8,256 research outputs found
Empirical Study of Noise Dependence in Electrochemical Sensors
We report the experimental study of noise in electrochemical biosensors as related to voltage and concentration. A comparison with experiments is performed for H2O2 and Ferrocyanide with bare sensors and with sensors functionalized with Multi-Walled Carbon Nanotubes (MWCNT) modified electrodes. Chronoamperometry measurements at different voltages were carried out, followed by fast Fourier transform analysis of noise at different concentration of analyte to understand the effect of concentration and voltage on the noise Power Spectral Density (PSD) and the Signal over Noise (SNR) ratio. Experimental results demonstrate the presence of 1/f noise and its dependence on the state variables. The parameters of 1/f noise i.e. the amplitude coefficient and frequency power coefficients are extracted by curve fitting, and are characterized by comparing the coefficient in different molecules, electrodes, voltages and concentration
Evaluation of coated QCM for the detection of atmospheric ozone
A coated acoustic wave sensor has been developed to selectively detect atmospheric ozone. The selective detection has been assessed using a variety of coatings: beeswax, gallic acid, indigo carmine, polybutadiene, potassium iodide and sodium nitrite. Polybutadiene was the most sensitive with a limit of detection of 55 ppb. The sensitivity was improved by operating at higher harmonics and was shown to increase linearly with harmonic up to the 11th harmonic. This novel work shows that ozone detection can be improved by operating at the crystals' harmonic frequencies and in conjunction with a suitable flow rate, a potentially highly sensitive and fast response sensor can be created based on acoustic wave technolog
Amplified Sensitivity of Nitrogen-Vacancy Spins in Nanodiamonds using All-Optical Charge Readout
Nanodiamonds containing nitrogen-vacancy (NV) centers offer a versatile
platform for sensing applications spanning from nanomagnetism to in-vivo
monitoring of cellular processes. In many cases, however, weak optical signals
and poor contrast demand long acquisition times that prevent the measurement of
environmental dynamics. Here, we demonstrate the ability to perform fast,
high-contrast optical measurements of charge distributions in ensembles of NV
centers in nanodiamonds and use the technique to improve the spin readout
signal-to-noise ratio through spin-to-charge conversion. A study of 38
nanodiamonds, each hosting 10-15 NV centers with an average diameter of 40 nm,
uncovers complex, multiple-timescale dynamics due to radiative and
non-radiative ionization and recombination processes. Nonetheless, the
nanodiamonds universally exhibit charge-dependent photoluminescence contrasts
and the potential for enhanced spin readout using spin-to-charge conversion. We
use the technique to speed up a relaxometry measurement by a factor of
five.Comment: 13 pages, 14 figure
Sensorless Battery Internal Temperature Estimation using a Kalman Filter with Impedance Measurement
This study presents a method of estimating battery cell core and surface
temperature using a thermal model coupled with electrical impedance
measurement, rather than using direct surface temperature measurements. This is
advantageous over previous methods of estimating temperature from impedance,
which only estimate the average internal temperature. The performance of the
method is demonstrated experimentally on a 2.3 Ah lithium-ion iron phosphate
cell fitted with surface and core thermocouples for validation. An extended
Kalman filter, consisting of a reduced order thermal model coupled with
current, voltage and impedance measurements, is shown to accurately predict
core and surface temperatures for a current excitation profile based on a
vehicle drive cycle. A dual extended Kalman filter (DEKF) based on the same
thermal model and impedance measurement input is capable of estimating the
convection coefficient at the cell surface when the latter is unknown. The
performance of the DEKF using impedance as the measurement input is comparable
to an equivalent dual Kalman filter using a conventional surface temperature
sensor as measurement input.Comment: 10 pages, 9 figures, accepted for publication in IEEE Transactions on
Sustainable Energy, 201
On-board monitoring of 2-D spatially-resolved temperatures in cylindrical lithium-ion batteries: Part II. State estimation via impedance-based temperature sensing
Impedance-based temperature detection (ITD) is a promising approach for rapid
estimation of internal cell temperature based on the correlation between
temperature and electrochemical impedance. Previously, ITD was used as part of
an Extended Kalman Filter (EKF) state-estimator in conjunction with a thermal
model to enable estimation of the 1-D temperature distribution of a cylindrical
lithium-ion battery. Here, we extend this method to enable estimation of the
2-D temperature field of a battery with temperature gradients in both the
radial and axial directions.
