Detecting supraglacial debris thickness with GPR under suboptimal conditions

The thickness of a supraglacial layer is critical to the magnitude and time frame of glacier melt. Field-based, short pulse, ground-penetrating radar (GPR) has successfully measured debris thickness during a glacier's melt season, when there is a strong return from the ice–debris interface, but profiling with GPR in the absence of a highly reflective ice interface has not been explored. We investigated the performance of 960 MHz signals over 2 km of transects on Changri Nup Glacier, Nepal, during the post-monsoon. We also performed laboratory experiments to interpret the field data and investigate electromagnetic wave propagation into dry rocky debris. Laboratory tests confirmed wave penetration into the glacier ice and suggest that the ice–debris interface return was missing in field data because of a weak dielectric contrast between solid ice and porous dry debris. We developed a new method to estimate debris thicknesses by applying a statistical approach to volumetric backscatter, and our backscatter-based calculated thickness retrievals gave reasonable agreement with debris depths measured manually in the field (10–40 cm). We conclude that, when melt season profiling is not an option, a remote system near 1 GHz could allow dry debris thickness to be estimated based on volumetric backscatter.

Dielectric confinement for designing compositions and optoelectronic properties of 2D layered hybrid perovskites

The possibility of using nanoscale dielectric contrast for designing 2D layered halide perovskite compositions for optoelectronic applications is discussed.

Assessing Changes in Dielectric Properties Due to Nanomaterials Using a Two-Port Microwave System

Detecting changes in the dielectric properties of tissues at microwave frequencies can offer simple and cost effective tools for cancer detection. These changes can be enhanced by the use of nanoparticles (NPs) that are characterised by both increased tumour uptake and high dielectric constant. This paper presents a two-port experimental setup to assess the impact of contrast enhancement on microwave signals. The study focuses on carbon nanotubes, as they have been previously shown to induce high microwave dielectric contrast. We investigate multiwall carbon nanotubes (MWNT) and their -OH functionalised version (MWNT-OH) dispersed in tissue phantoms as contrast enhancing NPs, as well as salt (NaCl) solutions as reference mixtures which can be easily dissolved inside water mixtures and thus induce dielectric contrast changes reliably. MWNT and MWNT-OH are characterised by atomic force microscopy, and their dielectric properties are measured when dispersed in 60% glycerol–water mixtures. Salt concentrations between 10 and 50 mg/mL in 60% glycerol mixtures are also studied as homogeneous samples known to affect the dielectric constant. Contrast enhancement is then evaluated using a simplified two-port microwave system to identify the impact on microwave signals with respect to dielectric contrast. Numerical simulations are also conducted to compare results with the experimental findings. Our results suggest that this approach can be used as a reliable method to screen and assess contrast enhancing materials with regards to a microwave system’s ability to detect their impact on a target.

Strategies for Dielectric Contrast Enhancement in 1D Planar Polymeric Photonic Crystals

Historically, photonic crystals have been made of inorganic high refractive index materials coupled to air voids to maximize the dielectric contrast and in turn the light confinement. However, these systems are complex, costly, and time-demanding, and the fabrication processes are difficult to scale. Polymer structures promise to tackle this issue thanks to their easy solution and melt processing. Unfortunately, their low dielectric contrast limits their performance. In this work, we propose a concise but exhaustive review of the common polymers employed in the fabrication of planar 1D photonic crystals and new approaches to the enhancement of their dielectric contrast. Transfer matrix method modeling will be employed to quantify the effect of this parameter in standardized structures and to propose a new polymer structure for applications dealing with light management.

High Refractive Index Inverse Vulcanized Polymers for Organic Photonic Crystals

Photonic technologies are nowadays dominated by highly performing inorganic structures that are commonly fabricated via lithography or epitaxial growths. Unfortunately, the fabrication of these systems is costly, time consuming, and does not allow for the growth of large photonic structures. All-polymer photonic crystals could overcome this limitation thanks to easy solubility and melt processing. On the other hand, macromolecules often do not offer a dielectric contrast large enough to approach the performances of their inorganic counterparts. In this work, we demonstrate a new approach to achieve high dielectric contrast distributed Bragg reflectors with a photonic band gap that is tunable in a very broad spectral region. A highly transparent medium was developed through a blend of a commercial polymer with a high refractive index inverse vulcanized polymer that is rich in sulfur, where the large polarizability of the S–S bond provides refractive index values that are unconceivable with common non-conjugated polymers. This approach paves the way to the recycling of sulfur byproducts for new high added-value nano-structures.

