Induced polarization (IP) is a

geophysical imaging Geophysical imaging (also known as geophysical tomography) is a minimally destructive geophysical technique that investigates the subsurface of a terrestrial planet. Geophysical imaging is a noninvasive imaging technique with a high parametrical ...

technique used to identify the electrical chargeability of subsurface materials, such as

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically including metals, concentrated above background levels, and that is economically viable to mine and process. The grade of ore refers to the concentration ...

. The polarization effect was originally discovered by

Conrad Schlumberger Conrad Schlumberger (2 October 1878 in Gebweiler (Alsace-Lorraine) – 9 May 1936 in Stockholm) and Emile Henry Marcel Schlumberger (21 June 1884 in Gebweiler – 9 May 1953 in Val-Richer) were brothers from the region of Alsace-Lorraine, Franc ...

when measuring the resistivity of rock. The survey method is similar to

electrical resistivity tomography Electrical resistivity tomography (ERT) or electrical resistivity imaging (ERI) is a geophysical technique for imaging sub-surface structures from electrical resistivity measurements made at the surface, or by electrodes in one or more borehol ...

(ERT), in that an

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

is transmitted into the subsurface through two

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s, and

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

is monitored through two other electrodes. Induced polarization is a geophysical method used extensively in mineral exploration and mining operations.

Resistivity Electrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity i ...

and IP methods are often applied on the ground surface using multiple four-electrode sites. In an IP survey (and when making resistivity measurements), capacitive properties of the subsurface materials are determined as well. As a result, IP surveys provide additional information about the spatial variation in lithology and grain-surface chemistry. The IP survey can be made in time-domain and frequency-domain mode: In the '' time-domain induced polarization'' method, the voltage response is observed as a function of time after the injected current is switched off or on. In the '' frequency-domain induced polarization'' mode, an alternating current is injected into the ground with variable frequencies. Voltage phase-shifts are measured to evaluate the impedance spectrum at different injection frequencies — this is commonly referred to as spectral IP. The IP method is one of the most widely used techniques in mineral exploration and in the mining industry. Additionally, IP has applications in hydrogeophysical surveying, environmental investigations and geotechnical engineering projects.

Measurement methods

Time domain

Time-domain In mathematics and signal processing, the time domain is a representation of how a signal, function, or data set varies with time. It is used for the analysis of function (mathematics), mathematical functions, physical signal (information theory), ...

IP methods measure the resulting voltage following a change in the injected current. The time domain IP potential response can be evaluated by considering the mean value on the resulting voltage, known as

integral In mathematics, an integral is the continuous analog of a Summation, sum, which is used to calculate area, areas, volume, volumes, and their generalizations. Integration, the process of computing an integral, is one of the two fundamental oper ...

chargeability or by evaluating the spectral information and considering the shape of the potential response (i.e. describing the response with a Cole-Cole model).

Frequency domain

Frequency-domain In mathematics, physics, electronics, control systems engineering, and statistics, the frequency domain refers to the analysis of mathematical functions or signals with respect to frequency (and possibly phase), rather than time, as in time ser ...

IP methods uses

alternating current Alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC), which flows only in one direction. Alternating current is the form in w ...

s (AC) to induce electric charges in the subsurface, and the

apparent resistivity Apparent may refer to: *Apparent magnitude, a measure of brightness of a celestial body as seen by an observer on Earth *Apparent places, the actual coordinates of stars as seen from Earth *Heir apparent, a person who is first in line of successio ...

is measured at different AC frequencies.

References

External links

Example IP equipment and image results Geophysical imaging

Measurement methods

Time domain

Frequency domain

See also

References

Further reading

External links