Patricia Nieva - Profile on Academia.edu (original) (raw)
Papers by Patricia Nieva
Impact of support material deformation in MEMS bulk micromachined diaphragm pressure sensors
Journal of Micromechanics and Microengineering, 2021
In this work, experimental data and finite element analysis reveals deflection in diaphragm suppo... more In this work, experimental data and finite element analysis reveals deflection in diaphragm supporting material leading to non-linear pressure-reflection response. These results are contrary to the standard assumptions presented in literature, where modelling of deflection response in diaphragm pressure sensors is primarily carried out assuming a rigid supporting structure. An extrinsic fiber-optic Fabry–Perot pressure sensor, based on micro-electromechanical system, is developed and used to investigate optical deflection response. While the sensor is not novel, a series of experiments to validate support deflection phenomena are designed and carried out using a silicon membrane at gauge pressures from 0 to 1000 PSI in ambient temperature. The device is packaged with an industry standard stainless-steel housing typically used in plastic injection moulding. Sensor performance is compared to analytical and finite element modelling. Results suggest that the device is experiencing great...
Fiber optic monitoring of lithium-ion batteries: A novel tool to understand the lithiation of batteries
2016 IEEE SENSORS, 2016
In this paper we present the implementation of a novel lithium ion pouch cell monitoring system t... more In this paper we present the implementation of a novel lithium ion pouch cell monitoring system that utilizes an optical fiber sensor (OFS). The OFS allows for direct optical interaction of near infrared light with graphite during its electrochemical lithiation process. This sensing system has been tested over multiple partial and full cycles showing repeatable signals that can be directly correlated with the lithiation of graphite. The results suggest that this sensor can function independently in determining the state of lithiation of graphite within a lithium ion battery, which can be used in a state of charge estimation algorithm.
Journal of Energy Storage, 2020
Increasing the efficiency and safety of battery management systems may require internal monitorin... more Increasing the efficiency and safety of battery management systems may require internal monitoring of lithium ion batteries. In this work, we present an analysis of the interaction between fiber-optic evanescent wave sensors (FOEWS) and graphite particles within a lithium ion battery over multiple cycles. Through slow charging and long rest periods, the FOEWS signal has shown sensitivity to lithium concentration at the surface of graphite particles by demonstrating a response to the slow diffusion of lithium ions within graphite particles during rest periods (i.e. relaxation of the electrode). The slope of the FOEWS signal during a full charge is found to exhibit three distinct peaks that occur within lithiated graphite's stage transitions zones IV, III and II. Deviation from the observed three peak trend correlates with significant battery capacity fade and thus indicate the sensors ability to detect capacity fade in real-time. During experiments, significant deviations in the slope during charging occurred at about ~5% SOC and minor disturbances to the slope were observed at ~80% SOC, which supports limiting the depth of charge and discharge to avoid accelerated capacity fade. These results deepen our understanding of the FOEWS's interaction with lithium ion batteries and supports the development of algorithms that optimize the control and monitoring of graphite lithiation with the aim of achieving safer operation as well as maximizing capacity and battery life.
ACS Applied Materials & Interfaces, 2017
The development, fabrication and embedding of fiber-optic evanescent wave sensors (FOEWS) to moni... more The development, fabrication and embedding of fiber-optic evanescent wave sensors (FOEWS) to monitor the state of charge (SOC) and the state of health (SOH) of lithium ion batteries (LIB)s is presented. The etching of the FOEWS is performed using a solution of 6:1, 40 wt % ammonium fluoride (NH 4 F) and 49 wt % hydrofluoric acid (HF), and found to be superior to an etching solution containing just 49 wt % HF. FOEWSs were characterized using glycerol and found to have the highest sensitivity in a lithium ion battery when they lose 92 % of their Page 1 of 20 ACS Paragon Plus Environment ACS Applied Materials & Interfaces transmittance in the presence of glycerol on their sensing region. The physical effect that the FOEWS has on the graphite anode is also investigated and found to be much more significant in Swagelok cells compared to in-house fabricated pouch cells, mainly due to pressure variation. The FOEWS was found to be most sensitive to the changes in the LIB when it was completely embedded using a slurry of graphite anode material within a pouch cell. The optimized fabrication process of the embedded FOEWS demonstrates the potential of using such sensors commercially for real-time monitoring of the SOC and SOH of LIBs while in operation.
