Page 19 - FOERSTER_Detection_Geophysics_en

TECHNOLOGY

Active magnetic inductive methods (EMIs) Passive magnetometer methods
These methods are well suited to the detection of met- These methods are ideal for detecting ferromagnetic
als. Detection performance depends on the transmis- metals. Highly responsive passive sensors measure Receiver coil

sion and reception parameters, as well as on the type the Earth’s homogeneous magnetic field and accurately

of metal and the local soil conditions, since the method recognize any disturbances in this field caused by near-
relies on conductivity and the magnetic permeability by ferromagnetic components. The position, orientation Exciter coil
properties of the metal. A search coil generates mag- and mass of the metal object are determined by ana-

netic fields that propagate through the soil, either as lyzing the anomalies in the magnetic field. These can
single pulses or continuously at one or more frequen- be recorded or sent as acoustic or optical alerts to the Eddy current
cies. When metal parts are struck by this magnetic operator, who then uses them to locate the object.
Magnetic field

field, eddy currents form, which in turn causes them to

emit a secondary magnetic field. The effects of this field Since soils and infrastructure elements also carry their

are detected and evaluated by the receiving coil of the own magnetic signatures, highly sensitive magnetom- Active magnetic inductive methods
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metal detector. At the same time, interference signals eters can be used in the context of archaeological and
generated in the ground must be compensated for. geological surveys. A distinction is made between ab-
Exciter coils Sensing coils

solute probes, which display the Earth’s magnetic field
The received signals are evaluated and set off acous- including possible anomalies, and differential probes,

tic or optical alerts, thus allowing for pinpointing which neutralize the Earth’s magnetic field and dis-
of the metal part. Or, the received signals can be stored play only the effect of the magnetic anomaly. FOERST-
Magnetic field

for later evaluation using appropriate algorithms. ER supplies highly sensitive (fluxgate) magnetometer
FOERSTER supplies detection systems in both pulse probes in both absolute and differential arrangements.
and continuous wave technologies.

Geomagnetic
field

Passive magnetometer methods