Radio Frequency Oscillator Research Articles

Amplitude and frequency modulation based on memristor-controlled spin nano-oscillators

Spin transfer nano-oscillators (STNOs) are a new type of radio frequency (RF) oscillators that utilize the current-induced magnetization precession in a magnetic tunnel junction device to generate high frequency microwave signal. Since both the frequency and the amplitude of STNOs can be tuned by changing the current, they are potentially used for amplitude shift keying and frequency shift keying modulation without the need for an RF mixer, which leads to compact RF components. In this letter, a novel strategy is proposed to modulate the frequency and the amplitude by memristor-controlled spin nano-oscillators, whereby the STNO is responsible for microwave emitting and memristor serves as a current regulator which further modulates the frequency and amplitude. In addition, the I–V curves show that a multilevel resistance behavior can also be achieved in the same architecture.

Spatiotemporal oscillation of an ion beam extracted from a potential-oscillating plasma source

A radiofrequency oscillation is successfully superimposed on a plasma potential of a filamented source plasma in an ion beam source while maintaining a constant plasma density, in order to investigate effects of oscillating source plasma potential on an extracted ion beam. The experiment is preliminarily performed with a positive argon ion beam source. A class-D amplifier operational over a wide range of a frequency from a few tens of kHz to several MHz is installed; leading the oscillation of the plasma potential in the plasma source for the frequency range being tested. The beam current profile downstream of the extraction grids shows an oscillation of the beam current at the peripheral region of the ion beam; implying that the oscillation of a beam halo is induced by the potential oscillation of the source plasma.

Silicon Carbide BJT Oscillator Design Using S-Parameters

Radio frequency (RF) oscillator design typically requires large-signal, high-frequency simulation models for the transistors. The development of such models is generally difficult and time consuming due to a large number of measurements needed for parameter extraction. The situation is further aggravated as the parameter extraction process has to be repeated at multiple temperature points in order to design a wide-temperature range oscillator. To circumvent this modelling effort, an alternative small-signal, S-parameter based design method can be employed directly without going into complex parameter extraction and model fitting process. This method is demonstrated through design and prototyping a 58 MHz, high-temperature (HT) oscillator, based on an in-house 4H-SiC BJT. The BJT at elevated temperature (up to 300 0C) was accessed by on-wafer probing and connected by RF-cables to the rest of circuit passives, which were kept at room temperature (RT).

Measuring the Power Law Phase Noise of an RF Oscillator with a Novel Indirect Quantitative Scheme

In conventional phase noise metrology, the phase noise of an oscillator is measured by instruments equipped with specialized and sophisticated devices. Such hardware-based testing usually requires high-performance and costly apparatuses. In this paper, we carried out a novel phase noise measurement method based on a mathematical model. The relationship between the phase noise of a radio frequency oscillator and its power spectral density (PSD) was established, different components of the power law phase noise were analyzed in the frequency domain with their characteristic parameters. Based on the complete physical model of an oscillator, we fitted and extracted the parameters for the near-carrier Gaussian and the power law PSD with Levenberg-Marquardt optimization algorithm. The fitted parameters were used to restore the power law phase noise with considerable precision. Experimental validation showed an excellent agreement between the estimation from the proposed method and the data measured by a high-performance commercial instrument. This methodology can be potentially used to realize fast and simple phase noise measurement and reduce the overall cost of hardware.

Tunnel magnetoresistance angular and bias dependence enabling tuneable wireless communication

Spin-transfer torques (STTs) can be exploited in order to manipulate the magnetic moments of nanomagnets, thus allowing for new consumer-oriented devices to be designed. Of particular interest here are tuneable radio-frequency (RF) oscillators for wireless communication. Currently, the structure that maximizes the output power is an Fe/MgO/Fe-type magnetic tunnel junction (MTJ) with a fixed layer magnetized in the plane of the layers and a free layer magnetized perpendicular to the plane. This structure allows for most of the tunnel magnetoresistance (TMR) to be converted into output power. Here, we experimentally and theoretically demonstrate that the main mechanism sustaining steady-state precession in such structures is the angular dependence of the magnetoresistance. The TMR of such devices is known to exhibit a broken-linear dependence versus the applied bias. Our results show that the TMR bias dependence effectively quenches spin-transfer-driven precession and introduces a non-monotonic frequency dependence at high applied currents. This has an impact on devices seeking to work in the ‘THz gap’ due to their non-trivial TMR bias dependences.

