• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    A flexible ultra-broadband metamaterial absorber working on whole K-bands with polarization-insensitive and wide-angle stability

    2022-03-12 07:49:32TaoWang汪濤HeHeHe何賀賀MengDiDing丁夢(mèng)迪JianBoMao毛劍波RenSun孫韌andLeiSheng盛磊
    Chinese Physics B 2022年3期
    關(guān)鍵詞:汪濤

    Tao Wang(汪濤) He-He He(何賀賀) Meng-Di Ding(丁夢(mèng)迪)Jian-Bo Mao(毛劍波) Ren Sun(孫韌) and Lei Sheng(盛磊)

    1School of Microelectronics,Hefei University of Technology,Hefei 230601,China

    2School of Information Science and Technology,University of Science and Technology of China,Hefei 230027,China

    3School of Electronic Science and Engineering,Southeast University,Nanjing 210096,China

    4Technical Institute of Physics and Chemistry,Chinese Academy of Sciences,Beijing 100190,China

    Keywords: flexible metamaterial absorber,periodic conductive patterns,ultra-broad band,wide-angle

    1. Introduction

    In recent years, with practical and potential applications in microwave stealth, satellite communications, electromagnetic (EM) compatibility, radar detection, and sensors, metamaterial absorber(MMA)has attracted extensive attention in these fields.[1,2]Nowadays, mostly advanced satellite communications and radar detections for military applications are working in the frequency range of 12 GHz-40 GHz,i.e.,the whole K-bands, which maintains Ku, K, and Ka bands.In these applications, MMA should be conformal with the surface of object to absorb various incident EM waves, but commonly MMAs always select FR-4 as substrate to obtain high absorption,[3,4]these rigid and bulky absorbers can only conformal with flat surface, which impede the adoption of MMA on curved surfaces,such as plane,satellite,and missile.In order to achieve practical concrete requirements, flexible,lightweight, easy-processing MMAs that can be conformal with curved surfaces of objects using for K-bands microwave absorbing should be explored.

    Nowadays, it is quite difficult to design and fabricate a flexible ultra-broadband MMA, due to the periodic conductive patterns is very difficult to transfer on the flexible substrate, such as PVC and PTFE,and the technological process is quite sophisticated which lead to a plenty of errors and deviations of the products. Moreover,deformation magnitude of periodic conductive patterns and substrate is quite disagreement when the absorber is bent in an arc,which results in poor performance when MMA is conformal with a curved surface.Recently, three-dimensional (3D) printing technology is usually used in MMA fabrication, but it is not suitable for the manufacture of flexible absorbers due to the bad mechanical flexibility of the 3D structure.[5,6]Fortunately, more additive manufacturing methods such as template printing and spraying can be used for the manufacture of flexible MMA.Especially,using screen-printing technology, single-layer or multi-layer absorbers can be fabricated on different flexible substrates,such as polyethylene terephthalate(PET),polydimethylsiloxane(PDMS),polyimide(PI),and so forth.[7,8]

    Up to date, through accurate regulation of the printing process, conductive ink can achieve efficient absorption from microwave to terahertz, or even in light bands.[9-14]Kimet al. reported a narrow-band flexible absorber with absorptivity over 99%at 9.21 GHz using an improved Jerusalem-cross annular resonator.[9]Genget al. reported a multi-layer flexible MMA operating in terahertz band using gold split-ring resonators, proving its wide applications in biosensors.[15]Huanget al.using layer-by-layer screen overprinting method produced a flexible MMA with absorptivity greater than 90% at 8.3 GHz-10.9 GHz.[16]Wuet al. reported a broadband millimeter-wave absorber with mechanical flexibility and optical transparency in the frequency range of 73.5 GHz-110 GHz.[17]Lvet al. reported a flexible electric-driven device composed of an insulating organic polymer substrate, a carriers transport layer, and a core-shell absorber, which can achieve narrow-band adjustable and effective absorption below 2 GHz by controlling the external voltage.[18]The above literatures on flexible MMA mostly focused on the efficient absorption of high frequency or narrowband, a flexible ultrabroadband absorber working on the frequency range covering the whole K-bands from 12 GHz to 40 GHz is still not been reported.

    To effectively absorb microwaves in the whole K-bands on a curved surface, a flexible sandwich MMA composed of PVC-PI-PTFE-metal plate is designed,analyzed,fabricated,and measured. All the conductive patterns are printed by silver conductive ink and located on a surface of flexible thin PI substrate. Traditionally,FSS is printed on the upper surface of the PI layer,it is worth noting that FSS in this proposed structure is arranged on the lower surface of the PI layer which directly results in the improvement of microwave absorption.Absorptivity of the proposed flexible absorber is more than 90%at 10.47 GHz-45.44 GHz, which contains the whole Kbands and portion of X-band and U-band. The consistency of simulation and measurement proves good flexibility and robustness of the flexible absorber.