Modeling, Signal Processing, and Control for Smart Structures 2008, 2008
ABSTRACT In this paper we present the modeling and simulation of a 2 degree-of-freedom (DOF) bidi... more ABSTRACT In this paper we present the modeling and simulation of a 2 degree-of-freedom (DOF) bidirectional electrothermal actuator. The four arm microactuator was designed to move in both the horizontal and vertical axes. By tailoring the geometrical parameters of the design, the in-plane and out-of-plane motions were decoupled, resulting in enhanced mobility in both directions. The motion of the actuator was modeled analytically using an electro-thermo-mechanical analysis. To validate the analytical model, finite element simulations were performed using ANSYS. The microactuators were fabricated using PolyMUMPS process and experimental results show good agreement with both the analytical model and the simulations. We demonstrated that the 2-DOF bidirectional electrothermal actuator can achieve 3.7 mum in-plane and 13.3 mum out-of-plane deflections with an input voltage of 10 V.
Microsystem Technologies, 2009
In this paper, a four hot-arm U-shape electrothermal actuator that can achieve bidirectional moti... more In this paper, a four hot-arm U-shape electrothermal actuator that can achieve bidirectional motion in two axes is introduced. By selectively applying voltage to different pairs of its four arms, the device can provide actuation in four directions starting from its rest position. It is shown that independent in-plane and out-of-plane motions can be obtained by tailoring the geometrical parameters of the system. The lumped model of the microactuator was developed using electro-thermal and thermo-mechanical analyses and validated using finite element simulations. The device has been fabricated using PolyMUMPs and experimental results are in good agreement with the theoretical predictions. Total in-plane deflections of 4.8 lm (2.4 lm in either direction) and upward out-of-plane deflections of 8.2 lm were achieved at 8 V of input voltage. The large achievable deflections and the higher degree-of-freedom of the proposed device compared to its counterparts, foresee its use in diverse MEMS applications.
Integrated Optical Fibers for Simultaneous Monitoring of the Anode and the Cathode in Lithium Ion Batteries
2019 IEEE SENSORS, 2019
We present optical fiber measurements for cell state determination via simultaneous observation o... more We present optical fiber measurements for cell state determination via simultaneous observation of both electrodes of a lithium-ion-battery. The integration of fiber optics is done using commercial electrodes set up in pouch configuration. This system extends the method, shown previously for the graphite anode. Lithium iron phosphate cathodes suffer from poor optical observability due to the addition of carbon black as conductive agent. Hence, carbon black is locally replaced by an electrochromic marker additive. Transmissions through integrated fibers were monitored during battery cycling and results show that the cell state of charge directly influences both transmission signals. Optical data can be utilized as a parameter independent of electrical measurements to estimate the state of charge.
A novel fishbone-shape parallel-plate-based capacitor with high tunability and linear C-V respons... more A novel fishbone-shape parallel-plate-based capacitor with high tunability and linear C-V response is presented. The electrodes consist of a set of lateral cantilever beams of different lengths, attached to a longitudinal fixed-fixed beam. An insulating layer prevents contact between the electrodes. When a DC voltage is applied, the longitudinal and lateral beams undergo out-of-plane deformations changing the gap between two electrodes and the capacitance. As bias voltage increases, depending on their length and location, local pull-in for beams occurs at different voltages leading to a controlled C-V response. Using ANSYS ® FEM simulations, a design optimization is performed to enhance the response for higher tunability and linearity. The simulation results of capacitors designed for PolyMUMPs exhibit tunability over 200%, 160% of which is highly linear. The presented design methodology, a combination of flexible structure and controlled displacements, is not limited to fishbone-shape electrodes and can be extended to different geometries to obtain higher tunability and linearity.
Size and Shape Effect in the Determination of the Fracture Strength of Silicon Nitride in MEMS Structures at High Temperatures
2018 IEEE 68th Electronic Components and Technology Conference (ECTC), 2018
Several applications require Micro electro mechanical systems MEMS devices to operate under high ... more Several applications require Micro electro mechanical systems MEMS devices to operate under high temperatures. Previous efforts to study the properties of MEMS materials have shown that an increase in temperature leads to a decrease in the fracture strength. In this paper, three different thin film silicon nitride dog-bone shaped structures suspended on a silicon substrate are used to determine their fracture strength as a function of temperature using tensile strength testing. Analytical modeling is used to determine the elastic resistance of the thin film dog-bones to stresses caused by the forces originated by the difference in coefficient of thermal expansion between the dog-bones and their substrate. The calculated forces incorporate the effect of temperature in these interactions and the mechanical properties of the two materials by considering the temperature dependence of elastic modulus and coefficient of thermal expansion. Analytical results show that the fracture strength...
