http://ieeexplore.ieee.org/iel5/5/31324/01456901.pdf

Microelectronic circuits

New smart technologies and the internet of things increasingly play a key role in healthcare and wellness, contributing to the development of novel healthcare concepts. These technologies enable a comprehensive view of an individual’s movement and mobility, potentially supporting healthy living as well as complementing medical diagnostics and the monitoring of therapeutic outcomes. This overview article specifically addresses smart shoes, which are becoming one such smart technology within the future internet of health things, since the ability to walk defines large aspects of quality of life in a wide range of health and disease conditions. Smart shoes offer the possibility to support prevention, diagnostic work-up, therapeutic decisions, and individual disease monitoring with a continuous assessment of gait and mobility. This overview article provides the technological as well as medical aspects of smart shoes within this rising area of digital health applications, and is designed especially for the novel reader in this specific field. It also stresses the need for closer interdisciplinary interactions between technological and medical experts to bridge the gap between research and practice. Smart shoes can be envisioned to serve as pervasive wearable computing systems that enable innovative solutions and services for the promotion of healthy living and the transformation of health care.

/pdf/an-overview-of-smart-shoes-in-the-internet-of-health-things-2ss5f2fi5h.pdf

An Overview of Smart Shoes in the Internet of Health Things: Gait and Mobility Assessment in Health Promotion and Disease Monitoring

This brief explores the design space for realizable solution of a broadband class-B/J continuous mode of power amplifier (PA). The PA is initially designed at the current-source reference plane with the correct voltage and current waveforms. The intrinsic impedances are then projected to the package reference plane using the model-based nonlinear-embedding technique. An insight is provided into engineering the extrinsic harmonic impedance to rotate clockwise on the Smith chart to be able to match it using a Foster circuit. It is concluded that decreasing the empirical parameter $ {\alpha }$ of a general class-B/J voltage equation with increasing frequency leads to a clockwise trajectory on the Smith chart of the second harmonic at the package plane. In order to validate the advantage of this analysis, the PA is implemented using a 15 W gallium nitride high electron mobility transistor in the frequency range of 1.3 to 2.4 GHz and drain efficiency between 63% and 72% in measurement was achieved over the entire bandwidth.

Continuous Class-B/J Power Amplifier Using a Nonlinear Embedding Technique

Traditionally employed human-to-human and human-to-machine communication has recently been replaced by a new trend known as the Internet of things (IoT). IoT enables device-to-device communication without any human intervention, hence, offers many challenges. In this paradigm, machine’s self-sustainability due to limited energy capabilities presents a great challenge. Therefore, this paper proposed a low-cost energy harvesting device using rectenna to mitigate the problem in the areas where battery constraint issues arise. So, an energy harvester is designed, optimized, fabricated, and characterized for energy harvesting and IoT applications which simply recycles radio-frequency (RF) energy at 2.4 GHz, from nearby Wi-Fi/WLAN devices and converts them to useful dc power. The physical model comprises of antenna, filters, rectifier, and so on. A rectangular patch antenna is designed and optimized to resonate at 2.4 GHz using the well-known transmission-line model while the band-pass and low-pass filters are designed using lumped components. Schottky diode (HSMS-2820) is used for rectification. The circuit is designed and fabricated using the low-cost FR4 substrate ( ${h}$ = 16 mm and $\varepsilon _{r} = 4.6$ ) having the fabricated dimensions of 285 mm $\times \,\,90$ mm. Universal software radio peripheral and GNU Radio are employed to measure the received RF power, while similar measurements are carried out using R&S spectrum analyzer for validation. The received measured power is −64.4 dBm at the output port of the rectenna circuit. Hence, our design enables a pervasive deployment of self-operable next-generation IoT devices.

Energy Harvesting Using a Low-Cost Rectenna for Internet of Things (IoT) Applications

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.202100698

Emerging Indoor Photovoltaic Technologies for Sustainable Internet of Things

A methodology for the design of multichannel, wideband, highly efficient hybrid Class-J power amplifiers for fourth-generation (4G) communication transmitters is proposed. The design procedure is based on the automatic generation and evaluation of a vast number of output matching networks of the same topology but different dimensions, with respect to efficiency, output power, and linearity. The approach can find application in the management of the efficiency/linearity/bandwidth tradeoff in amplifier design. In this paper, two matching network architectures have been considered. One multistubbed network and a stepped-impedance microstrip line network. The approach has been validated through the design, simulation, and measurement of two power amplifiers realized using the aforementioned procedure. The first amplifier covers 1.6-2.2 GHz (31.6% fractional bandwidth) with 55%-68% drain efficiency at the 2-dB compression point and worst case adjacent channel power ratio (ACRP) and error vector magnitude (EVM) of - 21.8 dBc and 8.35%, respectively, over the bandwidth. The second covers 0.5-1.8 GHz (113% fractional bandwidth) with 50%-69% drain efficiency at the 2-dB compression point and worst case ACRP of - 27.5 dBc and EVM of 4.22%. Both amplifiers are based on a commercial, packaged 10-W GaN HEMT transistor.

