Millimeter-wave Interferometry Research Articles

Characterizing Lossy Dielectric Materials in Shock Physics by Millimeter-Wave Interferometry Using One-Dimensional Convolutional Neural Networks and Nonlinear Optimization

When a dielectric material undergoes mechanical impact, it generates a shock wave, causing changes in its refractive index. Recent demonstrations have proven that the modified refractive index can be determined remotely using a millimeter-wave interferometer. However, these demonstrations are based on the resolution of an inverse electromagnetic problem, which assumes that the losses in the material are negligible. This restrictive assumption is overcome in this article, in which a new approach is proposed to solve the inverse electromagnetic problem in lossy and shocked dielectric materials. Our methodology combines a one-dimensional convolutional neural network architecture, namely Inverse problem of Lossless or Lossy Shocked Wavefront Network (ILSW-Net), with a nonlinear optimization technique based on the Nelder–Mead algorithm to estimate losses within dielectric materials under a mechanical impact. Experimental results for both simulated and real signals show that our method can successfully predict the velocities and the refractive index while accurately estimating the shock wavefront.

Large Displacement Motion Interferometry With Modified Differentiate and Cross-Multiply Technique

Millimeter-wave radar interferometry is superior in detecting small displacement motions owing to its short wavelength. However, it is subject to phase ambiguity as the target displacement may often exceed a quarter wavelength. In this article, a modified differentiate and cross-multiply (MDACM) technique is proposed to tackle the phase ambiguity issue for accurate reconstruction of the phase history in millimeter-wave interferometry. In addition, to resolve the imperfections of the interferometric radar system, an MDACM-based integral phase reconstruction approach is presented, which seamlessly integrates alternating current (ac)-coupling-induced distortion correction, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I/Q$ </tex-math></inline-formula> mismatch correction, and direct current (dc) offsets’ calibration. Without causing any phase ambiguity, the proposed technique acts as a black box to take in the raw <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I/Q$ </tex-math></inline-formula> signals and correct all the hardware imperfections, and it outputs the desired displacement motions with micrometer accuracy. The simulation results show that the proposed technique can not only linearly recover the displacement motions across a wide range in different noise conditions without any phase ambiguity but also improve the stability by 11 times under ac-coupling-induced distortion. With a custom-designed 120-GHz interferometric radar sensor, experiments were carried out to validate various scenarios including mechanical vibrations and gesture sensing. The experimental results show that the proposed technique can accurately track not only deep subwavelength motion of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~\mu \text{m}$ </tex-math></inline-formula> but also multiwavelength displacement of >40 times of the wavelength at 120 GHz.

W -Band Vibrometer for Noncontact Thermoacoustic Imaging.

Noncontact thermoacoustic imaging (TAI) has several desirable characteristics for applications such as explosive detection in high-water-content media. In this letter, we report a detection technique using millimeter-wave interferometry based on sensitive phase detection at W -band. The displacement sensitivity of the proposed W -band vibrometer at 95 GHz is of the order of 1 nm. We also analyze the effect of phase noise on the sensitivity of the vibrometer. Unlike laser-based sensors, a W -band sensor has several advantages; it can easily penetrate surface obscurants such as fur or cloth and it does not require a highly reflective surface of the target to detect the thermoacoustic vibrations.

Millimeter-wave interferometry and far-forward scattering for density fluctuation measurements on LTX-β.

The λ ≈ 1 mm (f = 288 GHz) interferometer for the Lithium Tokamak Experiment-β (LTX-β) will use a chirped-frequency source and a centerstack-mounted retro-reflector mirror to provide electron line density measurements along a single radial chord at the midplane. The interferometer is unique in the use of a single source (narrow-band chirped-frequency interferometry) and a single beam splitter for separating and recombining the probe and reference beams. The current work provides a documentation of the interferometry hardware and evaluates the capabilities of the system as a far-forward collective scattering diagnostic. As such, the current optical setup is estimated to have a detection range of 0.4 ≲ k ⊥ ≲ 1.7 cm-1, while an improved layout will extend the upper k ⊥ limit to ∼3 cm-1. Measurements with the diagnostic on LTX are presented, showing interferometry results and scattered signal data. These diagnostics are expected to provide routine measurements on LTX-β for high frequency coherent density oscillations (e.g., Alfvénic modes during neutral beam injection) as well as for broadband turbulence.

