1. A double reflecting structure comprising:
a first reflecting portion reflecting light that is emitted from a light source; and
a second reflecting portion formed on one side of the first reflecting portion to reflect again the light that is reflected by the first reflecting portion;
wherein the second reflecting portion is formed in a curved outer wall shape and is formed to protrude from the one side of the first reflecting portion and partially enclose the first reflecting portion.
2. The double reflecting structure according to claim 1, wherein the first reflecting portion is formed in a parabolic shape or a peaked-hat shape.
3. The double reflecting structure according to claim 1, wherein the second reflecting portion is formed in a curved outer wall shape and is formed to project upward from the one side of the first reflecting portion.
4. The double reflecting structure according to claim 1, wherein a plurality of first reflecting portions and a plurality of second reflecting portions are formed.
5. A double reflecting structure comprising:
a first reflecting portion reflecting light that is emitted from a light source; and
a second reflecting portion formed on one side of the first reflecting portion to reflect again the light that is reflected by the first reflecting portion;
wherein a curvature center of the second reflecting portion is formed along a center axis of the first reflecting portion.
6. A double reflecting structure comprising:
a first reflecting portion reflecting light that is emitted from a light source; and
a second reflecting portion formed on one side of the first reflecting portion to reflect again the light that is reflected by the first reflecting portion;
wherein a plurality of refracting portions are formed on an inside of the second reflecting portion.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method to determine a formation property of a subsurface formation, comprising:
providing a downhole logging tool having two or more antennas, at least two of the antennas having a transversely-sensitive element and an axially-sensitive element;
obtaining azimuthally-sensitive measurements using the antennas of the downhole logging tool;
fitting the measurements to a Fourier series having Fourier coefficients that include channel gains, if any;
determining a DC component, a first harmonic component, and a second harmonic component from the Fourier series;
determining a measurement type using the DC component, the first harmonic component, andor the second harmonic component; and
determining the formation property of the subsurface formation using the determined measurement type.
2. The method of claim 1, wherein the providing comprises disposing the downhole logging tool on a wireline, a drill string, or a wired drill pipe.
3. The method of claim 1, wherein each of the transversely-sensitive elements has a magnetic dipole moment that is either transverse or tilted, and each of the axially-sensitive elements has a magnetic dipole moment that is either axial or tilted.
4. The method of claim 1, wherein at least one of the antennas comprises an obliquely-sensitive element formed from a combination of the transversely-sensitive element and the axially-sensitive element of that antenna.
5. The method of claim 1, wherein the transversely-sensitive element and the axially-sensitive element of a particular antenna are co-located.
6. The method of claim 1, wherein the downhole tool further comprises a slotted conductive shield or a non-conductive shield, both of which are substantially electromagnetically transparent.
7. The method of claim 1, wherein the obtaining azimuthally-sensitive measurements comprises transmitting and receiving an electromagnetic signal transmitted at a certain frequency, or transmitting and receiving a plurality of electromagnetic signals, each of the electromagnetic signals being transmitted at different frequencies.
8. The method of claim 1, wherein the azimuthally-sensitive measurements are obtained while the downhole logging tool is rotating or sliding.
9. The method of claim 1, wherein one of the antennas is azimuthally offset from another of the antennas.
10. The method of claim 1, wherein the transversely-sensitive element of a particular antenna is wired in series with the axially-sensitive element of the particular antenna and a double throw, double switch relay to produce a combined coil, and further comprising switching the direction of the combined coil magnetic moment azimuthally by 180 degrees.
11. The method of claim 1, wherein the two or more antennas comprise a symmetric four antenna group, and further comprising performing borehole compensation on the measurements.
12. The method of claim 1, further comprising using the determined formation property for well placement, formation evaluation, andor look-ahead, look-around operations.
13. A system to determine a formation property of a subsurface formation, comprising:
a downhole logging tool having two or more antennas, at least two of the antennas having a transversely-sensitive element and an axially-sensitive element; and
a processor capable of:
obtaining azimuthally-sensitive measurements using the antennas of the downhole logging tool;
fitting the measurements to a Fourier series having Fourier coefficients that include channel gains, if any;
determining a DC component, a first harmonic component, and a second harmonic component from the Fourier series;
determining a measurement type using the DC component, the first harmonic component, andor the second harmonic component; and
determining the formation property of the subsurface formation using the determined measurement type.
14. The system of claim 13, wherein the downhole logging tool is disposed on a wireline, a drill string, or a wired drill pipe.
15. The system of claim 13, wherein each of the transversely-sensitive elements has a magnetic dipole moment that is either transverse or tilted, and each of the axially-sensitive elements has a magnetic dipole moment that is either axial or tilted.
16. The system of claim 13, wherein at least one of the antennas comprises an obliquely-sensitive element formed from a combination of the transversely-sensitive element and the axially-sensitive element of that antenna.
17. The system of claim 13, wherein the transversely-sensitive element and the axially-sensitive element of a particular antenna are co-located.
18. The system of claim 13, wherein the downhole tool further comprises a slotted conductive shield or a non-conductive shield, both of which are substantially electromagnetically transparent.
19. A system having a computer-readable medium having a set of computer-readable instructions encoded thereon that, when executed, perform acts comprising:
obtaining azimuthally-sensitive measurements using the antennas of the downhole logging tool;
fitting the measurements to a Fourier series having Fourier coefficients that include channel gains, if any;
determining a DC component, a first harmonic component, and a second harmonic component from the Fourier series;
determining a measurement type using the DC component, the first harmonic component, andor the second harmonic component; and
determining the formation property of the subsurface formation using the determined measurement type.
20. The system of claim 19, wherein the downhole logging tool is an induction or propagation-type while-drilling logging tool.