Multi-band reflectance spectroscopy of carbonaceous lithium iron phosphate battery electrodes versus state of charge
Optical Components and Materials XI, 2014
ABSTRACT This study aims to expand the body of knowledge about the optical properties of battery ... more ABSTRACT This study aims to expand the body of knowledge about the optical properties of battery cathode materials. Although some studies have been conducted on the optical properties of Lithium Iron Phosphate (LiFePO4), to the authors' knowledge, this is the first study of its kind on electrodes extracted from commercially available LiFePO4 batteries. The use of Vis/NIR and FTIR spectroscopy provides for a methodology to study the optical properties of LiFePO4 and may allow for the characterization of other properties such as particle size and the proportions of LiFePO4 versus FePO4 material. Knowledge of these properties is important for the development of a mechanism to measure the state-of charge (SOC) in lithium ion batteries. These properties are also important in a host of other applications including battery modeling and materials characterization. Cylindrical LiFePO4 batteries (from A123 Systems Inc.) were acquired from the commercial market and charged to 10 different states between 30% and 80% of their nominal capacity using a constant-current, constant-voltage (CCCV) cycling method. Visual inspection of the extracted electrodes shows that the LiFePO4/C-cathodes display subtle changes in color (shades of grey) with respect to SOC. Vis/NIR measurements support the visual observation of uniform intensity variations versus SOC. FTIR measurements show an absorbance signature that varies with SOC and is distinct from results found in the literature for similar LiFePO4-based material systems, supporting the uniqueness of the absorbance fingerprint.
Sadhana Acad Proc Eng Sci, Aug 1, 2009
This paper presents a novel MOEMS (Micro Opto Electromechanical Systems) pressure sensor suitable... more This paper presents a novel MOEMS (Micro Opto Electromechanical Systems) pressure sensor suitable for localized precision measurements in high temperature environments. The sensor is based on a micromachined Fabry-Perot device (MFPD) that uses a thin film microcantilever beam as the top mirror and a silicon substrate as the bottom mirror of the optical microcavity. The major effect that the viscosity and density of the air surrounding the MFPD have on the viscous damping provides the mechanism for the detection of the pressure. A major advantage of this configuration is that there is no need for a sealed microcavity since the air is trapped by the viscous damping effects. The sensor has been tested up to 90 psi and pressure sensitivities of about 0·04%/psi with a MFPD sensor with a resonant frequency of about 46·7 kHz have been measured.
A smaller footprint MEMS sensor for on-chip temperature measurement
Reliability, Packaging, Testing, and Characterization of MOEMS/MEMS and Nanodevices XII, 2013
ABSTRACT In this paper, a new MEMS capacitive temperature sensor is presented which is based on a... more ABSTRACT In this paper, a new MEMS capacitive temperature sensor is presented which is based on a circular silicon plate with a gold annulus deposited on top forming a novel bimaterial structure. The bimaterial structure is anchored to a substrate on its edge and forms the top electrode of a capacitor. A stationary silicon electrode beneath the bimaterial structure forms the second electrode. The PolyMUMPs® foundry process has been used to fabricate the device. Experiments show that for an effective area of about 0.1 mm2 this MEMS capacitive temperature sensor achieves a sensitivity of 0.75+/-0.25 fF/°C over the temperature range of 25 to 225 °C, which shows an improvement of more than 25% over equivalent microcantilever devices with the same effective area. Numerical modeling is used to show that the new design exhibits high flexibility in tailoring its thermomechanical response over the desired temperature range. The simplicity of its design and flexibility of the materials from which it can be constructed also makes this new MEMS sensor a good onchip temperature measurement device for MEMS characterization.
Method and Apparatus for an Interferometric Localized Surface Plasmon Resonance (Ilspr) Sensor
Axial Force Regulation in MEMS Resonant Sensors
Volume 12: Micro and Nano Systems, Parts A and B, 2009
Axial Force Regulation in MEMS Resonant Sensors. [ASME Conference Proceedings 2009, 321 (2009)]. ... more Axial Force Regulation in MEMS Resonant Sensors. [ASME Conference Proceedings 2009, 321 (2009)]. Pezhman A. Hassanpour, Chris T. Wong, Patricia M. Nieva, Amir Khajepour. Abstract. In this paper, a passive mechanism ...
2008 1st Microsystems and Nanoelectronics Research Conference, 2008
The increase in the demand of using infrared detectors for thermal imaging of high temperature sc... more The increase in the demand of using infrared detectors for thermal imaging of high temperature scenes initiated the research in microbolometer arrays with high operation temperature range. An efficient way of increasing this range is tuning the thermal conductance of the microbolometer array by electrostatic actuation, which is achieved by applying an actuation voltage to the substrate. However, using the substrate for actuation does not support pixel-by-pixel actuation, limiting the capabilities of the tunability. In this research, we demonstrate applying the actuation voltage to the micromirror which is located below the microbolometer. To avoid contact of the microbolometer to the micromirror, stoppers are used. We report that the thermal conductance is doubled at an actuation voltage of 12 volts, making it an efficient mechanism that can be used at next generation adaptive microbolometers.
A structurally multifunctional pressure-temperature sensor
Abstract A new multifunctional sensor for simultaneous mea-surement of pressure and temperature ... more Abstract A new multifunctional sensor for simultaneous mea-surement of pressure and temperature is proposed and modeled. The design includes elastic membranes and bi-layer beams as pressure and temperature sensing bodies, respectively, and capa-citance readout for transduction. ...
