{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,14]],"date-time":"2026-04-14T16:13:08Z","timestamp":1776183188730,"version":"3.50.1"},"reference-count":46,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2023,6,5]],"date-time":"2023-06-05T00:00:00Z","timestamp":1685923200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Energy and Water Agency Malta"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Agriculture is a major consumer of freshwater and is often associated with low water productivity. To prevent drought, farmers tend to over-irrigate, putting a strain on the ever-depleting groundwater resources. To improve modern agricultural techniques and conserve water, quick and accurate estimates of soil water content (SWC) should be made, and irrigation timed correctly in order to optimize crop yield and water use. In this study, soil samples common to the Maltese Islands having different clay, sand, and silt contents were, primarily, investigated to: (a) deduce whether the dielectric constant can be considered as a viable indicator of the SWC for the soils of Malta; (b) determine how soil compaction affects the dielectric constant measurements; and (c) to create calibration curves to directly relate the dielectric constant and the SWC for two different soil types of low and high density. The measurements, which were carried out in the X-band, were facilitated by an experimental setup comprising a two-port Vector Network Analyzer (VNA) connected to a rectangular waveguide system. From data analysis, it was found that for each soil investigated, the dielectric constant increases notably with an increase in both density and SWC. Our findings are expected to aid in future numerical analysis and simulations aimed at developing low-cost, minimally invasive Microwave (MW) systems for localized SWC sensing, and hence, in agricultural water conservation. However, it should be noted that a statistically significant relationship between soil texture and the dielectric constant could not be determined at this stage.<\/jats:p>","DOI":"10.3390\/s23115357","type":"journal-article","created":{"date-parts":[[2023,6,6]],"date-time":"2023-06-06T02:08:15Z","timestamp":1686017295000},"page":"5357","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Broadband Measurements of Soil Complex Permittivity"],"prefix":"10.3390","volume":"23","author":[{"given":"Justin","family":"Stellini","sequence":"first","affiliation":[{"name":"Department of Physics, University of Malta, MSD2080 Msida, Malta"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1816-0657","authenticated-orcid":false,"given":"Lourdes","family":"Farrugia","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Malta, MSD2080 Msida, Malta"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8401-997X","authenticated-orcid":false,"given":"Iman","family":"Farhat","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Malta, MSD2080 Msida, Malta"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1298-7645","authenticated-orcid":false,"given":"Julian","family":"Bonello","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Malta, MSD2080 Msida, Malta"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3213-2879","authenticated-orcid":false,"given":"Raffaele","family":"Persico","sequence":"additional","affiliation":[{"name":"Department of Environmental Engineering DIAM, University of Calabria, 87036 Cosenza, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7530-7758","authenticated-orcid":false,"given":"Anthony","family":"Sacco","sequence":"additional","affiliation":[{"name":"Institute of Earth Systems, University of Malta, MSD2080 Msida, Malta"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kyle","family":"Spiteri","sequence":"additional","affiliation":[{"name":"Institute of Earth Systems, University of Malta, MSD2080 Msida, Malta"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8138-3052","authenticated-orcid":false,"given":"Charles V.","family":"Sammut","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Malta, MSD2080 Msida, Malta"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2023,6,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1421","DOI":"10.1111\/j.1672-9072.2007.00556.x","article-title":"Deficit Irrigation as a Strategy to Save Water: Physiology and Potential Application to Horticulture","volume":"49","author":"Costa","year":"2007","journal-title":"J. Integr. Plant Biol."},{"key":"ref_2","unstructured":"Seckler, D.W., and International Water Management Institute (1998). World Water Demand and Supply, 1990 to 2025: Scenarios and Issues, International Water Management Institute."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"55","DOI":"10.1007\/s00271-005-0019-3","article-title":"Irrigation of Fruit Trees and Vines: An Introduction","volume":"24","author":"Fereres","year":"2006","journal-title":"Irrig. Sci."},{"key":"ref_4","unstructured":"Drechsel, P., Heffer, P., Magen, H., Mikkelsen, R., and Wichelns, D. (2015). Managing Water and Fertilizer for Sustainable Agricultural Intensification, International Water Management Institute."