Intermediate Frequency Research Articles

At What Frequencies Should Air-Core Magnetics Be Used?

Magnetic components for power conversion (inductors and transformers) are often designed with magnetic cores, which add core loss but reduce the required number of turns, copper loss, and usually total loss. At very high frequencies, poor core materials make this tradeoff less advantageous and air-core magnetic components are often preferred. The boundary between the magnetic-core-preferred and air-core-preferred regimes has not yet been theoretically identified, and intermediate frequency ranges (e.g., 5–30 MHz) see both cored and air-core examples. In this work, we calculate various expressions that suggest that cored inductors can outperform their air-core counterparts up to many tens of megahertz on a volumetric basis and about 10 MHz on a mass basis, based on the properties of currently available magnetic materials. We experimentally demonstrate the boundary frequencies by comparing the quality factors of optimized magnetic-core and air-core toroidal inductors. Formally demonstrating the advantage of magnetic-core over air-core inductors suggests more advantageous design strategies at tens of megahertz, with significant impact on applications at industrial, scientific, and medical frequency bands (6.78, 13.56, and 27.12 MHz) and other radio frequencies.

Improving the Performance of Direct-Conversion SDRs for Radiated Precompliance Measurements

In this letter, a highly linear front end to improve the performance of software-defined radio (SDRs) for radiated precompliance measurements is presented. In CISPR band C/D, the test receiver needs to fulfill stringent requirements for using the quasi-peak detector. Usually, an expensive preselection filter bank is necessary to make fully compliant measurements of broadband transients. Direct-conversion-based SDRs show a limited out-of-the-box performance for precompliance measurements caused by, e.g., harmonic mixing and saturation effects. With the use of a triple-balanced mixer, a highly linear upconversion stage is built, eliminating the need for a filter bank. The dynamic range (DR) requirements for the SDR are strongly reduced by a narrowband intermediate frequency filter, making CISPR 16-1-1 compliant measurements possible. The sensitivity of the front end is comparable to professional receivers on the market, although no low-noise amplifier is implemented. The performance is verified by continuous wave (CW) and transient signals according to CISPR norms. The broadband measurement results are compared with traditional characterizations of the DR using the compression level and the noise figure. It shows that assumptions on the RF-link budget for a compliant design can be made with CW measurements. Based on our results, the requirements for the SDR front end are derived.

Hydrothermal Seismic Tremor in a Wide Frequency Band: The Nonvolcanic CO2 Degassing Site of Mefite d’Ansanto, Italy

ABSTRACT Mefite d’Ansanto (Italy) is a nonvolcanic field characterized by persistent strong degassing activity. A seismic field monitoring carried out during the Summer 2021 reveals a persistent, extended, and complex source of seismic tremor characterized by a spectrum with a frequency content from about 1 Hz to more than 35 Hz. While at frequency smaller than 3 Hz the signal amplitude is stationary, in the intermediate frequency band (3–20 Hz) sudden changes of amplitude are often observed, suggesting the existence of an intermittent source (every few minutes to tens of minutes). Furthermore, very short bursts of high-frequency energy are recognized in the tremor signal. Results of array analysis and seismological observation indicate that the sources of the analyzed tremor are located in a small area centered on the main vent of the degassing area. The persistent low-frequency tremor and the intermediate frequency signals propagate as surface waves to the seismic stations installed around the source and indicate a very shallow source. On the contrary, impulsive signals at frequencies greater than 20 Hz propagate as body waves, revealing a deeper source likely located between 50 and 100 m depth.

Simplified independent triple-sideband signal generation and transmission scheme based on one I/Q modulator at 0.3-THz.

