A Sensor for the Measurement of the Moisture of Undisturbed Soil Samples

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1 Sensos 1, 1, 19-17; doi:1.9/s119 ticle OPEN ESS sensos ISSN Senso o the Measuement o the Moistue o Undistubed Soil Samples Goan Kitić * and Vesna nojević-bengin Faculty o Technical Sciences, Univesity o Novi Sad, Tg Dositeja Obadovića, 1 Novi Sad, Sebia; bengin@uns.ac.s * utho to whom coespondence should be addessed; kile@uns.ac.s; Tel.: ; Fax: Received: Novembe 1; in evised om: 1 Januay 1 / ccepted: 1 Januay 1 / Published: 9 Januay 1 bstact: This pape pesents a vey accuate senso o the measuement o the moistue o undistubed soil samples. The senso elies on accuate estimation o the pemittivity which is peomed independently o the soil type, and a subsequent calibation. The senso is designed as an upgade o the conventional soil sampling equipment used in agicultue the Kopecky cylinde. The detailed desciption o the device is given, and the method o detemining soil moistue is explained in detail. Soil moistue o unknown test samples was measued with an absolute eo below.7 g/g, which is only.% o the ull scale output, illustating the high accuacy o the senso. Keywods: soil moistue senso; senso modeling; pemittivity measuement 1. Intoduction Exact measuement o soil moistue is needed in vaiety o applications. In agicultue, pope gowth, development and maintenance o the plants depend vey signiicantly on soil wate content. Othe applications ange om monitoing o soil wate content in vaious types o soil studies o in ecosystem management, to geo-engineeing whee high soil wate content can indicate potential dange o landslides. They all have in common a geat need o pecise measuement o the soil wate content. Soil wate content measuement can be peomed in situ, o a sample can be measued in the laboatoy using vaious techniques. Howeve, both methods involve some distubance to the measued soil, eithe by inseting the senso into the gound o by handling the sample. lthough some

2 Sensos 1, 1 19 miniatue in situ sensos exist which tend to minimize soil distubance duing insetion [1 8], thei accuacy and eliability depend on the soil type and the use o the calibation pocess. Futhemoe, chaacteistics o some sensos degade with time [9,1]. ll this signiicantly limits the applicability o in situ sensos in eal-lie scenaios. On the othe hand, the most oten used laboatoy method o soil wate content measuement is based on dying o the sample and measuement o the esulting mass decease [11]. lthough this method leads to vey accuate esults and equies standad laboatoy equipment (oven and pecise scale), it is vey time consuming, as it lasts aound h. It also destoys the soil sample and allows no epeatability o the measuement. The pupose o this wok was to develop a eliable and accuate method o laboatoy measuement o soil wate content o undistubed samples o abitay soil type, that equies no dying and can be epeated as many times as needed. In Section we pesent the design o the poposed senso device, based on the upgade o the typical equipment o sampling o soil in an undistubed state the Kopecky cylinde. The opeational pinciple o the poposed device is explained in detail in Section. The opeational equency ange is detemined as the one ove which pecise chaacteization o the electic popeties o the soil is possible. The accuate tansmission-line model o the device is pesented and then simpliied using lumped elements, to obtain an analytical elation between the measued eactance o the device and the pemittivity o the sample. Section pesents a pocedue o the extaction o pecise values o the actual pemittivity and eective conductivity o the sample om the measued esults, which is independent o the soil type. The pocedue is validated using vaious liquid and ganula mateials with known pemittivity. In Section, the calibation cuves o the senso ae developed o two types o soil, clay loam (humogley) and sandy clay loam (cabonate chenozem), which elate actual soil pemittivity with thei wate content. The poposed senso has been tested using ou unknown soil samples o both soil types. The conclusions ae pesented in Section.. Senso Design Soil wate content can be detemined by measuing the pemittivity o the sample [1]. Since elative pemittivity o dy soil is about., and pemittivity o wate is 8, even a small amount o moistue causes signiicant changes in the pemittivity o the soil. This dependence allows the design o soil moistue sensos based on pemittivity measuement. Howeve, it should be noted that the soil pemittivity stongly depends on its bulk density. Theeoe, to accuately measue soil moistue, the distubance to the soil as a esult o sampling should be kept to the minimum. Typically, undistubed soil sampling in agicultue is peomed using a Kopecky cylinde, a stainless steel cylinde with diamete D c mm and height H c mm. The Kopecky cylinde is diectly intoduced into the soil by applying oce to its uppe im. The bottom im o the Kopecky cylinde is designed to minimize physical distubance o the sample, ensuing that its density will not die om that ound in the gound. I the sample wee to be emoved om the cylinde, especially in case o elatively low wate content, it could cumble o all apat, esulting in deceased density and, consequently, in changed pemittivity. Theeoe, the ist demand that had to be met in the design o the poposed senso was that the samples should not be emoved om the Kopecky cylinde and that the cylinde itsel should become a pat o the measuement

