In-phase Components Research Articles

Frequency-Domain Electromagnetic Forward and Sensitivity Modeling: Practical Aspects of Modeling a Magnetic Dipole in a Multilayered Half-Space

Frequency-domain electromagnetic (FDEM) data are commonly acquired to provide spatially continuous information about subsurface electrical conductivity (EC) and/or magnetic susceptibility [1]. To link the phase-sensitive instrument responses?the quadrature-phase (QP) and in-phase (IP) components of the EM field (i.e., data space)-with the subsurface physical properties (i.e., model space), a forward model is indispensable. In addition, a forward model is essential for calculating the FDEM instrument response theoretically, e.g., during an inversion, and can be used for additional purposes, such as instrument calibration, synthetic data generation, depth of investigation estimation, instrument design, survey design, assessment of the detection limit for a given target within a known host body, apparent EC estimation, and educational purposes [2]-[7].

An Efficient Interface Circuit for Lossy Capacitive Sensors

This paper presents a low-cost interface circuit for lossy capacitive sensors. Most of the capacitive sensors are lossy in nature, where the resistance value of the sensor significantly varies along with the capacitance value. Accurate measurement of those values of a lossy capacitive sensor is a challenging task. This paper deals with the development of an electronic interface circuit for such a capacitive sensor. The circuit is based on the measurement of quadrature and in-phase components of the signal. To extract the actual value of the capacitance and the resistance, an average of the quadrature and the in-phase components of output is required. This is implemented using a microcontroller and provides flexibility in averaging (e.g., adjustable length of data to be processed). A PCB of the circuit has been fabricated and tested in the laboratory using capacitors and resistors with known values. The accuracy of the circuit was better than 0.6% and −2.2% for the measurement of capacitance and resistance, respectively. Also, the circuit is highly linear (FS nonlinearity of 0.32%) for a wide range of capacitance measurement (162 pF–3.680 nF). To confirm the effectiveness of the circuit, it was interfaced to a lossy capacitive humidity sensor and another capacitive transducer to measure the dielectric constants of edible oils. The results were compared with a precision impedance analyzer (Agilent 4294A); the maximum relative error was noted as ±1.6% in the measurement of permittivity values of edible oil. The prototype developed has the option to easily adjust the sensitivity and operating range, depending on the application.

THE PROCESSING OF THE ELLIPTICALLY POLARIZED SIGNAL IN RADAR STATIONS WITH DIGITAL SYNTHESIS OF THE ANTENNA APERTURE

The processing of the elliptically polarized reflected signal in the Earth remote sensing systems makes it possible to obtain additional advantages when solving problems of recognition of the observable objects on the ground and under the ground. Full polarization reception implemented in radar stations with digital synthesis of the antenna aperture when remote sensing of the Earth increases the information content of such radars (the radar image of the investigated surface is detailed, the contrast of objects in the field of view is improved, and various negative effects of the image are minimized). The paper considers the quadrature processing of the reflected elliptically polarized signal in radar stations with digital synthesis of the antenna aperture in the mode of lateral survey of the terrestrial (water) surface. The processing of the reflected signal using the methods of radio polarimetry opens new possibilities for such radars while solving problems of remote sensing of the surface and recognition of radar targets. In addition, radar stations with digital synthesis of the antenna aperture with processing of an elliptically polarized signal have a higher interference immunity compared to radars, where a linearly polarized signal is processed. In the article, mathematical modeling is performed in the part of demodulation of the in-phase and quadrature components of the trajectory signal when the geometric parameters of the polarization ellipse change. The obtained analytical expressions allow estimating the influence of the geometric parameters of the polarization ellipse on the trajectory signal being processed. It is analytically confirmed that the angle of ellipticity affects the energy characteristics, and the orientation angle of the polarization ellipse introduces an additional phase shift in the characteristics of the trajectory signal being processed. Not taking into account these nuances while designing digital units and systems of such radars can lead to the loss of all the benefits of processing an elliptically polarized signal. The paper presents a structural scheme of the polarization radar station with digital synthesis of the antenna aperture.

