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ε" = EC ε d " + (82) 2π fε where f is the frequency of the applied electric field, ε 0 is the dielectric permittivity of free space. 0 ε’ ε’, ε” ε” frequency of electric field [Hz] Fig. 34. Frequency response of dielectric mechanisms: MW, IR, V and UV are respectively microwave, infrared, visible and ultraviolet spectrum Because water is present in all agricultural materials and its influence on the majority of agricultural properties is dominant, the specific property of water causing the orientation polarization is of primary area of interest of dielectric spectroscopy (Kraszewski [47]). 9.1. Hardware features of Time Domain Reflectometry method Time Domain Reflectometry method for the determination of dielectric permittivity is widely accepted, especially for soil water content determination [90,59,61], for its advantages: simplicity of operation, accuracy and fast response, usually does not need calibration, is non-destructive, portable systems are available, is able to automatize and multiplex probes. The construction of TDR meter for determination of velocity of propagation of electromagnetic pulse in the material is much simpler than the frequency domain reflectometer. The basic elements of the meter are (Fig. 35): two pulse generators, delay unit, sampling head with data conversion facilities, a TDR probe (sometimes several multiplexed probes) and a microcontroller. The construction of the TDR meter needs a lot of 85
skills and professional instrumentation [59] to maintain stable parameters in field applications. The pulses travel times along the parallel waveguide in the measured media must be determined with the resolution of picoseconds (Baranowski et al. [8]). The measurement error of the pulse travel time along the probe rods equal to 10 ps will give the error of soil water content measurement of about 0.2%. The applied frequency in Time Domain Reflectometry (TDR) method is not exactly defined as it can be done for Frequency Domain Reflectometry (FDR) represented by the Open-Ended Coax probe method. The application of a step pulse or a needle pulse of very short rise time, t r , corresponds to the frequency range with the upper limit, f max , that can be calculated by the following engineering formula [87]: −1 max t r = 0.35 f (83) The probe in TDR method is a waveguide consisting of two or three parallel metal rods inserted into the tested medium. Fig. 35. Basic elements of the time domain reflectometer for determination of velocity of propagation of electromagnetic waves in porous media The velocity of propagation of the pulse in this waveguide, v, is modified by the dielectric permittivity of the waveguide surroundings. In calculations it is usually assumed that the dielectric loss of the material does not influence the velocity of propagation of the pulse [90]. The real part of the medium complex 86
Page 2 and 3:
TDR METHOD FOR THE MEASUREMENT OF W
Page 4 and 5:
PREFACE The importance of water for
Page 6 and 7:
CONTENTS 1. Status of water as an s
Page 8 and 9:
12.2. New prototype version of FOM/
Page 10 and 11:
that stimulate the phenomena and pr
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The solution to the problem of elec
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3. ELECTRICAL MEASUREMENTS METHODS
Page 16 and 17:
v = c 1 2L = = ( θ ) n ∆t ε (2)
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The TDR probe consists of two waveg
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ε a =1 and φ=0.5 the Eq. (10) has
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The experiment description is given
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Results obtained with the discussed
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Notice that at C s = 0, ie when dis
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water orientation polarization [s],
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Fig. 8. Frequency dispersion of the
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The measurements were performed in
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5. EVALUATION OF DIELECTRIC MIXING
Page 36 and 37: ε α = ∑V α iε i (29) i where
Page 38 and 39: where SAND and CLAY are percents of
Page 40 and 41: Below the transition value, the soi
Page 42 and 43: To verify the observations concerni
Page 44 and 45: 6. TEMPERATURE EFFECT ON SOIL DIELE
Page 46 and 47: chamber and the freezer, only one w
Page 48 and 49: The user interface on the main comp
Page 50 and 51: soil sample volumetric water conten
Page 52 and 53: close vicinity of the analyzed obje
Page 54 and 55: process of measurement is non-destr
Page 56 and 57: dielectric permittivity change caus
Page 58 and 59: The values of the refractive index
Page 60 and 61: The relative, ∆n/∆T, and absolu
Page 62 and 63: Fig. 25. The temperature effect on
Page 64 and 65: The temperature effect of TDR soil
Page 66 and 67: The purpose of the above discussion
Page 68 and 69: ( ,25 + T )( 45 + T ) 49 9 f rel =
Page 70 and 71: 8. THE ACCURACY OF SOIL WATER CONTE
Page 72 and 73: gravimetric method and the soil ref
Page 74 and 75: where: a 0 ÷ a 6 are coefficients
Page 76 and 77: values of p F calculated for the re
Page 78 and 79: eason of this is the fact that wate
Page 80 and 81: 9 ∆θ = 0,2 ⋅10 ⋅ ∆t = 0.00
Page 82 and 83: values of θ rel for lower values o
Page 84 and 85: 9. COMPARISON OF OPEN-ENDED COAX AN
Page 88 and 89: dielectric permittivity, the dielec
Page 90 and 91: The applied lumped capacitance mode
Page 92 and 93: stainless steel wires soldered to t
Page 94 and 95: ε’ Open Coax and ε b-TDR , exce
Page 96 and 97: − − The difference of the imagi
Page 98 and 99: Integrated Circuit) recently introd
Page 100 and 101: 10.2. Electromechanical microwave s
Page 102 and 103: RF1. Two PIN diodes in series in ea
Page 104 and 105: The significant aspect of the proto
Page 106 and 107: visible for lower values of soil el
Page 108 and 109: In the TDR method the signal propag
Page 110 and 111: description of functional and techn
Page 112 and 113: MASTER modules are wireless transce
Page 114 and 115: time the Real Time Clock module wak
Page 116 and 117: ase station distinguishes A SLAVE d
Page 118 and 119: sensor, format the data received fr
Page 120 and 121: 12. SOIL WATER STATUS MONITORING DE
Page 122 and 123: D-LOG/mpts is a moisture/pressure/t
Page 124 and 125: For compatibility reasons it uses t
Page 126 and 127: D-LOG/mts (Fig. 59) is a TDR (Time-
Page 128 and 129: 12.4. FP/m, FP/mts - Field Probe fo
Page 130 and 131: inside of a separate polyethylene b
Page 132 and 133: differential water capacity and the
Page 134 and 135: − maximum number of LP/p probes t
Page 136 and 137:
12.7. LP/t - Laboratory Probe for s
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From the collected data set, after
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25. de Loor G.P.: Dielectric proper
Page 142 and 143:
TDR. Symposium on Time Domain Refle
Page 144 and 145:
100. Whalley W.R.: Considerations o
Page 146 and 147:
Fig. 14. Fig. 15. Fig. 16. Fig. 17.
Page 148 and 149:
Fig. 38. The three-rod TDR probe -
Page 150 and 151:
Fig. 67. A set of LP/ms and LP/p LO
Page 152:
Table 17. An example of the executa
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