An EKF using a parameterised 2-D spectral-Galerkin model with ITD measurement
input (the imaginary part of the impedance at 215 Hz) is shown to accurately
predict the core temperature and multiple surface temperatures of a 32113
LiFePO cell, using current excitation profiles based on an Artemis HEV
drive cycle. The method is validated experimentally on a cell fitted with a
heat sink and asymmetrically cooled via forced air convection.
A novel approach to impedance-temperature calibration is also presented,
which uses data from a single drive cycle, rather than measurements at multiple
uniform cell temperatures as in previous studies. This greatly reduces the time
required for calibration, since it overcomes the need for repeated cell thermal
equalization.Comment: 11 pages, 8 figures, submitted to the Journal of Power Source
Design and Implementation of an Integrated Biosensor Platform for Lab-on-a-Chip Diabetic Care Systems
Recent advances in semiconductor processing and microfabrication techniques allow the implementation of complex microstructures in a single platform or lab on chip. These devices require fewer samples, allow lightweight implementation, and offer high sensitivities. However, the use of these microstructures place stringent performance constraints on sensor readout architecture. In glucose sensing for diabetic patients, portable handheld devices are common, and have demonstrated significant performance improvement over the last decade. Fluctuations in glucose levels with patient physiological conditions are highly unpredictable and glucose monitors often require complex control algorithms along with dynamic physiological data. Recent research has focused on long term implantation of the sensor system. Glucose sensors combined with sensor readout, insulin bolus control algorithm, and insulin infusion devices can function as an artificial pancreas. However, challenges remain in integrated glucose sensing which include degradation of electrode sensitivity at the microscale, integration of the electrodes with low power low noise readout electronics, and correlation of fluctuations in glucose levels with other physiological data. This work develops 1) a low power and compact glucose monitoring system and 2) a low power single chip solution for real time physiological feedback in an artificial pancreas system.
First, glucose sensor sensitivity and robustness is improved using robust vertically aligned carbon nanofiber (VACNF) microelectrodes. Electrode architectures have been optimized, modeled and verified with physiologically relevant glucose levels.
Second, novel potentiostat topologies based on a difference-differential common gate input pair transimpedance amplifier and low-power voltage controlled oscillators have been proposed, mathematically modeled and implemented in a 0.18μm [micrometer] complementary metal oxide semiconductor (CMOS) process. Potentiostat circuits are widely used as the readout electronics in enzymatic electrochemical sensors. The integrated potentiostat with VACNF microelectrodes achieves competitive performance at low power and requires reduced chip space.
Third, a low power instrumentation solution consisting of a programmable charge amplifier, an analog feature extractor and a control algorithm has been proposed and implemented to enable continuous physiological data extraction of bowel sounds using a single chip. Abdominal sounds can aid correlation of meal events to glucose levels. The developed integrated sensing systems represent a significant advancement in artificial pancreas systems
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Nanoparticle characterization with nanopore sensors
textA silicon nitride, solid-state nanopore sensor for characterizing nanoparticles suspended in an aqueous medium is presented, and the fundamental theory of resistive-pulse sensing based on the Coulter principle is derived. Careful analytical and experimental considerations in the interrelationships between the electrolyte concentration, nanoparticles, applied bias voltage and electronic equipment are described in detail. Various electromagnetc noise sources present in low-current electrochemical experiments are identified and eliminated. Finally, 100 nm charged polystyrene beads are analyzed by pores ranging in diameter from 300 -- 500 nm. The experimental results are found to be in good agreement with the expected event depths and event durations as described by mathematical models found in the literature.Mechanical Engineerin
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