitution of Ti and Zn in lithium ferrite.     

10～500 kHz水听器的激光外差干涉法原级校准

阐述了水听器在10~500 kHz频率范围的激光外差干涉法原级校准的原理和测量装置。利用激光外差干涉系统非接触测量水中反光薄膜在声波调制下引起的多普勒频移,经过零点信号解调算法得到水质点振速,准确复现水下声压量值,之后将水听器置于水中测量点完成对其自由场电压灵敏度的原级校准。对各误差因素进行了分析,详细给出了系统测量不确定度的评定方法,在所测频段的不确定度为0.6 dB (k=2)。将激光外差干涉法水听器校准结果与自由场互易法结果进行了对比,在整个测量频率范围内结果等效,且前者不确定度更小。为建立新的水声计量基准和实现水声量值的扁平化传递奠定了基础。     

Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency rangeElectrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency rangeElectrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range

The perylene （C20H12） layer effect on the electrical and dielectric properties of Al/p-Si （MS） and Al/perylene/p-Si （MPS） diodes have been investigated and compared in the frequency range of 0.7 kHz-2 MHz. Experimental results show that C-V characteristics give an anomalous peak for two structures at low frequencies due to interface states （Nss） and series resistance （Rs）. The increases in C and G/o3 at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant （er） and dielectric loss （e＇） are subtracted using C and G/co data at 1.5 V. The eI and e＂ values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln（o＇ac）-ln（w） for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2-V characteristics, the doping acceptor atom concentration （NA） and barrier height （,~） for Schottky barrier diodes （SBDs） 1.303 ~ 1015 cm-3, and 1.10 and I. 13 eV, respectively. of MS and MPS types are also obtained to be 1.484 ~ 1015 and     

Low frequency in situ metrology of absorption and dispersion of sound absorbing porous materials based on high power ultrasonic non-linearly demodulated waves

The present work is related to acoustic in situ free-field measurements of sound absorption in porous materials, such as cellular plastic foams, glass-wool or recycled felt materials. The emphasis is given towards fine metrology of absorption in view of potential industrial applications. A powerful ultrasonic array working at 40 kHz is used. It enables to measure absorption acoustical data down to 100 Hz due to the exploitation of the non-linear ultrasonic demodulation phenomenon in air. Fine measurements of acoustic absorption are compared to numerical predictions based on the “equivalent-fluid” model (when the squeleton frame is motionless), and to some measurements performed on a Brüel and Kjaer impedance tube. Dispersion curves are also measured and compared to the numerical predictions for some automotive felt materials which are compressed at various ratios. Data obtained with a dedicated portable instrument are also discussed for the same type of materials and configurations.