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Acousto-magnetic system

Belongs to:
Electronic Article Surveillance
Description:

An acousto-magnetic system is an RFID system for electronic article surveillance (EAS) and usually works at frequencies between 58 kHz and 132 kHz. The acousto-magnetic systems and the radiofrequency systems are the most commonly used article surveillance systems.
As with all EAS systems, a tag is attached to the good which is detected by detectors in the exit area of a shop (see main category Electronic Article Surveillance).
The emitted electromagnetic field in the exit area mechanically excites a magnetic stripe in the passive transponder (tag) and brings it into vibration. The electromagnetic field is turned on and off about a few milliseconds. The vibration of the excited magnetic stripe in the tag dies away when the electromagnetic field is off and emits an own measurable field. The detection of this field results in an alarm.
A deactivator in the checkout counter modifies the tag by a magnetic field in a way that the detection method doesn't work anymore and the good can be carried outside the shop without an alarm.

Frequency ranges:
  • 40–50 Hz (on/off switching for detection)
  • 20–135 kHz
Type of field:
electric and magnetic

Measurements (acc. to literature)

deactivator
Measurand Value Feature Remarks
magnetic flux density 0.24 µT (measured) 58 kHz at the cashier's seat at a height of 0.5 - 1.7 m in a post office [1]
magnetic flux density 0.27 µT 58 kHz at the cashier's seat at a height of 0.5 - 1.7 m in a supermarket [1]
magnetic flux density 0.81 µT (measured) 58 kHz at the cashier's seat at a height of 0.5 - 1.7 m in a hardware store [1]
detector
Measurand Value Feature Remarks
electric field strength 0.11 V/m (simulated) 125 kHz induced electric field in the body of a standing child; size of the detector gates: 50 cm x 120 cm at a height of 20 cm above ground; current in the coils: 4 A [2]
electric field strength 0.14 V/m (measured) 125 kHz induced electric field in the body of a sitting child; size of the detector gates: 50 cm x 120 cm at a height of 20 cm above ground; current in the coils: 4 A [2]
electric field strength 1.12 V/m (simulated) 125 kHz induced electric field in the body of a standing child; size of the detector gates: 50 cm x 120 cm at a height of 20 cm above ground; current in the coils: 40 A [2]
electric field strength 1.38 V/m (simulated) 125 kHz induced electric field in the body of a sitting child; size of the detector gates: 50 cm x 120 cm at a height of 20 cm above ground; current in the coils: 40 A [2]
electric field strength 3.55–35.53 V/m (maximum, simulated) 125 kHz induced, maximum magnetic field in the body of a sitting child; size of detector gates: 50 cm x 120 cm at a height of 20 cm above the ground [2]
electric field strength 3.55 V/m (maximum, simulated) 125 kHz for a standing chinese male of 1.72 m in height; scaled on ICNIRP reference levels for general public exposure; 20 cm distance to detector [3]
electric field strength 5.39 V/m (maximum, simulated) 125 kHz for a standing infant of 0.74 m in height; scaled on ICNIRP reference levels for general public exposure; 20cm distance to detector [3]
electric field strength 5.63 V/m (maximum, simulated) 125 kHz for a standing child of 1.20 m in height; scaled on ICNIRP reference levels for general public exposure; 20cm distance to detector [3]
magnetic field strength 0.03–0.33 A/m (mean, simulated) 125 kHz induced, averaged magnetic field in the body of a standing child; size of detector gates: 50 cm x 120 cm at a height of 20 cm above the ground [2]
magnetic field strength 0.04–0.38 A/m (mean, simulated) 125 kHz induced, averaged magnetic field in the body of a sitting child; size of detector gates: 50 cm x 120 cm at a height of 20 cm above the ground [2]
magnetic field strength 0.7–14.5 A/m (measured) 58 - 132 kHz at a distance of 20 cm and a height of 1.3 m [4]
magnetic field strength 0.8–24.5 A/m (measured) 58 - 132 kHz at a distance of approx. 20 cm and a height of 1 m [4]
magnetic field strength 0.9–35 A/m (measured) 58 - 132 kHz at a distance of approx. 20 cm at various heights [4]
magnetic field strength 2.1 A/m (measured) - - [5]
magnetic field strength 3.22–32.23 A/m (maximum, simulated) 125 kHz induced, maximum magnetic field in the body of a standing child; size of detector gates: 50 cm x 120 cm at a height of 20 cm above the ground [2]
magnetic field strength 4.6–17 A/m (mean, measured) 58 kHz mean value out of 45 different measurement points, each at a distance of 5 cm [6]
magnetic flux density 2–52 µT (measured) 58 kHz at a distance of 0.2 m from the gates in a hardware store [1]
magnetic flux density 4–18 µT (measured) 58 kHz at a height of 0.8 - 1.7 m in the middle of the gates in a hardware store [1]
magnetic flux density 10–20 µT (measured) 58 kHz at a height of 0.8 - 1.7 m in the middle of the gates in a post office [1]
