Thermoformed Liquid Crystal Polymer Packages for Magnetoelastic Frame-Suspended Resonators

This paper describes a micromolding and bonding process for liquid crystal polymer (LCP) packages for miniaturized magnetoelastic resonators. Millimeter-scale magnetoelastic resonators are known to be attractive for tagging applications. To allow deployment in high pressure liquid phase environments, a suitable packaging approach is needed. In this paper, LCP, which is transparent to electromagnetic fields and also chemically resistant, is investigated for packaging. The package, consisting of two hemispherical shells, has an outer diameter of 2.45 mm. The shells are thermoformed with the use of three micro-electrodischarge machined stainless steel molds. Both shells have features to support the frame of the magnetoelastic resonator, ensuring that the active portion of the resonator can vibrate with minimal interaction with the package. A comparison between the response of packaged and unpackaged resonators demonstrates that the packaging does not affect the signal amplitude or resonant frequency of the resonators. The average shear force that the package can endure is 61.1 N. The package prevents the ingress of liquids and allows sensor operation at hydrostatic pressures in excess of 1000 psi (6.9 MPa).