Systems for transverse electromagnetic mode in-situ soil testing
A slotted TEM transmission line and an in-situ TEM transmission line are utilized to determine both complex permittivity and permeability of soil. The permittivity and permeability information may be used by underground sensing techniques such as GPR and EMI to enhance information from these techniques. The in-situ probe provides that both complex permittivity and permeability can be measured simultaneously over a broad frequency range without disturbing the soil conditions.
1. A soil probe for use in determining permittivity and permeability of a soil sample, comprising:
a slotted transverse electromagnetic mode (TEM) transmission line having opposite first and second ends and a pair of slot walls extending longitudinally in parallel between said first and second ends and spaced apart by a slot in between the slot walls;
a first port interconnected to the first end of said slotted TEM transmission line;
a second port interconnected to the second end of said slotted TEM transmission line; and
a soil sample receiver of a selected length and configured to be fitted in an intermediate segment of the slot of said slotted TEM transmission line, said soil sample receiver being adapted to receive a soil sample packed therein, said first and second ports being adapted to be connected to a network analyzer that provides electromagnetic signals thereto and receives electromagnetic signals reflected and radiated from the soil held in the soil sample receiver fitted in the intermediate segment of the slot of said slotted TEM transmission line.
2. The soil probe of claim 1 , wherein the length of said soil sample receiver is selected to be different than a half-wavelength multiple of signal frequencies received at said slotted TEM transmission line.
3. The soil probe of claim 1 , wherein said first port and said second port comprise coaxial connectors.
4. The soil probe of claim 3 , wherein each of said coaxial connectors comprises a center conductor that is interconnected to the slot walls of said slotted TEM transmission line and said soil sample receiver is fitted in the intermediate segment of the slot formed between the slot walls in order to minimize air gaps between the sample and each center conductor.
5. The soil probe of claim 1 , wherein said slotted TEM transmission line receives electromagnetic signals in the frequency range from about 50 MHz to about 1 GHz through said first and second ports.
6. The soil probe of claim 5 , wherein impedance of said slotted TEM transmission line may be measured over said frequency range to provide for simultaneous determination of permittivity and permeability of the soil sample.
7. A system for measuring reflection and radiation from a soil sample, the reflection and radiation usable to determine permittivity and permeability of the soil sample, comprising:
a soil probe comprising a transverse electromagnetic mode (TEM) transmission line and first and second ports;
a transmitter that generates electromagnetic energy across a frequency band of interest and forwards the electromagnetic energy to the first and second ports;
an impedance measurement circuit that measures an input impedance of the soil probe over the frequency band and generates measured impedance data, the impedance data providing for simultaneous determination of permittivity and permeability of the soil sample,
wherein said soil probe comprises a slotted TEM transmission line having opposite first and second ends and a pair of slot walls extending longitudinally in parallel between the first and second ends and spaced apart by a slot in between the slot walls, and a soil sample receiver of a selected length that is configured to be fitted into an intermediate segment of the slot of said slotted TEM transmission line and adapted to receive a soil sample packed therein.