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A Liquid Density Sensor Based on AlN Piezoelectric Micromachined Ultrasonic Transducer Insensitive to Liquid Viscosity
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DOI：10.1109/ted.2026.3705765.png)
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Abstract
En 中文
To overcome the limitations of conventional liquid density sensors, including bulky size, significant sample requirements, and challenges in automation, MEMS-based liquid density sensors have been developed. However, the viscosity–density coupling effect often compromises accuracy in high-viscosity liquids. Although various decoupling strategies have been proposed, they often suffer from complexity and inefficiency. For the first time, this study presents an AlN-based piezoelectric micromachined ultrasonic transducer (PMUT) liquid density sensor insensitive to viscosity interference. The sensor employs two identical PMUTs, functioning as transmitter and receiver, respectively. An ultrasonic wave generated by the transmitter is reflected by the liquid surface and detected by the receiver. Theoretical calculations demonstrate that when the excitation frequency remains constant, the amplitude of the received electrical signal exhibits a specific relationship with liquid density, while the viscosity-induced signal amplitude variation becomes negligible. Therefore, after calibrating the PMUT liquid density sensor by fitting the received signal amplitude versus density curves across 0%–100% glycerol aqueous solutions and 0%–100% ethanol aqueous solutions, the device can measure densities of homogeneous pure solutions with different viscosities within the range of 0.7890–1.2610 g/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>. It is primarily sensitive to liquid density and shows negligible sensitivity to viscosity variations under the tested conditions. Experimental results show that the sensor can accurately measure the density of isopropyl alcohol (IPA), propylene glycol, and polyethylene glycol 400 (PEG 400) aqueous solutions using the glycerol aqueous solutions and ethanol aqueous solutions calibrated fitting formula, with the calculated density error rate between measured densities by the calibration curves and actual densities below 0.125%, demonstrating measurement insensitivity to viscosity differences among the homogeneous pure liquids.
Keywords:
Liquid density
piezoelectric micromachined ultrasonic transducer (PMUT)
resolution
resonant frequency
segmented fixed-frequency
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