INVASIVE MICROWAVE MEASUREMENT OF SOIL ELECTROMAGNETIC PROPERTIES AND CORRELATION WITH PHYSICAL QUANTITIES K. Clay, M. Farid, A. N. Alshawabkeh, C. M. Rappaport Contact Info: This work was supported in part by CenSSIS, the Center for Subsurface Sensing and Imaging systems, under the Engineering Research Centers Program of the National Science Foundation (Award Number EEC ) ABSTRACT Modeling detailed spatial distributions and dynamics of the soil properties in the inherently inhomogeneous subsurface requires extensive site characterization. Characterizing this variability with conventional methods is invasive and thus, time consuming, costly, and subject to a large degree of uncertainty due to lack of densely populated sampled insitu measurements thus the need for none or less invasive techniques. It is known that the propagation of electromagnetic waves through a material is dependent on the electrical and magnetic properties of the material. These properties are dielectric permittivity, electrical conductivity and magnetic permeability. There is also need for correlation of measured EM properties to physical and mechanical properties of the soil. Most of these parameters are frequency dependent thus broad band frequency dielectric permittivity and conductivity is vital. INTRODUCTION Microwave measurements refer to electromagnetic measurements conducted at frequencies in the micro wave region. This region lies between 300MHz and 300GHz. In the electromagnetic spectrum for frequency and wavelength, the position of microwaves lies between radio waves and infrared. This region is bounded at the long-wavelength end by the radio wave region, and at the short- wavelength end by the infrared region. The interaction of microwaves with materials and structures is best described in terms of waves. Therefore microwave measurements such as amplitude and phase measurements of transmitted or reflected waves by the specimen, will contain information about internal flaws, material composition, structure, density, porosity, homogeneity, orientation, state of cure, and moisture content, as well as the geometry of the specimen. The fact that microwaves are sensitive to such a large number of material properties leads to a number of possible applications. PLANE WAVE PROPAGATION IN LOSSY MEDIA The propagation properties of an electromagnetic wave such as its phase velocity up and wavelength, are governed by the angular frequency w and the three constitutive parameters of the medium: To examine wave propagation in a conducting medium, we return to the wave equation give by LOW-LOSS DIELECTRIC AND GOOD CONDUCTOR When the medium is called a low-loss dielectric and when the medium is characterized as a good conductor. For a low-loss dielectric, For a good conductor SOILBED FACILITY AND LABORATORY MEASUREMENT SYSTEM The SoilBED testing facility has dimensions of 150 cm width by 120 cm depth by 275 cm length (5 ft x 4 x 9 ft). The longitudinal walls of the facility are made of reinforced concrete while the transverse walls and the gate to the small injection trench are made of 3.8 cm (1.5 in) thick acrylic sheets. The facility is filled with sand as the homogeneous and isotropic soil media. The laboratory measurement system is an Agilent 8714ES RF Network Analyzer (NA) and a computer for data acquisition using a Microsoft Excel based system. A NA is an instrument which measures the complex transmission and reflection characteristics of two-port devices in the frequency domain for the frquecy range 300kHz-3GHz. Its connected to connected to a 12 channel Agilent 87050ES multiport test set on which 12 co-axial cables are connected. LABORATORY SETUP Antenna set up 1: Antennas on top of each other (Vertical Plane) Antenna set up 2: Antennas in the same horizontal plane FREQUENCY DEPENDENCE OF EM PROPERTIES The relative permittivity of the sand does not show significant frequency dependence whatever the water content is. There is significant frequency and water content dependence of the electrical conductivity THEORETICAL BACKGROUND OF MEASUREMENTS AND DATA PROCESSING In this analysis, the problem is modeled as a plane wave boundary value problem which leads to a number of algebraic equations that can be solved for the relative permittivity and conductivity. We have restricted our study to the complex permittivity because most materials of geophysical interest are nonmagnetic, while conductivity is incorporated in the complex permittivity. We can deduce that the differential phase is equal to: j(ωt-βz)= j(β(z+dz) -βz) DETERMINATION OF THE CONDUCTIVITY EFFECT OF EXPERIMENTAL PROCEDURES ON RESULTS To investigate the impacts of saturating and draining on the relative permittivity, phase measurements for saturating cycles were done. Cycle Distance from Transmitter 8"12"16"Average INTRUSIVE MICROWAVE MEASUREMENTS FOR DENSITY INFERENCE The relative permittivity of saturated sand and dry density were determined at different levels of compaction. The relative permittivity was then plotted against the dry density, porosity and void ratio. Average dry density (g/cm 3 ) Relative Permittivity PorosityVoid ratio ONGOING WORK Design of a reliable 2D setup Collection of phase and transmission data from the 2D setup Validation of the 2D FDFD model using using 2D setup data. REFERENCES Blitz, Jack. “Electrical and magnetic methods of nondestructive testing” Bristol ; Philadelphia : A. Hilger, 1991.Blitz, Jack. Ida, Nathan. “Microwave NDT” Dordrecht ; Boston : Kluwer Academic, c1992.Ida, Nathan. Ida, Nathan.” Engineering electromagnetics” New York : Springer, c2000.Ida, Nathan.