To meet the ultra-bandwidth high-capacity communication, improve spectral efficiency and reduce the complexity of system structure, we have proposed the independent triple-sideband signal transmission system based on photonics-aided terahertz-wave (THz-wave). In this paper, we demonstrate up to 16-Gbaud independent triple-sideband 16-ary quadrature amplitude modulation (16QAM) signal transmission over 20 km standard single mode fiber (SSMF) at 0.3 THz. At the transmitter, independent triple-sideband 16QAM signals are modulated by an in-phase/quadrature (I/Q) modulator. Carrying independent triple-sideband signals optical carrier coupled with another laser to generate independent triple-sideband terahertz optical signals with a carrier frequency interval of 0.3THz. While at the receiver side, enabled by a photodetector (PD) conversion, we successfully obtain independent triple-sideband terahertz signals with a frequency of 0.3THz. Then we employ a local oscillator (LO) to drive mixer to generate intermediate frequency (IF) signal, and only one ADC is used to sample independent triple-sideband signals, digital signal processing (DSP) is finally performed to obtain independent triple-sideband signals. In this scheme, independent triple-sideband 16QAM signals is delivered over 20 km SSMF under the bit error ratio (BER) of 7% hard-decision forward-error-correction (HD-FEC) threshold of 3.8 × 10-3. Our simulation results show that the independent triple-sideband signal can further improve THz system transmission capacity and spectral efficiency. Our simplified independent triple-sideband THz system has a simple structure, high spectral efficiency, and reduced bandwidth requirements for DAC and ADC, which is a promising solution for future high-speed optical communications.

Calculation and measurement of coupling loss in a no-insulation ReBCO racetrack coil exposed to AC magnetic field

No-insulation coils are self-protecting and can therefore generally be operated at higher current densities. However, the electrical turn-to-turn connections may cause additional AC loss when charging the coil or when it is exposed to a time-dependent magnetic field. In this work, we study the case of a no-insulation ReBCO tape racetrack coil exposed to a uniform AC field applied parallel to the tape surface. We show that an anisotropic continuum model allows to formulate analytical approximations for coupling loss in the low- and high-frequency limits. For intermediate frequencies, the continuum model needs to be evaluated numerically. The model was validated with representative measurements of AC loss in the coils, measured calorimetrically as well as magnetically using pick-up coils. The validation experiment confirms the predicted frequency dependence of the coupling loss, which is at low frequencies and at high frequencies, due to the skin effect. The transition between low- and high-frequency regimes occurs around a characteristic frequency that is directly related to the characteristic time constant associated with the current decay in (dis)charge experiments.

The emergence of bubble-induced scaling in thermal spectra in turbulence

We report on the modification of the spectrum of a passive scalar inside a turbulent flow by the injection of large bubbles. Although the spectral modification through bubbles is well known and well analysed for the velocity fluctuations, little is known on how bubbles change the fluctuations of an approximately passive scalar, in our case temperature. Here we uncover the thermal spectral scaling behaviour of a turbulent multiphase thermal mixing layer. The development of a $-3$ spectral scaling is triggered. By injecting large bubbles ( ${Re}_{{bub}} = {O}(10^2)$ ) with gas volume fractions $\alpha$ up to 5 %. For these bubbly flows, the $-5/3$ scaling is still observed at intermediate frequencies for low $\alpha$ but becomes less pronounced when $\alpha$ further increases and it is followed by a steeper $-3$ slope for larger frequencies. This $-3$ scaling range extends with increasing gas volume fraction. The $-3$ scaling exponent coincides with the typical energy spectral scaling for the velocity fluctuations in high-Reynolds-number bubbly flows. We identify the frequency scale of the transition from the $-5/3$ scaling to the $-3$ scaling and show how it depends on the gas volume fraction.

Heterodyne performance and characteristics of terahertz MgB2 hot electron bolometers

