電氣工程外文翻譯---一種基于單壁碳納米管的納米可調(diào)諧壓力開關(guān)系統(tǒng)的設(shè)計(jì)

1、<p>　　A Nano-Tuneable Pressure Switch System Design Based On Single Wall Carbon Nanotubes</p><p>　　S.S.Hosseini Yazdi and M.Mousavi Mashadi Faculty of Mechanical Engineering,University of Tehran, Iran&l

2、t;/p><p>　　Abstract:Under hydrostatic pressure, the cross section of a Single Wall Carbon Nanotube(SWNT) reduces uniformly and proportionally to the applied pressure until it reaches to SWNT's first transit

3、ion pressure.In addition, SWNT kinks,becomes unstable and collapses on a ground plane due to bending loads.This phenomenon is a function of SWNT diameter. Bending loads can be generated by inducing a voltage between SWNT

4、 and a conductive ground plane. Therefore ,by inducing a certain Pull-in voltage rela</p><p>　　Key words:Single wall carbon nanotube, pull-in voltages, electrostatic bending forces, kink, phase transition, t

5、ransient pressure</p><p>　　INTRODUCTION</p><p>　　Single Wall Carbon Nanotubes(SWNTs) has novel mechanical properties and behaviors which have attracted many considerations and studies recently.

6、Under hydrostatic Pressure, SWNT's cross section is reduced uniformly and proportionally to applied pressure, until it reaches SWNT's first transient pressure. In this case the SWNT physical properties change and

7、 its cross section becomes elliptical. This characteristics has been used in previous presented nano pressure sensors by Wu et al.(2004), When </p><p>　　To overcome the pressure sensing range restriction of

8、the previous introduced switch, in this study, a tuneable pressure switch system has been introduced which can switches with higher resolution using much simpler system. It consists of a fixed ends SWNT and a graphite gr

9、ound plane which are conductive. When various Pull-in voltage are induced, SWNT collapses on the ground plane only if the relative hydrostatic pressures are applied. The upper bound of pressure sensing range of this swit

10、ch is </p><p>　　TRANSITION PRESSURE</p><p>　　Zang et al.(2004), Sun et al.(2004) and Sood (2004) showed that SWNTs under applied hydrostatic pressure encounter phase transition. This phase trans

11、ition is due to difference between energy which is needed to alter Carbon-Carbon bond length and Carbon-Carbon-Carbon angle. At first stage, the SWNT cross section reduces uniformly and proportionally under pressure, whi

12、ch is the result of Carbon-Carbon bond uniform length reduction. At a certain point, the cross section shape collapses from circula</p><p>　　The reason is:</p><p>　　Carbon-Carbon-Carbon angle va

13、riation needs much less energy in comparison to Carbon-Carbon bond length variation. Thus, SWNT undergoes a greater deformation after facing pressure higher than its first transition pressure. As a result, the isotropic

14、SWNT turns into an anisotropic SWNT which is semi-conductive substance. The first SWNT transition pressure is obtained by (Fig.3):</p><p>　　Where R0 is SWNT initial radius and D is SWNT elastic constant. For

15、 SWNTs, D=0.76eV which is obtained by Molecular Dynamics. In consequence, the dimension of Pt1 is:</p><p>　　PULL-IN PHENOMENON</p><p>　　Dequensnes ey al.(2004) has demonstrated when a voltage is

16、 include between a SWNT and a conductive ground plane, the SWNT deflects. When the deflection reaches to a certain amount, SWNT becomes unstable and collapses. This phenomenon is called Pull-in and the relative voltage,

17、Pull-in voltage. The applied electrostatic force per length is found by classic capacitance model as:</p><p>　　Where ε0 is vacuum permittivity, V is include voltage, Rnt is SWNT radius and r is SWNT and grou

18、nd plane distance.</p><p>　　Wang and Varadan(2005) prove that this instability is because of SWNT kink under bending conditions, which has been observed by high resolution transmission electron, when the str

19、ain energy at the inner wall of the compressive side reaches the critical value. Since stress and strain follow a linear distribution in radial direction, it is reasonable to assume that kink instability happens when in-

20、plane strain under uniformly distributed compression. The kink slope being a function of dnt can be f</p><p>　　That L is SWNT length, dNT, is its diameter and h is SWNT effective thickness.</p><p&

21、gt;　　DEFINITION OF TUNEABLE PRESSURE SWITCH</p><p>　　By combining the above mentioned concepts about Pull-in phenomenon and transition pressure of SWNTs, the tuneable pressure switch mechanism can be defined