    2. Physical model of the flexible absorber

    To explore the design method, working principle, and manufacture technology for flexible ultra-broadband absorber,as an example to illustrate the concept,a flexible absorber with PVC-PI-PTFE-metal plate structure is modeled herein. Incident wave from free space penetrate PVC, PI, and PTFE in turn, and is totally reflected by metal plate. Geometry of the unit cell is depicted in Fig. 1. Acted as a metallic ground plate, copper with thickness of 0.017 mm is attached on the lowest level of the unit cell and is combined with PTFE layer.Square conductive pattern is printed on the lower surface of PI (ε= 3.24+j0.031) layer, with resistance of 120 Ω/sq.Dielectric constants of PTFE and PVC are 2.1+j0.001 and 2.56+j0.025,respectively. Optimized parameters are as follows:a=4.2 mm,dPI=0.15 mm,dPTFE=1.7 mm,dPVC=1.5 mm.

    Fig.1. Physical model of the flexible absorber.

    Fig.2. Calibration of the physical model. (a)Equivalent circuit of the physical model. (b)Physical model analysis versus full-wave analysis.

    According to the working principle of MMA, absorption efficiency is determined by two major factors, one is the impedance matching between absorber and free space, the other is intensively EM loss caused by the materials of every layer. Based on equivalent circuit model,[19]FSS herein is developed as a band-stop resonating surface with a series ofR-L-Ccircuits in Fig.2(a),and absorption of this MMA is mainly caused by two adjacent resonances between FSS and grounded metal plate.ZFSSrepresents equivalent impedance of resistive film,andZinis input impedance of parallel circuit constituted byZFSSand transmission lines of each dielectric layer. Each equivalent parameter is calculated and optimized by simulation analysis. Normalized input impedance is analyzed as shown in Fig. 2(b), real part ofZinis near unity,and imaginary part is close to zero in 10.47 GHz-45.44 GHz.It is noticeable that equivalent circuit can achieve excellent impedance matching in the range of 10.47 GHz-45.44 GHz.

    To verify accuracy of the equivalent circuit model for flexible MMA, the calculated results from the equivalent circuit are compared against that obtained by the full-wave simulation analysis. Absorptivity of the flexible MMA can be characterized asA= 1-|S11|2-|S21|2, whereS11andS21represent reflection and transmission coefficients of the unit cell,respectively. Transmission coefficient is zero because of obstruction of the copper ground plate, as we all know, EM waves cannot penetrate metal plate, so the absorptivity is determined asA= 1-|S11|2. According to absorption spectrum in Fig.2(b),absorptivity is higher than 90%in frequency range of 10.47 GHz-45.44 GHz under normal incidence,and absorptivity is more than 96% in 11.25 GHz-43.69 GHz. It should be pointed out that two significant absorption peaks are observed at 13.91 GHz and 37.63 GHz, and the corresponding absorptivity is 99.88%and 99.99%,respectively. The absorptivity deduced from equivalent circuit is compared with that from full-wave analysis, and the two curves show good agreement except for small deviations as depicted in Fig.2(b),which means that the equivalent circuit model is quite effective and can be used for the design of a flexible MMA,and the ultra-broadband absorption is caused by two perfectR-L-Cresonances in the stacked layers.

    3. Results and discussion

    According to equivalent medium theory, some major properties of the flexible absorber are obtained fromSparameters based on Nicolson-Ross-Weir (NRW) method.[20]Permittivity,permeability,and equivalent impedance of the flexible MMA with thickness ofdcan be calculated by

    where wavenumberk0=2π f/c,fis microwave frequency,andcis speed of light. Results of the unit cell are presented in Fig. 3. It can be seen from Fig. 3(a) that real part of permittivity and permeability is negative alternately, which verifies single negative behavior of the flexible MMA.Figure 3(b)illustrates normalized impedance of the flexible MMA, it can be observed that there is a good input impedance matching between flexible MMA and free space, so that the backward reflection at the interface of MMA and free space is effectively reduced, which means that almost all of the incident wave is absorbed by the MMA.Impedance matching can be attributed to the appropriate input impedance of MMA designed by equivalent circuit model, which further verifies the effectively of modified circuit model and equivalent medium theory used in this work.

    Fig. 3. Crucial physical characters of the flexible absorber. (a) Complex permittivity and permeability. (b)Effective impedance.

    Fig. 4. Energy analysis of the flexible absorber: (a) energy directions and(b)power loss distributions.

    To gain insight into resonances absorption of the flexible MMA,power loss of each layer is analyzed.The percentage of power loss at each layer is presented in Fig.4. Combined with impedance conditions in Fig.3(b),figure 4(a)shows that more than 98% energy of the incident EM waves entered into the absorber in frequency range of 10.47 GHz-45.44 GHz,which means that only less than 2% of the incident waves are reflected from MMA to air. Figure 4(b) further illustrates perspective view of power loss of entered energy in the absorber,it can be seen that mostly power loss is focused on resistance film layer except less than 5% occurred in dielectrics layers,which means that resistance film layer is mainly responsible for the absorbing performance of this flexible MMA.

