Showing papers on "Phase (waves) published in 1996"
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TL;DR: In this article, it is shown that phase objects can lead to spurious contrast in x-ray diffraction images (topographs) of crystals, which can be eliminated through random phase plates, which provide an effective way of tailoring the angular size of the source.
Abstract: Phase objects are readily imaged through Fresnel diffraction in the hard x-ray beams of third-generation synchrotron radiation sources such as the ESRF, due essentially to the very small angular size of the source. Phase objects can lead to spurious contrast in x-ray diffraction images (topographs) of crystals. It is shown that this contrast can be eliminated through random phase plates, which provide an effective way of tailoring the angular size of the source. The possibilities of this very simple technique for imaging phase objects in the hard x-ray range are explored experimentally and discussed. They appear very promising, as shown in particular by the example of a piece of human vertebra, and could be extended to phase tomography.
782 citations
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01 Feb 1996
TL;DR: In this paper, a phase profile is imposed on an optical beam as it is either transmitted through or reflected from the phase shifter array, and the imposed phase profile steers, focuses, fans out, or corrects phase aberrations on the beam.
Abstract: Optical phased arrays represent an enabling new technology that makes possible simple affordable, lightweight, optical sensors offering very precise stabilization, random-access pointing programmable multiple simultaneous beams, a dynamic focus/defocus capability, and moderate to excellent optical power handling capability. These new arrays steer or otherwise operate on an already formed beam. A phase profile is imposed on an optical beam as it is either transmitted through or reflected from the phase shifter array. The imposed phase profile steers, focuses, fans out, or corrects phase aberrations on the beam. The array of optical phase shifters is realized through lithographic patterning of an electrical addressing network on the superstrate of a liquid crystal waveplate. Refractive index changes sufficiently large to realize full-wave differential phase shifts can be effected using low (<10 V) voltages applied to the liquid crystal phase plate electrodes. High efficiency large-angle steering with phased arrays requires phase shifter spacing on the order of a wavelength or less; consequently addressing issues make 1-D optical arrays much more practical than 2-D arrays. Orthogonal oriented 1-D phased arrays are used to deflect a beam in both dimensions. Optical phased arrays with apertures on the order of 4 cm by 4 cm have been fabricated for steering green, red, 1.06 /spl mu/m, and 10.6 /spl mu/m radiation. System concepts that include a passive acquisition sensor as well as a laser radar are presented.
689 citations
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TL;DR: A method is proposed that permits the derivation of algorithms that satisfy both requirements of phase-stepping methods, up to any arbitrary order, based on a one-to-one correspondence between an algorithm and a polynomial.
Abstract: If the best phase measurements are to be achieved, phase-stepping methods need algorithms that are 112 insensitive to the harmonic content of the sampled waveform and 122 insensitive to phase-shift miscalibration. A method is proposed that permits the derivation of algorithms that satisfy both requirements, up to any arbitrary order. It is based on a one-to-one correspondence between an algorithm and a polynomial. Simple rules are given to permit the generation of the polynomial that corresponds to the algorithm having the prescribed properties. These rules deal with the location and multiplicity of the roots of the polynomial. As a consequence, it can be calculated from the expansion of the products of monomials involving the roots. Novel algorithms are proposed, e.g., a six-sample one to eliminate the effects of the second harmonic and a 10-sample one to eliminate the effects of harmonics up to the fourth order. Finally, the general form of a self-calibrating algorithm that is insensitive to harmonics up to an arbitrary order is given.
485 citations
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TL;DR: The phase shift of cells from type L 929 fibroblast and mitochondria from liver cells was measured and the Fraunhofer diffraction of the measured phase object is calculated.
Abstract: With a phase microscope the phase shift of cells from type L 929 fibroblast and mitochondria from liver cells was measured. Compared to the total phase shift caused by the cell relative to vacuum (approximately 1400 nm) the single phase shift of the mitochondria (approximately 180 nm) is small. Only the nucleus and the membrane of the cell give a visibly different phase shift relative to the mean value of the cell. The Fraunhofer diffraction of the measured phase object is calculated. With a simplified scattering theory, i.e. Rayleigh - Gans scattering, different phase objects are investigated and their differential cross section is discussed.