IRC +10 216 in 3-D: morphology of a TP-AGB star envelope.

During their late pulsating phase, AGB stars expel most of their mass in the form of massive dusty envelopes, an event that largely controls the composition of interstellar matter. The envelopes, however, are distant and opaque to visible and NIR radiation: their structure remains poorly known and the mass-loss process poorly understood. Millimeter-wave interferometry, which combines the advantages of longer wavelength, high angular resolution and very high spectral resolution is the optimal investigative tool for this purpose. Mm waves pass through dust with almost no attenuation. Their spectrum is rich in molecular lines and hosts the fundamental lines of the ubiquitous CO molecule, allowing a tomographic reconstruction of the envelope structure. The circumstellar envelope IRC +10 216 and its central star, the C-rich TP-AGB star closest to the Sun, are the best objects for such an investigation. Two years ago, we reported the first detailed study of the CO(2-1) line emission in that envelope, made with the IRAM 30-m telescope. It revealed a series of dense gas shells, expanding at a uniform radial velocity. The limited resolution of the telescope (HPBW 11″) did not allow us to resolve the shell structure. We now report much higher angular resolution observations of CO(2-1), CO(1-0), CN(2-1) and C4H(24-23) made with the SMA, PdB and ALMA interferometers (with synthesized half-power beamwidths of 3″, 1″ and 0.3″, respectively). Although the envelope appears much more intricate at high resolution than with an 11″ beam, its prevailing structure remains a pattern of thin, nearly concentric shells. The average separation between the brightest CO shells is 16″ in the outer envelope, where it appears remarkably constant. Closer to the star (< 40″), the shell pattern is denser and less regular, showing intermediary arcs. Outside the small (r < 0.3″) dust formation zone, the gas appears to expand radially at a constant velocity, 14.5 km s-1, with small turbulent motions. Based on that property, we have reconstructed the 3-D structure of the outer envelope and have derived the gas temperature and density radial profiles in the inner (r < 25″) envelope. The shell-intershell density contrast is found to be typically 3. The over-dense shells have spherical or slightly oblate shapes and typically extend over a few steradians, implying isotropic mass loss. The regular spacing of shells in the outer envelope supports the model of a binary star system with a period of 700 years and a near face-on elliptical orbit. The companion fly-by triggers enhanced episodes of mass loss near periastron. The densification of the shell pattern observed in the central part of the envelope suggests a more complex scenario for the last few thousand years.

SIGNATURES OF GRAVITATIONAL INSTABILITY IN RESOLVED IMAGES OF PROTOSTELLAR DISKS

ABSTRACT Protostellar (class 0/I) disks, which have masses comparable to those of their nascent host stars and are fed continuously from their natal infalling envelopes, are prone to gravitational instability (GI). Motivated by advances in near-infrared (NIR) adaptive optics imaging and millimeter-wave interferometry, we explore the observational signatures of GI in disks using hydrodynamical and Monte Carlo radiative transfer simulations to synthesize NIR scattered light images and millimeter dust continuum maps. Spiral arms induced by GI, located at disk radii of hundreds of astronomical units, are local overdensities and have their photospheres displaced to higher altitudes above the disk midplane; therefore, arms scatter more NIR light from their central stars than inter-arm regions, and are detectable at distances up to 1 kpc by Gemini/GPI, VLT/SPHERE, and Subaru/HiCIAO/SCExAO. In contrast, collapsed clumps formed by disk fragmentation have such strong local gravitational fields that their scattering photospheres are at lower altitudes; such fragments appear fainter than their surroundings in NIR scattered light. Spiral arms and streamers recently imaged in four FU Ori systems at NIR wavelengths resemble GI-induced structures and support the interpretation that FUors are gravitationally unstable protostellar disks. At millimeter wavelengths, both spirals and clumps appear brighter in thermal emission than the ambient disk and can be detected by ALMA at distances up to 0.4 kpc with one hour integration times at ∼0.″1 resolution. Collapsed fragments having masses ≳1 M J can be detected by ALMA within ∼10 minutes.

