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Title: | 以行進波驅動微流體晶片內部液體之研發 Research & Development on a Traveling Wave Driver for a Liquid within a Microfluidic Chip |
Authors: | Pei-Wen Wang 王珮紋 |
Advisor: | 李世光(Chih-Kung Lee) |
Keyword: | 直線型超音波馬達,雙模態激發,微流體驅動, Linear ultrasonic motor,two modes excitation,micropump, |
Publication Year : | 2015 |
Degree: | 碩士 |
Abstract: | 本論文之研究目標乃是運用超音波馬達定子(stator)與轉子(rotator)整合之概念,透過兩片壓電材料PZT(Lead Zirconate Titanate) 黏貼至同一片金屬薄板,並運用這兩片PZT材料在空間上與時間上之相位差來產生行進波(traveling wave)以構成類同於傳統超音波馬達定子的架構,並將此行進波傳遞到類同於傳統超音波馬達轉子上的生醫晶片來驅動流體。操作時,這兩片PZT致動器(actuator)的驅動頻率乃是從這兩片PZT制動器和金屬薄板所構成複合結構的兩相鄰模態間擇定,這個系統操作頻率與傳統超音波馬達將其工作頻率設定在複合結構的共振頻率的情形不同。根據疊加原理(superposition principle),在此頻率驅動的模態形狀可視為兩模態相加,故一般稱之為雙模態激發(two modes excitation),此方法使得壓電材料之規格不需要如一般超音波馬達的要求那樣嚴格。
過往數十年來,一直判定直線式超音波馬達效率較低的主要原因乃是因為此類馬達,相較於更常見的旋轉式超音波馬達缺少一個旋轉半徑這個重要優化參數之故。在本論文的研究過程中,卻發現這個理念有著基本思路上的錯誤。行進波驅動的超音波馬達的各種架構中,最有效且最容易應用的方式,乃是在結構中產生兩個時間與空間均相差90度的駐波(standing wave),藉由這兩個駐波的合成,乃能形成一個可任意改變方向的行進波。前述這個早已熟知的基本原理,在旋轉式超音波馬達中,因為沒有邊界效應的限制,所以可以完美的被實現。但此一理念施行於本論文所嘗試建構的有限長度直線式超音波馬達時,卻面臨行進波到達邊界時,將依邊界的不同而產生不同的反射波,這些反射波將會與結構中原先被驅動的兩個行進波相疊合,進而破壞整個驅動架構所奠基的基本原理,導致整個直線式超音波馬達的超低效率,或甚至是無法驅動! 本論文在研究過程中,嘗試迴避前述所提邊界效應的影響,首次提出所謂的在結構中產生兩個空間相差90度駐波(standing wave)的必要條件,可以運用有限結構中模態正交(orthogonal)的條件來達成。依據這個創新的研究成果,本論文乃能建構出不同邊界條件下,ㄧ維板(one dimensional plate)與樑(beam)結構的四種基礎波動形式,不論其為正弦(sine)或是餘弦(cosine)函數的組合,還是雙曲正弦(hyperbolic sine)與雙曲餘弦(hyperbolic cosine)的共同組合,均可尋求出空間上模態正交的必要條件,經由這個理論與基本觀念的突破,借用習知的雙模態激發形式在ㄧ維直線結構中驅動附著於結構上的兩個壓電陶瓷致動器,乃能正確且有效率的激發出所需的行進體波。 研究過程中,藉由討論不同邊界條件下所形成之模態形狀,來分析各個相鄰模態間的相位差,以COMSOL有限元素挑選理想的工作頻率,接著透過調變外加電壓來改變致動器之形變量,進而達到流體驅動之流率控制,研究結果確認除了藉由電壓來控制流率之外,亦可以相位差之轉換來改變驅動方向。本論文製作的直線型行進波式微流體驅動裝置,所選擇的驅動頻率為13795.5 Hz,以COMSOL模擬不同電壓下之振幅與時間之關係,同時也透過雷射位移計來確認模擬值之誤差,隨著驅動電壓增加,致動器之振幅也隨之越大,實驗檢驗了施加電壓與流體驅動速度之關係,確認了流體驅動之流率與振幅、還有外加電壓均呈現線性關係。 值得注意的乃是,雖然本論文運用這類型的有限長度直線式超音波馬達來驅動生醫晶片,以驗證其可行性,更重要的乃是,本論文所完成的創新發明,突破了傳統直線式超音波馬達的限制,因此可擴展本論文的致動器成果到微小機器人、超精密移動/定位平台、自走式超精密機械等各種超精密的移動裝置,在運作過程中,更可透過驅動特定模態及其對應的固有頻率(eigen-frequency)來輕易控制移動方向及速度。 In this thesis, we present a non-traditional micro-pump with its working principle based on the same concept as that of a traditional linear ultrasonic motor. Two pieces of piezoelectric material PZT (Lead Zirconate Titanate) were bonded onto a thin steel plate to serve as the vibration source. The traveling wave generated by the phase difference of these two PZT actuators formed a structure similar to that of the stator of a traditional linear ultrasonic motor. The traveling wave generated was then transmitted to a biochip, which served the same function as that of the rotor of a traditional linear ultrasonic motor, to drive the liquid. The system working frequency was set at a frequency located between the resonant frequencies of two neighbored modes of the elastic structure formed by the steel plate and the two PZT’s. It is to be noted that this operating frequency is different from the operating frequency of the traditional linear ultrasonic motor, which is selected at one of the resonant frequency of the natural mode. According to the superposition principle, driving the two PZT actuators at the selected frequency mentioned above, the mode shape can be approximated as the superposition of the two natural modes. This excitation approach is thus properly called as two modes excitation. It is to be noted that this two modes excitation approach poses less stringent requirements on the piezoelectric materials and the structural design as that of the traditional ultrasonic motor. Over the last few decades, the low efficiency associated with linear ultrasonic motor has always been attributed to the one less optimization parameter, the radius of the stator and the rotor, when