Dielectric characterization of vegetation at L band using an open-ended coaxial probe

Decoupling the integrated microwave signal originating from soil and vegetation remains a challenge for all microwave remote sensing applications. To improve satellite and airborne microwave data products in forest environments, a precise and reliable estimation of the relative permittivity (ε = ε′ − iε′′) of trees is required. We developed an open-ended coaxial probe suitable for in situ permittivity measurements of tree trunks at L-band frequencies (1–2&thinsp;GHz). The probe is characterized by uncertainty ratios under 3.3&thinsp;% for a broad range of relative permittivities (unitless), [2–40] for ε′ and [0.1–20] for ε′′. We quantified the complex number describing the permittivity of seven different tree species in both frozen and thawed states: black spruce, larch, red spruce, balsam fir, red pine, aspen and black cherry. Permittivity variability is substantial and can range up to 300&thinsp;% for certain species. Our results show that the permittivity of wood is linked to the freeze–thaw state of vegetation and that even short winter thaw events can lead to an increase in vegetation permittivity. The open-ended coaxial probe proved to be precise enough to capture the diurnal cycle of water storage inside the trunk for the length of the growing season.</p

Assessing the Perspectives of Ground Penetrating Radar for Precision Farming

The United Nations 2030 Agenda for Sustainable Development highlighted the importance of adopting sustainable agricultural practices to mitigate the threat posed by climate change to food systems around the world, to provide wise water management and to restore degraded lands. At the same time, it suggested the benefits and advantages brought by the use of near-surface geophysical measurements to assist precision farming, in particular providing information on soil variability at both vertical and horizontal scales. Among such survey methodologies, Ground Penetrating Radar has demonstrated its effectiveness in soil characterisation as a consequence of its sensitivity to variations in soil electrical properties and of its additional capability of investigating subsurface stratification. The aim of this contribution is to provide a comprehensive review of the current use of the GPR technique within the domain of precision irrigation, and specifically of its capacity to provide detailed information on the within-field spatial variability of the textural, structural and hydrological soil properties, which are needed to optimize irrigation management, adopting a variable-rate approach to preserve water resources while maintaining or improving crop yields and their quality. For each soil property, the review analyses the commonly adopted operational and data processing approaches, highlighting advantages and limitations

Caractérisation diélectrique micro-onde (1,4 GHz) des arbres et des sols

Le découplage du signal d’émission micro-onde entre la végétation et le sol demeure une difficulté omniprésente pour toutes applications en télédétection. Pour améliorer les produits micro-ondes globaux (e.g. humidité du sol, état de gel/dégel du sol) en milieu forestier, une meilleure estimation de la permittivité électrique de la végétation et du sol est requise. Dans le cadre de ce projet, un nouveau prototype de sonde coaxiale à terminaison ouverte adaptée aux mesures sur le terrain a été développé. Nous montrons dans ce travail que la sonde est apte à mesurer la permittivité électrique en bande L (1.4 GHz) de la végétation et du sol. La sonde affiche des incertitudes maximales de 3,3% pour une large plage de valeurs de permittivité. La permittivité complexe de sept espèces d’arbres différentes a été caractérisée dans des conditions de gel et de dégel. Les résultats montrent que la permittivité électrique du tronc des arbres est fortement corrélée avec l’état de gel/dégel de la végétation et que cet état de gel/dégel de la végétation est sensible aux courts événements de dégel hivernal. Il a aussi été démontré que les différences de permittivité électrique interespèces sont importantes. La sonde coaxiale à terminaison ouverte s’est également révélée suffisamment précise pour capturer le cycle diurne de teneur en eau à l’intérieur du tronc des arbres. Les mesures de permittivité électrique de sols organiques en chambre froide mettent en évidence une hystérésis importante entre le cycle de gel et de dégel du sol. Un tel phénomène n’est pas considéré dans les modèles de permittivité du sol actuel ni dans les algorithmes de détection du gel/dégel des sols. La sonde devrait permettre d’améliorer la modélisation du transfert radiatif en milieu forestier et ainsi permettre d’améliorer les produits satellitaires en bande L.The decoupling of the signal between vegetation and soil remains an omnipresent difficulty for all remote sensing applications in the microwave spectrum. To improve global microwave products (e.g. soil moisture, freeze/thaw soil state) in the forest environment, a better estimate of the permittivity of vegetation and soil is required. As part of this project, a new prototype of open-ended coaxial probe adapted for field measurements has been developed. The probe is designed to measure the L-band permittivity (1.4 GHz) of vegetation and soil. The probe displays maximum uncertainties of 3.3% for a wide range of permittivity values. The complex permittivity of seven different tree species was characterized under freezing and thawing conditions. The results show that the permittivity of tree trunks is strongly correlated with the freeze/thaw state of vegetation, the tree freeze/thaw state is sensitive to short winter thawing events and the inter species differences in permittivity are important. The open-ended coaxial probe is also precise enough to capture the diurnal cycle of water content within the tree trunks. The permittivity measurements of organic soils in cold chamber show a significant hysteresis between the freezing and thawing cycles. Such phenomenon is not considered in current soil permittivity models or in soil freeze/thaw detection algorithms. The probe will allow to improve radiative transfer models in forest environment and thus improve L-band satellite products

