Lately, there has been significant progress in the field of wireless communications and networking. Furthermore, the number of applications that require context information as the user's location will increase in the coming years. However, this issue still has not been solved indoors due to the RF (Radio Frequency) signals' behaviour in this kind of scenarios. In this paper, we present a robust, easy to deploy and flexible indoor localization system based on ZigBee Wireless Sensor Networks. It is important to mention that our localization system is based on RSSI (Received Signal Strength Indicator) level measurements since this information can be obtained directly from the messages exchanged between nodes, so no extra hardware is required. Our localization system consists of two phases: calibration and localization. Anytime a blind node needs to be located, our system performs calibration using a matrices system, so that the environment can be characterized, taking into account possible changes on it since the last request. Then, in the localization phase, the central server processes all the information and calculates the blind node's position with the new iterative algorithm we present. With this indoor positioning algorithm we can estimate the blind node's position with a good resolution (3 m average error), so we can say that this ZigBee localization algorithm provides very promising results.

Fully textile smart wearables will be the result of the complete integration and miniaturization of electronics and textile materials. Off-body communications are key for connecting smart wearables with external devices, even for wireless power transfer or energy harvesting. They need to fulfill specific electromagnetic (EM) (impedance bandwidth (BW), gain, efficiency, and front to back radiation (FTBR)) and mechanical (bending, crumpling, compression, washing and ironing) requirements so that the smart wearable device provides the required performance. Therefore, textile and flexible antennas require a proper trade-off between materials, antenna topologies, construction techniques, and EM and mechanical performances. This review shows the latest research works for textile and flexible planar, fully grounded antennas for off-body communications, providing a novel design guide that relates key antenna performance parameters versus topologies, feeding techniques, conductive and dielectric textile materials, as well as the behavior under diverse measurement conditions.

The development of e-textiles is fostering research in wireless energy transmission. This paper presents a purely textile 2.4 GHz WiFi band 2 × 2 rectenna array for RF energy harvesting. It utilizes the electromagnetically coupled microstrip patch antenna topology and a simple and precise construction method that provides a good performance repeatability to create multilayer microstrip textile patch antennas. The rectifier is implemented with Schottky diodes and it takes the voltage doubling configuration. An average DC power of 1,1 mW was measured for 14 μW/cm² of RF input power density, while the end-to-end average power conversion efficiency (PCE) measured was 31%. The characterization of the end-to-end PCE was evaluated considering the physical size of the prototype to make the comparison with other designs easier. Measurements in a real WiFi scenario were also performed, demonstrating its feasibility for feeding e-textiles.

Novel combinations of materials and construction techniques are key for the development of new textile antenna configurations for on-body applications. Stretchable, flexible and conformable features of textile antennas are one of the hot research topics nowadays. This work gives a step forward with new designs of purely textile spiral antennas with flexible and robust features for Near Field Communications (NFC) on-body applications. Their performance is successfully validated with a real NFC chipset, and some design and construction considerations are offered for novel textile materials.

This communication presents an analytical framework that combines transmission line models for the design of electromagnetically coupled microstrip patch antennas for the 2.45 GHz industrial, scientific and medical band. It provides initial values for all dimensions of the antenna, with measured resonance frequency errors below 6%. The initial design is optimized in two subsequent phases to center the resonance frequency and to increase the impedance bandwidth (BW), obtaining measured resonance frequency errors below 0.6% and BW enhancements of more than 1.2 times the original ones, respectively. The model has been validated with antenna prototypes based on rigid and textile materials, exhibiting excellent freespace measured BW of 4% and 5.12%, maximal measured gains of 4.28 dBi and 7.33 dBi, and radiation efficiencies of 63.4% and 71.8%, respectively. Moreover, very stable on-body performance is obtained, with minimal frequency detuning when deploying the textile antenna on the human body. The measured maximum onbody gain for the textile antenna equals 5.5 dBi, with a simulated specific absorption rate of 0.323 W/kg at 2.45 GHz.

In the Master's of Telecommunication Engineering program at the University of Deusto, Spain, courses in communication circuit design, electronic instrumentation, advanced systems for signal processing and radiocommunication systems allow students to acquire concepts crucial to the fields of electronics and communication. During the educational project presented in this paper, students build a continuous-wave frequency-modulation (CWFM) Doppler radar system from components as simple as ordinary cocoa cans and common electronics components placed on a breadboard without any soldering. One of the goals of the project is to stimulate students' interest in building an entire, completely functional communication system that integrates the knowledge acquired in the various courses and whose functioning they can check in real scenarios. This paper describes this learning project and the ways in which it helps students understand and connect all the concepts that underlie a fully operative communications system, thus meeting the competencies and learning outcomes of the courses involved in the project.