薄圓盤型壓電變壓器之設計、製作與性能測試

Design, Fabrication and Performance Test of Thin Disc Piezoelectric Transformers

本文探討薄圓盤型壓電變壓器之設計、製作與性能測試。首先，利用薄圓盤型壓電蜂鳴片製作出薄圓盤型壓電變壓器，此蜂鳴片係由壓電陶瓷圓盤、鋁合金圓盤及銀電極所組成，以及在銀電極表面上施作一條環狀切割圓以製作出壓電變壓器之輸入、輸出電極，其中環狀切割圓與壓電陶瓷圓盤、鋁合金圓盤及銀電極為同心圓，且鋁合金圓盤被視為壓電變壓器之共同電極。其次，探討壓電變壓器之機電轉換原理，以及利用碳粉顯影技術直接觀測壓電蜂鳴片之振動模態及其節點圓，此振動模態勢辨別感應電荷分佈狀態之重要依據。接著，藉由壓電變壓器之等效電路模型可以推導出電壓增益公式，以及完成驅動與量測系統架構以獲取在不同的環狀切割圓直徑及負載電阻下之電壓增益量測數據。根據驗結果，探討環狀切割圓固定時之電壓增益、驅動頻率與負載電阻三者間之關係，以及探討環狀切割圓之大小對最大電壓增益及其對應頻率之影響。最後，探討如何安排環狀切割圓至最佳位置以製作出高電壓增益之薄圓盤型壓電變壓器。

This paper investigates the design, fabrication and performance test of a thin disc piezoelectric transformer (PT). The PT is based on a piezoelectric buzzer, including a piezoceramic disk, a nickel-alloy disk and a silver electrode, using a ring-shaped gap circle on the silver electrode to form an input electrode and an output electrode for the PT. The nickel-alloy disk acts as a common electrode of the PT. The gap circle, piezoceramic disk, nickel-alloy disk and silver electrode are concentric circles. Electromechanical conversion theorems for the PT are expressed, and a carbon power imaging technique is applied to directly observe vibration modes of the buzzer and their nodal circles. The vibration modes are very useful for judging distributions of positive and negative electric charges on the silver electrode. Moreover, a formula of voltage gain is derived from an equivalent circuit model of the PT connected to a sine wave voltage, and a driving and measuring system is constructed to measure amplitudes of input and output voltages applied to determine voltage gains under various diameters of gap circles and load resistances. From measured results, relationships between voltage gains, driving frequencies and load resistances for a constant diameter of gap circle are discussed, and effects of diameters of gap circles on maximum voltage gains and their related driving frequencies are studied. Finally, an optimal ring-shaped gap circle for creating a thin disc PT with high voltage gains is found.