Nuria Llombart

Miniature implantable and wearable on-body antennas: towards the new era of wireless body-centric systems [antenna applications corner]

Wireless body-centric sensing systems have an important role in the fields of biomedicine, personal healthcare, safety, and security. Body-centric radio-frequency identification (RFID) technology provides a wireless and maintenance-free communication link between the human body and the surroundings through wearable and implanted antennas. This enables real-time monitoring of human vital signs everywhere. Seamlessly integrated wearable and implanted miniaturized antennas thus have the potential to revolutionize the everyday life of people, and to contribute to independent living. Low-cost and low-power system solutions will make widespread use of such technology become reality. The primary target applications for this research are body-centric sensing systems and the relatively new interdisciplinary field of wireless brain-machine interface (BMI) systems. Providing a direct wireless pathway between the brain and an external device, a wireless brain-machine interface holds an enormous potential for helping people suffering from severely disabling neurological conditions to communicate and manage their everyday life more independently. In this paper, we discuss RFID-inspired wireless brain-machine interface systems. We demonstrate that mm-size loop implanted antennas are capable of efficiently coupling to an external transmitting loop antenna through an inductive link. In addition, we focus on wearable antennas based on electrically conductive textiles and threads, and present design guidelines for their use as wearable-antenna conductive elements. Overall, our results constitute an important milestone in the development of wireless brain-machine interface systems, and a new era of wireless body-centric systems.

Fluctuations in the electron system of a superconductor exposed to a photon flux

In a superconductor, in which electrons are paired, the density of unpaired electrons should become zero when approaching zero temperature. Therefore, radiation detectors based on breaking of pairs promise supreme sensitivity, which we demonstrate using an aluminium superconducting microwave resonator. Here we show that the resonator also enables the study of the response of the electron system of the superconductor to pair-breaking photons, microwave photons and varying temperatures. A large range in radiation power (at 1.54u2009THz) can be chosen by carefully filtering the radiation from a blackbody source. We identify two regimes. At high radiation power, fluctuations in the electron system caused by the random arrival rate of the photons are resolved, giving a straightforward measure of the optical efficiency (48±8%) and showing an unprecedented detector sensitivity. At low radiation power, fluctuations are dominated by excess quasiparticles, the number of which is measured through their recombination lifetime.

A kilo-pixel imaging system for future space based far-infrared observatories using microwave kinetic inductance detectors

spectrum will require very large arrays of ultra-sensitive detectors in combination with high multiplexing factors and e�cient lownoise nand low-power readout systems. We have developed a demonstrator system suitable for such applications. nMethods. The system combines a 961 pixel imaging array based upon Microwave Kinetic Inductance Detectors (MKIDs) with a nreadout system capable of reading out all pixels simultaneously with only one readout cable pair and a single cryogenic amplifier. We nevaluate, in a representative environment, the system performance in terms of sensitivity, dynamic range, optical e�ciency, cosmic nray rejection, pixel-pixel crosstalk and overall yield at an observation centre frequency of 850 GHz and 20% fractional bandwidth. nResults. The overall system has an excellent sensitivity, with an average detector sensitivity hNEPdeti = 3 � 10

Demonstration of The Leaky Lens Antenna at Submillimeter Wavelengths

This paper presents the first demonstration of the applicability of the leaky lens antenna concept at THz frequencies. The antenna is integrated with a Kinetic Inductance Detector, so that the two of them function as an ultra sensitive detector over a bandwidth ranging from 0.15 to 1.5 THz. The system has been manufactured and characterized in terms radiation pattern properties and frequency response. We find that the measurements agree very well with the calculations. This demonstrates the manufacturability of the Leaky Lens for use at THz frequency, opening the possibilities for novel broad-band detection concepts.

Design Guidelines for a Terahertz Silicon Micro-Lens Antenna

A silicon lens antenna suited for future integrated terahertz arrays has been proposed recently. The antenna consists of an extended hemispherical silicon lens fed by a leaky-wave waveguide feed. The primary advantage is that the antenna is compatible with silicon micro-fabrication techniques as only a small sector of the lens is actually used. Moreover, it can be easily integrated with other silicon micromachined front-end components. In this letter, the design and optimization details of such a micro-lens antenna is presented. The design is validated with a set of measurements at 550 GHz from a prototype that has been fabricated using laser micro-fabrication.

