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Microphones
Published in Alec Nisbett, The Sound Studio, 2003
Many solids and liquids are excellent conductors of sound – better than air. A device that picks up sound vibrations from a solid material such as the soundboard of an electric guitar is called a contact microphone. Because in this the whole microphone housing moves with the vibration of the solid surface, one way of generating a signal is for a suspended ‘active mass’ to remain still, by its own inertia. If the moving-coil principle is used, the mass of the magnet remains almost at rest, while the body of the microphone moves. For a massive source such as a girder or rail, the weight of the contact microphone does not matter much. For light sources, including most musical instruments, the mass of the moving capsule should be low, in order to avoid damping its motion. Where the condenser principle is used, the diaphragm requires added mass: in one design, this is achieved by coating it with rubber.
A review of medical wearables: materials, power sources, sensors, and manufacturing aspects of human wearable technologies
Published in Journal of Medical Engineering & Technology, 2023
Mohammad Y. Al-Daraghmeh, Richard T. Stone
Wearables mechanical sensors usually combine the embedded 3 D accelerometers, gyroscopes, and magnetometers in the inertial measurement units (IMUs) to collect kinematic data due to their portability and low power consumption [64,65]. Accelerometer-based wearables measure acceleration in three directions and can be used to estimate count steps, type of movement, calculate energy expenditure and energy intensity, alongside estimate sleep patterns [66]. Furthermore, [67] introduced an accelerometer-based hermetically-sealed contact microphone to capture the body's mechano-acoustic signals, which can record broad frequency range vibrations on human skin, ranging from shallow frequency (below 1 Hz) movements related to the chest wall and body position to high-frequency acoustic signals (up to 12 kHz) emanating from the heart and lungs.
Technical characterisation of digital stethoscopes: towards scalable artificial intelligence-based auscultation
Published in Journal of Medical Engineering & Technology, 2023
Youness Arjoune, Trong N. Nguyen, Robin W. Doroshow, Raj Shekhar
Electronic stethoscopes were developed to address these issues [5]. The first-generation electronic stethoscopes were susceptible to ambient noise due to their chest piece being a contact microphone and having a single-tube. Furthermore, the limited device memory allowed saving only a handful of recordings. Since their early days, electronic stethoscopes have undergone several technological advances, with adaptive noise cancellation being the most significant yet only a few provide real active noise cancellation.