Spl Deg Research Articles

Polarization characteristics of metallized polypropylene film capacitors at different temperatures

When the metallized polypropylene film capacitor (MPPFC) is used under high electric field in pulsed power systems, an obvious voltage decay phenomenon will occur. The voltage decay is mainly resulted from the relaxation polarization in dielectric applied under high electric field. This paper focuses on the relaxation polarization in metallized biaxially oriented polypropylene (BOPP) film capacitors. The extended Debye model of relaxation polarization is discussed and the parameters of each RC branch are obtained. Meanwhile, the relationship between the increasing proportion of polarization charge (ΔQa/Qh) and temperature is investigated. The experimental results show that under 1kV, ΔQa/Qh varies from 0.018 to 6.868 with the temperature varing from 10 to 70 /spl deg. Moreover, the equivalent capacitance of capacitors in frequency domain is analyzed with consideration of slow polarization. The analysis shows that both a lower frequency and a higher temperature can accelerate the relaxation polarization and increase the voltage decay. Based on the extended Debye model developed from the polarization charge test, the voltage drop is calculated and the results can match well with those of the voltage maintaining test.

High-temperature (>500/spl deg C) ultrasonic transducers: an experimental comparison among three candidate piezoelectric materials

High-temperature piezoelectric crystals, including YCa4O(BO3)3, LiNbO3, and AlN, have been studied for use in ultrasonic transducers under continuous operation for 55 h at 550°C. Additionally, thermal ratcheting tests were performed on the transducers by subjecting the crystals to heat treatments followed by ultrasonic performance testing at room temperature and 500°C. The changes resulting from the heat treatments were less than the statistical spread obtained in repeated experiments and were thus considered negligible. Finally, in situ measurements of the pulse-echo response of YCa4O(BO3)3 were performed at temperatures up to 950°C for the first time, showing stable characteristics up to these high temperatures.

Investigations on the polarimetric behavior of a target near the soil

The polarimetric behavior of the diffracted field from an object located close to the ground is investigated for a varying incidence angle. Here, the field is described by the geometrical theory of diffraction in accordance to its asymptotic formulas (k/spl rarr//spl infin/). As a result, a ray system composed of 13 different rays was implemented for the monostatic case by applying the principle of Fermat. The different spatial and creeping waves give a physical insight in the mechanisms involved in the entire scattering process. By varying the angle from perpendicular to grazing incidence 0/spl deg/-90/spl deg/, geometrical surface shadow boundaries are present for the backscattered field. At such boundaries, the spatial waves are replaced by their corresponding creeping waves, leading to a strong attenuation. The diffracted field for look angles related to the transition zones has a characteristic polarimetric behavior, which can be represented on the Poincare sphere. The typical locations on the sphere can be exploited to get information about the geometrical parameters of the target and its height above the ground.

Analysis of sensor platform dynamics in ground vehicle

A vehicular platform's dynamical behavior is analyzed as a basis for designing a laboratory test apparatus and an associated 2-dimensional orthogonal stabilizer. The test track caused inclination in the front direction to vary from -6.5/spl deg/ to 7.2/spl deg/ and from -5.5/spl deg/ to 5.0/spl deg/ in the side direction. The maximum angular rate was 19.8 /spl plusmn/ 0.1/spl deg//s in the front direction within a bandwidth of 0-2.5 Hz and 14.4 /spl plusmn/ 0.05/spl deg//s in the side direction. The platform's natural frequency in the front direction was found to be 0.8-1.0 Hz. In the side direction the most significant rate values appeared within 0-4 Hz but the natural frequency did not wake. Inclination measurements were based on sensor fusion where the basic model of stochastic Kalman filtering was applied.

Performance of a raster scanning laser display system using diamond shaped frame supported micromirror

We describe the design, fabrication, and experimental results of a raster scanning laser display system using micromachined electrostatic scanning micromirror. The micromirror is comprised of a diaphragm mirror plate supported by an array of diamond shaped support frame, and movable comb electrodes. A prototype raster scanning laser display system using the fabricated micromirror, having optical scan angle of 16.9/spl deg/ at resonance frequency of 19.55 kHz, as the horizontal scanner was developed and tested. To compensate for the nonlinear characteristics of the scanner, a simple image correction method was developed, and the projected image was analyzed and compared with the simulation results.

