International audienceThe aim of this paper is to show the possibility to harvest Radio Frequency (RF) energy to supply Wireless Sensor Networks (WSNs) in outdoor environment. In those conditions, the number of existing RF bands is unpredictable. The RF circuit has to harvest all the potential RF energy present and cannot be designed for a single RF tone. In this paper, the designed RF harvester adds powers coming from an unlimited number of sub-frequency bands. The harvester's output voltage ratios increase with the number of RF bands. As an application example, a 4-RF band rectenna is designed. The system harvests energy from GSM900 (Global System for Mobile Communications), GSM1800, UMTS (Universal Mobile Telecommunications System) and Wi-Fi bands simultaneously. RF-to-dc conversion efficiency is measured at 62% for a cumulative -10 dBm input power homogeneously widespread over the four RF bands and reaches 84% at 5.8 dBm. The relative error between the measured dc output power with all the 4 RF bands ON and the ideal sum of each of the four RF bands power contribution is less than 3%. It is shown that the RF-to-dc conversion efficiency is more than doubled compared to that measured with a single RF source, thanks to the proposed rectifier architecture
International audienceA wide-band 900 MHz to 2.45 GHz rectenna has been developed for Radio Frequency (RF) energy harvesting in the context of outdoors Wireless Sensor Nodes (WSN). Based on simulations of different rectifying circuits, the most appropriate one for low incident power levels has been manufactured and tested with a wide-band antenna. The theoretical analysis, confirmed by measurements, shows that the proposed method yields a 20% increase in average in the DC output voltage compared to a single frequency system
In this paper, a 1.8–2.6 GHz wideband rectenna is designed for radio frequency (RF) energy harvesting in the context of wireless sensor nodes (WSN). To assess the feasibility of ambient RF energy harvesting, the power density from RF base stations is analyzed through statistical measurements. Power density measurements are also performed close to Wi-Fi routers. Using these results, a methodology based on impedance matching network adaptation and maximum power transfer is proposed to design the wideband RF harvester. Using this method, three RF bands,i.e.GSM1800, UMTS and WLAN, are covered. The theoretical analysis is confirmed by simulations and measurements. From measurements results, the prototype RF-to-DC conversion efficiency is 15% at −20 dBm from 1.8 to 2.6 GHz. It is shown that with three RF sources in the chosen bands, each emitting at 10 dBm, the RF-to-DC conversion efficiency is 15% better compared to that measured with a single RF source. Finally, 7 µW is harvested at 50 m from a GSM1800 and UMTS base station. This value confirms the RF harvester workability to supply small sensors.
Background and objectivesLack of words is the second most common disorder after episodic memory loss in patients with Alzheimer's disease. Our objective was develop a speech therapy protocol for patients with Alzheimer's disease with a Mini-Mental State (MMS) score greater than or equal to 15 and suffering from a lack of words, in order to improve access to words. The relationship between cognitive deterioration as assessed by the MMS score and lack of words in Alzheimer's patients seems to be coincidental; no causal relationship has been established (Medina and al. (JEV08)).ProgrammeWe developed a computerised rehabilitation protocol for patients with Alzheimer's disease in order to stimulate the three stages in the mental lexicon described in Levelt's theoretical model of neuropsycholinguistics (1999): lexical selection, morphological encoding, and phonological encoding. Stimulation of lexical selection involved working on the multiple meanings of a word (finding its different meanings by facilitating naming through an indication of context), a search for the relevant and specific features of a word in order to make a guess, and evoking a target word from specific features.Stimulation of morphological encoding involved extracting the meaning of a morpheme by comparing two words, one of which is derived from the other, and then identifying the meaning of an affix by slipping it into a sentence.Phonological encoding was stimulated by the isolation of the initial two-syllable words and merging them to form a third word. A speech therapist assessed lexical naming and MMS score before and after administration of the rehabilitation protocol to patients who had been diagnosed with Alzheimer's disease at Béziers hospital.ResultsThirteen of 14 included patients completed the 20 training sessions of 30 min each, held once or twice a week with their speech therapist. Holding sessions in the same environment helped patients feel more secure and master the exercises better. After the rehabilitation protocol, 12 of the 14 patients were better at naming words after visual confrontation (pictures) and reproducing words after auditory confrontation. A decline was noted in every cognitive aspect in nine patients. Eight of these nine patients maintained or improved their lexical access.Discussion and conclusionAlthough there was a decline in cognitive abilities in our study population, systematic activation of the lexicon helped maintain or improve linguistic aspects of language. These aspects are essential to oral communication from an ecological and psychosocial standpoint. A limitation of our study is the small number of participants. We plan to include a wider range of patients and collaborate with more speech therapists.Cette étude porte sur un essai de formalisation d'une rééducation orthophonique du manque du mot chez des patients atteints de la maladie d'Alzheimer (avec un MMS supérieur ou égal à 15). En effet, après l'atteinte de la mémoire épisodique, ce trouble est le plus fréquemment rencontré chez les sujets Alzheimer...
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