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A highly efficient air-filled multiband antenna is presented for unobtrusive integration into smart surfaces. By introducing a capacitive loading ridge in the cavity formed by two coupled eighth-mode resonators, the higher order modes are judiciously manipulated. A supplementary slot-mode resonance is provided by a resonant U-slot in the first resonator. These measures yield dual-band impedance matching, covering the SRD860 (863-870 MHz), 2.4 GHz ISM (2.4-2.4835 GHz), and LTE-7 (2.5-2.69 GHz) standards. The antenna, fully realized in low-cost FR-4 substrate layers, complies with standard printed circuit board manufacturing. Measurements on a prototype reveal an impedance bandwidth of 51.8 MHz (6.1%) and 428.6 MHz (17.0%) in the lower and upper frequency band, respectively. Furthermore, a total efficiency and peak gain of 86.1% and 3.8 dBi at 866 MHz, 75.2% and 9.0 dBi at 2.45 GHz, and 70.1% and 8.1 dBi at 2.6 GHz were obtained in standalone conditions. At 2.4 GHz, a measured total efficiency and gain of 73.9% and 8.9 dBi are reported for the antenna covered by a cork superstrate, and 73.6% and 6.6 dBi for the antenna inside a drywall construction.

Fall accidents are a frequent problem with the elderly and lead to severe injuries and/or could have a lethal ending. To prevent these potential deaths the nursing personnel visits the elderly on a regular basis. This has an enormous influence on the mental and physical capabilities of the nursing personnel. In combination with the ever-growing presence of Internet of Things (IoT) applications, this paper proposes a low-power wireless fall detection and warning system based on Bluetooth Low Energy (BLE). The aim of the system is to lower the workload of the nursing personnel and prevent elderly from dying from hypothermia. The system consists of a patient wearable (P) monitoring the movement of the elderly, a Detection Node (DN) scanning the room of the elderly to pinpoint the position of the fallen elderly, multiple Network Nodes (NNs) in the hallways sending the alert messages to the closest caretaker wearing a Caretaker Node (CN). This node visualizes all vital parameters, so the nursing personnel can help in the fastest way possible. A proof-of-concept is proposed in this paper, together with measurements and power analysis.

Measurements at 5G Frequency Range 2 (FR2) and beyond (41.5 GHz and 60.5 GHz) were carried out in order to study how space diversity can be applied to compensate for the challenging conditions at those frequencies. Several indoor scenarios were analyzed, including Line-Of-Sight (LOS) and Non-Line-Of-Sight (NLOS). When considering an outage of 1%, space diversity was found to be a suitable impairment mitigation technique. Improvements in signal signal levels with increments from 7.98 dB up to 15.18 dB, depending on the case study in question were observed.

This paper outlines a hardware platform for half-duplex, real-time encrypted digital speech communication on 2.45 GHz. The platform is based on a STM32F415 MCU with a low power ADF7242 transceiver for wireless communication. The Advanced Encryption Standard (AES) Electronic Code Book encryption scheme is performed on the transmitted packets with symmetrically generated channel-based keys. Encryption keys of 128-bit are obtained, based on the unique reciprocal channel characteristics of the employed link. Key reconciliation is applied by means of a Hamming code and a cyclic redundancy check (CRC) to correct key mismatch. A multi-user system is introduced by splitting voice key distribution and speech communication into different abstraction layers. Measurements reveal a maximum communication range of 400 m without significant packet loss. A high key entropy of 0.94 bit is established with a packet rate of 167 packets/s and a key bit generation delay of four received signal strength (RSS) measurements.

Monitoring train integrity is a very important topic for economical, management and safety reasons. Knowing the localization, volume and other parameters is very valuable for most train and large industry companies. Current literature focuses on placing many sensors in a Wireless Sensor Network (WSN) around the train wagons, but do not take battery lifetime into perspective. With the increasing interest in industrial Internet of Things (IoT) applications, the connectivity and battery lifetime are very important parameters. In this paper, the vibrations measured on train wagons are analyzed in order to find the most optimal trigger point to wake up or to put the WSN in a deep sleep mode. This way, a large amount of power can be saved and extend the battery lifetime significantly. Furthermore, several Received Signal Strength Indicator (RSSI) measurements were performed to find the optimal Tx level and antenna topology for communication between different wireless sensor nodes on the train wagon. The proposed measurements show that an inexpensive accelerometer and a prefabricated antenna are perfectly usable in the WSN. RF measurements on the brakes results in an average Package Receive Rate (PRR) of approximately 92 % and an Average Received Power (ARP) of around −83 dBm starting from a Tx level of 4 dBm.

