Individual Sensor Elements Research Articles

Application of NaYF4:Yb/Er/Tm UCNPs in Array-Based Sensing of Neurotransmitters: From a Single Particle to a Multichannel Sensor Array.

A novel multichannel sensor array has been designed using a single, yet multiemissive lanthanide-doped upconversion nanoparticle (UCNP). The energy levels of lanthanide ions gave rise to several emission bands which were exploited as individual sensor elements for the recognition of four important neurotransmitters (NTs): dopamine, norepinephrine, levodopa, and serotonin. At alkaline conditions, the oxidation products of these NTs quenched the fluorescence emissions of UCNPs with different quenching degrees. The resulting fingerprint multichannel emission profiles from NaYF4:Yb/Er/Tm UCNPs allowed the discrimination of NTs with excellent accuracy. The recognition was further verified in artificial cerebrospinal fluid, as a complex biological media. We believe that the designed UCNP-based multichannel sensor array offers innovative insights into the discrimination of various chemical signatures using a single measurement.

Self-assembly of highly sensitive 3D magnetic field vector angular encoders.

Novel robotic, bioelectronic, and diagnostic systems require a variety of compact and high-performance sensors. Among them, compact three-dimensional (3D) vector angular encoders are required to determine spatial position and orientation in a 3D environment. However, fabrication of 3D vector sensors is a challenging task associated with time-consuming and expensive, sequential processing needed for the orientation of individual sensor elements in 3D space. In this work, we demonstrate the potential of 3D self-assembly to simultaneously reorient numerous giant magnetoresistive (GMR) spin valve sensors for smart fabrication of 3D magnetic angular encoders. During the self-assembly process, the GMR sensors are brought into their desired orthogonal positions within the three Cartesian planes in a simultaneous process that yields monolithic high-performance devices. We fabricated vector angular encoders with equivalent angular accuracy in all directions of 0.14°, as well as low noise and low power consumption during high-speed operation at frequencies up to 1 kHz.

Precision and Limits of Detection for Selected Commercially Available, Low-Cost Carbon Dioxide and Methane Gas Sensors.

The performance of a sensor platform for environmental or industrial monitoring is sensitive to the cost and performance of the individual sensor elements. Thus, the detection limits, accuracy, and precision of commercially available, low-cost carbon dioxide and methane gas concentration sensors were evaluated by precise measurements at known gas concentrations. Sensors were selected based on market availability, cost, power consumption, detection range, and accuracy. A specially constructed gas mixing chamber, coupled to a precision bench-top analyzer, was used to characterize each sensor during a controlled exposure to known gas concentrations. For environmental monitoring, the selected carbon dioxide sensors were characterized around 400 ppm. For methane, the sensor response was first monitored at 0 ppm, close to the typical environmental background. The selected sensors were then evaluated at gas concentrations of several thousand ppm. The determined detection limits accuracy, and precision provides a set of matrices that can be used to evaluate and select sensors for integration into a sensor platform for specific applications.

Optimal design of angular position sensors

PurposeThis paper aims to investigate the optimal placement and/or orientation of individual sensor elements within integrated angular position sensors, in particular magnetic sensors based on the Hall effect or magnetoresistive effects under consideration of random deviations (variations in the production process, environmental influences, noise) and correlations of these influences.Design/methodology/approachThe authors utilize methods from optimal design of experiments to consider random deviations in a system-level model. In this sensor model, they include spatial dependencies of random deviations by means of a Gaussian random field. Based on this, an approach for fast determination of D-optimal designs is presented.FindingsThe results show that the intuitive and commonly used distributions of magnetic field sensors are actually optimal for the determination of in-phase and quadrature signals in the presence of spatial correlations, provided that the number of field sensors is higher or equal to three. However, in the uncorrelated case, the intuitive solutions are not the only optimal solutions or even not optimal at all. It is found that a restriction to symmetric designs is not necessary; thus, the design space can be extended to allow for further improvements, e.g. miniaturization, of such angular position sensors.Originality/valueThe proposed approach allows for the fast optimization based on a system model. Correlated random influences are considered by means of a Gaussian random field, which can be obtained either from measurements or from field simulations, e.g. using the finite element method. As this is done before the actual simulation, such evaluations are not needed during the optimization, which allows for very fast solution of the optimization problem. Therefore, the approach is well suited for application-dependent adjustment of sensor designs.

Practical Use of Metal Oxide Semiconductor Gas Sensors for Measuring Nitrogen Dioxide and Ozone in Urban Environments.

