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This article presents an amplitude and 360° phase shift array measurement system. The basic cell of the measurement system uses a novel amplitude and phase detector based on switched dual multipliers. The phase shift measurement is characterized using an analog phase detector (mixer), detecting a maximum range of ±90°, and a double multiplication of the input signals, in phase and phase shifted. This method broadens the frequency and amplitude range beyond other solutions that require fulfilling the quadrature condition. This method broadens the frequency and amplitude beyond other solutions requiring fulfilling the quadrature condition or phase and amplitude balance. Thus, it enables to compensate significant phase imbalance in the 90° hybrid or use amplitudes out of the range that ensures the switching operation of mixer diodes. The circuit calibration that allows compensation for errors (amplitude, phase shift, mismatching, etc.) is detailed, and its relation to the required measurement accuracy is discussed. The design can be easily extrapolated to other frequency ranges because it uses commercial RF devices available in a wide frequency range and avoids the need of crossing lines or complex 90° hybrid. A prototype with $3 \times 3$ cells has been built to evaluate various test conditions on $1 \times 3$ cell configurations that show the advantages of the procedure. It should be highlighted that the cell prototype uses devices that will be operating outside the frequency and amplitude ranges recommended by their manufacturers. A calibration from 2.6 to 6 GHz and −15 to −3 dBm was performed to evaluate the measurement errors. An analysis of the isolation between cells and different calibration configurations is performed to analyze the measurement errors. Measurements show compensation of +30°/−25° phase imbalance and 13-dB power lower than mixer manufacturer recommendation. [ABSTRACT FROM AUTHOR]

This article presents a circuit for the precise vertical landing of drones based on a three phase-shifts detection of a single frequency transmitted from the landing point. The circuit can be considered as a new navigation sensor that assists in guidance corrections for landing at a specific point. The circuit has three inputs to which the signal transmitted from an oscillator located at the landing point arrives with different delays. The input signals are combined in pairs in each of the three analog phase detectors, after having passed through 3 dB at 90° hybrid couplers that guarantee a theoretical nonambiguous phase shift range of ±90°. Each output has a voltage that is proportional to the phase shift between each of the input signals, which in turn depends on the position relative to the landing point. A simple landing algorithm based on phase shift values is proposed, which could be integrated into the same flight control platform, thus avoiding the need to add additional processing components. To demonstrate the feasibility of the proposed design, a triangular phase shift detector prototype has been implemented using commercial devices. Calibration and measurements at 2.46 GHz show a dynamic range of 30 dB and a nonambiguous detection range of ±80° in the worst cases. Those specs let us track the drone during the landing maneuver in an inverted cone formed by a surface with a ±4.19 m radius at 10 m high and the landing point. [ABSTRACT FROM AUTHOR]

An accurate and cost-effective islanding detection is in a great need for distributed generation (DG) integration. An onsite contactless islanding detection scheme is proposed in this article, based on a small number of tiny and portable electric field (EF) sensors. In contrast to the existing mainstream detection techniques, which are heavily depended on the instrument transformer measurement in substations, the proposed contactless scheme is able to be deployed on the ground below the overhead feeders, enabled by a compact EF sensor and the associated accurate frequency measurement algorithm. The effectiveness, robustness, efficiency, and security advantages of the proposed method are investigated and verified by the simulations using various feeder configurations. It is further supported by the laboratory experiments based on a scale-down overhead feeder testbed. [ABSTRACT FROM AUTHOR]

