Millimeter-Scale Encapsulation of Wireless Resonators for Environmental and Biomedical Sensing Applications

Abstract:

Wireless micro resonators such as miniaturized magnetoelastic resonators are useful for remote mapping and sensing in environments that are harsh or otherwise difficult to access. Compared to other wireless resonators, magnetoelastic devices are attractive because of their inherently wireless nature, and their ability to operate passively without a power source, integrated circuitry, or antenna. An open challenge for using the miniaturized magnetoelastic resonators is application-tailored encapsulation and packaging. General packaging considerations for magnetoelastic resonators include not only the mechanical design but also electromagnetic transparency, adaptability of form factor with appropriate feature size, and chemical inertness and/or biocompatibility.
In this research, the packaging of magnetoelastic resonators is investigated in two contexts: one, environmental sensing and the other, biomedical sensing. The first context is for tagging and mapping applications in an environment that is at high temperature (‰¥ 150 °~C), is at high pressure (‰¥ 10 MPa), and is corrosive, such as a hydraulic fracture branching from a wellbore. This work utilizes for the first time a micro molding process to thermoform liquid crystal polymer (LCP) packages for protecting magnetoelastic resonators. The package is < –10 mm —^3 and includes micron-scale features to support the resonator and allow the resonator to vibrate with low loss. The second context is the encapsulation of implantable magnetoelastic resonators, which are used for sensing biological parameters. These packages must: protect the sensors during deployment through an endoscope, be biocompatible and chemically inert, be able to pass through a complex delivery path, and fit within a diameter of 2.54 mm. Protecting the resonator during delivery while still allowing interaction with biological fluids is achieved with 3D printed polymeric packages incorporating features like tapered and smoothed edges and a perforated housing. The wireless range of the sensor is larger than 15 cm and therefore can provide clinical utility.