    To explore wave absorption mechanism of the proposed MMA,distribution of surface current and electric field at frequencies of 13.91 GHz and 37.63 GHz are simulated using near field conditions. Figures 5(a)and 5(b)show the comparison of surface current between FSS layer and ground plate layer,an equivalent surface current at 13.91 GHz on FSS layer is mainly concentrated at the center area,which is antiparallel to the current flowing through the metallic ground plate. As a result,magnetic resonance occurred when a plane EM wave incident to the surface of MMA, so an equivalent circulating current is formed between the resistive film layer and ground plate layer.[21]For the similar reason, surface current formed by FSS layer at 37.63 GHz is antiparallel to the current on ground layer,while some parallel current at the center area is caused by electrical resonance. As compared in Figs. 5(c)-5(d),antiparallel currents are much stronger than parallel currents, so magnetic resonance is the key factor of EM wave absorption at 37.63 GHz. Figures 5(e)-5(f)show electric field distribution of FSS layer at two resonance frequencies,i.e.,13.91 GHz and 37.63 GHz, it can be observed that the electric fields are mainly concentrated on the fringe of FSS layer,so the resonance is closely related to the side length of FSS layer.[22]

    Fig.5. Surface current[(a)-(d)]and electric field[(e)-(f)]analysis on crucial layer of flexible absorber;(a)metallic ground at 13.91 GHz;(b)FSS at 13.91 GHz;(c)metallic ground at 37.63 GHz;(d)FSS at 37.63 GHz;(e)FSS at 13.91 GHz;and(f)FSS at 37.63 GHz.

    Fig. 6. Reflectance and absorbing performance of the flexible MMA with patterns on upper versus lower surface of the PI layer.

    Fig. 7. Influence of resistance and size of FSS patterns on absorption frequency spectrum: (a)various resistances of FSS and(b)various sizes of the unit cell.

    To further investigate sensitivity of absorption on resistive film patterns,numerical simulations are provided by changing resistancerand unit sizeaof resistive film as shown in Fig.7.It should be noted that the absorption spectrum occurs a blueshift with increasingr,while the absorptivity increased firstly and decreased later,as mentioned above,this is caused by variation of impedance matching between air and resistive film patterns. Furthermore, the absorption band expands to both sides firstly and shrinks later,whenaincreased from 3 mm to 5 mm. So the best absorption response can be obtained when resistance value and unit size is properly compromised and optimized.

    To reduce RCS of targets equipped with an MMA for stealth, EM control ability of the flexible MMA is explored.As shown in Fig.8,the simulated RCS reduction of the MMA reveals that there are two reduction peaks at 16.1 GHz and 36.81 GHz, with RCS reduction of 30.13 dB and 28.96 dB,respectively. Moreover, RCS reduction is much more than 10 dB in frequency band of 11.48 GHz-43.87 GHz,with relative bandwidth of 117%.

    Fig. 8. RCS reduction performance of incident microwaves with different frequencies.

    Fig. 9. The absorption spectrum with different incident angles of the EM waves: (a)TE wave and(b)TM wave.

    As aforementioned, absorption efficiency of MMA may be influenced by oblique incident and polarization angles of EM waves, and so the sensitivity of the absorber should be investigated. Due to the symmetry of the unit cell,the absorption is insensitive to incident polarization. To explore whether the flexible MMA can maintain ultra-broadband and highabsorption characteristics under conformal conditions,the absorption spectra under different oblique incidences are studied.The absorption spectrum is depicted in Fig. 9, when oblique incident angle is less than 55°, the flexible MMA still maintains more than 90% absorptivity for both transverse electric(TE)polarized wave and transverse magnetic(TM)polarized wave. Results of this MMA provide an essential reference for surface conformal of objects which should be insensitive to polarization and incidence.

    4. Fabrication and measurement verification

    To verify performance of the proposed flexible MMA,the structural prototype is fabricated as shown in Fig. 10. Because all patterns are located on the surface of the PI layer,the processing technology is quite simple. To increase precision of experimental testing, according to periodicity and symmetry of the MMA, overall size of the sample processed by screen-printing technology is 150 mm×150 mm with the whole weight of 132 g. Conductive ink in this technology is consist of carbon black, silver particles, water, and a certain proportion of emulsion,and resistance of ink film layer is adjusted by thickness of ink film. After heating and curing, all FSS patterns with specific resistances are produced by square areas filled with ink,and the printed block resistors are in close contact with the polymer substrate,which helps to reduce parasitic effects. A surface image of the resistive film under an electron microscope is shown in Fig.10(b). Resistance of the FSS film is measured using a four-probe resistance tester(ST-2258C), and a calibrated Rohde & Schwarz ZVA 40 vector network analyzer and two horn antennas are used to measure the fabricated prototype in microwave anechoic chamber.

    As shown in Fig. 11, the measurement of the proposed absorber under normal incidence exhibits a close similarity with the simulation except a slight red-shift, which demonstrates the accuracy of the simulation and the physical model of the MMA, and the little deviation is mainly caused by the machining precision and parasitic effects. To explore the effect of resistive film rearrangement of the PI layer,absorption spectrum of resistive film on upper surface of PI is measured and compared with that on lower surface of PI,as is depicted in Fig.12(a). It can be seen from the normalized absorptivity that the resistive film patterns exhibits better absorption characteristics when it is located on the lower surface of PI.

    Fig. 10. Photographs of the fabricated flexible MMA for test: (a) curved flexible MMA; (b) a unit cell in electron microscope test (Eclipse E200);(c)weight of the prototype;(d)size of the prototype;and(e)measurement system in microwave anechoic chamber.

