Mawahib Gafare Abdalrahman Ahmed

Modeling and Finite Element Analysis Simulation of MEMS Based Acetone Vapor Sensor for Noninvasive Screening of Diabetes

Diabetes is currently screened invasively by measuring glucose concentration in blood, which is inconvenient. This paper reports a study on modeling and simulation of a CMOS-MEMS sensor for noninvasive screening of diabetes via detection of acetone vapor in exhaled breath (EB). The sensor has two structures: movable (rotor) and fixed (stator) plates. The rotor plate is suspended on top of the stator by support of four flexible beams and maintaining certain selected initial gaps of 5, 6, 7, 8, 9, 10, or 11 μm to form actuation and sensing parallel plate capacitors. A chitosan polymer of varied thicknesses (1–20 μm) is deposited on the rotor plate and modeled as a sensing element for the acetone vapor. The minimum polymer coating thickness required to detect the critical concentration (1.8 ppm) of acetone vapor in the EB of diabetic subjects is found to be 4–7 μm, depending on the initial gap between the rotor and stator plates. However, to achieve sub-ppm detection limit to sense the acetone vapor concentration (0.4–1.1 ppm) in the EB of healthy people, up to 20 μm polymer thickness is coated. The mathematically modeled results were verified using the 2008 CoventorWare simulation software and a good agreement within a 5.3% error was found between the modeled and the simulated frequencies giving more confidence in the predicted results.

Optical and capacitive characterization of MEMS magnetic resonator

In this paper a Lorentz force driven Micro ELectro Mechanical Sytems (MEMS) resonator fabricated on PolyMUMP process with optical and capacitive sensing is presented. The resonator is designed by combining the two poly layers which result in an increase in the thickness of the resonator. Lorentz force generates lateral displacements at low driving voltages which are proportional to the magnetic field and the input current. A displacement of more than 9.8 μm was achieved with a magnetic field of 0.12T and a driving current of 27mA. Magnetic sensitivity of 1.41V/T in air was experimentally measured using permanent magnets and capacitive sensing circuitry. Optical results demonstrate the sensitivity values between 0.090μm/mT and 0.074μm/mT.

Characterization of CMOS-MEMS device for acetone vapor detection in exhaled breath

A MEMS vapor sensor for acetone detection in exhaled breath (EB) has been fabricated using 0.35 μm CMOS technology. Acetone vapor in EB is used as a non-invasive method for diabetes screening, which is currently conducted invasively by measuring blood glucose in blood. This paper studies the characterization of polysilicon piezoresistors, heater and temperature sensor embedded in the device. The measured resistances were found to be close to the modelled values within 1.1-6.8% error. Temperature coefficient of resistance (TCR) of the temperature sensor in a range of 25-100°C was found. TCR increases linearly with increasing the temperature and decreases linearly with decreasing the temperature. It was found to be 0.0033/°C for the increasing temperature and 0.0034/°C for the decreasing temperature, compared to 0.0038/°C reported in the literature, with an error of 13% and 10.5%, respectively.

Review on Exhaled Hydrogen Peroxide as a Potential Biomarker for Diagnosis of Inflammatory Lung Diseases

Exhaled breath (EB) contains thousands of volatile and nonvolatile biomolecules. EB analysis is non-invasive and convenient to patients than blood or urine tests. The exhaled biomolecules have long been studied and recognized to have some potential biomarkers for diagnosis of diseases, evaluation of metabolic disorders and monitoring drug efficiency. For instance, Biomarkers such as exhaled hydrogen peroxide (H2O2) and exhaled nitric oxide are associated with inflammatory lung diseases, ammonia is used as a biomarker for kidney diseases and exhaled acetone is related to glucose concentration in blood and so it is used for diabetes diagnosis. H2O2 concentration in EB increases with the severity of lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), and adult respiratory distress syndrome (ARDS). Different methods are used to measure H2O2 in exhaled breath condensate (EBC). In EBC the EB is collected in a condensate unit and then H2O2 concentration in the collected sample is detected using titrimetric, spectrophotometry, fluorescence, chemiluminescence and electrochemical sensors. Recently, some works have been done to measure the concentration of H2O2 in its vapor phase without a need for condensation units. The aim of this paper is to review and summarize the current methods being used to measure the concentration of H2O2 in EB to identify inflammatory lung diseases, and to discuss the advantages and disadvantages of these methods

Study of damping effect on CMOS-MEMS resonator for biomarker detection in exhaled breath

CMOS-MEMS resonators have found a broad usage in mass sensing applications. They can be used to detect biomarkers in exhaled breath (EB) for screening of diseases. Damping is believed to hinder the performance of these resonators. This paper focuses on investigating effects of damping in natural frequency, mass sensitivity and displacement of a proposed resonator for biomarker detection in EB. The resonator is electrostatically actuated using parallel plate capacitor principle. Squeeze film damping was found to affect the resonator performance when the gap distance between the plates was varied as 5, 7, 9, 10 and 11 μm, in which 5 μm led the resonator to be overdamped. For the rest of gaps the resonator is underdamped. FEA simulation using CoventorWare was used to confirm the mathematical modeling of the resonator, in which results agree with the modeling within an acceptable percentage error of 5 %.

Characterization of embedded microheater of a CMOS-MEMS gravimetric sensor device

A CMOS-MEMS device for mass detection has been designed using 2008 CoventorWare software and fabricated using 0.35źm CMOS technology. This paper reports the characterization of the microheater and the temperature sensor embedded in the device. The measured resistances of the microheater and the temperature sensor were found to be close to the modeled values within ~4.2% error. The average temperature coefficient of resistance (TCR) of the temperature sensor of five dies was determined by increasing or decreasing the temperature in a range of 25°C-100°C. The resistance of the temperature sensor was found to increase with either an increase in ambient temperature or the voltage applied to the microheater, with a correlation factor of 0.99. The average TCR was found to be 0.0034/°C for the increasing temperature and 0.0036/°C for the decreasing temperature as compared to 0.0037°C reported in the literature, indicating an error of 8.1% and 3.5%, respectively. These differences between the measured and reported values are believed to be due to fabrication tolerances in the design dimensions or the material properties. The humidity was found to have a negligible effect on the resistance of the temperature sensor for increasing humidity levels from 40% to 90%. The repeatability of the measurements has shown low standard errors, which gives confidence in the reliability of the fabricated device.

Design of PolyMUMPS device for diabetes screening via acetone vapor detection in exhaled breath

Diabetes is a chronic disease that occurs due to deficiency or improper use of insulin by body tissues. It is currently diagnosed invasively by measuring blood glucose. This paper reports modelling and simulation of a PolyMUMPS device proposed for a non-invasive screening of diabetes. The device is electromagnetically driven at its resonance frequency using Lorenz force, while the output is detected by capacitive means. The resonance frequency of the first mode was obtained by CoventorWare software and it was found to be 18.552 kHz compared to its modelled value of 17.211 kHz, within an error of 7.2 %. Maximum displacement of 8.35 µm and capacitance of 29.57 fF were obtained when the device was driven by applying 15 mA current and 50 mT magnetic field.