Additive Manufactured Antennas and Novel Frequency Selective Sensors

The research work carried out and reported in this thesis focuses on the application of additive manufacturing (AM) for the development antennas and novel frequency selective surfaces structures. Various AM techniques such as direct writing (DW), material extrusion, nanoparticle conductive inks are investigated for the fabrication of antennas and FSS based sensors. This research has two parts. The first involves the development of antennas at the microwave and millimetre wave bands using AM techniques. Inkjet printing of nanoparticle silver inks on paper substrate is employed in the fabrication of antennas for an origami robotic bird. This provides an exploration on the practicability of developing foldable antennas which can be integrated on expendable robots using low-cost household inkjet printers. This is followed using Aerosol jet printing in the fabrication of fingernail wearable antennas. The antennas are developed to operate at microwave and millimetre wave bands for potential use in 5G Internet of Things (IoT) or body-centric networks. The second part of the research work involves the development of frequency selective sensors. Trenches have been incorporated on an FSS structure to produce a new concept of liquid sensor. The sensor is fabricated using standard etching techniques and then using FDM method in conjunction with nanoparticle conductive ink. Finally, a new concept displacement sensor using an FSS coupled with a retracting substrate complement is introduced. The displacement sensor is a 3D structure which is conveniently fabricated using AM techniques

Advanced Sensors for Real-Time Monitoring Applications

It is impossible to imagine the modern world without sensors, or without real-time information about almost everything—from local temperature to material composition and health parameters. We sense, measure, and process data and act accordingly all the time. In fact, real-time monitoring and information is key to a successful business, an assistant in life-saving decisions that healthcare professionals make, and a tool in research that could revolutionize the future. To ensure that sensors address the rapidly developing needs of various areas of our lives and activities, scientists, researchers, manufacturers, and end-users have established an efficient dialogue so that the newest technological achievements in all aspects of real-time sensing can be implemented for the benefit of the wider community. This book documents some of the results of such a dialogue and reports on advances in sensors and sensor systems for existing and emerging real-time monitoring applications

Characterizing the Dielectric Properties of Geologic and Asteroid Regolith Analogue Material for Improved Planetary Radar Interpretation

Planetary radar has provided an increasingly growing number of datasets on the inner terrestrial planets and near-Earth and main-belt asteroid populations in our solar system. Physical interpretation of radar data for inference of surface properties requires constraints on the constitutive parameters of the material making up a given surface. For many planetary surfaces, the response to electromagnetic radiation is described by the complex permittivity. In this thesis, the dielectric response of several geologic materials as a function of frequency and porosity was characterized to supplement radar data interpretation. Using the coaxial transmission line method, the complex permittivity of seven powdered mineral samples was measured. The samples were characterized for their composition and structure using a variety of laboratory techniques. A detailed review of the theory and use of electromagnetic mixing equations was presented to introduce the range of models available to describe the experimental permittivity measurements. A thorough analysis of the experiments was performed which showed that the Looyenga-Landau-Lifshitz and Bruggeman (Symmetric) mixing models described the experimental results with the highest accuracy. Measurement bias in the coaxial transmission line method highlighted in previous research due to inhomogeneities at the sample/conductor interface was modelled using these mixing theories, providing a way to correct for these effects post-measurement. The variation in the permittivity of the solid mineral grains between different minerals was characterized based on the grain density of the minerals, as well as the chemical composition. The experimentally verified mixing models were incorporated into an existing asteroid radar model and were used to calculate the porosity in the near-surface of seven asteroids visited by robotic spacecraft. Comparing with bulk porosity estimates, the asteroid radar model indicated the presence of a porous regolith covering on each asteroid that is similar in porosity to the upper 30 cm of the Moon. The results from this research are important for future radar studies, and the model predictions for asteroid surface properties will be tested with results from upcoming space missions visiting asteroids, such as NASAs OSIRIS-REx and JAXAs Hayabusa2 missions

Latest Advances in Nanoplasmonics and Use of New Tools for Plasmonic Characterization

Nanoplasmonics is an area that uses light to couple electrons in metals, and can break the diffraction limit for light confinement into subwavelength zones, allowing for strong field enhancements. In the last two decades, there has been a resurgence of this research topic and its applications. Thus, this Special Issue presents a collection of articles and reviews by international researchers and is devoted to the recent advances in and insights into this research topic, including plasmonic devices, plasmonic biosensing, plasmonic photocatalysis, plasmonic photovoltaics, surface-enhanced Raman scattering, and surface plasmon resonance spectroscopy

Microwave resonant sensors

Microwave resonant sensors use the spectral characterisation of a resonator to make high sensitivity measurements of material electromagnetic properties at GHz frequencies. They have been applied to a wide range of industrial and scientific measurements, and used to study a diversity of physical phenomena. Recently, a number of challenging dynamic applications have been developed that require very high speed and high performance, such as kinetic inductance detectors and scanning microwave microscopes. Others, such as sensors for miniaturised fluidic systems and non-invasive blood glucose sensors, also require low system cost and small footprint. This thesis investigates new and improved techniques for implementing microwave resonant sensor systems, aiming to enhance their suitability for such demanding tasks. This was achieved through several original contributions: new insights into coupling, dynamics, and statistical properties of sensors; a hardware implementation of a realtime multitone readout system; and the development of efficient signal processing algorithms for the extraction of sensor measurements from resonator response data. The performance of this improved sensor system was verified through a number of novel measurements, achieving a higher sampling rate than the best available technology yet with equivalent accuracy and precision. At the same time, these experiments revealed unforeseen applications in liquid metrology and precision microwave heating of miniature flow systems.EThOS - Electronic Theses Online ServiceGBUnited Kingdo