串联耦合切比雪夫微环滤波器的设计

基于电路的设计方法,把N阶串联耦合微环谐振滤波器等价成为一个基带LC阶梯网络,通过求解LC阶梯网络的元件参量,求出微环滤波器的耦合系数.在此基础上设计出具有切比雪夫响应的微环滤波器,并与传统耦合模式理论方法和理想的切比雪夫响应进行比较,证明了这种方法的可靠性,最后讨论了耦合系数和环数对切比雪夫微环滤波器输出特性的影响.数值模拟表明,耦合系数的偏差率越大,通带的平坦性越差;耦合系数的值增大,通带的带宽加宽;当环数增加时,过渡带衰减速度变快,通带形状更接近方形.     

侧瓣抑制的直列阵

本文利用倍角函数的降幂展开式提出了切比雪夫阵的新设计方程,使设计工作变成直截了当的计算工作.对切比雪夫阵的指向性提出了用能量集中因数和指向性因数表达的概念,并给出了二者的计算方法和使用范围.最后提出用切比雪夫阵作声场扩散测量的方法,这种方法比过去的方法更为灵敏.     

切比雪夫渐变线TEM喇叭天线数值模拟

设计了一种采用切比雪夫渐变线的TEM喇叭天线,分析了其工作原理,采用数值模拟的方法研究了其阻抗特性、传输特性与辐射特性,并在不同的馈入脉冲下与常用的线性渐变TEM喇叭天线进行了性能对比。结果表明:切比雪夫渐变线TEM喇叭天线具有低反射、高带宽和高辐射场强的优点,其性能要明显优于线性渐变TEM喇叭天线,且馈入脉冲越宽,性能越明显。分析了最大反射系数对切比雪夫渐变线TEM喇叭天线辐射性能的影响,馈入脉冲越窄时,宜选择反射系数越大的辐射天线。     

宽带恒定束宽波束形成器的设计与实现

本文提出了一种设计宽带恒定束宽波束形成器的方法,这对应用于海底探测和分类问题的声纳系统来说十分重要,对于给定频带宽度的信号,选择一定数量的频率点来表达其频率响应,对于一个给定的频点,可以通过现有方法导出满足恒定宽要求的加权矢量,例如对于一个线阵列,可用切比雪夫多项多得到其加权矢量,因此对于一个具有Ｎ个阵元的宽带阵,如果选择Ｍ个频率点,可以得到一个ＮＭ的加权矩阵,这个矩阵的每一行代表一个阵元的频率响     

高温超导窄带广义切比雪夫函数滤波器

提出了一种用于高温超导滤波器制作的新结构窄带广义切比雪夫函数高、低通滤波器级联方式.该方式利用高温超导低插损特性,可以有效地降低极陡峭广义切比雪夫函数低通、高通滤波器的带边频滚降.依靠高、低通滤波器级联方式构建新形式的窄带极陡峭低插损高温超导滤波器,并与已有高温超导滤波器进行了比较分析.     

分部优化正则化在近场声全息技术中的应用

在基于等效源法近场声全息技术的基础上,对稳定重建过程不适定性的正则化技术进行深入研究.为改善正则化效果,综合考虑Tikhonov正则化和截断奇异值法,提出一种新的分部优化正则化技术.该技术兼取了两种方法的优点,比Tikhonov正则化稳定,避免了过滤波等正则化失效的情况;比截断奇异值法精度高,包含了更多的细节信息.通过对简支板的数值仿真,分别和Tikhonov正则化和截断奇异值法进行了比较,说明了本文所提方法稳定性较好和精度较高的优点.最后通过实验研究进一步证明了本文方法的有效性和正确性.     

处理NaCs光解离问题的两种方案比较

利用含时波包动力学方法中的劈裂算符-傅里叶变换传播方案和切比雪夫多项式展开方案研究了Na Cs分子的光吸收截面,并对由这两种方案计算得出的结果进行了比较.结果表明劈裂算符-傅立叶变换传播方案能更好地展示光吸收截面的中间动力学信息,而在研究初始波包与光吸收截面的关系时,由切比雪夫多项式展开方案获得的结果则更直观.利用后一方案计算的从基态X1∑+不同振动态跃迁到激发态B1∑+上相应的光吸收截面的结果表明,初始波包对光吸收截面有一定的影响,所有振动态的吸收截面均表现出谐振行为,即每一个振动态吸收截面最小值的个数恰好等于基态振动态波函数节点的个数,这种节点映射行为与映射原理相符合.     

