Thermal clearance blood flow sensor--sensitivity, linearity and flow depth discrimination.

A thermal clearance blood flow sensor has been designed which incorporates four separate sensing elements, permitting flow changes at four differing depths to be measured. Static and dynamic laboratory tests have confirmed the differing flow depth response of the sensor and demonstrated a linear response to flow over the physiological skin blood flow range. Flow depth response has been shown to be dependent upon sensor geometry. Response should also in theory be dependent on the thermal conductivity of the sensor body material. However, using conventional encapsulation materials, it does not seem possible to obtain a depth sensitivity of less than 0.2 mm.