Wideband Localization of the Dominant Leaky Wave Poles in Dielectric Covered Antennas

This letter discusses the properties of printed antennas whose radiation patterns (their directivity or their shape) are enhanced by means of dielectric superlayers which support leaky waves. In particular the characterizing complex leaky wave poles of the spectral Greens function are approximated analytically, for the first time over large frequency bandwidths. The localization of the poles is a simple mathematical trick, however, the results provide further physical insights into wave phenomena that before had to be investigated numerically

Directivity Enhancement and Spurious Radiation Suppression in Leaky-Wave Antennas Using Inductive Grid Metasurfaces

Fabry-Perot antennas (FPA) achieve high broadside directivity due to the simultaneous excitation of a pair of nearly degenerate TE/TM leaky-wave modes using a partially-reflecting surface on top of a ground plane. This partially-reflecting surface can be obtained using a dielectric superstrate or via a capacitive or inductive metasurface (MTS). By using an equivalence between the conventional dielectric superstrate and the MTS-based structures in terms of the dominant TE/TM modes, we show that the use of inductive grid MTSs leads to a directivity enhancement. A higher roll-of in the radiation patterns is achieved as a result of the intrinsic suppression of the spurious TM0 leaky wave mode. This suppression is mathematically demonstrated and validated with full-wave simulations. The achieved improvement in more than 1 dB for inductive strip grid based MTS with respect to dielectric based super-layers, for the same frequency band of 2.5%, is verified with measurements. Two prototypes, with the dielectric superlayer and inductive strip grid based MTS, have been fabricated and measured supporting the claim of this work.

EBG enhanced feeds for high aperture efficiency reflector antennas

Typical feed horns can be lengthy and bulky, especially at low frequencies. This aspect alone constitutes a significant drive to nd alternative technologies, more suited to mass production, that can be used to obtain equally performing feeds. In particular it is useful to explore the possibility of using printed circuit board technology to upgrade the performances of a moderately sized (in terms of the wavelength) waveguide horn, so that the resulting feed can be used to efciently illuminate a reector antenna.

On the Use of Leaky Wave Phased Arrays for the Reduction of the Grating Lobe Level

Dielectric superlayers can be used to reduce the grating lobe levels in thinned phased arrays, i.e., arrays with large periodicities. In this contribution we show how the mutual coupling impacts the active impedance and the roll-off of the embedded patterns necessary to achieve the grating lobe angular filtering in this type of arrays. The reduction of the grating lobes in the thinned array radiation pattern depends on the dielectric superlayer constant. The larger the dielectric constant the higher the attenuation of the grating lobe will be. However, this can only be obtained at the cost of an increased mutual coupling. This mutual coupling will impact on the embedded patterns reducing the actual roll-off that can be achieved. Several 11 × 11 phased arrays with different dielectric superlayers are studied in order to establish the maximum useful permittivity as a function of the mutual coupling level. We show that antenna elements based on dielectric superlayers leading to mutual coupling levels larger than -20 dB suffer from a loss of directivity in the embedded pattern and a loss of gain in the phased array because of the highly resonant active impedance. As a reference we also compare the performances of the 11 × 11 leaky wave phased array with an 11 × 11 phased array of standard conical horns. We show that an increase in the gain of more than 2.2 dB over all the frequency and scanning ranges is obtained in the leaky wave array with respect to the reference horn array. The leaky wave array leads to a reduction of the grating lobe of more than 10 dB.

Radially Polarized Annular-Slot Leaky-Wave Antenna for Three-Dimensional Near-Field Microwave Focusing

Microwave three-dimensional near-field focusing with radial polarization using a holographic annular-slot antenna is demonstrated in this letter. This radial polarization can generate axially polarized focused fields in the near-field regime, which complements the more conventional synthesis of transversally polarized near-field focusing patterns. Moreover, it is shown that more symmetrical focal region is obtained thanks to the radial polarization for similar Fresnel number N and operation frequency. The theory is demonstrated with experiments for a design operating at 10 GHz, with aperture diameter D=6λ and a Fresnel number N=4.