The particle velocity distribution on the surface of AT-cut quartz crystals oscillating in liquid is investigated. The distribution, amplitude, and direction of surface motion are determined. This study improves the understanding of the oscillation characteristics of quartz crystals in solution.

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The particle velocity distribution on an AT-cut quartz crystal oscillating in water is used to model the liquid flow profile near the crystal surface. The nonuniform particle velocity on the quartz surface results in vertical motion in the bulk liquid. This causes a pressure wave to be launched from the quartz surface. This wave is used to measure the velocity of sound in the liquid.

Flexural plate waves can propagate non-radiatively along liquid-immersed plates provided the plate wave velocity is lower than the speed of sound in the liquid. This low-loss condition has been exploited to measure biochemical processes in liquids. Proteins or other biomolecules that adsorb to the plate surface lower the plate wave velocity, while the viscosity of the liquid causes attenuation of the plate wave.Thin plate-wave structures have been formed with microfabrication techniques. The response of these structures has been experimentally calibrated and found to agree well with theory. The plate-wave delay-line oscillator tested has a mass sensitivity which permits the detection of less than ten nanograms of mass adsorbed over the 0.24 cm2 membrane area. Fluid viscosities were measured in the range of zero to 10.6 poise.The plate-wave delay-line oscillator frequency was monitored to study the adsorption of protein onto the Sensor surface in real time. Plate wave attenuation was seen to rise sharply over time as a drop of blood on the sensor coagulated.

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