Optical method for measuring the coupling constant of surface acoustic waves

The coupling constant of common or thin-layered-piezoelectric interdigital transducers for surface acoustic waves up to the highest frequencies can be determined in an optical way with reproducibility better than 3%. Being a nondestructive and noncontact method one can apply it in the technological process for fabricating uniform piezoelectric layered transducers.     

基于FTIR技术的酸牛奶营养成分快速检测方法研究

酸牛奶作为一种重要的发酵乳制品,伴随着发酵过程,其各种营养成分时刻发生着复杂的变化,因此,建立酸牛奶的快速高效检测技术可以实现对生产过程的实时监控,这也是食品安全监管要达到的重要目标。傅里叶变换红外光谱技术(FTIR)因其快速、高通量、无化学污染、可对掺假成分予以分辨等特点被广泛应用于食品安全领域。以FTIR技术为核心,利用氟化钙薄膜法,将酸牛奶FTIR光谱图与其营养成分(能量值,蛋白质、脂肪、碳水化合物和钠含量)对照,建立了基于最小二乘法(PLS)的定量化预测模型。结果表明,该模型样品校正集的能量值,蛋白质、脂肪、碳水化合物和钠含量的交叉检验R2值分别达到0.938 9,0.926 6,0.918 6,0.941 8和0.977 1;该模型用于预测,其样品验证集的交叉检验R2值分别为0.920 5,0.905 3,0.908 5,0.939 3和0.936 4。由此可见,该模型对酸牛奶各营养指标均具有较好的预测准确性,在时间上具备较好的稳定性。不同于传统的化学检测方法,本研究为实现对酸牛奶品质的快速检测提供了一种较为可行的方法。该方法作为乳制品质量监控技术的一项初步探索,具有较好的应用前景。     

Investigation of Bubbly Flow by Ultrasonic Tomography

Computerized tomography (CT) means reconstruction of pictures from projections taken at different angles. This method is well known in fields such as medical diagnostics and nondestructive testing. The application of CT to gas/liquid flow measurement results in a non-intrusive method for measuring the spatial distribution of the gas phase in a cross-section of the flow. In our application the projection data are obtained from measurement of the extinction along a set of ultrasonic rays in this cross-section, using piezo-ceramic ultrasonic transducers. The transducers are arranged in a circular sensor array which is directly integrated in the pipe wall of the flow; instead of mechanical rotation, the sensors are sequentially switched.     

Electromagnetic acoustic resonance and materials characterization

This paper reviews the operation principles and several applications of electromagnetic acoustic resonance (EMAR). EMAR is an emerging ultrasonic spectroscopy technique for nondestructive and noncontact materials characterization, relying on the use of electromagnetic-acoustic transducers (EMATs) and the superheterodyne circuitry for processing the received reverberation signals excited by long radio-frequency (RF) bursts. The transduction occurs through the Lorentz force mechanism and, for ferrous metals, the dynamic response of magnetostriction and the magnetic force as well. Weak coupling of the EMATs is now essential to realize the high accuracy of measuring ultrasonic velocities and attenuation in conducting materials. High signal to noise ratio is achieved by receiving the overlapping coherent echoes at resonant frequencies. Small changes in the related material properties are well detectable. The spectral response can be interpreted for simple geometries such as plate, cylinder and sphere. EMAR has been proven to be powerful for industrial purposes because of its robustness, the omission of surface preparations and the capacity for simple measurement in a short time. Stress application varies the propagation velocities of ultrasonics and then shifts the resonant frequencies in longitudinal and shear modes in the parallel-sided geometries. Promising applications include the two-dimensional stress distribution in thin plates, the axial stress in railroad rails and the residual stresses around the weldments. In addition, the attenuation is precisely measurable at resonant frequencies and can evaluate the grain size of polycrystalline metals. Furthermore, the EMAR technique serves for developing the basic research on the effects of the metallurgical changes on ultrasonics, leading to the damage estimation of the fatigued, crept or thermally aged metal parts.     

利用激光多普勒测振仪的空气耦合超声声场测量*

进行了空气耦合超声声场测量的实验研究。使用激光多普勒测振仪测量由声波引起的激光路径上的介质折射率变化,进而得到空气和固体材料内部的时域瞬态声压。通过直接测量空耦换能器的辐射声功率,给出对单个空耦换能器灵敏度的直接评价方法。用空耦换能器激励K9玻璃板的漏兰姆波,观测到空气中的直达波和反射波、固体板内和空气中的漏兰姆波,实现了空气和固体中微弱声波的非侵入式实验测量,为空耦换能器的特性评估和空耦检测系统的声场测量提供了实验方法。     

激光反射全息技术在超声换能器近场测量中的应用

研究了基于光学反射层析法的超声换能器近场测量方法。介绍了激光反射层析法测量超声场声压分布的原理,建立了一套实验测量系统,利用激光测振仪完成了对一多基元平面活塞换能器近场声压的测量,得到了该换能器辐射面附近声压的幅度和相位分布。使用探针式水听器对相同位置处的声压进行了直接测量,验证了激光层析法测量结果的正确性;声场反演结果进一步表明使用激光反射层析法适用于对换能器辐射面声压分布和阵元工作状况进行预报。      