342 citations
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TL;DR: An experimental apparatus capable of exploring the phase sensitivity of nonlinear-optical interactions is presented and a feasibility study of controlling the carrier phase in ultrashort light-wave packets emitted by a sub-10-fs laser is reported.
Abstract: A feasibility study of controlling the carrier phase in ultrashort light-wave packets emitted by a sub-10-fs laser is reported. An experimental apparatus capable of exploring the phase sensitivity of nonlinear-optical interactions is presented.
334 citations
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TL;DR: In this article, the authors examined the trade-off between spectral magnitude uniformity and frequency selectivity of the SWIFT waveform for both ICR and quadrupole ion trap mass spectrometry.
305 citations
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TL;DR: In this paper, an easily reproduced experiment that allows the student to investigate the intensity and phase structure of transverse laser modes is presented. But the results are limited to the Laguerre-Gaussian modes.
Abstract: We outline an easily reproduced experiment that allows the student to investigate the intensity and phase structure of transverse laser modes. In addition to discussing the usual Hermite–Gaussian laser modes we detail how Laguerre–Gaussian laser modes can be obtained by the direct conversion of the Hermite–Gaussian output. A Mach–Zehnder interferometer allows the phase structure of the Laguerre–Gaussian modes to be compared with the phase structure of a plane wave with the same frequency. The resulting interference patterns clearly illustrate the azimuthal phase dependence of the Laguerre–Gaussian modes, which is the origin of the orbital angular momentum associated with each of them.
236 citations
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TL;DR: A new optical encoding method for security applications that uses two phase‐only functions at both the input and frequency planes of the optical processor leading to maximum optical efficiency.
Abstract: A new optical encoding method for security applications is proposed. The encoded image (encrypted into the security products) is merely a random phase image statistically and randomly generated by a random number generator using a computer, which contains no information from the reference pattern (stored for verification) or the frequency plane filter (a phase‐only function for decoding). The phase function in the frequency plane is obtained using a modified phase retrieval algorithm. The proposed method uses two phase‐only functions (images) at both the input and frequency planes of the optical processor leading to maximum optical efficiency. Computer simulation shows that the proposed method is robust for optical security applications.
191 citations
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15 Jul 1996TL;DR: In this paper, a digital transmit beamformer system with multiple beam transmit capability has a plurality of multi-channel transmitters, each channel with a source of sampled, complex-valued initial waveform information representative of the ultimate desired waveform to be applied to one or more corresponding transducer elements for each beam.
Abstract: A digital transmit beamformer system with multiple beam transmit capability has a plurality of multi-channel transmitters, each channel with a source of sampled, complex-valued initial waveform information representative of the ultimate desired waveform to be applied to one or more corresponding transducer elements for each beam. Each multi-channel transmitter applies beamformation delays and apodization to each channel's respective initial waveform information digitally, digitally modulates the information by a carrier frequency, and interpolates the information to the DAC sample rate for conversion to an analog signal and application to the associated transducer element(s). The beamformer transmitters can be programmed per channel and per beam with carrier frequency, delay, apodization and calibration values. For pulsed wave operation, pulse waveform parameters can be specified to the beamformer transmitters on a per firing basis, without degrading the scan frame rate to non-useful diagnostic levels. Waveform parameters can be specified to the transmitters by an external central control system which is responsible for higher level flexibility, such as scan formats, focusing depths and fields of view. The transmit pulse delay specified per-channel to each transmitter is applied in at least two components: a focusing time delay component and a focusing phase component. The carrier frequency can be specified for each transmit beam, to any desired frequency within a substantially continuous predefined range of frequencies, and a beam-interleaved signal processing path permits operation in any of several predefined processing modes, which define different parameter sets in a trade-off among (1) the number of beams produced; (2) per-beam initial waveform sample interval; and (3) transmit frequency.
139 citations
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06 Feb 1996
TL;DR: In this paper, a differential ranging location system is described which uses a modified time-of-arrival technique to determine the location of a frequency-hopped spread spectrum radio signal, where the transmitter simultaneously transmits two radio frequency carriers having different frequencies such that a phase difference is observed between the two carriers at a distance from the transmitter.