We have studied THz heterodyne detection in sub-micrometer MgB2 hot electron bolometer (HEB) mixers based on superconducting MgB2 films of ∼5nm (HEB-A), corresponding to a critical temperature (Tc) of 33.9 K, and ∼7nm (HEB-B), corresponding to a Tc of 38.4 K. We have measured a double sideband (DSB) receiver noise temperature of 2590 K for HEB-A and 2160 K for HEB-B at 1.6 THz and 5 K. By correcting for optical losses, both HEBs show receiver noise temperatures of ∼1600 K referenced to the front of anti-reflection (AR)-coated Si lenses. An intermediate frequency (IF) noise bandwidth of 11 GHz has been measured for both devices. The required local oscillator (LO) power is about 13 μW for both HEBs. We have also measured a DSB receiver noise temperature of 3290 K at 2.5 THz and 5 K but with an AR-coated lens optimized for 1.6 THz. Besides, we have observed a step-like structure in current voltage (IV) curves, which becomes weaker when the LO power increases and observable only in their differential resistance. Such a correlated structure appears also in the receiver output power as a function of voltage, which is likely due to electronic inhomogeneities intrinsic to the variations in the thickness of the MgB2 films. Different behavior in the IV curves around the low bias voltages, pumped with the same LO power at 1.6 and 5.3 THz, was observed for HEB-B, suggesting the presence of a high-energy σ-gap in the MgB2 film.

End-to-End Real-Time Service Provisioning Over a SDN-Controllable Analog mmWave Fiber -Wireless 5G X-Haul Network

The current work presents the first experimental demonstration of real-time Ethernet (ETH) trial services and 4K-Ultra High Definition (UHD) video application transmission over a 2λ Wavelength Division Multiplexing (WDM) analog Fiber-Wireless (FiWi) mmWave X-haul network, supporting dynamic flexible capacity allocation through an integrated silicon photonic Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Reconfigurable Optical Add Drop Multiplexer (ROADM) and 60 GHz wireless transmission across a 7 m V-band link distance, while controlled by a Software Defined Network (SDN) controller based on Open Daylight. Analog X-haul transport of the radio signals is based on an Intermediate Frequency over Fiber (IFoF) scheme centered at 1.5 GHz using an Orthogonal Frequency Division Multiplexing (OFDM) radio-waveform with a bandwidth of 204 MHz, generated by a Field Programmable Gated Array (FPGA)-based RF System-on-Chip (SoC) processor that converts on-the-fly the real-time ETH downlink traffic to analog radio and vice-versa for the uplink. Dynamic allocation of the X-haul traffic capacity is handled through the use of the 802.1Q Virtual Local Area Network (VLAN) tag-mechanism, which controls the forwarding operation to the proper DAC and InP EML for optical modulation using Intensity Modulation/Direct Detection (IM/DD) schemes, while the wavelength routing operation is handled by the low-loss four-port Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ROADM featuring only 2.5 dB fiber-to-fiber losses based on a cascaded MZI-interleaver design on the TriPleX platform, routing the real-time traffic to a second mmWave antenna site. Detailed measurements and traffic statistics indicate end-to-end latency of less than 260 μs and a packet loss less than 0.0054% across a dynamic range of at least 6.5 dB in the optical domain, while the high user bandwidth and signal quality are validated by an uninterrupted 4K-UHD video transmission across the FiWi X-haul mmWave transport network. The current work aims to shape a complete technology roadmap for Point-to-Multipoint FiWi transport network architectures with high spectral efficiency X-haul transport for dense areas and 5G/6G hotspots of future mmWave Centralized Radio Access Networks (C-RANs).

A coherent MMW-ROF link employing mixed modulations and photonic down-conversion

We propose and experimentally demonstrate a coherent millimeter wave radio-over-fiber (MMW-ROF) link employing mixed modulations with a simple digital signal processing (DSP) unit. At the transmitter, a light wave is intensity and phase-modulated by two microwave vector signals in a dual-parallel Mach–Zehnder modulator (DP-MZM). At the receiver, by using a 3-line optical frequency comb (OFC) signal as the optical local oscillator (OLO), the microwave vector signals can be photonically down-converted to intermediate frequency (IF) signals. Then, instead of a complex digital phase-locked loop (DPLL), simple algorithms are used to remove the laser phase fluctuation between two free-running lasers and do the demodulations. In the 25 km fiber transmission experiments, we successfully down-convert two 50 Msymbol/s 16-quadrature amplitude modulation (16-QAM) signals at 25 GHz and 24 GHz to intermediate frequencies of 2 GHz and 1 GHz. The transmission performance of the proposed link in terms of error vector magnitudes (EVMs) are also investigated. The results show that when the receiver optical power is -20 dBm, the measured EVMs are still less than 12.5% which satisfies the 3rd Generation Partnership Project (3GPP) standard.

