Showing papers in "IEEE Transactions on Terahertz Science and Technology in 2016"
TL;DR: In this paper, a 3D printed metallic horn antenna was used for antenna implementation up to 325 GHz. But the performance of the antenna was not evaluated. But they used binder jetting/sintering on 316L stainless steel and selective laser melting (SLM) on Cu-15Sn.
Abstract: This paper presents a study to use the metallic three dimensional (3-D) printing technology for antenna implementations up to 325 GHz. Two different printing technologies and materials are used, namely binder jetting/sintering on 316L stainless steel and selective laser melting (SLM) on Cu–15Sn. Phases, microstructure, and surface roughness are investigated on different materials. Balancing between the cost and performance, the manually polished Cu–15Sn is selected to develop a series of conical horn antennas at the E-(60–90 GHz), D- (110–170 GHz), and H-band (220–325 GHz). Good agreement is observed between the simulated and measured antenna performance. The antennas’ impedance bandwidth ( $\vert S_{11}\vert ) cover the whole operational band, with in-band gain of >22.5, >22, and >21.5 dBi for the E-, D-, and H-band antennas, respectively. Compared with the traditional injection molding and micromachining for metallic horn antenna implementation, the 3-D printed metallic horn antenna features environmental friendliness, low cost, and short turn-around time. Compared with the nonmetallic 3-D printed antennas, they feature process simplicity and mechanical robustness. It proves great potential of the metallic 3-D printing technology for both industrial mass production and prototyping.
139 citations
TL;DR: The numerical results show that the developed resource allocation scheme improves the distances and exploitation of the THz spectrum significantly, and outperforms the existing millimeter-wave systems and the nonadaptive scheme.
Abstract: Terahertz (0.06–10 THz) band communication is envisioned as a key technology to satisfy the increasing demand for ultrahigh-speed wireless links. In this paper, a distance-aware bandwidth-adaptive resource allocation scheme is developed for THz band communication networks, which has the objective to improve the distance. The proposed scheme captures the unique channel peculiarities including the relationship between the distance and the bandwidth, and strategically utilizes the spectrum to enable multiple ultrahigh-speed links. Based on the developed scheme, the subwindows of the THz spectrum, the modulations, and the transmit power are adaptively allocated, for both single-user and multiuser communications. The numerical results show that the developed resource allocation scheme improves the distances and exploitation of the THz spectrum significantly. Specifically, 10 Gb/s can be supported at 4 m in the multipath channel, while 100 Gb/s is achieved up to 21 m in the line-of-sight transmission with the use of 20 dB gain antennas. Furthermore, in the multiuser network, 14 10 Gb/s links can be supported simultaneously in the multipath channel. With the use of 20 dB gain antennas, 13 100 Gb/s links can be supported at the same time. Moreover, the developed resource allocation scheme outperforms the existing millimeter-wave systems and the nonadaptive scheme. This paper achieves the design objective and contributes to enable multiple ultrahigh-speed links in the THz band communication network.
105 citations
TL;DR: In this article, the authors consider most sought after applications of phase imaging provided by this technique and experimentally demonstrate the ability of the method to reconstruct smooth and stepped relief features of an object that is transparent in the THz region.
Abstract: Terahertz pulse time-domain holography (THz PTDH) is the powerful technique for high-resolution amplitude and phase THz imaging that allows mapping spectroscopic information across the imaged object. In this paper, we consider most sought after applications of phase imaging provided by this technique and experimentally demonstrate the ability of the method to reconstruct smooth and stepped relief features of an object that is transparent in THz region. Unlike the amplitude distribution, which does not contain any significant information in this case, phase distribution not only reveals the object qualitatively, but also allows the reconstruction of the object thicknesses pattern, even in low signal-to-noise registration conditions. Main limitations of the proposed method, such as transverse resolution and low signal-to-noise environment are carefully studied and mitigated.
95 citations
TL;DR: In this article, a complete circularly polarized 210-270-GHz frequency-modulated continuous-wave radar with a monostatic homodyne architecture is presented, which consists of a highly integrated radio-frequency transceiver module, an in-house developed linear-frequency chirp generator, and a data acquisition chain.
