Continuous Millimeter Wave Research Articles

Structural displacement estimation using accelerometer and FMCW millimeter wave radar

Structural displacement plays a crucial role in structural health monitoring. However, its measurement remains challenging for many civil infrastructure applications. This study proposes a structural displacement estimation technique that fuses measurements from a collocated accelerometer and frequency-modulated continuous-wave millimeter wave radar at displacement estimation location on a structure. Automated initial calibration was first performed using short-period (less than 1 min) radar and acceleration measurements. The best target is automatically selected from the surroundings, and a conversion factor to convert the line-of-sight displacement to the structural displacement in the actual vibration direction is automatically estimated for the target. After calibration, the displacement is estimated in real time from radar measurements using the selected best target and its estimated conversion factor. Note that an accelerometer-aided phase-unwrapping algorithm is proposed and applied to address the phase-wrapping issue when the structural displacement is larger than the radar wavelength. The radar-based displacement is further fused with the acceleration measurement using a finite impulse response filter to estimate the displacement with improved accuracy at the cost of a short time delay. Laboratory tests on a four-story building model and a field test on a pedestrian bridge were conducted to validate the proposed displacement estimation technique. The displacements estimated by the proposed technique had an error of less than 1 mm in both tests compared to the ground-truth displacements measured by laser-based displacement sensors.

Micro-motion Gesture Recognition Based on Multi-channel Frequency Modulated Continuous Wave Millimeter Wave Radar

A micro-motion gesture recognition method based on multi-channel Frequency Modulated Continuous Wave (FMCW) millimeter wave radar is proposed, and an optimal radar parameter design criterion for feature extraction of micro-motion gestures is presented. The time-frequency analysis process is performed on the radar echo reflected by the hand, and the range Doppler spectrum, the range spectrum, the Doppler spectrum and the horizontal direction angle spectrum of the target are estimated. Then the range-Doppler-time-map feature is designed, range-time-map feature, Doppler-time-map feature, horizontal-angle-time-map feature, and three-joint feature with fixed frame time length are used to characterize the 7 classes micro-motion gestures, respectively. And these gesture features are captured and aligned according to the difference in amplitude and speed of the gesture motion process. Then a five-layer lightweight convolutional neural network is designed to classify the gesture features. The experimental results show that, the range-Doppler-time-map feature designed in this paper characterizes the micro-motion gesture more accurately and has a better generalization ability for untrained test objects compared with other features.

Effect of 99 GHz continuous millimeter wave electro-magnetic radiation on E. coli viability and metabolic activity

Purpose: To investigate time exposure dependence of continuous millimeter wave (CW) 99 GHz radiation on Escherichia coli bacterial cell viability and metabolic activity.Materials and methods: Suspensions of E. coli bacterial cells with an optical density of OD660nm = 0.1 were used for viability tests and OD660nm = 1.0 for metabolic activity tests. These suspensions were exposed to 99 GHz CW electromagnetic radiation, generated by a Backward Wave Oscillator (BWO) tube base instrument with a horn antenna at the BWO exit, to obtain an almost ideal Gaussian beam. Calculations of the Gaussian beam show that a power of 0.2 mW/cm2 was obtained at the bacterial plane.Results: The experimental results show that 1 hour of exposure to 99 GHz CW electromagnetic radiation had no effect on E. coli viability and colony characterisation. In 19 h of radiation, the number of colonies forming units was half order of magnitude higher than the sham-exposed and the control. However, 19 h of exposure did not affect the E. coli metabolic activity.Conclusions: Exposure of E. coli to millimeter wave (MW) CW 99 GHz radiation for a short period did not affect the viability of E. coli bacterial cells. However, exposure for 19 h caused a slight proliferation but did not influence the metabolic activities of about 90 biochemical reactions that were examined. Hence, we assume that the slight proliferation (half order of magnitude) after 19 h of exposure dose not have a biological meaning.

Detection through a dielectric cover on an optical waveguide and the generation of 50- to 60-GHz continuous wave millimeter wave using optical technology for future optical-to-radio systems and ubiquitous communications

A 50- to 60-GHz continuous wave (cw) millimeter wave (MMW) is generated by applying optical technology for optical-to-radio systems and ubiquitous communications. The generated MMW signals are radiated in a millimeter waveguide and detected through a dielectric cover on optical waveguide. The spectral linewidth of the MMW signals is less than 1 kHz. The power of the MMW signal obtained through alumina on an optical waveguide is larger than that detected from a strip-waveguide beyond 7 dBm at 55 GHz.

Numerical modeling and dosimetry of the 35 mm Petri dish under 46 GHz millimeter wave exposure

Experimental studies on effects of millimeter wave (MMW) exposure on cells cultured in Petri dishes have attracted interest in recent decades. To improve the quantification of the biological responses toward the MMW energy, an accurate and precise MMW dosimetry is to be provided. By using the finite difference time domain (FDTD) method, the numerical dosimetry is performed for a typical 35 mm Petri dish under 46 GHz continuous MMW exposure from an irradiator of a specified power pattern. With the aim of building a precise model, the meniscus at the interface between the culture solution and the Petri dish sidewall is taken into account, followed by the modeling of smooth edges of the Petri dish. The trilinear interpolation is introduced to assist the FDTD method to obtain a more precise dosimetric assessment. The specific absorption rate (SAR) distributions in the cornea cells covered by culture solution in the Petri dish are calculated and compared to display the effects of using Petri dish models of various precision and the trilinear interpolation on dosimetry results. In addition, the SAR distribution in the cells is analyzed to study its homogeneity. The results indicate that the precise Petri dish model and the application of the trilinear interpolation are helpful in improving the precision of numerical dosimetry. It is also revealed that the inhomogeneity of the SAR distribution is well beyond neglect, which deserves cautious consideration in experiments investigating MMW effects on cells in vitro.