Design and Characterization of an Electrothermally Driven Monolithic Long-Stretch Microdrive in Compact Arrangement

An electrothermally driven long stretch microdrive (LSMD) is presented for planar rectilinear motions in hundreds of micrometers. Design concept is based on connecting several actuation units in series to form a cascaded structure to accumulate relative displacement of each unit, and two cascaded structures are further arranged in parallel by a connection bar to double output force. The proposed area-saving design features monolithic compliant structure in compact arrangement to achieve long stroke. In experiments, the maximum reversible operating voltage is 3 V. In addition, the voltage-displacement relation shows good linearity within /spl plusmn/5% in 0.5-3.0 V. Fabricated nickel LSMD can generate displacement up to 215 /spl mu/m (W=8 /spl mu/m, /spl theta/=0.2/spl deg/, D=34 /spl mu/m) at 3 dc volts (669 mW). The maximum operation temperatures of tested LSMDs at 3 V are below 300 /spl deg/C. Output forces up to 495 /spl mu/N are measured by in situ passive micromechanical test beams. The LSMD can be operated at 100 Hz without degradation on displacement. Two geometrical design parameters, bent angle and constraint bar width, are also investigated analytically and experimentally.

Photonic RF phase shifter and tunable photonic RF notch filter

A new photonic RF phase shifter structure for phased array antennas is presented. It is based on a single dual-output modulator and two optical switches and optical attenuators. This can realize continuous phase shifting of 0/spl deg/-360/spl deg/ without altering the signal amplitude. It has the advantages of wide bandwidth, fast response time, and fine tuning resolution. Experimental results demonstrate phase shifts over a 360/spl deg/ phase range, with RF signal power changes of less than 0.2 dB, which is in close agreement with predictions. A tunable photonic RF notch filter, which is based on the new phase shifter, is also presented. Experimental results demonstrate continuous tuning of the photonic notch filter over a wide tuning range, which covers the full free spectral range, which is in good agreement with predictions.

Arbitrarily dual-band components using simplified structures of conventional CRLH TLs

Microwave components with nonlinear phase responses are developed using a simplified composite right/left-handed (CRLH) transmission-line (TL) structure without the series capacitance or the shunt inductance. Using such a simplified CRLH structure, arbitrarily dual-band microstrip components have been realized in compact sizes such as a quarter-wavelength short-circuited stub and dual- band branch-line couplers. Simulation and measurement results are given to demonstrate the efficiency and good performance of the proposed components. For the quarter- wavelength short-circuited stub based on the simplified CRLH-TL structure without the series capacitance, it has been shown that the insertion loss is less than -0.1dB. For the arbitrarily dual-band branch-line coupler, experiment results exhibit that S/sub 21/ and S/sub 31/ are larger than -3.6dB, the isolations are smaller than -30dB, the return losses are smaller than -20dB, and the phase differences are within 90/spl deg//spl plusmn/1.8/spl deg/.

Composite right/left-handed transmission line metamaterial phase shifters (MPS) in MMIC technology

This paper presents the modeling and design of one-dimensional metamaterial phase shifters (MPSs) in monolithic-microwave integrated-circuit technology based on the composite right/left-handed transmission-line approach. From a theoretical point-of-view, we show that existing design expressions are restricted to phase shifters behaving as effective media, which is the case only if sufficiently large L and C loading elements can be designed in the given technology and at the frequency of interest. Therefore, we propose new design expressions, which are exact on the basis of the circuit model of a unit cell in the structure. We show that the new expressions must be used to design integrated MPSs and the theory is verified by means of measurements of one- and two-cell phase shifters exhibiting a 0/spl deg/ phase shift at 17.5GHz. The designed one-cell phase shifter provides a -10-dB input return-loss bandwidth larger than 10% with phase shifts of +29/spl deg/ and -30/spl deg/ at 16.5 and 18.5 GHz, respectively. The insertion loss is -1.3 dB at the center frequency and -1.7 dB at the limit of the bandwidth.

Testing of “Venetian-Blind” Silicon Microstructures With Optical Methods

In this paper, we illustrate the design and testing of new silicon microstructures, fabricated by means of a conventional planar process. These Venetian-blind structures consist of arrays of narrow, rectangular suspended masses (width =31 /spl mu/m, length =400 /spl mu/m, thickness =15 /spl mu/m), which can be tilted using electrostatic actuation. Characterization of their static and dynamic behavior was performed with optical methods. The diffraction patterns in monochromatic light were analyzed and vibration measurements were performed by means of semiconductor laser feedback interferometry: experimental data on the tilt angle as a function of the applied voltage and on the resonance frequencies are reported. A maximum tilt angle of approximately 1.9/spl deg/ was obtained with a driving voltage in the range of 70-95 V. All the tested devices showed resonance frequencies higher than 80 kHz, which is fast enough (i.e., switching time in the millisecond range) for future use in optical interconnections. Numerical analyses were performed to evaluate the coupled electromechanical behavior of the microstructures, confirming the observed experimental behavior.

