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![Emissivity of human skin at various frequency ranges, as given in Reference [52] (diamonds), Reference [51] (triangles) and Reference [48] (squares). Grey dots connected by a grey line show the mean emissivity over the bandwidth BW = f − f 0 = f −30 GHz, were f is the frequency of the x-axis, and f 0 = 30 GHz is the lower bound of the detection band.](profile/Dovile-Cibiraite/publication/343140277/figure/fig5/AS:916178608328704@1595445410651/Emissivity-of-human-skin-at-various-frequency-ranges-as-given-in-Reference-52.png)
Emissivity of human skin at various frequency ranges, as given in Reference [52] (diamonds), Reference [51] (triangles) and Reference [48] (squares). Grey dots connected by a grey line show the mean emissivity over the bandwidth BW = f − f 0 = f −30 GHz, were f is the frequency of the x-axis, and f 0 = 30 GHz is the lower bound of the detection band.
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This work presents, to our knowledge, the first completely passive imaging with human-body-emitted radiation in the lower THz frequency range using a broadband uncooled detector. The sensor consists of a Si CMOS field-effect transistor with an integrated log-spiral THz antenna. This THz sensor was measured to exhibit a rather flat responsivity over...
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... [51] reports three values for the emissivity of the inner arm at 0.1 THz, 0.5 THz and 1.0 THz. Figure 7 depicts GHz and THz emissivity values of the literature obtained either for the palm or the inner arm, for the IR frequency range, the choice of the region of the body is insignificant. In order to obtain the emissivity values for various detector bandwidths, we linearly interpolated the depicted data points and calculated the mean emissivity value for the bandwidth ∆ f = f − f 0 = f -30 GHz, were f is the respective frequency value of the x-axis and f 0 is the assumed lower limit of the detection band of the TeraFET as determined by the spectral characteristics of its antenna. ...
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In this paper, a terahertz hyperspectral imaging architecture based on an electro-optic terahertz dual-comb source is presented and demonstrated. In contrast to single frequency sources, this multi-heterodyne system allows for the characterization of the whole spectral response of the sample in parallel for all the frequency points along the spectr...
Citations
... Refs. [15][16][17][18][19][20][21] explore different antenna designs used in patient monitoring applications, with a special emphasis on their diversity and applications. We then shift our attention to small implantable antennas for in-body critical usage and other purposes, as highlighted in [22][23][24][25][26][27][28]. ...
... In this section, a comprehensive overview of the most recent advancements in device development within this specific field is derived. These studies [15][16][17][18][19][20][21] delve more into different antenna designs used in various patient monitoring applications whereas [22][23][24][25][26][27][28] focus more on small implantable antenna for in-body critical usage and other purposes. Refs. ...
... Moreover, ref. [18] uses a different antenna technique. Ref. [18] introduces a method of passive imaging using radiation emitted by the human body in the lower THz frequency range. ...
The development of remote health monitoring systems has focused on enhancing healthcare services’ efficiency and quality, particularly in chronic disease management and elderly care. These systems employ a range of sensors and wearable devices to track patients’ health status and offer real-time feedback to healthcare providers. This facilitates prompt interventions and reduces hospitalization rates. The aim of this study is to explore the latest developments in the realm of remote health monitoring systems. In this paper, we explore a wide range of domains, spanning antenna designs, small implantable antennas, on-body wearable solutions, and adaptable detection and imaging systems. Our research also delves into the methodological approaches used in monitoring systems, including the analysis of channel characteristics, advancements in wireless capsule endoscopy, and insightful investigations into sensing and imaging techniques. These advancements hold the potential to improve the accuracy and efficiency of monitoring, ultimately contributing to enhanced health outcomes for patients.
... The dominance of III-V high electron mobility devices is gradually decreasing due to the development of bipolar CMOS (BiCMOS) technologies as well as the accessibility of CMOS technologies for a wide range of research groups 12,13 . For example, it is proven that THz detectors fabricated in CMOS allow for an efficient detection at 4 THz and above 14 as well as for demonstration of a passive detection of human body radiation in THz range below 2 THz at room-temperature conditions 15 . ...