3 Sensos 1, 1 19 device. In this way, the existing sampling equipment can be easily upgaded to allow electic chaacteization o the samples as well. Howeve, since Kopecky cylindes wee designed to satisy only cetain mechanical constaints, thei integation into an electical device needed o the measuement o pemittivity was not a staightowad task. In the poposed senso, the Kopecky cylinde seves as an oute conducto o a coaxial tansmission line ealized by inseting a metal cylinde with a smalle diamete d c into the middle o the soil sample. In this manne, a Kopecky coaxial line has been obtained. The coss-section o the poposed device is shown in Figue 1. The bottom im o the inne cylinde has been designed to minimize the distubance o the sample between two cylindes. The diamete o the inne cylinde d c has been detemined om the condition that the chaacteistic impedance o the Kopecky coaxial line, Equation (1), should be equal to Ω: 1 μ Dc Z ln( ) Ω π ε d c (1) whee μ and ε ae the pemeability and pemittivity o the medium inside the Kopecky coaxial line, espectively. The Ω condition is necessay to obtain impedance matching between the measuement device, standad Ω SM connecto, and a Vecto Netwok nalyze (VN), which is used to measue the input eactance o the senso. The obtained diamete o the inne conducto is d c. mm. Figue 1. oss-section o the Kopecky coaxial line the cental pat o the poposed senso. Oute conducto (Kopecky cylinde) Inne conducto (cylinde) H c d c D c To connect the Kopecky coaxial line to the SM connecto and the VN pobes, an adapte was designed, as shown in Figue. The adapte consists o two bass cones with a diamete atio that ulills the Ω condition in Equation (1) at each coss section. t the top o the adapte a standad SM connecto is placed. Holdes ae mounted at the bottom end o both cones, to obtain a good electical contact between the adapte and the Kopecky coaxial line. photogaph o the complete senso and its pats is shown in Figue. Since the coaxial tansmission lines ae vey sensitive to the mutual position o oute and inne conducto, a diecto (shown in the back) was used to align the axes o the inne and the oute cylinde exactly. In the ont, the open Kopecky cylinde with its inne conducto emoved is shown, while the completely assembled senso is on the ight hand side o the photo.

4 Sensos 1, 1 19 Figue. (a) oss-section o the adapte (b) Photogaphs o two pats o the adapte. (a) (b) Figue. The poposed senso (on the ight) and its pats.. Opeational Pinciple and Model o the Senso The capacitance o Kopecky coaxial line vaies with soil pemittivity and thus with soil moistue as well. Howeve, this capacitance cannot be measued diectly. Instead, the input eactance o the entie senso X in can be measued by VN. To obtain an analytical elation between the measued X in and the actual value o, an electical model o the senso has been developed. We note hee that measuing X in is not the only way to detemine. Fo example, in [1,1] the complex election coeicient measued using VN was used to detemine the capacitance o the open-ended coaxial pobe and, consequently, the pemittivity o the sample. Howeve, such an appoach esulted in ambiguous solutions o the pemittivity and a speciic pocedue had to be used to detemine the valid one. The pupose o this wok was to develop a ast, eicient and eliable method o non-ambiguous estimation o the pemittivity. Since the wate content pedominantly inluences the eal pat o pemittivity, accuate detemination o its imaginay pat is not necessay. By elying on the measuement o input eactance o the senso, we have developed a simple and staightowad method o estimation o the eal pat o pemittivity, which yields unique solutions, thus avoiding the need o speciic pocedues o choosing between ambiguous solutions. To allow the chaacteization o dielectic popeties o the soil in a wide equency ange, we ist analyze the opeational equency limits o the poposed senso. The uppe equency limit is detemined by the appeaance o highe modes in the Kopecky coaxial line. The undamental popagation mode is TEM mode, while the unwanted TE 11 mode appeas at the equency: c c Dc dc π μ () ε

