利用纳米力学方法对皮肤进行超声组织定征的研究

纳米力学方法适用于具有离散特性的材料.利用纳米力学方法,得出声波在多层皮肤组织中的波动方程.分别改变黑素瘤皮肤的泊松比、黑素瘤侵袭厚度(Breslow深度)、节间距离,计算多层皮肤结构模型对垂直入射纵声波的反射系数.同时计算了声速和声衰减系数随组织参数的变化.计算结果表明,可综合利用一定频率段内反射系数最小点数、声速和衰减系数的变化来表征正常皮肤和病变皮肤.     

Experimental investigation of reflection coefficients for lossy liquid-solid-liquid systems

The reflection coefficient for a bounded ultrasonic beam incident on a liquid-solid-liquid system (LSL) is studied. Systematic measurements were carried out to investigate the variations of the amplitude of the reflection modulus ∣R_LSL∣ with incident angle and parameter Fd (frequency-thickness of the plate). The experimental plots confirm the theoretical works of Claeys et al¹ and Bogy and Gracewski². It is shown that the attenuation of the media has a great influence on the variations of this coefficient as has been already mentioned in the literature, for liquid-solid configurations.     

单光束扩束扫描激光周视探测系统参数对探测能力的影响

针对现有单光束激光同步扫描周视探测对脉冲重复频率要求较高,难以实际应用的问题,提出单光束扩束扫描激光周视探测方法.基于单光束扩束扫描激光周视探测工作原理,推导了最低扫描频率和脉冲频率解析式;分析了圆柱目标回波特性及关键参数截面衰减系数,建立了脉冲扩束激光圆柱目标回波功率数学模型,讨论了系统参数对截面衰减系数的影响,得到最大相邻脉冲光束夹角表达式;重点分析了脉冲频率、光束角和光束入射角对不同直径目标的探测能力的影响;得到了探测系统对典型条件下最大光束角、最低脉冲频率的计算方法.结果表明,对扫描光束稍加扩束可有效降低脉冲重复频率要求.研究结果可为单光束脉冲激光周视探测系统设计、优化提供理论依据.     

浅海起伏海面下气泡层对声传播的影响

分析了起伏海面下风浪引起的气泡层对海面反射损失和对声传播的影响.一方面,气泡层会改变原来水中的声速剖面;另一方面,气泡层会对声波产生散射和吸收作用.考虑以上两方面的因素,分析了不同风速下气泡层对海面反射损失和声传播损失的影响,仿真发现,在风速大于10 m/s时,对于2 k Hz以上频率时气泡层对小掠射角下海面反射损失的影响不可忽视.在给定的水声环境中,当声源深度和接收深度都为7 m时,风速为16 m/s的风浪下生成的气泡层,在10 km处对3 k Hz的声传播损失的影响达到8.1 d B.当声源深度和接收深度都为18 m时,风速为16 m/s的风浪下生成的气泡层,在10 km处对3 k Hz的声传播损失的影响达到4 d B.     

Attenuation of ultrasound in skeletal muscle

Ultrasonic attenuation in fresh and 5% formalin fixed beef skeletal muscle has been measured, as a continuous function of frequency, in the range 1–8 MHz, for muscle fibre orientations both parallel and normal to the direction of propagation. Good agreement was found in all cases between two independent sets of measurements employing transmission and reflection techniques respectively. The data are consistent with a power law dependence of attenuation coefficient on frequency, with an exponent that is not significantly different from unity. For propagation normal to the fibres attenuation values are found as 1.1 ± 0.15 and 1.6 ± 0.15 dB cm^?1 MHz^?1 for fresh and fixed tissue respectively, the corresponding values for parallel propagation being 2.9 ± 0.23 and 4.1 ± 0.25 dB cm^?1 MHz^?1.     

Interaction of ultrashort elliptically polarized laser pulses with nonlinear helical photonic metamaterial

The effect of nonlinear properties of a material with a periodic structural cell (three-dimensional spiral) on the specificity of transmission and reflection of elliptically polarized laser pulses normally incident on the metamaterial is studied using the finite-difference time-domain method. An analysis of the hodograph of electric-field strength vector showed that an increase in the peak intensity of a linearly polarized laser pulse incident on a sample leads to an increase in the orthogonal component of the electric-field strength vector in the pulse transmitted through the medium. When pulses containing few electric-field periods are incident on a metamaterial, the latter demonstrates radically different optical properties for right- and left-handed circularly polarized light passing through the medium. It was shown that an increase in the intensity of a right-handed (left-handed) circularly polarized ultrashort pulse, incident on a sample composed of a rather large number of right-handed (left-handed) spirals made of nonlinearmaterial, widens the frequency range within which the incident light is almost entirely reflected from the medium.     

REFLECTION OF PLANE WAVES BY THE FREE BOUNDARY OF A POROUS ELASTIC HALF-SPACE

In the present paper, we study reflection of inclined incident plane waves from a free boundary of the half-space in which the material is described by constitutive equations valid for elastic solids with voids. Both the cases of the transverse and longitudinal incident waves are considered, and it is shown that only the transverse one can propagate in the solid without attenuation, after having been reflected from the free boundary surface. The reflection coefficient and the amplitude of the surface oscillations are expressed in explicit form. The general results are demonstrated for several hypothetical porous materials, and it is shown that the reflection coefficient and the vibration amplitude are typically less than in classical media without voids. However, for relatively large transverse wave speed and high porosity, free boundary oscillation can exceed the classical one.     

