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A soil moisture sensing device for sensing moisture levels in a particular soil area. The device has a porous body with at least two zones, a first one of the zones having pore sizes that approximate a range of pores in typical soils, a second one of the zones having pores arranged to be small enoug

A soil moisture sensing device for sensing moisture levels in a particular soil area. The device has a porous body with at least two zones, a first one of the zones having pore sizes that approximate a range of pores in typical soils, a second one of the zones having pores arranged to be small enough to remain hydrated at higher matric tensions. The first and second zones contain respective electrodes, each being paired with an electrode common to both zones. As the matric tension of the soil solution increases, the pores within the first zone dehydrate causing increased resistance between the first electrode and the common electrode while the pores in the second zone remain hydrated, the resistance between the second electrode and the common electrode changing only in response to conductivity of the soil solution in the second zone.

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A soil moisture sensing device for sensing moisture levels in a particular soil area. The device has a porous body with at least two zones, a first one of the zones having pore sizes that approximate a range of pores in typical soils, a second one of the zones having pores arranged to be small enoug

A soil moisture sensing device for sensing moisture levels in a particular soil area. The device has a porous body with at least two zones, a first one of the zones having pore sizes that approximate a range of pores in typical soils, a second one of the zones having pores arranged to be small enough to remain hydrated at higher matric tensions. The first and second zones contain respective electrodes, each being paired with an electrode common to both zones. As the matric tension of the soil solution increases, the pores within the first zone dehydrate causing increased resistance between the first electrode and the common electrode while the pores in the second zone remain hydrated, the resistance between the second electrode and the common electrode changing only in response to conductivity of the soil solution in the second zone. ethod of claim 1 wherein said electromagnet comprises at least one coil wound with windings in a plane substantially perpendicular to a longitudinal axis of said borehole. 10. The method of claim 9 wherein generating said first and second RF fields further comprises using a coil on the logging tool with windings in a plane substantially parallel to said longitudinal axis. 11. The method of claim 1 wherein said logging tool is conveyed into the borehole in one of (i) a wireline, (ii) a drillstring, and, (iii) coiled tubing. 12. The method of claim 1 wherein at least one of the first, second and third frequencies is different from one of the other frequencies. 13. In a method of nuclear magnetic resonance (NMR) sensing of earth formations, using, in a borehole containing a ferromagnetic casing and ferromagnetic debris, a logging tool designed to have (i) a permanent magnet for generating a static magnetic field in the earth formations, and (ii) at least one antenna for generating a modulated radio frequency (REF) magnetic field in the earth formations and receiving NMR signals therefrom, an improvement comprising: (a) replacing said permanent magnet by an electromagnet operated between an activation time and deactivation time for inducing the static magnetic field; and (b) initiating at least one pulse for modulating said RF field at a start time delayed relative to said activation time by a wait time related to a longitudinal relaxation time T1of material within said region. 14. The method of claim 13 wherein said wait time is at least equal to T1. 15. The method of claim 13 wherein the at least one pulse further comprises a plurality of pulses forming one of: (i) a CPMG sequence, and, (ii) a modified CPMG sequence. 16. The method of claim 13 further comprising repeating (b) at least once and acquiring NMR signals with a plurality of wait times. 17. The method of claim 13 wherein said static magnetic field has a field strength between 0.6 and 6.0 mT. 18. The method of claim 13 wherein said electromagnet comprises at least one coil with windings in a plane substantially parallel to a longitudinal axis of said borehole. 19. The method of claim 18 wherein said at least one antenna further comprises a coil on the logging tool with windings in a plane substantially parallel to said longitudinal axis and substantially parallel to a total dipole moment of said electromagnet. 20. The method of claim 13 wherein said electromagnet comprises at least one coil wound with windings in a plane substantially perpendicular to a longitudinal axis of said borehole. 21. The method of claim 20 wherein said at least one antenna further comprises a coil on the logging tool with windings in a plane substantially parallel to said longitudinal axis. 22. A method for nuclear magnetic resonance (NMR) sensing comprising: (a) using a magnet for inducing a static magnetic field for polarization of spins of nuclei in materials to be analyzed, said static magnetic field having a time-varying field intensity; (b) generating a radio frequency (RF) magnetic field having a first frequency for causing precession of spins of said nuclei, wherein said first frequency is generated during a first time interval and is related to a first intensity of the static field induced during said first time interval; and (c) receiving at a second time interval delayed relative to the first time interval a NMR signal from said precessing nuclei at a second frequency, wherein said second frequency is related to a second intensity of the static field induced during said second time interval, wherein said second frequency is different from said first frequency. 23. The method of claim 22 further comprising generating a third RF magnetic field at a third time interval between the first and second time intervals for refocusing of said precessing spins. 24. The method of claim 22 wherein said magnet comprises an electromagnet. 25. The method of claim 22