共查询到20条相似文献，搜索用时 31 毫秒
1.
给出了一种紧凑的可用于WUSB的新型带陷超宽带印刷单极子天线．天线由内嵌条带的U形环组成并采用部分接地技术,从而使天线具有带陷超宽带特性．实测结果表明该天线输入端驻波比小于2的绝对阻抗带宽为7．88GHz,覆盖了3．12～11GHz的频率范围,其中5．06～5．89GHz范围内具有带阻特性．讨论了各几何参数对天线性能的影响,同时获得了该天线相对稳定的、近似全向且对称的测试方向图．由于此种天线无需额外的带阻滤波器来隔离天线与其他通信系统的干扰,从而大大简化了WUSB系统的设计． 相似文献
2.
介绍了光纤通信1 550 nm波段全介质带通滤光片的设计原理、制备工艺和研制过程,获得了可供实用的光纤通信滤波器件.实验测试结果表明:所设计并研制的3腔和4腔具有0.8 nm波长间隔的窄带通滤波片,具有很好的带通透射光谱特性,其中心波长、通带宽度、通带纹波、峰值插入损耗等主要技术指标,以及温度稳定性等,均能满足光纤通信密集波分复用(D-WDM)系统应用的要求.另外,具有20 nm带宽的粗波分复用(C-WDM)滤波片,也具有符合工业应用的带通透射光谱性能. 相似文献
3.
A novel simplified method is presented to design FIR filter with controllable center frequency. The properties of transfer curves for all-phase filters are illustrated under 3 windowing conditions. By combining single-window all-phase filter design steps and double phase-shift combination, a series of design formulas for point-pass filter, notch filter, band-pass filter and band-stop filter are derived, thus the design computation complexity is greatly reduced. Experiments prove that the center frequency of all the filters can be accurately specified at arbitrary position by adjusting frequency parameters m and λ. 相似文献
4.
作为低中频接收机关键模块之一,多相滤波器在镜像抑制和邻道干扰方面扮演着重要的角色.它的性能指标直接影响整个接收链路的灵敏度.本文采用有源RC电路架构设计了一个五阶切比雪夫多相滤波器.仿真结果表明,该滤波器的中心频率在100kHz,3dB带宽是220kHz.最大电压增益为63dB,镜像抑制比大于30dB.设计的滤波器完全满足GSM手持设备的要求. 相似文献
5.
ＲｅｊｅｃｔｉｏｎｏｆＮａｒｏｗＢａｎｄＩｎｔｅｒｆｅｒｅｎｃｅｉｎＤＳＳｐｒｅａｄＳｐｅｃｔｒｕｍＳｙｓｔｅｍｓＵｓｉｎｇＲｅｃｕｒｅｎｔＮｅｕｒａｌＮｅｔｗｏｒｋｓＹｏｕＸｉａｏｈｕ（尤肖虎）ＦｕＬｉ（傅莉）（ＮａｔｉｏｎａｌＣｏｍｍｕｎｉｃ... 相似文献
6.
Wan Wanggen Yu Xiaoqing Yuan Jingxian Li Yonghua 《上海大学学报(英文版)》1998,2(3):208-212
１ＩｎｔｒｏｄｕｃｔｉｏｎＩＲｂａｎｄｐａｓｓｆｉｌｔｅｒｓｈａｖｅｍａｎｙａｄｖａｎｔａｇｅｓｏｖｅｒｔｈｅｉｒＦＩＲｃｏｕｎｔｅｒｐａｒｔｓ．Ｔｈｅｙｒｅｑｕｉｒｅｆｅｗｅｒｃｏｅｆｉｃｉｅｎｔｓａｎｄｈａｖｅａｓｉｍｐｌｅｒｓｔｒｕｃｔｕｒｅ．... 相似文献
7.
提出了一个新型的平面微带双频段带通滤波器,由加载双分支线的开环阶梯阻抗谐振器和平行耦合微带线组成.通过调节开环阶梯阻抗谐振器、平行耦合微带线和加载分支线的长度,带通滤波器在2.55与5.35GHz具有很好的双通带特性且在其间有很好的隔离度.两者的相对带宽分别为11.8%与16.8%.与传统的开环阶梯阻抗谐振器相比,该带通滤波器在第2频带有更宽的带宽,可以覆盖WLAN在高频段的整个范围.该双频段带通滤波器具有低损耗、高隔离、低纹波的特性.通过比较HFSS软件的仿真结果与实际测得的结果发现,两者具有很好的一致性. 相似文献
8.