The potential of inexpensive Metal Oxide Semiconductor (MOS) gas sensors to be used for urban air quality monitoring has been the topic of increasing interest in the last decade. This paper discusses some of the lessons of three years of experience working with such sensors on a novel instrument platform (Small Open General purpose Sensor (SOGS)) in the measurement of atmospheric nitrogen dioxide and ozone concentrations. Analytic methods for increasing long-term accuracy of measurements are discussed, which permit nitrogen dioxide measurements with 95% confidence intervals of 20.0 and ozone precision of 26.8 , for measurements over a period one month away from calibration, averaged over 18 months of such calibrations. Beyond four months from calibration, sensor drift becomes significant, and accuracy is significantly reduced. Successful calibration schemes are discussed with the use of controlled artificial atmospheres complementing deployment on a reference weather station exposed to the elements. Manufacturing variation in the attributes of individual sensors are examined, an experiment possible due to the instrument being equipped with pairs of sensors of the same kind. Good repeatability (better than 0.7 correlation) between individual sensor elements is shown. The results from sensors that used fans to push air past an internal sensor element are compared with mounting the sensors on the outside of the enclosure, the latter design increasing effective integration time to more than a day. Finally, possible paths forward are suggested for improving the reliability of this promising sensor technology for measuring pollution in an urban environment.

Piezoelectric Vibratory-Cantilever Force Sensors and Axial Sensitivity Analysis for Individual Triaxial Tactile Sensing

Vibratory force sensors are fabricated using piezoelectric capacitors on microcantilever structures for triaxial sensitivity by the individual sensor element. The cantilevers have been formed into a 3-D curved shape by controlling residual stress combination of the multilayered structure. Triaxial tactile sensitivity of the cantilever sensor is analyzed under a tactile load application onto the surface of an elastomer in which the cantilever is embedded, mimicking human skin structure. The cantilever is converse-piezoelectrically excited by an external ac voltage and three resonant modes are developed to detect the applied load vector components by the single sensor element. Resonant frequency shifts of each mode are investigated upon load applications. The results show that the frequencies vary to the three axial tactile loads independently and they can be superposed with corresponding to the superposition of the load components. The applied load vectors are estimated by resonant frequencies of the single cantilever sensor with compensating nonlinearities of the sensor response. The estimated error is less than 1.1% to the full scale of the load ±4 kPa.

Temperature Grid Sensor for the Measurement of Spatial Temperature Distributions at Object Surfaces

This paper presents results of the development and application of a new temperature grid sensor based on the wire-mesh sensor principle. The grid sensor consists of a matrix of 256 Pt1000 platinum chip resistors and an associated electronics that measures the grid resistances with a multiplexing scheme at high speed. The individual sensor elements can be spatially distributed on an object surface and measure transient temperature distributions in real time. The advantage compared with other temperature field measurement approaches such as infrared cameras is that the object under investigation can be thermally insulated and the radiation properties of the surface do not affect the measurement accuracy. The sensor principle is therefore suited for various industrial monitoring applications. Its applicability for surface temperature monitoring has been demonstrated through heating and mixing experiments in a vessel.

Realistic camera noise modeling with application to improved HDR synthesis

Due to the ongoing miniaturization of digital camera sensors and the steady increase of the “number of megapixels”, individual sensor elements of the camera become more sensitive to noise, even deteriorating the final image quality. To go around this problem, sophisticated processing algorithms in the devices, can help to maximally exploit the knowledge on the sensor characteristics (e.g., in terms of noise), and offer a better image reconstruction. Although a lot of research focuses on rather simplistic noise models, such as stationary additive white Gaussian noise, only limited attention has gone to more realistic digital camera noise models. In this article, we first present a digital camera noise model that takes several processing steps in the camera into account, such as sensor signal amplification, clipping, post-processing,.. We then apply this noise model to the reconstruction problem of high dynamic range (HDR) images from a small set of low dynamic range (LDR) exposures of a static scene. In literature, HDR reconstruction is mostly performed by computing a weighted average, in which the weights are directly related to the observer pixel intensities of the LDR image. In this work, we derive a Bayesian probabilistic formulation of a weighting function that is near-optimal in the MSE sense (or SNR sense) of the reconstructed HDR image, by assuming exponentially distributed irradiance values. We define the weighting function as the probability that the observed pixel intensity is approximately unbiased. The weighting function can be directly computed based on the noise model parameters, which gives rise to different symmetric and asymmetric shapes when electronic noise or photon noise is dominant. We also explain how to deal with the case that some of the noise model parameters are unknown and explain how the camera response function can be estimated using the presented noise model. Finally, experimental results are provided to support our findings.

