Alexander V. Mamishev

Interdigital sensors and transducers

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.

Moisture equilibrium in transformer paper-oil systems

This paper provides an overview of the classic moisture equilibrium curves and their history and provides useful information on the relationships among them and their validity.

Battery-free wireless identification and sensing

The Wireless Identification and Sensing Platform (WISP) project explores an approach to provide power for sensor networks, based on passive radio-frequency-identification technology. In traditional passive RFID systems, ambient high-power readers interrogate battery-free devices, called tags, that modulate the interrogating signal to communicate a unique identifier to the reader. The WISP project aims to augment RFID tags with sensors so that tags can also send sensed data to the readers. We call these augmented tags wisps. Basing wisps on RFID has some immediate advantages. RFID tags communicate to ambient readers over distances of up to eight meters. Solutions compatible with RFID standards might therefore find quicker acceptance and see faster improvement than other solutions.

RFID-based techniques for human-activity detection

The iBracelet and the Wireless Identification and Sensing Platform promise the ability to infer human activity directly from sensor readings.

A wirelessly-powered platform for sensing and computation

We present WISP, a wireless, battery-free platform for sensing and computation that is powered and read by a standards compliant Ultra-High Frequency (UHF) RFID reader. To the reader, the WISP appears to be an ordinary RFID tag. The WISP platform includes a general-purpose programmable flash microcontroller and implements the bi-directional communication primitives required by the Electronic Product Code (EPC) RFID standard, which allows it to communicate arbitrary sensor data via an EPC RFID reader by dynamically changing the ID it presents to the reader. For each 64 bit “packet,” the WISPs microcontroller dynamically computes the 16-bit CRC that the EPC standard requires of valid packets. Because the WISP device can control all bits of the presented ID, 64 bits of sensor data can be communicated with a single RFID read event. As an example of the system in operation, we present 13 hours of continuous-valued light-level data measured by the device. All the measurements were made using power harvested from the RFID reader. No battery, and no wired connections (for either power or data) were used. As far as we are aware, this paper reports the first fully programmable computing platform that can operate using power transmitted from a long-range (UHF) RFID reader and communicate arbitrary, multi-bit data in response to a single RFID reader poll event.

Energy Scavenging for Inductively Coupled Passive RFID Systems

Deployment of passive radio-frequency identification (RFID) systems or RFID-enhanced sensor networks requires good understanding of the energy scavenging principles. This paper focuses on the energy scavenging design considerations of inductively coupled passive HF RFID systems. The theoretical estimation of the power by a loop antenna is derived, and the effect of the design parameters on the harvested power is investigated. It is shown that the power delivery performance is largely affected by the tag load at the reader. An adaptive matching circuit at the reader is proposed for achieving optimum power delivery performance when the reader has a variable load. Experimental studies confirm analytical derivations

Analysis of high impedance faults using fractal techniques

Phase currents and voltages in a distribution power system change with a certain degree of chaos when high impedance faults (HIFs) occur. This paper describes application of the concepts of fractal geometry to analyze chaotic properties of high impedance faults. Root-mean-square rather that instantaneous values of currents are used for characterization of temporal system behavior; this results in relatively short time-series available for analysis. An algorithm is presented for pattern recognition and detection of HIFs; it is based on techniques suited for analysis of relatively small data sets. Examples are given to illustrate the ability of this approach to discriminate between faults and other transients in a power system.

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

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.

Effects of conductor sag on spatial distribution of power line magnetic field

Traditional extremely low frequency (ELF) magnetic field computation techniques assume that the current carrying power line conductors are straight horizontal wires. This assumption results in a model whose magnetic fields are distorted from those produced in reality. An exact solution and an approximation are proposed for modeling magnetic fields produced by the sagged conductors of power lines, by taking advantage of the fact that the equation of the catenary exactly describes the line sag. The proposed approaches differ in the required computational burden and in the precision of the results. A field mapping measurement example illustrates the applicability and the need for this analysis. The relative importance of the catenary effect is discussed.

Moisture content estimation in paper pulp using fringing field impedance spectroscopy

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.