Thickness and conductivity of metallic layers from pulsed eddy-current measurements

Cheng-Chi Tai, James H. Rose, John C. Moulder

Research output: Contribution to journalArticle

78 Citations (Scopus)

Abstract

We describe a time-domain (pulsed) eddy-current technique for determining the thickness and conductivity of conductive coatings on metal plates. The pulsed eddy-current instrument records the transient current induced in an absolute, air-cored coil placed next to a layered sample and excited with a step-function change in voltage. Signals are digitized with 16-bit resolution at a sampling rate of 1 megasamples per second, and the excitation is repeated at a rate of 1 kHz. The instrument displays the difference in the transient current measured on the substrate and on the substrate plus coating. We measured pulsed eddy-current signals for a series of metal foils of varying thickness placed over 1 cm thick metal plates. Seven combinations of foil and substrate metals were studied including pure aluminum, copper, and titanium foils over substrates of aluminum, titanium alloy, and stainless steel. We report results for three types of samples: aluminum foils on Ti-6Al-4V substrate, titanium foils on 7075 aluminum alloys, and aluminum foils on AISI 304 stainless steel. Foil thickness ranged from 0.04-1.00 mm. We found that three features of the signal - the peak height, the time of occurrence of the first peak, and a characteristic zero-crossing time - depend sensitively upon the thickness of the layers and the relative electrical conductivity of coating and substrate. Theoretical calculations were compared to the measurements. Absolute agreement between calculated and measured signals was, in most cases, within 3%. No calibration with respect to artifact standards was used. Finally, a feature-based rapid inversion method was developed and used to infer the thickness and conductivity of the layers. The accuracy of the inversion depends upon the thickness of the layer and the contrast in conductivity between layer and substrate. For the materials studied the thickness could be determined within 13%, while the error in determining conductivity was 20%-30%. The time-domain method is much simpler and hundreds of times faster than the frequency-domain method previously reported by Moulder et al.

Original languageEnglish
Pages (from-to)3965-3972
Number of pages8
JournalReview of Scientific Instruments
Volume67
Issue number11
DOIs
Publication statusPublished - 1996 Jan 1

Fingerprint

Electric current measurement
Eddy currents
eddy currents
foils
Metal foil
conductivity
Substrates
aluminum
Aluminum foil
Plate metal
metal plates
coatings
Coatings
stainless steels
Instrument displays
Stainless steel
titanium
Titanium
inversions
Aluminum

All Science Journal Classification (ASJC) codes

  • Instrumentation

Cite this

@article{97109d8bb30e4877abbb3fb2801346d4,
title = "Thickness and conductivity of metallic layers from pulsed eddy-current measurements",
abstract = "We describe a time-domain (pulsed) eddy-current technique for determining the thickness and conductivity of conductive coatings on metal plates. The pulsed eddy-current instrument records the transient current induced in an absolute, air-cored coil placed next to a layered sample and excited with a step-function change in voltage. Signals are digitized with 16-bit resolution at a sampling rate of 1 megasamples per second, and the excitation is repeated at a rate of 1 kHz. The instrument displays the difference in the transient current measured on the substrate and on the substrate plus coating. We measured pulsed eddy-current signals for a series of metal foils of varying thickness placed over 1 cm thick metal plates. Seven combinations of foil and substrate metals were studied including pure aluminum, copper, and titanium foils over substrates of aluminum, titanium alloy, and stainless steel. We report results for three types of samples: aluminum foils on Ti-6Al-4V substrate, titanium foils on 7075 aluminum alloys, and aluminum foils on AISI 304 stainless steel. Foil thickness ranged from 0.04-1.00 mm. We found that three features of the signal - the peak height, the time of occurrence of the first peak, and a characteristic zero-crossing time - depend sensitively upon the thickness of the layers and the relative electrical conductivity of coating and substrate. Theoretical calculations were compared to the measurements. Absolute agreement between calculated and measured signals was, in most cases, within 3{\%}. No calibration with respect to artifact standards was used. Finally, a feature-based rapid inversion method was developed and used to infer the thickness and conductivity of the layers. The accuracy of the inversion depends upon the thickness of the layer and the contrast in conductivity between layer and substrate. For the materials studied the thickness could be determined within 13{\%}, while the error in determining conductivity was 20{\%}-30{\%}. The time-domain method is much simpler and hundreds of times faster than the frequency-domain method previously reported by Moulder et al.",
author = "Cheng-Chi Tai and Rose, {James H.} and Moulder, {John C.}",
year = "1996",
month = "1",
day = "1",
doi = "10.1063/1.1147300",
language = "English",
volume = "67",
pages = "3965--3972",
journal = "Review of Scientific Instruments",
issn = "0034-6748",
publisher = "American Institute of Physics Publising LLC",
number = "11",

}

Thickness and conductivity of metallic layers from pulsed eddy-current measurements. / Tai, Cheng-Chi; Rose, James H.; Moulder, John C.