Remote sensing of patterns of cardiac activity on an ambulatory subject using millimeter-wave interferometry and statistical methods

Using a 94-GHz millimeter-wave interferometer, we are able to calculate the relative displacement of an object. When aimed at the chest of a human subject, we measure the minute motions of the chest due to cardiac activity. After processing the data using a wavelet multiresolution decomposition, we are able to obtain a signal with peaks at heartbeat temporal locations. In order for these heartbeat temporal locations to be accurate, the reflected signal must not be very noisy. Since there is noise in all but the most ideal conditions, we created a statistical algorithm in order to compensate for unconfident temporal locations as computed by the wavelet transform. By analyzing the statistics of the peak locations, we fill in missing heartbeat temporal locations and eliminate superfluous ones. Along with this, we adapt the processing procedure to the current signal, as opposed to using the same method for all signals. With this method, we are able to find the heart rate of ambulatory subjects without any physical contact.

Kinematics of the inner thousand AU region around the young massive star AFGL 2591–VLA3: a massive disk candidate?

[Context] Recent detections of disks around young high-mass stars support the idea of massive star formation through accretion rather than coalescence, but the detailed kinematics in the equatorial region of the disk candidates is not well known, which limits our understanding of the accretion process. [Aims] This paper explores the kinematics of the gas around a young massive star with millimeter-wave interferometry to improve our understanding of the formation of massive stars though accretion. [Methods] We use Plateau de Bure interferometric images to probe the environment of the nearby (~1 kpc) and luminous (~20000 Lsun) high-mass (10-16 Msun) young star AFGL 2591-VLA3 in continuum and in lines of HDO, H218O and SO2 in the 115 and 230 GHz bands. Radiative transfer calculations are employed to investigate the kinematics of the source. [Results] At ~0.5" (500 AU) resolution, the line images clearly resolve the velocity field of the central compact source (diameter of ~ 800 AU) and show linear velocity gradients in the northeast-southwest direction. Judging from the disk-outflow geometry, the observed velocity gradient results from rotation and radial expansion in the equatorial region of VLA3. Radiative transfer calculations suggest that the velocity field is consistent with sub-Keplerian rotation plus Hubble-law like expansion. The line profiles of the observed molecules suggest a layered structure, with HDO emission arising from the disk mid-plane, H218O from the warm mid-layer, and SO2 from the upper disk. [Conclusions] We propose AFGL 2591-VLA3 as a new massive disk candidate, with peculiar kinematics. The rotation of this disk is sub-Keplerian, probably due to magnetic braking, while the stellar wind may be responsible for the expansion of the disk. The expansion motion [...]

Remote Sensing of Heart Rate and Patterns of Respiration on a Stationary Subject Using 94-GHz Millimeter-Wave Interferometry

Using continuous wave, 94-GHz millimeter-wave interferometry, a signal representing chest wall motion can be obtained that contains both the heart rate and respiration patterns of a human subject. These components have to be separated from each other in the received signal. Our method was to use the quadrature and in-phase components of the signal, after removing the mean of each, to find the phase, unwrap it, and convert it to a displacement measurement. Using this, the power spectrum was examined for peaks, which corresponded to the heart rate and respiration rate. The displacement waveform of the chest was also analyzed for discrete heartbeats using a novel wavelet decomposition technique.

Characterization of Laser Produced Tetrakis (Dimethylamino) Ethylene Plasma in a High-Pressure Background Gas

We present an interferometric and spectroscopic characterization of ultraviolet (UV) laser photoionization of a low ionization potential organic vapor, tetrakis (dimethylamino) ethylene (TMAE), seeded in high-pressure air component gases. These experiments are performed to explore the feasibility of using an electrodeless UV laser preionization of TMAE to initiate a plasma seeded in atmospheric pressure gases that can later be sustained by radiofrequency (RF) power by inductive wave coupling, thereby reducing the initiation RF power budget. A large volume (500 cc), high-density (/spl sim/10/sup 13/cm/sup -3/), electrodeless plasma is created by single-photon, 193 nm excimer laser ionization. 105 GHz millimeter-wave interferometry along with optical spectroscopy is employed to investigate the plasma formation and decay characteristics. The TMAE plasma decay mechanisms including two-body and three-body recombination with and without high pressure gases are examined and the dominant loss processes discussed and evaluated. Both density and optical emission measurements show a delay of 140 /spl plusmn/ 10 ns in the peak plasma density and emission indicating that the dominant ionization process is delayed ionization via excitation of super-excited states. The experiment also shows that TMAE remains a viable seed gas for UV ionization in the presence of air for t/spl les/10 min.