A Flexible Polymer Sensor for Light Point Localization

Abstract We present a flexible polymer sensor for light point localization based on the pyroelectric polymer poly(vinylidene fluoride) (PVDF) in combination with large area resistive electrodes. This large area sensor is simple in design; a division of the sensor surface into an array of individual sensor elements as used in active matrix technology is avoided. Electronic circuitry is placed only at the edges of the device. We have fabricated a flexible sensor strip with a length of 12 cm and a width of 1.6 cm according to the proposed concept. The position sensitive output signals of the sensor strip have been measured in response to the intensity-modulated light of a red laser diode. Two model-based normalization procedures have been developed in order to increase the quality of the measurement signals. The results indicate that the sensor strip can be treated mathematically analogous to a transmission line. Calculations based on the solutions of the telegrapher's equations under the appropriate boundary conditions are in good agreement with the experimental results, proving the suitability of the proposed concept for position sensitive detection.

Vector Tactile Sensing by a Single Sensor Element of Vibratory Microcantilever Based on Multimode Resonant Frequency Shift

Vibratory force sensors have been fabricated using piezoelectric capacitors on microcantilevers for triaxial sensitivity by a single sensor element. The cantilevers have been formed into three-dimensionally curved shape by controlling residual stress combination of the multilayered structure. Triaxial tactile sensitivity of the cantilever has been analyzed under a load application onto the surface of an elastomer in which the cantilever is embedded. The cantilever is converse-piezoelectrically excited by an external ac voltage and three resonant modes have been developed to detect the applied load vector components by individual sensor element. The applied load vectors are estimated by measured resonant frequencies of the single cantilever sensor in an error less than 1.1% to the full scale of the load 4kPa.

Harnessing a Ratiometric Fluorescence Output from a Sensor Array

Ratiometric fluorescence-based sensors are widely sought after because they can effectively convert even relatively small changes in optical output into a strong and easy-to-read signal. However, ratiometric sensor molecules are usually difficult to make. We present a proof-of-principle experiment that shows that efficient ratiometric sensing may be achieved by an array of two chromophores, one providing an on-to-off response and the second yielding an off-to-on response in a complementary fashion. In the case that both chromophores emit light of different color, the result is a switching of colors that may be utilized in the same way as from a true ratiometric probe. The chromophore array comprises two sensor elements: i) a polyurethane membrane with embedded N-anthracen-9-yl-methyl-N-7-nitrobenzoxa-[1,2,5]diazo-4-yl-N',N'-dimethylethylenediamine hydrochloride and ii) a membrane with N,N-dimethyl-N'-(9-methylanthracenyl)ethylenediamine. A combination of photoinduced electron transfer (PET) and fluorescence resonance energy transfer (FRET) allows for green-to-blue emission switching in the presence of Zn(II) ions. The sensing experiments carried out with different Zn(II) salts at controlled pH revealed that the degree of color switching in the individual sensor elements depends on both the presence of Zn(II) ions and the counter anion. These results suggest that sensing of both cations and anions may perhaps be extended to different cation-anion pairs.

Steering vector sensor array elements with linear cardioids and nonlinear hippioids

The purpose of this work is to study the impact due to individual vector sensor element steering patterns on linear array beamforming. Standard, linear beamformers employ cardioid beampatterns for each vector sensor. In this work, a class of vector sensor element steering patterns beyond the standard cardioid was examined. The element weighting is nonlinear but nonadaptive, making it simple to implement in hardware processing. The new sensor steering patterns, referred to as hippioids, are products of cardioids and various powers of hippopedes. The angular resolution of individual sensors, the impact on angular resolution from arrays of varying aperture, and peak-to-sidelobe levels will serve as performance measures. An example of the differences in vector sensor steering patterns is provided using measured directional frequency and recorded buoy data.

Steering vector sensor array elements with cardioids, hippopedes, and other beam shapes

The purpose of this report is to study the impact on linear beamforming due to individual vector sensor element steering patterns. Standard, linear beamformers employ cardioid beampatterns for each vector sensor. In this work, we examine a class of vector sensor element steering patterns beyond the standard cardioid. The element weighting is nonlinear but nonadaptive, making it simple to implement in hardware processing. The new sensor steering patterns, referred to as hippioids, are products of cardioids and various orders of hippopedes. The angular resolution of individual sensors, and the impact on angular resolution from arrays of varying aperture, will serve as the performance measure along with peak‐to‐sidelobe levels. An example of the differences in vector sensor steering patterns is provided using measured, DIFAR buoy data. [Work supported by the Office of Naval Research, Code 321OA, the Naval Postgraduate School, and the Netherlands Defense Academy.]

