Characterization of the magnetic fields around walk-through and hand-held metal detectors.
Magnetic field strength measurements were made around eight hand-held and 10 walk-through metal detectors. The method was similar to that used in previous research for Electronic Article Surveillance units except a Cartesian rather than cylindrical coordinate system was used. Special magnetic field probes specifically designed for metal detector measurements were used. A non-metallic positioning apparatus was designed and fabricated. Magnetic field strength measurements were collected on one hand-held metal detector in the laboratory. The remaining data were collected at airport terminals, federal and state government buildings, and a local high school. Walk-through metal detectors had considerably higher magnetic field strengths [up to 299 Am(-1) p-p (3,741 mG)] than hand-held metal detectors [up to 6 Am(-1) p-p (76 mG)]. The frequencies of the magnetic field signal for walk-through detectors were between 0.1 kHz and 3.5 kHz while those for hand-held detectors were between 89 kHz and 133 kHz. Waveforms for all hand-held metal detectors were sinusoidal; those for walk-through metal detectors varied with most being saw-toothed or pulsed. Due to their higher field strengths and the pulsed nature of their magnetic fields, walk-through metal detectors likely pose a higher risk for medical device electromagnetic interference than do hand-held units. Root mean squared magnetic field strengths were calculated from the peak-to-peak values and compared to occupational and general public exposure limits. None of these limits were exceeded. Measurement repeatability was examined for one hand-held and two walk-through metal detectors. For the hand-held metal detector measurements at the location of the maximum magnetic field strength, measurements by three individuals had a repeatability (percent standard deviation) of 5.9%. Limited repeatability data were collected for on-site measurements of walk-through detectors. One unit showed repeatability of 0.1 to 4.5%; a multi-zone unit showed repeatability of 2.7 to 67.5%.
U.S. Food and Drug Administration, Winchester Engineering and Analytical Center, 109 Holton Street, Winchester, MA 01890, USA. wboivin@ora.fda.gov
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Boivin
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Coletta
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Kerr
D004574:Electromagnetic Fields; D055590:Electromagnetic Phenomena / Q000295:instrumentation / Q000379:methods / Q000592:standards; D019544:Equipment Failure Analysis / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D006801:Humans; D008670:Metals; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation / Q000379:methods* / Q000592:standards*; D015203:Reproducibility of Results; D012637:Security Measures / Q000592:standards*; D012680:Sensitivity and Specificity; D014481:United States
D008670:Metals