Search

The giant magnetoimpedance (GMI) and giant stress impedance (GSI) behaviors of amorphous ribbons composed of three commercially available materials (Co66Si15B14Fe4Ni1, Fe81B13Si3.5C2, and Ni40Fe40Si + B19Mo1−2) with differing saturation magnetostriction constants [Formula: see text] and Young's moduli ( E) were studied under longitudinal stress/strain. The linearity of the ribbons' GSI responses and gauge factors was measured to create a figure of merit and compare their stress/strain sensing performance for strains up to ɛ = 10 × 10−3. We observed that the Ni40Fe40Si + B19Mo1−2 ribbon displayed the best performance for low strains ( ɛ −3), whereas the Co66Si15B14Fe4Ni1 ribbon displayed the best performance for higher strains ( ɛ −3). We conclude that the suitability of a material for sensing strains in any given strain regime has a complex dependence on both [Formula: see text] and E, the former of which dictates both the absolute magnitude of the impedance variation materials exhibit (i.e., the dynamic range), while both [Formula: see text] and E control how their impedances vary with applied strain.

Understanding dynamically-induced stochastic switching effects in soft ferromagnetic nanowires is a critical challenge for realising spintronic devices with deterministic switching behaviour. Here, we present a micromagnetic simulation protocol for qualitatively predicting dynamic stochastic domain wall (DW) pinning/depinning at artificial defect sites in Ni80Fe20 nanowires, and demonstrate its abilities by correlating its predictions with the results of focused magneto-optic Kerr effect measurements. We analyse DW pinning configurations in both thin nanowires (t = 10 nm) and thick nanowires (t = 40 nm) with both single (asymmetric) and double (symmetric) notches, showing how our approach provides understanding of the complex DW-defect interactions at the heart of stochastic pinning behaviours. Key results explained by our model include the total suppression of stochastic pinning at single notches in thick nanowires and the intrinsic stochasticity of pinning at double notches, despite their apparent insensitivity to DW chirality.

Finite temperature micromagnetic simulations were used to investigate the magnetisation structure, propagation dynamics and stochastic pinning of domain walls in rare earth-doped Ni80Fe20 nanowires. We first show how the increase of the Gilbert damping, caused by the inclusion rare-earth dopants such as holmium, acts to suppress Walker breakdown phenomena. This allows domain walls to maintain consistent magnetisation structures during propagation. We then employ finite temperature simulations to probe how this affects the stochastic pinning of domain walls at notch-shaped artificial defect sites. Our results indicate that the addition of even a few percent of holmium allows domain walls to pin with consistent and well-defined magnetisation configurations, thus suppressing dynamically-induced stochastic pinning/depinning phenomena. Together, these results demonstrate a powerful, materials science-based solution to the problems of stochastic domain wall pinning in soft ferromagnetic nanowires.

A distinctive vocalization of the sperm whale, Physeter macrocephalus (=P. catodon), is the coda: a short click sequence with a distinctive stereotyped time pattern [Watkins and Schevill, J. Acoust. Soc. Am. 62, 1485-1490 (1977)]. Coda repertoires have been found to vary both geographically and with group affiliation [Weilgart and Whitehead, Behav. Ecol. Sociobiol. 40, 277-285 (1997)]. In this work, the click timings and repetition patterns of sperm whale codas recorded in the Mediterranean Sea are characterized statistically, and the context in which the codas occurred are also taken into consideration. A total of 138 codas were recorded in the central Mediterranean in the years 1985-1996 by several research groups using a number of different detection instruments, including stationary and towed hydrophones, sonobuoys and passive sonars. Nearly all (134) of the recorded codas share the same "3+1" (/// /) click pattern. Coda durations ranged from 456 to 1280 ms, with an average duration of 908 ms and a standard deviation of 176 ms. Most of the codas (a total of 117) belonged to 20 coda series. Each series was produced by an individual, in most cases by a mature male in a small group, and consisted of between 2 and 16 codas, emitted in one or more "bursts" of 1 to 13 codas spaced fairly regularly in time. The mean number of codas in a burst was 3.46, and the standard deviation was 2.65. The time interval ratios within a coda are parameterized by the coda duration and by the first two interclick intervals normalized by coda duration. These three parameters remained highly stable within each coda series, with coefficients of variation within the series averaging less than 5%. The interval ratios varied somewhat across the data sets, but were highly stable over 8 of the 11 data sets, which span 11 years and widely dispersed geographic locations. Somewhat different interval ratios were observed in the other three data sets; in one of these data sets, the variant codas were produced by a young whale. Two sets of presumed sperm whale codas recorded in 1996 had 5- and 6-click patterns; the observation of these new patterns suggests that sperm whale codas in the Mediterranean may have more variations than previously believed.

