Output Phase Shift Research Articles

Stabilized fiber-optic extrinsic Fabry–Perot sensor system for acoustic emission measurement

A fiber-optic Fabry–Perot (F–P) acoustic emission (AE) sensor system based on an improved double wavelength stabilization technique is described. Without stabilization, the sensor system drifts out of quadrature due to the presence of low-frequency dynamic strains. The stabilization is achieved by using a dense wavelength division multiplexer (DWDM) to generate two quadrature phase-shifted output signals. An optimum model of double wavelength stabilization is established. The filtering wavelengths of DWDM are calculated using an optimization design method. The performance of the developed sensor system was verified by two preliminary tests. One was a test on the stabilization of operating point of fiber-optic F–P sensor, and other was the detection of simulated AE signals generated by the impact and pencil lead breaking. The test results demonstrate that simulated AE signals are successfully detected using this stabilized sensor system, which solves the fade-out problem.

Surface acoustic wave sensors to detect volatile gases by measuring output phase shift

This paper presents properties of saw acoustic wave (SAW) gas sensors to detect volatile gases such as acetone, methanol, and ethanol by measuring phase shift. A dual-delay-line saw sensors with a center frequency of 100 MHz were fabricated on 128∘ Y-Z LiNbO3 piezoelectric substrate. In order to improve sensitivity of SAW sensors, a thin titanium (Ti) film as mass sensitive layer was deposited using e-beam evaporation on the surface of the SAW sensors. In our investigation the response time and sensitivity of SAW sensors were measured. The response time and sensitivity of SAW sensor with thin Ti film were strongly improved because of changing electrical and mechanical properties in the mass sensitive layer. As a result, high sensitivity and fast response time could be achieved by deposition of thin Ti film as mass sensitive layer on the surface of SAW sensor. It can be applied for high performance electronic nose system by assembling an array of different sensors.

Strong and fast phase modulation for quantitative analysis of photorefractive gratings

A new approach for studying photorefractive gratings in two-wave mixing experiments by a phase modulation technique is presented. The introduction of a large-amplitude, high-frequency sinusoidal phase modulation in one of the input beams blurs the interference pattern and provides powerful harmonic signals for accurate measurements of the grating diffraction efficiency η and the output phase shift ϕ between the transmitted and diffracted waves. The blurring of the light fringes can be used to suppress the higher spatial harmonics of the grating, allowing a space-charge field with sinusoidal profile to be recorded. Although the presence of such a strong phase modulation affects the beam coupling in a rather complicated way, it is shown that for the special case of equal intensity input beams, the effect of the phase modulation on η and ϕ is reduced to a weakening of the coupling strength. The potentialities of the technique are illustrated in a study of refractive-index waves excited by running interference patterns in a Bi12TiO20 crystal. Expressions for the diffraction efficiency and the output phase shift are derived and used to match numerically calculated curves to the experimental data. The theoretical model is supported by the very good data fitting and allows the computation of important material parameters.

Common path interferometric wavefront sensor for extreme adaptive optics

We describe a method of implementing a common-path phase-shifting point diffraction interferometric wavefront sensor suitable for extreme adaptive optics. The sensor simultaneously gives two phase-shifted outputs which can be used to drive a phase-only wavefront corrector. The device can also give a null output which can be used to calibrate any scintillation. Simulations are performed showing the utility of the device and experimental results of a high speed single channel closed loop system are presented.

New voltage and current-mode APS using current controlled conveyor

A first-order all-pass section (APS) is introduced employing a single second-generation current conveyor and three passive components. The translinear conveyor version of the circuit employing only two passive components is also proposed. A fully tunable version of the circuit employing two current controlled conveyors (CCCIIs) and a single capacitor is finally derived. All the three versions of APS can be operated both in voltage as well as current mode without changing the circuit configuration. As an application, a quadrature oscillator providing two quadrature currents and two phase-shifted voltage outputs simultaneously, is realized using the proposed APS. RSPICE simulation results for the translinear-C APS, and the translinear-C quadrature oscillator are included to verify the theory.

