Magnetic Viscosity Meter - MVM1
Archaeology, Demining, Rock & Soil Magnetics, Environmental Magnetism, Science Education.
One instrument that has long been lacking from the tools available for soil and rock magnetic studies is a portable, reliable, and easy to use, magnetic viscosity meter. This type of instrument would be a valuable addition to the geophysical tool kit of those engaged in soil and rock magnetics, archaeological prospection, and humanitarian demining. The MVM1 measures the magnetic lag, or viscosity, of super-paramagnetic particles when an applied magnetic field is suddenly removed. This magnetic lag is related to frequency dependent susceptibility that is measured on some multi-frequency magnetic susceptibility meters (such as the Bartington MS2B). For soil scientists, the MVM1 is a useful accessory for those already possessing the MS2, as a much more complete picture of rock and soil magnetics can be obtained. For those in the field of humanitarian demining, the MVM1 is a rapid way of evaluating soil as to its potential effect on mine detector performance.
Features of the MVM1
- Four easy to use controls, plus ON/OFF and ZERO pushbuttons.
- Rugged, yet lightweight and field portable.
- Clear readout on 3.5 digit LCD meter. 0 -1500 viscosity range.
- MVM B laboratory sensor that accommodates 10ml sample pots.
- Unique sample lift mechanism on the MVM B sensor.
- MVM D 10in coil and shaft for field survey.
- MVM K probe for spot testing materials and geological sections.
- MVM H down-hole sensor.
- Battery operation from 12 AAA alkaline or rechargeable cells.
- Low battery warning on LCD display.
- Provision for separate transmit and receive coils for field use.
Controls
- Illuminated ON/OFF
- Press for ZERO
- Calibrated SAMPLE DELAY
- Sample Delay multiplier (x1 & x2)
- COARSE and FINE CALIBRATE
Uses:
MVM-B Sensor with 10ml Volume or 10g Mass Sample
Use a calibrated magnetic viscosity sample (supplied) with a known low frequency – high frequency magnetic susceptibility difference to calibrate the MVM1. Compare the MVM1 readings with your laboratory’s LF – HF magnetic susceptibility instrument.
Plot Linear-Linear, Logarithmic-Linear, or Logarithmic-Logarithmic viscous decays of soil, rock, or metal samples. Easily calculate the exponent of the log log viscosity decay. Observe the effect of an external magnetic field on the viscosity signal.
See how temperature affects viscosity by cooling samples to 0°C or heating up to 100°C prior to measurement.
MVM D Sensor for Field Use
Important for humanitarian demining and archaeological survey is the ability to test soil in situ for the level of near surface magnetic viscosity. Viscosity, or frequency dependent susceptibility, is the main factor that affects the performance of mine detectors that operate on the pulse induction (PI) principle. As the MVM operates on the same principle, its reading directly relates to the potential effect on PI detectors. Furthermore the ubiquitous use of fire in prehistoric times often increases the magnetic viscosity in many archaeological features and soil context. The MVM-D can help archaeologists map and delineate areas of enhanced viscosity, which are possibly related to domestic or industrial activity.
MVM-K Sensor
This is a 20mm diameter probe for more localized testing of soil, rocks, archaeological materials, geological sections, or for use in otherwise inaccessible places. A version of this probe is also under development for use in shallow, small diameter (1”) boreholes.
Plotting Results
In addition to spot readings, a succession of readings at the various sample delays can be taken and a graph plotted showing the form, or slope, of the viscous decay. This is best achieved with the B sensor and two examples are shown below, plotted both linearly and on log log scales. The plots are of Tiva Canyon Tuff (Yucca Mountain, Nevada), which is an unusual material which exhibits a very high (24%) frequency dependence of susceptibility.