Measurement of optical transfer delay (OTD) is crucial to applications such as fiber-distributed multiantenna systems, fiber-optic sensors, and high-capacity optical fiber communications. However, present OTD measurement techniques are inadequate for the demands of high accuracy, high speed, and large measurement range, simultaneously. Here, we propose a novel method based on nonlinear frequency sweeping and phase derived ranging to achieve all the above-mentioned performance. A continuous-wave light modulated by a microwave signal propagates in a device under test. Then, the OTD is mapped into the phase variation of the microwave signal by photodetection. A microwave phase discriminator is used to extract the phase variation from the microwave signal, while the nonlinear frequency sweeping and a novel phase unwrapping algorithm are proposed to resolve $2\pi $ phase ambiguity caused by phase detection. Frequencies of the microwave swept signals are set at four selected points in a range of 10 MHz, which ensures high speed and large measurement range. Our experiment results verify an accuracy of ±0.05 ps in measuring an ultrahigh-accuracy optical delay line. In addition, long fiber is also tested, which proves that a measurement range of at least 37 km (theoretically 100 km) can be achieved. Moreover, the measurement speed reaches milliseconds per measurement. [ABSTRACT FROM AUTHOR]

Considering the particularity of fragile people with reduced mobility, we design a nonintrusive platform called EVAL cane to assist and monitor the user’s walking. On the one hand, it has important walking-assistance functions, such as obstacle warning and fall detection. On the other hand, it collects the user’s long-term walking data in the background, which may be the potential physical-health-assessment data. Compared with an ordinary cane, the above two functions are implemented without any burden on the user’s life. In addition, we have considered the authentication security for that the walking data are private. To this end, we propose a novel user-identification scheme, leveraging the user walking gait data collected by EVAL cane. To the best of our knowledge, it is the first time that the gait information collected by cane is used for reinforcing monitoring system security. This scheme does not require the user to remember and enter any identity (such as a password), which is user-friendly for fragile people. In the scheme, a statistics-based rough gait feature-extraction method is put forward at first. Then, in order to improve the identification precision, we design a performance-based feature-deletion (PFD) algorithm to remove the bad features. Finally, a minimum Mahalanobis distance classifier is used. Experimental results show that the user-identification rate without the PFD algorithm can reach as high as 90.48%. In addition, the PFD algorithm further improves the performance by about 6%, reaching an excellent result of 96.43%. [ABSTRACT FROM AUTHOR]

This article proposes a novel multibeam dual-frequency sensor system to assess the quality of thick rind fruits based on phase difference between lower- and higher-frequency reflection coefficients ($\Phi _{12}$). The proposed sensor system consists of five dual-band antennas and a customized circuit that approximates lower- and higher-frequency phase difference. The main components of the customized circuit are down-conversion mixers and a phase detector module. For comparison, simulations were initially carried out using single- (1 GHz) and dual-frequency (1 GHz/2.3 GHz) sensor systems, and results indicated lower accuracy in classification of thick rind fruits of the single-frequency scheme. As a result, a dual-frequency sensor prototype was fabricated and experimented with normal and granulated plastic pomelo models and real pomelo fruits. The experimental results revealed that the average $\Phi _{12}$ of the normal and granulated pomelos are almost identical, while the standard deviation (SD) of $\Phi _{12}$ of the granulated pomelo is significantly larger than the normal pomelo. SD is thus used as the determinant of pomelo quality. The multibeam 1-GHz/2.3-GHz dual-frequency sensor system efficiently differentiates between normal and granulated pomelo fruits. As such, the proposed sensor system is operationally appropriate for quality control of thick rind fruits. [ABSTRACT FROM AUTHOR]

This article presents a simple, cost-effective system for complex measurements of the field radiated by an antenna. In particular, the proposed architecture is based on an array of antenna probes connected to a set of phase difference detectors and a power detector. Phase difference measurements are processed to recover the phase of the antenna under test. The main novelty of the proposed system is that it does not require regular sampling, making it suitable for in situ antenna measurements. The influence of parameters, such as the number of antennas composing the array (and hence the number of phase difference detectors) and the positioning errors, is analyzed. The proposed architecture, implemented with off-the-shelf hardware, has been assessed for antenna measurement and diagnostics. A discussion of the issues related to the implementation of the system has been included, as well as the proposed solutions to improve its accuracy. Finally, diagnostics and radiation pattern measurement results are compared with those calculated with other phaseless techniques. [ABSTRACT FROM AUTHOR]