Current injection electrodes for electrical impedance tomography

Current conveyors have been identified as a possible component within the current injection electrodes of an electrical impedance tomography system, where accurate current generation or precise measurement of the current injected is required. Several circuit configurations have been investigated through simulation to determine the most suitable to meet the specifications of the EIT system. A bipolar (floating source) circuit configuration employing the use of current conveyors has been designed, which achieves greater than 12 mA output current without saturation, over an accepted body impedance range. Simulations were performed over frequencies in excess of 1 MHz, and the output phase shift was less than 0.15° up to 250 kHz, and 0.6° up to 1 MHz.

The increase of gravitational-wave interferometer sensitivity by employing stochastic resonance mechanism in nonlinear white-light cavity

We consider a nonlinear white-light cavity (WLC), operating in gravitational-wave (GW) interferometer arm. By using coupled-wave equations for nonlinear waves, we analyze nonlinear resonance and obtain a simple asymptotic equation for calculating of WLC output phase shift, when the operation point is placed very close to instability point. In a standard nonlinear cavity it would require the instability of laser frequency less than 10 −21; however in the nonlinear WLC the requirement to frequency instability is much more tolerant – about 10 −14. We calculated the shift of output phase and output signal-to-displacement noise ratio (SDNR out) in bistable regime assuming that cavity length changes under the action of a quasi-sinusoidal GW and a displacement noise. Due to the stochastic resonance (SR) phenomenon presented here, the SDNR out decreases non-monotonically when displacement noise increases: at an optimum level of displacement noise the SDNR out sharply increases before further decrease. Therefore due to the SR mechanism the output signal becomes less noisy. For example: if the conventional value of SDNR out is 0.05 at detection bandwidth 100 Hz, then the performance of SR increases this value ∼7 times, and SDNR out becomes ∼0.35. Thus we propose for the first time an approach, which is capable to increase the SDNR out of GW interferometer at given amplitude of displacement noise.

First pass TWT design success

Making use of an ensemble of computer codes, Hughes Electron Dynamics (HED) has achieved first pass success in the design of slow wave circuits for several traveling wave tubes (TWTs) during the last year. By first pass design success we mean that when tested, the first device fabricated achieved the design goals for RF output power, basic efficiency, gain and phase shift. The design goals are derived from the predictions of a computer model, based on the exact dimensions of the TWT. The establishment of accurate computer models for the TWT slow wave circuit has enabled the optimization of a new design on the computer, eliminating the need for several experimental iterations in the development process. This accomplishment has enabled HED to significantly reduce the time required to develop new devices and demonstrate new design concepts.

Simultaneous AM-AM/AM-PM distortion measurements of microwave transistors using active load-pull and six-port techniques

A programmable active load-pull measurement system using two six-port reflectometers and three passive two-port standards has been developed to obtain load-pull contours of the transistor's input-output phase shift variations over a wide dynamic range of the input power. The output power, gain, power-added efficiency, and phase shift are measured simultaneously at the transistor's input and output reference planes. The phase distortion versus input power, /spl phi//spl sim/P/sub in/, and the AM-PM conversion coefficient at various power levels, k/spl sim/P/sub in/, are obtained for different load impedances by post-measurement calculations. A NE8001 MESFET is tested at f=1.7 GHz for the class A operation. The experimental results are also given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electromagnetic analysis of RFEC differential probes

A differential probe (DP) for defect detection in the remote field eddy current (RFEC) technique is proposed. The analysis of the DP response to a sinusoidal steady-state excitation and a sinusoidal pulse excitation has been carried out by an equivalent network model, which allows easy modeling of axisymmetric defects. In the case of a sinusoidal steady-state excitation, the possibility of having clearer defect detection with respect to the conventional phase shift output, exploiting the phase shift between the induced signals in the two pickup coils, is shown. The differential output signal is equally sensitive to outer and inner defects, while the signal amplitude decreases as the distance between the coils increases. In the case of a sinusoidal pulse excitation, the differential configuration allows defect detection, but the transient nature of the induced voltages presents the phase shift effect, and the differential probe output amplitude is lower than the conventional one. >

