1,720,984 research outputs found
Acoustic characterization of polyvinyl alcohol cryogels for fabrication of brain phantom
No full textEntwicklung eines hochauflösenden Ultraschallimpulsgebers für medizinische Blutdruckmessungen
No full textAnalysis, design, and experimental evaluation of sub-THz power amplifiers based on GaAs metamorphic HEMT technology
No full textThe interest for devices operating in the millimeter-wave (mmW) range (30-300 GHz) and submillimeter-wave (sub-mmW) range (above 300 GHz) is increasing due to the advantages they provide such as compactness, low weight, broad bandwidth, and the capability of these frequencies to penetrate dust, smog and adverse weather conditions. The availability of compact and broadband single-chip solid state power amplifiers (SSPAs) at sub-THz (0.1-1 THz) frequencies can have a decisive impact in many applications including: instrumentation, high-resolution imaging radar and high-data rate communication.Significant improvements in high-speed transistor technologies have enabled the realization of SSPAs in the sub-THz regime. One of them is the GaAs metamorphic high electron mobility transistor (mHEMT) technology available at the Fraunhofer Institute for Applied Solid State Physics, whose processes with gate lengths of 50 nm and 35 nm achieve impressive cut-off frequencies of 380 GHz and 515 GHz. Although InP heterojunction bipolar transistor (HBT) SSPAs offer higher output power due to the higher breakdown voltage, the GaAs mHEMT is a more robust, cheaper and lower DC power consuming technology. Besides the low breakdown, there are other difficulties in the design of sub-THz SSPAs, such as high parasitic effects, losses, and stability issues.To overcome the low-breakdown voltage limitation of GaAs mHEMTs, this work investigates the potential of amplifier topologies based on stacked field effect transistor (stacked-FET) configurations. A theoretical investigation of unit power cell topologies based on different series configurations is presented, including the evaluation and classification of their performance through the definition of novel figures of merit. A design methodology suitable for the sub-THz frequency range is developed and practical examples of unit power cell SSPAs based on the different stacked-FET configurations are presented. PA cells based on a series connection of more than two transistors had previously been published only up to W-band. The results in this research work represent the first experimental demonstrations of stacked-FET topologies up to the onset of the sub-mmW range.As the number of transistors that can be stacked in series is limited, in-phase parallel combining or balanced topologies are also implemented in combination with the best stacked-FET cell configurations to achieve the required power levels. In this context, the design of compact in-phase splitters/combiners and hybrid couplers with low-loss and broadband performance is a key aspect. Different configurations of on-chip couplers and combiners are studied. This investigation also explores the potential of a novel three-metallization-layer process variant, which has allowed to develop a broadband broadside coupler, with higher isolation and compactness than the standard state of the art. As a result, an SSPA with four parallel stacked-FET cells has been demonstrated at 240 GHz, leading to improved bandwidth and power levels compared to previous results in the same technology. In a further step, an ultra-broadband balanced SSPA was packaged into a waveguide module for use as an instrumentation amplifier. These PAs, while making use of novel topology configurations, significantly increase the published performance in terms of bandwidth or power added efficiency while achieving enough output power for the considered applications
Estimation of blood pressure by image-free, wearable ultrasound
No full text1.28 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
Mini-Symposium : recent advances on clinical ultrasound: From diagnose to therapeutic applications
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Non-invasive waerable ultrasound sensors to measure continuously medical arterial parameters
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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