magnetic flux density 17.4 µT (maximum, measured) 58 kHz at a distance of 62.5 cm to the transmitter (pulsed modulated sinusoid) [7]
magnetic flux density 19 µT (measured) 58 kHz at a height of 0.8 - 1.7 m in the middle of the gates in a supermarket [1]
magnetic flux density 22.3 µT (maximum, measured) 58 kHz Digital Euro ProMax: at a distance of 50 cm to the antenna [8]
magnetic flux density 31–189 µT (measured) 58 kHz at a distance of 0.2 m from the gates in a post office [1]
magnetic flux density 34.8 µT (maximum, measured) 58 kHz ProMax IV: at a distance of 50 cm to the antenna [8]
magnetic flux density 35 µT (maximum, measured) 58 kHz Stargate: at a distance of 50 cm to the antenna [8]
magnetic flux density 37 µT (maximum, measured) 58 kHz Digital Euro ProMax: at a distance of 35 cm to the antenna [8]
magnetic flux density 45.5 µT (maximum, measured) 58 kHz Ultra Exit: at a distance of 50 cm to the antenna [8]
magnetic flux density 52 µT (maximum, measured) 58 kHz at a distance of 37.2 cm (continuous wave) [7]
magnetic flux density 56 µT (maximum, measured) 58 kHz Stargate: at a distance of 35 cm to the antenna [8]
magnetic flux density 61.7 µT (mean, measured) 58 kHz measured in 36 cm distance between two antennas in a width of 274.3 cm. [9]
magnetic flux density 62.2 µT–64.9 T (mean, measured) 58 kHz measured in 36 cm distance between two antennas in a width of 182.9 cm. [9]
magnetic flux density 65 µT (maximum, measured) 58 kHz at a distance of 36 cm to the transmitter (pulsed modulated sinusoid) [7]
magnetic flux density 69.6 µT (maximum, measured) 58 kHz ProMax IV: at a distance of 35 cm to the antenna [8]
magnetic flux density 75.7 µT (maximum, measured) 58 kHz Digital Euro ProMax: at a distance of 20 cm to the antenna [8]
magnetic flux density 91 µT (maximum, measured) 58 kHz Ultra Exit: at a distance of 35 cm to the antenna [8]
magnetic flux density 106.7 µT (maximum, measured) 58 kHz Digital Euro ProMax: at a distance of 10 cm to the antenna [8]
magnetic flux density 120 µT (maximum, measured) 58 kHz Stargate: at a distance of 20 cm to the antenna [8]
magnetic flux density 138 µT (measured) 58 kHz at a distance of 0.2 m from the gates in a supermarket [1]
magnetic flux density 145 µT (maximum, measured) 58 kHz ProMax IV: at a distance of 20 cm to the antenna [8]
magnetic flux density 156 µT (maximum, measured) 58 kHz Ultra Exit: at a distance of 20 cm to the antenna [8]
magnetic flux density 222 µT (maximum, measured) 58 kHz Stargate: at a distance of 10 cm to the antenna [8]
magnetic flux density 237 µT (maximum, measured) 58 kHz ProMax IV: at a distance of 10 cm to the antenna [8]
magnetic flux density 298 µT (maximum, measured) 58 kHz Ultra Exit: at a distance of 10 cm to the antenna [8]
SAR 1.67 µW/kg (simulated) 125 kHz averaged over 10 g of tissue of a standing child; size of the detector gates: 50 cm x 120 cm at a height of 20 cm above the ground; current in coils: 4 A [2]
SAR 2.28 µW/kg (simulated) 125 kHz averaged over 10 g of tissue of a sitting child; size of the detector gates: 50 cm x 120 cm at a height of 20 cm above the ground; current in coils: 4 A [2]
SAR 166 µW/kg (simulated) 125 kHz averaged over 10 g of tissue of a standing child; size of the detector gates: 50 cm x 120 cm at a height of 20 cm above the ground; current in coils: 40 A [2]
SAR 228 µW/kg (measured) 125 kHz averaged over 10 g of tissue of a sitting child; size of the detector gates: 50 cm x 120 cm at a height of 20 cm above the ground; current in coils: 40 A [2]
tag
Measurand Value Feature Remarks
magnetic flux density 0.068 µT (measured) 125 kHz at a distance of 1 m [10]

References

  1. Roivainen P et al. (2014): Occupational exposure to intermediate frequency and extremely low frequency magnetic fields among personnel working near electronic article surveillance systems.
  2. Li C et al. (2014): Numerical evaluation of exposure to the electromagnetic fields of an electronic article surveillance system with postured infant model.
  3. Li C et al. (2015): Dosimetry for infant exposures to electronic article surveillance system: Posture, physical dimension and anatomy.
  4. Harris C et al. (2000): Electromagnetic field strength levels surrounding electronic article surveillance (EAS) systems.
  5. Börner F (2011): [Electromagnetic fields at plants, machinery and equipment].
  6. Trulsson J et al. (2007): Assessment of magnetic fields surrounding electronic article surveillance systems in Sweden.
  7. (2007): Extremely low frequency fields (WHO EHC Monograph No. 238)
  8. Schmid G et al. (2012): [Exposure assessement of electromagnetic fields generated by radio frequency identification (RFID) technologies. Project 3609S80002].
  9. Casamento J (1999): Characterizing Electromagnetic Fields of Common Electronic Article Surveillance Systems.
  10. van der Togt R et al. (2008): Electromagnetic interference from radio frequency identification inducing potentially hazardous incidents in critical care medical equipment.