22、. As it can be seen, from Eq.3, the θer is a function of SWNT diameter. While a hydrostatic pressure is applied on SWNT, its diameter reduces uniformly and proportionally to the applied pressure:</p><p>　　Wh

23、eredNT0 is SWNT's initial diameter (at zero pressure) and E is its effective young Modulus (Fig.5)</p><p>　　To calculate the Pull-in voltage, elastic and electrostatic domains should be considered. Van d

24、er Waals forces are quite small in comparison to electrostatic force; therefore, they are neglected in this study.</p><p>　　The system obeys the classical beam equation</p><p>　　Which is highly

25、none-linear. Therefore, it has no analytical solution. Without losing the generality, it is possible to use lump model derived by Dequensenes et al.(2002) which assumes bending electrostatic force distribution is uniform

26、 before Pull-in phenomenon happens. The pull-in voltage for a lump model is calcuated by:</p><p>　　That rinit is the initial distance between SWNT and ground plane and rpl=2rinit/3 is the distance which Pull

27、-in happens.</p><p>　　By considering RNT as a function of applied pressure, the relation between Pull-in voltage and applied pressure is obtained(Fig.6).</p><p>　　In consequence, the mechanism o

28、f suggested pressure switch consists of a both end fixed SWNT, a conductive ground plane and a tuneable voltage source to induce voltage between the SWNT and the ground plane(Fig.7).</p><p>　　CONCLUSIONS<

29、/p><p>　　In summary, a tuneable pressure switch has been obtained which uses only one SWNT and its mechanism run as following:</p><p>　　When a Pull-in voltage related to a certain pressure is induc

30、ed to the system, the SWNT does not kink and does not on the ground plane, until the applied pressure reaches to that certain amount.When due to the application of pressure and voltage, SWNT collapses on the ground plane

31、, because both of them are conductive, an electric circuit is closed and the switch is considered ON.As a result, its sensing and switching mechanism is much simpler in comparison to previous presented pressure sensor b&

32、lt;/p><p>　　Here for such a typical system, the kink and deflection graphs for two pressure conditions are brought. The SWNT effective physical properties are as followings, which was calculated by authors base

33、d on inter-atomic force field constants for Carbon lattice presented by Leamy(2005);L=27.14nm,dNT0=1.88nm,rinit=6nm,h=0.34nm and Eeffective=1.03nm(Fig.8 and 9).</p><p>　　一種基于單壁碳納米管的納米可調(diào)諧壓力開關(guān)系統(tǒng)的設(shè)計(jì)</p>

34、<p>　　SSHosseini亞茲迪和M.穆薩維Mashadi機(jī)械工程學(xué)院，德黑蘭大學(xué)，伊朗</p><p>　　摘要：在靜水壓力下，單壁碳納米管（SWNT）的截面按比例均勻減少所施加的壓力，直到它達(dá)到單壁碳納米管的第一個(gè)過渡壓力。此外，單壁碳納米管的扭曲，由于彎曲的通道在水平面上變得不穩(wěn)定和塌陷。這種現(xiàn)象顯示的是單壁碳納米管直徑的函數(shù)。彎曲的載荷可以通過誘導(dǎo)產(chǎn)生在單壁碳納米管和傳導(dǎo)的地平面之間的電壓

35、。因此，通過相對(duì)于一定直徑（壓力）施感一定的吸合電壓，直到所施加的壓力達(dá)到一個(gè)可以引起單壁碳納米管直徑減少的確定的數(shù)值，單壁碳納米管才會(huì)倒塌。I在這種情況下，由于單壁碳納米管在水平面的塌陷，在它們之間的就會(huì)有連接使電路斷開。在這項(xiàng)研究中，這些功能是由于采用一個(gè)可調(diào)諧的壓力開關(guān)。這種壓力開關(guān)與前面提出的一個(gè)相比，只是用一種單壁碳納米管的開關(guān)，是能夠在較高的分辨率下感覺壓力并且有一個(gè)簡(jiǎn)單得多的系統(tǒng)。</p><p>

36、　　關(guān)鍵詞：?jiǎn)伪谔技{米管，吸合電壓，靜電彎曲力，扭結(jié)，相變，瞬態(tài)壓力</p><p><b>　　簡(jiǎn)介 </b></p><p>　　單壁碳納米管（SWNTs）最近以其新穎的機(jī)械性能和面板吸引了眾多的使用者和研究者。在靜水壓力作用下，單壁碳納米管的截面按比例均勻減少所施加的壓力，直到它達(dá)到單壁碳納米管的第一個(gè)短暫的壓力。在這種情況下，單壁碳納米管的物理性質(zhì)的改變并且其

