TABLE OF CONTENTS In 1880, Jacques and Pierre Curie [8] showed that when anisotropic crystals were compressed in particular directions, a potential difference, or voltage, was produced between the deformed surfaces and this voltage was found to be proportional to the force applied. The converse effect is also true. Therefore, when a voltage is applied across an anisotropic crystal, such as quartz, it will induce an acoustic wave, which will cause the crystal lattice to move. This acoustic wave will match that of the fundamental frequency, or harmonics, of the crystal and is dependent on its mass. These sensors can thus be called acoustic or mass sensors. In 1959, it was proposed that if a coating of uniform distribution and comparable density was attached to a quartz crystal, a change in the fundamental frequency would result and this change would be proportional to the coating mass. It was proposed that if the polymer film rigidly attached to the quartz surface was a gas chromatography (GC) stationary phase then the polymer could somewhat selectively absorb certain volatile organic solvents. The absorption of these solvents would change in the mass of the polymer, which would be then seen as a change in the fundamental frequency of the quartz to which it was bound. GC coatings were the first coatings used due to their excellent sorption properties and the pre-existing knowledge of their applications.
When the acoustic wave travels through the bulk of the crystal, the sensor is called a bulk acoustic...