海面冰层对声波的反射和散射特性

北极海面冰层复杂多变,其对声波的反射和散射严重影响冰下水声信道的传输特性,建立海面冰层的声波反射和散射模型对冰下水声通信研究具有重要意义.假设海面冰层为多层固体弹性介质且冰-水界面粗糙,满足微扰边界条件,导出声波从海水介质入射到海面冰层时相干反射系数满足的线性方程组.对相干反射系数随声波频率、掠射角、冰层厚度的变化进行数值分析.进一步引入根据散射声场功率谱密度计算散射系数的方法,改变掠射角,对冰层厚度、散射掠角对散射系数的影响进行研究.     

Model and experimental analysis of oblique incident ultrasound in a tissue layer using doublet mechanics theory

The fundamental framework of doublet mechanics (DM) is used to analyze high-frequency ultrasound wave propagation in materials with discrete microstructure. Ultrasonic reflection coefficients were measured from a thin layer of tissue embedded between two glass substrates at oblique incidence. Theoretical calculations for the reflection coefficients of a multi-layered system at oblique angles are performed using both DM theory and the classical continuum mechanics theory (CCM). For example, at the frequency of 10 MHz at incident angle 8° in sample with 30 μm thickness, the discrepancy in the magnitude of the reflection coefficient between experimental results and theoretical prediction is 15.8% for DM but 79.0% for CCM; similar results at other frequencies and incident angle in the samples with 30 and 60 μm thickness have also been obtained, which demonstrates that the DM theory can better describe the wave propagation in tissue. The influence of the incident angles and tissue thickness are also discussed in this paper.     

Utilizing vector hydrophones to achieve an active anechoic terminal in an acoustic tube

A new integrated active sound absorptive terminal using vector hydrophones is developed for the anechoic terminal of impedance tube,with which the reflected and the incident waves can be separated.The method overcomes the limitations imposed by the sensor spacing and measuring frequency range in the traditional two-hydrophone method,and can effectively expand low-frequency sound absorption band of the terminal.The effect of hydrophone sensitivity on the sound absorptive performance of the terminal is evaluated,a correction method is also provided for the reflection and transmission coefficient.The experimental results show that the absorption coefficient in the frequency band of 0.1-2 kHz is over 0.98,which agrees well with the theoretical results.     

Textile materials for electromagnetic field shielding made with the use of nano- and micro-technology

Studies have been carried out aimed at the development of structures and technology for making special multi-layer textile-polymeric systems of shielding electromagnetic field (EMF). The use of textiles as EMF shielding materials is commonly known, however the EMF attenuation obtained practically exclusively results from the reflection of EMF, while the materials used for this purpose as a rule, show poor EMF absorption abilities. The basic assumption for a new solution is the exploitation of the multiple internal reflection of incident EMF either in textile-polymeric coating materials containing fine-particle electromagnetic materials or in special textile structures. This paper presents the results of investigating the EMF shielding effectiveness of several selected and developed textile-polymeric materials in respect of both their practical applications (protective clothing elements, technical materials, masking elements, etc.) and the structure and content of components with various EMF reflection and absorption properties. The measurement method for independent determination of reflection and transmission coefficients with a wavequide applicator was used. The results obtained with the 2.5 GHz to 18 GHz frequency range show a low value of transmission coefficient (min. ?35 dB) and accepted reflection attenuation from about ?4 dB to ?15 dB for higher frequencies.     

3-D voltage model for detection of sound radiated from anisotropic materials

The elastic behavior of composite materials has been characterized experimentally by employing a 3-D voltage calculation to model transmission or reflection experiments. With sound propagation along material symmetry directions, integration over the incident-plane angle alone is generally sufficient to model the transducer voltage accurately. In general material directions this integration must be extended to account for asymmetrical variations in the reflection or transmission coefficient out of the incident plane. Theoretical and experimental results illustrate this effect and the relationship between 2-D and 3-D calculations. Experimental measurements are used to in the reconstruction of viscoelastic properties in composite plates. The influence of the phi-dependent integration on the voltage, in the 3-D calculation, is particularly strong when the incident angles are small and the wave paths are large, as typically experienced in air-coupled measurements.     

Scattering-parameter measurements of laser diodes

An accurate and simple technique for measuring the input reflection coefficient and the frequency response of semiconductor laser diode chips is proposed and demonstrated. All the packaging parasitics could be obtained accurately using a calibrated probe, and the impedance of the intrinsic diode chip is deduced from the directly measured reflection coefficient. The directly measured impedance of a laser diode is affected strongly by the short bond wire. In the frequency response (S ₂₁) measurements of semiconductor laser diode chips, the test fixture consists of a microwave probe, a submount, and a bond wire. The S-parameters of the probe could be determined using the short-open-match (SOM) method. Both the attenuation and the reflection of the test fixture have a strong influence on the directly measured frequency response, and in our proposed technique, the effect of test fixture is completely removed.     