Abstract: A complete circularly polarized 210–270-GHz frequency-modulated continuous-wave radar with a monostatic homodyne architecture is presented. It consists of a highly integrated radio-frequency transceiver module, an in-house developed linear-frequency chirp generator, and a data acquisition chain. The radar front end featuring a fundamentally operated $\times$ 16 multiplier-chain architecture is realized as a single chip in 0.13- $\mu$ m SiGe heterojunction bipolar transistor technology with a lens-coupled circularly polarized on-chip antenna and wire-bonded on a low-cost printed circuit board. In combination with a 9-mm-diameter silicon lens, the module achieves an average in-band directivity of 26.6 dB. The measured peak radiated power from the packaged radar module is $+$ 5 dBm and the noise figure is 21 dB. For a 60-GHz frequency sweep, the radar achieves a range resolution of 2.57 mm after calibration, which is close to the theoretical bandwidth-limited resolution of 2.5 mm. With a simple scanning optical setup, this paper further demonstrates the 3-D imaging capability of the radar for detection of hidden objects with a remarkable dynamic range of around 50 dB.
95 citations
TL;DR: In this article, a state-of-the-art 520-620 GHz receiver front end working at room temperature was designed, built, and measured, and the receiver front-end features a GaAs-Schottky diode-based subharmonic mixer and a 260-307 GHz doubler.
Abstract: A state-of-the-art 520-620-GHz receiver front end working at room temperature was designed, built, and measured. The receiver front-end features a GaAs-Schottky diode-based subharmonic mixer and a 260-307-GHz doubler, both fabricated with the new LERMA-LPN Schottky process on a 4- μm-thick GaAs membrane suspended in a waveguide with metal beamleads. Small-area mesas and optimized transmission lines with low dielectric loading are used. At 295 K ambient temperature, an average of 1284 K DSB receiver noise temperature was measured over the 520-620-GHz frequency range, including the 3.5-8.5-GHz IF chain loss. A record 1130 K minimum DSB receiver noise temperature at 557 GHz was measured. At 134 K ambient temperature, an average DSB receiver noise temperature of 685 K from 538 to 600 GHz was measured when correcting for the cryostat window loss. A minimum DSB receiver noise of 585 K was measured at an RF center frequency of 540 GHz. The 520-620-GHz receiver presented in this article allows an increase in the sensitivity of the JUpiter ICy Moons Explrorer-SWI instrument of about a factor of two compared with requirements. It will allow study of the Jovian system with particular emphasis on the chemistry, meteorology, structure, and atmospheric coupling processes of Jupiter and its icy satellites, thereby providing important data for the exploration of their habitable zones.
75 citations
TL;DR: The upGREAT THz heterodyne arrays for far-infrared astronomy were presented in this article, where the low-frequency array (LFA) was designed to cover the 1.9-2.5 THz range using 2π × 2π waveguide-based HEB mixer arrays in a dual polarization configuration.
Abstract: We present the upGREAT THz heterodyne arrays for far-infrared astronomy. The low-frequency array (LFA) is designed to cover the 1.9–2.5 THz range using 2 $\, \times \,$ 7-pixel waveguide-based HEB mixer arrays in a dual polarization configuration. The high-frequency array (HFA) will perform observations of the [OI] line at ${\sim}$ 4.745 THz using a 7-pixel waveguide- based HEB mixer array. This paper describes the common design for both arrays, cooled to 4.5 K using closed-cycle pulse tube technology. We then show the laboratory and telescope characterization of the first array with its 14 pixels (LFA), which culminated in the successful commissioning in May 2015 aboard the SOFIA airborne observatory observing the [CII] fine structure transition at 1.9005 THz. This is the first successful demonstration of astronomical observations with a heterodyne focal plane array above 1 THz and is also the first time high-power closed-cycle coolers for temperatures below 4.5 K are operated on an airborne platform.
70 citations
TL;DR: Results in this paper highlight the issues and related challenges while characterizing the communication in such a medium, thus paving the way towards novel research activities devoted to the design and the optimization of advanced applications in the healthcare domain.
