Abstract
This paper presents a comprehensive study on a low-cost, real-time frequency matching circuit for a high sensitivity gas flow sensor based on cMUTs (Capacitive Micromachined Ultrasonic Transducer). The gas flow sensor is designed with a focus on the mechanical resonance of the moving membrane. It measures gas velocity using the differential transit time method. Custom cMUTs with a resonance frequency of 2.44 MHz were designed and fabricated. The fabrication process involves a 7-step lithography process with thin-film surface micro-machining technology. The frequency matching circuit, implemented around a microcontroller, uses conductance measurement and bias voltage sweeping to match resonance frequencies of two cMUTs to the excitation frequency. The flow sensor was tested over a full-scale range with air flow of ± 50 standard cubic centimeters per minute (sccm), showing a maximum flow error within 0.8 % of the full-scale (FS), demonstrating the state-of-the-art sensitivity of cMUT-based gas flow sensors in the literature. The real-time frequency matching circuit significantly reduces zero-flow drift over a temperature range of 0–50 °C, from 1.3 % FS to 0.3 % FS. The sensor offers high accuracy and low-cost advantages for ultrasound-based gas flow measurement applications.
Original language | English |
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Article number | 116252 |
Journal | Sensors and Actuators A: Physical |
Volume | 383 |
DOIs | |
Publication status | Published - 1 Mar 2025 |
MoE publication type | A1 Journal article-refereed |
Funding
This research was funded by the Finnish Government Grant to VTT.
Keywords
- CMUT
- Frequency matching
- Ultrasound flow measurement