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1524","DOI":"10.1126\/science.1089967","article-title":"Global Freshwater Resources: Soft-Path Solutions for the 21st Century","volume":"320","author":"Gleick","year":"2003","journal-title":"Science"},{"key":"ref_6","first-page":"1163","article-title":"Nitrates, Agriculture and Environment","volume":"79","year":"2000","journal-title":"Curr. Sci."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"349","DOI":"10.1080\/10934528909375486","article-title":"Nitrate Leaching under Irrigation in the United States\u2014A Review","volume":"24","author":"Ritter","year":"1989","journal-title":"J. Environ. Sci. Health A Environ. Sci. Eng."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"37","DOI":"10.1146\/annurev.py.18.090180.000345","article-title":"Soil Anaerobiosis, Microorganisms, and Root Function","volume":"18","author":"Drew","year":"1980","journal-title":"Annu. Rev. Phytopathol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1109\/TGRS.1985.289497","article-title":"Microwave Dielectric Behavior of Wet Soil-Part 1: Empirical Models and Experimental Observations","volume":"GE-23","author":"Hallikainen","year":"1985","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"201","DOI":"10.1029\/93WR02949","article-title":"Frequency Domain Analysis of Time Domain Reflectometry Waveforms: 2. A Four-Component Complex Dielectric Mixing Model for Soils","volume":"30","author":"Heimovaara","year":"1994","journal-title":"Water Resour. Res."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1699","DOI":"10.1029\/JB079i011p01699","article-title":"Dielectric Properties of Soils at UHF and Microwave Frequencies","volume":"79","author":"Hoekstra","year":"1974","journal-title":"J. Geophys. Res."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"98","DOI":"10.1109\/PROC.1974.9389","article-title":"Soil Electromagnetic Parameters as Functions of Frequency, Soil Density, and Soil Moisture","volume":"62","author":"Hipp","year":"1974","journal-title":"Proc. IEEE"},{"key":"ref_13","unstructured":"Lundien, J.R. (1971). Terrain Analysis by Electromagnetic Means, Waterways Experiment Station."},{"key":"ref_14","unstructured":"Wang, J., Schmugge, T., and Williams, D. (1978). Dielectric Constants of Soils at Microwave Frequencies-II."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"288","DOI":"10.1109\/TGRS.1980.350304","article-title":"An Empirical Model for the Complex Dielectric Permittivity of Soils as a Function of Water Content","volume":"GE-18","author":"Wang","year":"1980","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"977","DOI":"10.1029\/RS015i005p00977","article-title":"The Dielectric Properties of Soil-Water Mixtures at Microwave Frequencies","volume":"15","author":"Wang","year":"1980","journal-title":"Radio Sci."},{"key":"ref_17","unstructured":"Wiebe, M.L. (1971). Laboratory Measurements of the Complex Dielectric Constant of Soils."},{"key":"ref_18","first-page":"562","article-title":"Electrical Parameters of Sandy and Loamy Soils in the Range of Centimeter, Decimeter and Meter Wavelength","volume":"14","author":"Leschanskiy","year":"1971","journal-title":"Izv. Vyss. Ucheb. Zaved. Radiofiz."},{"key":"ref_19","unstructured":"Geiger, F.E., and Williams, D. (1972). Dielectric Constants of Soils at Microwave Frequencies, NASA TMS-65987."},{"key":"ref_20","unstructured":"Newton, R.W. (1977). Microwave Remote Sensing and Its Application to Soil Moisture Detection, Texas A&M University. Tech. Rep. RSC-81."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"101","DOI":"10.1016\/0022-1694(95)02970-2","article-title":"Passive Microwave Remote Sensing of Soil Moisture","volume":"184","author":"Njoku","year":"1996","journal-title":"J. Hydrol."},{"key":"ref_22","unstructured":"Davis, J.L., Topp, G.C., and Annan, A.D. (1976, January 8\u201310). Electromagnetic Detection of Soil Water Content, Progress Report II. Proceedings of the Remote Sensing of Soil Moisture and Groundwater: Workshop Proceedings, Toronto, ON, Canada."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Persico, R., Farhat, I., Farrugia, L., and Sammut, C. (2022). A Numerical Investigation of the Dispersion Law of Materials by Means of Multi-Length TDR Data. Remote Sens., 14.","DOI":"10.3390\/rs14092003"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"377","DOI":"10.1109\/TIM.1970.4313932","article-title":"Measurement of the Intrinsic Properties of Materials by Time-Domain Techniques","volume":"19","author":"Nicolson","year":"1970","journal-title":"IEEE Trans. Instrum. Meas."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"33","DOI":"10.1109\/PROC.1974.9382","article-title":"Automatic Measurement of Complex Dielectric Constant and Permeability at Microwave Frequencies","volume":"62","author":"Weir","year":"1974","journal-title":"Proc. IEEE"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1096","DOI":"10.1109\/22.57336","article-title":"Improved Technique for Determining Complex Permittivity with the Transmission\/Reflection Method","volume":"38","author":"Vanzura","year":"1990","journal-title":"IEEE Trans. Microw Theory Tech."