... Whereas a loss for the D#1 can be attributed to a combination of 30% Fresnel loss at the silicon-air interface, a 30% loss in 280 µm-thick p-doped substrate with 10 cm resistivity and about 50% by antenna efficiency, the additional 50% loss for device D#2 currently remains unaccounted for. The nearly 100 mV shift in base bias between the simulated and experimentally measured characteristics can be attributed to a voltage drop on about 3 additional resistance introduced by the analog switch in biasing For a coarse determination of the oscillation frequency, we have employed a home-built Michelson interferometer combined with a wideband TeraFET THz detector 15 . Figure 3a presents the implemented setup. ...
In this work, we present the effect of self-mixing in compact terahertz emitters implemented in a 130 nm SiGe BiCMOS technology. The devices are based on a differential Colpitts oscillator topology with optimized emission frequency at the fundamental harmonic. The radiation is out-coupled through the substrate side using a hyper-hemispheric silicon lens. The first source is optimized for 200 GHz and radiates up to 0.525 mW of propagating power. The second source emits up to 0.325 mW at 260 GHz. We demonstrate that in these devices, feedback radiation produces the change in bias current, the magnitude of which can reach up to several percent compared to the bias current itself, enabling feedback interferometric measurements. We demonstrate the applicability of feedback interferometry to perform coherent reflection-type raster-scan imaging.
... The beam which emanated straight was collected by another off-axis parabolic mirror (OAP1) and focused on the sample at the right angle. The reflected back beam was collimated by the same OAP1 mirror and reached BS which divided it by half and directed it to the plasmonic field-effect transistor (FET) THz sensor [23] through the OAP3 mirror. Here the decoupling of the input and reflected optical beams was not applied. ...
The possibility of overcoming some hardware limitations resulting in low quality of terahertz images is considered. The set of images obtained at different distances from the source of terahertz radiation at frequency 0.1 THz is studied. It is shown that the noise in these images is of mixed type and has quite high level of spatial correlation. A fully automatic denoising method based on the use of discrete cosine transform with spatially adapted spectrum is proposed. It is shown that despite initially low spatial resolution of terahertz images and intensive noise, the proposed denoising method provides good noise reduction with good preservation of edges and details, which allows to noticeably enhance the quality of these images.
... Thus, the responsivity can be taken as the lower limit without compensating the losses from the optical components [146]- [155]. However, a more moderate measurement is also reported in which the total power measured by the reference detector includes the attenuation from the cryostat optical window, silicon lens transmission coefficient, antenna radiation efficiency, and additional losses caused by the probing mechanism [156]- [161]. ...
The field of terahertz (THz) science and technology research area have been exponentially growing recently, motivated by the increasing demand for safer security imaging, better quality control within manufacturing industries, space and astronomical investigation, biomedical diagnostics, and larger communication bandwidth. The THz waves detection mechanism is one of the critical components in developing a high efficiency and high sensitivity THz communication system. This paper reviews the principle and instrumentation of THz optical metrology for the precise and accurate characterization of THz detectors in the range of 0.1 THz to several THz. In this context, we individually discuss the determination of radiation input power and effective area followed by a survey of THz optical measurement methodology used in the state-of-the-art THz detectors. In addition, challenging issues remaining in the THz detector measurements are provided. This paper sets out a guideline to address the main concept behind the THz detector measurement as well as their challenges and opportunities. Additionally, useful insight is given through a summary of available power meter instrumentation for THz input power calibration.
... Figure 3 presents two home-built setups implemented in order to determine the spectrum of CMOS sources. The harmonic content of the emission was investigated with a Michelson-type interferometer with a broadband detector [33], see Fig. 3(a). Whereas the high-resolution spectroscopy, as well as phase noise measurements, have been performed using the heterodyne setup presented in Fig. 3(b). ...
This paper presents a fully-electronic wireless link operating at the 250 GHz frequency. The key elements of the developed system are the voltage-controlled harmonic oscillator implemented in 65 nm complementary metal-oxide-semiconductor technology (CMOS) and a quasi-optical detector with a resonantantenna- coupled field-effect transistor completed in 90 nm CMOS. The source is optimized for the third harmonic emission at 252 GHz with radiated power reaching up to –11 dBm (decibels with reference to one milliwatt) level. The detector has a resonance maximum of 254 GHz with a bandwidth of 25% and a minimal optical noise equivalent power of 22 pW/√−H−z . We employ an on-off keying technique for data coding and demonstrate digital signal transmission from 0.4 to 18 m distances. At 0.4 m distance and modulation frequency of 32 MHz, we achieve a 15.9 dB signal-to-noise ratio. The channel capacity of assembled communication link reaches 266 Mbit/s. However, it is limited by external electronic components – the amplifier and the modulator bandwidths. Implementing state-of-the-art high-frequency circuits should allow directly scaling the throughput to 10 Gbit/s.
