COMPARISON OF 2 METHODS FOR COATING PIEZOELECTRIC-CRYSTALS

Quartz piezoelectric crystals were coated with triethanolamine using t wo procedures: spray and syringe methods. The reproducibility of both coating methods was evaluated comparing the relative standard deviatio n of batches of four crystals coated by each of the procedures. The re lative standard deviation obtained with the spray method is a hyperbol ic function of the coating frequency and is, at least, three times low er than the one calculated from results of the syringe method, which i s not frequency dependent. An explanation for the poorer reproducibili ty of the syringe method is given, based on the radial sensitivity the ory and the non-uniformity of the coating distribution over the crysta l, as evidenced by microscopic photographs.