María Elena de Cos

A Novel Approach for RCS Reduction Using a Combination of Artificial Magnetic Conductors

A thin Artiflcial Magnetic Conductor (AMC) structure for Radar Cross-Section (RCS) reduction applications is presented. The manufactured prototype, which combines two unit-cell metallization sizes, presenting two resonant frequencies, shows broad AMC operation bandwidth, polarization angle independency, and its angular margin when operating under oblique incidence is also tested. It is shown that signiflcant RCS reduction can be achieved with the proposed AMCs combination even if a 180 - phaseshift between re∞ected waves is not met. Two designs are considered: the already mentioned design combining AMCs with overlapped frequency bands and the second one combining Perfect Electric Conductor (PEC) and AMC surfaces. A comparison between these two designs regarding RCS reduction, supported by measurements in an anechoic chamber, is presented.

Flexible Uniplanar Artificial Magnetic Conductor

A flexible uniplanar Artificial Magnetic Conductor (AMC) design is presented. FEM simulations used to design and analyze the performance of the AMC structure are shown. Its performance under flat and bent conditions is characterized by means of reflection coefficient phase measurements of a manufactured prototype in an anechoic chamber. Broad AMC operation bandwidth and polarization angle independency is found for the prototype in both flat and bent situations. In addition, its angular margin under oblique incidence operation is also measured.

Novel received signal strength-based indoor location system: development and testing

A received signal strength- (RSS-)based indoor location method (ILS) for person/assets location in indoor scenarios is presented in this paper. Theoretical bases of the method are the integral equations relating the electromagnetic (EM) fields with their sources, establishing a cost function relating the measured field at the receivers and the unknown position of the transmitter. The aim is to improve the EM characterization of the scenario yielding in a more accurate indoor location method. Regarding network infrastructure implementation, a set of receivers are deployed through the coverage area, measuring the RSS value from a transmitter node which is attached to the asset to be located. The location method is evaluated in several indoor scenarios using portable measurement equipment. The next step has been the network hardware implementation using a wireless sensor network: for this purpose, ZigBee nodes have been selected. Finally, RSS measurements variability due to multipath effects and nonline-of-sight between transmitter and receiver nodes is mitigated using calibration and a correction based on the difference between the free space field decay law and the measured RSS.

On the Influence of Coupling AMC Resonances for RCS Reduction in the SHF Band

A novel approach to Radar Cross-Section reduction using a thin Artiflcial Magnetic Conductor (AMC) structure is presented. The novel AMC structure combines two unit-cell metallization sizes and so it presents two resonant frequencies. RCS reduction is based on destructive interference of two partial re∞ections. Taking as starting point a previous work showing signiflcant RCS reduction based on the combination of two AMC surfaces with overlapped AMC operation bandwidths (so that they have similar re∞ection coe-cient amplitude) without a 180 - -phaseshift, the key point of this contribution is to analyze the in∞uence of the degree of the aforementioned overlapping on RCS reduction and to show that this achievement is based on coupling phenomena. A comparison of the achieved RCS reduction when combining two AMCs whose AMC operation bandwidth overlaps, two AMCs with non-overlapped AMC operation bandwidths, and PEC-AMC is presented. Prototypes of these three combinations have been manufactured (having them the same size) and their RCS has been measured in an anechoic chamber.

Troubleshooting RFID Tags Problems with Metallic Objects Using Metamaterials

Radiofrequency Identification (RFID) is a technology that is being rapidly developed and that uses radiofrequency (RF) signals for the automatic identification of objects or persons. Although the first article regarding modulated electromagnetic backscattering (basic principle of passive RFID) was published in 1948 (Stockman, 1948) it has been a long way to progress for reaching today levels (Rao, 1999; Finkenzeller, 2004; Pozar, 2004). Nowadays RFID finds many applications in logistics, supply chain management, access control, electronic toll systems, targets identification, vehicle security, animals tracking and patients’ identification in hospitals. An RFID system is composed of a reader, a reader antenna (usually circularly polarized patch antenna), RFID ‘tags’ or transponders and a middleware or subsystem of data processing. A passive RFID tag consists of an antenna and an application specific integrated circuit (ASIC) chip. IC chips have complex input impedances, and their impedances vary with frequency. A key point for tag antenna design is that it must be conjugately matched with the desired IC chip for the maximum power transfer (Gevi, 2004; Rao et al, 2005). The different types of RFID systems are distinguished by two major characteristics: the power source of the tag and the frequency of operation. With regards to the power source of the tag, they can either be active (powered by battery), passive (powered by the reader field) or semi-passive (battery assisted backscatter). According to the frequency of operation the RFID systems are generally distinguished into four frequency ranges; i.e., low frequency (LF) (125-134.2 kHz), high frequency (HF) (13.56 MHz), ultra high frequency (UHF) (433, 860-960 MHz) and microwave frequency (2.45, 5.8 GHz). In addition, the standards of the UHF RFID are different for each country: 866-869 MHz in Europe, 902-928 MHz in America and 950-956 MHz in Asia. The communication frequencies used depends to a large extent on the application. Regulations are imposed by most countries (grouped into 3 Regions: US, Europe and Asia) to control emissions and prevent interference with other Industrial, Scientific and Medical equipment (ISM). The higher the frequency band the faster the speed of tag reading and also the larger the information storage capacity. This is the reason why UHF RFID has gained popularity in many applications and it can be expected that the same will happen in the near future with microwave RFID. In a typical application tags are attached to objects (or persons). Each tag has a certain amount of internal memory (EEPROM) in the chip in which it stores information about the