Due to the global growth in popularity of Fifth Generation (5G) cellular communications, the demand for shielding against it has risen for a variety of applications, mainly related to cybersecurity but also to isolation, calm areas and so on. This research paper aims to provide a suitable dual-band fractal FSS (Frequency Selective Surface) for the 5G lower band frequencies: 750 MHz and 3.5 GHz. The unit cell is in the shape of a bow tie, where each of the triangular parts are Sierpiński triangles. One major addition to the unit cell is a central metal strip to make the manufacturing of the FSS more feasible and to tune the operation frequencies and bandwidths. As with each different stage of a fractal antenna, the different stages of the fractal FSS design behave differently. For this application, stage 2 is sufficient, as we are able to cover frequency bands among those included in the FR1 5G spectrum. Some equations were derived using linear regression in order to provide specific design tools for building an FSS. These equations have high accuracy and can be used to adapt the proposed design to other frequencies. Some other parameters, which are not represented in the aforementioned equations, can also be adjusted for minor tweaking of the final design. This design performs well except under large incidence angles. This should be taken into account when proposing the installation of a structure based on it. A good agreement between simulation and measurement results is observed. Xunta de Galicia | Ref. ED431C 2019/26 Ministerio de Ciencia e Innovación | Ref. PID2020-112545RB-C52 Fundaçao para a Ciencia e Tecnologia | Ref. UIDB / EEA / 50008/2021

Annually, approximately 10 people are involved in a lethal blind spot accident on Belgian roads, even though a lot of money is invested in the development of blind spot detection systems and in raising the awareness of this phenomenon. In previous research, we developed a blind spot detection and warning system based on Bluetooth Low Energy (BLE) and received signal strength indicator (RSSI) measurements. In this paper, the miniaturization of the detection node and wearable is presented. There will be a closer look at the development of the Printed Circuit Board (PCB) and the folded Shorted Patch (S-P) antenna that will be integrated into the side lights of trailers. In a future step, the wearable design will be updated with the same miniaturization steps taken in this paper.

A mechanically flexible textile antenna-backed sensor node is designed and manufactured, providing accurate personal localization functionality by application of Decawave’s DW1000 Impulse Radio Ultra-Wideband (IR-UWB) Integrated Circuit (IC). All components are mounted on a flexible polyimide foil, which is integrated on the backplane of a wearable cavity-backed slot antenna designed for IR-UWB localization in Channels 2 and 3 of the IEEE 802.15.4-2011 standard (3744 MHz–4742.4 MHz). The textile antenna’s radiation pattern is optimized to mitigate body effects and to minimize absorption by body tissues. Furthermore, its time-domain characteristics are measured to be adequate for localization. By combining the antenna and the bendable Printed Circuit Board (PCB), a mechanically supple sensor system is realized, for which the performance is validated by examining it as a node used in a complete localization system. This shows that six nodes around the body must be deployed to provide system coverage in all directions around the wearer. Even without using sleep mode functionalities, the measurements indicate that the system’s autonomy is 13.3 h on a 5 V 200 mAh battery. Hence, this system acts as a proof of concept for the joining of localization electronics and other sensors with a full-textile antenna into a mechanically flexible sensor system.

This paper handles the design and verification of a localisation sensor with a cavity-backed slot antenna. The sensor node uses a Decawave DW1000 chipset, together with a basic sensor, a microcontroller and a flash memory card. It is designed on a mechanically flexible Printed Circuit Board (PCB), where component edges and vias are aligned forming rigid lines. As antenna a Substrate Integrated Waveguide (SIW) design is proposed: a cavity-backed slot antenna combining vulcanised rubber foam and electrotextile. Impulse-Radio Ultra-Wideband (IR-UWB) localisation is analysed by the pulse deformation in the System Fidelity Factor (SFF) and the phase shift in the Distance Estimation Error (DEE). On-body measurements show that everything works fine.