... However, many of the available imaging devices are not field-deployable or rely on raster scanning of the sample or instrument for image formation. Current THz camera systems do not provide spectroscopic information from the sample [13]- [18]. Therefore, images obtained from today's THz cameras are not Research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number R01GM112693. ...
Recently, we introduced a Portable HAndheld Spectral Reflection (PHASR) Scanner to allow THz Time-Domain Spectroscopic (THz-TDS) imaging in clinical and industrial settings using a fiber-coupled and alignment-free telecentric beam steering design. The key limitations of the version 1.0 of the PHASR Scanner were its field-of-view and speed of time-domain trace acquisition. In this paper, we address these limitations by introducing a heliostat geometry for beam scanning to achieve an extended field-of-view, and by reconfiguring the ASynchronous OPtical Sampling (ASOPS) system to perform Electronically Controlled OPtical Sampling (ECOPS) measurements. The former change improved the deflection range of the beam, while also drastically reducing the coupling of the two scanning axes, the combination of which resulted in a larger than four-fold increase in the FOV area. The latter change significantly improves the acquisition speed and frequency domain performance simultaneously by improving measurement efficiency. To accomplish this, we characterized the non-linear time-axis sampling behavior of the electro-mechanical system in the ECOPS mode. We proposed methods to model and correct the non-linear time-axis distortions and tested the performance of the high-speed ECOPS trace acquisition. Therefore, here we introduce the PHASR Scanner version 2.0, which is capable of imaging a 40$\times$27 mm$^2$ FOV with 2000 traces per second over a 100 picosecond TDS range. This new scanner represents a significant leap towards translating the THz-TDS technology from the lab bench to the bedside for real-time clinical imaging applications.
... With human pose estimation, tracking a person or multiple people in real space can be done at an incredibly granular level. This powerful capability unlocks a wide range of industrial applications [1][2][3][4][5][6][7][8], including gaming, animation, motion transfer, augmented reality, human-robot cooperation and training, biomechanical analysis for medical/healthcare, sports fields, gesture control, autonomous driving, human fall detection, action prediction, security and surveillance, etc. ...
Two-dimensional (2D) multi-person pose estimation and three-dimensional (3D) root-relative pose estimation from a monocular RGB camera have made significant progress recently. Yet, real-world applications require depth estimations and the ability to determine the distances between people in a scene. Therefore, it is necessary to recover the 3D absolute poses of several people. However, this is still a challenge when using cameras from single points of view. Furthermore, the previously proposed systems typically required a significant amount of resources and memory. To overcome these restrictions, we herein propose a real-time framework for multi-person 3D absolute pose estimation from a monocular camera, which integrates a human detector, a 2D pose estimator, a 3D root-relative pose reconstructor, and a root depth estimator in a top-down manner. The proposed system, called Root-GAST-Net, is based on modified versions of GAST-Net and RootNet networks. The efficiency of the proposed Root-GAST-Net system is demonstrated through quantitative and qualitative evaluations on two benchmark datasets, Human3.6M and MuPoTS-3D. On all evaluated metrics, our experimental results on the MuPoTS-3D dataset outperform the current state-of-the-art by a significant margin, and can run in real-time at 15 fps on the Nvidia GeForce GTX 1080.
... The requirement of low cryogenic temperature controller in photon detector operation is sometimes expensive and not practical to be used in the room temperature. Numerous THz thermal detector research have been reported recently based on the microbolometer [4], MOSFET [5], or pyroelectric material [6]. ...
... 3. Une détection directe par rectification électrique dans un transistor FET 5 , à température ambiante [33,34,35] ou refroidi à l'azote liquide [35]. ...
... (A) Un groupe de l'Université Goethe en Allemagne a réalisé une démontration d'imagerie passive de la peau humaine avec un TeraFET silicium en 2020, dans une atmosphère à température ambiante [33]. ...