Multichannel and Wideband Power Amplifier Design Methodology for 4G Communication Systems Based on Hybrid Class-J Operation

The design and implementation of a high efficiency Class-J power amplifier (PA) for basestation applications is reported. A commercially available 10W GaN HEMT device was used, for which a large-signal model and an extrinsic parasitic model were available. Following Class-J theory, the needed harmonic terminations at the output of the transistor were defined and realised. Experimental results show good agreement with simulations verifying the class of operation. Efficiency above 70% is demonstrated with an output power of 39.7dBm at an input drive of 29dBm. High efficiency is sustained over a bandwidth of 140MHz.

/pdf/a-2ghz-gan-class-j-power-amplifier-for-base-station-1uk4c4p8qb.pdf

A 2GHz GaN Class-J power amplifier for base station applications

Modulation of load impedance is an effective way to maintain efficient power amplifier (PA) operation over high dynamic range modulated signals. For high efficiency, a load modulation approach can be applied to inherently efficient classes of PAs such as those with harmonic tuning: Class J, Class F, and Inverse Class F. This paper presents an analysis of harmonically tuned (HT) amplifiers operating under load modulation conditions, deriving the optimal loading trajectories for these multiple classes of operation. Because these load trajectories are complex, it is then shown—through a series of analysis, simulations, and measurements—that HT amplifiers are better suited for outphasing systems, than conventional amplifiers such as Class B. A design methodology is proposed and validated through design and measurement of a 900-MHz outphasing system, comprising of two Gallium Nitride Class J branch PAs, delivering 44.6 dBm with 75% PAE at saturation, while mantaining PAE above 60% over a 7-dB output power back-off.

/pdf/load-modulation-of-harmonically-tuned-amplifiers-and-4ucmtyurx7.pdf

Load Modulation of Harmonically Tuned Amplifiers and Application to Outphasing Systems

The global move toward wireless access point (AP) densification has alluded toward the possibility of harvesting the unused ambient RF energy, especially in the 2.4-GHz unlicensed band, in order to power useful electronic devices, which collectively make up the so-called low energy Internet of Things (LE-IoT). Despite the huge market demand for free ambient energy and the research community’s efforts in prototyping efficient rectifiers, there is, however, little knowledge about the available power densities in dense indoor and outdoor AP deployments. Obtaining this information is, therefore, vital for engineering the power requirements of LE-IoT devices and managing expectations for their subsequent commercialization. In this paper, we present power density measurements in a controlled indoor ultra-dense deployment corresponding to approximately one AP per square meter. We detail our methodology and hardware and offer a variety of ambient RF measurement results suggesting that Wi-Fi AP densification cannot solely power personal devices such as wearables, but at best can trickle charge them in the hopes of extending battery life, the main hurdle being the small form factor of such mobile devices. In contrast, our measurements suggest that household devices, such as smoke detectors, can be powered by ambient RF harvesting. To this end, AP densification aids in increasing the total available power density, but also in distributing a smooth blanket of available RF energy thus minimizing harvesting-holes.

How Many Wi-Fi APs Does it Take to Light a Lightbulb?

This study investigates the feasibility of ambient radio frequency (RF) energy harvesting for powering low-power electronic devices, in domestic environments. An RF spectrum survey was carried out in a variety of locations around the city of Bristol, UK between 500 MHz and 6 GHz. Locations are limited to indoor residential environments, and as a comparison an office. The measurement setup consists of an omnidirectional, broadband, discone antenna and a handheld spectrum analyser. On the basis of the measured power consumption of a number of low-power electronic devices and the analysed results, the required harvesting time to power each device is calculated. The results show that in order to harvest enough energy to power-up a small calculator (2 μW) for 1 s, an antenna array covering 1.7–2.5 GHz with effective area of 1 m2 requires on average about 10 min of harvesting.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-map.2014.0406

Konstantinos Mimis

Papers

Multichannel and Wideband Power Amplifier Design Methodology for 4G Communication Systems Based on Hybrid Class-J Operation

A 2GHz GaN Class-J power amplifier for base station applications

Load Modulation of Harmonically Tuned Amplifiers and Application to Outphasing Systems

How Many Wi-Fi APs Does it Take to Light a Lightbulb?

Ambient RF energy harvesting trial in domestic settings