Accelerometer-Based Acoustic Control: Enabling Auscultation on a Black Hawk Helicopter

During aeromedical patient transport, acoustic noise levels in excess of 90 dB make auscultation with a stethoscope virtually impossible. Existing approaches to address this noise in literature have relied on the use of either passive shielding of the stethoscope sensing element or active noise cancellation (ANC) with the use of additional reference microphone sensors. These solutions have achieved inadequate performance. In this paper, custom instrumented stethoscopes are used to obtain structural vibration and acoustic data from a UH-60 Black Hawk helicopter. The data show that the structural vibrations contribute significantly more to stethoscope signals than air-borne acoustic noise. Therefore, a novel adaptive acoustic control system using a reference accelerometer is pursued. By varying the levels of acoustic and vibrational noise sources in a controlled laboratory environment, the benefits and limitations of microphone or accelerometer-based active noise control are investigated and compared. Experimentally simulating the field acoustic and vibration characteristics of the UH-60 Black Hawk helicopter, the accelerometer-based ANC system is shown to provide significantly superior performance. The accelerometer-based ANC system yields an average 25-dB reduction in ambient noise levels over the entire relevant frequency range, thereby enabling successful auscultation for the first time in this military aircraft environment.