Chambre anéchoïque | EPFL Graph Search

Une chambre anéchoïque (ou « chambre sourde ») est une salle d'expérimentation dont les parois absorbent les ondes sonores ou électromagnétiques, en reproduisant des conditions de champ libre et ne provoquant donc pas décho'' pouvant perturber les mesures. De telles chambres sont utilisées pour mesurer des ondes acoustiques ou électromagnétiques dans des conditions de champ libre, c'est-à-dire en l'absence de composantes ayant subi une réverbération sur des parois. L'équivalent subaquatique existe, avec les piscines anéchoïques par exemple utilisées par les militaires pour produire des revêtements acoustiques complexes (élastomères découplant ou anéchoïques) comme la tuile anéchoïque et autres peintures susceptibles d'absorber ou réduire les échos radars ou de sonars pour les sous-marins, coques de navires ou ROV, etc. Chambre anéchoïque acoustique La « chambre anéchoïque acoustique » (appelée aussi « chambre sourde ») est une chambre recouverte de dièdres (parfois de

Scale Model Evaluation and Optimization of Sodar Acoustic Baffles

Adrien Chabbey, Fernando Porté Agel

A 21: 1 scaled sodar, operating at 40 kHz, has been built and tested in the laboratory. Sodars, which use sound scattered by turbulence to profile the lowest few hundred meters of the atmosphere, need good acoustic shielding to diminish annoyance and to reduce unwanted reflections from nearby objects. Design of the acoustic shielding is generally inhibited by the difficulty of testing on full-scale systems and uncertainty as to accuracy of models. In contrast, the scale model approach described allows for "bench testing" of many designs under controlled conditions, and efficient comparison with models. Measured beam patterns from the scale model were compared with those from a numerical model based on the Kirchhoff integral theorem. Satisfactory agreement has allowed using the numerical model to optimize the acoustic shield design, both for the gross acoustic baffle geometry and for the geometry of rim modulations known as thnadners. Optimization was performed in the specific case of a scaled model of a commercial phased array sodar.

American Meteorological Society2015

Passive UHF RFID Systems for Capacitive Sensing Applications

Kerem Kapucu

In this work, a complete passive UHF RFID system for capacitive sensing applications is developed to be used in food quality monitoring and supply chain management. All the components of the RFID system including the base station, the base station antenna, the tag chip, and the tag antenna is designed, implemented, and tested. The operation of all the components are shown by measurements and their performance is characterized. The remote powering subsystem consists of the tag antenna and the rectifier. Measurement results showed a maximum power conversion efficiency of 65% for the antenna-rectifier pair operated at 866 MHz. The rectifier is a three-stage, differential rectifier with threshold compensation, that offers high power conversion efficiency. The tag antenna is an inductively-coupled, meandered dipole that is impedance matched to the tag chip. The dimensions of the tag antenna are 83 x 20mm, and the measured far-field gain of the tag antenna is 1.2 dB. A supply generation subsystem is implemented in order to generate a stable, regulated supply voltage for high-precision sensor interfaces. The supply generation subsystem consists of the low drop-out (LDO) voltage regulator, a bandgap voltage reference, and a supply insensitive current source. The power supply rejection ratio (PSRR) of the LDO is greater than 55 dB. Data communication is realized by backscatter modulation because it offers lower circuit complexity and low power consumption on the tag side. The scattering properties of the tag antenna and the backscatter modulation is theoretically analyzed and an optimum antenna impedance for backscatter communication is calculated. The scattering properties of the tag antenna are characterized by measurements in an anechoic chamber. One of the innovations of this work is the novel pulse-width modulation based backscatter communication, in which the information is encoded in the duty-cycle of the signal. This method decreases the circuit complexity and power consumption on the tag side when used with phase-locked loop (PLL) based sensor interfaces. A monostatic base station with a homodyne receiver is implemented for the passive RFID system. A microstrip patch antenna is custom designed and fabricated for the base station. The input return loss of the base station antenna is measured to be -20 dB, whereas its measured far-field gain is 3.6 dB. An isolator that is based on a directional coupler with an intentional mismatch at the unused port is designed and fabricated for the base station. The measured directivity of the isolator is 50.5 dB. A PLL-based capacitive sensor interface is implemented for differential sensors. The integration of such a low-power circuit in an RFID tag is the main innovation of this work. The differential nature of this sensor interface makes it immune to supply voltage variations. The sensor interface can work with supply voltages as low as 0.3 V. The power consumption of the interface is 300 nW, for 0.3 V supply voltage. The resolution of the sensor interface is determined to be 6.4 bit by post-layout simulations. Two tag architectures for two different approaches for sensor interfaces are proposed: the generic passive UHF RFID platform for sensing applications and the SimpleTag - a novel, low-power UHF RFID tag for differential printed capacitive sensors. The circuits are implemented in UMC 0.18 um CMOS technology.

EPFL2015

Localization of Electromagnetic Interference Sources Using a Time-Reversal Cavity

Mohammad Azadifar, Hamidreza Karami, Amirhossein Mostajabi, Marcos Rubinstein

In this article, we propose and implement a novel technique to locate electromagnetic interference (EMI) sources using the concept of time-reversal (TR) cavity. We show in an intuitive manner that reflections from the surfaces of a cavity can emulate an infinite number of sensors in the TR method. In order to locate EMI sources, the equipment under test (EUT) is placed in a rectangular metallic cavity, of suitable dimensions according to the considered frequency band and the EUT size, equipped with a simple monopole or dipole antenna. We demonstrate that by using only one sensor, we are able to locate EMI sources by taking advantage of the focusing properties of a TR cavity. The entropy criterion is applied to obtain the focusing time slice in which the maximum electric field determines the location of the EMI source. Both 2- and 3-D numerical simulation schemes are deployed to demonstrate the ability of the proposed technique. The validity of numerical simulations is tested against frequency domain measurements. Compared with the conventional EMI tests in anechoic chambers and scanning methods, the proposed technique represents a simpler and cost-effective test method requiring only one sensor (a monopole or dipole antenna).

2021

Passive UHF RFID Systems for Capacitive Sensing Applications

Kerem Kapucu

EPFL2015