Backscattering strength measurements are usually extracted from short‐range reverberation data using direct‐path returns or from long‐range reverberation data for which the dominant source of reverberation (e.g., a bottom seamount) is known. The small area ensonified by short‐range direct paths provides only a relatively small data sample for backscattering strength estimates. While long‐range data cover a much larger area, the returns from the surface and bottom are not always easily identified in the data. In the Arctic both the surface (ice) and bottom contribute significantly to the reverberation at low frequencies. The contributions of ice and bottom must be separated by signal processing means before their backscattering strengths can be measured separately. In this paper a method to separately measure the surface and bottom backscattering strengths using medium‐range (5‐ to 20‐km) reverberation data is investigated. The method of separation is based on the time versus vertical arrival angle contour...

Under‐ice scattering strengths in the backward direction were measured in April 1989 during the CEAREX 89 field experiment in the Norwegian‐Greenland Sea using a large‐aperture (1200‐m) vertical hydrophone array and 1.8‐lb SUS explosive sources. Scattering strength estimates for frequencies of 24–105 Hz are presented as a function of scattering angle (2.5°–40° grazing), averaged over incident angles in the range 10°–15° grazing. The corresponding (monostatic) backscattering strength is found to be approximately 10 dB below that reported by Milne [J. Acoust. Soc. Am. 36, 1551–1556 (1964)] for data collected at approximately the same time of year in 1962 near the Canadian Archipelago. The results are compared with scattering functions derived from a Burke–Twersky model [J. Acoust. Soc. Am. 40, 883–895 (1966)], which represents the ice ridges as rigid elliptical half‐cylinders. The variations of the measured scattering strength with both scattering angle and frequency are well fitted by this model for scattering angles below 20° grazing.

In the Arctic ocean, very low‐frequency (10–50 Hz) reverberation returns from the ice and bottom both contribute to the total received reverberation and are not easily distinguishable in long‐range reverberation data, except where there is a dominant bottom or ice feature. In this paper, a normal‐mode model of scattering from surface and bottom protuberances is applied to model long‐range reverberation data collected during the CEAREX 89 experiment in the Norwegian/Greenland Seas. Modeled reverberation spectrum levels at 23 Hz are compared with data to investigate the relative contributions of the ice and bottom to the measured reverberation. The normal‐mode model of boundary scattering is based on a generalization of recent work of Ingenito [F. Ingenito, J. Acoust. Soc. Am. 82, 2051–2059 (1987)] treating scattering from a rigid sphere in a stratified waveguide. Adiabatic normal mode theory is used to model the propagation to and back from the scatterer in a range‐dependent waveguide. Using the small‐ka a...

Research into lab‐on‐a‐chip multiplexed bioassays has focused on libraries of biochemical probes, indexed by optically encoded micron‐sized labels. However, few current methods have reconciled large multiplexing capability with a rapid detection system amenable to miniaturization. Magnetic identification of labels provides a strong candidate solution to this problem, yet no proposed single‐label magnetic detection system can both read and encode magnetic labels. We present a magnetic multiplexed assay in lab‐on‐a‐chip format which identifies target biomolecules from the hybridization results by reading encoded magnetic beads. We show that a microfabricated magnetoresistive ring‐shaped sensor can read the magnetic moments of individual commercially available paramagnetic beads using an active digital technique. This work provides proof of principle for a new approach to magnetic labeling of biomolecules for high‐throughput bioassays.

Ferromagnetic metal rings of nanometre range widths and thicknesses exhibit fundamentally new spin states, switching behaviour and spin dynamics, which can be precisely controlled via geometry, material composition and applied field. Following the discovery of the 'onion state', which mediates the switching to and between vortex states, a range of fascinating phenomena has been found in these structures. In this overview of our work on ring elements, we first show how the geometric parameters of ring elements determine the exact equilibrium spin configuration of the domain walls of rings in the onion state, and we show how such behaviour can be understood as the result of the competition between the exchange and magnetostatic energy terms. Electron transport provides an extremely sensitive probe of the presence, spatial location and motion of domain walls, which determine the magnetic state in individual rings, while magneto-optical measurements with high spatial resolution can be used to probe the switching behaviour of ring structures with very high sensitivity. We illustrate how the ring geometry has been used for the study of a wide variety of magnetic phenomena, including the displacement of domain walls by electric currents, magnetoresistance, the strength of the pinning potential introduced by nanometre size constrictions, the effect of thermal excitations on the equilibrium state and the stochastic nature of switching events.

Acoustic reverberation data from SUS explosions collected during the CEAREX 89 Arctic experiment are analyzed to estimate both under-ice and bottom backscattering strengths at very low frequencies (below 50 Hz). Short range direct-path returns are analyzed to measure the backward scattering strengths of the under-ice surface for scattering angles between 2.5° and 40° grazing and frequencies between 24 Hz and 105 Hz. Medium range (5–20 km) ice and bottom reverberation returns received on a 1200-m vertical array are separated using the time-arrival angle relationship to measure ice and bottom backscattering strengths at 23 Hz for grazing angles of 15°–60°. Long range reverberation is modeled by combining a normal-mode based scattering description with grazing angle dependent scattering functions based on small-ka (low frequency) approximations. Reverberation data at 23 Hz are successfully modeled for four cases of different bottom bathymetry and source depth.