The directivity pattern of an interferometer for measuring thermal acoustic radiation

The directivity patterns of a pair of piezoelectric transducers for measuring the spatial correlation function of sound pressures produced by sources of thermal acoustic radiation in the megahertz frequency range are calculated. Sources in the form of a heated plane or strip are considered. The signal detection by two circular or rectangular piezoelectric transducers and by focusing transducers is studied. It is demonstrated that, for measuring the correlation function, the piezoelectric transducers must partially overlap. To determine the directivity pattern with a strong dependence on the distance between the heated object and the pair of piezoelectric transducers, focusing piezoelectric transducers should be used. The results obtained offer possibilities for a noninvasive measurement of the absorption coefficient of a medium and also for the realization of the previously proposed [20] passive acoustic thermotomograph, which does not use a priori information on the absorption coefficient of the medium.     

An ultrasound technique for monitoring the alcoholic wine fermentation

In this paper an ultrasonic technique, usually used in non-destructive-testing (NDT), is applied to the monitoring of alcoholic wine fermentation. This technique consists in placing a test tube, containing the analyzing fluid, between two matched ultrasonic piezoelectric transducers, one used as transmitter and the other as receiver. The transmitter generates an ultrasonic wave in the liquid sample which is received by the receiver; the attenuation and the delay of the received signal in respect to the transmitted one are used to characterize the testing fluid. As first experiments this technique was applied to some test solutions of saccharose in water, ethanol in water and of both solvents in water, in order to evaluate the method applicability and resolution. Best results are obtained by the propagation velocity measurement, with a resolution less than 2%. The method was then applied to monitor the wine fermentation: the propagation velocity in the must was measured every day and the results were related to chemical analyses. The obtained results show that the propagation velocity has the same behaviour of the saccharose concentration, putting in evidence the possibility of monitoring the process state by measuring the ultrasound propagation velocity.     

Nonlinear characterization with burst excitation of 1-3 piezocomposite transducers

Ultrasonic transducers made with 1-3 connectivity piezocomposites are frequently used in Medical applications and nondestructive testing. When the transducer is used for special applications as, for instance air-coupled transmission, it is necessary to compensate for the high difference of acoustic impedance between transducer and medium using high amplitude pulses to generate high acoustic signal. Thus, the nonlinear behavior of the transducer must be taken into account in similar application conditions. The newly developed method, which performs the nonlinear characterization with burst signal excitation near the thickness resonance frequency, is based on the measure of the current as well as the vibration velocity of the piezocomposite transducer. The current of the stationary response is measured before the end of the burst signal excitation. Burst excitation enables us to measure the nonlinear characterization without producing overheating in the transducers. The amplitude level dependence of mechanical losses tandelta(m) and the stiffness increases |Deltac/c(0)| have been studied, as well as the velocity dependence of a point of the transducer, measured with a laser vibrometer. In this method, the power level applied to the transducers can be higher than other nonlinear measurement methods, providing measurements of high accuracy.     

Measurement of ultrasonic power and electro-acoustic efficiency of high power transducers

In this paper, an improved method for the measurement of acoustic power and electro-acoustic efficiency of high power ultrasonic transducers is presented. The measuring principle is described, the experimental results are given. In comparison with traditional methods, the method presented in this paper has the advantages of simplicity, economy and practicality. The most important is that it can measure the output acoustic power and the electro-acoustic efficiency of the transducer under the condition of high power and practical applications, such as ultrasonic cleaning and soldering.     

Measurement of the acoustic nonlinearity parameter B/A in human tissues by a thermodynamic method

A thermodynamic method for measuring the acoustic nonlinearity parameter B/A in tissues is presented. It is based on the measurement of change in phase velocity as a function of time as the hydrostatic pressure of the sample is quickly reduced from a known value. This technique circumvents the effect of the attenuation in the medium and does not require a prior knowledge of the thermodynamic parameters of the tissues. The method is used to estimate nonlinearity parameters for normal and malignant tissues in the temperature range 20 degrees to 37 degrees C. The values and the temperature dependence of these parameters are found to vary with the nature of the tissues.     

Acoustic Vortex Beam Generation by a Piezoelectric Transducer Using Spiral Electrodes

We propose an innovative method to generate acoustic vortex waves based on a disc piezoelectric transducer that is coated with multi-arm coiled electrodes. Finite element simulation results for single-arm to four-arm coiled electrodes indicate that the method could modulate amplitude and phase spatial distribution of the acoustic waves near the acoustic axis by acoustic field synthesis principle, making the waves rotate spirally in space and form stable focused vortex beams. Compared with the traditional method that requires electronic control of an array consisting of a large number of transducers, this method provides a more effective and compact solution.     

