Showing papers by "Alexander Mamishev published in 2004"

Interdigital sensors and transducers

Abstract: This review paper focuses on interdigital electrodes-a geometric structure encountered in a wide variety of sensor and transducer designs. Physical and chemical principles behind the operation of these devices vary so much across different fields of science and technology that the common features present in all devices are often overlooked. This paper attempts to bring under one umbrella capacitive, inductive, dielectric, piezoacoustic, chemical, biological, and microelectromechanical interdigital sensors and transducers. The paper also provides historical perspective, discusses fabrication techniques, modeling of sensor parameters, application examples, and directions of future research.

Classification of power quality events using optimal time-frequency representations-Part 1: theory

Abstract: Better software and hardware for automatic classification of power quality (PQ) disturbances are desired for both utilities and commercial customers. Existing automatic recognition methods need improvement in terms of their capability, reliability, and accuracy. This paper presents the theoretical foundation of a new method for classifying voltage and current waveform events that are related to a variety of PQ problems. The method is composed of two sequential processes: feature extraction and classification. The proposed feature extraction tool, time-frequency ambiguity plane with kernel techniques, is new to the power engineering field. The essence of the feature exaction is to project a PQ signal onto a low-dimension time-frequency representation (TFR), which is deliberately designed for maximizing the separability between classes. The technique of designing an optimized TFR from time-frequency ambiguity plane is for the first time applied to the PQ classification problem. A distinct TFR is designed for each class. The classifiers include a Heaviside-function linear classifier and neural networks with feedforward structures. The flexibility of this method allows classification of a very broad range of power quality events. The performance validation and hardware implementation of the proposed method are presented in the second part of this two-paper series.

Classification of power quality events using optimal time-frequency representations-Part 2: application

Abstract: Classification of power-quality (PQ)-related voltage and current waveform disturbances is a key task for power system monitoring. A new method based on the optimized time-frequency representation (TFR) has been proposed in the first paper of this two-paper series. This paper (the second paper) presents a case study of PQ event classification with the proposed method. The classification algorithm has been successfully tested with 860 real world PQ events that cover five classes, achieving a recognition rate of 98%. The algorithm is implemented on a digital signal processor (DSP) based hardware system and optimized according to the DSP architecture to meet the hard real-time constraints. The DSP-based system is capable of processing a five-cycle (83.3 ms) PQ waveform within 11.2 ms. The real-time computing capability of the algorithm has been verified with this result. The scalability of this method is also discussed.

Moisture content estimation in paper pulp using fringing field impedance spectroscopy

Abstract: Currently used methods for estimation of moisture content in paper pulp are restricted to levels of moisture concentration below 90%. Some of the existing methods require less practical double-sided contact measurements. A few other methods make restrictive assumptions, such as the constituents of the pulp that determine its conductance. This paper presents a technique that uses fringing field interdigital sensors to measure moisture concentration in paper pulp at levels as high as 96%. The method proposed in this paper uses single-sided measurements, offers high sensitivity, and does not require special operating conditions. The accuracy of the proposed method is also demonstrated. The repeatability and reproducibility of the sensor measurements are also shown.

Robotic monitoring of power systems

Abstract: Monitoring of electric power systems in real time for reliability, aging status, and presence of incipient faults requires distributed and centralized processing of large amounts of data from distributed sensor networks. To solve this task, cohesive multidisciplinary efforts are needed from such fields as sensing, signal processing, control, communications, optimization theory, and, more recently, robotics. This review paper focuses on one trend of power system monitoring, namely, mobile monitoring. The developments in robotic maintenance for power systems indicate significant potential of this technological approach. Authors discuss integration of several important relevant sensor technologies that are used to monitor power systems, including acoustic sensing, fringing electric field sensing, and infrared sensing.

