Non-Contact Radiofrequency Inductive Sensor for the Dielectric Characterization of Burn Depth in Organic Tissues

International audienceA flat circular transmission line-based 300 MHz resonator was implemented for the non-contact assessment of burn depths in biological tissues. Used as a transmit-and-receive sensor, it was placed at a 2 mm distance from organic material test samples (pork fillet samples) which were previously burned on their surface in various heating conditions involving different temperatures, durations, and procedures. Data extracted from the sensor by means of a distant monitoring coil were found to clearly correlate with the depth of burn observed in the tissue samples (up to 40% sensor output changes for a 7 mm burn depth) and with the heating conditions (around 5% sensor output changes observed in samples burned with identical heating procedures but at two different temperatures—75 °C and 150 °C—and around 40% sensor output changes observed between samples heated at the same temperature but with different heating procedures). These results open the way for the development of easy-to-implement assessment and monitoring techniques for burns, e.g., integrated in wearable medical dressing-like monitoring devices

Spatial diagnostics of plasma produced by a VHF multi-tile electrode

A scalable multi-tile electrode plasma source operating at 150MHz and 162MHz is described. An investigation into the spatial structure of plasmas produced in such as source is reported. Four dierent plasma diagnostics are applied to examine this spatial structure; they are time-varying magnetic ux probe measurements of the magnetic ux, planar Langmuir probe measurements of the ion saturation cur- rent density, capacitive probe measurements of the plasma oscillation potential and measurement of rf current and voltage on tiles. Spatial proles of the plasma potential oscillation and the ion saturation high-light the spatial structure imposed on plasmas produced in the PASTIS source. Analysis of the rf tile current and voltage in the segmented electrode array yields information on the nature of the impedance of both the source and plasma. rf currents in the tiles cause a magnetic dipole to be induced in the regions between tiles. Thus, although the PASTIS source is a capacitive discharge, we must consider a model that includes both capacitively and inductively coupled plasma. This induced dipole moment is measured with a specically designed VHF time-varying magnetic ux probe. Analysis of the diagnostics presented show that there is a well dened spatial structure imposed on the plasma by the segmented electrode tile array

RF Sensors for Monitoring the Electrical Properties of Electrolyte Solutions

A radio frequency electrical sensor for the qualitative analysis and monitoring of the electrical properties of electrolyte solutions is designed, simulated and experimentally tested in this research. This work is based on the use of planar inductors for the detection of a change in the concentration of ionic species in a liquid sample. At first a literature review on the physical chemistry of electrolyte solutions is provided. This will include topics on the conductivity and relaxation properties of electrolytes. This will be followed by a look at dielectric spectroscopy sensors, electrochemical sensors and inductive sensing devices. The principles of electrodynamics and constitutive equations are discussed. Based on these, the principles of operation of the RF electrical sensors are analysed. Two methods of theoretical analysis of such structures are investigated. These methods are; analytical solution and finite element computation method. The former offers greater insight into the system’s parameters whilst the latter offers more information regarding the whole system. Given the qualitative nature of the sensors under investigation and finite element approach was selected and used in latter chapters to obtain grater insight into the behaviour of the system. Planar inductor coils are designed on an FR4 substrate and packaged using PDMS to be used as sensors in the monitoring of electrical properties of electrolytes. Experimental results on these sensors are provided and discussed. The effects of solvent, acidity of the solutions, and environmental factors on the behaviour of the sensors shall be discussed. This is followed by finite element simulations of the sensor and the effect of various parameters on the overall behaviour of the sensing device. A transformer apparatus is also constructed and experimental data are provided for it. An electrolyte is placed on one of the coils of the transformer and scattering parameters are looked upon for data analysis. The results obtained using the FE method, is then used to obtain further information about the principle of operation of the device