The power of frequency domain EM; principles and case histories

Frequency domain EM uses tuned circuitry to get maximum efficiency out of a small electromagnetic system. This small size allows for measurements unique to FDEM, including vertical coaxial (X component) transmitters and the in-phase component of the secondary field. These measurements provide spatial resolution and sensitivity to a range of conductivity wider to commercially available time domain EM systems.

Effective focusing of a diverging atomic beam by a sequence of alternatively chirped few-cycle pulsed laser fields

We theoretically show how the effective focusing and defocusing of a diverging atomic beam can be realized using an appropriate sequence of linearly chirped few-cycle pulsed laser fields. First, we investigate and show that the time averaged optical dipole force induced by the sequence of either positively or negatively chirped pulses vanishes due to the periodic oscillations of the phases of in-phase components of atomic dipole moments. Then, we demonstrate that this issue could be overcome by utilizing a sequence of alternatively chirped pulses instead of either positively or negatively chirped pulses. It is shown that for such a sequence of pulses, the phases of in-phase components of atomic dipole moments does not oscillate periodically and in fact remain constant at either 0 or $\ensuremath{\pi}$ depending on the chirping direction of the initial pulse, resulting in either an effective focusing or defocusing optical dipole force. The trajectory of atoms under an optical dipole force is also investigated to actually show the focusing and defocusing. Finally, the role of beam shape on the proposed scheme is investigated and it turns out that a super-Gaussian pulse of order $m=2$ shows more efficacy compared to the normal Gaussian pulse.

High-Efficiency Modes Contiguous With Class B/J and Continuous Class F<inline-formula> <tex-math notation="LaTeX">$^{-1}$ </tex-math> </inline-formula> Amplifiers

We propose a new formulation for high-efficiency modes of power amplifiers in which both the in-phase and out-of-phase components of the second harmonic of the current are varied, in addition to the second-harmonic component of the voltage. A reduction of the in-phase component of the second harmonic of current allows reduction of the phase difference between the voltage and current waveforms, thereby increasing the power factor and efficiency. Our proposed waveforms offer a continuous design space between the class B/J continuum and continuous $\text{F}^{-1}$ achieving an efficiency of up to 91% in theory but over a wider design space than $\text{F}^{-1}$ . These waveforms require a short at third and higher harmonic impedances, which are easier to achieve at higher frequency. The fabricated amplifier using a GaN HEMT CGH40010F achieves 79.7% drain efficiency and 42.2-dBm saturated output power at 2.6 GHz, which gives a frequency weighted efficiency of 92.4% $\sqrt [{4}]{\mathrm{ GHz}}$ with this device.

Compact, high-sensitivity atomic magnetometer utilizing the light-narrowing effect and in-phase excitation.

A high-sensitivity optically pumped atomic magnetometer working in the geomagnetic range utilizing the light-narrowing effect and in-phase excitation is described. The setup is based on a simple pump-probe arrangement built around a Cs vapor cell whose active volume is 64 mm3. The transverse oscillating field is applied parallel to the probe beam to drive Zeeman resonance, and the in-phase component of the resonance signal is measured to determine the field. The sensitivity of the magnetometer is improved by pumping most atoms into the stretched state. Consequently, spin-exchange relaxation is suppressed, and a sensitivity of 0.1 pT/Hz1/2 in the range of 10μT is achieved. This magnetometer has the advantages of large dynamic range, high performance of low-frequency stabilization, high response speed, and compact size. It can be used for many cutting-edge applications such as detection of magnetic anomalies.

A comparative study for the source depth estimation of very low frequency electromagnetic (VLF-EM) signals