A novel method for the measurement of acoustic speed

Traditional methods for measuring acoustic speed require knowledge of either the specimen thickness or the distances between the transducers and the specimen. In general, the accuracy in measuring these quantities determines the accuracy of the experimental technique for measuring speed. This problem is particularly acute in measuring sound speed in biological specimens. A new method for measuring acoustic speed of materials, which eliminates the need for determining these quantities, has been developed. The technique, which necessitates the use of only one transducer, requires measurement of four times of flight of a sound pulse and the knowledge of the speed of sound in a reference fluid medium in which the specimen is placed. Ultrasonic speed in stainless steel and Plexiglas was measured using this method to verify its validity. Results on measurements on porcine liver, myocardium, and soft fat are also reported.     

Interference acoustical method for measuring velocity,attenuation and reflection of acoustic surface waves

An interference acoustical method for measuring velocity, attenuation and reflection of acoustic surface waves was developed. Applications to diagnostics and nondestructive testing of acoustic surface wave devices are discussed.     

Application of Brillouin scattering to the local anisotropy and birefringence measurements of thin layers

Brillouin scattering is an efficient nondestructive and noncontact measurement method to obtain the wave properties of thin layers at hypersonic frequencies. The reflection induced ThetaA (RIThetaA) scattering geometry enables the simultaneous measurement of the phonons, which propagate in each direction of wave vectors of q(Theta A) (propagation in the film plane) and q(180) (back scattering). Using this scattering geometry, we could observe the refractive indices and birefringence of the piezoelectric poly-vinylidene fluoride (PVDF) film as a function of temperature. By introducing the microscopic technique, the elastic anisotropy and refractive index measurements in the minute area of polycrystalline ZnO films were also performed.     

Noncontact ultrasound stimulated optical vibrometry study of coupled vibration of arterial tubes in fluids

Coupled vibration of arterial tubes is analyzed with the wave propagation approach and first-order shear deformation theory. Both the interior and exterior fluids are considered as compressible so that acoustic waves can be generated and propagated in the fluids. Results obtained using the theory have been evaluated against those available in the literature and the agreement has been found to be good. The theory can be used for future research on the vibration and acoustics of arterial walls. Vibration experiments were carried out on a silicone rubber tube in a water tank with a novel ultrasound stimulated optical vibrometry system. This system uses the radiation force of ultrasound to vibrate the tube at low frequency and records the resulting response by a laser vibrometer. Both the excitation and measurement are remote and noncontact. The silicone rubber tube was chosen because it has mechanical properties close to those of arteries. The fundamental frequency is well excited by the radiation force and measured with the laser. The measured fundamental frequency is in good agreement with the present theory.     

The application of laser reflective tomography in near-field measurements of ultrasonic transducers

With Laser Reflective Tomography（LRT）,the near fields of ultrasonic transducers were measured and analyzed.The principle of LRT measurement of ultrasonic field distribution was introduced and an experimental system was set up.Acoustic pressure of a multiple element piston transducer was measured by using of a laser vibrometer.Its distribution in amplitude and phase was obtained.The acoustic pressure in the same region was measured with a needle hydrophone to validate the LRT method.Furthermore,through reconstruction of acoustic fields,it indicated that LRT method is suitable for predicting the distribution on transducers＇surface and conditions of active elements.     

高速动态非接触激光光学法测量光纤外径

光纤拉丝过程中必须对纤丝外径进行精密测控,但是通常用于圆柱形物体动态非接触测量的方法(如相关光通量比较法、电压鉴别法、补偿光通量法等等)精度太低,测量范围难适于光纤测量。本文介绍了四种测量高速运动的光纤外径很有效的非接触式激光光学测量方法:1.前向光散射法。它测量的是激光束射到光纤上的散射角和散射条纹;2.后向光散射法。它测量后向散射条纹的间隔; 3.直接衍射法。它测量激光束直射到光纤上产生的衍射图象;4.计量光脉冲法。它测量与光纤外径有关的光脉冲效。文中还对此四种方法进行了讨论。     

Extension of the distributed point source method for ultrasonic field modeling

The distributed point source method (DPSM) was recently proposed for ultrasonic field modeling and other applications. This method uses distributed point sources, placed slightly behind transducer surface, to model the ultrasound field. The acoustic strength of each point source is obtained through matrix inversion that requires the number of target points on the transducer surface to be equal to the number of point sources. In this work, DPSM was extended and further developed to overcome the limitations of the original method and provide a solid mathematical explanation of the physical principle behind the method. With the extension, the acoustic strength of the point sources was calculated as the solution to the least squares minimization problem instead of using direct matrix inversion. As numerical examples, the ultrasound fields of circular and rectangular transducers were calculated using the extended and original DPSMs which were then systematically compared with the results calculated using the theoretical solution and the exact spatial impulse response method. The numerical results showed the extended method can model ultrasonic fields accurately without the scaling step required by the original method. The extended method has potential applications in ultrasonic field modeling, tissue characterization, nondestructive testing, and ultrasound system optimization.     

Measuring technique for static electricity using focused sound

A novel method is proposed for non-contact measurement of the distribution of electrostatic charge on a surface based on scanning the sample surface with a focused high frequency acoustic beam to excite movement of the sample surface. An electric field is induced by exciting a charged film-like object, and an electric field sensor measures it instead of an electrostatic field. The focused ultrasound waves are generated by controlling individually the phase of each 285 airborne ultrasound transducers.