Human influenza virus infection elicits distinct patterns of monocyte and dendritic cell mobilization in blood and the nasopharynx.

During respiratory viral infections, the precise roles of monocytes and dendritic cells (DCs) in the nasopharynx in limiting infection and influencing disease severity are incompletely described. We studied circulating and nasopharyngeal monocytes and DCs in healthy controls (HCs) and in patients with mild to moderate infections (primarily influenza A virus [IAV]). As compared to HCs, patients with acute IAV infection displayed reduced DC but increased intermediate monocytes frequencies in blood, and an accumulation of most monocyte and DC subsets in the nasopharynx. IAV patients had more mature monocytes and DCs in the nasopharynx, and higher levels of TNFα, IL-6, and IFNα in plasma and the nasopharynx than HCs. In blood, monocytes were the most frequent cellular source of TNFα during IAV infection and remained responsive to additional stimulation with TLR7/8L. Immune responses in older patients skewed towards increased monocyte frequencies rather than DCs, suggesting a contributory role for monocytes in disease severity. In patients with other respiratory virus infections, we observed changes in monocyte and DC frequencies in the nasopharynx distinct from IAV patients, while differences in blood were more similar across infection groups. Using SomaScan, a high-throughput aptamer-based assay to study proteomic changes between patients and HCs, we found differential expression of innate immunity-related proteins in plasma and nasopharyngeal secretions of IAV and SARS-CoV-2 patients. Together, our findings demonstrate tissue-specific and pathogen-specific patterns of monocyte and DC function during human respiratory viral infections and highlight the importance of comparative investigations in blood and the nasopharynx.

Study on optimization of the dynamic performance of the robot bonnet polishing system

To solve the problem of processing quality degradation due to vibration in the robot bonnet polishing system (RBPS), the vibration generation mechanism of the polishing system is revealed based on the modal analysis and dynamic modeling of the RBPS. The modal analysis results showed that the operating frequency of the system is near the natural frequency, which makes the system susceptible to resonance. On the other hand, the forced vibration caused by the polishing force leads to high vibration at the end of the robot during the polishing process. In order to suppress the vibration generated by the polishing system and optimize the dynamic characteristics of the polishing system, a vibration suppression method to increase the damping ratio of the system was proposed. The experiments of SiC fixed point polishing were performed using both vibration suppression bonnet and original bonnet. The surfaces RMS and PV of the parts polished by the vibration suppression bonnet were generally better than those of the original bonnet. The vibration suppression bonnet has improved the convergence ratio of RMS and PV by 42.59% and 19.56% respectively over the original bonnet in the whole surface polishing experiments. The PSD analysis illustrated that the vibration suppression bonnet can better suppress the intermediate frequency errors. The effectiveness of the method in suppressing vibration and improving machining quality is demonstrated.

Multi-physics coupling simulation investigation of semi-solid A380 aluminum alloy during intermediate frequency electromagnetic stirring process

Multi-physics coupling simulation investigation of semi-solid A380 aluminum alloy during intermediate frequency electromagnetic stirring process

Development of VHF-Band Conformal Antenna for UAV Mounting

In this paper, a VHF band conformal antenna for UAV mounting was developed. The proposed antenna was designed as an shape-adaptive structure by minimizing the antenna height to be advantageous in RCS reduction performance. As for the antenna radiator, the outer radiator was arranged around the inner radiator to apply the CRLH zeroth-order resonance structure. With this structure, the height of the antenna was minimized, and it was reduced by about 70 % compared to the existing blade antenna. In addition, for impedance matching, the intermediate frequency bandwidth of the VHF band was improved through the sleeve pin of the inner radiator, and the low frequency bandwidth of the VHF band was improved by applying an EMI shielding gasket to the shorting pin of the outer radiator. The proposed antenna was manufactured and measured to verify the performance of the device and the performance after UAV mounting. As a result, the standard was satisfied for the operating frequency.