    To measure the flexibility of the proposed absorber, the prototype is attached on the outside surface of a cylinder with diameters of 100 mm and 200 mm, respectively. As normalized absorption spectrum is presented in Fig.12(b),strong absorption can be observed in a frequency range of 10 GHz-40 GHz under different bending degrees. When the curvature of the cylinder increased,the size of the effective caliber area decreased, which deteriorated absorbing performance of the flexible MMA. Fortunately, high-efficiency absorption over 80%can still be obtained when diameter of the cylinder is not less than 100 mm,which means that the flexible MMA can be conformal on an object with different curvature surfaces.

    A comprehensive comparison of the purposed flexible MMA with other similar microwave absorbers is presented in Table 1, whereλmaxis the largest wavelength in absorption spectrum. Some crucial parameters such as absorption bandwidth, relative bandwidth, periodicity, and thickness of MMA are listed herein. Compared with other MMAs,[24-27]the purposed MMA is flexible and covers the whole Ku, K,Ka bands, and some of X, U bands. Furthermore, due to the pattern is located on the lower surface of the PI layer,the resonance peaks at 13.91 GHz and 37.63 GHz is improved obviously.It should be pointed out that the absorber reported in the present research is structurally different from other absorbers and shows the ultra-broadband microwave absorption and the excellent flexibility.

    Fig.11. Measured reflectance and normalized absorptivity of the fabricated flexible prototype MMA.

    Fig.12. Comparison of measured absorption spectra under different conditions: (a) patterns on upper versus lower surface of the PI layer; (b) without curve versus on a cylinder with D=200 mm versus on a cylinder with D=100 mm.

    Table 1. Comprehensive comparison of the proposed flexible MMA with typically reported absorbers.

    5. Conclusion

    A flexible MMA working on all K-bands with ultrabroadband, polarization-insensitive, and wide-angle stability is designed by equivalent circuit model, simulated by fullwave analysis method, fabricated by screen-printing technology, measured by a vector network analyzer, and compared with some typical MMAs. Different from the reported absorbers, resistive film patterns are arranged on the lower surface of the PI layer in this work, which leads to the improvement of microwave absorbing performance. Based on equivalent circuit model and equivalent medium theory, the absorption mechanism is analyzed and verified by numerical simulations. The simulated results show that the flexible MMA can obtain absorptivity greater than 90% in the whole Ku, K, Ka bands, and parts of X and U bands, and the absorptivity can even exceed 96% in the frequency range of 11.25 GHz-43.69 GHz. Absorption spectra under different polarizations and oblique incidences indicate that the absorber is polarization-insensitive and wide-angled. The free-space method is used to measure the fabricated prototype, and experimental results show good agreement with numerical results. Due to characteristics of easy conformal, high absorption,and ultra-broadband,the flexible MMA is applicable for EM shielding,radar stealth,sensors,and satellite communications working on the K-band.

    Acknowledgements

    Project supported by the Fundamental Research Funds for the Central Universities of China (Grant No. JD2020JGPY0010), the China Post-doctoral Science Foundation (Grant No. 2020M671834), and the Anhui Province Post-doctoral Science Foundation, China (Grant No.2020A397).

