21 February 2013 Oxygen saturation in free-diving whales: optical sensor development
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Mass stranding of live whales has been explained by proposing many natural or human-related causes. Recent necropsy reports suggest a link between the mass stranding of beaked whales and the use of naval mid-frequency sonar. Surprisingly, whales have experienced symptoms similar to those caused by inert gas bubbles in human divers. Our goal is to develop a compact optical sensor to monitor the consumption of the oxygen stores in the muscle of freely diving whales. To this end we have proposed the use of a near-infrared phase-modulated frequency-domain spectrophotometer, in reflectance mode, to probe tissue oxygenation. Our probe consists of three main components: radiofrequency (RF) modulated light sources, a high-bandwidth avalanche photodiode with transimpedance amplifier, and a RF gain and phase detector. In this work, we concentrate on the design and performance of the light sensor, and its corresponding amplifier unit. We compare three state-of-the-art avalanche photodiodes: one through-hole device and two surface-mount detectors. We demonstrate that the gain due to the avalanche effect differs between sensors. The avalanche gain near maximum bias of the through-hole device exceeds by a factor of 2.5 and 8.3 that of the surface-mount detectors. We present the behavior of our assembled through-hole detector plus high-bandwidth transimpedance amplifier, and compare its performance to that of a commercially available module. The assembled unit enables variable gain, its phase noise is qualitatively lower, and the form factor is significantly smaller. Having a detecting unit that is compact, flexible, and functional is a milestone in the development of our tissue oxygenation tag.
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Enoch Gutierrez-Herrera, Enoch Gutierrez-Herrera, Paulino Vacas-Jacques, Paulino Vacas-Jacques, Rox Anderson, Rox Anderson, Warren Zapol, Warren Zapol, Walfre Franco, Walfre Franco, "Oxygen saturation in free-diving whales: optical sensor development", Proc. SPIE 8592, Biomedical Applications of Light Scattering VII, 859201 (21 February 2013); doi: 10.1117/12.2008547; https://doi.org/10.1117/12.2008547

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