Abstract: This paper focuses on the development of a novel radio channel model inside the human skin at the terahertz range, which will enable the interaction among potential nano-machines operating in the inter cellular areas of the human skin. Thorough studies are performed on the attenuation of electromagnetic waves inside the human skin, while taking into account the frequency of operation, distance between the nano-machines and number of sweat ducts. A novel channel model is presented for communication of nano-machines inside the human skin and its validation is performed by varying the aforementioned parameters with a reasonable accuracy. The statistics of error prediction between simulated and modeled data are: mean $(\mu )=\hbox{ 0.6 dB}$ and standard deviation $(\sigma )=\hbox{ 0.4 dB}$ , which indicates the high accuracy of the prediction model as compared with measurement data from simulation. In addition, the results of proposed channel model are compared with terhaertz time-domain spectroscopy based measurement of skin sample and the statistics of error prediction in this case are: $\mu =\hbox{ 2.10 dB}$ and $\sigma =\hbox{ 6.23 dB}$ , which also validates the accuracy of proposed model. Results in this paper highlight the issues and related challenges while characterizing the communication in such a medium, thus paving the way towards novel research activities devoted to the design and the optimization of advanced applications in the healthcare domain.
65 citations
TL;DR: In this paper, an 820-GHz 8 × 8 diode-connected NMOS transistor active imaging array with an on-chip pixel selection circuit was demonstrated in a 130-nm CMOS technology, which is comparable to the state-of-the-art MOSFET and Schottky diode detector arrays.
Abstract: An 820-GHz 8 $\,\times\,$ 8 diode-connected NMOS transistor active imaging array with an on-chip pixel selection circuit was demonstrated in a 130-nm CMOS technology. The noise performance of this architecture is comparable to the state-of-the-art MOSFET and Schottky diode detector arrays. The imaging array consists of a row and column selector, an array of diode-connected NMOS transistor passive pixels, an analog multiplexer, and a low-noise amplifier bank. At 823 GHz, it achieves 2.56 kV/W of measured mean responsivity with a standard deviation of 18% and 36.2 $\hbox{pW/Hz}^{1/2}$ of measured mean noise equivalent power (NEP) at 1-MHz modulation frequency with a standard deviation of 67%. The mean responsivity is greater than $\sim \hbox{2 kV/W}$ between 815 to 835 GHz. The minimum NEP of 12.6 $\hbox{pW/Hz}^{1/2}$ is the lowest for CMOS based detectors at $\sim \hbox{1 THz}$ . The 8 $\,\times\,$ 8 imaging array occupies 2.0 $\,\times\,$ 1.7 $\hbox{mm}^{2}$ and consumes 9.6 mW of power. Reducing device sizes to support the increase of operating frequency is expected to increase the variability and mitigation approaches will be required. The measured access time for the pixel is $\sim \hbox{40 nS}$ . The number of elements that can be connected in a row is determined by the modulation frequency and can be more than 1000 elements while supporting a frame rate greater than 1000 per second. Lastly, the expressions of responsivity and NEP including $1/{\rm f}$ noise that can be used for the detector optimization are derived and presented .
62 citations
TL;DR: A low-power and high-performance 340-GHz heterodyne receiver front end (RFE) optimized for terahertz (THz) biomedical imaging applications is proposed in this paper.
Abstract: A low-power and high-performance 340-GHz heterodyne receiver front end (RFE) optimized for terahertz (THz) biomedical imaging applications is proposed in this paper. The THz RFE consists of an on-chip patch antenna, a single-balanced mixer, and a triple-push harmonic oscillator. The oscillator adopts a proposed harmonic oscillator architecture which can provide differential output by extracting output signals from the same current loop without any additional balun required. The mixer biased in the subthreshold region is designed not only to have high conversion gain and low noise figure by choosing the output intermediate frequency well above the flicker-noise corner frequency, but the required local oscillator (LO) power can also be as low as –11 dBm. Such a low demand on the LO power makes the proposed mixer very suitable for THz applications in which the achievable LO power is very limited. The impact of unavoidable slots for passing design rule checks on the performance of an on-chip patch antenna is also presented. The proposed THz RFE is implemented in a 40-nm digital complementary metal–oxide–semiconductor technology. The measured voltage conversion gain is –1.7 dB at 335.8 GHz, while the mixer and the oscillator only consume 0.3 and 52.8 mW, respectively, from a 1.1 V supply. The proposed THz RFE is employed to set up a THz transmissive imaging system which can provide spatial resolution of 1.4 mm.
60 citations
TL;DR: In this article, a silicon deep reactive-ion etching (DRIE) process has been developed, using multiple SiO2 masks to enable multidepth waveguide features with ±2% tolerance.