5 Sensos 1, 1 19 whee c is the speed o light in vacuum. bove c, two waves with dieent popagation constants would supeimpose, esulting in deteioated peomances o the device [1]. Fo given dimensions o the senso, and taking into account the theoetical maximal pemittivity o humid samples (equal to 8), the uppe equency limit o the device is calculated to be MHz. To exclude the esponse o capacitos at D, the lowe opeating equency has to be set above Hz. Futhemoe, the lowe equency limit is detemined by the Maxwell-Wagne polaization which has a signiicant eect on the pemittivity estimate o clay ich soils at low equencies [1]. Theeoe, the lowe equency limit o the device is set to 1 MHz. It should be noted that the uppe limit o MHz is set o measuement o soil pemittivity only. The poposed device can be used to measue the pemittivity o vaious liquid and ganula mateials. Depending on the expected value o the pemittivity, the uppe limit o the opeating equency ange can be extended up to 1 GHz. In that case, opeating equencies ae elatively high with espect to the dimensions o the senso. Theeoe, in ode to accuately model the senso, elements with distibuted paametes i.e., tansmission lines should be used. The tansmission-line model o the poposed senso is shown in Figue. Figue. The tansmission-line model o the poposed senso. engths o the tansmission lines ae l c H mm, l. mm, inging capacitance.1 pf. The adapte and the Kopecky coaxial line ae modeled by two seially connected tansmission lines o cetain lengths (Figue ). Since the Kopecky coaxial line is open at one o its ends, the capacito is included to account o inging ields at the open end o the tansmission line. The value o has been detemined though numeical simulations in OMSO Multiphysics. and it is equal to.1 pf. s conimed by additional simulations, is independent o the electic popeties o the sample placed inside the Kopecky coaxial line. The initial model with distibuted paametes can be simpliied by eplacing each tansmission line with an appopiate lossless lumped element model. n electically shot section o the tansmission line, appoximately one quate o the guided wavelength long, can be modeled using one section shown in Figue. Having in mind the physical length o the poposed senso, two sections ae needed to model the Kopecky coaxial line and one section to model the adapte. The inal lumped element model o the poposed senso is shown in Figue. Values o the lumped elements in the model can be calculated using known expessions o inductance and capacitance o a tansmission line [17]:

6 Sensos 1, (a) (b) whee l is the length o the tansmission line, Z is its chaacteistic impedance, and is angula equency. Figue. umped element model o an electically shot section o the lossless tansmission line. Figue. umped element model o the poposed senso. Fom the lumped element model, input eactance o the device can be easily ound as: () whee and B ae: ( ) ( ) [ ] ( ) ( ) ( ) [ ] ( ) ( ) [ ] [ ] 1 (a) ( ) ( ) [ ] ( ) ( ) ( ) ( ) ( ) [ ] ( ) ( ) ( ) [ ] [ ] B (b) tan Z l c ε ε ε ε l c Z sin 1 B X in

7 Sensos 1, The input eactance is a unction o angula equency π, as well as o all elements o the model:,,, and. Howeve, only depends on the soil pemittivity, since it can be assumed that the inductance o a shot section o tansmission line in Equation (b) does not depend eithe on the pemittivity o the medium o on the opeating equency: Theeoe, and can be egaded as constant ove the whole equency ange o inteest and o all measued mateials. The capacitance o the adapte is given by Equation (a). Since the adapte is always ai-illed, the capacitance does not depend on the pemittivity o the sample. In the case o measuement o soil pemittivity, whee opeating equencies ange om 1 MHz to MHz, equency dependency o can also be neglected since it inluences only to the amount o.1%. Using Equations (a) and (b), the ollowing values o the lumped elements o the model have been obtained:.7 nh,.819 pf, and.1 nh. When these values ae substituted in Equations (a) and (b), the dependence between the input eactance and the sample capacitance is obtained: whee and B ae: ( ) 1 ( ) ε Z X in l ε c B Zl c () () (a) B ( ) ( ) 7 ( ) (b) is opeating equency in MHz, and is given in pf. To validate the model, Figue 7 shows a compaison between the measued input eactance and the input eactance o the model calculated using Equation (), o the ai-illed device. The compaison has been peomed in a vey wide equency ange, up to GHz. vey good ageement can be obseved, illustating the validity o the model. The dieence in the magnitudes o the esponses aound 1.9 GHz is solely due to the act that the lumped model does not include any losses. Howeve, this does not diminish its validity, even moe so since the esonance aound 1.9 GHz is out o the opeational equency ange o the poposed senso.

