Active antenna

About: Active antenna is a research topic. Over the lifetime, 2246 publications have been published within this topic receiving 26493 citations.

Time reversal through a solid–liquid interface and super‐resolution

Abstract: Time‐reversal can be used to refocus optimally a signal back onto the source that emitted it. An active array antenna is used to record the wave as a function of time and then, the recorded field is time reversed and retransmitted. The time reversed wave backpropagates through the medium and refocuses approximately on the initial source position. From the experimental point of view, time‐reversal devices are designed to work primarily in a fluid environment. However, time reversal refocusing can be realized also in solids. To do so, the solid is surrounded by a fluid in which the active antenna is located. We propose a numerical formulation describing the time reversal phenomenon through a fluid–solid interface and we analyze with numerical simulations the refocusing resolution obtained in homogeneous media. We also show numerically that multipathing caused by random inhomogeneities improves the focusing of the back‐propagated elastic waves beyond the diffraction limit. This phenomenon is called super‐resolution and was seen previously in acoustic wave propagation.

Dual disk active antenna

Abstract: An antenna that can be used as an active receiving antenna and a transmitting antenna is formed by forming dual disk antenna elements. The dual disk antenna elements are formed by etching a pattern in a layer of conducting material, such as copper, formed on a substrate of dielectric material. One of the disks acts as the active antenna element and the other disk acts as a counterpoise antenna element. In one embodiment a RF amplifier chip is used to form an active receiving antenna. In another embodiment the RF amplifier chip is removed and the antenna can be used either as a receiving antenna or a transmitting antenna. In another embodiment a RF amplifier chip is used with an electronic switch to include the RF amplifier chip when the antenna is used as a receiving antenna and to switch the RF chip out of the circuit when the antenna is used as a transmitting antenna.

The role of power and magnetic connection to the active antenna in the suppression of intermittent structures by ion cyclotron resonance heating

Abstract: The effect of the ion cyclotron resonance heating (ICRH) on the scrape-off layer (SOL) is still an open issue, where, lately it was shown on the ASDEX-Upgrade tokamak that turbulence large-scale structures, known as blobs or avaloids, are suppressed by ICRH (Antar et al 2010 Phys. Rev. Lett. 105 165001). Furthermore, it was shown that the edge localized mode-induced turbulent transport is also reduced significantly. However, the reasons behind this interaction remain unknown. On the Tore Supra tokamak, we confirm that the ICRH suppresses large-scale structures while small-scale structures are enhanced; overall, the turbulence level of fluctuations is reported to drop from about 40% to 25%. This confirms that the effects on turbulence are independent of the type of plasma confinement, L-mode on Tore Supra versus H-mode on ASDEX-Upgrade. The dependence on the ICRH power showed that if a threshold existed it would be below 500 kW and that above this power, no additional effects on the SOL turbulence are reported. The other study reported in this paper deals with the importance of the magnetic field line connections or, in other words, whether the interaction between ICRH and turbulence is global, affecting the whole plasma, or local, affecting regions that are magnetically connected to the active antenna. We found that the toroidal connection to the active antenna is not critical in the sense that turbulence in regions close to the antenna but not necessarily connected are affected. For regions that are not connected and far from the active antenna, turbulence does not change much when applying ICRH.

A cost-effective wearable vital-sign sensor with self-oscillating active antenna based on envelope detection technique

Abstract: A wearable vital-sign sensor with the self-oscillating active antenna is proposed in this paper. The active antenna is employed to radiate the radio-frequency signal and receive the injection signal reflected from the moving human chest. Since the envelope detection technique is adopted to demodulate the vital signs from the modulated output of the active antenna, the circuit complexity, cost, and circuit size can be significantly reduced. The developed sensor is experimentally validated to detect the respiration and heartbeat rate of a human adult. The measured heartbeat rate agrees that obtained by the finger pulse oximeter very well.

Antenna and active antenna system

Abstract: The invention discloses an antenna and an active antenna system. The antenna and the active antenna system are used for lowering the complexity and power consumption of an antenna device and lowering the production cost. The antenna comprises an antenna array, a multichannel leading end, a multi-beam receiving network and a multi-beam transmitting network. An antenna array comprises w antenna oscillators, wherein the w is a natural number larger than or equal to 2. The multi-beam transmitting network is used for conducting beam forming processing on j-path transmitting signal beams, and m-path transmitting signals are obtained, wherein the j is a natural number. The multichannel leading end is used for converting the w-path first radio-frequency signals received by the w antenna oscillators into n-path receiving signals and converting the m-path transmitting signals of the multi-beam transmitting network into w-path second radio-frequency signals, wherein both the n and m are the natural number smaller than or equal to the w. The multi-beam receiving network is used for conducting beam forming processing on n-path receiving signals generated by the multichannel leading end, and k-path receiving signal beams are obtained, and the k is a natural number.