In general, a quantitative interpretation of geophysical data yields information on the nature of subsurface structures of geologic interest besides depth of the source and the associated physical property contrast. However, all geophysical interpretation invariably incurs an inherent ambiguity including VLF-EM method. Techniques such as Karous-Hjelt (KH) current density, Hilbert transform etc. are in vogue to estimate the depth to the source that are either qualitative or semi quantitative. Here, we present a comparative analysis of the depth derived from VLF-EM signals by different methods over a uranium rich basement fractures of Raigarh District, Chhattisgarh, India. The obtained results are based on techniques that are not very common in VLF-EM data interpretation such as Euler deconvolution (ED), Hartley spectral analysis and analytical signal approach of denoised in-phase component realized by Empirical Ensemble Mode Decomposition (EEMD). The estimated depth from ED and Hartley spectral analysis range 10–62 m and 12–40 m respectively are compared with KH pseudo section, Hilbert transform and drilling depth. Overall, the results of the aforesaid techniques have shown satisfactory comparison wherein the Hilbert transform of EEMD de-noised in-phase component of traverse T1 (35 m), Hartely power spectrum of the principal profile PPQ (40 m) and the radially averaged power spectrum (38.8 m and 40 m) are close to the drilling depth. Therefore, the results obtained by methods presented emphasize that these techniques are equally applicable to VLF-EM signals for estimation of depth to subsurface conductors.

On-Chip Optical Vector Quadrature De-Multiplexer Proposal for QAM De-Aggregation by Single Bi-Directional SOA-Based Phase-Sensitive Amplifier

In this paper, a simple optical vector quadrature de-multiplexer (QD) scheme is proposed for de-aggregating input 10 Gbaud 16/32/64 quadrature amplitude modulation (QAM) signals into two pulse amplitude modulation (PAM) streams. The proposed QD is based on a single bi-directional degenerate phase-sensitive amplifier (PSA), where the wavelength and the polarization status of the extracted in-phase and quadrature components stay the same as the input signal. Since the proposed QD is realized using PSA based on semiconductor optical amplifier (SOA), it is also possible to realize an on-chip QD system, providing an integrated platform for optical signal processing. Through numerical simulation, the transfer characteristics of the proposed QD system show that the SOA-based PSA has a high phase-sensitive gain extinction ratio of 44.1 dB. The constellations, error vector magnitudes (EVMs), and bit-error rates (BERs) of the data streams after the de-aggregation are numerically investigated to verify the proposed QD scheme. For the 10 Gbaud 16/32/64 QAM signals with an input optical signal-to-noise ratio (OSNR) of 25 dB, the de-aggregated PAM4/PAM6/PAM8 signals show 6.1, 5.6, and 8.2 dB receiver OSNR improvements at the BER of 10−3, respectively. Also, to optimize the performance of the subsystem, the BER performance dependence on the phase difference between two arms in the subsystem is also examined. The simulation results reveal that the proposed QD can accomplish the function of optical vector de-aggregation well for the high-level QAM signals. The proposed QD can be applied to information de-aggregation, format conversion, and direct detection for optical vector signals, which may have great potential values for the flexible optical networks.

A Phasor-Based Analysis of Sinusoidal Injection Locking in LC and Ring Oscillators

A new perspective into the locking behavior of LC and ring oscillators is presented. By decomposing a sinusoidal injection current into in-phase and quadrature-phase components, exact expressions for the amplitude and phase of an injection-locked LC oscillator which hold for any injection strength and frequency are derived and confirmed by simulation. The analysis, which can be naturally extended to an arbitrary LC resonator topology, leads to a rigorous understanding of the fundamental physics underlying the locking phenomenon. Furthermore, an investigation of the different necessary and sufficient conditions for injection locking to occur is carried out, leading to a more precise notion of the lock range. The ring oscillator is also analyzed in an analogous fashion, resulting in simple yet accurate closed-form expressions for the fractional lock range in the small-injection and long-ring regimes; the expressions are validated by simulations of single-ended inverter-based ring oscillators in 65-nm CMOS. The mathematics behind how the injection modifies the phase delay contributed by each stage in the ring is discussed. A corollary that generalizes the small-injection lock range to any feedback-based oscillator topology is established. Conceptual and analytical connections to the existing literature are reviewed.