Design and Modelling of a MEMS Capacitive Temperature Sensor With Linear Capacitance-Temperature Response
Volume 12: Micro and Nano Systems, Parts A and B, 2009
ABSTRACT A capacitive temperature sensor with separate thermal actuation and capacitive readout i... more ABSTRACT A capacitive temperature sensor with separate thermal actuation and capacitive readout is introduced. A bi-layer plate with fixed-free boundary condition is used for the thermal actuation to change the gap between two parallel electrodes used for capacitance measurement. Different coefficients of thermal expansion (CTE) of the two layers in actuator cause out-of-plane deformations in the plate when the temperature changes. The proposed design has the capability to control the response of the sensor by increasing its sensitivity in a given temperature range. To obtain the desired characteristic C-T curve, the design utilizes asymmetric geometries. Different design parameters such as the size of the bi-layer plate and the sense electrodes are considered as design variables. ANSYS® FEM simulations are used to extract the C-T responses of different geometries. The results of the FEM simulations show that for a given fabrication process and material properties, the design can be modified to provide the highest sensitivity and linearity in the C-T response for a given temperature range. This temperature sensor can be used for remote and on-chip temperature measurement or temperature compensation.
MEMS-based Fabry-Perot vibration sensor for harsh environments
Proceedings of Spie the International Society For Optical Engineering, 2006
This paper presents the design, fabrication and testing results of a Fabry-Perot Micro-Opto-Mecha... more This paper presents the design, fabrication and testing results of a Fabry-Perot Micro-Opto-Mechanical Device (FPMOD) used as a vibration sensor. The un-cooled high-temperature operational capability of the FPMOD provides a viable low-cost alternative to sensors that require environmentally controlled packages to operate at high temperature. The FPMOD is a passive MEMS device that consists of a micromachined cavity formed between a substrate and a top thin film structure in the form of a cantilever beam. When affixed to a vibrating surface, the amplitude and frequency of vibration are determined by illuminating the FPMOD with a monochromatic light source and analyzing the back reflected light to determine the deflection of the beam with respect to the substrate. Given the Fabry-Perot geometry, a mechanical transfer function is calculated to permit the substrate motion to be determined from the relative motion of the beam with respect to the substrate. Because the thin film cantilever beam and the substrate are approximately parallel, this convenient two-mirror cavity arrangement needs no alignment, no reference arm, and no sophisticated stabilization techniques. The small size of the FPMOD (85-175μm), the choice of materials in which it can be manufactured (Silicon Nitride and Silicon Carbide), and its simple construction make it ideal for harsh high-temperature applications. Relative displacements in the sub-nanometer range have been measured and close agreement was found between the measured sensor frequency response and the theoretical predictions based on analytical models.
Optical Characterization of Commercial Lithiated Graphite Battery Electrodes and in Situ Fiber Optic Evanescent Wave Spectroscopy
ACS applied materials & interfaces, Jan 27, 2016
Optical characterization of graphite anodes in lithium ion batteries (LIB) is presented here for ... more Optical characterization of graphite anodes in lithium ion batteries (LIB) is presented here for potential use in estimating their state of charge (SOC). The characterization is based on reflectance spectroscopy of the anode of commercial LIB cells and in situ optical measurements using an embedded optical fiber sensor. The optical characterization of the anode using wavelengths ranging from 500 to 900 nm supports the dominance of graphite over the solid electrolyte interface in governing the anode's reflectance properties. It is demonstrated that lithiated graphite's reflectance has a significant change in the near-infrared band, 750-900 nm, compared with the visible spectrum as a function of SOC. An embedded optical sensor is used to measure the transmittance of graphite anode in the near-infrared band, and the results suggest that a unique inexpensive method may be developed to estimate the SOC of a LIB.
Microelectronic Engineering, Nov 1, 2010
This paper introduces a modified structure for parallel-plate-based MEMS tunable capacitors. The ... more This paper introduces a modified structure for parallel-plate-based MEMS tunable capacitors. The capacitor has triangular electrodes with geometric and structural asymmetry, which enhances its performance. The device structure is also equipped with a set of cantilever beams between capacitor's electrodes, called middle beams. These beams provide extra stiffness as tuning voltage increases and delay the pull-in which results in a higher tunability. They also reduce the high sensitivity of the capacitance to the voltage change and linearize the C-V response. An analytical model is developed to optimize the capacitor's dimensions for maximum linearity of the response. Numerical simulations demonstrate tunabilities over 150% where more than 2/3 of which is highly linear. Capacitors fabricated with PolyMUMPs verify that the design technique proposed in this paper can improve the linearity of the device and increase the maximum tunability. The proposed design has a simple geometry and is fabricated using three structural layers, and therefore, it can be easily integrated in tunable filters or other RF circuits.