This paper proposes a novel method for the integration of channel-based key generation in a real-time digital voice communication system. For this purpose, a specific hardware platform was developed. To obtain the keys for the cipher, channel-based key generation is used to generate identical keys on both sides of the channel, based on the unique reciprocal channel characteristics. Hamming code key reconciliation drastically reduces the probability of remaining key errors, while a cyclic redundancy check (CRC) is used as a final checking mechanism. As a proof of concept, the generated key is used to encrypt as well as decrypt the audio by means of an XOR operation at both sides of the link. Several measurements were performed, showing that new keys are continuously being formed and replaced. Additional measurements also create more insight into the key update rate and key entropy for different parameter settings in the algorithm.

A measurement campaign was carried out in order to characterize the channel response when people are passing between transmitter and receiver in the 5G Frequency Range 2 and beyond (40 GHz and 60 GHz). We also studied the possibility of using angular diversity to compensate for the resultant fading. After analyzing the data, interesting results are obtained: fading values over 25 dB were measured at both bands; the level crossing rate is very similar in value and distribution at both frequencies, and the average duration of the resultant fadings is almost double at 60 GHz. It was also observed that the fading depth seems to be related to the stature of the person obstructing the radio link. A deeper fading is observing with taller individuals.

A deep knowledge of radio propagation is necessary before deploying wireless networks. In indoor environments, when people are moving, experimental analysis is needed, as many elements are difficult to model with a deterministic simulation tool. Thus, before deploying 5G systems at the 3.5 GHz band, insights on the effect of people moving in the indoor channel are required. This contribution describes the results of a measurement campaign considering different conditions. For analyzing the results, box plots of measured attenuations due to the people moving are compiled. Both the speed of the people and their concentration seem to influence the narrowband parameters of the radio channel. However, the position of the people seems to provide fewer effects on the radio channel.

Blind spot road accidents are a frequently occurring problem. Every year, several deaths are caused by this phenomenon, even though a lot of money is invested in raising awareness and in the development of prevention systems. In this paper, a blind spot detection and warning system is proposed, relying on Received Signal Strength Indicator (RSSI) measurements and Bluetooth Low Energy (BLE) wireless communication. The received RSSI samples are threshold-filtered, after which a weighted average is computed with a sliding window filter. The technique is validated by simulations and measurements. Finally, the strength of the proposed system is demonstrated with real-life measurements.

The electromagnetic characterization of liquids could be of great interest to manufacturing companies, as it could provide information about the quality of beverages. They could use this knowledge to optimize production processes. Using the probe reflection system, dielectric properties of different varieties of Coca-Cola and Pepsi products in cans have been examined. Measurements have been performed at several temperatures between 0 and 60 degrees Celsius and at periods after opening of 0, 6, 24 and 48 h. The applied frequency range goes from 0 to 20 GHz in steps of 200 Hz. Both experimental and theoretical approaches have been used to model the results. Although all varieties follow the same trend, the results clearly show that differences exist in the electromagnetic behavior of the two brands and of the different varieties.

An all-textile multimoded cavity-backed slot antenna has been designed and fabricated for body-worn impulse radio ultra-wideband (IR-UWB) operation in the 3,744-4,742.4 MHz frequency band, thereby covering Channels 2 and 3 of the IEEE 802.15.4a standard. Its light weight, mechanical flexibility, and small footprint of 35 mm x 56 mm facilitate integration into textile for radio communication equipment for first aid responders, personal locator beacons, and equipment for localization and medical monitoring of children or the elderly. The antenna features a stable radiation pattern and reflection coefficient in diverse operating conditions such as in free space, when subject to diverse bending radii and when deployed on the torso or upper right arm of a test person. The high isolation toward the wearer's body originates from the antenna's hemispherical radiation pattern with a -3 dB beamwidth of 120 degrees and a front-to-back ratio higher than 11 dB over the entire band. Moreover, the antenna exhibits a measured maximum gain higher than 6.3 dBi and a radiation efficiency over 75%. In addition, orientation-specific pulse distortion introduced by the antenna element is analyzed by means of the System Fidelity Factor (SFF). The SFF of the communication link between two instances of this antenna is higher than 94% for all directions within the antenna's -3 dB beamwidth. This easily wearable and deployable antenna is suitable to support IR-UWB localization with an accuracy in the order of 5 cm.

