The Quadrature Theory-based Quartz Crystal Microbalance System With Broad Frequency Range And Adaptive Response Capacity

Nowadays, high precision measuring instruments are regarded as essential tools of scientific research. However, with the more meticulous and deeper technological exploration in all fields, researchers have higher requirements to these low-cost, high- precision and intelligent instruments. Of them, Quartz Crystal Microbalance( QCM), as a new-type resonant micro-parameter sensor, is gaining extensive attention while facing some technical challenges.In order to overcome the shortcomings of existing QCM instruments, such as high requirements for hardware devices, low measurement accuracy, high material cost and high challenge to measure dissipation factor D, a new system scheme based on the Quadrature Demodulation was proposed with the self-adaptive fundamental frequency range of 1-9 MHz. Moreover, it was also capable of measuring both resonant frequency shift △f and factor D continuously.Based on the Direct Digital Frequency Synthesis( DDS) technique, this system utilizes STM32 processor to control several key processes, including signal generation, signal conditioning, data collection and data upload by USB2.0, and uses LABVIEW software on upper computer to process the date and display the measurement results.The effectiveness of the system was verified by three actual experiments. The 7.99 MHz single crystal test indicated that the system reduced the requirements for hardware devices and the measurement accuracy of resonance frequencies was up to expected 0.1 Hz; The superposition of film thickness test of multiply crystals indicated that crystals in the range of 1-9 MHz could be matched and work effectively; And the test of dissipation factor D indicated that the factor D could be more easily measured by this system.