Abstract: A differential ranging location system is described which uses a modified time-of-arrival technique to determine the location of a frequency-hopped spread spectrum radio signal. The transmitter simultaneously transmits two radio frequency carriers having different frequencies such that a phase difference is observed between the two carriers at a distance from the transmitter. The phase difference is proportional to the range from the transmitter that the carrier signals have observed. The two carrier signals from the single transmitter are received by at least three and in special cases four base stations which calculate the differential time of arrival based on the phase differences of the received carriers. The calculated phase differences are then sent to a central location which locates the position of the transmitter based upon a planer hyperbolic location algorithm. Since a large number of narrow band frequencies across a wide spectrum are used in a frequency hopping transmission protocol, the accuracy in determining the phase differences between the two carriers is increased and the immunity to interference is also increased.
135 citations
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TL;DR: In this article, a new method for synthesizing arbitrary intensity patterns based on phase contrast imaging is presented, which is grounded on an extension of the Zernike phase contrast method into the domain of full range [0, 2π] phase modulation.
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18 Oct 1996TL;DR: In this paper, a phase error detection method is applied to a VSB receiver or a QAM receiver, and the phases of the I-channel data and the Q-channel signals are corrected according to a fed-back phase error.
Abstract: A phase error detecting method is applied to a VSB receiver or a QAM receiver. Q-channel data is recovered by digitally filtering transmitted I-channel data, and the phases of the I-channel data and the Q-channel data are corrected according to a fed-back phase error. A decided I-channel level value is chosen approximating the phase-corrected I-channel data among predetermined reference I-channel level values. A phase error value for the received data is obtained by subtracting the decided I-channel level value from the phase-corrected I-channel data, and multiplying the sign of the difference by the difference itself, and applying a weight value from a predetermined weighting function to the phase error value weighted phase error value is fed back to be used for phase correction of received data. Thus, the reliability of phase error detection can be increased by use of the weighting function.
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29 Aug 1996
TL;DR: In this paper, a phase difference plate is formed by sticking the quarter wave plate and the half wave plate to each other in the state of intersecting their respective optical axes at a preset angle.
Abstract: PROBLEM TO BE SOLVED: To obtain a phase difference plate which has decreased phase differences by wavelengths and has the excellent consistency thereof by sticking a quarter-wave plate and a halfwave plate to each other in the state of intersecting their respective optical axes. SOLUTION: This phase difference plate is formed by sticking the quarter- wave plate (a double refractive film of which the phase difference of the double refractive light is a quarter wave) 13 and the halfwave plate (a double refractive film of which the phase difference of the double refractive light is a half wave) 11 to each other in the state of intersecting the respective optical axes at a preset angle. The halfwave plate 11 and the quarter-wave plate 13 are formed by subjecting high-polymer films to stretching treatments. In such a case, a polycarbonate material which is often used as a wavelength material is selected. This phase difference plate is designed to function as the quarter-wave plate improved in the wavelength dispersion characteristic when linearly polarized light of a perpendicular direction (0 deg. direction) is made incident from the halfwave plate 11 side. The phase difference plate is thus capable of converting the light to nearly perfectly circularly polarized light regardless of wavelengths in a range of visible light.
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TL;DR: A model-based phase unwrapping method which represents the unwrapped phase function by a truncated Taylor series and a residual function and an efficient, noniterative computational algorithm is proposed for calculating the model parameters from the phase derivatives.
Abstract: Presents a model-based phase unwrapping method which represents the unwrapped phase function by a truncated Taylor series and a residual function. An efficient, noniterative computational algorithm is also proposed for calculating the model parameters from the phase derivatives. Sample experimental results are shown to demonstrate the effectiveness of the algorithm for extracting unwrapped phase images from two-dimensional (2-D) magnetic resonance imaging (MRI) data.
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TL;DR: The objective of this paper is to investigate general solutions having rotating intensity distributions around and along the propagation axis and demonstrate that these solutions are easily obtained in terms of the superposition of Gauss-Laguerre ~GL! modes.