高功率圆波导多孔阵列定向耦合器设计

设计了一种应用于8 mm回旋管输出功率测量和频谱监测的圆波导-矩形波导多孔阵列耦合定向耦合器。利用弱耦合波理论推导了多孔阵列耦合公式，从数值计算和模拟仿真两个方面对比分析了8孔孔径阵列分别呈正反分布的等孔径、二项式、切比雪夫和高斯分布的耦合特性。在此基础上，结合等孔径分布耦合度带内波动小和切比雪夫分布高定向性的优点，提出了复合孔径阵列的设计思想。模拟结果显示:复合孔径阵列很好地兼顾了多种孔径阵列分布的优势，带内耦合度波动较小，有效频带范围较宽，且定向性优越。同时对定向耦合器的方向性改善进行了探讨，可以看出,适当的孔径分布阵列如切比雪夫分布和阵列边缘尾孔间距的调整都可以有效地提高定向性。     

处理NaCs光解离问题的两种方案比较

利用含时波包动力学方法中的劈裂算符-傅里叶变换传播方案和切比雪夫多项式展开方案研究了NaCs分子的光吸收截面，并对由这两种方案计算得出的结果进行了比较.结果表明劈裂算符-傅立叶变换传播方案能更好地展示光吸收截面的中间动力学信息，而在研究初始波包与光吸收截面的关系时，由切比雪夫多项式展开方案获得的结果则更直观.利用后一方案计算的从基态 不同振动态跃迁到激发态 上相应的光吸收截面的结果表明，初始波包对光吸收截面有一定的影响，所有振动态的吸收截面均表现出谐振行为，即每一个振动态吸收截面最小值的个数恰好等于基态振动态波函数节点的个数，这种节点映射行为与映射原理相符合.     

一种基于Radon逆变换的半覆盖螺旋锥束CT重建算法

半覆盖螺旋锥束计算机断层成像能够扩展传统螺旋锥束计算机断层成像的成像视野, 实现小面板探测器成像超视野物体. 但是, 各角度下的投影都存在数据截断, 会使重建结果中产生截断伪影, 降低图像质量. 本文提出了一种基于Radon逆变换的半覆盖螺旋锥束重建算法, 该算法在滤波时先使用局部算子, 再使用全局算子. 局部算子不受数据截断的影响, 并且降低了运算后的值由于数据截断所造成的不连续性, 因此, 减少了随后全局运算产生的截断误差. 仿真和实际实验结果均验证了本文算法的有效性. 和现有算法的对比也表明, 本文算法针对半覆盖螺旋锥束投影具有更强的截断伪影抑制能力, 能够有效提高重建图像的质量.     

Bilateral filtering of magnetic resonance phase images

High-pass filtering is required for the removal of background field inhomogeneities in magnetic resonance phase images. This high-pass filtering smooths across boundaries between areas with large differences in phase. The most prominent boundary is the surface of the brain where areas with large phase values inside the brain are located close to areas outside the brain where the phase is, on average, zero. Cortical areas, which are of great interest in brain MRI, are therefore often degraded by high-pass filtering. Here, we propose the use of the bilateral filter for the high-pass filtering step. The bilateral filter is essentially a Gaussian filter that stops smoothing at boundaries. We show that the bilateral filter improves image quality at the brain's surface, without sacrificing contrast within the brain.     

Analysis and filtering of scanning probe images

Two methods for processing and filtering of images obtained by scanning probe microscopy (SPM) are proposed. The data recovery algorithm not only locates line faults, but also restores distorted brightness heights. A self-consistent rank high-pass filter highlights the boundaries of scanned objects. The results of the processing of model structures demonstrate the advantages of the proposed filtering methods.     

Correcting Low-Frequency Phase Distortion in Electroglottograph Waveforms

Dynamic high-pass filtering with a -3 dB frequency that is a factor of ten or more below the voice fundamental frequency has a negligible effect on the amplitudes of the Fourier components of an EGG waveform. However, such a filter can significantly distort the waveform due to distortion in the phase or time alignment of these Fourier components. Such high-pass filtering can be introduced purposefully to stabilize the waveform by attenuating low-frequency noise, or may be an undesired effect of using an amplification or data acquisition system designed for acoustic signals. For a given voice fundamental frequency, the amount of distortion depends greatly on the order or attenuation characteristics of the filter and on the type of EGG waveform. Both a high-order filter and a breathy voice tend to increase the amount of distortion. If the characteristics of the high-pass filter are known, there are a number of digital filter techniques that can be used to reduce the phase distortion. However, it is shown that a relatively simple analogue network can also be used to obtain a correction that suffices for most applications. If the precise characteristics of the filter are not known, the response to a square wave can be used to adjust the compensator parameters for an optimal correction.     