A continuous-wave millimeter wave generated from optical signals by applying optical technology for optical-to-radio systems

A 50-GHz continuous-wave millimeter wave was generated from optical signals by applying optical technology for optical-to-radio systems. The generated MMW signals were radiated in a millimeter waveguide and detected by a detector. The spectral linewidth of the MMW signals was less than 1 kHz, and the power fluctuation of the MMW was less than 1.5 dB over the 30–50-GHz range. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 122–123, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21099

Continuous-wave millimeter wave generation at 94 GHz in a lithium niobate nonlinear optical waveguide using modulated optical input

Continuous-wave millimeter wave signals are generated at 94 GHz in a LiNbO3 nonlinear optical waveguide. Optical light with two frequency components is introduced into an optical waveguide, and the generated millimeter waves are obtained from a terminal connected to the metallic traveling waveguide. The configuration is made with a LiNbO3 commercial phase modulator. The generated signals have square-law characteristics between the output and the input power. Experimentally obtained results show that the probable candidate of this physical mechanism is difference frequency generation in nonlinear optical materials.

MPACVD-diamond windows for high-power and long-pulse millimeter wave transmission

To satisfy the electrical, thermomechanical and nuclear requirements for continuous wave (CW) millimeter (mm)-wave vacuum windows for electron cyclotron heating in thermonuclear plasma fusion energy research, water-edge-cooled window assemblies using large synthesized diamond disks have been developed in Europe, Japan, Russia and the USA. The diamond employed in these studies has been manufactured predominantly at DeBeers Industrial Diamond Division (UK) Ltd. by microwave plasma assisted chemical vapor deposition (MPACVD) and consists of polycrystalline diamond disks with diameter and thickness up to 119 mm and 2.23 mm, respectively. Due to low mm-wave losses (tan δ=2–3×10 −5), outstanding thermal conductivity (≈1800 W/mK), good ultimate bending strength (400 MPa) and radiation insensitivity up to a neutron fluence of 10 20 n/m 2 (10 −5 dpa), water-edge-cooled MPACVD-diamond windows promise to provide a practical technical solution for the transmission of CW millimeter waves at power levels in excess of 1 MW. MPACVD-diamond gyrotron windows with a bakeout temperature of 450°C (Al-braze) have been tested up to 0.55 MW, 10 s at 110 GHz (CPI, Palo Alto, USA) and 0.45 MW, 8 s at 170 GHz (JAERI/FZK, Naka, Japan). A thermally matched ceramic graded seal prototype 75-mm diameter window mounting which is bakeable to 550°C was developed successfully by DeBeers. The present paper reviews the development status and future prospects of this novel application of MPACVD diamond.

Chemical vapor deposition diamond window for high-power and long pulse millimeter wave transmission

To satisfy the electrical and thermomechanical requirements for a continuous wave millimeter wave beam transmission, a window assembly using a large size synthesized diamond disk has been developed. Such window systems are needed as a vacuum barrier and tritium shielding in future electron cyclotron heating systems for fusion plasma heating and noninductive electron cyclotron current drive. The diamond used in this study was manufactured by chemical vapor deposition (CVD) and consists of a polycrystalline diamond disk 96 mm in diameter and 2.23 mm thick. The disk was built into an assembly in which two Inconel tubes were bonded on both sides of the plate to provide vacuum shielding and water cooling to the edge of the disk, leaving an effective window aperture of 83 mm. It will be shown that, as a result of the high thermal conductivity and low dielectric loss exhibited by this grade of CVD diamond, the temperature increase of the window due to the absorption of high-power millimeter wave radiation could be minimized by simple water edge cooling at room temperature. During transmission of a focused Gaussian beam of 170 GHz, 110 kW, 10 s, the temperature increase at the center of the window reached a steady state condition at a value of approximately 40 K, in good agreement with calculated values. Water-edge-cooled CVD diamond windows promise to provide a practical technical solution for the transmission of continuous millimeter wave transmission in excess of 1 MW.

A forced gas-cooled single-disk window using silicon nitride composite for high power CW millimeter waves

Silicon nitride composite as a candidate of a window material for high power CW (Continuous Wave) millimeter-waves was high power tested especially with a surface cooling by impinging gas nitrogen jets on the single-disk surface. Gas-cooling dramatically suppressed the temperature of the window disk even with gas flow rate of around 100 l/min. With gas cooling of 465l/min., 130kW CW power of HE11 mode could be transmitted through the silicon nitride window with a diameter of 88.9mm. The peak window temperature was completely saturated on 123.6 °C. Without gas-cooling it did not saturate and reached 323 °C during 30 seconds pulse. A possibility of 1MW CW single disk Brewster windows with a forced gas-cooling is discussed, resulting in convinced prospects of the windows with realistic size and thickness.

A 1-MW, 1-mm continuous-wave FELtron for toroidal plasma heating

A powerful, continuous-wave millimeter radiation source is presented. An electrostatic Cockcroft-Walton accelerator (2.5 MV) drives an FEL (free-electron laser) of 1 MW power. The accelerator has a new design in order to obtain a very powerful (50 MW) electron beam and very small ripple. A recovery system is used to increase RF power and efficiency. The FEL oscillator is 1.5-m long, with a permanent magnet helical wiggler. The cavity is equipped with Bragg mirrors. The FEL is set at the high voltage terminal.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>