Impact of support material deformation in MEMS bulk micromachined diaphragm pressure sensors
Journal of Micromechanics and Microengineering, 2021
In this work, experimental data and finite element analysis reveals deflection in diaphragm suppo... more In this work, experimental data and finite element analysis reveals deflection in diaphragm supporting material leading to non-linear pressure-reflection response. These results are contrary to the standard assumptions presented in literature, where modelling of deflection response in diaphragm pressure sensors is primarily carried out assuming a rigid supporting structure. An extrinsic fiber-optic Fabry–Perot pressure sensor, based on micro-electromechanical system, is developed and used to investigate optical deflection response. While the sensor is not novel, a series of experiments to validate support deflection phenomena are designed and carried out using a silicon membrane at gauge pressures from 0 to 1000 PSI in ambient temperature. The device is packaged with an industry standard stainless-steel housing typically used in plastic injection moulding. Sensor performance is compared to analytical and finite element modelling. Results suggest that the device is experiencing great...
Fiber optic monitoring of lithium-ion batteries: A novel tool to understand the lithiation of batteries
2016 IEEE SENSORS, 2016
In this paper we present the implementation of a novel lithium ion pouch cell monitoring system t... more In this paper we present the implementation of a novel lithium ion pouch cell monitoring system that utilizes an optical fiber sensor (OFS). The OFS allows for direct optical interaction of near infrared light with graphite during its electrochemical lithiation process. This sensing system has been tested over multiple partial and full cycles showing repeatable signals that can be directly correlated with the lithiation of graphite. The results suggest that this sensor can function independently in determining the state of lithiation of graphite within a lithium ion battery, which can be used in a state of charge estimation algorithm.
Journal of Energy Storage, 2020
Increasing the efficiency and safety of battery management systems may require internal monitorin... more Increasing the efficiency and safety of battery management systems may require internal monitoring of lithium ion batteries. In this work, we present an analysis of the interaction between fiber-optic evanescent wave sensors (FOEWS) and graphite particles within a lithium ion battery over multiple cycles. Through slow charging and long rest periods, the FOEWS signal has shown sensitivity to lithium concentration at the surface of graphite particles by demonstrating a response to the slow diffusion of lithium ions within graphite particles during rest periods (i.e. relaxation of the electrode). The slope of the FOEWS signal during a full charge is found to exhibit three distinct peaks that occur within lithiated graphite's stage transitions zones IV, III and II. Deviation from the observed three peak trend correlates with significant battery capacity fade and thus indicate the sensors ability to detect capacity fade in real-time. During experiments, significant deviations in the slope during charging occurred at about ~5% SOC and minor disturbances to the slope were observed at ~80% SOC, which supports limiting the depth of charge and discharge to avoid accelerated capacity fade. These results deepen our understanding of the FOEWS's interaction with lithium ion batteries and supports the development of algorithms that optimize the control and monitoring of graphite lithiation with the aim of achieving safer operation as well as maximizing capacity and battery life.
ACS Applied Materials & Interfaces, 2017
The development, fabrication and embedding of fiber-optic evanescent wave sensors (FOEWS) to moni... more The development, fabrication and embedding of fiber-optic evanescent wave sensors (FOEWS) to monitor the state of charge (SOC) and the state of health (SOH) of lithium ion batteries (LIB)s is presented. The etching of the FOEWS is performed using a solution of 6:1, 40 wt % ammonium fluoride (NH 4 F) and 49 wt % hydrofluoric acid (HF), and found to be superior to an etching solution containing just 49 wt % HF. FOEWSs were characterized using glycerol and found to have the highest sensitivity in a lithium ion battery when they lose 92 % of their Page 1 of 20 ACS Paragon Plus Environment ACS Applied Materials & Interfaces transmittance in the presence of glycerol on their sensing region. The physical effect that the FOEWS has on the graphite anode is also investigated and found to be much more significant in Swagelok cells compared to in-house fabricated pouch cells, mainly due to pressure variation. The FOEWS was found to be most sensitive to the changes in the LIB when it was completely embedded using a slurry of graphite anode material within a pouch cell. The optimized fabrication process of the embedded FOEWS demonstrates the potential of using such sensors commercially for real-time monitoring of the SOC and SOH of LIBs while in operation.
Modeling, Signal Processing, and Control for Smart Structures 2008, 2008
ABSTRACT In this paper we present the modeling and simulation of a 2 degree-of-freedom (DOF) bidi... more ABSTRACT In this paper we present the modeling and simulation of a 2 degree-of-freedom (DOF) bidirectional electrothermal actuator. The four arm microactuator was designed to move in both the horizontal and vertical axes. By tailoring the geometrical parameters of the design, the in-plane and out-of-plane motions were decoupled, resulting in enhanced mobility in both directions. The motion of the actuator was modeled analytically using an electro-thermo-mechanical analysis. To validate the analytical model, finite element simulations were performed using ANSYS. The microactuators were fabricated using PolyMUMPS process and experimental results show good agreement with both the analytical model and the simulations. We demonstrated that the 2-DOF bidirectional electrothermal actuator can achieve 3.7 mum in-plane and 13.3 mum out-of-plane deflections with an input voltage of 10 V.
