以壓電式微加工超音波感測器陣列實現指向性麥克風系統

Abstract

隨著物聯網與工業4.0的發展，傳感器需求持續增長，微機電系統(MEMS)技術的成熟推動了壓電式微加工超音波感測器(PMUT)的廣泛應用。PMUT因其小型化、低功耗與高性能，廣泛應用於消費電子、車用電子、智慧工廠及醫療領域。相較傳統單體感測器，PMUT陣列具備更優異的性能，其可進行距離測量與三維空間掃描，適用於智慧工廠及先進駕駛輔助系統(ADAS)等應用。 本研究旨在開發壓電式微加工超音波感測器陣列，以實現指向性麥克風的功能。製程上採用不鏽鋼基板，結合微機電製程與氣膠沉積技術製作壓電感測器陣列元件，並與自行設計含有pogo pin的PCB板整合，取代傳統使用探針連接試片的方式，提升了系統的穩定性與實用性。 在性能量測中，當量測距離為30 cm，高音喇叭驅動電壓為12 Vpp時，感測器共振頻率為39.5 kHz。在聲壓位準94 dB的條件下，感測器輸出電壓為19.15 mV，背景雜訊為0.82 mV，對應的訊噪比為27.37 dB。並計算得出感測器平均靈敏度為 - 40.65 dBV，其推算之聲壓位準的相對誤差小於1.83%。在遠距離測量中，當高音喇叭以8-12 Vpp驅動且以訊噪比12 dB為閥值時，感測器的有效量測距離達1.5 m。此外，指向性量測顯示，感測器在水平與垂直方向上均呈現全指向性分佈。 在感測器陣列的應用中，基於測量結果，選取共振頻率相近的33至36號感測器組成一維線性均勻陣列，實現了指向性麥克風的功能，並進一步驗證了壓電感測器陣列結合波束形成技術在不同聲源角度下的方向估算能力。

The rapid advancement of the Internet of Things (IoT) and Industry 4.0 has significantly increased the demand for sensors. The maturation of micro-electromechanical systems (MEMS) technology has enabled the widespread adoption of piezoelectric micromachined ultrasonic transducers (PMUTs). With their miniaturized design, low power consumption, and high performance, PMUTs have shown great potential in consumer electronics, automotive applications, smart manufacturing, and healthcare. Compared to conventional single-element sensors, PMUT arrays offer superior performance, supporting both precise distance measurement and three-dimensional spatial scanning. These attributes make PMUT arrays ideal for smart factories and advanced driver assistance systems (ADAS) This study aims to develop a piezoelectric micromachined ultrasonic sensor array to realize directional microphone functionality. The fabrication process utilizes stainless steel substrates in conjunction with MEMS technology and aerosol deposition techniques to produce piezoelectric sensing elements. These elements are integrated with a custom-designed PCB board featuring pogo pins, replacing traditional probe-based sample connections. This design enhances both the stability and practicality of the system. In performance evaluations, the sensor demonstrated a resonance frequency of 39.5 kHz when tested at a distance of 30 cm with a tweeter driving voltage of 12 Vpp. Under a sound pressure level (SPL) of 94 dB, the sensor achieved an output voltage of 19.15 mV with background noise of 0.82 mV, resulting in a signal-to-noise ratio (SNR) of 27.37 dB. The average sensitivity of the sensor was calculated to be -40.65 dBV, and the relative error in SPL estimation was less than 1.83%. For long-range detection, the sensor achieved an effective measurement range of 1.5 m when the tweeter was driven at 8–12 Vpp and an SNR threshold of 12 dB was used. Additionally, directivity measurement revealed an omnidirectional distribution of the sensor’s performance in both horizontal and vertical orientations. For sensor array applications, measurement results identified sensors numbered 33 to 36, which exhibited closely matched resonance frequencies, as suitable candidates to form a one-dimensional linear uniform array. This array not only successfully achieved directional microphone functionality but also validated the piezoelectric sensor array’s ability to estimate directional angles using beamforming techniques across various sound source conditions.