Wideband Frequency and Angle-of-Arrival Measurement System Based on Optical Subsampling

We proposed a system that simultaneously supports measuring the frequency and the angle of arrival (AOA) of the radio frequency (RF) signal. In the proposed system, the RF signals from different antennas are loaded on different arms of a dual-polarization Mach-Zehnder modulator (Dpol-MZM) and are subsampled by dual optical combs, respectively. The frequency of the receiving RF signal can be obtained from two intermediate frequencies (IF), and AOA can be obtained from the phase difference between the upper- and lower-channel IF signals. In the experiment, 0.5–40 GHz frequency measurement range with an error of ±0.06 MHz and ±180 phase shift measurement range with an error of 1.8 can be achieved based on a low-frequency electronic analog-to-digital converter (ADC). The processing of both broadband signal and multitone signal and the system stability are also verified.

Design of a Simultaneous Information and Power Transfer System Based on a Modulating Feature of Magnetron

According to the nonlinear response characteristics of magnetron, this article proves that a 2.45 GHz band continuous-wave magnetron can perform as a modulator in communication system. The intermediate frequency (IF) signal coupled to the power supply of magnetron, as the ripple of anode voltage, can be modulated to a nearby band centered on the resonant frequency of magnetron. We deduced the output expression of free oscillating magnetron under the influence of anode voltage ripple. And electromagnetic simulation was accomplished to testify the validity of the theoretical derivation. Moreover, we designed the circuit to couple signal with frequencies of 2, 3, and 4 MHz to the anode voltage. The output spectrum of magnetron changed as the frequencies were tuned, to satisfy the frequency requirements for modulating. Finally, a simultaneous information and power transfer system based on a magnetron combined with the power supply coupling circuit was developed and tested. This system achieved the modulation, amplification, transmission, and demodulation of low-frequency signal which is equivalent to human voice. This research reveals that the proposed techniques have great potential for future simultaneous wireless information and power transfer (SWIPT) system because they provide higher power at lower cost.

Analysis of Error Rate and Capacity in the Presence of I/Q Imbalances Over an Impulsive Noise Channel

Many state-of-the-art unmanned aerial vehicle-assisted communication systems adopt quadrature amplitude modulation (QAM) and zero intermediate frequency (IF) architecture. In zero-IF QAM devices, in-phase/quadrature (I/Q) amplitude and phase imbalances cause severe performance degradation. In addition, the performance of the devices in close proximity to the impulsive noise sources can also be significantly degraded. In this article, we derive and analyze the symbol error rate (SER) of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary square QAM and the channel capacity of a system in the presence of I/Q imbalance over an impulsive noise channel. We first present an exact expression for the joint probability density function (PDF) of the demodulated I/Q signals affected by impulsive noise. By using the derived PDF, we then provide exact expressions for SER and SER floor of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary square QAM and average and asymptotic channel capacities of the system with I/Q amplitude and phase imbalances over an impulsive noise channel. We validate the theoretical results through computer simulations.

A room-temperature, low-impedance and high-IF-bandwidth terahertz heterodyne detector based on bowtie-antenna-coupled AlGaN/GaN HEMT

In this paper, a 330 GHz terahertz heterodyne detector based on bowtie-antenna-coupled AlGaN/GaN high-electron-mobility transistor (HEMT) is designed and demonstrated. The bowtie antenna and a silicon lens couple the terahertz wave into a transmission line, in which the HEMT's channel generates both self-mixing and heterodyne signals. Compared to field-effect detectors without front low-noise amplifiers and output impedance matching, this detector boosts the intermediate-frequency (IF) bandwidth to 2.9 GHz due to a low output impedance of 505 Ω while maintaining a comparable sensitivity. With further sensitivity enhancement, such detectors would be developed into room-temperature, high-sensitivity, and high-IF-bandwidth heterodyne arrays.