High-Accuracy Real-Time Monitoring of Heart Rate Variability Using 24 GHz Continuous-Wave Doppler Radar

This paper presents a novel algorithm for the estimation of heart rate variability (HRV) features using 24-GHz continuous-wave Doppler radar with quadrature architecture. The proposed algorithm combines frequency and time domain analysis for high-accuracy estimation of beat-to-beat intervals (BBIs). Initially, band pass filtered in-phase (I) and quadrature (Q) radar components are fused into a single combined signal that contains information on the heartbeats. Its frequency domain analysis is used for coarse heart rate estimation. At the same time, the combined signal is processed using a filter bank containing narrowband band pass filters with different center frequencies. One of the band pass filter outputs is selected as the valid output based on the coarse heart rate estimation. Zero crossings in the resulting filter bank output signal represent heartbeats that are used to extract the BBIs. Finally, four HRV features are calculated from the BBIs. The algorithm is tested on real data obtained from recordings on ten human subjects. The mean relative error of extracted BBIs compared to electrocardiogram (ECG) measurement is in the 1.02–2.07% range. Furthermore, two time-domain and two frequency domain HRV features were calculated from the BBIs. The obtained results show a high level of agreement between radar-extracted and ECG-extracted HRV features. Low computation complexity makes this algorithm suitable for real-time monitoring.

Energy and Spectrally Efficient Modulation Scheme for IoT Applications.

Due to the Internet of Things (IoT) requirements for a high-density network with low-cost and low-power physical (PHY) layer design, the low-power budget transceiver systems have drawn momentous attention lately owing to their superior performance enhancement in both energy efficiency and hardware complexity reduction. As the power budget of the classical transceivers is envisioned by using inefficient linear power amplifiers (PAs) at the transmitter (TX) side and by applying high-resolution analog to digital converters (ADCs) at the receiver (RX) side, the transceiver architectures with low-cost PHY layer design (i.e., nonlinear PA at the TX and one-bit ADC at the RX) are mandated to cope with the vast IoT applications. Therefore, in this paper, we propose the orthogonal shaping pulses minimum shift keying (OSP-MSK) as a multiple-input multiple-output (MIMO) modulation/demodulation scheme in order to design the low-cost transceiver architectures associated with the IoT devices. The OSP-MSK fulfills a low-power budget by using constant envelope modulation (CEM) techniques at the TX side, and by applying a low-resolution one-bit ADC at the RX side. Furthermore, the OSP-MSK provides a higher spectral efficiency compared to the recently introduced MIMO-CEM with the one-bit ADC. In this context, the orthogonality between the in-phase and quadrature-phase components of the OSP are exploited to increase the number of transmitted bits per symbol (bps) without the need for extra bandwidth. The performance of the proposed scheme is investigated analytically and via Monte Carlo simulations. For the mathematical analysis, we derive closed-form expressions for assessing the average bit error rate (ABER) performance of the OSP-MSK modulation in conjunction with Rayleigh and Nakagami-m fading channels. Moreover, a closed-form expression for evaluating the power spectral density (PSD) of the proposed scheme is obtained as well. The simulation results corroborate the potency of the conducted analysis by revealing a high consistency with the obtained analytical formulas.

Simulations and Measurements of Eddy Current Magnetic Signatures

Abstract Eddy current magnetic signature is, together with magnetization of ferromagnetic hull, mechanisms and devices on board, corrosion related and stray field sources one of the main sources of ship’s magnetic signature. Due to roll, pitch and yaw of the ship in external magnetic field, eddy currents are induced in conducting materials on board ship, mainly in conducting hull. Flow of those currents is a source of magnetic field around a ship. Principal eddy current component is related to roll movement as it depends on rate of change of external field which is the highest for roll. Induced currents have both in-phase and quadrature components. Magnitude of the eddy current magnetic field can have significant effect on total magnetic field signature after degaussing for ships such as mine sweepers and mine hunters. Paper presents calculations and simulations as well as measurements of model and physical scale model made of low magnetic steel performed in Maritime Technology Center. Contribution of eddy current magnetic field in total field in low roll frequencies has been estimated.