托卡马克磁体电源无源滤波器阻抗-频率特性计算与测量

针对托卡马克磁体电源无源滤波器运行特点，计算推导了单调谐和高通滤波器等效频率偏差工况下的阻抗特性，提供了一种基于低压高精度电压/电流的阻抗频率特性测量方法，通过ITER极向场电源测试用无源滤波器阻抗实验验证了该方法的有效性，所得结论可为ITER谐波抑制及无功补偿系统现场试验提供有益的理论和工程参考。     

The effects of hearing loss on the contribution of high- and low-frequency speech information to speech understanding. II. Sloping hearing loss

The speech understanding of persons with sloping high-frequency (HF) hearing impairment (HI) was compared to normal hearing (NH) controls and previous research on persons with "flat" losses [Hornsby and Ricketts (2003). J. Acoust. Soc. Am. 113, 1706-1717] to examine how hearing loss configuration affects the contribution of speech information in various frequency regions. Speech understanding was assessed at multiple low- and high-pass filter cutoff frequencies. Crossover frequencies, defined as the cutoff frequencies at which low- and high-pass filtering yielded equivalent performance, were significantly lower for the sloping HI, compared to NH, group suggesting that HF HI limits the utility of HF speech information. Speech intelligibility index calculations suggest this limited utility was not due simply to reduced audibility but also to the negative effects of high presentation levels and a poorer-than-normal use of speech information in the frequency region with the greatest hearing loss (the HF regions). This deficit was comparable, however, to that seen in low-frequency regions of persons with similar HF thresholds and "flat" hearing losses suggesting that sensorineural HI results in a "uniform," rather than frequency-specific, deficit in speech understanding, at least for persons with HF thresholds up to 60-80 dB HL.     

Cross-correlation in band-limited ocean ambient noise fields

Observations of ambient noise in the ocean are generally band limited, because of the natural spectral shape of the noise or the restricted bandwidth of the detection system. Either way, the noise may be regarded as white noise to which a band-limiting filter has been applied. An analysis of the two-point cross-correlation function of such filtered noise is presented for two cases, isotropic and surface-generated noise. The most pronounced effects occur with high-pass and bandpass filters when the low-frequency cut-off falls well above the first few zeros in the coherence function. In this situation, the sensor separation is very many times the longest acoustic wavelength (associated with the lowest frequency) in the passband. The filtering then produces sharp pulses at correlation delays equal to the numerical value of the acoustic travel time between the sensors. Although these pulses are narrow, they have a finite width, within which a fine structure appears in the form of multiple rapid oscillations, due to the differentiating action of the filter. The number of such oscillations increases as the low-frequency roll-off of the filter becomes steeper. This fine structure is evident in several recently published experimental determinations of the cross-correlation function of band-limited ocean ambient noise.     

红外探测器三波段高通滤光片的研制

 红外探测器在空间探测以及目标发现和跟踪技术中具有极为重要的应用,其性能的优劣直接关系到获取数据的准确性和可信性。为了提高红外信号的分析灵敏度,降低探测器的噪声,在（CVD）ZnS基底上,采用电子束及离子辅助沉积技术,研制了3 μm～5 μm高透、1.064 μm～2.5 μm波段截止的高通滤光膜。为了有效防止1.064 μm波段处的激光对探测器造成的激光损伤,以保证探测器的正常工作,根据激光器的输出功率制备了对1.064 μm激光波段具有1%,0.1%,0.01%数量级衰减能力的系列高通滤光膜,使红外探测器更具灵活性与智能化的特征。     

傅里叶变换轮廓术中二维非对称滤波器的设计

傅里叶变换轮廓术(FTP)复原三维形貌时，用来提取基频成分的带通滤波器对测量精度有很大影响。传统二维滤波器如汉宁窗或高斯窗为对称滤波器，其截止频率的大小受条纹空间频率即基频与零频间的距离所限，经常会导致基频成分提取不完整，有用信息缺失。为解决此问题，在二维汉宁滤波器基础上，提出一种椭圆形底部形状的二维非对称滤波器，在不同频率方向上具有不同的频率响应和截止频率，可提取出更为完整的基频成分。台阶和阵列物体的模拟实验表明，二维非对称滤波器对2个物体的复原精度相比于传统汉宁滤波器分别提高了39.5%和55.6%。     

Spatiotemporal shaping of terahertz pulses

We report temporal shaping of few-cycle terahertz pulses, using a slit in a conductive screen as a high-pass filter. The filter's cutoff frequency was tuned by changing the width of the slit; the slope of the cutoff transition was altered by changing the thickness of the screen. We measured the transmission function of the filters, using large-aperture photoconducting antennas to create and detect the incident and transmitted electric field. Our experimental results were in excellent agreement with the performed finite-difference time-domain simulations of the propagation of the pulse through the slit. When the screen thickness was greater than the slit width, the filter was well modeled by a short, planar waveguide. Using a simple transfer function, we accurately describe the sharp cutoff and dispersion of such a filter.     

Zero-frequency elimination using the filtering characteristics of a volume grating

Angular selectivity of a volume grating has been exploited to generate a high-pass filtering function that cuts off the zero frequency and attenuates the low frequencies. The filter can be used for the edge enhancement of amplitude and phase objects. Partially coherent light is used in the reading process.