隨著智慧監測系統與低功耗感測元件日益普及，如何在低速旋轉機械、風力設備及不易更換電池的環境中，需要可以提供穩定且長時間運作的電力來源。壓電獵能器具有結構簡單、體積小及輸出電壓較高等優點，可將環境中的機械振動轉換為電能。傳統壓電獵能器僅能於激振頻率接近自然頻率時獲得較佳輸出，在低頻、低轉速或變動頻率的環境中，容易受到頻率不匹配的限制。
本研究提出一種應用非對稱磁性撥動之低速旋轉升頻轉換壓電獵能器，當大旋轉臂受馬達驅動時，偏心盤在重力與旋轉慣性作用下產生週期性擺動，使磁鐵反覆接近壓電懸臂樑，形成非接觸式磁力撥動，將低頻旋轉運動轉換為壓電樑之振動響應。
理論分析方面，本研究利用點磁偶極近似建立磁力模型，並透過傅立葉級數展開分析磁力函數中的諧波成分。並採用能量法與拉格朗日方程推導偏心盤運動方程，包含推導二模態之壓電懸臂樑機電耦合模型。實驗部分則透過影像追蹤、自然頻率掃描、靜態剛性量測、阻尼辨識、磁力曲線量測及機電耦合係數實驗，取得模型所需參數並進行驗證。
實驗結果顯示，壓電懸臂樑之第一與第二模態自然頻率分別約為 9.49 Hz 與 65.01 Hz，最佳負載電阻約為 330 kΩ，與理論預測趨勢相符。非對稱式雙磁鐵兩點激發可改變磁力波形與諧波組成，使系統於多個低速轉速區間產生局部輸出峰值。頻域分析亦顯示，接近第二模態自然頻率的範圍內可觀察到局部峰值，證明第二模態可受到磁力激發，但其對總輸出之貢獻仍相對有限。
綜合而言，本研究所提出之非對稱式雙磁鐵兩點磁力激發架構，可改善傳統單點激發僅能於特定轉速下獲得較佳輸出的限制。所建立之磁力模型、傅立葉展開方法及二模態機電耦合模型，可作為將來進行磁鐵配置最佳化與低速旋轉壓電獵能器設計之參考。

This study proposes a low-speed rotational frequency up-conversion piezoelectric energy harvester based on asymmetric magnetic plucking to address the frequency mismatch of conventional resonant harvesters. The system uses the periodic oscillation of an eccentric pendulum to generate non-contact magnetic excitation, converting low-frequency rotation into vibration of a piezoelectric cantilever beam. A magnetic force model was established using the point magnetic dipole approximation, and Fourier series expansion was applied to identify the harmonic components. The eccentric pendulum motion was derived using the energy method and Lagrange’s equation, while a two-mode electromechanical coupling model was developed for the piezoelectric beam.
Experiments including image tracking, natural frequency measurement, stiffness measurement, damping identification, magnetic force measurement, load resistance testing, and electromechanical coupling tests were conducted to obtain model parameters and verify the analysis.
The results show that the first and second natural frequencies are approximately 9.49 Hz and 65.01 Hz, and the optimal load resistance is about 330 kΩ. The asymmetric multi-magnet two-point excitation increases harmonic components and modifies the magnetic force waveform, producing local output peaks over several low-speed ranges and broadening the operating bandwidth. Frequency-domain analysis also shows that the second vibration mode can be excited, but its contribution remains limited. The proposed model and excitation structure can serve as references for future magnet arrangement optimization.

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