Radio Frequency Oscillations in Gyrotropic Nonlinear Transmission Lines

The paper considers the quasi-monochromatic radio frequency oscillations that are observable in transmission lines of doubly connected cross-sections, partially filled with a magnetized ferrite. The frequencies and amplitudes of the oscillations appearing under the impact of short carrier-free electric pulses are determined by dispersive and non-linear properties of the line’s structure. The dispersion characteristics are governed by the geometry and size of the line and the spatial arrangement in the line of the ferromagnetic material with its intrinsic dispersion. The dependences shown by the oscillation parameters in real physical experiments are reproduced and analyzed via numerical simulation within models which account separately for different physical properties of the material and the structure.

Dielectric properties, effect of geometry, and quality changes of whole, nonfat milk powder and their mixtures associated with radio frequency heating

Radio frequency (RF) heating is a promising pasteurization technique providing a fast and more uniform heat generation throughout a sample. In this paper, the effect of composition, frequency (1–30 MHz) and temperature (20–90 °C) on the dielectric properties of whole, nonfat milk powder and their mixtures were studied to develop an effective RF pasteurization. Moreover, the effect of the shape and dimension of the container on RF heating were evaluated. Milk powders were loaded into rectangular and cylindrical boxes with the same volume and different heights (3, 6 and 9 cm), and heated in a 6 kW, 27.12 MHz pilot scale free-running oscillator RF oven. The heating rate, temperature profile, penetration depth, and electric field strength were determined. The quality of the RF heated milk powders was evaluated by measuring moisture content, water activity, solubility, and color. Overall, heating milk powder in the 6 cm height cylindrical box showed a relatively more uniform temperature distribution than 6 cm height rectangular box, with moderate heating rate as well as improved quality in the finished product with less changes in moisture content, water activity, solubility and color. Electric field strength increased with the increase in the height of the container.

Features of the effective potential formed by multipole ion trap

Here we present a new model of the effective field in multielectrode ion traps. The proposed method involves averaging over radio frequency oscillations, through which we derive stationary equations of ion motion in the trap. We apply our approach to the 22-pole trap and compare the resulting potential distribution with both numerical calculations and experimental data. We show that the multipole trap with 2n electrodes excluding quadrupole traps has n points of stable quasi-equilibrium. We also calculate the stability diagram for the 22-pole trap, the main features of which can also be described by the proposed method. The proposed approach is of importance for particle trap dynamics analysis and mass-to-charge selection techniques.

Wideband photonic microwave channelization and image-reject down-conversion

A wideband photonic microwave channelization and image-reject down-conversion system is proposed and experimentally demonstrated. The broadband radio frequency (RF) and electrical local oscillator (LO) signals are applied to Mach–Zehnder modulators (MZMs) and be multiplexed for channelized reference. By employing DPMZMs, different optical frequency shifting LO signals for channelization are generated. Due to the frequency difference between the modulated RF signals and frequency shifted LO signals, multichannel intermediate frequency (IF) signals can be easily separated by the followed photonic I/Q receiver. Experimental results show that the RF signal with a bandwidth of 3 GHz could be down-converted into six IF signals with the same center frequency of 750 MHz and the same bandwidth of 500 MHz. The measured spurious free dynamic range (SFDR) is 101 dB•Hz 2∕3, the passband fluctuation is less than 0.5 dB; the channel isolation is over 22 dB, and the image-rejection is over 22 dB. A QPSK vector signals with 50 Msym/s and 16.5–19.5 GHz operating frequency is successfully demonstrated using the proposed scheme, and good EVMs and constellation diagrams are obtained. The proposed photonic channelization and image-reject down-conversion system may have potential applications in the RF frontends of future systems such as broadband integrated satellite communication and multi-service wireless networks.