The precise frequency comparison system is of great importance in many applications. A frequency comparison method based on the phase coincidence demarcation (PCD) is proposed, and a frequency comparison system based on the proposed method is realized. The proposed method solves the uncertainty problem of the phase coincidence detection circuit by using two analog-to-digital converter (ADC) chips to demarcate the phase coincidence points. The test results indicate that the precision of the realized frequency comparison system is 10−16 (Allan deviation) at 1000 s. [ABSTRACT FROM AUTHOR]

This article presents a simple, cost-effective system for complex measurements of the field radiated by an antenna. In particular, the proposed architecture is based on an array of antenna probes connected to a set of phase difference detectors and a power detector. Phase difference measurements are processed to recover the phase of the antenna under test. The main novelty of the proposed system is that it does not require regular sampling, making it suitable for in situ antenna measurements. The influence of parameters, such as the number of antennas composing the array (and hence the number of phase difference detectors) and the positioning errors, is analyzed. The proposed architecture, implemented with off-the-shelf hardware, has been assessed for antenna measurement and diagnostics. A discussion of the issues related to the implementation of the system has been included, as well as the proposed solutions to improve its accuracy. Finally, diagnostics and radiation pattern measurement results are compared with those calculated with other phaseless techniques. [ABSTRACT FROM AUTHOR]

Incorporation of automated electrocardiogram (ECG) analysis techniques in home monitoring applications can ensure early detection of myocardial infarction (MI), thus reducing the risk of mortality. Most of the published techniques use advanced signal processing tools, a huge number of ECG features, and complex classifiers, which make their hardware implementation difficult. This paper proposes the use of harmonic phase distribution pattern of the ECG data for MI identification. The morphological and temporal changes of the ECG waveform caused by the presence of MI are reflected in the phase distribution pattern of the Fourier harmonics. Two discriminative features, clearly reflecting these variations, are identified for each of the three standard ECG leads (II, III, and V2). Classification of the healthy and MI data is performed using a threshold-based classification rule and logistic regression. The proposed technique has achieved an average detection accuracy of 95.6% with sensitivity and specificity of 96.5% and 92.7%, respectively, for classifying all types of MI data from the Physionet Physikalisch-Technische Bundesanstalt diagnostic ECG database. The robustness of the algorithm is confirmed with real data as well. The algorithm is also implemented and validated on a microcontroller-based Arduino board, which can serve as a prototype ECG analysis device. Apart from providing comparable performance to other reported techniques, the proposed technique provides distinct advantages in terms of computational simplicity of the features, significantly reduced feature dimension, and use of simple linear classifiers which ensure faster and easier MI identification. [ABSTRACT FROM AUTHOR]

In this paper, we present a high performance, automatic fully analog phase-to-voltage converter (PVC) circuit for phase shift measurements of periodic waveforms and repeated pulsed signals with zero and nonzero mean values. The PVC operation is fully automatic because an internal closed feedback loop guarantees the self-phase alignment (self-locking) between the reference and input signals. The system has been tested by measuring the phase shifts between the electrical signals generated by digital waveform generators and by photodiodes. The PVC output voltage dynamic range is ±10 V, independently from the phase-shift full-scales equal to ±10°, ±1°, and ±0.1°. The increase of the PVC sensitivity, expressed in volts/degree, which can be easily set to about 1, 10, and 100 V/°, is achieved without any amplification of the signal so avoiding the increasing and/or introduction of additional electronic noise to the measurements. As a consequence, for the smallest phase-shift full-scale equal to ±0.1°, the proposed PVC circuit is capable to achieve phase resolutions in the order of 0.0001°, a value one order of magnitude better than that one of commercial lock-in amplifiers. In the case of optical applications, the PVC is able to detect laser power variations with sensitivity values settable to about 6, 60, and 600 V/ $\mu \!$ W so achieving the best resolution of 16 pW. [ABSTRACT FROM PUBLISHER]

