共查询到20条相似文献,搜索用时 187 毫秒
1.
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. 相似文献
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We investigate transcranial magneto–acoustical stimulation(TMAS) for noninvasive brain neuromodulation in vivo.TMAS as a novel technique uses an ultrasound wave to induce an electric current in the brain tissue in the static magnetic field. It has the advantage of high spatial resolution and penetration depth. The mechanism of TMAS onto a neuron is analyzed by combining the TMAS principle and Hodgkin–Huxley neuron model. The anesthetized rats are stimulated by TMAS, resulting in the local field potentials which are recorded and analyzed. The simulation results show that TMAS can induce neuronal action potential. The experimental results indicate that TMAS can not only increase the amplitude of local field potentials but also enhance the effect of focused ultrasound stimulation on the neuromodulation. In summary, TMAS can accomplish brain neuromodulation, suggesting a potentially powerful noninvasive stimulation method to interfere with brain rhythms for diagnostic and therapeutic purposes. 相似文献
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《Journal of Electrostatics》2014,72(2):136-139
We generated an electromagnetic field using the spatial oscillation of a charged material such as a polyimide film. The film was vibrated with acoustic waves at 1 Hz–1 kHz. For charged films, changes in electric field intensity with acoustic wave irradiation were detected using an antenna. The electric field intensity and phase were found to be related to the surface voltage and electrical polarity. The surface potential distribution matches the electric field distribution that was measured by scanning the local excitation. These results indicate that this phenomenon can be used to measure the electrical properties of charged materials. 相似文献
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Electromagnetic interaction between local surface plasmon polaritons and an atmospheric surface wave plasma jet 下载免费PDF全文
We analyze the electromagnetic interaction between local surface plasmon polaritons (SPPs) and an atmospheric surface wave plasma jet (ASWPJ) in combination with our designed discharge device. Before discharge, the excitation of the SPPs and the spatial distribution of the enhanced electric field are analyzed. During discharge, the critical breakdown electric field of the gases at atmospheric gas pressure and the surface wave of the SPPs converted into electron plasma waves at resonant points are studied. After discharge, the ionization development process of the ASWPJ is simulated using a two- dimensional fluid model. Our results suggest that the local enhanced electric field of SPPs is merely the precondition of gas breakdown, and the key mechanism in maintaining the discharge development of a low-power ASWPJ is the wave-mode conversion of the local enhanced electric field at the resonant point. 相似文献
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We theoretically derive the electric field distribution of an astigmatic Gaussian laser beam after it is focused through a high-aperture objective. We show that astigmatism values that are hard to detect in the collimated laser beam can have a large effect after diffraction-limited focusing. Such astigmatic beams may be frequently encountered in fluorescence correlation measurements and in laser-scanning confocal microscopy. We present experimental measurements of the excitation intensity distribution measured by 3D scanning of single fluorescent molecules immobilized on a glass surface. 相似文献
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The field near a sharp metal tip can be strongly enhanced if irradiated with an optical field polarized along the tip axis. We demonstrate that the enhanced field gives rise to local second-harmonic (SH) generation at the tip surface thereby creating a highly confined photon source. A theoretical model for the excitation and emission of SH radiation at the tip is developed and it is found that this source can be represented by a single on-axis oscillating dipole. The model is experimentally verified by imaging the spatial field distribution of strongly focused laser modes. 相似文献
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Mitri FG Trompette P Chapelon JY 《The Journal of the Acoustical Society of America》2003,114(5):2648-2653
