The thin dielectric film capacitive displacement transducer to nanometer

The paper reviews the use of transducers for small displacements (from micrometers to few millimeters) and the advantages of capacitive transducers over other transducers types, and discusses the basic principle of two new transducers de-noted "thin dielectric film capacitive transducer" (TFCT). This principle is based on the properties of a very thin dielectric film between the faced electrodes. The film may be applied, when featured with thickness (TH) TH<1 /spl mu/m, by metallic dielectric, such as allumina, either in gas phase or by electrolysis deposited form. The transducers are designed in a differential form. Two implementation prototypes (IPs) have been designed. The first one (I/spl deg/IP) have been constructed for both linear and rotary displacement transducers by a dielectric spray varnish with TH/spl cong/2 /spl mu/m. In the second one (II/spl deg/IP), in course of construction, a linear displacement transducer has been designed, by a metallic dielectric of allumina deposited by electrolysis with TH/spl cong/510/sup -2/ /spl mu/m. The test results obtained on the I/spl deg/IP and, on this basis previewed for the II/spl deg/IP are critically analyzed. The sensitivity (S) and linearity (L) in ppm detected and previewed respectively are 5 pF/mm, 0.6 pF//spl deg/ and 25; /spl cong/40 pF//spl mu/m and <1; the features for pursuing an L<0.1 ppm are illustrated as well. Based on these previewed results an absolute both scale of capacitance and capacitive voltage divider are proposed as well.