8 Sensos 1, Figue 7. ompaison between the measued input eactance o the senso, and the input eactance o the lumped-element model, in the case o the ai-illed device. -1 Xin [Ω] Xin [Ω] [MHz] Measuement Model [GHz]. Pemittivity Measuement and the Inluence o osses The input eactance o the senso illed with a mateial unde test is measued ove a ange o equencies using VN. s mentioned above, the uppe limit o this equency ange depends on the actual value o the pemittivity, and it extends to 1 GHz o mateials with pemittivity close to 1. Using the measuement esults and the expessions Equations () and (a), the pemittivity o the sample is then obtained as a unction o equency, independently o the type o the mateial unde test. To illustate this, the pemittivity o vaious samples has been detemined, Figue 8. It can be seen that the measued pemittivity o ai, kitchen salt, sunlowe oil and quatz sand coespond vey well to the actual values [18 ]. Futhemoe, the measued pemittivity o these mateials is constant ove the equency ange o inteest. Howeve, a equency dependence o pemittivity is obseved in the case o sunlowe oil (weak) and a humogley soil sample with unknown wate content (much stonge), due to the act that these samples exhibit dielectic losses which have not been taken into account by the model. Figue 8. Measued pemittivity o vaious samples, illustating that the poposed device can be used to estimate pemittivity independently o the type o mateial unde test. ε a 1 8 i Kitchen salt Sunlowe oil Quatz sand Soil 8 1 [MHz] The pemittivity obtained om the measued input eactance and shown in Figue 8 is in act the appaent pemittivity ε a, which is a unction o equency, o the actual elative pemittivity ε (which is constant ove the equency ange o inteest), and o the eective conductivity σ e (which accounts

9 Sensos 1, 1 17 o the actual conductivity o the sample as well as o dielectic losses in the sample i.e., o non-zeo imaginay pat o the pemittivity) [1]. The actual pemittivity ε and the eective conductivity σ e can be extacted om the measued appaent pemittivity by a itting pocedue, using [1]: lthough initially poposed o time-domain measuements [1], we show that the expession Equation (7) can be successully used in equency domain as well, to model the inluence o the losses on measuements. We note hee that, theoetically, the poposed pocedue could be peomed without using Equation (7), by measuing complex input impedance o the senso instead o its input eactance. Howeve, in that case, the model pesented in Figue would have to include seies esistos and shunt conductos, to account o the losses. This would in tun lead to inal expessions a moe complicated than Equation (), om which it would not be possible to easily calculate the capacitance. Theeoe, we have opted to use the lossless model, to easily calculate and ε a, and then to use Equation (7) to account o the inluence o the losses. By using the poposed appoach, values o ε and σ e have been obtained o all measued samples, and they ae shown in Table 1. The obtained values coespond vey well to the actual ones [18 ]. In the case o ai, kitchen salt and quatz sand, the actual and appaent pemittivity ae pactically identical, due to the act that these mateials ae all vey good dielectics and exhibit a conductivity close to zeo. Table 1. ctual elative pemittivity ε and eective conductivity σ e o vaious samples.. alibation and Testing σ ε ε a ε ε Mateial σ e [S/m] ε i.99 Kitchen salt.1 Sunlowe oil..7 Quatz sand. Soil sample In the pevious Section, we have shown that the poposed senso can be used to measue the actual elative pemittivity ε and the eective conductivity σ e, independently o the mateial unde test. Howeve, to use the poposed senso to coectly estimate soil moistue, the measued pemittivity ε a has to be coelated with the actual soil moistue values. calibation pocedue has to be peomed which elies on the act that the soil wate content inluences the mass o the sample as well as its dielectic popeties. To that end, gavimetic wate content θ g [] has been used, deined as the atio between mass o the wate m w and the mass o the dy soil m ds : m θ g m w ds whee the mass o the wet soil sample is denoted with m ws. The cuves that elate the appaent pemittivity and the gavimetic wate content o the soil sample have been obtained using samples o a e mws m m ds ds (7) (8)

