Home
>
Journals & magazines
>
IEE Proceedings - Science, Measurement and Techno...
>
Volume 145
Issue 5
IEE Proceedings - Science, Measurement and Technology
Volume 145, Issue 5, September 1998
Volumes & issues:
Volume 145, Issue 5
September 1998
-
- Author(s): A. Castellani ; A. Bondiou-Clergerie ; P. Lalande ; A. Bonamy ; I. Gallimberti
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 185 –192
- DOI: 10.1049/ip-smt:19982206
- Type: Article
- + Show details - Hide details
-
p.
185
–192
(8)
In-flight experiments have shown that in most cases the aircraft striking process is initiated by the bidirectional propagation of two leaders of opposite polarities. A laboratory experiment has been designed to analyse in detail the development of such a ‘bi-leader’ from an electrically floating conductor suspended in a 10.5 m plane-to-plane gap, submitted to an impulse voltage. The shape of the floating object, the electrode configuration and the voltage waveshape have been optimised to allow the observation of the simultaneous development of both discharges before their junction with the planes. Current and electric field probes have been installed at both ends of the floating object, and synchronised with time-resolved optical diagnostics. The authors give a detailed description of the observed phenomena and compare the characteristics of the positive and negative discharges with those already studied in classical rod-to-plane gaps. - Author(s): A. Castellani ; A. Bondiou-Clergerie ; P. Lalande ; A. Bonamy ; I. Gallimberti
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 193 –199
- DOI: 10.1049/ip-smt:19982011
- Type: Article
- + Show details - Hide details
-
p.
193
–199
(7)
A specific experiment has been designed to study the simultaneous development of two leaders of opposite polarities from a floating electrode suspended in a plane-to-plane gap. In the paper, the physical properties of both discharges are investigated in detail, and a quantitative analysis of inception thresholds, corona charges, leaders velocities, etc. is presented. Special attention has been devoted to the analysis of the mechanisms of the negative discharge, including the specific processes of the ‘pilot system’ and the ‘space leader’, already observed in previous experiments in point-to-plane gaps. The coupling mechanism between the positive and the negative discharges have been studied according to the temporal evolution of the floating potential of the conductor. These results will be used for the development and validation of the self-consistent model of the ‘bileader’ process to obtain numerical simulations of the aircraft lightning stroke. - Author(s): N.L. Allen ; K.J. Cornick ; D.C. Faircloth ; C.M. Kouzis
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 200 –206
- DOI: 10.1049/ip-smt:19982209
- Type: Article
- + Show details - Hide details
-
p.
200
–206
(7)
Experiments are described which are designed to test two devices based on the ‘early streamer emission’ (ESE) principle, for lightning protection, against the traditional Franklin rod. In all three cases, the device was subjected to a steady negative electric field from a sphere, simulating the field beneath a thundercloud, prior to application of a superimposed negative impulse field, simulating the field due to the downward leader. The first device consisted of a vertical rod to which a subsidiary 1/50 µs positive impulse voltage, variable up to 40 kV peak, could be applied with varying delays from the start of the negative impulse field. Energising of the rod was thus independent of the applied, negative, field. The second device was a commercial product, energising of which was controlled by its own power supply. Sparkover voltages in the sphere/device gaps and times to breakdown were measured. It is shown that the ESE devices showed a small advantage, in time to breakdown, over the Franklin rod. - Author(s): N.L. Allen ; C.F. Huang ; K.J. Cornick ; D.A. Greaves
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 207 –214
- DOI: 10.1049/ip-smt:19982208
- Type: Article
- + Show details - Hide details
-
p.
207
–214
(8)
Experiments are described in which composite voltages, produced by superimposing positive and negative switching impulse voltages on pre-stressing positive or negative direct voltages, are applied to a rod–plane gap of lengths up to 1 m. Changes in 50% sparkover voltages are described over a range of positive and negative pre-stressing voltages; it is shown that negative pre-stressing always reduces the composite sparkover voltage, but that positive pre-stress increases the positive composite sparkover voltage and reduces the negative one. Recordings of photomultiplier observations and ‘still’ photography of pre-breakdown corona have been made at the 50% sparkover level and the results related to the sparkover characteristics. It is shown that the latter depend on the way in which leader initiation is affected by the preceding DC corona. - Author(s): L. Lindberg
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 215 –221
- DOI: 10.1049/ip-smt:19981979
- Type: Article
- + Show details - Hide details
-
p.