When 5G networks are to be deployed, the usability of millimeter-wave frequency allocations seems to be left out of the debate. However, there is an open question regarding the advantages and disadvantages of the main candidates for this allocation: The use of the licensed spectrum near 40 GHz or the unlicensed band at 60 GHz. Both bands may be adequate for high performance radio communication systems, and this paper provides insight into such alternatives. A large measurement campaign supplied enough data to analyze and to evaluate the network performance for both frequency bands in different types of indoor environments: Both large rooms and narrow corridors, and both line of sight and obstructed line of sight conditions. As a result of such a campaign and after a deep analysis in terms of wideband parameters, the radio channel usability is analyzed with numerical data regarding its performance. Xunta de Galicia | Ref. ED431C 2019/26 Ministerio de Ciencia, Innovación y Universidades (España) | Ref. TEC2017-85529-C3-3R

This paper reports the characterization of the 2.45-GHz-ISM-band radio wave propagation channel. Specifically, measurements were performed in an underground parking garage, with the aim of optimizing breadcrumb systems for a Rapid Intervention Team application. The effects of the high penetration loss and large reflections by the concrete reinforced building structure on the path loss and the large-scale fading were studied. Based on the analysis of the wireless channel, critical points for reliable communication between members of a Rapid Intervention Team were identified. In particular, attention was paid to dealing with large, spatially confined signal losses due to shadowing, the anticipation of corner losses and the ability of the system to operate on multiple floors.

In this work, a new fabrication methodology for the production of textile cavity-backed substrate integrated waveguide slot antennas is proposed. This methodology involves laser cutting the entire electrotextile part in one single patch, which is then folded around a dielectric textile substrate. Since this procedure realizes the vertical cavity walls by slabs protruding from the electrotextile patch, heavy metal eyelet vias can be omitted, leading to a drastic reduction in antenna weight and improving wearability. Furthermore, this method is more suitable for automated mass production compared to existing design procedures: it requires fewer manipulations, diminishes alignment errors and suffers less from textile cutting inconveniences such as inaccuracies and textile fraying. This leads to a higher yield, and thus lower production costs. As a proof of concept, a broadband multi-moded cavity backed slot antenna is realized in this novel fabrication methodology. Measurements show a broadside gain of 6.5 dBi, a radiation efficiency of 70% and a fractional impedance bandwidth of 16%.

A precise electromagnetic characterization of liquids can be useful to beverage producers, as its variations can provide information about the quality of the beverages. In this chapter, the probe reflection method is used to characterize different kinds of beers, in a variety of conditions of temperature and of times after opening. We present measurements of dielectric constant, and analyze their variations when changing different of conditions in a controlled manner. We have also determined the uncertainty of measurements, and some possible source of errors: the foam and the bubbles. Finally, a way to take advantage of those gathered data is also proposed: we could transmit a radio wave across tubes of liquids (i.e., beer) within factories (i.e., breweries) and then detect the received signals in the opposite side. This setup would allow detecting changes in quality or production parameters related to modifications in the electromagnetic behavior of the liquid itself.

The widespread use of sensor nodes forces a straightforward, low‐cost, and easy‐to‐implement design of these nodes. Instead of using separate batteries and antennas, this letter proposes a dual‐band microstrip antenna for both communication and energy‐harvesting applications. The energy required for the sensor node is harvested from the broadcast television band and then used in the cellular phone communication band. A previous design of a circular polarized broadband patch antenna is adapted and optimized for the defined requirements with the electromagnetic simulation software CST Studio Suite. The simulations helped in an antenna design with a reflection coefficient below −10 dB in the 600 MHz ‐ 700 MHz television frequency band for the energy harvesting. Furthermore, the antenna is also able to operate in the 850 MHz cellular mobile phone communication band, in order to provide coverage in shadowed remote areas or even to be of use for the transmission of the sensor data. The final design is prototyped and then characterized through the measurement of the reflection coefficient. Xunta de Galicia | Ref. GRC1015/019 Agencia Estatal de Investigación | Ref. TEC2017-85529-C3-3

We leverage a generalized polynomial chaos (GPoC) expansion to model the effect of correlated random antenna element displacements in a uniform circular antenna array (UCA) on the probability density function of the estimated directions-of-arrival (DOAs). To limit the number of antenna array realizations to be evaluated through full-wave simulations, we determine the GPoC expansion coefficients based on the stochastic collocation method. The method yields a speedup factor of about 40 compared to the Monte-Carlo approach, for a UCA with two displaced antenna elements and for DOA estimates obtained via the sparse-UCA-root-MUSIC algorithm.