A Novel Digital-Intensive Hybrid Polar-I/Q RF Transmitter Architecture

A novel digital-intensive hybrid transmitter (TX) architecture is presented, combining conventional inphase and quadrature (I/Q) with constrained phase modulation. The proposed architecture utilizes an RF-DAC with phase modulated RF clock and adjusted I/Q components. By incorporating phase modulation the quadrature component is kept small while the inphase component approaches the complex signal envelope. Compared to a digital-quadrature TX architecture this results in a significantly reduced average and peak RF-DAC cell utilization. Therefore, the RF-DAC can be operated in less back-off at higher average output power and drain efficiency. The phase modulation is constrained in order to relax the phase modulators system requirements. Compared to a digital polar TX architecture utilizing an RF digital phase-locked loop with two-point phase modulation, this results in reduced frequency modulation and digital-controlled oscillator tuning range requirements. In addition, the design effort is further shifted from analog to digital domain in order to better exploit the benefits of CMOS technology scaling.

Geophysical and geochemical investigation for structures favorable to uranium mineralization in Dhofar region, Sultanate of Oman

The very low frequency electromagnetic (VLF-EM) method is a rapid and reliable geophysical method was used in the investigation for uranium bearing structures in the Proterozoic basement of the Dhofar region that may be a potential source and trap for uranium and associated minerals in Sultanate of Oman. Accordingly, the in-phase and out of phase components of VLF-EM field along 11 traverses were recorded at two different transmitter frequencies viz. 16 kHz and 16.4 kHz at an approximate line interval of 20 m with a measurement interval of 10 m. These measured components were subjected to Fraser and Karous-Hjelt filtering in order to decipher the nature and depth to the sub-surface conductor. The Fraser filtered in-phase VLF-EM components yield a strong amplitude almost over the top of the conductor. On the other hand, the Hjelt filtered responses yield the depth to the source in the range 10–80 m. Spectral analysis of selected a few traverses result the depth to source in the range 31–39 m. Analytical signal approach of total magnetic field of line-I substantiates this depth. The peaks of Fraser filtered stacked profiles delineate approximately the trend of the sub-surface fault which mimic the trend inferred from the combined interpretation of VLF-EM and magnetic anomalies. The results of Fraser and Karous-Hjelt filter output suggest a mineralized conductive sub-surface fault aligned along NW-SE. It may be noted that the random sampling of gamma ray spectrometer has recorded a maximum uranium concentration of up to 30–40 ppm prior to VLF-EM survey.

Multi-frequency effect towards High Conductivity Overburden Responses using Vertical Coplanar (VCP) coil configuration for Landslide Instrumentation

A novel instrumentation for landslide application has been made and calibrated using Vertical Coplanar (VCP) coil orientation. The early instrumentation and commonly used right now for landslide slopes was gradually equipped with standard and automatic instrumentation: three the piezometric cells, two deep-seated steel wire extensometers, four inclinometric tubes, a rainfall gauge, a snow gauge and an air thermometer. This novel instrumentation works in electromagnetic methods similar with electromagnetic methods in geophysics; otherwise, the system was mechanics and electronics. VCP coil orientation is a coplanar array where both coils are vertical. In VCP, the depth of sounding is about 1.5 times of the coils separation. The overburden thicknesses in the field exploration are often covering the tropical area and presented as weathering layer. The more of overburden thickness then the more of energy of electromagnetic wave will be absorbed, as the result that the electromagnetic wave becomes smaller. The electromagnetic wave that reaches the target of the subsurface is also become smaller in amplitude. The multi-frequency application would be helpful in the data interpretation of the anomaly position and the conductive overburden caused by the domination trends between out-of-phase (OP) and in-phase (IP) components could be determined. In the higher frequencies (3037.5 Hz and 1012.5 Hz), the curve of IP is raised up, with the result that the positive peak values become higher and the negative peak values become lower in levels. The multi-frequency application gives the results that in the higher frequency examinations, the anomaly response is influenced significantly by the conductive overburden. In the lower frequency measurements, the anomaly response is not influenced significantly by overburden response. In the higher frequency measurements, when the electromagnetic wave is passing through the conductive material, the amplitude attenuation and the phase shifting are occurred. Therefore, the OP response becomes inverted in the peaks.

