The advent of flexible, compact, energy-efficient, robust, and user-friendly wearables has significantly impacted the market growth, with an estimated value of 61.30 billion USD in 2022. Wearable sensors have revolutionized in-home health monitoring by warranting continuous measurements of vital parameters. Ultrasound is used to non-invasively, safely, and continuously record vital parameters. The next generation of smart ultrasonic devices for healthcare integrates microelectronics with flexible, stretchable patches and body-conformable devices. They offer not only wearability, and user comfort, but also higher tracking accuracy of immediate changes of cardiovascular parameters. Moreover, due to the fixed adhesion to the skin, errors derived from probe placement or patient movement are mitigated, even though placement at the correct anatomical location is still critical and requires a user's skill and knowledge. In this review, the steps required to bring wearable ultrasonic systems into the medical market (technologies, device development, signal-processing, in-lab validation, and, finally, clinical validation) are discussed. The next generation of vascular ultrasound and its future research directions offer many possibilities for modernizing vascular health assessment and the quality of personalized care for home and clinical monitoring.

This paper reports on the first stacked field-effect transistor (stacked-FET) submillimeter-wave monolithic integrated circuit (S-MMIC) power amplifier cell operating at 0.3 THz and the first stacked-FET medium power amplifier (MPA) at 240 GHz. Both circuits are fabricated using a 35-nm InGaAs-on-GaAs metamorphic high electron mobility transistor (mHEMT) technology with grounded coplanar waveguide lines. In both cases, compactness and performance are enhanced thanks to the use of an in-house process, based on three-metallization layers, instead of the usual two-layer process. The single-stacked cell exhibits an ultrawide small-signal 3-dB relative bandwidth (RBW) of $\hbox{47.3}{\%}$, with output power levels higher than 4.3 dBm from 280 to 308 GHz (9.5%). The MPA MMIC combining four triple-stacked mHEMT cells in parallel achieves a small-signal 3-dB RBW of 24.2%, 10.8 dBm of output power, and a power-added efficiency of 5.02%. These values outperform the state-of-the-art results of MPAs published within a comparable technology.

Vascular ageing (vascular ageing) is the deterioration of arterial structure and function which occurs naturally with age, and which can be accelerated with disease. Measurements of vascular ageing are emerging as markers of cardiovascular risk, with potential applications in disease diagnosis and prognosis, and for guiding treatments. However, vascular ageing is not yet routinely assessed in clinical practice. A key step towards this is the development of technologies to assess vascular ageing. In this Roadmap, experts discuss several aspects of this process, including: measurement technologies; the development pipeline; clinical applications; and future research directions. The Roadmap summarises the state of the art, outlines the major challenges to overcome, and identifies potential future research directions to address these challenges.

As cardiovascular diseases are one of the most prominent illnesses, a continuous, non-invasive, and comfortable monitoring of blood pressure (BP) is indispensable. This paper investigates the best method for obtaining highly accurate BP values in non-invasive measurements through the extraction of hemodynamic variables from the arteries of young subjects. After literature review, five state-of-the-art BP models were analysed and qualitatively compared in a novel in-silico study. Relevant arterial parameters such as luminal area, flow velocity, and pulse wave velocity, of 1458 subjects were extracted from a computer-simulated database and served as input parameters in the BP models’ simulation. The five models were calibrated to each arterial-site. Contrarily to the expected, the linear model (linear transformation of the distending diameter into BP) revealed more accuracy than the commonly used exponential transformation. In an ex-vivo experimental setup, the linear model was used for the extraction of BP by using an ultrasound (US) sensor and validated with a commercial pressure sensor. The results showed an in-silico pulse pressure correlation of 0.978 and mean difference of (-2.845 ± 2.565) mmHg at the radial artery and ex-vivo pulse pressure correlation of 0.986 and mean difference of (1.724 ± 3.291) mmHg. Thus, with the linear model, the US measurement complies with the Association for the Advancement of Medical Instrumentation standard with smaller deviations than ±5 mmHg.

1.28 billion adults worldwide have high pressure, and only 21% of people have it under control. If high blood pressure (BP) is not diagnosed and treated properly, then there is a high risk for cardiovascular diseases, the main cause of mortality. Ultrasound has emerged as a potential medical imaging system to monitor cardiovascular health. It is comfortable, noninvasive, safe, and a very well-established and well-known technology. However, there are currently no commercial single ultrasound systems to directly quantify vascular parameters, without the need for complex imaging algorithms, additional software-based solutions, and high energy demands that limit portable and prolonged measurements. In this paper, we present the steps to design an image-free novel ultrasound device to continuously extract vital parameters, with a focus on BP. Moreover, as the BP waveforms are amplified toward the periphery (i.e., from the aorta to the radial artery), we applied mathematical models and algorithms, specific to the site of measurement, to accurately extract BP. We validated these algorithms in silico, in vitro, and ex vivo, where tissue and artery phantoms help emulate human physiology. In young subjects, an in silico pulse pressure (PP) correlation of 0.978 and a mean difference of (– 2.85 ± 2.57) mmHg at the radial artery were achieved. The ex vivo PP correlation was 0.986, with a mean difference of (1.72 ± 3.29) mmHg. Soon thereafter, in vivo measurements of BP and stiffness, and their correlation analysis will be performed to corroborate the accuracy of the developed proof-of-concept device.

This paper reports on the first H-band broadside hybrid coupler based on a three-metallization layer process and a grounded coplanar waveguide environment. The performance of this integrated coupler is carefully examined through electromagnetic (EM) simulations and experimental evaluation, and compared to a Tandem-X hybrid, which is based on a two-metallization layer process and requires twice the chip area. The EM analysis covers S-parameter simulations of the coupler structures as well as even- and odd-mode impedance analysis of the edge- and broadside-coupled lines. The broadside hybrid exhibits insertion losses of 3.8-4.3 dB in the through and coupled ports from 246 to 297 GHz. This corresponds to a fractional bandwidth of 19%. In this frequency range, the imbalance is lower than 0.2 dB and a phase difference of 93.6° ± 1.4° is obtained. It is demonstrated that the broadside coupler overcomes the performance of Tandem-X hybrids when applied to medium power amplifiers (MPAs). An MPA monolithic microwave integrated circuit based on triple-stacked FETs and broadside couplers achieves at least 4.5 dBm at 300 GHz and large-signal gain of 7.5 dB at the 3-dB compression point.