The transmitted noise reduction (NR) of passive and active hybrid panels is experimentally studied. The concept of hybrid panels is based on a combined approach for noise controls: a passive approach for mid and high frequencies and an active approach for low frequencies. Active and passive hybrid panels are demonstrated. An active-hybrid single panel is made with a plate structure on which piezoelectric sensor/actuators are bonded in conjunction with a simple controller. Sound absorbing material is bonded on the structure to effectively reduce the transmitted noise in mid frequencies. An active-hybrid double panel is also made by using another single plate to maintain an air gap. To prove the concept of hybrid panels, an acoustic measurement experiment is performed. Instead of using the active control system, a passive shunt damping is used for the NR in low frequencies. This is called a passive-hybrid panel. The use of sound absorbing material and an air gap is effective for noise control in mid and high frequencies. Meanwhile, the active approach and the passive shunt approach are useful for noise control at lower resonance modes. These hybrid panels demonstrate the potential for NR at broadband frequencies.
Noise generated in the intensive care unit (ICU) adversely affects both critically ill patients and medical staff. Recently, several attempts have been made to reduce ICU noise levels, but reliable and effective solutions remain elusive. This study aimed to provide evidence on noise distributions in the ICU to protect patient health. For one week, we measured noise levels in isolated rooms, open units, and nursing stations in medical, surgical, and pediatric ICUs, respectively. We additionally analyzed the noise generated by medical equipment that is frequently used in ICUs. The median (interquartile range) noise exposure level (dBA) of all ICU units was 54.4 dB (51.1–57.5) over 24 h. The highest noise exposure was noted in the surgical ICU’s daytime open unit at 57.6 dB (55.0–61.1). Various ICU medical devices continuously generated low-frequency noise. Mechanical noise levels ranged from a minimum of 41 dB to a maximum of 91 dB. It was also confirmed that patient-monitoring devices generated loud, high-frequency noise at 85 dB. ICU noise levels were much higher than expected. Noise reduction that focuses on behavior modification of medical staff has limited potential; instead, structural improvements should be considered to reduce the transmission of noise.
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