A PCB-compatible 3-dB coupler using microstrip-to-CPW via-hole transitions

A 3-dB coupler by implementing microstrip-to-coplanar waveguide (CPW) via-hole transitions is proposed. The proposed coupler, with the advantages of wider coupled line widths and spacing without using any bonding wires, can eliminate the uncertain factors of conventional Lange couplers caused by the printed circuit board (PCB) manufacturing processes. The proposed coupler can be easily fabricated on a single-layer PCB substrate instead of using multilayer substrates. Good agreements between the simulation and the measurement in the frequency range from 0.45 to 5 GHz can be achieved. The measured results at the center frequency of 2.4 GHz have the return loss better than -15dB; the insertion loss of coupled and direct ports is about 3/spl plusmn/ 0.2dB and the relative phase difference of 89/spl plusmn/0.3/spl deg/. The dimension of the coupler is 3.1cm /spl times/ 1.8cm.

Estimating lateral straggling of boron profiles ion implanted into crystalline silicon with a tilt angle of 0/spl deg/ using off-angle substrates

Boron was ion implanted into /spl theta//spl deg/ off-angle crystalline silicon substrates with a tilt angle of /spl theta//spl deg/. It is assumed that the B profiles along the ion-beam direction are identical, enabling the lateral straggling of B ion implanted with a tilt angle of 0/spl deg/ to be evaluated experimentally for the first time. The measurements show that the lateral straggling of channeling ions is small.

Design and field-of-view calibration of 114-660-GHz optics of the Earth observing system microwave limb sounder

This paper describes the optics design and field-of-view (FOV) calibration for five radiometers covering 114-660 GHz which share a common antenna in the Microwave Limb Sounder instrument on the National Aeronautics and Space Administration's Aura satellite. Details of near-field pattern measurements are presented. Estimated systematic scaling uncertainties (3/spl sigma/) on calibrated limb emissions, due to FOV calibration uncertainties, are below 0.4%. 3/spl sigma/ uncertainties in beamwidth and relative pointing of radiometer boresights are 0.006/spl deg/ and 0.003/spl deg/, respectively. The uncertainty in modeled instrument response, due to the scan dependence of FOV patterns, is less than /spl plusmn/0.24 K equivalent black-body temperature. Refinements to the calibration using in-flight data are presented.

Single-mode blue-violet laser diodes with low beam divergence and high COD level

We demonstrate GaN-based high-power single transverse-mode laser diodes (LDs) emitting at 405 nm. LD structures are designed to exhibit a high level of catastrophic optical damage and small beam divergence angle. By the control of refractive index profiles, we achieved a vertical beam divergence angle of as low as 17.5/spl deg/ and maximum output power of as high as 470 mW under continuous-wave operation condition. In addition, nearly fundamental transverse-mode operation is demonstrated up to 500-mW pulsed output power by far-field investigation.

V-band CPW 3-dB Tandem coupler using air-bridge structure

We present a uniplanar coplanar waveguide 3-dB tandem coupler operating at V-band frequencies. The uniplanar structure is monolithically fabricated by using two-section parallel-coupled lines and air-bridge crossovers replacing the conventional multilayer or the bonded structures. Due to an optimized tandem structure and nonbonded crossovers minimizing the parasitic components, a maximum coupling of 2.5dB is measured at 62GHz with a 2-dB bandwidth of 83%, while a high directivity factor of 33dB is simultaneously obtained at 58-62GHz. Over the entire design frequency range of 30-90GHz, we achieve good phase unbalance of 90/spl plusmn/6.0/spl deg/, return loss, and isolation lower than -23 and -16dB, respectively.

Vibration of micromachined circular piezoelectric diaphragms

Electrically and mechanically excited resonances in micromachined circular piezoelectric diaphragms have been investigated. The diaphragm structures were piezoelectric unimorphs consisting of Pb(Zr0.52,Ti0.48)O3 (PZT) films and thermally grown silicon oxide (SiO2) layers. For electrical excitation, ring-shaped interdigitated (IDT) electrodes formed on the top of the PZT layer were used to induce strain in the diaphragms. The diaphragm structures behaved much like circular membranes in which the membrane tension was approximately 206 N/m, at the fundamental modes. For higher modes, the resonance frequencies deviated from the theoretical values due to the finite stiffness of the diaphragms. Under mechanical drive, both symmetric and asymmetric modes were excited. However, for electrical excitation, the symmetric modes were dominant due to the symmetry of the driving IDT electrodes. At a pressure of 727 Torr, the quality factor was approximately 250, and this rose to 2000 at pressures below 1 Torr. When a forward bias was applied to the diaphragm, the membrane tension decreased, but under reverse biases the tension increased. However, because of repoling under reverse biases greater than the coercive field of the PZT film, the achievable increase in the membrane tension was limited. In the diaphragm structure, the nonlinear vibration was governed by geometric nonlinearity rather than material nonlinearity. In addition, evidence of non-180 degrees domain wall motion of the PZT layer in released diaphragms was observed.