Lan-he Zhang Xiu-li Meng Ying Wang Li-dan Liu 《Journal of Zhejiang University. Science. B》2009,10(8):595-601
In the industrial operation of biotrickling filters for hydrogen sulfide (H2S) removal, shock loads or starvation was common due to process variations or equipment malfunctions. In this study, effects
of starvation and shock loads on the performance of biotrickling filters for H2S removal were investigated. Four experiments were conducted to evaluate the changes of biomass and viable bacteria numbers
in the biotrickling filters during a 24-d starvation. Compared to biomass, viable bacteria numbers decreased significantly
during the starvation, especially when airflow was maintained in the absence of spray liquid. During the subsequent re-acclimation,
all the bioreactors could resume high removal efficiencies within 4 d regardless of the previous starvation conditions. The
results show that the re-acclimation time, in the case of biotrickling filters for H2S removal, is mainly controlled by viable H2S oxidizing bacteria numbers. On the other hand, the biotrickling filters can protect against shock loads in inlet fluctuating
H2S concentration after resuming normal operation. When the biotrickling filters were supplied with H2S at an input of lower than 1700 mg/m3, their removal efficiencies were nearly 98% regardless of previous H2S input.
Project supported by the Foundation for Society Development of Jilin Province (No. 20080412-1), the Education Research Foundation
for Science and Technology Development of Jilin Province, and the Foundation for Doctor Research in Northeast Dianli University
of Jilin Province (No. BSJXM-200710), China 相似文献
9.
采用传输矩阵的计算方法,研究了一维光子晶体掺杂结构对光传输特性的影响,利用MATLAB绘制不同结构参数的一维光子晶体第一带隙透射率图谱.通过绘图发现：对称一维光子晶体的周期结构（（BA）m（AB）m）,在带隙内部出现光子局域,在中心波长处产生共振隧穿效应;增加对称周期层数,能够降低隧穿效应的透射率,降低光子局域带宽;提高掺杂层折射率,降低光子局域带宽,局域中心向短波方向移动;增大入射角,光子局域中心向短波方向移动;选择适当的结构参数能够实现在1 550 nm光波附近的窄带滤波器的设计. 相似文献
10.
利用传输矩阵法,通过数值模拟,研究周期不对称度、介质折射率等因素对双负材料光子晶体(AB)m1BCB(BA)m2能带性能的影响,结果发现:当周期不对称度△m=0,且m1=m2=m时,随着周期数m的增大,禁带中心单透射峰带宽逐渐变窄,禁带中心形成一条透射率为100%的超窄透射峰;当周期不对称度△m≠0,且△m逐渐增大时,禁带中心透射峰透射率逐渐降低,且禁带宽度越来越窄;当介质A折射率nA增大时,禁带宽度逐渐变窄,禁带中的透射峰带宽逐渐变宽;而介质B折射率nB逐渐增大时,禁带中心透射峰带宽逐渐变窄,禁带带宽逐渐变宽;当介质C折射率nC随着负值减小时,禁带宽度几乎保持不变,但禁带中透射峰带宽明显变窄。影响双负材料光子晶体能带性能的规律对设计诸如新型光学滤波器、光开关和全反射镜等光学器件有一定参考价值。 相似文献
11.
BAI Lei-shi HE Li-ming TIAN Zuo-hua SHI Song-jiao 《浙江大学学报(A卷英文版)》2006,7(10):1733-1741
INTRODUCTION Due to increasing demand for higher perform- ance, as well as for higher safety and reliability standards, the model-based approaches to fault de- tection and isolation (FDI) for dynamic systems have received more and more attention during the last two decades (Chen and Patton, 1999; Chen and Saif, 2006 Frank and Ding, 1997; Gao and Wang, 2006; Jiang and Zhou, 2005; Zhou et al., 1998). Among these model-based approaches, the most common way is the observer-based approach… 相似文献
12.
We report that the ultraviolet （UV） light induced photochromic behavior of layered organic-inorganic perovskite material of （C4H9NH3）2CuCl4, changed from yellow to brown after irradiation with UV light （10 mW/cm^2） and partially recovered through storage in the dark. （C4H9NH3）2CuCl4 exhibited two distinct absorption bands centered at 286 nm （band Ⅰ） and 384 nm （band Ⅱ）, which were attributed to the photo-induced exciton formed in 2D inorganic layers sandwiched by organic layers. The blue shift of band Ⅰ from 287 to 269 nm as well as the decrease of the intensity of band Ⅰ and band Ⅱ could be found when samples were irradiated under UV light for different length of time. The simultaneous weakening of the intensity of the N-H...Cl hydrogen bond as well as the vibration of the long Cu-Cl bond in the distorted CuCl6^4- octahedron could be detected from the Fourier transform infrared （FTIR） spectra, which resulted the change of charge distribution of the dissymmetric Cl-Cu...Cl bond and the resulting photochromic behavior. 相似文献
13.
具有很高隔离度的双极化缝隙耦合微带天线 总被引：3，自引：0，他引：3
A wideband dual-polarized slot-coupled stacked microstrip antenna with very high isolation and low cross-polarization is presented. To improve isolation between two poiarization ports, the stacked patches are excited by an open-ended and a T-shaped microstrip lines both via two H-shaped slots placed in a ＂T＂ configuration. The measured isolation is better than 40.5 dB over the bandwidth from 8.8 to 9.8 GHz with cross-polarization level less than - 28.5 dB. The measured VSWR ≤ 2 bandwidths reach 20.7 96 and 19.196 at the verrical and horizontal polarization ports, respectively. This antenna is suitable to be used as array elements in spacebome synthetic aperture radars （SAR） and active phased array radars. 相似文献
14.
