We present a model, verified by experiment, for predicting the moisture absorption and desorption of a range of plastic encapsulant and organic circuit board materials under both nonsaturated and supersaturated steam conditions. This paper was carried out as part of the development of embedded plastic-encapsulated modules (PEMs) for monitoring the internal atmosphere parameters of medical steam sterilizers (autoclaves). The rapid cycles of temperature, pressure, and humidity that are a feature of autoclave operation present unique challenges for the reliability of embedded PEMs. Analysis of moisture absorption and desorption in candidate encapsulant and circuit board materials was, therefore, required for prediction of both moisture ingress and of hygroscopic swelling. This analysis was carried out at three different temperature/humidity/pressure levels (85°C/85%RH/atmospheric, 121°C/100%RH/2 bar, and 134°C/100%RH/3 bar), while desorption was analyzed at both ambient temperature/pressure and in a vacuum oven (0.6 and 0.3 bar) at 85°C, 121°C, and 134°C. Interval weighing was used to monitor the moisture diffusion in the samples and to identify when saturation/desiccation was reached. The moisture diffusion coefficients and the saturated moisture concentrations of the materials were extracted from the test results and a model, verified by experiment, was developed to predict these values for any temperature and humidity combination between 85°C/85%RH and 134°C/100%RH. Measurements of hygroscopic swelling were also carried out as part of the analysis. This is believed to be the first detailed analysis of moisture diffusion in these types of materials over this range of parameters.
Archival electronic tags can be used as standalone data loggers for sampling the ocean for gathering the environmental parameters and studying the migratory patterns of marine species, identifying their feeding and spawning grounds, etc. A prototype archival electronic tag for monitoring the ocean parameters like temperature, pressure and light intensity has been developed. A digital temperature sensor is used to sample the temperature from the tag's surroundings, while a micro machined piezoresistive silicon digital pressure sensor, which is capable of measuring absolute pressure levels upto 14 bars, provides the depth information. One of the important parameters to be measured is the geolocation of the species, which is computed from the ambient light intensities recorded by the digital light sensor in the tag. These parameters can be sampled and recorded in the memory at preset time intervals, as set at the time of deployment of the tag. This minuaturised tag provides the temperature data with 13 bit resolution, while the pressure and light intensity values have 15 bit resolutions. When used in fisheries studies, the size of the device has to be miniaturised, so that by way of attaching such devices, the normal behaviour of the species remain unaffected.
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