Abstract: A silicon deep reactive-ion etching (DRIE) process has been developed, using multiple SiO2 masks to enable multidepth waveguide features with ±2% tolerance. The unique capability of this process is demonstrated by designing, fabricating, and testing an orthomode transducer working in the 500–600 GHz frequency range. Straight waveguide measurements are also performed to characterize the losses associated with the multistep DRIE process, giving results slightly better than expected for metal-machined waveguides. This process enables the integration of multiple terahertz waveguide components such as mixers, multipliers, quadrature hybrids, and polarization twists onto a single silicon package.
52 citations
TL;DR: In this paper, an efficient terahertz (THz) waveguiding in multichannel sapphire shaped crystals is demonstrated, using edge-defined film-fed growth (EFG) technique (or stepanov technique) of shaped crystal growth has been implemented to manufacture the THz photonic crystalline (PC) waveguide.
Abstract: In this paper, an ability for highly efficient terahertz (THz) waveguiding in multichannel sapphire shaped crystals is demonstrated. The edge-defined film-fed growth (EFG) technique (or Stepanov technique) of shaped crystal growth has been implemented to manufacture the THz photonic crystalline (PC) waveguide. The PC waveguide has been characterized using both numerical simulations and experimental study. It allows guiding the THz waves in multimode regime with the minimal dispersion in frequency range of $1.0$ – $1.55$ THz and the minimal power extinction coefficient of $0.02$ dB $/$ cm at $1.45$ THz. The mode interference phenomenon has been observed in this waveguide highlighting the prospectives of its use for intrawaveguide interferometry. These results demonstrate the capabilities of combining the EFG/Stepanov technique advantages with unique properties of sapphire, such as relatively low THz-wave absorption, high mechanical, thermal, chemical, and radiation strength, for manufacturing the THz waveguides characterized with low loss and dispersion and suitable for use in wide range of THz technology applications in biomedical and material sciences, including sensing in aggressive environment.
TL;DR: In this paper, a terahertz (THz) bandpass frequency-selective surface (FSS) with high selectivity is proposed, which consists of identical tripole resonators located on the top and bottom layers and rectangular coupling apertures etched on a conducting plane in between.
Abstract: A terahertz (THz) bandpass frequency-selective surface (FSS) with high selectivity is proposed in this work. The three-layered FSS filter consists of identical tripole resonators located on the top and bottom layers and rectangular coupling apertures etched on a conducting plane in between. Multiple signal paths exist between the top and bottom resonators through the coupling apertures. Therefore, this aperture-coupled resonator (ACR) structure exhibits a narrow bandpass response, and two transmission zeros appear near the skirts of the passband. These zero points considerably improve the frequency selectivity and suppress the sidebands of the FSS. For demonstration, a microfabrication process was used to realize an ACR FSS at 850 GHz. The frequency performance of the ACR FSS in terms of insertion loss is investigated numerically and experimentally. The measured transmission responses at normal incidence based on time-domain as well as frequency-domain measurements agree well with the simulated one, thus verifying the proposed design. Furthermore, the frequency-domain measurement reveals that the FSS response remains stable at various incident angles for both TE and TM polarizations.
TL;DR: In this article, a compact, polarization-independent, broadband, omnidirectional terahertz (THz) absorber is proposed, fabricated, and evaluated based on the combined effect of the multi-interference and diffraction.
Abstract: High absorption over a wide frequency band has attracted considerable interest due to its potential applications in imaging and anti-radar cloaking devices. In order to make these devices more integrated, the thickness of the absorber is crucial. In this paper, a compact, polarization-independent, broadband, omnidirectional terahertz (THz) absorber is proposed, fabricated, and evaluated. This THz absorber is based on the combined effect of the multi-interference and diffraction. It is experimentally demonstrated that over 95% absorption can be obtained in the frequency range from 0.75 to 2.41 THz. This well-designed thinner absorber not only reduces the device thickness to 120 μm, but also introduces more interference peaks so that the absorption spectrum is significantly enlarged. Five successive absorption peaks at 0.88, 1.20, 1.53, 1.96, and 2.23 THz are combined into a broadband THz absorption spectrum.
TL;DR: In this paper, an optical network compatible high-speed optoelectronics THz wireless transmission system operating at 400 GHz band is demonstrated, where optical Nyquist quadrature phase-shift keying signals in a 12.5-GHz ultradense wavelength-division multiplexing grid is converted to the THz radiation by photomixing in an antenna integrated unitravelling photodiode.