Single Ping-multiple measurements: sonar bearing angle estimation using spatiotemporal frequency filters

Presented is a mixed-signal full-custom VLSI chip designed to receive sonar return signals from an ultrasonic microphone array, and extract input bearing angles of the incoming signals. Processing utilizes simple low-power analog spatiotemporal bandpass filters to extract wavefront velocity across the array, which translates to input bearing angle. Processing uses phase information of array signals, not onset or offset of ultrasonic burst. With such synchronous processing, multiple angle readings from different returns of the same ultrasonic transmit burst are possible. Compatible microphone arrays are compact in size-test array has a total baseline of 26.5 mm. In a test with ultrasonic beacon 65 cm from a microphone array, angular precision of 1/spl deg/ was demonstrated in most instances in the range -60/spl deg/ to 60/spl deg/. Applications include sonar localization of remote objects, sonar imaging, and improved interference rejection between objects within the field of view of the sensor microphones. The chip was fabricated on a standard 3M2P CMOS process with a 0.5-/spl mu/m feature size.

Inherently Robust Micromachined Gyroscopes With 2-DOF Sense-Mode Oscillator

Commercialization of reliable vibratory micromachined gyroscopes for high-volume applications has proven to be extremely challenging, primarily due to the high sensitivity of the dynamical system response to fabrication and environmental variations. This paper reports a novel micromachined gyroscope with two degrees-of-freedom (DOF) sense-mode oscillator that provides inherent robustness against structural parameter variations. The 2-DOF sense-mode oscillator provides a frequency response with two resonant peaks and a flat region between the peaks, instead of a single resonance peak as in conventional gyroscopes. The device is nominally operated in the flat region of the sense-mode response curve, where the amplitude and phase of the response are insensitive to parameter fluctuations. Furthermore, the sensitivity is improved by utilizing dynamical amplification of oscillations in the 2-DOF sense-mode oscillator. Thus, improved robustness to variations in temperature, damping, and structural parameters is achieved, solely by the mechanical system design. Prototype gyroscopes were fabricated using a bulk-micromachining process, and the performance and robustness of the devices have been experimentally evaluated. With a 25 V dc bias and 3 V ac drive signal resulting in 5.8 /spl mu/m drive-mode amplitude, the gyroscope exhibited a measured noise-floor of 0.64/spl deg//s//spl radic/Hz over 50 Hz bandwidth in atmospheric pressure. The sense-mode response in the flat operating region was also experimentally demonstrated to be inherently insensitive to pressure, temperature, and dc bias variations.

High-Density Directional Display for Generating Natural Three-Dimensional Images

A high-density directional display can produce natural three-dimensional(3-D) images by projecting a large number of directional images using directional rays. When the angle pitch of the directional rays is 0.2/spl deg//spl sim/0.4/spl deg/, more than two directional rays passing through a point in 3-D space enter the viewer's eye simultaneously so that the viewer's eye can focus on that point. No discrepancy appears between the convergence function and the accommodation function so that the display does not induce visual fatigue. Two different system configurations are presented: a projection configuration and a thin configuration. A prototype display based on the projection configuration was constructed. The prototype display displayed 64 directional images with directional rays having a horizontal angle pitch of 0.34/spl deg/. The screen size was 9.2 in. The preliminary experimental results showed that a viewer could focus on 3-D images produced by the prototype display.

Deep-space calibration of the WindSat radiometer

The WindSat microwave polarimetric radiometer consists of 22 channels of polarized brightness temperatures operating at five frequencies: 6.8, 10.7, 18.7, 23.8, and 37.0 GHz. The 10.7-, 18.7-, and 37.0-GHz channels are fully polarimetric (vertical/horizontal, /spl plusmn/45/spl deg/ and left-hand and right-hand circularly polarized) to measure the four Stokes radiometric parameters. The principal objective of this Naval Research Laboratory experiment, which flys on the USAF Coriolis satellite, is to provide the proof of concept of the first passive measurement of ocean surface wind vector from space. This paper presents details of the on-orbit absolute radiometric calibration procedure, which was performed during of a series of satellite pitch maneuvers. During these special tests, the satellite pitch was slowly ramped to +45/spl deg/ (and -45/spl deg/), which caused the WindSat conical spinning antenna to view deep space during the forward (or aft portion) of the azimuth scan. When viewing the homogeneous and isotropic brightness of space (2.73 K) through both the main reflector and the cold-load calibration reflector, it is possible to determine the absolute calibration of the individual channels and the relative calibration bias between polarimetric channels. Results demonstrate consistent and stable channel calibrations (with very small brightness biases) that exceed the mission radiometric calibration requirements.