Hi everyone! In the battle for the low-power wide network market share in the scope of the Internet-of-Things, a huge blow emerged: Sigfox, the French IoT startup files for bankruptcy after raising more than 300M€ in funding. https://techcrunch.com/2022/01/27/sigfox-the-french-iot-startup-that-had-raised-more-than-300m-files-for-bankruptcy-protection-as-it-seeks-a-buyer/ Sigfox blames COVID-19 for the slower than expected adoption and revenue growth, which puts pressure on the companies financials. This is indeed an interesting development in the IoT market. Helium, Powered by the Helium Blockchain, The People’s Network represents a paradigm shift for decentralized wireless infrastructure. This novel approach enables Helium to offer a much more competitive cost per byte over the SigFox network. Given the exponential deployment rate of this network, coupled with major players adopting it as their data transport service, maybe SigFox fallout is more to do with fierce competition than COVID-related disruptions. What do you think?
This letter presents an automatic power amplifier (PA) design methodology that uses a multidimensional search algorithm to find the best compromise between fundamental and harmonic impedance terminations for a specified bandwidth. In conventional design methodologies, PA designers need to preselect the optimum impedances, which normally follow non-Foster trajectories, and are thus impossible to achieve with passive matching networks (MNs) for a wide frequency range. Instead, the proposed automatic design method directly synthesizes the MNs to achieve the desired output power, efficiency, and gain performance, without forcing any impedance profiles. For that, load-pull data are interpolated using artificial neural networks and an algorithm based on the simplified real frequency technique is used to obtain the MNs. Finally, the method is validated with a single-ended PA implementation.
Vertigo-like sensations or apparent perception of movement are reported by some subjects and operators in and around high field whole body magnetic resonance body scanners. Induced currents (which modulate the firing rate of the vestibular hair cell), magneto-hydrodynamics (MDH), and tissue magnetic susceptibility differences have all been proposed as possible mechanisms for this effect. In this article, we examine the theory underlying each of these mechanisms and explore resulting predictions. Experimental evidence is summarised in the following findings: 30% of subjects display a postural sway response at a field-gradient product of 1 T2m−1; a determining factor for experience of vertigo is the total unipolar integrated field change over a period greater than 1 s; the perception of dizziness is not necessarily related to a high value of the rate of change of magnetic field; eight of ten subjects reported sensations ranging from mild to severe when exposed to a magnetic field change of the order of 4.7 T in 1.9 s; no subjects reported any response when exposed to 50 ms pulses of dB/dt of 2 Ts−1 amplitude. The experimental evidence supports the hypothesis that magnetic-field related vertigo results from both magnetic susceptibility differences between vestibular organs and surrounding fluid, and induced currents acting on the vestibular hair cells. Both mechanisms are consistent with theoretical predictions.
The field of foldable and physically reconfigurable antennas has recently attracted significant interest from diverse scientific communities, including researchers on antennas, material science, mechanical engineering and numerical modeling. Deployable, packable and multifunctional systems are very important for many applications, including satellite communications, UAVs, CubeSats as well as airborne and spaceborne communication systems. Foldable and physically reconfigurable antennas, particularly origami-based antennas, can provide new capabilities for the aforementioned applications. In this work, we present emerging research on foldable and physically reconfigurable antennas. Such antennas morph their shape to adapt and reconfigure their EM performance (e.g., frequency of operation, bandwidth, polarization, beamwidth, etc.). Also, origami antennas provide ultra-compact stowage, easy deployment, reduced weight, enhanced EM performance and multifunctional utility.
The rapid release of 5G wireless communications networks has spurred renewed concerns regarding the interactions of higher radiofrequency (RF) radiation with living species. We examine RF exposure and absorption in ex vivo bovine brain tissue and a brain simulating gel at three frequencies: 1.9 GHz, 4 GHz and 39 GHz that are relevant to current (4G), and upcoming (5G) spectra. We introduce a highly sensitive thermal method for the assessment of radiation exposure, and derive experimentally, accurate relations between the temperature rise (ΔT), specific absorption rate (SAR) and the incident power density (F), and tabulate the coefficients, ΔT/ΔF and Δ(SAR)/ΔF, as a function of frequency, depth and time. This new method provides both ΔT and SAR applicable to the frequency range below and above 6 GHz as shown at 1.9, 4 and 39 GHz, and demonstrates the most sensitive experimental assessment of brain tissue exposure to millimeter-wave radiation to date, with a detection limit of 1 mW. We examine the beam penetration, absorption and thermal diffusion at representative 4G and 5G frequencies and show that the RF heating increases rapidly with frequency due to decreasing RF source wavelength and increasing power density with the same incident power and exposure time. We also show the temperature effects of continuous wave, rapid pulse sequences and single pulses with varying pulse duration, and we employ electromagnetic modeling to map the field distributions in the tissue. Finally, using this new methodology, we measure the thermal diffusivity of ex vivo bovine brain tissue experimentally.