10 Sensos 1, humogley soil taken om the depth o to cm (humogley is a vey etile typical agicultual soil, which, accoding to USD classiication, belongs to clay loam type o soils. The samples wee taken om the egion o Banat in noth-east Sebia.) The calibation pocess stated with a completely dy undistubed soil sample placed in the Kopecky cylinde. The mass o the dy soil was ist measued. The sample was subsequently immesed in distilled wate o 8 h, to allow the satuation to be achieved by capillay eect. The satuated sample was weighed again. The inne conducto was inseted, and the input eactance was measued. The sample was let to dy and new measuements o input eactance wee peomed wheneve the sample lost g o its weight, until it became completely dy. In this way, a total o 19 measuements wee peomed. Fo each measuement, the appaent pemittivity was extacted ove the equency ange om 1 to MHz. The obtained values o appaent pemittivity ove a speciied equency ange ae pesented in Figue 9, o all 19 measuements. We note hee that vey simila esults wee obtained o measuements o 1 soil samples taken om the same location. s expected, highe wate content esulted in highe aveage appaent pemittivity ove the equency ange o inteest. lso, in all cases a equency-dependence o appaent pemittivity can be obseved. Figue 9. ppaent pemittivity calculated om 19 measuements o the humogley soil sample with known wate contents. The aow indicates the incease o wate content. Wate content ε a [MHz] Using Equation (7), ε and σ e can be extacted om the measued appaent pemittivity. The actual pemittivity ε obtained in this way does not depend on the soil conductivity and theeoe the poposed appoach yields good esults o the pemittivity independently o the soil type. The obtained values o ε and σ e ae shown in Table o all nineteen measuements and they coespond vey well to the typical values ound in [1,,]. s could be expected, both the actual pemittivity ε and the eective conductivity σ e incease with the soil wate content. calibation cuve, shown in Figue 1, has been ceated by polynomial itting o 19 calibation points om Table (indicated with ed cicles in Figue 1), each detemined by the value o the actual pemittivity and the known wate content.

11 Sensos 1, 1 17 Table. ctual elative pemittivity ε and eective conductivity σ e o the humogley soil, extacted om 19 measuements o the soil sample with dieent gavimetic wate contents. No. θ g [g/g] σ e [S/m] ε Figue 1. alibation cuve o the senso (black line), which elates the actual pemittivity o humogley soil to the gavimetic wate content. The calibation cuve has been ceated om 19 calibation points (ed cicles). lso shown ae the esults o independent test measuements (blue tiangles) θ g.1. alibation cuve alibation points Test points ε The absolute eo due to polynomial itting is below.9 g/g, i.e., only.% o the ull scale output. To test the poposed soil moistue senso, the input eactance o ou unknown test soil samples with dieent gavimetic wate contents was measued. The samples wee taken om the same location and om the same depth ( cm), as those used o calibation. Using the pocedue

12 Sensos 1, 1 17 descibed above and the calibation cuve om Figue 1, gavimetic wate contents θ g o all samples wee detemined. They wee compaed to the actual values o gavimetic wate contents (also known), indicated in Figue 1 by blue tiangles. The poposed soil moistue senso poved to be vey accuate, with the geatest absolute eo equal to only.7 g/g which is only.% o the ull scale output. Futhemoe, the senso poduced accuate esults o a wide ange o soil moistues which include all values encounteed in eal-lie scenaios ( %). To investigate the applicability o the poposed senso to vaious soil types, we have epeated the same measuement pocedue o anothe set o soil samples. This time, samples o cabonate chenozem soil wee measued, etilized with kg o nitogen pe ha, and taken om the depth o 1 cm. The obtained calibation cuve is shown in Figue 11, with both calibation and test points denoted. gain, the poposed soil moistue senso poved to be vey accuate, with the geatest absolute eo equal to only. g/g, i.e., only.% o the ull scale output. Figue 11. alibation cuve o the senso (black line) o cabonate chenozem soil. Red cicles denote calibation points, while blue tiangles denote independent test measuements... θ g.1 alibation cuve alibation points Test points ε. onclusions vey accuate and obust senso o measuement o soil moistue o undistubed soil samples has been pesented, based on an upgade o the conventional soil sampling equipment used in agicultue the Kopecky cylinde. Owing to the pocedue developed, the senso povides accuate pemittivity measuements independently o the soil type. By using a calibation cuve which elates the measued pemittivity to the wate content o the soil in question, the poposed senso allows ast and epeatable estimate o soil moistue with an eo below.% with espect to the ull scale output, ove a wide ange o soil moistues which include all values encounteed in eal-lie scenaios ( %). Ou utue wok is aimed at the development o calibation cuves o all typical types o soil in Sebia, including vaious types and quantities o applied etilizes. Once inalized, such a bank o calibation cuves will allow ast and staightowad measuement o soil moistue ove a wide ange o soil types, without the need to peom calibations o each set o dieent samples.

