Passive Noise Control in Incubators

Incubators in the Neonatal Intensive Care Unit (NICU) are known to produce high Sound Pressure Levels (SPL) that can have detrimental effects on infants. Currently measured SPL in NICU's using traditional incubators are above the recommended 45 dB[A] threshold value [1]. Due to operating equipment and environmental noise, the sound level that is perceived by the developing newborn can cause both short and long term hearing loss as well as psychological damage [1].This thesis presents a study on how passive noise control devices can be used to reduce SPL levels in incubator NICU environments. A combination of experimental testing coupled with Finite Element simulations were performed for a modern incubator. In the experimental portion, porous mattresses were analyzed to reduce SPL values. These same test scenarios were modeled using the FE software. Using this model, extensive studies were performed on an arrangement of porous mattress materials with simple foam shapes to determine sound absorbing characteristics of several designs. Data was collected and studied at a NICU at Children's Hospital in Norfolk, Va. Experimental work showed improvement in reducing SPL with multiple thicknesses for different sound absorbing mattresses. The experimental outcomes validated the FE simulation model by showing similar trends at the baby's ears. In simulation work, polyimide foam had the best low frequency performance while polyurethane had the greatest performance in middle and high frequencies. Designs that used full-width foam treatments across the incubator produced the overall greatest reduction in noise around the baby control volume by approximately 26%.