可攜式高壓模組之開發及微電漿氣體感測器系統之建立

Abstract

微電漿指的是放電尺度落在個位數毫米(mm)以下的電漿，常壓下微電漿具有低成本、低功耗、高反應性、體積小等優點。本研究旨在建立一可攜式常壓微電漿系統應用於揮發性有機物(Volatile Organic Compounds, VOCs)之檢測。一般高壓電源具有體積大、價格高昂等缺點，而市售之可攜式高壓模組則具有較差的可調性而難以完美取代笨重的高壓電源。因此本研究中設計一藍芽遙控、可調整操作頻率之高壓模組作為微電漿系統之電壓源。本研究可分為兩部份，首先是藍芽遙控高壓模組之開發與演進，接著是微電漿氣體檢測器之建立。 藍芽遙控高壓模組以智慧型手機作為訊號產生裝置，利用手機內的應用程式設定輸出訊號正弦波的頻率、振幅，輸出訊號藉由藍芽傳輸送至高壓模組上的藍芽音訊接收模組，隨後經過LM386功率放大器，進行波型修飾和功率放大後，作為控制BJT的開關訊號。本研究之高壓模組以行動電源作為直流電壓源，由於直流電無法透過變壓器調整輸出電壓，因此以藍芽訊號控制BJT開關製造電流變化，透過變壓器將電壓升至數千伏用於點起電漿。 藍芽遙控高壓模組有三種操作模式，分別為調節模式、掃描模式、突衝模式。調節模式以固定振幅、頻率輸出正弦波之訊號，固定藍芽遙控模組之操作條件，用於微電漿系統操作窗之尋找和VOCs檢量線之建立；掃描模式則可將振幅或頻率以線性方式連續變化，可在數秒內蒐集未知氣體對不同條件之響應；突衝模式下藍芽訊號以設定之突衝頻率、訊號頻率和開啟訊號時間不斷交替開關，潛在應用為長時間之氣體檢測、以及利用不同粒子之存活時間差調整電漿中粒子的比例等。本研究利用電性和光譜分析不同條件下的電漿表現，以掃描模式分析甲醇、乙醇、異丙醇等VOCs在不同頻率下之光譜差異，顯示微電漿氣體檢測系統發展為電子鼻之可能性；此外，掃描模式可用於尋找不同VOCs最適當之檢量線操作條件，接著利用調節模式建立檢量線。在氬氣環境下當頻率為18kHz時監測CH特徵峰可測得甲醇、乙醇、異丙醇之LOD分別為2.40 ppm、1.25 ppm、761 ppb。

Microplasma refers to plasma discharge with dimensions falling below a few millimeters (mm). Microplasma at atmospheric pressure offers advantages such as low cost, low power consumption, high reactivity, and small size. The aim of this study is to establish a portable atmospheric microplasma system for the detection of Volatile Organic Compounds (VOCs). Conventional high-voltage power supplies used for plasma generation are bulky and expensive. Portable high-voltage modules available in the market lack adjustability, making it difficult to replace the conventional high-voltage power supply. Therefore, in this study, a Bluetooth-controlled high-voltage module with adjustable operating frequency is designed as the voltage source for the microplasma system. The research can be divided into two parts: the development and evolution of the Bluetooth-Modulated Power Source (BMPS), and the establishment of the microplasma gas detector. The Bluetooth-Modulated Power Source (BMPS) uses a smartphone as a signal generation device. The output signal's frequency and amplitude of the sine wave are set through an application on the phone. The output signal is transmitted via Bluetooth to the Bluetooth audio receiver module on the BMPS. It then goes through an LM386 power amplifier for waveform modification and power amplification, serving as the control signal for the BJT switch. In this research, a mobile power supply is used as the DC voltage source for the high-voltage module. Since DC voltage cannot be adjusted through a transformer, the BJT switch is controlled by the Bluetooth signal to create changes in current. The voltage is then increased to several kilovolts using a transformer for plasma ignition. The BMPS has three operating modes: regulate mode, sweep mode, and burst mode. In regulate mode, a fixed amplitude and frequency sinusoidal signal is output, and the operating conditions of the BMPS are fixed. This mode is used to search for the operating window of the microplasma system and establish the VOCs calibration curve. Sweep mode allows continuous linear variations of amplitude or frequency, enabling the collection of responses from unknown gases under different conditions within seconds. In burst mode, the Bluetooth signal alternates between set burst frequency, waveform frequency, and signal-on time, potentially applicable for long-term gas detection and adjusting the particle ratio in plasma based on the difference in particle survival time. This study analyzes plasma performance under different conditions through electrical and spectral analysis. In sweep mode, the spectral differences of VOCs such as methanol, ethanol, and isopropanol at different frequencies are examined, demonstrating the potential of the microplasma gas detection system as an electronic nose. Furthermore, sweep mode can be used to find the optimal operating conditions for different VOCs and establish calibration curves. In an argon environment, when the frequency is 18 kHz, the LODs (Limits of Detection) for detecting methanol, ethanol, and isopropanol are measured as 2.40 ppm, 1.25 ppm, and 761 ppb, respectively.