The fundamental shear horizontal（SH0） wave has several unique features that are attractive for long-range nondestructive testing（NDT）. By a careful design of the geometric configuration, electromagnetic acoustic t...The fundamental shear horizontal（SH0） wave has several unique features that are attractive for long-range nondestructive testing（NDT）. By a careful design of the geometric configuration, electromagnetic acoustic transducers（EMATs） have the capability to generate a wide range of guided wave modes, such as Lamb waves and shear-horizontal（SH） waves in plates. However, the performance of EMATs is influenced by their parameters. To evaluate the performance of periodic permanent magnet（PPM） EMATs, a distributed-line-source model is developed to calculate the angular acoustic field cross-section in the far-field. Numerical analysis is conducted to investigate the performance of such EMATs with different geometric parameters, such as period and number of magnet arrays, and inner and outer coil widths. Such parameters have a great influence on the directivity of the generated SH0 waves that arises mainly in the amplitude and width of both main and side lobes. According to the numerical analysis, these parameters are optimized to obtain better directivity. Optimized PPM EMATs are designed and used for NDT of strip plates. Experimental results show that the lateral boundary of the strip plate has no perceivable influence on SHO-wave propagation, thus validating their used in NDT. The proposed model predicts the radiation pattern ofPPM EMATs, and can be used for their parameter optimization.展开更多
Traditional technique such nanoindenter(NI)can't measure the local elastic modulus at nano-scale(lateral).Atomic force acoustic microscopy(AFAM)is a dynamic method,which can quantitatively determine indentation mo...Traditional technique such nanoindenter(NI)can't measure the local elastic modulus at nano-scale(lateral).Atomic force acoustic microscopy(AFAM)is a dynamic method,which can quantitatively determine indentation modulus by measuring the contact resonance spectra for high order modes of the cantilever.But there are few reports on the effect of experimental factors,such length of cantilever,contact stiffness on measured value.For three different samples,including copper(Cu)film with 110 nm thickness,zinc(Zn)film of 90 nm thickness and glass slides,are prepared and tested,using referencing approach in which measurements are performed on the test and reference samples(it's elastic modulus is known),and their contact resonance spectra are measured used the AFAM system experimentally.According to the vibration theory,from the lowest two contact resonance frequencies,the tip-sample contact stiffness is calculated,and then the values for the elastic properties of test sample,such as the indentation modulus,are determined.Using AFAM system,the measured indentation modulus of copper nano-film,zinc nano-film and glass slides are 113.53 GPa,87.92 GPa and 57.04 GPa,which are agreement with literature values Mcu--105-130 GPa,Mzn=88.44 GPa and Molass=50-90 GPa.Furthermore,the sensitivity of contact resonance frequency to contact stiffness is analyzed theoretically.The results show that for the cantilevers with the length 160 pm,225μm and 520μm respectively,when contact stiffness increases from 400 N/m to 600 N/m,the increments of first contact resonance frequency are 126 kHz,93 kHz and 0.6 kHz,which show that the sensitivity of the contact resonance frequency to the contact stiffness reduces with the length of cantilever increasing.The novel method presented can characterize elastic modulus of near surface for nano-film and bulk material,and local elasticity of near surface can be evaluated by optimizing the experimental parameters using the AFAM system.展开更多
为了研究基于矩形贴片天线的应变测量技术,根据传输线模型,分析了矩形贴片天线与应变间的作用机理,明确了天线辐射单元尺寸受应变影响,可导致贴片天线中心频率发生偏移,且获得了频率偏移量与应变间的线性关系理论表达式.设计3种不同中...为了研究基于矩形贴片天线的应变测量技术,根据传输线模型,分析了矩形贴片天线与应变间的作用机理,明确了天线辐射单元尺寸受应变影响,可导致贴片天线中心频率发生偏移,且获得了频率偏移量与应变间的线性关系理论表达式.设计3种不同中心频率的矩形贴片天线,利用高频结构模拟器(high frequency structure simulator,HFSS)电磁仿真软件和拉伸应变检测系统,对不同应变状态下,贴片天线中心频率随应变的变化趋势进行了仿真与实验测试.仿真和实验结果表明:贴片天线的中心频率的偏移量与应变之间线性关系明显,且贴片天线的中心频率越高,应变灵敏度越大.利用矩形贴片天线作为应变传感器,可满足结构应变测量要求,为结构健康无线监测研究奠定了基础.展开更多