Microsystem Technologies, 2009
In this paper, a four hot-arm U-shape electrothermal actuator that can achieve bidirectional moti... more In this paper, a four hot-arm U-shape electrothermal actuator that can achieve bidirectional motion in two axes is introduced. By selectively applying voltage to different pairs of its four arms, the device can provide actuation in four directions starting from its rest position. It is shown that independent in-plane and out-of-plane motions can be obtained by tailoring the geometrical parameters of the system. The lumped model of the microactuator was developed using electro-thermal and thermo-mechanical analyses and validated using finite element simulations. The device has been fabricated using PolyMUMPs and experimental results are in good agreement with the theoretical predictions. Total in-plane deflections of 4.8 lm (2.4 lm in either direction) and upward out-of-plane deflections of 8.2 lm were achieved at 8 V of input voltage. The large achievable deflections and the higher degree-of-freedom of the proposed device compared to its counterparts, foresee its use in diverse MEMS applications.
Integrated Optical Fibers for Simultaneous Monitoring of the Anode and the Cathode in Lithium Ion Batteries
2019 IEEE SENSORS, 2019
We present optical fiber measurements for cell state determination via simultaneous observation o... more We present optical fiber measurements for cell state determination via simultaneous observation of both electrodes of a lithium-ion-battery. The integration of fiber optics is done using commercial electrodes set up in pouch configuration. This system extends the method, shown previously for the graphite anode. Lithium iron phosphate cathodes suffer from poor optical observability due to the addition of carbon black as conductive agent. Hence, carbon black is locally replaced by an electrochromic marker additive. Transmissions through integrated fibers were monitored during battery cycling and results show that the cell state of charge directly influences both transmission signals. Optical data can be utilized as a parameter independent of electrical measurements to estimate the state of charge.
A novel fishbone-shape parallel-plate-based capacitor with high tunability and linear C-V respons... more A novel fishbone-shape parallel-plate-based capacitor with high tunability and linear C-V response is presented. The electrodes consist of a set of lateral cantilever beams of different lengths, attached to a longitudinal fixed-fixed beam. An insulating layer prevents contact between the electrodes. When a DC voltage is applied, the longitudinal and lateral beams undergo out-of-plane deformations changing the gap between two electrodes and the capacitance. As bias voltage increases, depending on their length and location, local pull-in for beams occurs at different voltages leading to a controlled C-V response. Using ANSYS ® FEM simulations, a design optimization is performed to enhance the response for higher tunability and linearity. The simulation results of capacitors designed for PolyMUMPs exhibit tunability over 200%, 160% of which is highly linear. The presented design methodology, a combination of flexible structure and controlled displacements, is not limited to fishbone-shape electrodes and can be extended to different geometries to obtain higher tunability and linearity.
Size and Shape Effect in the Determination of the Fracture Strength of Silicon Nitride in MEMS Structures at High Temperatures
2018 IEEE 68th Electronic Components and Technology Conference (ECTC), 2018
Several applications require Micro electro mechanical systems MEMS devices to operate under high ... more Several applications require Micro electro mechanical systems MEMS devices to operate under high temperatures. Previous efforts to study the properties of MEMS materials have shown that an increase in temperature leads to a decrease in the fracture strength. In this paper, three different thin film silicon nitride dog-bone shaped structures suspended on a silicon substrate are used to determine their fracture strength as a function of temperature using tensile strength testing. Analytical modeling is used to determine the elastic resistance of the thin film dog-bones to stresses caused by the forces originated by the difference in coefficient of thermal expansion between the dog-bones and their substrate. The calculated forces incorporate the effect of temperature in these interactions and the mechanical properties of the two materials by considering the temperature dependence of elastic modulus and coefficient of thermal expansion. Analytical results show that the fracture strength...