65nm CMOS phase conjugator for retro‐directive short‐range wireless power transfer

AbstractWe present an ultra‐compact phase conjugator for a radio frequency (RF) system of a retro‐directive array (RDA) that is, suitable for a short‐range wireless power transfer (WPT) application. The proposed phase conjugator consists of a mixer, buffer, and limiter, and provides not only an accurate conjugate phase but also small jitter, variable gain, and linear phase characteristics. The phase conjugator was implemented using Samsung 65 nm RF CMOS technology. The size of the core chip was 1150 × 880 μm2. The circuit used a supply voltage of 1.4 V and a current of 10 mA. All ports are matched to 50 Ω. In the measurements, the RF, intermediate frequency (IF), and local oscillator (LO) frequency of the mixer are 2.5, 2.4, and 4.9 GHz, respectively. The phase conjugator provides an excellent RF‐IF isolation of less than −45 dB and small RMS jitter of less than 4.3 ps. The limiter enables the phase conjugator to exhibit a constant phase of 168.1 ± 0.10 and a constant output power of about −22.5 ± 0.3 dBm in the input power range from −10 dBm to 0 dBm.

Opto-Electronic Oscillator with Mach-Zender Modulator

The non-standard opto-electronic oscillator (OEO) operation is discussed in the generation mode of a single-side optical harmonic on the base of external and internal modulation of the laser signal. The OEO mathematical model is formed basing on laser differential equations for the closed radiofrequency network. With the help of the model offered, the phase noise of OEO radiofrequency oscillations is analyzed. It is shown that phase noise reduction in the circuit with external modulation depends not only on the increased laser power and growth of the geometric length of the optical fiber, but on reduction of the laser phase noise.

Black phosphorus frequency mixer for infrared optoelectronic signal processing

Black phosphorus possesses several attractive properties for optoelectronics, notably a direct and layer dependent bandgap that varies from the visible to mid-infrared and the ability to transfer the material to nearly arbitrary substrates. A less utilized property of black phosphorus for optoelectronics is the nonlinear photoresponse. The photocarrier lifetime in black phosphorus exhibits a strong nonlinear dependence on the excitation density that is utilized in the present work for optoelectronic mixing. In this scheme, two telecommunications-band lasers are intensity-modulated by a radio frequency (RF) and local oscillator (LO) frequency and focused onto a black phosphorus photoconductive detector. Above the saturation carrier density, the photocurrent is proportional to the square root of the optical power which produces photocurrents at the sum and difference frequencies of the input beams. The bandwidth of the mixing process increases from 10 to 100 MHz for incident powers of 0.01 to 1 mW, respectively. An excess carrier model accurately describes the power dependence of the cutoff frequency and mixing conversion, which are both limited by photocarrier recombination. Optimizing our device geometry to support larger bias fields and decreased carrier transit times could increase the maximum RF/LO frequency beyond a GHz by reducing the excess carrier lifetime. Frequency mixing based on the photocarrier nonlinearity in multilayer black phosphorus demonstrated here can be readily extended to mid-infrared wavelengths as long as 4 µm.

Microwave emission from superconducting vortices in Mo/Si superlattices

Most of superconductors in a magnetic field are penetrated by a lattice of quantized flux vortices. In the presence of a transport current causing the vortices to cross sample edges, emission of electromagnetic waves is expected due to the continuity of tangential components of the fields at the surface. Yet, such a radiation has not been observed so far due to low radiated power levels and lacking coherence in the vortex motion. Here, we clearly evidence the emission of electromagnetic waves from vortices crossing the layers of a superconductor/insulator Mo/Si superlattice. The emission spectra consist of narrow harmonically related peaks which can be finely tuned in the GHz range by the dc bias current and, coarsely, by the in-plane magnetic field value. Our findings show that superconductor/insulator superlattices can act as dc-tunable microwave generators bridging the frequency gap between conventional radiofrequency oscillators and (sub-)terahertz generators relying upon the Josephson effect.