i»?The information exchange has evolved from traditional books to computers and Internet in a few years’ time. Our current university students were born in this age: they learn and have fun with different methods as previous generations did. These digital natives enjoy computer games. Thus, designing games for learning some selected topics could be a good teaching strategy for such collective and also for undergraduate university students. This paper describes the development and test of an educational computer game revolving around radar. The objective of the game RADAR Technology is to teach students about the fundamentals of radar, while having fun during the learning experience. Based on the principle that you learn better what you practice, the authors want to induce students to discover a difficult to understand topic by proposing them a different experience, in a format better adapted to their generation skills. The computer game has been tested with actual students and the obtained results seem to be very promising.

The accurate, reliable and cost-effective mass production of textile wireless systems remains an important challenge and a major impediment to achieve market penetration. Therefore, we propose some novel design, characterization and manufacturing procedures to make the development of such systems more compatible with mass production in traditional assembly line processes. First, we propose a novel non-destructive characterization procedure that determines the dielectric properties of the textile substrate directly within the assembly line, just before manufacturing the textile wireless node. Then, we describe an innovative manufacturing procedure that requires less manipulations and yields more accurate ultra-wideband textile antennas. Finally we introduce a holistic design framework for autonomous textile wireless nodes with communication, sensing and energy-harvesting functionality.

A novel manufacturing procedure for the fabrication of ultra-wideband cavity-backed substrate integrated waveguide antennas on textile substrates is proposed. The antenna cavity is constructed using a single laser-cut electrotextile patch, which is folded around the substrate. Electrotextile slabs protruding from the laser-cut patch are then vertically folded and glued to form the antenna cavity instead of rigid metal tubelets to implement the vertical cavity walls. This approach drastically improves mechanical flexibility, decreases the antenna weight to slightly more than 1 g and significantly reduces alignment errors. As a proof of concept, a cavity-backed substrate integrated waveguide antenna is designed and realized for ultra-wideband operation in the [5.15-5.85] GHz band. Antenna performance is validated in free space as well as in two on body measurement scenarios. Furthermore, the antenna's figures of merit are characterized when the prototype is bent at different curvature radii, as commonly encountered during deployment on the human body. Also the effect of humidity content on antenna performance is studied. In all scenarios, the realized antenna covers the entire operating frequency band, meanwhile retaining a stable radiation pattern with a broadside gain above 5 dBi, and a radiation efficiency of at least 70%.

In this article a Multiple Input Single Output (MISO) hardware design is reported, comprising both a transmitter and a receiver for space-time coded signals. The transmitter implements Alamouti space-time coding, while the receiver uses maximum likelihood estimation to decode the space-time codes. As a result, the hardware communication system is configured as a 2×1 MISO link. The hardware is designed modularly, in order for the system to be easily extendible for the connection of multiple antennas. A digital core allows high-speed data generation in the signal generator units, forwarding analog I and Q signals to the radio-frequency modules connected to it. The Bit Error Rate (BER) performance of the Alamouti diversity scheme is compared to the performance of Single Input Single Output (SISO) and Maximum Ratio Combining (MRC) systems. This comparison is based on simulation results, providing a good approximation of the theoretical BER performance, and a series of hardware measurements to empirically support this theoretical performance.

With the advent of the Internet of Things, body-worn sensor nodes are continuously becoming more important. In case of bio-medical, rescue-worker or military applications sensitive data are often transmitted, requiring the need for encryption. The distribution of symmetric encryption keys is often an issue leading to security risks. Body-worn sensor nodes are generally employed in quickly varying channel conditions due to body movement. The radio-communication channel between such nodes is however reciprocal, allowing the extraction of an array of similar channel measurements at both ends of the link. These data can be used to build equal encryption keys at both link ends without the need for actual over-the-air key distribution. This paper studies the practical performance of an enhanced channel-based key generation system with a very short round-trip delay, allowing reciprocal channel assessment with increased accuracy. Measurements were performed using the new system and the results of the enhanced key generation are evaluated. Although the performance is slightly increased thanks to the shorter round-trip delay, the accuracy of the signal level detector still imposes limits.