... Technologie de détecteur SBD GaAs [30] HBT SiGe [31] 3.(A) Si MOSFET [33] 3.(B) HEMT AlGaN/GaN [35] condensateur électrique dans son fonctionnement, car il est un réservoir dynamique de phonons. Sa fonction est de mesurer le flux optique incident, modélisé par une puissance P opt uniforme sur la surface du pixel. ...
L'imagerie passive en temps réel et à distance dans la gamme sub-térahertz (THz) ouvre la voie vers des applications comme la détection d'objets cachés (armes, explosifs) sous les vêtements ou dans les colis et la vision en environnement dégradé à travers des obscurants (nuage de poussières ou de sable). Elle est cependant très exigeante car elle requiert une puissance minimale détectable inférieure au picowatt. Les détecteurs actuels assurant ce niveau de sensibilité sont pénalisés par l'emploi de systèmes de refroidissement à très basse température, proche de l’hélium liquide, qui rend problématique la réalisation d'un système transportable.Ce travail de thèse a donc pour objectif d'évaluer la faisabilité d'un détecteur sub-THz hautes performances, fonctionnant dans une gamme de température intermédiaire, réalisé sur la base d'un micro-bolomètre à antennes et compatible avec une filière CMOS silicium, susceptible d'être facilement intégrable en une matrice de plan focal.Ce détecteur s'appuie sur un transducteur thermique constitué d'une jonction PN latérale en silicium refroidie à 80 K, qui a été étudiée de manière théorique et expérimentale. Son coefficient de température en courant dépasse 20 %/K en régime de faible injection directe, soit un gain de presque une décade par rapport aux thermistances usuelles des micro-bolomètres non refroidis. Un modèle analytique du bruit basse fréquence a aussi été proposé pour rendre compte des mesures effectuées à 300 K et à 80 K. Le régime de diffusion de la diode s'est révélé comme le meilleur compromis pour optimiser sa résolution thermique.Dans un second temps, un pixel bolométrique sub-THz a été proposé et a fait l'objet d'un dimensionnement à partir de simulations 3D par éléments finis. Une architecture d'antenne patch couplée à un dipôle résistif a été optimisée pour atteindre une absorption en polarisation linéaire proche de 90 % à 350 GHz avec une bande passante de 120 GHz et un pas pixel de 250 µm. La structure complète du micro-bolomètre a été définie avec une intégration technologique cohérente. La constante de temps thermique résultante permet une cadence maximale de 20 images par seconde en utilisant une lecture par obturation globale.Ces valeurs, associées aux résultats obtenus pour le transducteur thermique, ont permis de réaliser un modèle électrothermique du micro-bolomètre en fonctionnement et de proposer une architecture de lecture différentielle. Une puissance minimale détectable de 300 fW pourrait être théoriquement atteinte à une cadence effective de 10 images par seconde, soit une résolution en température sur une scène inférieure à 0.4 K , valeur proche des spécifications typiques requises pour l'imagerie passive en gamme sub-THz.
... Despite the absence of spectroscopic information, an intensity-based THz image is, in fact, sufficient to identify dangerous items hidden under clothes, paper or plastic 18 , without being harmful to human health 19 . It seems therefore that a small market has formed, requiring inexpensive THz cameras with low-medium resolution (320x240 pixels), operating at room temperature with video acquisition rate and, possibly, with low noise (NEP<100 pW Hz -1/2 ) in order to also passively detect human blackbody radiation 20 . One of the most frequently adopted solutions for THz detection in these commercial cameras are microbolometer-based focal plane arrays (FPA) [21][22][23][24][25][26][27] . ...
Fast, room temperature imaging at THz and sub-THz frequencies is an interesting feature which could unleash the full potential of plenty applications in security, healthcare and industrial production. In this Letter we introduce micromechanical bolometers based on silicon nitride trampoline membranes as broad-range detectors, down to the sub-THz frequencies. They show, at the largest wavelengths, room-temperature noise-equivalent-powers comparable to state-of-the-art commercial devices (~100 pW Hz-1/2); adding the good operation speed and the easy, large-scale fabrication process, the trampoline membrane could be the next candidate for cheap, room temperature THz imaging and related applications.