37、截面變成橢圓形。這一特點(diǎn)在以前由吳等人在2004年提出的納米壓力傳感器中已經(jīng)使用過。當(dāng)施加的壓力達(dá)到了單壁碳納米管的過渡壓力，其橫截面形狀將會(huì)變化，使單壁碳納米管變成一個(gè)半導(dǎo)電材料。它的壓力傳感系統(tǒng)有能力感知單壁碳納米管開關(guān)從導(dǎo)電材料的變化到半導(dǎo)電物質(zhì)。因此，以這種方式，壓力傳感器需要許多單壁碳納米管。然而，單壁碳納米管數(shù)量的使用由高等人在1998年提出，當(dāng)單壁碳納米管直徑超過一定限制，其天然的形狀是倒塌的形式。因此，在系統(tǒng)中它們是不可

38、能被使用的。結(jié)論，壓力傳感器只能夠感應(yīng)一定數(shù)值的壓力（單壁碳納米管的過渡壓力）（圖1和2）。 </p><p>　　為了克服以前推出的開關(guān)的壓力感應(yīng)范圍的限制，在這項(xiàng)研究中，一個(gè)可調(diào)諧的可以使用非常簡(jiǎn)單的系統(tǒng)切換較高的分辨率壓力開關(guān)系統(tǒng)已經(jīng)推出。它由一端固定的壁碳納米管和可導(dǎo)電的石墨平面組成。當(dāng)各種吸合電壓的誘導(dǎo)，單壁碳納米管倒塌在地平面上只有相對(duì)靜水壓力得到應(yīng)用。此開關(guān)的傳感壓力范圍的上限是第一個(gè)單壁碳納米管的

39、限制壓力。要了解關(guān)于開關(guān)基本的機(jī)械設(shè)計(jì)，單壁碳納米管過渡壓力和上拉的現(xiàn)象都在后續(xù)部分進(jìn)行闡釋。</p><p><b>　　過渡壓力 </b></p><p>　　臧，孫，蘇德等人在2004年研究表明，單壁碳納米管在靜水壓力下相位發(fā)生變化。這種相變現(xiàn)象是由于需要改變碳碳鍵長(zhǎng)和碳碳碳角度的能量不同。在第一階段，單壁碳納米管在壓力下其橫截面部分統(tǒng)一地均勻地減少，這是碳碳鍵

40、統(tǒng)一長(zhǎng)度減少所致。在某一個(gè)點(diǎn)，橫截面形狀由圓形塌陷成橢圓形。在這種情況下，單壁碳納米管的變形也遠(yuǎn)遠(yuǎn)大于先前的。 </p><p><b>　　理由是： </b></p><p>　　碳碳碳角度的變化與碳碳鍵的長(zhǎng)度變化相比需要少得多的能量的。因此，單壁碳納米管在面對(duì)的壓力高于它的過渡壓力時(shí)經(jīng)歷了一次較大的變形。因此，各向同性的單壁碳納米管變成一個(gè)各向異性的半導(dǎo)電物質(zhì)的單

41、壁碳納米管。第一單壁碳納米管的過渡壓力如（圖3）所示： </p><p>　　R0是單壁碳納米管的初始半徑，D為單壁碳納米管彈性常數(shù)。對(duì)于單壁碳納米管，D= 0.76eV這是由分子動(dòng)力學(xué)獲得。結(jié)論，對(duì)Pt1尺寸是：</p><p><b>　　吸合現(xiàn)象 </b></p><p>　　Dequensnes在2004年已經(jīng)證明當(dāng)單壁碳納米管和導(dǎo)電地

42、平面之間有電壓時(shí)，單壁碳納米管偏轉(zhuǎn)。當(dāng)變形達(dá)到一定量時(shí)，單壁碳納米管變得不穩(wěn)定和塌陷。這種現(xiàn)象被稱為吸合和相對(duì)電壓，稱為吸合電壓。適用于發(fā)現(xiàn)的單位長(zhǎng)度的靜電力經(jīng)典電容模型為： </p><p>　　當(dāng)ε0為真空介電常數(shù)，V為包括電壓，Rnt是單壁碳納米管的半徑，R是單壁碳納米管和地平面的距離。 王和Varadan在2005年證明，這種不穩(wěn)定性是因?yàn)閱伪谔技{米管彎曲扭結(jié)條件下，當(dāng)在壓力側(cè)內(nèi)壁應(yīng)變能量達(dá)到臨界值時(shí)，已

