A flowmeter operating with plate waves induced by piezoelectric thick films

Using PZT-based thick films on alumina, volumetric and mass liquid flowmeters have been implemented and their performances have been tested. The flat metal pipe walls serve as acoustic wave guides. Two pairs of piezoelectric devices provided with interdigital electrodes launch and detect plate flexural waves, whose patterns propagate in mutually opposite directions while their velocities appear to be affected by the liquid flow in the pipe. Two different flowmeter designs have been studied. In the first one, efficient propagation of plate waves in the MHz region is obtained by injecting in the guides waves generated by a proper piezoelectric thick film device; in the second design, plate waves with operating frequencies lower than 100 KHz are induced in the guides by a piezoelectric device of different configuration. Both designs are provided with an oscillator which synchronously drives the two guides at the same operating frequency. The change in phase difference between the piezoelectric signals induced in the two receivers, due to the change of the flow velocity, is taken as the sensors´ output. Procedures of implementation as well as performance characteristics of the tested flowmeters are presented