Multi-band reflectance spectroscopy of carbonaceous lithium iron phosphate battery electrodes versus state of charge
Optical Components and Materials XI, 2014
ABSTRACT This study aims to expand the body of knowledge about the optical properties of battery ... more ABSTRACT This study aims to expand the body of knowledge about the optical properties of battery cathode materials. Although some studies have been conducted on the optical properties of Lithium Iron Phosphate (LiFePO4), to the authors' knowledge, this is the first study of its kind on electrodes extracted from commercially available LiFePO4 batteries. The use of Vis/NIR and FTIR spectroscopy provides for a methodology to study the optical properties of LiFePO4 and may allow for the characterization of other properties such as particle size and the proportions of LiFePO4 versus FePO4 material. Knowledge of these properties is important for the development of a mechanism to measure the state-of charge (SOC) in lithium ion batteries. These properties are also important in a host of other applications including battery modeling and materials characterization. Cylindrical LiFePO4 batteries (from A123 Systems Inc.) were acquired from the commercial market and charged to 10 different states between 30% and 80% of their nominal capacity using a constant-current, constant-voltage (CCCV) cycling method. Visual inspection of the extracted electrodes shows that the LiFePO4/C-cathodes display subtle changes in color (shades of grey) with respect to SOC. Vis/NIR measurements support the visual observation of uniform intensity variations versus SOC. FTIR measurements show an absorbance signature that varies with SOC and is distinct from results found in the literature for similar LiFePO4-based material systems, supporting the uniqueness of the absorbance fingerprint.
Sadhana Acad Proc Eng Sci, Aug 1, 2009
This paper presents a novel MOEMS (Micro Opto Electromechanical Systems) pressure sensor suitable... more This paper presents a novel MOEMS (Micro Opto Electromechanical Systems) pressure sensor suitable for localized precision measurements in high temperature environments. The sensor is based on a micromachined Fabry-Perot device (MFPD) that uses a thin film microcantilever beam as the top mirror and a silicon substrate as the bottom mirror of the optical microcavity. The major effect that the viscosity and density of the air surrounding the MFPD have on the viscous damping provides the mechanism for the detection of the pressure. A major advantage of this configuration is that there is no need for a sealed microcavity since the air is trapped by the viscous damping effects. The sensor has been tested up to 90 psi and pressure sensitivities of about 0·04%/psi with a MFPD sensor with a resonant frequency of about 46·7 kHz have been measured.
A smaller footprint MEMS sensor for on-chip temperature measurement
Reliability, Packaging, Testing, and Characterization of MOEMS/MEMS and Nanodevices XII, 2013
ABSTRACT In this paper, a new MEMS capacitive temperature sensor is presented which is based on a... more ABSTRACT In this paper, a new MEMS capacitive temperature sensor is presented which is based on a circular silicon plate with a gold annulus deposited on top forming a novel bimaterial structure. The bimaterial structure is anchored to a substrate on its edge and forms the top electrode of a capacitor. A stationary silicon electrode beneath the bimaterial structure forms the second electrode. The PolyMUMPs® foundry process has been used to fabricate the device. Experiments show that for an effective area of about 0.1 mm2 this MEMS capacitive temperature sensor achieves a sensitivity of 0.75+/-0.25 fF/°C over the temperature range of 25 to 225 °C, which shows an improvement of more than 25% over equivalent microcantilever devices with the same effective area. Numerical modeling is used to show that the new design exhibits high flexibility in tailoring its thermomechanical response over the desired temperature range. The simplicity of its design and flexibility of the materials from which it can be constructed also makes this new MEMS sensor a good onchip temperature measurement device for MEMS characterization.
Method and Apparatus for an Interferometric Localized Surface Plasmon Resonance (Ilspr) Sensor
Axial Force Regulation in MEMS Resonant Sensors
Volume 12: Micro and Nano Systems, Parts A and B, 2009
Axial Force Regulation in MEMS Resonant Sensors. [ASME Conference Proceedings 2009, 321 (2009)]. ... more Axial Force Regulation in MEMS Resonant Sensors. [ASME Conference Proceedings 2009, 321 (2009)]. Pezhman A. Hassanpour, Chris T. Wong, Patricia M. Nieva, Amir Khajepour. Abstract. In this paper, a passive mechanism ...
2008 1st Microsystems and Nanoelectronics Research Conference, 2008
The increase in the demand of using infrared detectors for thermal imaging of high temperature sc... more The increase in the demand of using infrared detectors for thermal imaging of high temperature scenes initiated the research in microbolometer arrays with high operation temperature range. An efficient way of increasing this range is tuning the thermal conductance of the microbolometer array by electrostatic actuation, which is achieved by applying an actuation voltage to the substrate. However, using the substrate for actuation does not support pixel-by-pixel actuation, limiting the capabilities of the tunability. In this research, we demonstrate applying the actuation voltage to the micromirror which is located below the microbolometer. To avoid contact of the microbolometer to the micromirror, stoppers are used. We report that the thermal conductance is doubled at an actuation voltage of 12 volts, making it an efficient mechanism that can be used at next generation adaptive microbolometers.
A structurally multifunctional pressure-temperature sensor
Abstract A new multifunctional sensor for simultaneous mea-surement of pressure and temperature ... more Abstract A new multifunctional sensor for simultaneous mea-surement of pressure and temperature is proposed and modeled. The design includes elastic membranes and bi-layer beams as pressure and temperature sensing bodies, respectively, and capa-citance readout for transduction. ...