compared to the rotary type ultrasonic motor. This concept was identified to have a fundamental flaw. More specifically, generating two standing waves with 90 degree spatial and temporal phase difference to create a traveling wave within the stator of an ultrasonic motor has been identified to be the most fundamental configuration of an ultrasonic motor. This concept can be perfectly executed in rotary type ultrasonic motor as the boundary effect will not come into play. In comparison, when the traveling wave impinge on the boundary of a finite-dimensional linear ultrasonic motor, the reflected wave generated by the boundary will superimpose onto the original traveling waves to destroy the underlying driving principle mentioned above. This effect was identified to be the cause of low efficiency or even non-functional in linear ultrasonic motor during the course of this thesis study. Trying to circumvent the detrimental effects induced by the boundary mentioned above, this thesis first proposed that the requirement of having two spatial 90 degree difference standing waves can be achieved by having two orthogonal modes serve as the two standing waves with 90 degree spatial phase difference. Taking these research results, the four waves, i.e., sine, cosine, hyperbolic sine, and hyperbolic cosine waves, then can be adopted to understand and to design the spatially driving conditions needed. It is also to be noted that the traditional two-mode excitation approach then can be perfectly implemented to excite the two piezoelectric ceramic actuators so as to create the high efficiency traveling bulk wave. The boundary effect had been considered by analyzing the different mode shapes in different conditions. The proper operating frequency was first chosen by simulation done by a commercial finite element software COMSOL. The traveling wave generated by the actuator was utilized to drive the fluid in the channel and the steel plate excited accordingly was identified to be tailorable by varying the applying voltage. Changing the phase difference between the stator and the rotor that forms the actuator was found to vary the driven direction of the liquid. The operating frequency of the device developed in this thesis is 13795.5 Hz. By simulating the relationship between the applied voltage and the induced deformation, the deformation was found to increase with the increase of the externally applied voltage. This simulation results were verified by using a laser displacement sensor to measure the induced steel plate deformation with respect to different driving voltage. The speed and the direction of the driving fluid were verified both by simulation and by experiments to be controllable by varying the amplitude and the phase difference of the applied voltage and the flow rate of the liquid driven was linearly dependent to the steel plate vibration amplitude and thus linearly dependent to the externally applied voltage. It is worth noting that even though this thesis utilized biochip as the verification platform for the newly invented linear ultrasonic motor, the innovative results achieved can have applications ranging from micro-robots, ultra-high precision moving stages, self-walking high-precision machineries. The moving speed and traveling directions can all be easily controlled by inducing different vibrational modes and their corresponding eigen-frequencies. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/52201 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 工程科學及海洋工程學系 |
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ntu-104-1.pdf Restricted Access | 5.53 MB | Adobe PDF |
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