Transcript Measuring electrical and mechanical properties of rocks

wave propagation via laser
ultrasound
Laser line source
IR laser focused on 19 mm line
Transmitted EM phase image of
granite at 150 GHz
Measuring electrical and mechanical
properties of rocks on the
submillimeter scale
JS, M. Batzle, M. Prasad,
N. Greeney & A. Yuffa
Colorado School of Mines
Collaboration between Physics, Geophsysics and Petroleum Engineering
All data and software will be
available
•
http://mesoscopic.mines.edu
•
http://physics.mines.edu/~jscales
•
Common Ground free database of rock
properties
High spatial resolution techniques
now available
•
Laser ultrasound
•
millimeter/submillimeter wave EM
•
Strain microscopy
•
Acoustic microscopy (Prasad)
•
Micro-CT scan (Batzle)
Motivation
•
Complimentary measurements
•
Submillimeter waves sample on same length
scale as ultrasound.
•
measurements fully noncontacting and can
be done on same samples without other
preparation.
Length scale of measurement easily
controlled optically
'low' frequency normal mode
Laser spot size measured in microns
'high' frequency normal mode
But how to get local elastic properties from
waveforms?
Electrical properties at sub-mm
resolution

CSM submillimeter system covers from
microwaves (8-10 GHz) to 1 THz (1000 GHz)

Allows us to do bulk dielectric spectroscopy

And now, near-field scanning
ABMillimetre submm VNA
Funded by NSF MRI
Unique instrument
•
measure amplitude and phase of the electric
field over broad range of millimeter to
submillimeter wave frequencies
•
In free-space or in waveguide
•
Produces linearly polarized Gaussian beams
of high optical quality: quasi-optics
•
Allows 'easy optics'
quasi-optics
Dielectric spectroscopy
Fit E field with 1D Fabry-Perot
model to get complex permittivity
Measuring water content
Measuring anisotropy in shale
MMW rock physics applications
Scales and Batzle APL papers
•
Measure organic content in rocks and
oil/water emulsions
•
Resolve sedimentation at the 100 micron
level (implications for climate models)
•
Check mixing models (such as MaxwellGarnett)
Recent: cavity perturbation
•
Have recently built ultra-high-Q millimeter
wave cavity for measuring (e.g.,) conductivity
of thin films.
•
Use ultrasonic cavity perturbation to measure
minute changes in samples
Getting high-resolution EM results
First work at 150 GHz

Greeney & JS, Appl. Phys. Letts.

Bare teflon probes

Later, went to higher frequency, 260 GHz

Clad teflon in aluminum

Small hole at tip to prevent leakage

Weiss et al, J. Appl. Phys.

Finite element modeling of tip surface coupling
Transmitted phase image of granite
at 150 GHz
Transmitted phase image of shale at
150 GHz
Seeing inside dielectrics: rfid card
@ 260 GHz
Seeing vascular structure
True near-field scanning
Tip-sample distance .2mm
Wavelength about 1 mm
Can see standing waves in the
shadow (backside of dime)
Circular drum modes
Tip-sample distance .6mm
small scale effects of Pyrolisis
McEvoy et al, 2009 oil shale conf.
Comparison with acoustic
microscopy (M. Prasad's lab)
Laser ultrasound analog
Pulsed laser sources
•
Pulses from 10 ns to 100 fs
•
Looking at first arriving energy as we scan
across the sample.
•
Scanning resolution measured in nm
Measuring spatial strain in real time
at video frame rates
Electronic Speckle Pattern Interferometry
•
Illuminate a surface with laser speckle
•
Take a picture of the speckle
•
Apply a strain
•
Take another picture
•
Subtract the two
•
The result is an interferogram
ESPI through a microscope
Speckle interferograms of concrete
Are grains floating?
Trick is in the image processing
Skeletonization by nonlinear pde
filtering
conclusion
•
Are acquiring independent high-spatial
resolution data sets for relevant rocks
•
Expect to have high-res mechanical
properties soon.
•
Batzle now has micro-CT scanner. Again, no
rock prep required.
•
Have a high-speed video camera for the
ESPI