Wide-band π/2 phase shifter using a stepped sweeping dual phase-locked loop technique

A wide-band π/2 phase shifter based on stepped sweeping phase-locked loops (PLLs) is introduced and constructed. Results indicate that the system can work over a wide range of input frequencies limited only by the gain and saturation of the voltage-controlled oscillator (VCO) of the PLLs. For a noise-free signal, the phase error between the input and the π/2 phase-shifted output is 3° and it is constant regardless of the input frequency. The system can be modified to produce any phase shift from 0 to n with the same performance.

Determination of the impedance of the guinea pig skin.

The impedance of guinea-pig skin has been studied using anin vitro method which consists of placing the recording chamber containing a strip of guinea-pig skin in the feedback branch of a closed-loop amplifier having an adjustable resistor in its input circuit. The chamber consists of two cylinders filled with a circulating Krebs solution at 37°C and two platinum electrodes facing one another inside the cylinders. At a given frequency, the series resistor is adjusted to obtain a gain of unity between input and output sinewave voltages (gain=10). The value of the series resistor is then equal to the modulus of the impedance in the feedback loop and its argument is calculated by a phase/amplitude convertor on the basis of the input and output phase shift. The impedance measurement is made separately for the recording chamber and the whole system in which the tissue is inserted. Substracting vectorially both values obtained enables the impedance of the tissue itself to be deduced. This procedure is repeated over a wide frequency band and the resulting values are represented on a Bode diagram of phase and amplitude. The Bode diagram shows the variations of the electrical characteristics of the tissues as the frequency varies, and indicates nonlinear filtering especially for low-frequency values (10−2 Hz).

New All-Pass Phase-Shifter Configurations

Two new inductorless all-pass phase-shifter configurations are reported. They use only one difference amplifier, and the output phase shift is insensitive to the gain of the amplifier.

A Hybrid Integrated Pulsewidth Modulator

A hybrid integrated circuit is described which generates two phase-shifted 20-kHz output pulse trains whose duty cycles are related to the amplitude of an applied input signal. The circuit was designed primarily for use in power conditioning schemes utilizing pulsewidth modulated signals for regulated dc-to-dc voltage conversion. Realization of this hybrid circuit has been accomplished with a beam-lead sealed-junction monolithic silicon chip and several tantalum thin-film resistors and capacitors which are bonded/ deposited on a ceramic substrate in the form of a 28-terminal dual-in line package (DIP).

Generalized potential and uniqueness in the calculation of the pion-nucleon P 33 state

Two different iteration procedures are used to calculate the P 33 phase shift of pion-nucleon scattering: a modified N/ D method and the Newton-Kantorovich method. It is possible to find the correct generalized potential for the P 33 partial wave amplitude from threshold up to T π = 870 MeV without using the P 33 phase shift. With this input the iterations converge exactly to the phase-shift-analysis values [1] only if we introduce two parameters. It turns out that the output phase shift is very sensitive to small variations in the potential. Since we have to use parameters we conclude that in the usual N/ D method a solution is only possible if one includes at least one CDD pole.

Selective amplifier based on multilayer distributed RC network

The authors describe a general active feedback distributed RC network that provides cutoff low-pass characteristics. The network consists of a passive distributed circuit having two capacitive layers and a single controlled voltage source. The input and output resistances and phase-shift of the open-loop gain of the source are considered.

Forcing function generator employing conductive plastic

This paper describes a forcing-function generator which uses a conductive-plastic potentiometer to provide a forcing-function signal for testing servo systems and components. The unit described gives a sine-wave signal, but methods for generating a square wave or triangular wave are also discussed. A phase-measuring device is made an integral part of the function generator, and allows output versus input phase shift to be read directly from a calibrated dial.