Abstract: We experimentally demonstrate an optical network compatible high-speed optoelectronics THz wireless transmission system operating at 400-GHz band. In the experiment, optical Nyquist quadrature phase-shift keying signals in a 12.5-GHz ultradense wavelength-division multiplexing grid is converted to the THz wireless radiation by photomixing in an antenna integrated unitravelling photodiode. The photomixing is transparent to optical modulation formats. We also demonstrate in the experiment the scalability of our system by applying single to four channels, as well as mixed three channels. Wireless transmission of a capacity of 60 Gb/s for four channels (15 Gb/s per channel) at 400-GHz band is successfully achieved, which pushes the data rates enabled by optoelectronics approach beyond the envelope in the frequency range above 300 GHz. Besides those, this study also validates the potential of bridging next generation 100 Gigabit Ethernet wired data stream for very high data rate indoor applications.
TL;DR: In this paper, a hybrid HE11 output window based on the multilayer concept for high power gyro-amplifiers operating in the low terahertz region is proposed.
Abstract: Broadband HE11 mode output windows, based on the multilayer concept, are studied for high power gyro-amplifiers operating in the low terahertz region. As the wave power in the hybrid HE11 mode is concentrated in the center of the circular waveguide, smaller reflection and better coupling to the fundamental free space Gaussian mode can be achieved for the windows. Two windows are designed for optimized performance through simulations for operation in two frequency ranges of 360– 400 GHz and 90–100 GHz. The simulated performance, practical constraints in realization and manufacturing methods of the 90–100 GHz window is discussed. This window was constructed and microwave properties measured showing a lower than -27 dB reflection. This result agrees with simulation data which validates the simulation methodology and effectiveness of the design.
TL;DR: In this paper, a superconductor-insulator-superconductor (SIS) mixers based on Nb/AlN/NbN twin tunnel junctions for waveguide receivers operating in a frequency range of 790-950 GHz are presented.
Abstract: We have designed, fabricated, and tested superconductor-insulator-superconductor (SIS) mixers based on Nb/AlN/NbN twin tunnel junctions for waveguide receivers operating in a frequency range of 790-950 GHz. Electromagnetic simulations and measurement results of the mixer performance are presented. The junctions have a high gap voltage of 3.15 mV and a high current density of about 30 kA/cm
2
, providing a wide receiver band, which was confirmed by Fourier transform spectrometer (FTS) and noise temperature measurements. The corrected receiver noise temperature varies from 240 K at low frequencies to 550 K at the high end of the band. The influence of the SIS junction heating on its characteristics has been studied and compared to another similar high current density technologies. The heating does not have a critical impact on the mixer performance.
TL;DR: In this article, an advanced image processing sequence is presented to perform nondestructive inspection from 3D terahertz (THz) images, which leads to 3D visualization and dimensional measurements.
Abstract: In this paper, we present an advanced image processing sequence to perform nondestructive inspection from 3-D terahertz (THz) images. We develop all the steps starting from a 3-D tomographic reconstruction of a sample from radiographs acquired with a monochromatic millimeter-wave imaging system to an automated segmentation, extracting the different volumes of interest (VOI) composing the sample. This leads to 3-D visualization and dimensional measurements. This inspection is completed by a skeletonization and caliber analysis providing an accurate assessment of the structure, geometry, and morphology of the acquired object. Overall sequence is implemented onto an unique software and validated through different sample analysis.
TL;DR: In this paper, a vector network analyzer was used with new numerical de-embedding and parameter inversion techniques to determine the relative permittivity (dielectric properties) of materials within the frequency range 750-1100 GHz.
Abstract: A simple system, based on a vector network analyzer, has been used with new numerical de-embedding and parameter inversion techniques to determine the relative permittivity (dielectric properties) of materials within the frequency range 750–1100 GHz. Free-space (noncontact), nondestructive testing has been performed on various planar dielectric and semiconducting samples. This system topology is well suited for quality control testing in an industrial setting requiring high throughput. Scattering parameters, measured in the absence of a sample, were used to computationally move the measurement plane to the surface of the samples being characterized. This de-embedding process can be completed much faster than a traditional calibration process and does not require exact knowledge of system geometric lengths. An iterative method was developed for simultaneously determining both sample geometric thickness and electric permittivity, through calculation of theoretical scattering parameters at material boundaries. A constrained nonlinear optimization process was employed to minimize the discrepancy between measured transmission and reflection data with this simulated data, in lieu of a closed-form parameter inversion algorithm. Monte Carlo simulations of parameter retrieval in the presence of artificial noise have demonstrated our method's robustness and superior noise rejection compared with a noniterative method. The precision of derived results has been improved by a factor of almost 50, compared to a closed-form extraction technique with identical input.
