A non-invasive optical measurement system based on a broadband light source and color filters has been developed for determining pulse rate and arterial blood oxygen saturation (SaO2). In contrast to classical pulse oximetry using red and infrared LEDs to measure the peripheral capillary oxygen saturation (SpO2), we use color filters in our system. Spectral analysis of human tissue can be easily achieved by combining a tiny color filter matrix and a commercial CMOS/CCD image sensor. During system operation, white LED light illuminates our tissue (e.g., a finger), while a CCD sensor covered by filters detects the light transmitted through that tissue. The CCD sensor is controlled by a Field Programmable Gate Array (FPGA) and a microcontroller. The detected photoplethysmographic (PPG) signal is transferred to a host computer and analyzed with MATLAB. After sensor system calibration, pulse rate and SpO2 can be simply extracted from the PPG signal. The heart rate and SpO2 of different volunteers are then measured simultaneously by commercial pulse oximetry and the proposed sensor system, in which results from both devices show good agreement. To integrate more functions into system, nanostructured color filter matrix containing 15 filters for different wavelengths is designed and fabricated. This filter can be designed to provide transmission peaks over the visible and near-infrared range (i.e., the human tissue optical transparent window) and has a high potential to be fabricated directly on top of pixels of an image sensor.
The asymmetric resonance responses of a thermally actuated silicon microcantilever of a portable, cantilever-based nanoparticle detector (Cantor) is analysed. For airborne nanoparticle concentration measurements, the cantilever is excited in its first in-plane bending mode by an integrated p-type heating actuator. The mass-sensitive nanoparticle (NP) detection is based on the resonance frequency (f0) shifting due to the deposition of NPs. A homemade phase-locked loop (PLL) circuit is developed for tracking of f0. For deflection sensing the cantilever contains an integrated piezo-resistive Wheatstone bridge (WB). A new fitting function based on the Fano resonance is proposed for analysing the asymmetric resonance curves including a method for calculating the quality factor Q from the fitting parameters. To obtain a better understanding, we introduce an electrical equivalent circuit diagram (ECD) comprising a series resonant circuit (SRC) for the cantilever resonator and voltage sources for the parasitics, which enables us to simulate the asymmetric resonance response and discuss the possible causes. Furthermore, we compare the frequency response of the on-chip thermal excitation with an external excitation using an in-plane piezo actuator revealing parasitic heating of the WB as the origin of the asymmetry. Moreover, we are able to model the phase component of the sensor output using the ECD. Knowing and understanding the phase response is crucial to the design of the PLL and thus the next generation of Cantor.
Low-cost and low-power piezoresistive cantilever resonators with integrated electrothermal heaters are developed to support the sensing module enhancement of the second generation of handheld cantilever-based airborne nanoparticle (NP) detector (CANTOR-2). These sensors are used for direct-reading of exposure to carbon engineered nanoparticles (ENPs) at indoor workplaces. The cantilever structures having various shapes of free ends are created using silicon bulk micromachining technologies (i.e, rectangular, hammer-head, triangular, and U-shaped cantilevers). For a complete wearable CANTOR-2, all components of the proposed detector can be grouped into two main units depending on their packaging placements (i.e., the NP sampler head and the electronics mounted in a handy-format housing). In the NP sampler head, a miniaturized electrophoretic aerosol sampler and a resonant silicon cantilever mass sensor are employed to collect the ENPs from the air stream to the cantilever surfaces and measuring their mass concentration, respectively. After calibration, the detected ENP mass concentrations of CANTOR-2 show a standard deviation from fast mobility particle sizer (FMPS, TSI 3091) of 8–14%.
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