Effect of Environmental Humidity on the Ionic Transport of Poly(ethylene Oxide) Thin Films by Local Dielectric Spectroscopy

<div><div><div><p>The effect of humidity on the ionic transport in the amorphous phase of poly(ethylene oxide) thin films has been studied by via local dielectric spectroscopy. We explored a controlled humidity range between 15 %RH and 50 %RH. AFM-based local dielectric imaging allowed to obtain simultaneously the thin films topography and the corresponding dielectric contrast maps. No humidity effect on the film topography was observed whereas large variation of the dielectric signal could be detected. In addition, we observed a clear dielectric contrast in different locations on the thin film surface. At selected regions with high contrast in the dielectric maps, we performed nanoDielectric Spectroscopy (nDS) measurements covering the frequency range from 10 Hz to 100 kHz. By modeling these spectroscopy results, we quantified the conductivity of the amorphous phase of the semicrystalline poly(ethylene oxide) films. The crystalline fraction of the PEO thin films was extracted and found to be about 36%, independently of humidity. However, the average conductivity increased drastically from 2×10-10 to 5×10-9 S/cm, by changing environmental humidity in the explore %RH range.</p></div></div></div>

Effect of Environmental Humidity on the Ionic Transport of Poly(ethylene Oxide) Thin Films by Local Dielectric Spectroscopy

<div><div><div><p>The effect of humidity on the ionic transport in the amorphous phase of poly(ethylene oxide) thin films has been studied by via local dielectric spectroscopy. We explored a controlled humidity range between 15 %RH and 50 %RH. AFM-based local dielectric imaging allowed to obtain simultaneously the thin films topography and the corresponding dielectric contrast maps. No humidity effect on the film topography was observed whereas large variation of the dielectric signal could be detected. In addition, we observed a clear dielectric contrast in different locations on the thin film surface. At selected regions with high contrast in the dielectric maps, we performed nanoDielectric Spectroscopy (nDS) measurements covering the frequency range from 10 Hz to 100 kHz. By modeling these spectroscopy results, we quantified the conductivity of the amorphous phase of the semicrystalline poly(ethylene oxide) films. The crystalline fraction of the PEO thin films was extracted and found to be about 36%, independently of humidity. However, the average conductivity increased drastically from 2×10-10 to 5×10-9 S/cm, by changing environmental humidity in the explore %RH range.</p></div></div></div>

Effect of Environmental Humidity on the Ionic Transport of Poly(ethylene Oxide) Thin Films by Local Dielectric Spectroscopy

<div><div><div><p>In this work, we study the effect of humidity on the ionic transport in the amorphous phase of poly(ethylene oxide) thin films via local dielectric spectroscopy measurements. We explored a controlled humidity range between 15 %RH and 50 %RH. AFM-based local dielectric imaging allowed us to obtain the thin films topography and dielectric contrast maps, simultaneously. No humidity effect on the film topography was observed whereas large variation of the dielectric signal occurred. In addition, we observed a clear dielectric contrast among different locations on the thin film surface. In two selected regions with high contrast in the dielectric maps, we performed nanoDielectric Spectroscopy (nDS) measurements covering the range from 10 Hz to 100 kHz. By modeling these spectroscopy results, we quantified the conductivity of the amorphous phase of the semicrystalline poly(ethylene oxide) films. The crystalline fraction of the PEO thin films were extracted being about 36%, independently of humidity conditions. On the contrary, the average conductivity increased drastically from 2 10-10 to 5 10-9 S/cm, by changing environmental humidity in the explore %RH range.</p></div></div></div>

The response of supraglacial debris to elevated, high frequencyGPR: Volumetric scatter and interfacial dielectric contrastsinterpreted from field and experimental studies

The thickness of supraglacial debris affects the surface energy balance and retreat patterns of mountain glaciers. Therefore, knowing a debris layer’s thickness is crucial for understanding the magnitude and timeframe of glacier melt. Field- based ground-penetrating radar (GPR) has recently gained attention as a possible method for measuring debris thickness. Airborne assessments achieve extensive coverage and characterization, but the use of GPR for such platforms remains relatively unexplored. We investigated the performance of 960 MHz and 2.6 GHz GPR signals through dry laboratory rock debris, and of 960 MHz over ∼ 2 km of transects on the debris cover of Changri Nup Glacier, Nepal Himalaya. On the glacier, 960 MHz profiles were characterized by no clear reflection from the ice interface and volumetric backscatter from within ∼ 10–40 cm, a depth that corresponds to approximate ground-truth debris thicknesses on all transects. The laboratory results show that the lack of an ice-debris interface return in field data was likely caused by a weak dielectric contrast between solid ice and porous dry debris and that surface scatter is coherent but weak. This suggests that the debris-ice interface reflection was also likely coherent, supporting our conclusion of a weak dielectric contrast. The laboratory 2.6 GHz results show significant penetration for only smaller clast sizes up to 4 cm. We used a statistical approach to estimate ice depth from volumetric scatter, which gave reasonable agreement with ground-truth depth measurements. We conclude that a remote system operating near 1 GHz could successfully estimate dry debris cover thicknesses based on depth of volumetric backscatter.