Chalk sphere and cylinder resonance frequencies related to compressional and bending modes were detected in water, using vibro-acoustography, a relatively new imaging technique. The variable (radiation) force of low-frequency excitation, produced by intersecting two primary focused ultrasound waves with slightly different frequencies, forces the object to vibrate. The low-frequency acoustic emission field, resulting from object vibration, was detected by a hydrophone. By fixing the object at the focus of the ultrasound beam and sweeping the frequency of one of the primary beams within a chosen bandwidth, it was possible to detect some of the resonance frequencies (those related to compressional and bending modes) via variations in acoustic emission amplitude. Experimental results showed excellent agreement with finite element calculations. This method can be used to characterize the presence of heterogeneities in various media, in the field of materials science or biology. 相似文献
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为了从聚焦超声声场纹影图像直接重建声场声压分布图像,首先根据水中声波与光波的作用规律,利用Zernike相衬技术得到纹影系统中空间声压分布与纹影图像中光强的关系,再通过纹影系统获得聚焦超声声场实时图像,最后根据纹影系统的物理特性经过反投影重建算法重建出凹球壳聚焦超声换能器的空间声压分布。分析可知,理论声焦域横向与声轴大小分别为0.15 mm、1.4 mm,重建声场电功率为12 W时横向最接近为0.25 mm,30 W时声轴最接近为1.35 mm。与球壳换能器的理论声压分布进行对比的结果表明,该方法具有一定可行性,可以用于聚焦超声换能器的声场分布检测。 相似文献
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高强度聚焦超声(HIFU)是一种新型的无创治疗肿瘤新技术,其中换能器声场数值计算能够为HIFU治疗提供重要的依据。传统非线性KZK和SBE模型广泛应用于换能器声场数值计算,但依然存在某些不足。我们采用一种介观尺度的新型流体力学方法,即格子Boltzmann方法(LBM),基于2维9离散速度(D2Q9)格子构建了轴对称多弛豫参数LBM模型,并通过调节弛豫参数分析其对模型的影响;利用该模型对两个具有不同张角的球面聚焦换能器的声场进行数值模拟,并与KZK和SBE模型的计算结果进行比较。结果表明LBM模型能够很好地描述超声波的激发和传播机制,从流体力学的角度描述聚焦声场的分布,具有清晰的物理意义,且计算过程不受换能器张角的限制,在换能器声场的理论分析和模拟计算及其在HIFU治疗中的应用有着积极的意义。 相似文献
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采用离散偶极子近似方法系统地研究了金纳米环双体的消光光谱及其电场分布. 计算结果表明, 金纳米环双体在耦合作用下的共振消光峰对应着不同振动模式, 改变金纳米环双体的排列方式、 间距和尺寸大小, 其表面等离子体共振消光峰发生红移或蓝移. 因此可以通过对金纳米环双体结构参数和排列方式的设定, 调节其表面等离子体共振消光峰的位置. 电场分布表明, 水平排列的金纳米环双体较单个金纳米环产生更强的局部表面增强电场. 适当的小间距, 较大的内外半径的金纳米环水平阵列更适合做表面增强拉曼散射的衬底, 在生物分子检测等领域具有潜在的应用. 相似文献
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A numerical simulation of surface wave excitation in a rectangular planar-type plasma source 下载免费PDF全文
The principle of surface wave plasma discharge in a rectangular
cavity is introduced simply based on surface plasmon polariton
theory. The distribution of surface-wave electric field at the
interface of the plasma-dielectric slab is investigated by using the
three-dimensional finite-difference time-domain method (3D-FDTD)
with different slot-antenna structures. And the experimental image
of discharge with a novel slot antenna array and the simulation of
the electric field with this slot antenna array are both displayed.
Combined with the distribution of surface wave excitation and
experimental results, the numerical simulation performed by using
3D-FDTD is shown to be a useful tool in the computer-aided antenna
design for large area planar-type surface-wave plasma sources. 相似文献
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表面等离激元自诞生以来已有一百多年的历史,并逐渐形成了一门新的学科——表面等离激元光子学。位于金属纳米结构中的局域表面等离激元可产生非常显著的近表面电场增强,并成功应用于诸多研究领域当中,而对局域表面等离激元与外界入射光中磁场的相互作用的研究则相对较少。该研究在前期已有的研究基础之上模拟计算了金属纳米球-纳米圆盘结构间隙处的近表面电、磁场增强,研究结果表明该结构在单束紧聚焦径向偏振光束的激发下,金属纳米圆盘产生局域表面等离激元呼吸模式和上下表面处的电偶极矩模式,该模式使圆盘中心纵向表面电场得到增强。由于金属纳米圆盘与金属纳米球的局域表面等离激元电偶极矩的耦合共振相互作用,可以形成纵向电场得到有效增强的局域表面等离激元共振间隙模式。通过数值模拟计算研究,证明该金属纳米结构间隙模式的纵向电场分量相对于径向偏振入射光的有效激发横向电场分量即近表面电场的增强因子高达250倍;而近表面磁场的增强因子高达170倍。为了更清晰地展现出这种新型金属纳米结构的光谱特性以及近表面电、磁场分布特征,还展示出了该金属纳米结构的近表面电场增强分布、近表面磁场振幅分布以及近表面电、磁场共振波长的对比分析,计算结果表明所提出的金属纳米球-纳米圆盘结构具有明显的局域近表面电、磁场增强优势以及较宽的频谱波段。由于本文提出的金属纳米结构具有电、磁场增强优势,希望计算结果能应用到更多的研究领域当中,尤其是生物医学等领域,为人们抗击疫情提供一点点参考和帮助。 相似文献
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Khankina S. I. Yakovenko V. M. Yakovenko I. V. 《Radiophysics and Quantum Electronics》2004,47(7):500-509
We study the energy lost by a particle moving along the helical line in a static magnetic field due to Vavilov–Cherenkov radiation of volume and surface helicons. It is found that the energy losses related to excitation of volume helicons are equivalent to the energy losses of a magnetic moment created due to the charge rotation. The magnetic moment moves at a constant velocity along the magnetic field. It is shown that collisionless damping of volume helicons in plasmas is based on the Cherenkov radiation of magnetic moment. Radiation of surface helicons by a particle does not correspond to the energy losses of a moving magnetic moment. This is related to the fact that not only magnetic (H) waves but also electric (E) waves contribute to the excitation of surface helicons, which leads to an increase in the energy losses of a particle. 相似文献