TL;DR: In this article, circuit models of transmission line elements and of a terahertz resonant tunneling diode (RTD) have been developed for a reliable design of RTD-based oscillator and detector circuits.
Abstract: Circuit models of transmission line elements and of a terahertz resonant tunneling diode (RTD) have been developed. The models allow for a reliable design of RTD-based oscillator and detector circuits. The transmission line elements have been modeled based on electromagnetic field simulations and dc measurements. Their accuracy has been verified through S-parameter measurements. The RTD has been modeled on the basis of dc and S-parameter measurements. The models have been used for the circuit design. A new circuit has been developed that can provide a load impedance that allows for high-output-power oscillators and high-sensitivity detectors. The circuit has been manufactured and measured as an oscillator and as a detector at frequencies around 300 GHz. An excellent agreement between measurement and simulation has been obtained, proving the accuracy of the developed models.
TL;DR: In this paper, a gas spectroscopy system with a TX and a receiver in SiGe BiCMOS technology with 300 GHz/500 GHz output power is demonstrated by measuring the high-resolution absorption spectrum of gaseous methanol.
Abstract: A 245-GHz transmitter (TX) array with an integrated antenna-array for a gas spectroscopy system has been realized. It consists of a push–push VCO with a 1/64 frequency divider, power amplifiers, frequency doublers, and on-chip antennas with localized backside etching. The TX-frequency is tunable in the range from 238 to 252 GHz. The TX-array has been fabricated in a 0.13- $\mu\hbox{m}$ SiGe:C BiCMOS technology with ${\rm f} _{\rm T} /{\rm f} _{\max}$ of 300 GHz/500 GHz. Its output power is approximately 7 dBm at 245 GHz, and the effective isotropically radiated power (EIRP) reaches 18 dBm at 245 GHz. The main components of the gas spectroscopy system are a TX and a receiver (RX) in SiGe BiCMOS as well as a gas absorption cell. The sensitivity of this spectroscopy system is demonstrated by measuring the high-resolution absorption spectrum of gaseous methanol ( $\hbox{CH}_{3}\hbox{OH}$ ). Due to the increased power provided by the TX-array, the sensitivity of the spectrometer can be increased significantly.
TL;DR: In this article, the design, fabrication, and measurements of reconfigurable terahertz (THz) filters using vanadium dioxide (VO2) phase-change material (PCM), which undergoes a transition between an insulator and metal phase at 68°C (∼341 K), are reported.
Abstract: We report the design, fabrication, and measurements of reconfigurable terahertz (THz) filters using vanadium dioxide (VO2) phase-change material (PCM), which undergoes a transition between an insulator and metal phase at 68 °C (∼341 K). The filters are made of frequency selective surfaces (FSS) and heater are integrated for VO2 excitation. Two THz spatial filters are developed. A broadband on/off filter at 0.35 THz is demonstrated with 20 dB change in transmission between the on and off states. Then, a reconfigurable stopband FSS filter with tunable rejection from 0.75 to 0.55 THz is presented. The latter shows a peak with rejection of more than 90%. The two states of both filters are achieved at relatively low temperature of 68 °C, making them suitable for practical applications. Comparisons between simulation and measurement show excellent agreement for both 0.35 THz on/off filter and 0.75 to 0.55 THz tunable filters.
TL;DR: In this article, a phase shifter using MEMS-reconfigurable surfaces to individually block/unblock the E-plane stubs from the micromachined waveguide is presented.
