Microacoustic Sensors for Liquid Monitoring

Abstract

In recent years, much effort has been expended to developing miniaturized, reliable sensors for measuring physical and chemical liquid properties. Microacoustic devices may be employed to determinate physical quantities perturbing the propagation conditions of the acoustic wave, even in liquid environments. For liquid sensors, acoustic modes with shear polarization are often used in order to avoid radiation losses. Examples are shear bulk modes, surface skimming bulk waves, shear-horizontal acoustic plate modes, and Love modes. Furthermore, modes with sagittal polarization may be applied if their phase velocity is sufficiently lower than the sound velocity in the adjacent liquid. General interactions between acoustic waves and liquids are viscous coupling, acoustoelectric effects, and mass loading. The resulting changes in device frequency and attenuation may be utilized for sensing purposes.The general advantages of microacoustic sensors are high sensitivity, simple fabrication, and quasidigital frequency readout. Hence, a wide variety of devices based on different modes for very different applications has been discussed in the relevant literature. The aim of this review is to provide a systematic overview of microacoustic sensors particularlay suited for operation in liquids.First, we provide a brief introductionto surfaceacousticwave devices and the underlying physics, basic microacoustic structures, and general measurement techniques. A description of the mechanisms of interaction between liquids and acoustic waves is then followed by a comprehensive survey covering the different types of microacoustic liquid sensors, with emphasis on the mode-specific device properties. Thereafter, aspects of material selection and device fabrication are summarized. Lastly, an overview is given indicating where microacoustic liquid sensors have already been put into practice and where their application may be expected in the near future.

Taste sensors utilizing high-frequency SH-SAW devices

“…The 'optical electronic tongue' [6] mimics the mammalian tongue and has the ability to assay solution content for Ca 2+ , Ce 3+ , H + and fructose using colourimetric indicators. In the field of acoustic devices, quartz crystal microbalances (QCM) were the first ones used as sensors and they rely on the frequency changes due to mass changing on the device surface [7,8]. Using an array of such devices coated with hydrophilic mono-and dicarbon acids, organic and inorganic acids and amines in drinking water have been detected [9].…”

“…One advantage of high-frequency acoustic devices is that of increased sensitivity-e.g. for quartz crystal microbalances the sensitivity increases with the square of the resonant frequency [8]. The majority of SAW resonators have been used mainly for gaseous phase measurements [14][15][16][17] and very few liquid applications with SAW resonators have been reported.…”

Lamb wave sensors array for nonviscous liquid sensing

“…Furthermore, these effects on the sensors usually couple together. In order to separate these effects and measure a certain liquid property, a variety of liquid microacoustic sensors with different modes and configurations are presented [1,4,5] . As far as sensitivity is concerned, Lamb wave sensors are the best among various sensors.…”

“…Microacoustic sensors can be employed to measure physical, chemical and biological liquid properties, which get rapid developments in recent years [1][2][3][4][5][6][7][8][9] . The sensors are influenced by the mechanical properties of the adjacent liquid, such as liquid density and the added mass loading in the liquid.…”

“…However, most of these configurations require bilayer or multilayer plate structures and sometimes even additional membranes, resulting in the complexity of fabrication [1,8,9] . Joshi [10] studied the characteristics of Lamb wave in a piezoelectric plate with free boundary conditions, and recently Yang [11] pursued the theoretical and experimental research on Lamb wave propagation in a piezoelectric plate www.scichina.com www.springerlink.com subjected to fluid loadings.…”