13 Sensos 1, 1 17 It should inally be noted that the application o the poposed senso is not esticted only to the measuements elated to soil, i.e., it can be used to accuately estimate the pemittivity and eective conductivity o vaious othe liquid o ganula mateials, independently o the type o the mateial used. Reeences 1. Regtien, P.P.. Humidity sensos. Meas. Sci. Technol. 1,, doi:1.188/97-//1/11.. Xing, H.; i, J.; iu, R.. GHz On-Boad Paallel Plate Soil Moistue Senso System. In Poceedings o the Sensos o Industy oneence, Houston, TX, US, 8 1 Febuay.. Padossi,.; Incocci,.; Incocci, G.; Malogio, F.; Battista, P. Root zone sensos o iigation management in intesive agicultue. Sensos 9, 9, how,.; Xing, Z.; Rees, H.W.; Meng, F. Field peomance o nine soil wate content sensos on a Sandy oam soil in New Bunswick, Maitime egion, anada. Sensos 9, 9, Spectum Technologies, Inc. vailable online: soil-moistue/soil-moistue-sensos/ (accessed on 1 June 1).. Venie. vailable online: (accessed on 1 June 1). 7. Dynamax. vailable online: (accessed on 1 June 1). 8. ampbell Scientiic. vailable online: (accessed on 1 June 1). 9. Iomete. vailable online: (accessed on 1 June 1.). 1. Weemczuk, J.; Taapata, G.; Jachowicz, R.S. The ink-jet pinting humidity soption senso Modelling, design, technology and chaacteization. Meas. Sci. Technol. 1,, doi:1.188/97-//1/ Gadne, W.H. Wate content. In Methods o Soil nalysis, Pat 1. Physical and Minealogical Methods, nd ed.; nold Klute: Madison, WI, US, 198; pp Topp, G..; Davis, J..; nnan,.p.; Electomagnetic detemination o soil wate content: Measuements in coaxial tansmission lines. Wate Resou. Res. 198, 1, Wilczek,.; Szypłowska,.; Skieucha, W.; ieśla, J.; Pichle, V. Janik, G. Detemination o soil poe wate salinity using an FDR senso woking at vaious equencies up to MHz. Sensos 1, 1, Skieucha, W.; Wilczek,. FDR Senso o measuing complex soil dielectic pemittivity in the 1 MHz equency ange. Sensos 1, 1, Poza, D.M. Tansmission lines and waveguides. In Micowave Engineeing, nd ed.; Robey,., Dwye, S., Eds.; John Wiley & Sons, Inc.: New Yok, NY, US, 1998; pp hen, Y.; O, D. Eects o Maxwell-Wagne polaization on soil complex dielectic pemittivity unde vaiable tempeatue and electical conductivity. Wate Resou. Res.,, Matthaei, G.; Young,.; Jones, E.M.T. ow-pass and high-pass iltes using semi-lumped elements o waveguide cougations. In Micowave Filtes, Impedance-Matching Netwoks, and oupling Stuctues, 1st ed.; tech House: Nowood, M, US, 198; pp..

14 Sensos 1, Komaov, V.; Wang, S.; Tang, J. Pemittivity and measuements. In Encyclopedia o RF and Micowave Engineeing; hang, K., Ed.; John Wiley and Sons, Inc.: New Yok, NY, US, ; pp Faktoova, D. omplex pemittivity o biological mateials measuement at micowave equencies. Meas. Sci. Rev. 7, 7, Robinson, D..; Fiedman, S.P. The eective pemittivity o dense packings o glass beads, quatz sand and thei mixtues immesed in dieent dielectic backgounds. J. Non-ystal. Solid.,, Bittelli, M.; Salvatoelli, F.; Pisa, P.R. oection o TDR-based soil wate content measuements in conductive soils. Geodema 8, 1, Geoge, B.H. ompaison o Techniques o Measuing the Wate ontent o Soil and Othe Poous Media. M.Sc. Thesis, Univesity o Sidney, Sidney, ustalia, Dobson, M..; Ulaby, F.T.; Hallikainen, M.T.; El-Rayes, M.. Micowave dielectic behaviou o wet soil. Pat II: Dielectic mixing models. IEEE Tans. Geosci. Rem. Sens. 198,,.. Topp, G..; Zegelin, S.; White, I. Impacts o the eal and imaginay components o elative pemittivity on time domain electomety measuements in soils. Soil Sci. Soc. m. J.,, by the authos; licensee MDPI, Basel, Switzeland. This aticle is an open access aticle distibuted unde the tems and conditions o the eative ommons ttibution license (