Thierry Alves

Antenna design and channel modeling in the BAN context - part II: channel

The first results achieved in the French ANR (National Research Agency) project BANET (Body Area NEtwork and Technologies) concerning the channel characterization and modeling aspects of Body Area Networks (BANs) are presented (part II). A scenario-based approach is used to determine the BAN statistical behavior, trends, and eventually models, from numerous measurement campaigns. Measurement setups are carefully described in the UWB context. The numerous sources of variability of the channel are addressed. A particular focus is put on the time-variant channel, showing notably that it is the main cause of the slow fading variance. Issues related to the data processing and the measurement uncertainties are also described.

PIFA top-loaded monopole antenna with diversity features for WBAN applications

A miniaturized diversity antenna dedicated to wireless body area network (WBAN) applications is described. The combination of a planar inverted-F antenna (PIFA) and a top-loaded monopole yields distinct patterns fitting the different natures of the received waves. The strong isolation observed between the broadside and endfire ports is an important feature to limit the correlation between the received signals. The diversity gain is measured for three links and three scenarios between body-worn antennas, showing the improvement brought by the antenna diversity in the WBAN context.

Intelligent antenna selection decision in IEEE 802.15.4 wireless sensor networks

Display Omitted We design a new radio module, an Inverted-F Antenna for 2.4GHz bandwidth WSNs.Experiments performed in garden, office, reverberation and anechoic chamber.Experimental results confirm the gain of 6-10dB of the proposed radio module.We propose an intelligent antenna selection strategy to exploit antenna diversity.We propose a prototype of diversity antenna and the intelligent switch design. The goal of this paper is to study the feasibility of making intelligent antenna selection decision in IEEE 802.15.4 Wireless Sensor Networks (WSNs). This study provides us the basis to design and implement software defined intelligent antenna switching capability to wireless sensor nodes based on Received Signal Strength Indicator (RSSI) link quality metric. First, we discuss the results of our newly designed radio module (Inverted-F Antenna) for 2.4GHz bandwidth (WSNs). Second, we propose an intelligent antenna selection strategy to exploit antenna diversity. Third, we propose the prototype of our diversity antenna for the TelosB mote and the intelligent switch design. Finally, we compare the performance of the built-in TelosB antenna with our proposed external antenna in both laboratory and realistic environments. Experimental results confirm the gain of 6-10dB of the proposed radio module over the built-in radio module of the TelosB motes.

A Multilayered Coil Antenna for Ingestible Capsule: Near-Field Magnetic Induction Link

A compact multilayered stacked ingestible coil antenna is investigated for medical systems. The inductive link, comprising a 5-layer transmitter coil antenna and a 3-turn receiver spiral coil, is modeled through a tissue-simulating liquid modeling the human body. The diameter and the thickness of the transmitter coil are respectively equal to 1 cm and 5 mm, while the dimensions of the receiver coil are equal to 7 × 8 cm2. The variations of the position and the orientation of the capsule antenna are taken into account to evaluate the coupling response between the two magnetically coupled coils. We found that the inductive link presents an attractive option for improving the lifetime of ingestible capsules.

Towards intelligent antenna selection in IEEE 802.15.4 wireless sensor networks

We plan to design and implement software defined intelligent antenna switching capability to wireless sensor nodes based on link quality metric, such as Received Signal Strength Indicator (RSSI). In this paper, as a first step, we discuss the preliminary results of our newly designed radio module (Inverted-F Antenna) for 2.4 GHz bandwidth wireless sensor networks. In this perspective, we consider the TelosB motes and compare the performance of the built-in TelosB antenna with our proposed antenna. Experimental results confirm the effectiveness of the proposed radio module i.e., 5% to 12% gain over the built-in radio module of the TelosB motes.

Magnetic loop antenna for wireless capsule endoscopy inside the human body operating at 315 MHz: Near field behavior

In ingestible systems, the antenna suffers from deterioration of performances due to surrounding dissipative tissues. A small circular magnetic loop antenna, whose diameter is equal to 1 cm and thickness is equal to 0.5 mm operating at the frequency of 315 MHz in the ISM band, is proposed to limit this degradation. The electric properties of the human body, having a high dielectric constant and low impedance, are considered to design and simulate the loop antenna. We found that the magnetic field is less attenuated than the electric field in the human body that improves the signal level received by near field magnetic coupling.

Analysis of the Transmission Between On-Body Devices Using the Bilateral Dual-Grid FDTD Technique

This letter deals with a new technique to efficiently analyze on-body radio channel problems. The bilateral dual-grid finite-difference time-domain (FDTD) method is applied to determine the transmission between two on-body devices, considering various positions of the receiving antenna on the chest of the body. This new technique aims at efficiently simulating a full-duplex link where both transmitting and receiving antennas require a precise description while their environment does not imply a particularly fine mesh. Comparisons to measurements show good agreement, and results are obtained in a considerably reduced computation time.

Diversity Antennas For BAN Applications

Wireless body area network (WBAN) defines a network of wearable devices showing wireless communication capabilities. First, WBANs were initially used in the healthcare domain for continuous monitoring and logging vital parameters of patients suffering from chronic diseases (such as diabetes). Sports, military, or security were other applications [1]. Body-worn antennas have two requirements: they must be efficient in the presence of biological tissues and their polarization/pattern features should match the incoming direction and the polarization of the incident waves. In a radio link between two body-worn antennas, several types of waves contribute to the channel, i.e. creeping and surface waves guided around the body surface, direct waves, waves reflected/scattered by the environment (ground, walls, etc.), and waves reflected by other parts of the body (legs or arms). As a result, deep fadings are commonly observed and antenna diversity makes sense to fight the fadings in the BAN context [2–6]. In [2], it was demonstrated that on-body antenna diversity is less effective for line-of-sight (LOS) links like the waist–chest link. In [3], the spatial diversity was investigated for monopoles at 2.4, 5.8, and 10 GHz and it was shown that the best diversity gain is obtained at any frequency for the waist–head and waist– ankle links, i.e. for non-line-of-sight (NLOS) links. In [4], space and pattern diversities were tested with monopoles (space diversity) and annular slot-monopole antennas (pattern diversity), the conclusion being that space diversity is the best choice at 2.45 GHz for spacings as small as 3 cm (~l0/4). In [5] and [6], planar inverted-F antennas (PIFAs) and printed IFAs were used to evaluate the influence of the antenna orientation. All these studies conclude that a good diversity gain is only reached for NLOS channels and dynamic channels with large movements.

Combined RFID tag antenna for recipients containing liquids

RFID systems are characterized by a changing environment which perturbs and degrades the performances of each system component. Passive tag antennas are the most affected by these variations, the tag functionalities vary by changing the surface where it is attached and in some case even the content of boxes or recipients has an influence. A combined antenna is designed in order to ensure a read range for a plastic recipient containing water or not. Before, two particular antennas are proposed to work in each case, both situations are analyzed separately to observe their performances and extract their advantages to join them in one unique structure less sensitive within a limited read range.