A time reversal (TR) method is investigated for wireless power transmission in an indoor environment. Experiments performed with nanosecond pulses modulated at the frequency of 2.45 GHz reveal that the temporal and spatial focusing makes this technique valuable for applications of wireless power transmission. It is shown that the TR scheme avoids the fading phenomena that usually appear in an indoor environment when the power transmission is realized with a continuous wave: the voltage gain (respectively, the energy gain) can reach 30 dB (respectively, 20 dB) for the proposed scenarios. Moreover, it is theoretically proved that the TR technique is the optimal solution for an energy transmission, whatever the density of the multipath environment. In addition, simulations show that the voltage gain (respectively, the energy gain) of the TR technique is 3 dB (respectively, 9 dB) compared with the inverse filtering technique for a representative scenario. Other potential benefits of the method are discussed, notably concerning the power management of rectennas.

In this paper, we present a Transverse Electric (TE) polarized Bessel-beam antenna in the microwave range based on a leaky radial waveguide. According to the dispersion equation, an inductive sheet over a ground plane is needed. To achieve the inductive sheet, a grid structure printed on a dielectric substrate is designed. Besides, the radial waveguide is coaxially fed with a quasi-loop shaped structure to excite TE mode. The proposed antenna is investigated by simulation and measurement. In the measurement, a small loop is used to probe near magnetic field, and accurate measured magnetic intensity profiles are presented. The measurements show that TE-polarized Bessel beams can be launched within the non-diffractive range of 145 mm (2.803 λ0) at 5.8 GHz.

Given a correlated Gaussian signal, may a chi-squared law of probability always be used to describe a spectrogram coefficient distribution? If not, would a "chi-squared description" lead to an acceptable amount of error when detection problems are to be faced in the time-frequency domain? These two questions prompted the study reported in this paper. After deriving the probability distribution of spectrogram coefficients in the context of a non centered Gaussian correlated signal, the Kullback-Leibler divergence is first used to evaluate to what extent the nonwhiteness of the signal and the Fourier analysis window impact the probability distribution of the spectrogram. To complete the analysis, a detection task formulated as a binary hypothesis test is considered. We evaluate the error committed on the probability of false alarm when the likelihood ratio test is expressed with chi-squared laws. From these results, a chi-squared description of the spectrogram distribution appears accurate when the analysis window used to construct the spectrogram decreases to zero at its boundaries, regardless of the level of correlation contained in the signal. When other analysis windows are used, the length of the window and the correlation contained in the analyzed signal impact the validity of the chi-squared description.

A novel rectifying circuit topology is proposed for converting electromagnetic pulse waves (PWs), that are collected by a wideband antenna, into dc voltage. The typical incident signal considered in this paper consists of 10-ns pulses modulated around 2.4 GHz with a repetition period of 100 ns. The proposed rectifying circuit topology comprises a double-current architecture with inductances that collect the energy during the pulse delivery as well as an output capacitance that maintains the dc output voltage between the pulses. Experimental results show that the efficiency of the rectifier reaches 64% for a mean available incident power of 4 dBm. Similar performances are achieved when a wideband antenna is combined with the rectifier in order to realize a rectenna. By increasing the repetition period of the incident PWs to 400 ns, the rectifier still operates with an efficiency of 52% for a mean available incident pulse power of -8 dBm. Finally, the proposed PW rectenna is tested for a wireless energy transmission application in a low-Q cavity. The time reversal technique is applied to focus PWs around the desired rectenna. Results show that the rectenna is still efficient when noisy PW is handled.

Many marine mammals produce highly nonlinear frequency modulations. Determining the time-frequency support of these sounds offers various applications, which include recognition, localization, and density estimation. This study introduces a low parameterized automated spectrogram segmentation method that is based on a theoretical probabilistic framework. In the first step, the background noise in the spectrogram is fitted with a Chi-squared distribution and thresholded using a Neyman–Pearson approach. In the second step, the number of false detections in time-frequency regions is modeled as a binomial distribution, and then through a Neyman–Pearson strategy, the time-frequency bins are gathered into regions of interest. The proposed method is validated on real data of large sequences of whistles from common dolphins, collected in the Bay of Biscay (France). The proposed method is also compared with two alternative approaches: the first is smoothing and thresholding of the spectrogram; the second is thresholding of the spectrogram followed by the use of morphological operators to gather the time-frequency bins and to remove false positives. This method is shown to increase the probability of detection for the same probability of false alarms.