    猜你喜歡
    汪濤
    A flexible ultra-broadband multi-layered absorber working at 2 GHz–40 GHz printed by resistive ink
    基于Web的城市交叉口虛擬仿真實(shí)驗(yàn)教學(xué)系統(tǒng)
    物流科技(2022年2期)2022-05-07 21:54:09
    High efficiency ETM-free perovskite cell composed of CuSCN and increasing gradient CH3NH3PbI3
    汪濤、張寧:從宏觀視角解析中國(guó)房地產(chǎn)行業(yè)對(duì)中國(guó)經(jīng)濟(jì)有多重要
    汪濤:到目前為止房地產(chǎn)銷(xiāo)售和投資都比之前想象的強(qiáng),下半年將會(huì)怎樣?
    2021年高考數(shù)列經(jīng)典問(wèn)題聚焦
    汪濤:購(gòu)房意愿走弱是否會(huì)拖累房地產(chǎn)銷(xiāo)售大跌
    打折
    “死去”20多年的弟弟復(fù)活了
    方圓(2020年23期)2020-01-07 00:51:47
    Impacts of bridge piers on water level during ice jammed period in bend channel–An experimental study *
    嫩草影院精品99| 91午夜精品亚洲一区二区三区 | 久久久久久九九精品二区国产| 全区人妻精品视频| av天堂中文字幕网| 三级男女做爰猛烈吃奶摸视频| 三级男女做爰猛烈吃奶摸视频| 亚洲中文字幕日韩| 99视频精品全部免费 在线| 亚洲性久久影院| 亚洲在线观看片| 精品国内亚洲2022精品成人| 一本精品99久久精品77| 亚洲国产精品久久男人天堂| 蜜桃亚洲精品一区二区三区| 午夜精品久久久久久毛片777| 99在线视频只有这里精品首页| 欧美xxxx黑人xx丫x性爽| 精品久久国产蜜桃| 久久久久久伊人网av| 国产老妇女一区| 亚洲电影在线观看av| 日本-黄色视频高清免费观看| av福利片在线观看| av天堂中文字幕网| 国产一区二区三区视频了| 老熟妇仑乱视频hdxx| 午夜福利在线在线| 成人三级黄色视频| 欧美bdsm另类| 国产伦精品一区二区三区视频9| 国产乱人视频| 亚洲av中文av极速乱 | 成年人黄色毛片网站| 欧美色视频一区免费| 99精品久久久久人妻精品| 人妻少妇偷人精品九色| 亚洲成人久久爱视频| bbb黄色大片| 很黄的视频免费| 97超级碰碰碰精品色视频在线观看| 99久国产av精品| 中文字幕免费在线视频6| 蜜桃久久精品国产亚洲av| 又爽又黄a免费视频| 九色国产91popny在线| 啦啦啦观看免费观看视频高清| 99热这里只有是精品50| 国产探花在线观看一区二区| 国产欧美日韩精品一区二区| 免费观看精品视频网站| 亚洲午夜理论影院| 不卡视频在线观看欧美| 国产精品98久久久久久宅男小说| 免费观看在线日韩| 99久久久亚洲精品蜜臀av| 国产乱人视频| 国产三级在线视频| 五月伊人婷婷丁香| 国产91精品成人一区二区三区| 久久精品影院6| 一级毛片久久久久久久久女| а√天堂www在线а√下载| 天天躁日日操中文字幕| 午夜福利视频1000在线观看| 国模一区二区三区四区视频| 国产亚洲精品久久久com| 亚洲四区av| bbb黄色大片| 干丝袜人妻中文字幕| 老司机午夜福利在线观看视频| 欧美日韩亚洲国产一区二区在线观看| av黄色大香蕉| 国内精品久久久久精免费| 人人妻人人看人人澡| 日本熟妇午夜| 在线观看免费视频日本深夜| 国产精品一区二区性色av| 国产视频一区二区在线看| 干丝袜人妻中文字幕| 大又大粗又爽又黄少妇毛片口| 国产一级毛片七仙女欲春2| 精品久久久久久久久av| 欧美日韩瑟瑟在线播放| 欧美三级亚洲精品| 国产乱人视频| 国产 一区精品| 国产伦精品一区二区三区视频9| 欧美黑人欧美精品刺激| 俄罗斯特黄特色一大片| 日韩av在线大香蕉| 一边摸一边抽搐一进一小说| 久9热在线精品视频| 在线看三级毛片| 亚洲精品乱码久久久v下载方式| 亚洲在线观看片| 欧美日韩国产亚洲二区| 黄色一级大片看看| 日韩欧美 国产精品| 国产男靠女视频免费网站| 久久精品夜夜夜夜夜久久蜜豆| 十八禁网站免费在线| 国产一区二区三区在线臀色熟女| av在线天堂中文字幕| 一区二区三区免费毛片| 51国产日韩欧美| 亚洲av不卡在线观看| 久久人妻av系列| 久久久久免费精品人妻一区二区| 黄色配什么色好看| 人妻夜夜爽99麻豆av| 亚洲欧美日韩无卡精品| 