Sensor Antenna Transmitter System for Material Detection in Wireless-Sensor-Node Applications

This paper presents a fully combined sensor-antenna transmitter system for sensing relative permittivity of material at microwave frequencies. The transmit (Tx) antenna senses the relative permittivity of specimen and loads the radio frequency (RF) oscillator which translates the relative permittivity to the operational frequency of the carrier signal. At the same time, independent data, which can be the Radio Frequency Identification (RFID) information, are ON-OFF keying modulated over the carrier. At the receiver, a demodulator system extracts the data stream as well as recovers the carrier frequency using a zero-crossing detector. Therefore, the relative permittivity of the sample can be obtained from the extracted frequency shift as a digital number. As all the sensing elements in the proposed structure are passive, the sensor does not increase the power consumption of the system. The sensor-transceiver capability at low powers makes it ideal for sensor nodes in the Internet of Things applications. Since the sensing and demodulation are implemented at the same time, the complexity for detection reduces significantly compared with traditional RF/microwave sensing techniques which need complicated frequency spectrum monitoring equipment. The output of the system is a digital number correlated to the dielectric constant of the specimen and the independent data stream for communication. The proposed sensor node is fabricated at the 2.45-GHz ISM band as an evaluation and the measurement results with some known samples are presented.

Equivalent circuit and numerical analyses of an inductively coupled plasma torch with a tapped induction coil

Equivalent circuit and numerical analyses of an Ar-N2 inductively coupled plasma (ICP) were conducted in order to clarify the effect of the induction coil with a grounded tap on the electrical characteristics of an ICP torch system. First, from the computational results, it was revealed that the load resistance of tank circuit for a free running radio-frequency (RF) oscillator can be reduced to about 25% with a center-tap of the induction coil grounded. Despite the asymmetric distributions of the electric fields in the inside of the ICP torch, this effect was found due to the equivalent resistance and inductance of ICP that were divided in approximately half into each part of the center-tapped induction coil. The reduction of the load resistance by a grounded tap was also observed in generation experiments of Ar-N2 ICPs using a vacuum tube oscillator for various N2 contents ranging from 6.3 % to 25.0 %. By providing a way to reduce the load resistance of the tank circuit, the induction coil with a grounded tap can be used to improve the impedance matching condition of ICP systems with the load resistances higher than the internal resistance of a free running RF oscillator.

Numerical simulation of atmospheric-pressure 200 kHz/13.56 MHz dual-frequency dielectric barrier discharges

A 1D drift-diffusion model is used to study atmospheric-pressure dual-frequency (DF) dielectric barrier discharges in argon using the plasma modeling platform PLASIMO. The simulation exhibits an excellent agreement with the experimental results and gives insight into the DF plasma dynamics e.g. the electric field, sheath edge profiles, ionization/excitation rate and electron energy distribution function (EEDF) profiles. The results indicate that due to the radio-frequency oscillation, the electric field, sheath edge and thus the ionization/excitation are temporally modulated. As a result, the plasma conductivity is enhanced as the plasma density is higher. The discharge development is slowed down with a lower current amplitude and a longer duration. The time-averaged sheath is getting thinner with a more pronounced ionization rate and a longer contacting time near the substrate, which could help to improve the efficiency of plasma-assisted surface processing. In addition, the DF excitation exhibits a capability of modifying the EEDF profiles and controlling the plasma chemical kinetics, which can be applied to other relevant fields e.g. gas-phase chemical conversion.

Thermal inactivation of fungi in chestnuts by hot air assisted radio frequency treatments

Infestations with fungi in chestnuts are one of the major safety issues during process and storage, resulting in short shelf-life and high economic losses. The purpose of this research was to study possible applications of radio frequency (RF) treatments for pasteurization of chestnuts to replace chemical methods. Thermal lethal kinetic models of fungi isolated from spoilage chestnuts and parameters of the developed model were determined. A 6 kW, 27 MHz free-running oscillator RF system combined with hot air heating was used to validate the treatment parameters based on thermal lethal kinetic models of fungi. The results showed that four mycotoxigenic fungi dominated and were isolated at frequency of 58.31 ± 2.39% for Penicillium crustosum, 17.78 ± 5.00% for Penicilluim discolor, 15.66 ± 7.67% for Penicillium expansum, and 14.24 ± 6.71% for Penicillium glabrum from a total sample size of one hundred spoilage nuts. Modified Weibull distribution model (R2 = 0.939 to 0.999) had a better description of the inactivation behavior of Penicillium sp. than the first-order kinetic model (R2 = 0.829 to 0.993) and P. crustosum was the most heat resistant fungi in chestnuts. Heating chestnuts to 60 °C or higher using hot air assisted RF energy resulted in 4-log reductions of P. crustosum isolated from moldy chestnuts. Quality of chestnuts was not influenced by the hot air assisted RF treatments because no significant differences in moisture, firmness, and color were observed between thermal treatments and untreated controls. Meanwhile, RF treatments also help to inhibit the growth of fungi during accelerated shelf life storage. The RF treatments may provide a rapid and environmentally friendly method to replace chemical fungicide for pasteurizing chestnuts.