215
–221
(7)
Two methods of reducing the magnetic fields around electric power transmission lines and installation lines are discussed, splitting of conductors, and twisting. General design parameters and criteria are derived. The division of each phase conductor into a pair, at equal distance from a centre, makes the far field decay as the inverse cube of the distance as compared to the inverse square for an ordinary line. It is shown that all split phases should have a common centre, but that the separation distances may be different for individual phases and also the angles between the phase planes may be arbitrary. Applications to existing power lines are discussed. Twisting of telephone cables has long been practised to reduce crosstalk. It is shown that twisting of cables and installation lines also results in a drastic reduction of the external magnetic field. Both methods also result in a great reduction of the sensitivity to disturbances from external sources. - Author(s): S.S. Al-Harbi and K.A. Nabulsi
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 222 –225
- DOI: 10.1049/ip-smt:19982205
- Type: Article
- + Show details - Hide details
-
p.
222
–225
(4)
A prespecified electromagnetic field on the axis of a two-layer lossy cylinder will be assumed. The required excitation (source) that produces this field on the surface of the outer layer is calculated and then discretised to obtain an array of circumferential slots that produce the required field on the axis of the lossy cylinder. A confirming forward calculation is done to show that the array of circumferential slots produces an accurate approximation to the required field on the axis of the lossy cylinder. Results are presented to show the required surface source for different cylinder parameter and field produced by the discrete source. This process has applications in hyperthermia, biomedical treatment, subsurface geophysical probing, focusing and nondestructive testing.
Laboratory study of the bi-leader process from an electrically floating conductor. Part 1: General results
Laboratory study of the bi-leader process from an electrically floating conductor. Part 2: Bi-leader properties
Tests of the ‘early streamer emission’ principle for protection against lightning
Sparkover in the rod–plane gap under combined direct and impulse voltages
Reduction of magnetic fields from electric power and installation lines
Generation of a prespecified electromagnetic field on the axis of a two-layer lossy cylinder
-
- Author(s): G. Hayward
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 227 –228
- DOI: 10.1049/ip-smt:19982215
- Type: Article
- + Show details - Hide details
-
p.
227
–228
(2)
- Author(s): A. McNab ; K.J. Kirk ; A. Cochran
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 229 –236
- DOI: 10.1049/ip-smt:19982210
- Type: Article
- + Show details - Hide details
-
p.
229
–236
(8)
There is an increasing demand for ultrasonic transducers to work at high temperatures. Transducers operating in the range from 400 to 1000°C are being applied in the power, process, automotive and aeroengine industries, as well as in materials research. To date, the majority of high temperature transducer designs have been based on adaptations of conventional single and dual-element probes for nondestructive testing (NDT). Such designs are outlined. It is noted, however, that the attempt to construct high temperature versions of conventional transducers has led to overcomplicated, expensive structures. In particular, they are modelled on probes used for scanning at ambient temperatures, although scanning is unlikely to be possible at high temperatures. An alternative approach is therefore described, based on the monolithic ultrasonic array structure. This offers not only lower transducer costs, but also full electronic control of the ultrasonic beam angle and emission point, thus facilitating inspection of a region within a test component using only one or two devices in fixed positions. Typical results demonstrating the beam-steering performance of the array, as well as those from B-scan time-of-flight testing, are presented. It is concluded that the problems of transducer development for ultrasonic, high-temperature NDT are not yet completely solved, and that further effort is required in the key areas of materials science and transducer structure. Moreover, a simple design with the minimum of bond lines is most likely to succeed on the grounds of cost and reliability. - Author(s): A.G. Bashford and D.A. Hutchins
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 237 –243
- DOI: 10.1049/ip-smt:19982211
- Type: Article
- + Show details - Hide details
-
p.