Influence of variable plate separation on fringing electric fields in parallel-plate capacitors

Abstract: Measurement of bulk physical properties in dielectric materials is typically performed using a parallel-plate capacitor configuration, where a dielectric material is placed between two conducting plates and the complex permittivity is found by measuring capacitance and conductance between the electrodes. Fringing electric fields exist between any two parallel conducting plates of finite length and the additional capacitance these fields add is not easily accounted for. It is important to account for edge effects in many capacitive sensing applications in order to ensure accurate results. Unfortunately, these edge effects are not easily quantifiable and are subject to change with varying sensor geometries. A quantitative relationship between fringing field strength and sensor geometry will improve the accuracy of many capacitive sensing applications. This work presents finite element simulations showing the influence of variable plate separation on fringing field effects in a system designed to measure the dielectric properties of a fluid. A quantitative relationship is established that relates the sensor response to the plate distance and fluid position. This relationship can be applied to experimental data in order to compensate for any edge effects present in the system.

Design of multichannel fringing electric field sensors for imaging. Part I. General design principles

Abstract: Multichannel electric field sensors are used for electrical impedance and capacitance tomography applications. In cases where only one-sided access can be accommodated, fringing electric field sensors (FEF) sensors are used. The genera! design principles of multichannel fringing electric field sensors are discussed in This work. Analysis of the figures of merit of FEF sensors, such as penetration depth, signal strength, measurement sensitivity, and imaging resolution, are presented. The effects of design parameters on sensor performance are also evaluated. The qualitative design principles described in this part of the paper provide intuitive guidelines for the simulation-based design optimization procedure to be presented in the second part of the paper.

Numerical simulation and optimization of electrostatic air pumps

Abstract: Electrostatic air propulsion is a promising technology with such potential applications as energy-efficient ventilation, cooling of electronics, and dehumidification. The challenges of existing designs include the need to increase air speed, backpressure, energy efficiency, heat exchange capability, and longevity. This paper presents the numerical simulation results of an electrostatic air pump for the purpose of optimizing device characteristics through control of the inner pump electric field profile. A sharp-edge-to-parallel-plane electrode geometry with unipolar positive corona is chosen to generate linear electric field distribution and minimize energy loss. Simulations were performed for multiple collector electrode voltage distributions. A method to quantify the change in pump performance between different voltage distributions is presented. The influence of space charge on pump performance is also discussed. The ultimate goal is to create multi-channel energy efficient ionic pumps, however, single cell analysis is conducted in this study as a building block of future designs.

Simulation of a sensor array for multiparameter measurements at the prosthetic limb interface

Abstract: Sensitive skin is a highly desired device for biomechanical devices, wearable computing, human-computer interfaces, exoskeletons, and, most pertinent to this paper, for lower limb prosthetics. The measurement of shear stress is very important because shear effects are key factors in developing surface abrasions and pressure sores in paraplegics and users of prosthetic/orthotic devices. A single element of a sensitive skin is simulated and characterized in this paper. Conventional tactile sensors are designed for measurement of the normal stress only, which is inadequate for comprehensive assessment of surface contact conditions. The sensitive skin discussed here is a flexible array capable of sensing shear and normal forces, as well as humidity and temperature on each element.

Estimation of Moisture Content in Paper Pulp Containing Calcium Carbonate Using Fringing Field Impedance Spectroscopy

Abstract: Currently used methods for estimation of moisture content in paper pulp are restricted to levels of moisture concentration under 90%, and also assume that there are no additives in the pulp. This paper presents a technique that uses fringing field interdigital sensors to measure moisture concentration in paper pulp in the presence of calcium carbonate. The method proposed in this paper uses single-sided measurements, offers high sensitivity, and does not require special operating conditions. A self-adapting algorithm used for data extraction is also introduced. The accuracy of the proposed method is also demonstrated.

Design of multichannel fringing electric field sensors for imaging. Part II. Numerical examples

Abstract: Two concentric-ring fringing electric field (FEF) sensors are designed for dielectrometry measurement of round samples, as a specific example to further illustrate the design principles for FEF sensors introduced in part I of the paper. Finite element simulations are carried out to analyze and compare such sensor performance characteristics as signal strength and penetration depth. The effects of changes in sensor substrate thickness and shielding electrode width are also evaluated. Simulation results show a clear dependence between these design parameters and sensor performance.