We report a method for the temporal synchronization of two photoelastic light modulators. For synchronizing, we used the transistor-transistor logic output signals from each modulator, which contain the information on the light polarization. These signals were introduced in a phase-detector circuit, which provided the phase difference value between both modulators. Three optical devices were used to test the synchronization method proposed: a polarizer, a half-wave, and a quarter-wave retarder plate. The value of each of the elements of the Müeller matrix for these devices was obtained using the method of the 36 measurements. The results show a high correlation between the theoretical and experimental values obtained. The results are also in accordance with other values obtained by different methods reported in the literature. Errors calculated by the proposed method are approximately in the order of a thousandth. The advantages and disadvantages of the method are discussed. [ABSTRACT FROM PUBLISHER]

A new algorithm for phasor estimation is proposed. It is based on a signal model that allows amplitude and phase dynamic variations. An autoregressive moving average (ARMA) model is assumed for the oscillating signal. Its autoregressive part is fixed, and it is defined only by the nominal fundamental frequency. Its best moving average parameters are estimated with Shanks' method. These parameters provide the key information from which the phasor state vector is estimated through the partial fraction expansion of the ARMA rational polynomial. These estimates could be useful, not only for the monitoring and controlling of the power system, but also for discriminating between a fault and an oscillation state. [ABSTRACT FROM AUTHOR]

An effective built-in self-test (BIST) structure of a phase-locked loop (PLL) in digital applications is presented in this paper. The proposed BIST structure can identify possible faults In any block such as the phase detector, charge pump, loop filter, voltage-controlled oscillator and divide-by-N of the PLL. The key advantage of this approach is that it uses all existing blocks in PLL for measuring and testing, reducing the chip area overhead. Restated, the proposed approach does not alter any existing analog circuits. Rather, the proposed approach only adds some small circuits to the PLL and requires a slight modification of the digital part. The final test outputs are digital values which can increase the reliability of the proposed BIST structure. Physical chip design and fault simulation results indicate the characteristics of the proposed BIST structure, namely, high fault coverage (97.2%) and low area overhead (2.78%). [ABSTRACT FROM AUTHOR]

This paper describes a measuring system developed to investigate time-variant impedances. The initial points for the development of the measuring system were investigations on coaxial λ/4-resonators. At a frequency close to the fundamental resonant frequency of the resonator, plasma can be generated at the tip of the inner conductor, operating the coaxial resonator on a high power level. First investigations had shown a significant change of the resonator input impedance at the feeding point during the process of plasma generation. To optimize the geometry of the resonator with regard to power consumption, time-, frequency- and power-dependent network models of the resonator including the plasma effects were to be found. In the following, a low-cost measuring system is described that facilitates accurate measurements of complex, time-variant input impedances in a defined frequency and power range. The measurement principle-like in commercially available network analyzers-is the determination of the magnitude and phase of the reflection coefficient with the subsequent calculation of the input impedance. To determine the time-variant behavior of the reflection coefficient, a modified detector circuitry is used. The measurement setup consists mainly of a directional coupler, a combined magnitude and phase detector, and an oscilloscope for sampling. Due to the applications the setup requires high-frequency and high-power supply. [ABSTRACT FROM AUTHOR]

Equivalent time oscilloscopes are widely used as an alternative to real-time oscilloscopes when high timing resolution is needed. For their correct operation, they need the trigger signal to be accurately aligned to the incoming data, which is achieved by the use of a clock and data recovery circuit (CDR). In this paper, a new multilevel bang-bang phase detector (BBPD) for CDRs is presented; the proposed phase detection scheme disregards samples taken close to the data transitions for the calculation of the phase difference between the inputs, thus eliminating metastability, one of the main issues hindering the performance of BBPDs. [ABSTRACT FROM PUBLISHER]