15.
BaFe12O19 powders with nanocrystaUine sizes were produced by sol-gel auto-combustion method. The precursors were prepared under the molar ratios of citric acid to the metal nitrate of 0.5, 1.0 and 1.5. Appropriate ethylene diamine （C2H8N2） was added in order to adjust pH of 7. The ions distribution of citric acid at different pH explains the effect of citric acid in the starting solution. The XRD patterns of the as-burnt powders and annealing powders show different phases for different citric acid content. In addition, the lattice constants （a, c） derived from X-ray diffraction pattern were changed from 0.58881 nm to 0.58997 nm and 2.32057 nm to 2.32296 nm respectively. The data from VSM indicated that the powder with high citric acid content took on good magnetic properties. Pure single BaFe12O19 of the specific maximum magnetization M（1 T）≈ 49.73 Am^2/kg, the specific remanent magnetization Mr ≈ 30.77 Am^2/kg and the coercive force He≈ 467 kA/m was produced when the molar ratios of citric acid to the metal nitrate was 1.5. 相似文献
16.
INTRODUCTION Determination of fruit and vegetable quality is very important for both producers and processors. Watermelon as a delicious fruit has been widely ac-cepted in the world and its internal quality is impor-tant for consumers and merchants. The current fa-vorite way for checking a watermelon is to sense sound or vibration by slapping or rapping it. It is time consuming, tedious, and subject to error. Several studies on assessing the quality of watermelon based on its acoustic o… 相似文献
17.
A novel nano-TiO2-xNx composite was used as photocatalyst and added to the interior wall paint. The average diameter of nano-TiO2-xNx was about 20 nm. The majority crystal component of the sample was anatase and its optical absorption edge was shifted from 387 nm to 520 nm significantly. Nano-composite paint containing different dosage of nano- TiO2-xNx was investigated to study the properties of formaldehyde decomposition in the air. Testing results show that the formaldehyde decomposition ratio of that nano-paint can almost reach above 80%, especially for that of the paint containing 3% （w/w） nano-TiO2-xNx which exceeded 90%. The primary investigation on the reaction kinetics of photocatalytic formaldehyde decomposition indicated that the experiment data well fit the model of first-order reaction kinetics. 相似文献
18.
A. Simon J. L. Thomas 《Educational research; a review for teachers and all concerned with progress in education》2013,55(1):46-50
Sixth‐formers were questioned in all four grammar schools in a city where all LEA provision of 16‐plus education is to be concentrated in the college of further education. Their replies showed no widespread rejection of ‘authority’ and little enthusiasm for a complete separation from younger students. The most obvious theme was the ambivalent attitude towards direction from teachers‐‐a demand for clear direct instruction and informal discussion, for independence and guidance. 相似文献
19.
Study on hydrogen sulfide removal based on bench-scale experiment by bio-trickling filter 总被引：1，自引：0，他引：1
TIAN Shu-lei ZHANG Lan-he WANG Qun-hui WANG Xu-ming XIE Wei-min 《浙江大学学报(A卷英文版)》2007,8(7):1141-1148
A bench-scale experiment for control of hydrogen sulfide (H2S) emissions was carried out continuously for nearly four months by using bio-trickling filter packed with ZX01 stuffing. The results suggested that the bio-trickling filter had proven excellent performance over substantial operational periods. Removal efficiency of H2S was nearly 100% when volumetric loading of the bio-trickling filter varied from 0.64 g/(m3·h) to 38.20 g/(m3·h) and metabolism products of H2S were mainly composed of SO42–. When inlet concentration of H2S was 250 mg/m3, the optimum gas retention time was 30 s and the optimum spray water flow rate was 0.005 9~0.012 L/(cm2·h). The bio-trickling filter had good ability to resist shock of high volumetric loading, and was not blocked during experiments for nearly four months during which resistance was maintained at relatively lower value, so that the bio-trickling filter need not carry out back washing frequently and can be operated steadily for long-term. 相似文献
20.
Díaz MP Rizo OD Díaz AL Aparicio EE Díaz RR 《Journal of Zhejiang University. Science. B》2006,7(12):947-956
A discriminant method for optimizing activity in nuclear medicine studies is validated by comparison with ROC （received operating characteristic）-curves. The method is tested in 21 single photon emission computerized tomography （SPECT）, performed with a cardiac phantom. Three different lesions （Lb L2 and L3） were placed in the myocardium-wall by pairs fbr each SPECT. Three activities （84, 37 or 18.5 MBq） of 99mTc were used as background. Linear discriminant analysis was used to select the parameters that characterize image quality among the measured variables in the images [（Background-to-Lesion （B/Li） and Signal-to-Noise （S/N） ratios）]. Two clusters with different image quality （P=0.021 ） were obtained. The ratios B/Lj, B/L2 and B/L3 are the parameters used to construct the function with 100% of cases correctly classified into the clusters. The value of 37 MBq was the lowest tested activity for which good results for the B/Li ratios were obtained. The result coincides with the applied ROC-analysis （r=0.89）. 相似文献