In: Review of Scientific Instruments, Vol. 67, No. 11, 01.01.1996, p. 3965-3972.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Thickness and conductivity of metallic layers from pulsed eddy-current measurements

AU - Tai, Cheng-Chi

AU - Rose, James H.

AU - Moulder, John C.

PY - 1996/1/1

Y1 - 1996/1/1

N2 - We describe a time-domain (pulsed) eddy-current technique for determining the thickness and conductivity of conductive coatings on metal plates. The pulsed eddy-current instrument records the transient current induced in an absolute, air-cored coil placed next to a layered sample and excited with a step-function change in voltage. Signals are digitized with 16-bit resolution at a sampling rate of 1 megasamples per second, and the excitation is repeated at a rate of 1 kHz. The instrument displays the difference in the transient current measured on the substrate and on the substrate plus coating. We measured pulsed eddy-current signals for a series of metal foils of varying thickness placed over 1 cm thick metal plates. Seven combinations of foil and substrate metals were studied including pure aluminum, copper, and titanium foils over substrates of aluminum, titanium alloy, and stainless steel. We report results for three types of samples: aluminum foils on Ti-6Al-4V substrate, titanium foils on 7075 aluminum alloys, and aluminum foils on AISI 304 stainless steel. Foil thickness ranged from 0.04-1.00 mm. We found that three features of the signal - the peak height, the time of occurrence of the first peak, and a characteristic zero-crossing time - depend sensitively upon the thickness of the layers and the relative electrical conductivity of coating and substrate. Theoretical calculations were compared to the measurements. Absolute agreement between calculated and measured signals was, in most cases, within 3%. No calibration with respect to artifact standards was used. Finally, a feature-based rapid inversion method was developed and used to infer the thickness and conductivity of the layers. The accuracy of the inversion depends upon the thickness of the layer and the contrast in conductivity between layer and substrate. For the materials studied the thickness could be determined within 13%, while the error in determining conductivity was 20%-30%. The time-domain method is much simpler and hundreds of times faster than the frequency-domain method previously reported by Moulder et al.

AB - We describe a time-domain (pulsed) eddy-current technique for determining the thickness and conductivity of conductive coatings on metal plates. The pulsed eddy-current instrument records the transient current induced in an absolute, air-cored coil placed next to a layered sample and excited with a step-function change in voltage. Signals are digitized with 16-bit resolution at a sampling rate of 1 megasamples per second, and the excitation is repeated at a rate of 1 kHz. The instrument displays the difference in the transient current measured on the substrate and on the substrate plus coating. We measured pulsed eddy-current signals for a series of metal foils of varying thickness placed over 1 cm thick metal plates. Seven combinations of foil and substrate metals were studied including pure aluminum, copper, and titanium foils over substrates of aluminum, titanium alloy, and stainless steel. We report results for three types of samples: aluminum foils on Ti-6Al-4V substrate, titanium foils on 7075 aluminum alloys, and aluminum foils on AISI 304 stainless steel. Foil thickness ranged from 0.04-1.00 mm. We found that three features of the signal - the peak height, the time of occurrence of the first peak, and a characteristic zero-crossing time - depend sensitively upon the thickness of the layers and the relative electrical conductivity of coating and substrate. Theoretical calculations were compared to the measurements. Absolute agreement between calculated and measured signals was, in most cases, within 3%. No calibration with respect to artifact standards was used. Finally, a feature-based rapid inversion method was developed and used to infer the thickness and conductivity of the layers. The accuracy of the inversion depends upon the thickness of the layer and the contrast in conductivity between layer and substrate. For the materials studied the thickness could be determined within 13%, while the error in determining conductivity was 20%-30%. The time-domain method is much simpler and hundreds of times faster than the frequency-domain method previously reported by Moulder et al.

UR - http://www.scopus.com/inward/record.url?scp=0030287388&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0030287388&partnerID=8YFLogxK

U2 - 10.1063/1.1147300

DO - 10.1063/1.1147300

M3 - Article

VL - 67

SP - 3965

EP - 3972

JO - Review of Scientific Instruments

JF - Review of Scientific Instruments

SN - 0034-6748

IS - 11

ER -