Bio-inspired flow sensor and its application in spirometry

Accurate flow measurements are a ubiquitous task in fields such as industry, medical technology, or chemistry; they remain however challenging. As the flow profile varies over the flow velocity range, the measurement range of many devices is low. Additionally, the flow of erosive fluids may damage the sensor. A low-cost sensor based on an optical principle is proposed. The lateral line consists of numerous tiny but accurate flow sensors, which are called the neuromasts. Each neuromast comprises hair cells embedded in a gelatinous cupula that is exposed to fluid flow. In the biomimetic sensor, an elastic fiber that is bent in flow mimics the cupula. It is fabricated out of several layers to create an optical waveguide with a low refractive index contrast, hence, the waveguide is highly sensitive to bending. The bending intensity is evaluated optically as light guided through the waveguide is detected by a photodiode. The applicability of the proposed sensor for medical technology is evaluated. In particular, spirometers are used in lung function diagnostics to detect obstructions of the upper airways. For this measurement, the air flow or volume during inspiration and expiration needs to be determined with high accuracy. Furthermore, high requirements on hygiene need to be fulfilled to prevent cross-contamination between patients or between a patient and staff. A new type of low-cost spirometer could increase the availability of spirometers at general practitioners as well as reduce the costs for each test. The waveguide was stressed with masses to simulate the bending in fluid flow. The results indicate a high sensitivity of the fiber with a linear relation between the light loss and the bending intensity. As the material is resistant to heat, it can be autoclaved for cheap and fast disinfection.