Abstract: Wave fields containing invariant features have recently stimulated the interest of the scientific community. Typical examples of such fields are Gaussian modes, Bessel beams @1#, and wave fronts containing phase dislocations @2#. Bessel beams are solutions of the wave equation that propagate with invariant intensity. Phase dislocations are discontinuities of the phase in a wave front such that the circulation of the phase around its axis is an integral multiple of 2p. Thus, they determine lines of zero intensity in space. Experimental evidences of optical dislocations can be found, for example, in Refs. @3‐5#. It was noted in Refs. @4,6# that, under certain circumstances, an array of dislocations nested in a Gaussian beam rotates by p/2 rad from the waist to the far field, expanding with the host beam. The objective of this paper is to investigate general solutions having rotating intensity distributions around and along the propagation axis. We start by demonstrating that these solutions are easily obtained in terms of the superposition of Gauss-Laguerre ~GL! modes. The rotation rate along the propagation is then derived and the set of all possible solutions presenting a specific total rotation angle is characterized. Finally, we analyze the limit of the rotation rate and present experimental results for optical beams. Let a scalar wave be represented by the function
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TL;DR: This work presents five different eight-point phase-shifting algorithms, each with a different window function, and demonstrates that the shape of the window function significantly influences phase error.
Abstract: We present five different eight-point phase-shifting algorithms, each with a different window function. The window function plays a crucial role in determining the phase (wavefront) because it significantly influences phase error. We begin with a simple eight-point algorithm that uses a rectangular window function. We then present alternative algorithms with triangular and bell-shaped window functions that were derived from a new error-reducing multiple-averaging technique. The algorithms with simple (rectangular and triangular) window functions show a large phase error, whereas the algorithms with bell-shaped window functions are considerably less sensitive to different phase-error sources. We demonstrate that the shape of the window function significantly influences phase error.
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TL;DR: It is shown that oscillations at multiples of the main frequency of the oscillator system may occur in the phase and amplitude due to the choice of a coordinate system and how these oscillations can be eliminated.
Abstract: We study the dynamics of a system of coupled nonlinear oscillators that has been used to model coordinated human movement behavior. In contrast to earlier work we examine the case where the two component oscillators have different eigenfrequencies. Problems related to the decomposition of a time series (from an experiment) into amplitude and phase are discussed. We show that oscillations at multiples of the main frequency of the oscillator system may occur in the phase and amplitude due to the choice of a coordinate system and how these oscillations can be eliminated. We derive an explicit equation for the dynamics of the relative phase of the oscillator system in phase space that enables a direct comparison between theory and experiment.
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TL;DR: In this article, the authors used the bary center of spectral lines in the main lobe to obtain the coordinate of the spectrum peak and obtained the accurate frequency, amplitude and phase of the rms spectrum peak.
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24 May 1996
TL;DR: In this paper, a photonic device for controlling the phase shift between optical waves of orthogonal polarizations traveling in an electro-optic optical waveguide is described, which is directly proportional to the voltage applied to a control electrode and to the length of that electrode.
Abstract: A photonic device for controlling phased array beam direction includes an electro-optic substrate; a plurality of waveguides formed in the substrate, each of which is capable of simultaneously propagating light signals with orthogonal polarizations; an input waveguide for inputting into each one of the plurality of waveguides a pair of copropagating polarized light signals having orthogonal polarizations and different frequencies; a plurality of electrodes on the substrate configured to phase shift the signals traveling through each waveguide by a different amount in response to a common applied voltage, thereby creating phase shifted polarized signals; and means for combining the phase shifted polarized signals within each one of the waveguides and propagating these combined signal to an antenna element The basic operating principle of the invention is based on the differential phase shift between optical waves of orthogonal polarizations traveling in an electro-optic optical waveguide This differential phase shift is directly proportional to the voltage applied to a control electrode and to the length of that electrode If the two optical waves are slightly offset in optical frequency, they produce a beat frequency when photodetected whose phase shift equals the optical differential phase shift An array of such phase shifters forms the basis for the photonic beam controller of the invention
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TL;DR: In this article, a robust procedure for the measurement of absolute phase values with high accuracy is presented based on the derivation of a precision adapted sequence of grid orientations and the stepwise reconstruction of the continuous phase field without phase unwrapping.