237
–243
(7)
Air-coupled ultrasonic transducers have been used to study the properties of green-state ceramic components. The work used electrostatic (capacitance) transducers. In a first set of experiments, the transducers were C-scanned over the entire area of selected disc-shaped samples to locate changes in structure that could lead to problems in the firing stage. The transducers were modified subsequently to operate at elevated temperatures for monitoring the manufacturing process, and it was shown that good sensitivity could be obtained in silicon nitride samples at temperatures in excess of 200°C. It was shown that ultrasonic velocity was related to both softening of the polymer binder and the change in weight of the samples as they were heated, the latter giving an indication of polymer burn-out rates. - Author(s): S.G. Pierce and B. Culshaw
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 244 –249
- DOI: 10.1049/ip-smt:19982212
- Type: Article
- + Show details - Hide details
-
p.
244
–249
(6)
Laser generated ultrasound is a convenient noncontact broad bandwidth source of test radiation for ultrasonic nondestructive evaluation (NDE). However, conventional laser ultrasound exploits high pulse energies in short duration pulses typically involving peak powers in the tens to hundreds of megawatts range. Consequently, surface damage is frequently problematic. The prospects are examined for low peak power sources based on laser diode excitation of mechanical samples. With peak powers of significantly less than 1 W and a 2% duty cycle, the authors have demonstrated broadband Lamb wave excitation in a thin metal sample, including observation of the dispersion curves. The same principle can be extended to full continuous wave (CW) operation. This enhances the received SNR while involving minimal probabilities of sample damage. - Author(s): P.D. Wilcox ; P. Cawley ; M.J.S. Lowe
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 250 –259
- DOI: 10.1049/ip-smt:19982213
- Type: Article
- + Show details - Hide details
-
p.
250
–259
(10)
Interdigital transducers (IDTs) made from the piezoelectric polymer PVDF have been built; they transmit ultrasonic Lamb waves into 1–2 mm thick steel and aluminium plates and receive signals reflected from features in the structure. The IDTs are designed to be permanently bonded to the structure under inspection. Such IDTs have considerable potential for use in smart-structure monitoring applications. However, before this potential can be realised, the nature of the acoustic field that they produce must be thoroughly understood. Experimentally measured acoustic fields are presented for two example IDTs, one that produces a collimated beam for line inspection and one that produces a divergent beam for sector inspection. The development of modelling software based on Huygens' principle, which enables the acoustic field from such IDTs to be predicted rapidly, is then described. Example results from this software are presented and compared with experimental measurements. Further predictions made with the model are then used to elucidate certain basic guidelines for IDT design. - Author(s): D. Atkinson and G. Hayward
- Source: IEE Proceedings - Science, Measurement and Technology, Volume 145, Issue 5, p. 260 –268
- DOI: 10.1049/ip-smt:19982214
- Type: Article
- + Show details - Hide details
-
p.
260
–268
(9)
The authors describe and demonstrate a system exploiting the use of cylindrical ultrasonic waveguides for ‘remote’ Lamb wave generation and detection in thin plates. Ultrasonic energy is introduced into the cylindrical waveguides from a piezoceramic transducer via an epoxy bond, and the nature of this coupling is investigated theoretically using finite element analysis. The results show that lateral modes in the transducer (related to width and length, or diameter) couple into the waveguide more effectively than the more efficient thickness modes, as a result of the epoxy bond converting lateral motion into longitudinal motion. The thin cylindrical waveguides are then used to deliver ultrasonic signals to specific points in plate-type structures. As such, the waveguides may be considered as point sources, a combination of which can behave as a line array. To demonstrate this, it is shown that Lamb waves are generated and detected by bonding the ends of several copper wires, at half-wavelength spacing, to the surface of a sheet of aluminium. The fundamental symmetric and asymmetric modes are then used to explore possible non-destructive evaluation measurements. Following this, a form of portable ‘wire’ transducer, comprising an array of waveguide sources, is presented that allows the detection of synthetic flaws in an aluminium plate.
Editorial: Developments in transducer technology for ultrasonic non-destructive testing applications
Ultrasonic transducers for high temperature applications
Air-coupled ultrasonic transducers for measurement of green-state ceramics at elevated temperatures
Laser generation of ultrasonic Lamb waves using low power optical sources
Acoustic fields from PVDF interdigital transducers
Fibre waveguide transducers for Lamb wave NDE
Most viewed content for this Journal
Article
content/journals/ip-smt
Journal
5
Most cited content for this Journal
We currently have no most cited data available for this content.