Design and Modelling of a MEMS Capacitive Temperature Sensor With Linear Capacitance-Temperature Response
Volume 12: Micro and Nano Systems, Parts A and B, 2009
ABSTRACT A capacitive temperature sensor with separate thermal actuation and capacitive readout i... more ABSTRACT A capacitive temperature sensor with separate thermal actuation and capacitive readout is introduced. A bi-layer plate with fixed-free boundary condition is used for the thermal actuation to change the gap between two parallel electrodes used for capacitance measurement. Different coefficients of thermal expansion (CTE) of the two layers in actuator cause out-of-plane deformations in the plate when the temperature changes. The proposed design has the capability to control the response of the sensor by increasing its sensitivity in a given temperature range. To obtain the desired characteristic C-T curve, the design utilizes asymmetric geometries. Different design parameters such as the size of the bi-layer plate and the sense electrodes are considered as design variables. ANSYS® FEM simulations are used to extract the C-T responses of different geometries. The results of the FEM simulations show that for a given fabrication process and material properties, the design can be modified to provide the highest sensitivity and linearity in the C-T response for a given temperature range. This temperature sensor can be used for remote and on-chip temperature measurement or temperature compensation.
MEMS-based Fabry-Perot vibration sensor for harsh environments
Proceedings of Spie the International Society For Optical Engineering, 2006
This paper presents the design, fabrication and testing results of a Fabry-Perot Micro-Opto-Mecha... more This paper presents the design, fabrication and testing results of a Fabry-Perot Micro-Opto-Mechanical Device (FPMOD) used as a vibration sensor. The un-cooled high-temperature operational capability of the FPMOD provides a viable low-cost alternative to sensors that require environmentally controlled packages to operate at high temperature. The FPMOD is a passive MEMS device that consists of a micromachined cavity formed between a substrate and a top thin film structure in the form of a cantilever beam. When affixed to a vibrating surface, the amplitude and frequency of vibration are determined by illuminating the FPMOD with a monochromatic light source and analyzing the back reflected light to determine the deflection of the beam with respect to the substrate. Given the Fabry-Perot geometry, a mechanical transfer function is calculated to permit the substrate motion to be determined from the relative motion of the beam with respect to the substrate. Because the thin film cantilever beam and the substrate are approximately parallel, this convenient two-mirror cavity arrangement needs no alignment, no reference arm, and no sophisticated stabilization techniques. The small size of the FPMOD (85-175μm), the choice of materials in which it can be manufactured (Silicon Nitride and Silicon Carbide), and its simple construction make it ideal for harsh high-temperature applications. Relative displacements in the sub-nanometer range have been measured and close agreement was found between the measured sensor frequency response and the theoretical predictions based on analytical models.
Optical Characterization of Commercial Lithiated Graphite Battery Electrodes and in Situ Fiber Optic Evanescent Wave Spectroscopy
ACS applied materials & interfaces, Jan 27, 2016
Optical characterization of graphite anodes in lithium ion batteries (LIB) is presented here for ... more Optical characterization of graphite anodes in lithium ion batteries (LIB) is presented here for potential use in estimating their state of charge (SOC). The characterization is based on reflectance spectroscopy of the anode of commercial LIB cells and in situ optical measurements using an embedded optical fiber sensor. The optical characterization of the anode using wavelengths ranging from 500 to 900 nm supports the dominance of graphite over the solid electrolyte interface in governing the anode's reflectance properties. It is demonstrated that lithiated graphite's reflectance has a significant change in the near-infrared band, 750-900 nm, compared with the visible spectrum as a function of SOC. An embedded optical sensor is used to measure the transmittance of graphite anode in the near-infrared band, and the results suggest that a unique inexpensive method may be developed to estimate the SOC of a LIB.
Microelectronic Engineering, Nov 1, 2010
This paper introduces a modified structure for parallel-plate-based MEMS tunable capacitors. The ... more This paper introduces a modified structure for parallel-plate-based MEMS tunable capacitors. The capacitor has triangular electrodes with geometric and structural asymmetry, which enhances its performance. The device structure is also equipped with a set of cantilever beams between capacitor's electrodes, called middle beams. These beams provide extra stiffness as tuning voltage increases and delay the pull-in which results in a higher tunability. They also reduce the high sensitivity of the capacitance to the voltage change and linearize the C-V response. An analytical model is developed to optimize the capacitor's dimensions for maximum linearity of the response. Numerical simulations demonstrate tunabilities over 150% where more than 2/3 of which is highly linear. Capacitors fabricated with PolyMUMPs verify that the design technique proposed in this paper can improve the linearity of the device and increase the maximum tunability. The proposed design has a simple geometry and is fabricated using three structural layers, and therefore, it can be easily integrated in tunable filters or other RF circuits.