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TL;DR: In this paper, the authors demonstrate and compare several techniques for direct measurement of the phase of the nonlinear susceptibilities through nonlinear interferometry, and different ways of imparting a controllable phase shift are discussed.
Abstract: Measurement of the phase, and not only the intensity, of the nonlinear optical response of a system is important in many applications which are reviewed here. We demonstrate and compare several techniques for direct measurement of the phase of the nonlinear susceptibilities through nonlinear interferometry. Different ways of imparting a controllable phase shift are discussed. Unless the coherence length is impractically large, the preferred method is to use a variable-pressure gas cell to control the phase difference between the input laser pulse and the nonlinear optical signal.
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27 Nov 1996
TL;DR: In this paper, a precision direction finding system for making precision angle of arrival estimates for a signal received through two antenna elements separated in space is presented, with multiple ambiguities due to the periodic nature of the phase difference related to geometric angle.
Abstract: A precision direction finding system for making precision angle of arrival estimates for a signal received through two antenna elements separated in space. Phase interferometry is used to determine a precise angle of arrival, with multiple ambiguities due to the periodic nature of the phase difference related to geometric angle. The interferometric ambiguities are resolved using the time difference of arrival (TDOA) of the signal at the two antenna elements. TDOA is measured using leading edge envelope detection for simple pulsed signals, and predetection correlation for phase and frequency modulated signals.
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TL;DR: This Letter presents a more direct means for measuring the canonical quantum optical phase probability distribution which involves synthesising the projection onto a phase state and may be applied more generally to measure the probability distribution associated with other observables.
Abstract: Experimental determination of the canonical quantum optical phase probability distribution has, until now, required sufficient measurements to determine the complete state of the field. In this Letter we present a more direct means for measuring this distribution which involves synthesising the projection onto a phase state. Projection synthesis may be applied more generally to measure the probability distribution associated with other observables. {copyright} {ital 1996 The American Physical Society.}
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28 May 1996TL;DR: In this paper, a phase modulator and a frequency multiplier are used to obtain a modulated carrier signal in a transmission system for transmitting digital symbols according to a phase constellation, and the number of phase states of the constellation at the input of the frequency multiplier is N times the number at the output of the phase multipplier.
Abstract: In a transmission system for transmitting digital symbols according to a phase constellation, a transmitter (2) is provided with a phase modulator (8) and a frequency multiplier (18) to obtain a modulated carrier signal. To prevent degradation of the modulated carrier signal, the input constellation of the frequency multiplier (18) has at least one additional phase state with respect to the output constellation of the frequency multiplier. Advantageously, the number of phase states of the constellation at the input of the frequency multiplier (18) is N times the number of phase states of the constellation at the output of the frequency multipplier (18).
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16 Dec 1996TL;DR: In this paper, an optical communication system compensating for chromatic dispersion and a phase conjugate light generator for use therewith is described, which includes an optical transmitter which receives an input signal and transmits signal light over an optical transmission line which is then input to an optical generator unit.
Abstract: An optical communication system compensating for chromatic dispersion and a phase conjugate light generator for use therewith. The system includes an optical transmitter which receives an input signal and transmits signal light over an optical transmission line which is then input to a phase conjugate light generation unit. The phase conjugate light generation unit generates phase conjugate light corresponding to the signal light and outputs the phase conjugate light to an optical receiver which reproduces a demodulated signal corresponding to the input signal. The system compensates for chromatic dispersion by having the phase conjugate light generator generate phase conjugate light corresponding to signal light received over a first optical transmission line and then transmitting the generated phase conjugate light over a second optical transmission line.
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TL;DR: The Fourier-transform evaluation of TV holograms for spatial phase stepping with a small angular offset between the object and the reference beams is reported to obtain their phase data and the direct calculation of the phase difference between successive recordings is demonstrated.