Evolution of Osmosensory MAP Kinase Signaling Pathways1

Mitogen-activated protein (MAP) kinases constitute a large family of proteins with many functions. They are represented by a multitude of paralogous isoforms in yeast, vertebrates, and other eukaryotes. A phylogenetically conserved function of MAP kinases is to carry osmotic signals from sensory to target elements of cells. Even though this function of MAP kinases is ubiquitous and characteristic of unicellular and multicellular eukaryotes alike the contingencies between individual MAP kinases, sensor elements, and target elements have been subject to vast modification during evolution. Extensive networking of MAP kinase cascades with other signaling pathways is reflected by the large number of diverse signals that can be carried by a single MAP kinase pathway and flexible activation kinetics. It is emerging that the most important function of MAP kinase networks may not be signal amplification but integration of information about the setpoint of environmental parameters (including osmolality) with other physiological processes to control cell function. Insight into how this cellular integration of information is achieved by MAP kinase networks will shed light on the principles of cell dynamics and adaptation.

Design, fabrication and vapor characterization of a microfabricated flexural plate resonator sensor and application to integrated sensor arrays

A chemical vapor detection and biosensor array based on microfabricated silicon resonators coated with thin film polymer sorption layers is described. The resonators within the array are micro-electromechanical (MEM) flexural plate wave (FPW) sensors that have been miniaturized to allow many independently addressable sensors to be integrated within a single silicon chip. The target analyte of an individual sensor within the chip is selected by placing a polymer coating onto the resonating membrane. Detection is performed by monitoring changes in the frequency and damping factor of the resonance as the coating interacts with the environment. This work documents vapor response characterization of an individual sensor element within an array and reports on the operation of an eight-element sensor array. Polymer coatings targeted toward detection of chemical weapon agents have been applied to the sensor and chemical vapor exposure tests using two chemical weapon simulants and four vapor phase interferents have been performed. Data describing temperature dependence, long-term/short-term drift stability, detection limits, detection linearity and vapor selectivity will be presented. The use of resonant damping information is shown to provide the ability to discriminate between vapor analytes that produce equal resonant frequency shifts.

Intensity mappings within the context of near-sensor image processing

In the original near-sensor image processing (NSIP) concept, the intensity level for an individual sensor element is mapped onto the time axis so that the time to reach the threshold is inversely proportional to the intensity. In many cases this is favorable, in some cases there is a need for another mapping between time and intensity. We show that such mappings can be achieved by either inserting delays or by varying the threshold voltage. The result is that to achieve a linear mapping it is much more favorable to use a variable threshold since the processing power of the sensor is then better utilized. An interesting result, when it comes to adaptive mapping, is that the traditionally time consuming operation histogram equalization can be accomplished almost for free in the NSIP concept. We also show that other histogram-based, i.e., data-dependent, mapping can be easily implemented.

A stress-component-selective tactile sensor array

A stress-component-selective tactile array, based on piezoelectric polymers, and its associated data acquisition system are described. The seven-taxel sensor array is made up of elements sensitive to one or more components of the stress field acting upon them. The six independent components of the stress tensor can be calculated from a linear combination of the responses of the six miniaturized elements composing each taxel. The array is developed with the aim of obtaining a skin-like tactile sensor able to perform fine-form discrimination of objects in contact with it. It is also thought to be instrumental in revealing phenomena related to incipient slippage during object manipulation and grasping. The multi-component sensor, based on 42 miniaturized piezoelectric polymer discs, is supported by a polyimide sheet with microlithographically defined electrodes. The sensor elements are embedded into a rubber layer with appropriate thickness in order to sample properly the stress field and to obtain good signal-to-noise ratio at the input of the electronic signal processing unit. Preliminary experiments to test the ability of individual sensor elements to resolve normal and shear stress components have shown good agreement with the responses predicted by analytical solutions of elastic contact problems.

Contact-type line image sensor using Pb_2CrO_5 thin film

A contact-type line image sensor using a semiinsulating Pb(2)CrO(5) thin film deposited on a glass substrate by an electron beam evaporation deposition technique is described. The sensor has a simple structure and a high scanning rate of 1 ms/line. An individual sensor element responds to light modulated at 100-kHz frequency, so a higher scanning rate is expected. A matrix driving method using a simple reading circuit is used to operate a sensor composed of 32 elements at a rate of 8 elements/mm. Some practical results on image reading are demonstrated.