Film-Shaped Flow Sensor Temperature Distribution

The patent applies local quality by making the sensor film portion extremely thin (film-shaped) so that the temperature distribution within the film itself is uniform, while the thicker fluid below the film experiences the thermal gradient needed for flow rate measurement. This localized differentiation in thickness allows the sensor to experience uniform temperature while the measurement environment maintains the necessary temperature distribution.

The patent transitions from a three-dimensional bulk sensor to a two-dimensional film-shaped sensor by making the sensor substrate thickness much smaller than its length and width dimensions. This dimensional reduction allows the sensor to effectively measure temperature at a specific plane in the fluid without being affected by temperature gradients in the thickness direction, resolving the contradiction between heating and measurement accuracy.

The sensor substrate is made thin only in the thickness direction while maintaining adequate dimensions in the length and width directions. This selective thinning ensures uniform temperature distribution within the sensor for accurate measurement, while the thin profile allows efficient heat transfer from the heating element to the fluid below, maintaining heating efficiency.

By reducing the sensor to a two-dimensional film structure, the patent enables the sensor to be highly responsive to temperature changes in the fluid plane without requiring excessive thermal mass. The thin film geometry allows rapid thermal equilibrium with the fluid while maintaining sufficient surface area for effective heating, resolving the contradiction between measurement accuracy and heating efficiency.