HTHP Home · Issue Contents · Forthcoming Papers
Low velocity airflow sensing using a 3ω microheater on a SiNx membrane
Hyeong-Jun Jo and Dong-Wook Oh
Low-velocity airflow produces only subtle changes in convective heat transfer, making it difficult to resolve with compact thermal sensors. This study investigates the frequency-dependent thermal response of a 3ω microheater supported on a SiNₓ membrane. Removal of the silicon beneath the heater exposes the membrane to gas on both sides and enhances the influence of flow-induced heat transfer on the sensor response. The sensor was characterized in a rectangular chamber under no-flow and finite low-velocity airflow conditions over a broad excitation-frequency range. The temperature amplitude decreased with increasing frequency and airflow, with the clearest separation among the flow conditions occurring in the low-frequency regime. The low-frequency response was interpreted using a lumped thermal-resistance framework that combines a baseline heat-transfer pathway with an additional forced-convection conductance that increases with flow velocity. The resulting correlation captured the nonlinear decrease in temperature amplitude under finite-flow conditions, whereas the no-flow condition was retained as a separate reference rather than imposed on the finite-flow regression. These results show that the low-frequency 3ω temperature amplitude provides a quantitative response to changes in low-velocity airflow within the present sensor–chamber configuration and supports the use of membrane-based 3ω microheaters as compact thermal flow sensors.
Keywords: 3ω method, membrane microheater, low velocity gas flow, thermal flow sensing, forced convection, frequency domain thermometry
DOI: 10.32908/hthp.v55.2117