Abstract: This paper presents a submillimeter-wave 500–550-GHz MEMS-reconfigurable phase shifter, which is based on loading a micromachined rectangular waveguide with 9 E-plane stubs. The phase shifter uses MEMS-reconfigurable surfaces to individually block/unblock the E-plane stubs from the micromachined waveguide. Each MEMS-reconfigurable surface is designed so that in the nonblocking state, it allows the electromagnetic wave to pass freely through it into the stub, while in the blocking state, it serves as the roof of the main waveguide and blocks the wave propagation into the stub. The phase-shifter design comprises three micromachined chips that are mounted in the H-plane cuts of the rectangular waveguide. Experimental results of the first device prototypes show that the microelectromechanical system (MEMS)-reconfigurable phase shifter has a linear phase shift of 20 $\mathbf {^{\circ }}$ in ten discrete steps (3.3 bits). The measured insertion loss is better than 3 dB, of which only 0.5–1.5 dB is attributed to the MEMS surfaces and switched stubs, and the measured return loss is better than 15 dB in the design frequency band of 500–550 GHz. It is also shown that the major part of the insertion loss is attributed to misalignment and assembly uncertainties of the micromachined chips and the waveguide flanges, shown by simulations and reproducibility measurements. The MEMS-reconfigurable phase shifter is also operated in an analog tuning mode for high phase resolution. Furthermore, a detailed study has been carried out identifying the reason for the discrepancy between the simulated (90 $\mathbf {^{\circ }}$ ) and the measured (20 $\mathbf {^{\circ }}$ ) phase shift. Comb-drive actuators with spring constant variations between 2.13 and 8.71 N/m are used in the phase shifter design. An actuation voltage of 21.94 V with a reproducibility better than $\mathbf {\sigma }=$ 0.0503 V is measured for the actuator design with a spring constant of 2.13 N/m. Reliability measurement on this actuator was performed in an uncontrolled laboratory environment and showed no deterioration in the functioning of the actuator observed over one hundred million cycles.
TL;DR: In this article, a real human skin material parameter extraction based on terahertz (THz) time-domain spectroscopy in the band 0.1-2.5 was presented.
Abstract: This paper presents experimental study of real human skin material parameter extraction based on terahertz (THz) time-domain spectroscopy in the band 0.1–2.5 THz. Results in this paper show that electromagnetic properties of the human skin distinctively affect the path loss and noise temperature parameters of the communication link, which are vital for channel modeling of in-body nanonetworks. Refractive index and absorption coefficient values are evaluated for dermis layer of the human skin. Repeatability and consistency of the data are accounted for in the experimental investigation and the morphology of the skin tissue is verified using a standard optical microscope. Finally, the results of this paper are compared with the available work in the literature, which shows the effects of dehydration on the path loss and noise temperature. The measured parameters, i.e., the refractive index and absorption coefficient are 2.1 and 18.45 cm−1, respectively, at 1 THz for a real human skin, which are vital for developing and optimizing future in-body nanonetworks.
TL;DR: In this article, two THz reflectarray surfaces have been designed and fabricated in order to deflect a plane wave with any polarization and with a specific incident angle to three different specific directions each at distinct three frequencies of 0.7, 1.0 and 1.5 THz.
Abstract: In this paper, two THz reflectarray surfaces have been designed and fabricated in order to deflect a plane wave with any polarization and with a specific incident angle to three different specific directions each at distinct three frequencies of 0.7, 1.0 and 1.5 THz. The surface is composed of an array of 100 $\times$ 100 cells, each comprised of gold crosses and parasitic dipoles printed on thin grounded high resistivity silicon. Finite-element method (FEM) simulations are in line with the measurement results obtained using THz time-domain spectroscopy (THz TDS) showing the intended deflections for the two fabricated samples each with an arbitrary frequency-vs-deflection angle relationship. In addition, the use of silicon as the substrate paves the way for the integration of reconfigurable technologies which enhances the reflectarray versatility.
TL;DR: In this article, a new micro-bolometer array with a resonant cavity structure for a real-time terahertz (THz) camera is presented, along with a new method for evaluating the sensitivity across a wide range of the THz frequency region.
Abstract: Terahertz (THz) cameras comprising an uncooled micro-bolometer array have been developed for simple THz imaging, and the improvement of their sensitivity is one of the important issues. We fabricated a new micro-bolometer array with a resonant cavity structure for a real-time THz camera, alongside a new method for evaluating the sensitivity across a wide range of the THz frequency region. The frequency dependence of the sensitivity of the THz camera is measured in the 0.5–2.0-THz frequency range taking the polarization dependence into account. It was found that the resonant cavity structure effectively increased the sensitivity of the THz camera, and, actually, the improvement by one order of magnitude was achieved in the frequency range below 1 THz. The THz camera with much enhanced sensitivity will expand the frontiers of real-time THz imaging such as molecular imaging and nondestructive inspection.
