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Thick (800 microns) polyvinylidene fluoride/trifluoroethylene copolymer films for transducer applications were poled under applied voltage at high temperatures. A uniformly poled film with a single resonance peak at 1.3 MHz, a nonuniformly poled film with two resonances (1.3 and 2.6 MHz), and a film with bimorph structure with a single resonance at 2.6 MHz, were prepared by utilizing various heat treatments, poling temperatures and poling time. The nonuniform polarization which results from charge injection from the cathode was checked by the pressure wave propagation technique.

The value of acetylcholinesterases (AChE) qualitative analysis as a tool for the diagnosis of fetal neural tube defect has been investigated in a series of 2,815 amniotic fluid samples. This test successfully identified all the 84 cases of open neural tube defects, 16 of which had been missed by ultra-sonography. AChE electrophoresis made it possible to exclude one false positive ultrasound diagnosis of neural tube defect, and to differentiate meningocele from myelomeningocele. Our experience suggests that AChE electrophoresis should be carried out in place of amniotic fluid alpha-fetoprotein estimations, in all cases of fetal abnormality detected by ultrasound scanning especially in fetal hydrocephaly, and in all pregnant women with an history of a previous pregnancy with a neural tube defect.