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Local field distribution and configuration of CO molecules adsorbed on the nanostructure platinum surface 下载免费PDF全文
This paper shows that the local electric field distribution near the nanostructure
metallic surface is obtained by solving the Laplace equation, and furthermore, the
configuration of CO molecules adsorbed on a Pt nanoparticle surface is obtained by
using Monte Carlo simulation. It is found that the uneven local electric field
distribution induced by the nanostructure surface can influence the configuration of
carbon monoxide (CO) molecules by a force, which drags the adsorbates to the poles
of the nanoparticles. This result, together with our results obtained before, may
explain the experimental results that the nanostructure metallic surface can lead to
abnormal phenomena such as anti-absorption infrared effects. 相似文献
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采用有损耗介质和色散介质的二维时域有限差分方法,数值模拟了以光波长514.5nm的p偏振基模高斯光束为入射光源,激发Kretschmann型表面等离子体共振,并通过探针的局域场增强效应实现纳米光刻的新方法——探针诱导表面等离子体共振耦合纳米光刻.分别就探针与记录层的间距以及探针针尖大小,模拟分析了不同情况下探针的局域场增强效应和记录层表面的相对电场强度振幅分布.结果表明,探针工作在接触模式时,探针的局域场增强效应最明显,记录层表面的相对电场强度振幅的对比度最大;当探针针尖距记录层5nm时,针尖下方记录层表面的相对电场强度振幅大于光刻临界值的分布宽度与针尖尺寸相近.
关键词:
纳米光刻
表面等离子体共振
时域有限差分方法 相似文献
18.
Wetzels A Gürtler A Noordam LD Robicheaux F Dinu C Muller HG Vrakking MJ van der Zande WJ 《Physical review letters》2002,89(27):273003
The asymptotic velocity distribution of electrons ionized in half-cycle-pulse excitation of high Rydberg states (n=34), placed in a static electric field, is studied using electron velocity-map imaging. At weak half-cycle pulse strengths, the electrons escape over the saddle point in the potential. For strong half-cycle pulses, the electrons are emitted in the direction of the field kick. The much slower and less intense half cycle of opposite polarity, which necessarily follows the main half-cycle pulse, strongly affects the momentum distribution and reduces the excess energy of the electrons significantly. 相似文献
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J. Krile G. Edmiston K. Morales A. Neuber H. Krompholz M. Kristiansen 《Laser Physics》2006,16(1):194-201
Mechanisms in vacuum surface flashover caused by rf (f < 10 GHz) or unipolar voltages are virtually identical. Similarities between rf (representing high-power microwave window
breakdown on the high-pressure side) and unipolar surface flashover are expected in an atmospheric environment as well. Two
separate experimental setups were utilized to investigate both unipolar flashover and rf window flashover under atmospheric
conditions while controlling excitation, temperature, pressure, humidity, and type of gas present, all under a similar electric
field-surface geometry. The local electric field at the flashover initiating points has been numerically calculated in detail
for all test geometries. For both rf and unipolar pulsed excitation, the flashover dynamics are changed by the application
of UV light to the dielectric surface. A UV prepulse has a distinct impact on the arc’s path and a tendency to decrease the
hold-off electric field. The effect of humidity on the hold-off electric field for both pulsed unipolar and rf excitations,
along with temporally resolved emission spectroscopy of the flashover event, is discussed.
This work was funded by the Cathode and HPM Breakdown MURI program and managed by the Air Force Office of Scientific Research
(AFOSR) and by Sandia National Laboratories. 相似文献
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Plasmonic metallic nanoholes are widely used to focus or image in the nanoscale field. In this article, we present the results
of the design, fabrication, and plasmonic properties of a two-dimensional metallic pentagram nanohole array. The nanoholes
can excite the extraordinary transmission phenomenon. We used the finite-difference time-domain method to design the transmission
and the localized surface plasmon resonance electric field distribution in the near field. The focused ion beam method was
used to fabricate the nanoholes. The transmittance in the far field was measured by a scanning spectrophotometer. The difference
between the design and the experimental results may be caused by the conversion between the near field and the far field.
The near field electric field distribution on the surface plasmonic nanoholes was measured by a near-field scanning optical
microscope. From our results, we found that the maximum transmission of the nanoholes is 2.4. Therefore, our plasmonic nanohole
can significantly enhance the transmission by exciting the plasmonic phenomenon on the surface of the nanostructures. 相似文献