Single shot measurements of the E-field vector with pigtailed optical probes
Summary form only given. Over the variety of available sensors dedicated to electric (E)-field characterization, the use of antennas constitutes the most widespread technique. While such probes are convenient and provide a good sensitivity, they remain invasive and bandwidth limited. At the opposite, fibered electro-optic transducers1 are fully dielectric, millimeter sized and allow to perform measurements of the E-field vector from DC to several gigahertz and even up to terahertz frequencies using equivalent-time sampling. Furthermore, recent developments lead to a simultaneous characterization of 2 transverse E-field vector components with a single EO probe2. Based on polarization state modulation, the EO transducer is linked to a remote (up to 30 meters) optoelectronic set-up including a ultra low noise laser feeding the probe and a real time optical set-up to manage the modulation treatment. The automated and servo controlled measurement bench is temperature dependent free. The available measurement dynamics exceeds 100 dB, ranging from less than 1 V. m-1. Hz-1/2 up to the breakdown electric field in air.An exhaustive comparison between BO sensors and other technologies will be firstly given during the conference. This analysis will be based on intrinsic sensor properties, such as sensitivity, frequency bandwidth, vectorial selectivity, spatial resolution and induced perturbation on the field to be measured. After recalling the principles of the BO effect, the optical arrangement of the optical probes will be described. The characterization of the BO system will be presented together with experimental results illustrating the potentialities of BO sensors. Among these examples, measurements of pulsed B-field in air (pulsed power), water (specific absorption rate evaluation in pulsed regime) or in plasma (real time evolution of the electrical discharge associated B-field) will be shown.
Développement d'une sonde électro-optique dédiée à la mesure simultanée du champ électrique et de la température au sein des milieux biologiques
Le bioelectromagnetisme, domaine de recherche se situant au carrefour de la biologie et de l'electromagnetisme, s'interesse a l'etude des interactions entre les ondes electromagnetiques et le vivant. La finalite de ces travaux de these concerne le developpement d'un capteur optique dedie a la mesure simultanee du champ electrique et de la temperature au sein de milieux biologiques exposes a un rayonnement radiofrequence. Il s'agit donc, plus specifiquement, de realiser une sonde electro-optique repondant aux differents besoins metrologiques des applications dosimetriques et qui soit, de plus, compatible avec les milieux d'etude. Une campagne de mesure preliminaire a ete dediee a la caracterisation les proprietes optiques, thermo-optiques et electro-optiques des cristaux d'interet (elements de transduction de ces sondes). Un capteur fibre a ensuite ete realise. Ce dernier a permis d'effectuer des mesures simultanees de champ electrique et de temperature dans le cadre d'experimentations en dosimetrie radiofrequence, permettant ainsi une caracterisation duale inedite du Debit d'Absorption Specifique (DAS). Cette sonde, entierement dielectrique, a egalement rendu possible une premiere discrimination du profil temporel d'impulsions nanosecondes de fortes amplitudes au sein d'une solution biologique, dans le cadre d'experimentations en electroporation cellulaire.
The effect of collimation on image quality and radiation safety in digital radiography of small animals
Collimating the primary x-ray beam to the specific area of anatomic interest has traditionally been strongly recommended to produce high quality radiographic images, even though some small animal patients can fit their entire torso on a single radiographic casette or detector. However, modern digital radiography may allow for whole-body projections for these patients at similar quality to specific collimated projections. Lateral and ventrodorsal projections of 31 small dogs were obtained to evaluate the effect of collimation on the quality of the resulting digital radiograph. Each projection was performed using both a collimated and whole-body technique. Scatter radiation was detected during each exposure as well to determine the effect of collimation on radiation safety for veterinary personnel. The resulting images were cropped to portray only the thorax, and were evaluated by five radiologists blinded to the procedure used for each image. Visual grading characteristics analysis was performed. An overall trend towards higher image quality was found in the collimated approach compared to the whole-body, but in most cases this change was not significant. Overall image quality for the ventrodorsal images was found to be significantly better in the collimated approach compared to the whole-body. Evaluation of image histograms suggests that the application of digital processing and the look-up table differs between them, and this may account for a large portion of any quality difference. Over twice as much scatter radiation was detected during the whole-body images as during the collimated images. Overall image quality was rated as adequate to high for almost all images with both approaches. Adequate collimation remains recommended to provide the highest quality images with the lowest exposure to veterinary personnel.