Abstract: TV holograms for spatial phase stepping are formed with a small angular offset between the object and the reference beams to give a spatial frequency bias to the pattern recorded by the TV camera. It is common to set the bias so that there is a 90° or 120°phase shift between adjacent pixels and to use the irradiance of three or more adjacent pixels to evaluate the phase of the interference. We report the Fourier-transform evaluation of such recordings to obtain their phase data. We also demonstrate the direct calculation of the phase difference between successive recordings without intermediate calculation of the random phase of each hologram. This technique is proposed as an approach to pulsed TV holography.
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TL;DR: In this paper, the phase angles of the phase shifters are updated at a slower rate than the focusing update rate of the beamformer processors, and phase angles for any one of the sub-array processors are independent of the time delay of the respective digital beamformer processor.
Abstract: An ultrasonic receive beamformer includes transducers forming receive signals that are applied to sub-array processors. Each sub-array processor includes at least one phase shifter and a summer, and each phase shifter is responsive to at least one of the transducer signals to shift the transducer signal by a respective phase angle and to apply the phase shifted transducer signals to the summer. Each of the summers supplies a summed sub-array signal to a respective beamformer processor. The phase angles for any one of the sub-array processors form a sum substantially equal to zero. Furthermore, the phase angles for any one of the sub-array processors are independent of the time delay of the respective digital beamformer processor. The time resolution of the time delay of the digital beamformer processors is substantially as fine as the time resolution of the phase angles of the phase shifters. The phase angles of the phase shifters are updated at a slower rate than the focusing update rate of the beamformer processors. Quadrature filter network and heterodyning circuit implementations of the phase shifters are disclosed.
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03 Sep 1996TL;DR: In this paper, a voltage controlled ferroelectric lens was proposed for phase shift control in the Radant lens, which introduces an analog phase shift rather than a digital phase shift.
Abstract: Phased array antennas can steer transmitted and received signals without mechanically rotating the antenna. Each radiating element of a phased array is normally connected to a phase shifter, which determines the phase of the signal at each element to form a beam at the desired angle. The most commonly used phase shifters are ferrite and diode phase shifters. Phase shifters using ferroelectric materials have been proposed previously. A typical phased array may have several thousand elements and is very expensive. Therefore, reducing the cost and complexity of the phase shifters and the phase shifter controls is an important consideration in the design of phased arrays. The phased array described uniquely incorporates bulk phase shifting, the array does not contain individual phase shifting, using a ferroelectric material along with simpler phase shift control. Bulk phase shifting using diodes has been proposed and developed in the Radant lens. The lens described uses a voltage controlled ferroelectric, which introduces an analog phase shift rather than a digital phase shift as in the Radant lens. The ferroelectric lens has further advantages of smaller lens thickness, higher power handling, simpler beam steering controls, and it uses less power to control the phase shift compared to the Radant lens. Thus, it can potentially lead to low cost phased arrays.
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TL;DR: The use of principal-component analysis in spectral quantification is extended to the estimation of frequency and phase shifts in a single resonant peak across a series of spectra, resulting in more accurate peak-area estimation.
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26 Sep 1996TL;DR: In this paper, a device for generating plasma for use in semiconductor fabrication, which includes a first radio frequency excitation source for outputting a first excitation current having a first phase and a first amplitude, was presented.
Abstract: A device for generating plasma for use in semiconductor fabrication, which includes a first radio frequency excitation source for outputting a first excitation current having a first phase and a first amplitude. The device further includes a second radio frequency excitation source for outputting a second excitation current having a second phase and a second amplitude and a plasma generating element having a first end and a second end for receiving respectively the first excitation current and the second excitation current. Moreover, the inventive device includes a control circuit having a control input for receiving a user-variable signal indicative of a desired phase difference between the first phase and the second phase. The control circuit, responsive to the control input, outputs a control signal to one of the first radio frequency excitation source and the second radio frequency excitation source for controlling respectively one of the first phase and the second phase, thereby causing an actual phase difference between the first phase and the second phase to substantially approximate the desired phase difference. In so doing, the device becomes essentially an inductive coupling device when the first phase and the second phase are opposite in phase. When the first phase and the second phase are in phase, the device becomes essentially a capacitive coupling device. Finally, when the first phase and the second phase differ by an angle that is between in phase and opposite in phase, the device becomes a combination inductive and capacitive coupling device.