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Bartley, P.G., and Begley, S.B. (2010, January 3\u20136). A New Technique for the Determination of the Complex Permittivity and Permeability of Materials. Proceedings of the 2010 IEEE International Instrumentation and Measurement Technology Conference, I2MTC 2010\u2014Proceedings, Austin, TX, USA.","DOI":"10.1109\/IMTC.2010.5488184"},{"key":"ref_28","unstructured":"Chatzimpaloglou, P., Patrick, J.S., French, C., Ruffell, A., and Stoddart, S. (2020). Temple landscapes Fragility, Change and Resilience of Holocene Environments in the Maltese Islands, McDonald Institute for Archaeological Research."},{"key":"ref_29","unstructured":"Hyde, P.T. (1955). The Geology of the Maltese Islands: With Special Reference to Water Supply and the Possibilities of Oil, Lux Press."},{"key":"ref_30","unstructured":"Lang, W.M. (1960). Soils of Malta and Gozo, H.M.S.O."},{"key":"ref_31","unstructured":"Bowen-Jones, H., Dewdney, J.C., and Fisher, W.B. (1961). Malta, Background for Development, University of Durham."},{"key":"ref_32","unstructured":"Svarajasingham, S. (1971). The Soils of Malta (UNOP\/SF Project MAT\/5, Water Disposal and Water Supply), Food and Agriculture Organization of the United Nations."},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Gauci, R., and Schembri, J.A. (2019). Landscapes and Landforms of the Maltese Islands, Springer Nature.","DOI":"10.1007\/978-3-030-15456-1"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"9","DOI":"10.1111\/j.1365-2389.1958.tb01893.x","article-title":"The Classification of Soils","volume":"9","year":"1958","journal-title":"J. Soil Sci."},{"key":"ref_35","unstructured":"European Commission (2003). MALSIS, a Soil Information System for the Maltese Islands LIFE 00\/TCY\/MT\/000036 Interim Report, European Commission."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"29","DOI":"10.1097\/00010694-193401000-00003","article-title":"Estimation of Soil Organic Carbon by the Chromic Acid Titration Method","volume":"37","author":"Walkley","year":"1934","journal-title":"Soil Sci."},{"key":"ref_37","unstructured":"FAO-ISRIC-ISSS (1998). World Soil Resources Report Nr. 84, FAO."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"47","DOI":"10.2528\/PIER06111204","article-title":"Measurement of Dielectric Constant and Loss Factor of the Dielectric Material at Microwave Frequencies","volume":"69","author":"Kumar","year":"2007","journal-title":"Prog. Electromagn. Res."},{"key":"ref_39","unstructured":"Qureshi, A.A., Afzal, M.U., Taqueer, T., and Tarar, M.A. (2011, January 20\u201322). Performance Analysis of FR-4 Substrate for High Frequency Microstrip Antennas. Proceedings of the 2011 China-Japan Joint Microwave Conference, Hangzhou, China."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"287","DOI":"10.1007\/BF02657420","article-title":"Dielectric Properties of FR-4 Laminates as a of Thickness and the Electrical Frequency of the Measurement!\u2014Function","volume":"18","author":"Mumby","year":"1989","journal-title":"J. Electron. Mater."},{"key":"ref_41","first-page":"1","article-title":"Electrical Characterization of Bambusa Vulgaris as a New Microwave Substrate","volume":"10","author":"Yusof","year":"2017","journal-title":"J. Telecommun. Electron. Comput. Eng. (JTEC)"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/S0167-9317(97)00185-8","article-title":"Low Dielectric Constant Materials for Interlayer Dielectric (Invited Paper)","volume":"40","author":"Treichel","year":"1998","journal-title":"Microelectron. Eng."},{"key":"ref_43","unstructured":"Hippel, V.A. (1954). Dielectric Materials and Applications, Wiley."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"1643","DOI":"10.1080\/09205071.2016.1208592","article-title":"Dielectric Constant Measurement of Materials by a Microwave Technique: Application to the Characterization of Vegetation Leaves","volume":"30","author":"Krraoui","year":"2016","journal-title":"J. Electromagn. Waves Appl."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"106242","DOI":"10.1016\/j.compositesa.2020.106242","article-title":"Efficient Fabrication of Highly Exfoliated and Evenly Dispersed High-Density Polyethylene\/Expanded Graphite Nanocomposite with Enhanced Dielectric Constant and Extremely Low Dielectric Loss","volume":"142","author":"Xu","year":"2021","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_46","doi-asserted-by":"crossref","unstructured":"Cataldo, A., Farhat, I., Farrugia, L., Persico, R., and Schiavoni, R. (2022). A Method for Extracting Debye Parameters as a Tool for Monitoring Watered and Contaminated Soils. Sensors, 22.","DOI":"10.3390\/s22207805"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/23\/11\/5357\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T19:48:49Z","timestamp":1760125729000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/23\/11\/5357"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,6,5]]},"references-count":46,"journal-issue":{"issue":"11","published-online":{"date-parts":[[2023,6]]}},"alternative-id":["s23115357"],"URL":"https:\/\/doi.org\/10.3390\/s23115357","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2023,6,5]]}}}