A displacement measurement technique using millimeter-wave interferometry

A displacement measurement sensor, capable of sub-millimeter resolution, using millimeter-wave interferometry has been developed. The sensor operates at 37.6 GHz and is realized using both microwave integrated circuits and monolithic microwave integrated circuits. It has been used to accurately measure the displacement of metal plate location and water level. A resolution of only 0.05 mm is achieved. A maximum error of 0.3 mm is also attained without correction for the nonlinearity of the phase-detection processor and agrees well with the theoretical calculation.

Перспективы развития радиоинтерферометрии миллиметрового диапазона волн

Перспективы развития радиоинтерферометрии миллиметрового диапазона волн

Gas and Dust in Ultraluminous Galactic Nuclei

Millimeter-wave interferometry has clearly shown the existence of enormous masses (109 – 1010M⊙) of molecular gas concentrated in the nuclear regions (R &lt; 500 pc) of many luminous and ultraluminous infrared galaxies. In these systems, molecular gas is an obvious source of fuel for nuclear starbursts and active galactic nuclei (AGN). In several ultraluminous systems (e.g., Arp 220 and Mrk 231), there now exists CO (2-1) interferometry at ≤ 1″ resolution which reveals for the first time extremely dense, gaseous accretion disks on the scale 50-300 pc. Based on the low velocity dispersion of the molecular gas in the nuclear disks, we believe them to be extremely thin (10-50 pc). In addition, high brightness temperatures in the CO lines (10-20 K) imply that these disks are nearly uniformly filled with a continuous gas distribution, rather than being relatively isolated, self-gravitating GMCs. Although the gas is ‘uniformly’ distributed, the gas densities must be high, &gt; 104 cm−3. When viewed near the plane of the disk, the central AGNs, if they exist, will be totally obscured at optical and near infrared wavelengths. In Mrk 231, our line of sight is probably within 60° of the disk axis, but in Arp 220 the disk is closer to edge-on. In fact, recent near infrared imaging of Arp 220 with the NICMOS camera on the HST reveals totally opaque dust disks embedded within the central star clusters of both nuclei.

5.1. Molecular gas in luminous galactic nuclei

In the last five years, millimeter-wave interferometry has clearly shown the existence of enormous masses (109–1010 M⊙) of molecular gas concentrated in the nuclear regions (R &lt; 500 pc) of many luminous and ultra-luminous infrared galaxies. In these systems, molecular gas is an obvious source of fuel for nuclear starbursts and active galactic nuclei (AGN). For nearer, lower-luminosity systems there exists less systematic characterization of either the properties or the structure of the nuclear gas. Here we review recent results on the molecular gas in the nuclei of two near, lower-luminosity systems (M51 and NGC 1068) and contrast these results with those for the best studied ultra-luminous IRAS galaxy, Arp 220. For all three galaxies, there now exists CO(2–1) interferometry at high resolution which reveals, for the first time, disks of extremely dense, highly excited gas on scales of 50-300 pc. These structures vary in their levels of axisymmetry, thickness, and clumpiness. However, they share the ability to extinguish optical and near-infrared emission from active or stellar nuclei and perhaps to collimate radio jets and ionized outflows. Within the nuclear regions of these three galaxies, the molecular gas constitutes 10-50% of the total mass, with the most luminous systems having the highest gas mass-fractions.

Broadband superheterodyne tracking circuits for millimeter-wave measurements

Superheterodyne stimulus-response measurements can be made with high dynamic range, but are often sensitive to oscillator frequency drift and noise. The usual techniques for reducing this sensitivity often become impractical at millimeter-wave frequencies and above. This paper describes a feedforward tracking technique and its application to single frequency millimeter-wave interferometry and Doppler-shift scattering measurements on tokamak plasmas. Swept frequency transmission measurements can also be made with high dynamic range using this technique.

An 8-mm interferometer for solar radio astronomy at Bordeaux, France

A small two-antenna interferometer working at a wavelength of 8 mm, with a baseline of 64 m is now completed at the Observatory in Bordeaux. The new instrument is designed for solar studies and for experimentation in millimeter-wave interferometry. The main characteristics are given with some details on techniques used, in particular for local-oscillator (LO) transmission and phase stability, and for antenna drive and encoding systems.