色吧在线观看| 亚洲狠狠婷婷综合久久图片| 日本 欧美在线| 国产精品美女特级片免费视频播放器| 极品教师在线视频| 一本精品99久久精品77| 91在线观看av| 亚洲专区国产一区二区| 91久久精品电影网| 精品国产三级普通话版| 精品久久久久久久久av| 欧美激情在线99| 成人性生交大片免费视频hd| 特大巨黑吊av在线直播| 久久久精品大字幕| 老司机深夜福利视频在线观看| 小说图片视频综合网站| 亚洲专区中文字幕在线| 婷婷六月久久综合丁香| 国产一区二区激情短视频| 69av精品久久久久久| 男插女下体视频免费在线播放| 亚洲欧美精品综合久久99| 久久国产精品人妻蜜桃| 免费av观看视频| 女同久久另类99精品国产91| 99国产极品粉嫩在线观看| 黄色女人牲交| 18禁在线播放成人免费| 免费观看的影片在线观看| 一级av片app| 淫妇啪啪啪对白视频| 国产伦在线观看视频一区| 日本黄色视频三级网站网址| 国产精品福利在线免费观看| 久久久久久久久大av| 国产精品女同一区二区软件 | 国产亚洲精品综合一区在线观看| 国产亚洲精品久久久久久毛片| 婷婷精品国产亚洲av在线| 黄色女人牲交| av在线天堂中文字幕| 国内精品宾馆在线| 精品午夜福利视频在线观看一区| 亚洲人成网站高清观看| 黄色一级大片看看| 婷婷精品国产亚洲av在线| 日韩欧美一区二区三区在线观看| 久久精品综合一区二区三区| 91久久精品国产一区二区成人| 日韩 亚洲 欧美在线| 久久精品国产鲁丝片午夜精品 | 麻豆国产97在线/欧美| 国产精品自产拍在线观看55亚洲| 91久久精品国产一区二区成人| 美女 人体艺术 gogo| 国内久久婷婷六月综合欲色啪| 亚洲av中文字字幕乱码综合| 国产精品1区2区在线观看.| 美女cb高潮喷水在线观看| 欧美色视频一区免费| 又爽又黄无遮挡网站| 男女那种视频在线观看| 国产伦在线观看视频一区| 精品一区二区三区人妻视频| 午夜影院日韩av| 国产精品一区二区三区四区久久| 欧美日韩乱码在线| 午夜爱爱视频在线播放| 亚洲美女搞黄在线观看 | 亚洲在线观看片| 人妻制服诱惑在线中文字幕| 国内少妇人妻偷人精品xxx网站| 婷婷六月久久综合丁香| 中文字幕熟女人妻在线| 国产亚洲av嫩草精品影院| 亚洲精品456在线播放app | 亚洲av成人av| 亚洲黑人精品在线| 午夜激情福利司机影院| 老女人水多毛片| 久久久久国产精品人妻aⅴ院| 午夜福利高清视频| 日韩欧美一区二区三区在线观看| 欧美性感艳星| 久久午夜亚洲精品久久| 国内久久婷婷六月综合欲色啪| 国产亚洲精品综合一区在线观看| 国产亚洲精品久久久久久毛片| 亚洲精品日韩av片在线观看| 丰满乱子伦码专区| 99久久精品国产国产毛片| 国产精品伦人一区二区| 久久人妻av系列| 色综合色国产| 亚洲av中文av极速乱 | 最近最新中文字幕大全电影3| 亚洲,欧美,日韩| 国产精品综合久久久久久久免费| 久久久久久伊人网av| 免费人成视频x8x8入口观看| 熟女人妻精品中文字幕| 又黄又爽又刺激的免费视频.| 久久久久久久久久成人| 国内少妇人妻偷人精品xxx网站| 久久精品国产亚洲av香蕉五月| 综合色av麻豆| 毛片女人毛片| 日韩欧美在线二视频| 黄色配什么色好看| 午夜影院日韩av| 舔av片在线| 亚洲欧美日韩高清专用| 精品人妻一区二区三区麻豆 | 亚洲久久久久久中文字幕| 搡老熟女国产l中国老女人| 嫩草影视91久久| 精品久久国产蜜桃| 国内精品宾馆在线| 午夜久久久久精精品| 欧美精品啪啪一区二区三区| 日韩欧美国产一区二区入口| 亚洲精品粉嫩美女一区| 禁无遮挡网站| 级片在线观看| 国产乱人伦免费视频| 亚洲精品日韩av片在线观看| 久久精品综合一区二区三区| 欧美色视频一区免费| 久久人妻av系列| 在线a可以看的网站| 一a级毛片在线观看| 女人十人毛片免费观看3o分钟| bbb黄色大片| 日日摸夜夜添夜夜添小说| 国产一区二区三区视频了| 在线免费观看的www视频| 麻豆成人午夜福利视频| 精品一区二区三区av网在线观看| 亚洲av二区三区四区| 搡女人真爽免费视频火全软件 | 久久精品国产亚洲av香蕉五月| 99国产精品一区二区蜜桃av| 成熟少妇高潮喷水视频| 少妇熟女aⅴ在线视频| 国产男靠女视频免费网站| 精品久久国产蜜桃| 简卡轻食公司| 免费人成在线观看视频色| 永久网站在线| 日本精品一区二区三区蜜桃| 国产成人影院久久av| 中文在线观看免费www的网站| 亚洲中文字幕日韩| 亚洲av.av天堂| 色精品久久人妻99蜜桃| 亚洲久久久久久中文字幕| 亚洲欧美日韩东京热| 一级a爱片免费观看的视频| 国内毛片毛片毛片毛片毛片| x7x7x7水蜜桃| 欧美人与善性xxx| 久久国产乱子免费精品| 亚洲av一区综合| 色视频www国产| 