A Photonically Enabled Compact 0.5–28.5 GHz RF Scanning Receiver

An innovative and effective photonics-based radio frequency (RF) spectrum scanner is presented and demonstrated, enabling the detection in the 0.5–28.5 GHz range. The proposed receiver scans the whole frequency range at discrete steps, down-converting at baseband single portions of the detected spectrum, where they can be precisely acquired, without using RF bandpass filters nor optical filters. The wideband scansion is achieved by simply tuning an optical carrier only, avoiding the use of an RF synthesizer or of multiple parallel local oscillators. In more detail, the optical carrier is modulated by the detected RF signal through an electro-optical modulator, and photomixed with an optical local oscillator to down-convert the modulation sideband to baseband. The optical carrier also feeds an optical frequency comb generator—driven by a fixed RF oscillator at 1 GHz—whose output injects the local oscillator. This way, the optical carrier and oscillator are phase locked and can be tuned at steps of 1 GHz. The developed demonstrator achieves an input range up to 28.5 GHz, and a simulative analysis suggests the capability of exceeding the 0.5–40 GHz range employing commercially available devices. Moreover, it shows a linear dynamic range of 160 dB/Hz and a spuriousfree dynamic range of 109 dB/Hz2/3 , aligned with the state-of-the-art broadband RF receivers. The proposed solution appears to fulfill the performance requirements of the demanding electronic support measures applications, with the potentials for largely reducing the receiver size.

Fully Integrated Single-Chip 305–375-GHz Transceiver With On-Chip Antennas in SiGe BiCMOS

A fully integrated single-chip transceiver (TRX) with on-chip antennas for transmitting and receiving signals within a continues frequency range from 305 to 375 GHz is presented. The radio-frequency (RF) and local oscillator signals are generated using a wideband push–push voltage-controlled oscillator, a three-stage power amplifier, and a frequency doubler. A heterodyne receiver using a fundamental mixer converts the received RF signal to an intermediate frequency (IF) signal, which drives an IF amplifier. Additionally, a divide-by-64 frequency divider is integrated to provide a low-frequency output for measurement purposes and to enable later the addition of a phase-locked loop for frequency stabilization and synthesis. A 130-nm silicon–germanium BiCMOS process with $f_t/f_{\max}$ = 250 GHz/370 GHz is used. The TRX chip is wire bonded to a printed circuit board and a TPX (Polymethylpentene) lens is placed on top of the chip for focusing the radiation. At a frequency of 343 GHz, the measurements show an effective isotropic radiated power of 18.4 dBm, a phase noise of $-$ 79 dBc/Hz@1 MHz, and an IF conversion gain of 28 dB. The obtained tuning bandwidth of 70 GHz is the highest reported so far for fully integrated TRXs.

Atmospheric-pressure diffuse dielectric barrier discharges in Ar/O2 gas mixture using 200 kHz/13.56 MHz dual frequency excitation

Atmospheric-pressure diffuse dielectric barrier discharges (DBDs) were obtained in Ar/O2 gas mixture using dual-frequency (DF) excitation at 200 kHz low frequency (LF) and 13.56 MHz radio frequency (RF). The excitation dynamics and the plasma generation mechanism were studied by means of electrical characterization and phase resolved optical emission spectroscopy (PROES). The DF excitation results in a time-varying electric field which is determined by the total LF and RF gas voltage and the spatial ion distribution which only responds to the LF component. By tuning the amplitude ratio of the superimposed LF and RF signals, the effect of each frequency component on the DF discharge mechanism was analysed. The LF excitation results in a transient plasma with the formation of an electrode sheath and therefore a pronounced excitation near the substrate. The RF oscillation allows the electron trapping in the gas gap and helps to improve the plasma uniformity by contributing to the pre-ionization and by controlling the discharge development. The possibility of temporally modifying the electric field and thus the plasma generation mechanism in the DF discharge exhibits potential applications in plasma-assisted surface processing and plasma-assisted gas phase chemical conversion.