A novel measurement method for liquid density sensing using piezoelectric excited millimetric sized sensors

The piezoelectric excited millimetric sized cantilevers (PEMCs) have excellent advantages to be used in liquid environments for sensory applications since their quality factor decreases less, compared to micro and nano-sized ones. This makes PEMCs very useful for measuring density and viscosity of liquids. The principle is based on the fact that any environmental and/or structural changes lead to a shift in resonant frequency determined by measuring the electro-mechanical impedance of piezoelectric layer attached to cantilever. In this study, a novel measurement method instead of conventional chirp method is proposed, developed and implemented to measure, record and process the impedance signal of piezoelectric patches attached to PEMC using a data acquisition card. In this method, a discrete frequency sinusoidal signal is used to excite PEMC for density measurement in liquid for a wide range of frequency (<100 kHz). The conventional chirp method has disadvantages such as inaccuracy in measurements and underestimation of sensor sensitivity at low frequencies (<10 kHz) and needing a large amount of memory to store the measured data. Applying this novel measurement method, a high resolution of 0.01 Hz is achieved which allows detecting a liquid density change as small as 0.0072 kg/m3.