不卡视频在线观看欧美| 久久精品国产自在天天线| 欧美成人性av电影在线观看| 精品日产1卡2卡| 不卡视频在线观看欧美| 黄片wwwwww| 69av精品久久久久久| 国产久久久一区二区三区| 成年版毛片免费区| 热99在线观看视频| 欧美成人一区二区免费高清观看| 亚洲不卡免费看| 日本成人三级电影网站| 色综合亚洲欧美另类图片| 欧美激情在线99| 日韩av在线大香蕉| 麻豆av噜噜一区二区三区| 亚洲无线观看免费| 一级a爱片免费观看的视频| 欧美成人性av电影在线观看| 蜜桃亚洲精品一区二区三区| 两性午夜刺激爽爽歪歪视频在线观看| 精品人妻视频免费看| 日韩欧美免费精品| 成年免费大片在线观看| 亚洲性久久影院| 在线观看一区二区三区| 一边摸一边抽搐一进一小说| 观看免费一级毛片| 成年版毛片免费区| 亚洲美女视频黄频| 亚洲欧美清纯卡通| 免费在线观看日本一区| 男女啪啪激烈高潮av片| 国产精品精品国产色婷婷| 色视频www国产| 国产伦一二天堂av在线观看| 精品人妻视频免费看| 亚洲国产精品成人综合色| 91精品国产九色| 少妇熟女aⅴ在线视频| 草草在线视频免费看| 最后的刺客免费高清国语| 免费在线观看日本一区| 欧美+亚洲+日韩+国产| 校园人妻丝袜中文字幕| 老司机福利观看| 欧美区成人在线视频| 99在线人妻在线中文字幕| 一进一出抽搐动态| 国产精品亚洲美女久久久| 美女大奶头视频| 嫩草影院入口| 国产在线精品亚洲第一网站| 22中文网久久字幕| 18禁在线播放成人免费| 免费黄网站久久成人精品| 色哟哟哟哟哟哟| 中文字幕熟女人妻在线| 欧美中文日本在线观看视频| 精品不卡国产一区二区三区| 国产av不卡久久| bbb黄色大片| 日本熟妇午夜| 国产精品久久久久久精品电影| 亚洲欧美日韩高清专用| 国产伦在线观看视频一区| 少妇被粗大猛烈的视频| 色精品久久人妻99蜜桃| 大又大粗又爽又黄少妇毛片口| 日本五十路高清| 嫩草影院入口| 国产色婷婷99| 午夜福利在线在线| 一区二区三区四区激情视频 | 国产男人的电影天堂91| 18禁裸乳无遮挡免费网站照片| 99热精品在线国产| 亚洲 国产 在线| 岛国在线免费视频观看| 久久久久久久亚洲中文字幕| 在线观看av片永久免费下载| 在线观看美女被高潮喷水网站| 在线播放国产精品三级| 亚洲成人久久性| 一个人免费在线观看电影| av黄色大香蕉| 午夜福利高清视频| 校园人妻丝袜中文字幕| 午夜久久久久精精品| 神马国产精品三级电影在线观看| 欧美激情在线99| 成人一区二区视频在线观看| 国产精品无大码| 一边摸一边抽搐一进一小说| 精品人妻一区二区三区麻豆 | 国产精品人妻久久久久久| 午夜a级毛片| 精品人妻熟女av久视频| 一个人免费在线观看电影| 特大巨黑吊av在线直播| 日本成人三级电影网站| 五月玫瑰六月丁香| 日本撒尿小便嘘嘘汇集6| 三级男女做爰猛烈吃奶摸视频| 国国产精品蜜臀av免费| 欧美成人免费av一区二区三区| 久久香蕉精品热| 久久久久久国产a免费观看| 成人亚洲精品av一区二区| 日本黄大片高清| 嫩草影院新地址| 天堂网av新在线| 国产真实伦视频高清在线观看 | 亚洲经典国产精华液单| 国产精品三级大全| 欧美日韩亚洲国产一区二区在线观看| 1000部很黄的大片| 在线观看美女被高潮喷水网站| 国产大屁股一区二区在线视频| 波多野结衣高清无吗| 99久久无色码亚洲精品果冻| 国产探花在线观看一区二区| 婷婷色综合大香蕉| 午夜精品久久久久久毛片777| 白带黄色成豆腐渣| 日韩强制内射视频| 国产大屁股一区二区在线视频| 亚洲乱码一区二区免费版| 毛片女人毛片| 亚洲国产精品合色在线| 精品久久久久久久久av| 日本三级黄在线观看| 午夜影院日韩av| 精品欧美国产一区二区三| 国产午夜精品论理片| 国产欧美日韩精品亚洲av| 九九爱精品视频在线观看| 男人舔奶头视频| 久久天躁狠狠躁夜夜2o2o| 欧美绝顶高潮抽搐喷水| 男女边吃奶边做爰视频| av在线老鸭窝| 亚洲精品成人久久久久久| 亚洲成人久久爱视频| 国产熟女欧美一区二区| 观看美女的网站| 国产在线男女| 国产精品,欧美在线| 婷婷丁香在线五月| 成人av一区二区三区在线看| 欧美xxxx黑人xx丫x性爽| 久久精品国产亚洲av涩爱 | 国产欧美日韩精品亚洲av| 精品午夜福利视频在线观看一区| 国产爱豆传媒在线观看| 国产精品久久视频播放| 亚洲无线观看免费| 天堂动漫精品| 久久久久久久久久久丰满 | 一级毛片久久久久久久久女| 人妻丰满熟妇av一区二区三区| 少妇被粗大猛烈的视频| 免费在线观看成人毛片| 欧美三级亚洲精品| 一个人观看的视频www高清免费观看| 欧美日本视频| 色哟哟·www| 久久久久久久亚洲中文字幕| 久久精品夜夜夜夜夜久久蜜豆| 成年免费大片在线观看| 国产高潮美女av| 