Thermal peripheral blood flowmeter with contact force compensation

Abstract

In this thesis, a thermal peripheral blood flowmeter integrated with force sensor, capable of contact force compensation, has been proposed. The peripheral blood flow is easily affected by the contact force between skin and device [1]. To minimize contact force effect, conventional approaches tried to fix the device on the skin to maintain constant contact force. However, manual fixation process arouses contact force difference in each trial. In this thesis, we integrate force sensor in a thermal type blood flowmeter using Heat-washout principle[2] to measure both blood flow and contact force simultaneously thus achieving novel detection method with contact force compensation. The present device is composed of two sensing elements: blood flow sensor with RTD & heater for using Heat-washout method [2] and piezoresistive force sensor. Using COMSOL simulation, we designed 0.3μm thickness nickel heater having 800mW under 10V to obtain 1 minute detection time. The thickness of membrane, 50μm is designed to endure 5N contact force of fingertip. Using micro-fabrication technology, the present device was successfully fabricated including metal deposition and patterning process for RTD & heater, and boron-doping process for piezoresistors. In the experiment study, we evaluated individual element and applied to human blood flow measurement. The sensitivity of force sensor was 1.7V/1N having accuracy of 0.05N. The RTD & heater showed temperature sensing resolution of 0.02Ω/0.1℃ and heating time to reach 40℃ was 20 second at 18V. In the blood flow measurement test, the performance of present device was compared with that of Laser Doppler flowmeter. We obtained the correlation coefficient of 0.94 which is competitive with the previous conventional work (0.73~0.98). We measured blood flow decreasing trend under 1~3N contact force. The decrement showed a linear model having decrease rate of 31.7%/N. We can apply this simple model to detection data to compensate contact force...