Behavior of rigid-porous layers at high levels of continuous acoustic excitation: theory and experiment

A model for the propagation of high amplitude continuous sound through hard-backed rigid-porous layers has been developed which allows for Forchheimer's correction to Darcy's law. The nonlinearity associated with this is shown to be particularly important in the range of frequencies around layer resonance. The model is based on the introduction of particle velocity dependent flow resistivity into the equivalent fluid model expression for complex tortuosity. Thermal effects are accounted for by means of a linear complex compressibility function. The model has been used to derive analytical expressions for surface impedance and reflection coefficient as a function of incident pressure amplitude. Depending on the material parameters, sample thickness, and frequency range the model predicts either growth or decrease of reflection coefficient with sound amplitude. Good agreement between model predictions and data for three rigid-porous materials is demonstrated.     

太赫兹波斜入射到磁化等离子体的数值研究

针对“黑障”问题,借助于电磁波斜入射到磁化等离子体的传输模型,研究了太赫兹(THz)波在磁化、均匀等离子体中的传输特性,分析了太赫兹波在磁化等离子体中传播的反射、透射以及衰减。仿真结果表明,等离子体碰撞频率、电子密度、入射角度以及磁场强度,对衰减产生不同的影响。单纯的增加碰撞频率,衰减值呈现出先增大后减小的变化趋势;电子密度的增加,与衰减峰值的大小有关;外加磁场加入,衰减值降低。通过调节外加恒定磁场,可以有效地解决“黑障”问题。     

压力罐中水声材料声学特性的参量源测量法

设计了一种原波频率500 kHz、差频范围1~30 kHz的截断宽带参量阵,作为水声材料测量系统的声源。通过分析典型频率下的宽带参量源指向性理论计算和实际测量结果,发现两者结果的曲线基本吻合,证明计算模型是正确的。应用钟形短时脉冲实现水声材料声特性的宽带测量,有益于降低样品边缘衍射干扰。并建立了测量水声材料大面积板状样品声压反射系数、声压透射系数和吸声系数的压力罐测量系统,罐体内尺寸Φ4 m×12 m,最高静水压4.5 MPa,测量频率范围1~30 kHz。对标准样品(尺寸1m×1m)进行了测量实验,其测量结果和理论曲线有很好的吻合,参量源测量法得到了验证;之后,通过对一块橡胶板样品在不同静压力下的吸声性能进行了测量和有效评估,进一步确认了参量源测量法在压力罐这样有限水域中的潜在应用价值。      

钢-铅粘接结构的粘接强度对超声体波反射与 透射特性的影响*

针对多层异种金属粘接结构中粘接强度的超声检测与表征困难的问题,采用线性弹簧模型和等效弹性模量模型来分别表征界面粘附强度和内聚强度,推导了超声体波斜入射N层粘接结构的反射与透射系数表达式。通过在不同入射面和入射声波模式等条件下,同时连续改变两种参数来系统研究粘接层界面粘附强度与内聚强度变化对超声波反射与透射特性的影响关系,确定了能够敏感表征粘接强度的超声参量,为粘接强度的无损检测与评价提供理论依据。     

Peculiarities of Acoustic Wave Reflection from a Boundary or Layer of a Two-Phase Medium

A mathematical model is presented for determining the oblique incidence of an acoustic wave at both a boundary and layer of a gas–drop mixture or a bubbly liquid of finite thickness. The basic wave reflection and transmission patterns are established for the incidence of a low-frequency acoustic wave at an interface between a pure gas and a gas–drop mixture, as well as between a pure and bubbly liquid. A range of varying volume fractions for a drop is determined, for which the zero value of the reflection coefficient is possible for low frequencies at oblique incidence. It is shown that the reflection coefficient will never be zero at angles of incidence above 24.5° from a gas–drop mixture at a pure gas boundary; however, when a wave is incident from a pure gas at a gas–drop mixture boundary, a zero reflection coefficient is possible for nonzero angles of incidence and the volume fraction of inclusions. The results of calculating reflection of an acoustic wave from a two-phase layer of a medium with a finite thickness are presented. It is established that the minimum reflection coefficient is possible depending on the perturbation frequency for a certain range of angles of incidence for the boundary or the layer of the gas–drop mixture, which is governed mainly by difference in densities between it and the pure gas.     

Attenuation of ultrasound in post rigor bovine skeletal muscle

A pulse transmission method for measuring the attenuation of 1-7 MHz ultrasound in bovine skeletal muscle is described. Measurements of the attenuation coefficient at -20, 0, 20 and 40 degrees C conformed to the relation alpha = Afn, where A and n are temperature-dependent coefficients and f is the frequency. alpha/f varied slowly with frequency, and at 4 MHz and 20 degrees C mean values were 1.3 dB cm-1 MHz-1 along the fibres and 0.55 dB cm-1 MHz-1 across the fibres. These data are lower than most previous measurements of skeletal muscle, but comparable with recent measurements of canine heart muscle.