美女cb高潮喷水在线观看| 国产毛片a区久久久久| 亚洲男人的天堂狠狠| 伊人久久精品亚洲午夜| 久久久久久国产a免费观看| 精品人妻一区二区三区麻豆 | 日本-黄色视频高清免费观看| 日韩av在线大香蕉| 亚洲午夜理论影院| 长腿黑丝高跟| 久久久精品大字幕| 国产蜜桃级精品一区二区三区| 欧美中文日本在线观看视频| 男女啪啪激烈高潮av片| 一本一本综合久久| 久久香蕉精品热| 夜夜爽天天搞| 天天一区二区日本电影三级| 狂野欧美激情性xxxx在线观看| 欧美一级a爱片免费观看看| 99久久精品热视频| 欧美成人免费av一区二区三区| 此物有八面人人有两片| 午夜爱爱视频在线播放| 熟女电影av网| 毛片一级片免费看久久久久 | 亚洲成人精品中文字幕电影| 成人性生交大片免费视频hd| 黄色日韩在线| 少妇裸体淫交视频免费看高清| 国产伦精品一区二区三区四那| 亚洲av美国av| 一本精品99久久精品77| 一区福利在线观看| 国产精品伦人一区二区| 99国产极品粉嫩在线观看| 麻豆国产av国片精品| 在线观看66精品国产| 免费搜索国产男女视频| 搞女人的毛片| 俄罗斯特黄特色一大片| 国产欧美日韩精品一区二区| 亚洲av美国av| 中文在线观看免费www的网站| 久久久成人免费电影| 亚洲avbb在线观看| 久久人人精品亚洲av| 午夜激情欧美在线| 国产一级毛片七仙女欲春2| 午夜老司机福利剧场| 国产精品国产高清国产av| 免费大片18禁| 韩国av一区二区三区四区| 亚洲无线在线观看| 美女被艹到高潮喷水动态| 亚洲av免费在线观看| 乱码一卡2卡4卡精品| 久久99热这里只有精品18| 一卡2卡三卡四卡精品乱码亚洲| 欧美又色又爽又黄视频| 国产精品美女特级片免费视频播放器| 身体一侧抽搐| 久久国内精品自在自线图片| 女同久久另类99精品国产91| 99久久无色码亚洲精品果冻| 成人国产综合亚洲| 亚洲国产精品成人综合色| 国产精品乱码一区二三区的特点| 欧美性感艳星| 亚洲国产日韩欧美精品在线观看| 哪里可以看免费的av片| 国产在视频线在精品| 婷婷六月久久综合丁香| 成年女人毛片免费观看观看9| 国产男靠女视频免费网站| bbb黄色大片| 精品不卡国产一区二区三区| 国模一区二区三区四区视频| 国产乱人伦免费视频| 少妇猛男粗大的猛烈进出视频 | www.色视频.com| 亚洲久久久久久中文字幕| www日本黄色视频网| 国产精品伦人一区二区| 午夜福利在线在线| 三级毛片av免费| 中文字幕av成人在线电影| 别揉我奶头~嗯~啊~动态视频| 色哟哟哟哟哟哟| 久久午夜亚洲精品久久| 亚洲中文字幕一区二区三区有码在线看| 男插女下体视频免费在线播放| 国产熟女欧美一区二区| 亚洲欧美清纯卡通| 国产亚洲精品久久久久久毛片| 成人无遮挡网站| 国产精品98久久久久久宅男小说| 午夜福利在线观看吧| 国产亚洲精品久久久久久毛片| 亚洲va在线va天堂va国产| 亚洲中文字幕一区二区三区有码在线看| 日本欧美国产在线视频| 12—13女人毛片做爰片一| 久9热在线精品视频| 欧美一区二区精品小视频在线| 人妻少妇偷人精品九色| 97碰自拍视频| 夜夜夜夜夜久久久久| 国产真实伦视频高清在线观看 | 村上凉子中文字幕在线| 免费看日本二区| 男女下面进入的视频免费午夜| 中文字幕免费在线视频6| 搡女人真爽免费视频火全软件 | 一本一本综合久久| ponron亚洲| 国产中年淑女户外野战色| av中文乱码字幕在线| 国产单亲对白刺激| 少妇人妻一区二区三区视频| 欧美极品一区二区三区四区| 黄色女人牲交| 精品久久久噜噜| 欧美一区二区国产精品久久精品| netflix在线观看网站| 免费观看人在逋| 人妻制服诱惑在线中文字幕| 啪啪无遮挡十八禁网站| 国产视频一区二区在线看| 精品欧美国产一区二区三| 成人毛片a级毛片在线播放| 国产中年淑女户外野战色| 日本五十路高清| 国产淫片久久久久久久久| 日本-黄色视频高清免费观看| 别揉我奶头~嗯~啊~动态视频| 国产一级毛片七仙女欲春2| 简卡轻食公司| 国产av在哪里看| 亚洲欧美精品综合久久99| 国产精品久久久久久精品电影| 观看免费一级毛片| 免费高清视频大片| 赤兔流量卡办理| 观看美女的网站| .国产精品久久| 亚洲最大成人手机在线| 22中文网久久字幕| 日本黄色片子视频| 男女下面进入的视频免费午夜| 别揉我奶头 嗯啊视频| 久久中文看片网| 午夜精品一区二区三区免费看| 亚洲精品粉嫩美女一区| 韩国av一区二区三区四区| 最近中文字幕高清免费大全6 | 国产一区二区在线观看日韩| 色尼玛亚洲综合影院| 亚州av有码| 亚洲精华国产精华液的使用体验 | 国产一级毛片七仙女欲春2| 日韩 亚洲 欧美在线| 国产 一区精品| av黄色大香蕉| 国国产精品蜜臀av免费| 国产伦一二天堂av在线观看|