Augmented Hammerstein model for the calibration of six-port based dual band wireless receivers

Two architectures of concurrent dual-band six-port-based receiver (SPR), which are modeled and calibrated using the augmented Hammerstein model (AHM) are proposed for the first time in this article. The receivers are based on six-port junctions with one or two local oscillators (LO). The proposed single step calibration algorithms achieve the recovery of the two in-phase (I1 and I2) and quadrature (Q1 and Q2) components of an RF signal with two frequency components (RF1 and RF2). Experimental validations have been performed to verify the performance of the proposed concurrent dual-band receivers and to test the efficiency of the AHM based calibration algorithms. As a performance metric, the Error Vector Magnitude (EVM) has been measured to compare the transmitted and recovered baseband signals and to evaluate the performance and efficiency of the proposed calibration algorithms for the two receiver topologies. The IQ data has been recovered with EVMs no higher than 2% for the two LOs based receiver excited with a QAM modulated dual-band RF signal. The single LO based receiver has been tested with a dual-band LTE signal and the recovered IQ data exhibited EVMs no higher than 4%.

Evaluation of two-point Dixon water-fat separation for liver specific contrast-enhanced assessment of liver maximum capacity

Gadoxetic acid-enhanced magnetic resonance imaging has become a useful tool for quantitative evaluation of liver capacity. We report on the importance of intrahepatic fat on gadoxetic acid-supported T1 mapping for estimation of liver maximum capacity, assessed by the realtime 13C-methacetin breathing test (13C-MBT). For T1 relaxometry, we used a respective T1-weighted sequence with two-point Dixon water-fat separation and various flip angles. Both T1 maps of the in-phase component without fat separation (T1_in) and T1 maps merely based on the water component (T1_W) were generated, and respective reduction rates of the T1 relaxation time (rrT1) were evaluated. A steady considerable decline in rrT1 with progressive reduction of liver function could be observed for both T1_in and T1_W (p < 0.001). When patients were subdivided into 3 different categories of 13C-MBT readouts, the groups could be significantly differentiated by their rrT1_in and rrT1_W values (p < 0.005). In a simple correlation model of 13C-MBT values with T1_inpost (r = 0.556; p < 0.001), T1_Wpost (r = 0.557; p < 0.001), rrT1_in (r = 0.711; p < 0.001) and rrT1_W (r = 0.751; p < 0.001), a log-linear correlation has been shown. Liver maximum capacity measured with 13C-MBT can be determined more precisely from gadoxetic acid-supported T1 mapping when intrahepatic fat is taken into account. Here, T1_W maps are shown to be significantly superior to T1_in maps without separation of fat.

Differential equations for recovery of the average differential susceptibility of superconductors from measurements of the first harmonic of magnetization

In the paper, inhomogeneous differential equations are obtained to reconstruct the average differential susceptibility of type-II superconductors from the in-phase (real) component of the magnetization’s first harmonic in the hysteresis case. Basing on the second-order differential equation, mathematical modeling of the average differential susceptibility for the theoretical and experimental dependence of the real part of the magnetization’s first harmonic is performed. The Cauchy problem was solved numerically by the Runge-Kutta method of the fourth order of accuracy. To do this, the differential equation for the restoration of the average susceptibility was reduced to a system of differential equations. On the basis of the method developed in the work, the average differential susceptibility of a disc-shaped polycrystalline superconductor YBa2Cu3O7−x was reconstructed from the experimentally obtained first harmonic of magnetization in interval of magnetic fields from 0 to 800 Oe.

Differential equations for recovery of the average differential susceptibility of superconductors from measurements of the first harmonic of magnetization

In the paper, inhomogeneous differential equations are obtained to reconstruct the average differential susceptibility of type-II superconductors from the in-phase (real) component of the magnetization’s first harmonic in the hysteresis case. Basing on the second-order differential equation, mathematical modeling of the average differential susceptibility for the theoretical and experimental dependence of the real part of the magnetization’s first harmonic is performed. The Cauchy problem was solved numerically by the Runge-Kutta method of the fourth order of accuracy. To do this, the differential equation for the restoration of the average susceptibility was reduced to a system of differential equations. On the basis of the method developed in the work, the average differential susceptibility of a disc-shaped polycrystalline superconductor YBa2Cu3O7−x was reconstructed from the experimentally obtained first harmonic of magnetization in interval of magnetic fields from 0 to 800 Oe.