The predominant source of human exposure to radio frequency radiation (RFR) occurs through usage of cellular phone handsets. The Food and Drug Administration nominated cell phone RFR emission for toxicology and carcinogenicity testing in 1999. At that time, animal experiments were deemed crucial because meaningful human exposure health data from epidemiological studies were not available. Male and female Hsd:Sprague Dawley SD rats were exposed to time-averaged whole-body specific absorption rates of Global System for Mobile Communications (GSM)- or Code Division Multiple Access (CDMA)-modulated cell phone RFR at 900 MHz in utero, during lactation, and after weaning for 28 days or 2 years. Genetic toxicology studies were conducted in rat peripheral blood erythrocytes and leukocytes, brain cells, and liver cells.
With the increasing demand for higher data rates and more reliable service capabilities for wireless devices, wireless service providers are facing an unprecedented challenge to overcome a global bandwidth shortage. Early global activities on beyond fourth-generation (B4G) and fifth-generation (5G) wireless communication systems suggest that millimeter-wave (mmWave) frequencies are very promising for future wireless communication networks due to the massive amount of raw bandwidth and potential multigigabit-per-second (Gb/s) data rates ?. Both industry and academia have begun the exploration of the untapped mmWave frequency spectrum for future broadband mobile communication networks. In April 2014, the Brooklyn 5G Summit , sponsored by Nokia and the New York University (NYU) WIRELESS research center, drew global attention to mmWave communications and channel modeling. In July 2014, the IEEE 802.11 next-generation 60-GHz study group was formed to increase the data rates to over 20 Gb/s in the unlicensed 60-GHz frequency band while maintaining backward compatibility with the emerging IEEE 802.11ad wireless local area network (WLAN) standard .
Typical polar digital power amplifiers (DPAs) employ unit-cells operated in class-E or D-1, denoting a switched-resistance operation which degrades linearity. Besides introducing higher demand on digital predistortion (DPD), it also requires extra quantization bits, impacting the overall efficiency and system complexity. To address this, the present work makes use of an optimized constant-current cascode unit-cell which is combined with reduced conduction angle to achieve linear and efficient operation, while minimizing the effort on DPD and/or calibration. A design strategy is developed which focuses on the cascode bias voltage and transistor relative dimensions as design parameters, allowing cascode efficiency optimization without compromising linearity or reliability. A single-ended polar switched constant-current DPA is implemented in 180-nm standard CMOS. Continuous-wave measurements performed at 800 MHz demonstrate an output power of 24 dBm with a PAE of 47%. The DPA dynamic behavior was tested with a 64-QAM signal with 10 MS/s, achieving an average PAE of 20.9% with a peak-to-average power ratio (PAPR) of 8.7 dB and adjacent-channel leakage ratio (ACLR) = 40.34 dB. These results demonstrate comparable performance with the prior art while using only 6-bits clocked at 100 MHz baseband sampling frequency.
The concept of Smart Cities has been introduced as a way to benefit from the digitization of various ecosystems at a city level. To support this concept, future communication networks need to be carefully designed with respect to the city infrastructure and utilization of resources. Recently, the idea of `smart' environment, which takes advantage of the infrastructure in order to enable better performance of wireless networks, has been proposed. This idea is aligned with the recent advances in design of reconfigurable intelligent surfaces (RISs), which are planar structures with the capability to reflect impinging electromagnetic waves toward preferred directions. Thus, RISs are expected to provide the necessary flexibility for the design of the `smart' communication environment, which can be optimally shaped to enable cost- and energy-efficient signal transmissions where needed. Upon deployment of RISs, the ecosystem of the Smart Cities would become even more controllable and adaptable, which would subsequently ease the implementation of future communication networks in urban areas and boost the interconnection among private households and public services. In this article, we provide our vision on RIS integration into future Smart Cities by pointing out some forward-looking new application scenarios and use cases and by highlighting the potential advantages of RIS deployment. To this end, we identify the most promising research directions and opportunities. The respective design problems are formulated mathematically. Moreover, we focus the discussion on the key enabling aspects for RIS-assisted Smart Cities, which require substantial research efforts such as pilot decontamination, precoding for large multiuser networks, distributed operation and control of RISs. These contributions pave the road to a systematic design of RIS-assisted communication networks for Smart Cities in the years to come.