A Steam Sterilizable Plastic-Encapsulated Wireless Sensor Module

This paper presents a plastic-encapsulated wireless sensor module (WSM), using commercial off-the-shelf components, which has been demonstrated to be reliable for 180 cycles in a medical steam sterilizer with an environment involving highrate temperature, pressure, and humidity cycles up to 134 °C, 3 bar, 100% RH. The WSM continuously transmits temperature and pressure data from the sterilizer, allowing the quality of sterilization to be verified. Twelve WSMs were assembled and encapsulated with substrate material and encapsulant type as experimental variables. These samples were then stress tested over multiple sterilization cycles, with continuous wireless data collection, until failure. Scanning acoustic microscope analysis was carried out before and after the reliability testing in the steam sterilizer. The results demonstrate that, with appropriate choice of materials, the WSM can survive for 180 full-steam sterilization cycles without any electrical failure of the components or any deterioration in the package structure except for delamination between the substrate and the encapsulant that did not cause electrical failure. The overall results demonstrate the reliability of a plastic-encapsulated module in an exceptionally harsh use environment, the ability to steam sterilize a plastic-encapsulated module for medical applications, and the potential for using a plastic-encapsulated WSM for continuous, high-resolution sterilizer parameter monitoring as a replacement for the currently used color-change chemical and biological indicators. This is believed to be the first plastic-encapsulated WSM for monitoring of steam sterilizer parameters and the first plastic-encapsulated module of any sort, which is capable of surviving multiple steam sterilization cycles.