基金supported by National Natural Science Foundation of China(Grant Nos.51075012,10772008)Beijing Municipal Natural Science Foundation of China(Grant No.1122005)
文摘The fundamental shear horizontal（SH0） wave has several unique features that are attractive for long-range nondestructive testing（NDT）. By a careful design of the geometric configuration, electromagnetic acoustic transducers（EMATs） have the capability to generate a wide range of guided wave modes, such as Lamb waves and shear-horizontal（SH） waves in plates. However, the performance of EMATs is influenced by their parameters. To evaluate the performance of periodic permanent magnet（PPM） EMATs, a distributed-line-source model is developed to calculate the angular acoustic field cross-section in the far-field. Numerical analysis is conducted to investigate the performance of such EMATs with different geometric parameters, such as period and number of magnet arrays, and inner and outer coil widths. Such parameters have a great influence on the directivity of the generated SH0 waves that arises mainly in the amplitude and width of both main and side lobes. According to the numerical analysis, these parameters are optimized to obtain better directivity. Optimized PPM EMATs are designed and used for NDT of strip plates. Experimental results show that the lateral boundary of the strip plate has no perceivable influence on SHO-wave propagation, thus validating their used in NDT. The proposed model predicts the radiation pattern ofPPM EMATs, and can be used for their parameter optimization.
基金supported by National Natural Science Foundation of China(Grant No.50775005)General Program of Science and Technology Development Project of Beijing Municipal Education Commission(Grant No.KM201110015009)
文摘Traditional technique such nanoindenter(NI)can't measure the local elastic modulus at nano-scale(lateral).Atomic force acoustic microscopy(AFAM)is a dynamic method,which can quantitatively determine indentation modulus by measuring the contact resonance spectra for high order modes of the cantilever.But there are few reports on the effect of experimental factors,such length of cantilever,contact stiffness on measured value.For three different samples,including copper(Cu)film with 110 nm thickness,zinc(Zn)film of 90 nm thickness and glass slides,are prepared and tested,using referencing approach in which measurements are performed on the test and reference samples(it's elastic modulus is known),and their contact resonance spectra are measured used the AFAM system experimentally.According to the vibration theory,from the lowest two contact resonance frequencies,the tip-sample contact stiffness is calculated,and then the values for the elastic properties of test sample,such as the indentation modulus,are determined.Using AFAM system,the measured indentation modulus of copper nano-film,zinc nano-film and glass slides are 113.53 GPa,87.92 GPa and 57.04 GPa,which are agreement with literature values Mcu--105-130 GPa,Mzn=88.44 GPa and Molass=50-90 GPa.Furthermore,the sensitivity of contact resonance frequency to contact stiffness is analyzed theoretically.The results show that for the cantilevers with the length 160 pm,225μm and 520μm respectively,when contact stiffness increases from 400 N/m to 600 N/m,the increments of first contact resonance frequency are 126 kHz,93 kHz and 0.6 kHz,which show that the sensitivity of the contact resonance frequency to the contact stiffness reduces with the length of cantilever increasing.The novel method presented can characterize elastic modulus of near surface for nano-film and bulk material,and local elasticity of near surface can be evaluated by optimizing the experimental parameters using the AFAM system.
文摘为了研究基于矩形贴片天线的应变测量技术,根据传输线模型,分析了矩形贴片天线与应变间的作用机理,明确了天线辐射单元尺寸受应变影响,可导致贴片天线中心频率发生偏移,且获得了频率偏移量与应变间的线性关系理论表达式.设计3种不同中心频率的矩形贴片天线,利用高频结构模拟器(high frequency structure simulator,HFSS)电磁仿真软件和拉伸应变检测系统,对不同应变状态下,贴片天线中心频率随应变的变化趋势进行了仿真与实验测试.仿真和实验结果表明:贴片天线的中心频率的偏移量与应变之间线性关系明显,且贴片天线的中心频率越高,应变灵敏度越大.利用矩形贴片天线作为应变传感器,可满足结构应变测量要求,为结构健康无线监测研究奠定了基础.