The response of a conical flame to a dual-frequency excitation

This work investigates the response of a conical premixed flame to a dual-frequency excitation, based on the integrated CH* signal collected from a photomultiplier tube (PMT), the upstream velocity disturbance measured by a hotwire, and the chemiluminescence signal captured by high-speed imaging. The results show that, in addition to the excitation frequencies, a notable flame response can also be observed at the difference frequency, where the corresponding velocity fluctuation is relatively small. This result means that, at the difference frequency, the velocity fluctuation contributes little to the flame response. Such interacted response generally occurs at intermediate excitation frequencies but tends to disappear as either excitation frequency is below the cut-off frequency. And it increases linearly with the excitation amplitude, with nearly zero dependence on the phase difference. Furthermore, the flame front is extracted based on the chemiluminescence images to analyze the flame area fluctuation. The resultant phase response implies that the fluctuation of the difference frequency propagates downstream convectively, similar to that of the excitation frequencies. Interestingly, the flame area fluctuation at the difference frequency shows significant response and a low-pass characteristic, whereas the CH* fluctuation approaches zero at those low frequencies.

Machine learning assisted hepta band THz metamaterial absorber for biomedical applications

A hepta-band terahertz metamaterial absorber (MMA) with modified dual T-shaped resonators deposited on polyimide is presented for sensing applications. The proposed polarization sensitive MMA is ultra-thin (0.061 λ) and compact (0.21 λ) at its lowest operational frequency, with multiple absorption peaks at 1.89, 4.15, 5.32, 5.84, 7.04, 8.02, and 8.13 THz. The impedance matching theory and electric field distribution are investigated to understand the physical mechanism of hepta-band absorption. The sensing functionality is evaluated using a surrounding medium with a refractive index between 1 and 1.1, resulting in good Quality factor (Q) value of 117. The proposed sensor has the highest sensitivity of 4.72 THz/RIU for glucose detection. Extreme randomized tree (ERT) model is utilized to predict absorptivities for intermediate frequencies with unit cell dimensions, substrate thickness, angle variation, and refractive index values to reduce simulation time. The effectiveness of the ERT model in predicting absorption values is evaluated using the Adjusted R2 score, which is close to 1.0 for nmin = 2, demonstrating the prediction efficiency in various test cases. The experimental results show that 60% of simulation time and resources can be saved by simulating absorber design using the ERT model. The proposed MMA sensor with an ERT model has potential applications in biomedical fields such as bacterial infections, malaria, and other diseases.

Photonic-Assisted Scheme for Simultaneous Self-Interference Cancellation, Fiber Dispersion Immunity, and High-Efficiency Harmonic Down-Conversion.

A photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity and harmonic frequency down-conversion function is proposed based on an integrated, dual-parallel, dual-drive Mach-Zehnder modulator (DP-DMZM). A dual-drive Mach-Zehnder modulator (DMZM) is used as an optical interference canceller, which cancels the self-interference from the impaired signal before fiber transmission to avoid the effect of fiber transmission on the cancellation performance. Another DMZM is used to provide carrier-suppressed, local-oscillation (LO)-modulated, high-order double optical sidebands for harmonic frequency down-conversion to release the strict demand for high-frequency LO sources. By regulating the DC bias of the main modulator, the signal of interest (SOI) can be down-converted to the intermediated frequency (IF) band after photoelectric conversion with improved frequency-conversion efficiency, immunity to the fiber-dispersion-induced power-fading (DIPF) effect, and effective signal recovery. Theoretical analyses and simulation results show that the desired SOI in the X and K bands with a bandwidth of 500 MHz and different modulation formats can be down-converted to the IF frequency. The self-interference noise with the 2 GHz bandwidth is canceled, and successful signal recovery is achieved after a 10 km fiber transmission. The recovery performance of down-converted signals and the self-interference cancellation depth under different interference-to-signal ratios (ISRs) is also investigated. In addition, the compensation performance of DIPF is verified, and a 6 dB improvement in frequency conversion gain is obtained compared with previous work. The proposed scheme is compact, cost-effective, and thus superior in wideband self-interference cancellation, long-range signal transmission, and effective recovery of weak desired signals.