TL;DR: In this paper, a fully integrated transmission line with simple structure that overcomes the long-standing bottleneck problems of high attenuation, strong dispersion, and low mode confinement in the guided-wave signal transmission from dc to terahertz (THz) is presented.
Abstract: Transmission lines or waveguides are the most fundamental building blocks of all electronic and photonic circuits and systems. Efforts have been made to incrementally evolve and improve existing transmission line structures to meet the increasingly stringent demands for signal transmission bandwidth and performance. However, a potentially revolutionary scheme or disruptive concept is required in support of future technological needs and bridging the gap between electronics and photonics. In this paper, we report on a fully integrated transmission line with simple structure that overcomes the long-standing bottleneck problems of high attenuation, strong dispersion, and low mode confinement in the guided-wave signal transmission from dc to terahertz (THz). This so-called mode-selective transmission line (MSTL) supports super-broadband and/or ultrafast pulse signal propagation, making it a disruptive solution for building future high-performance analog and digital integrated electronics and photonics. To demonstrate this scheme, an MSTL on fused silica substrate is designed, fabricated, and experimentally measured from near-dc to 0.5 THz, showing less than 0.35 dB/mm attenuation and low dispersion characteristics over the entire frequency range.
TL;DR: In this paper, the results of GOL-PET experiments on subterahertz (0.1 − 0.5 THz) emission from a magnetized plasma column during passing of a high-current $(\sim \hbox{10 kA})$ relativistic electron beam were described.
Abstract: This paper describes results of GOL-PET experiments on subterahertz (0.1–0.5 THz) emission from a magnetized plasma column during passing of a high-current $(\sim \hbox{10 kA})$ relativistic $(\sim \hbox{0.6 MeV})$ electron beam. The subterahertz radiation is generated in the plasma due to high-level turbulence induced by two-stream instability of the electron beam. These experiments are carried out at the specialized GOL-3T device. For the plasma density range 10 $^{14}\hbox{–10}^{15}~\hbox{cm}^{-3}$ , we have studied emission dynamics from the plasma column in its transverse and longitudinal directions. The spectral composition and polarization of the radiation was also investigated.
TL;DR: In this article, a hybrid measurement methodology was employed to investigate electric properties of thin conductive layers based on graphene nanoplatelets in the frequency band spanning from dc up to terahertz range.
Abstract: This paper describes results obtained using a hybrid measurement methodology employed to investigate electric properties of thin conductive layers based on graphene nanoplatelets in the frequency band spanning from dc up to terahertz range. As many as four different measurement methods were employed to cover the band of interest, including the terahertz time-domain spectroscopy and the Fourier-transform infrared spectroscopy besides resonator techniques applicable in the microwave band and the four-point dc technique. Raw measurement data obtained using these approaches were processed and based on the results a relationship between frequency and sheet resistance for various types of new graphene-based conductive layers was extracted. Eventually, several models that help to explain the observed behavior of each of the analyzed conductive inks were proposed.
TL;DR: In this article, a double bow-tie slot antenna is proposed to fill the gap between standard double-slot antennas and log periodic and sinuous antennas, with applications areas in radio astronomy and imaging systems.
Abstract: This paper presents millimeter-wave and terahertz double bow-tie slot antennas on a synthesized elliptical silicon lens. Two different antennas are designed to cover 0.1–0.3 and 0.2–0.6 THz, respectively. The double bow-tie slot antenna results in a wide impedance bandwidth and 78–97% Gaussian coupling efficiency over a 3:1 frequency range. A wideband coplanar-waveguide low-pass filter is designed using slow-wave techniques, and the measured filter response shows an S $_{21}$ < −25 dB over a 3:1 frequency range. Absolute gain measurements done at 100–300 GHz and 200–600 GHz confirm the wideband operation of this design. The double bow-tie slot antenna is intended to fill the gap between standard double-slot antennas and log periodic and sinuous antennas, with applications areas in radio astronomy and imaging systems.
TL;DR: In this paper, the authors used time-domain spectroscopy for the examination of sugar beet seeds, including an algorithm for automated classification of the seeds, and showed that the results showed that it is possible to distinguish proper and defective seeds.
Abstract: Sugar beet seeds have a comparably high rate of defective seeds of about 35%–40% which are discarded before dissemination in the field. The separation of proper and defective seeds is a complex and labor-intensive process. We show how THz time-domain spectroscopy can be used for the examination of the seeds including an algorithm for automated classification of the seeds.