In the Arctic ocean, very low‐frequency (10–50 Hz) reverberation returns from the ice and bottom both contribute to the total received reverberation and are not easily distinguishable in long‐range reverberation data, except where there is a dominant bottom or ice feature. In this paper, a normal‐mode scattering model for surface and bottom protuberance is used to model long‐range reverberation data collected during the CEAREX 89 experiment in the Norwegian/Greenland Seas. Modeled reverberation spectrum levels at 23 Hz are compared with data to investigate the relative contributions of the ice and bottom to the measured reverberation. It is found that for a source at 91‐m depth in the 3000‐m‐deep basin, the reverberation level for a receiver at 91 m is dominated by scattering from the ice except for reverberation associated with certain identifiable bottom features. For the same environment but a deeper (244‐m) source, reverberation levels from the ice and bottom are more comparable. For a strongly range‐...

A new flowmeter under development at NEL is described, consisting of an orifice plate with a spring-loaded disc moving in an annular expansion. The differential pressure across the annular orifice is directly proportional to the flowrate. Tests on a first prototype of 105 mm diameter have given encouraging results.

All instrumentation systems need calibrating to allow removal or correction of systematic errors introduced into the measurement by transducer and other systems component inaccuracies. In some cases, where system components are subject to drift, or where extreme accuracy is required, a calibration procedure may be used many times a day. In other cases, where long-term stability of components is good, calibration may only occur once a week or once a month. Without such calibration, credibility in the results of the measurement cannot be established.

This is an enormous subject which really needs a book-or, rather, a series of books-to itself, and this chapter must therefore have a very limited aim. This is firstly to deal with a few matters of special importance to flowmeter users, such as the design of piezometer rings and thermometer pockets, secondly to give some idea of the great variety of equipment now available, and thirdly to offer a few practical tips on the use of some of the devices most commonly found in flow metering situations.

Thus far this book has been concerned with meters for measuring total flow and flowrate in pipes. We come now to instruments of a related but essentially different type, namely instruments for measuring the velocity at a point of a flowing fluid.

There are two alternative ways to tackle the problem of measuring mass flowrate. One is to design a meter whose response is a function of mass flowrate only, so that a knowledge of the physical properties of the fluid is not necessary. Such meters are known as ‘true mass flowmeters’.

This book is about measuring the flow of fluids, and especially of fluids contained in pipes and ducts. To understand this subject it is useful to know something about the way fluids behave, and especially about the properties mentioned below.

The electromagnetic flowmeter utilises the same basic principle as the electrical generator: when a conductor moves across a magnetic field a voltage is induced in the conductor, and the magnitude of the voltage is directly proportional to the speed of the moving conductor. If the conductor is a section of conductive liquid flowing in a non-conductive pipe through a magnetic field, and electrodes are mounted in the pipe wall at the positions shown in Figure 6.1, the voltage induced across the electrodes should be proportional to flowrate.

This chapter is concerned with rotating mechanical flowmeters of the ‘full-bore’ type, for measuring either the total volume or the volumetric flowrate of a fluid flowing in a pipe. Rotating mechanical devices used for measuring velocity at a point are dealt with in Chapter 7, and those used for mass flow measurement in Chapter 8.

There are many other flowrate meters which, although not qualifying as differ­ential pressure meters, make use of pressure differences generated in flowing fluids. The most important types of these are described in this chapter.

The purpose of this chapter is to bring together a collection of miscellaneous information likely to benefit the flowmeter user faced with the need for calibrations, for advice or for information. Sources of published information on specific areas have already been given in the ‘Where to learn more’ sections at the end of the earlier chapters; this chapter fills in the gaps by listing the information sources of a more general character.

One thing must be made plain at the outset: the way a flowmeter is installed matters a lot.

In principle there is no room for argument about what ‘the right flowmeter for the job’ means. The right flowmeter is the one that will do the job adequately at the lowest possible total cost, including initial cost, running costs, and the indirect costs arising from inaccurate measurements and from loss of plant utilisation when the flowmeter is out of action.

For many years, differential pressure meters were the only devices available for measuring volumetric flowrate in a pipe with reasonable accuracy at a reasonable cost. Nowadays there are many alternatives, but even so, the differential pressure meter family still holds the largest slice of the market.

The author of the book 'Flowmeters' (Macmillan, 1979) replies to criticism of 'incorrect or misleading statements' which allegedly appeared in his original work.

The letter from a member of The Institute of Physics in Trinidad in the March issue of Physics Bulletin (p79) is a useful reminder of the difficulties facing physicists in Third World countries. It seems to me that it would be reasonable for British physicists to show a measure of practical sympathy towards their less fortunate colleagues overseas.