43、經(jīng)被高分辨透射電子器觀察到。當(dāng)壓力和應(yīng)變力在徑向方向呈線性分布，當(dāng)發(fā)生在平面內(nèi)均勻分布下的壓縮應(yīng)變時(shí)，扭結(jié)不穩(wěn)定的假設(shè)是合理的?？梢园l(fā)現(xiàn)扭結(jié)形狀變?yōu)镈NT的函數(shù)： </p><p>　　當(dāng)L是單壁碳納米管的長(zhǎng)度，dNT是其直徑，H是單壁碳納米管和有效厚度。 </p><p>　　可調(diào)諧的定義壓力開關(guān) </p><p>　　通過結(jié)合上述關(guān)于吸合現(xiàn)象和單壁碳納米管的躍遷

44、壓力的概念，可調(diào)諧壓力開關(guān)的結(jié)構(gòu)可以被定義。從圖3可以看出θer是單壁碳納米管直徑的函數(shù)。當(dāng)靜水壓力應(yīng)用到單壁碳納米管，它的直徑按比例均勻減少所施加的壓力： </p><p>　　dNT0是單壁碳納米管的初始直徑（在零壓力）和E是其有效楊氏模量（圖5） </p><p>　　為了計(jì)算上拉電壓，彈性和靜電領(lǐng)域應(yīng)予以考慮。范德華力相比于靜電引力要小的多，因此，他們?cè)谶@項(xiàng)研究中被忽略。 該系統(tǒng)遵

45、循的經(jīng)典線性方程 沒有哪一個(gè)是高度非線性的。因此，它沒有解析解。又不失一般性，可以使用Dequensenes在2002年提出的一次性模型得到，即假設(shè)彎曲靜電力分布均勻，然后吸合現(xiàn)象發(fā)生。上拉電壓一次性模型計(jì)算公式： </p><p>　　這rinit是單壁碳納米管和地平面之間和RPL = 2rinit / 3的初始距離是吸合發(fā)生的距離。 </p><p>　　通過考慮RNT作為一種施加壓力

46、的函數(shù)，上拉電壓和施加壓力的關(guān)系就能得到（圖6）。 </p><p>　　結(jié)果，建議的壓力開關(guān)的結(jié)構(gòu)由一個(gè)兩端固定的單壁碳納米管組成，一個(gè)導(dǎo)電地平面和可調(diào)諧電壓源包含單壁碳納米管和地平面的電壓（圖7）。 </p><p><b>　　結(jié)論 </b></p><p>　　綜上所述，一個(gè)只使用一個(gè)單壁碳納米管的可調(diào)諧壓力開關(guān)已經(jīng)生產(chǎn)出來，其運(yùn)行機(jī)制

47、如下： </p><p>　　當(dāng)關(guān)于一定的壓力的吸合電壓誘導(dǎo)系統(tǒng)，直到施加的壓力達(dá)到一定數(shù)值，單壁碳納米管才不會(huì)扭結(jié)并且不會(huì)在地平面上。由于壓力和電壓的應(yīng)用，單壁碳納米管在地平面上塌陷，因?yàn)樗麄兌紝?dǎo)電，電路閉合但開關(guān)被認(rèn)為是打開的。結(jié)果，它的感應(yīng)和轉(zhuǎn)換結(jié)構(gòu)與以前的壓力傳感器相比要簡(jiǎn)單得多，因?yàn)橐粋€(gè)復(fù)雜的系統(tǒng)，可以感受到兩種不同導(dǎo)電和半導(dǎo)電材料的差異被消除。最近的系統(tǒng)，也可以在任何愿望的壓力開關(guān)，它是通過決議索取檢

48、測(cè)范圍內(nèi)是（它的壓力感應(yīng)范圍從零和使用單壁碳納米管的壓力是第一次轉(zhuǎn)換）。因此，它不局限于單壁碳納米管的數(shù)量有限的幾個(gè)轉(zhuǎn)變壓力的壓力。決議的電壓誘因，決定了壓力開關(guān)的決議，其中PtV 。</p><p>　　這是一個(gè)典型的系統(tǒng)，兩個(gè)壓力條件下的扭結(jié)和撓度圖被帶到。單壁碳納米管有效的物理性能如下，這是由原子間力的利米提出碳晶格常數(shù)場(chǎng)的作者在2005年計(jì)算的L = 27.14nm，dNT0 = 1.88nm，rini