Radiofrequency Excitation Research Articles

Microcrystalline silicon thin film deposition from silicon tetrafluoride: Isolating role of ion energy using tailored voltage waveform plasmas

The energy of ions during plasma enhanced chemical vapor deposition (PECVD) is known to impact material quality, but isolating this effect from other process parameters (plasma density, pressure) in a capacitively coupled plasma (CCP) is not straightforward. In this work, we utilize a novel radio-frequency (RF) excitation technique – tailored voltage waveforms (TVW) – as a solution to achieve ion flux-energy decoupling through the electrical asymmetry effect. This makes it possible to independently study the impact of ion energy on material deposition. We study the impact of ion energy - more precisely the maximum ion bombardment energy (IBEmax) before collisions - on the PECVD of hydrogenated microcrystalline silicon (µc-Si:H) thin films from an SiF4/H2/Ar chemistry. Through structural and electronic analysis, we find that the variation of IBEmax directly translates into material quality, even at relatively high process pressure. Better material properties (crystalline grain features, material density and photoelectronic response) are obtained for films deposited with moderate values of IBEmax around 45–55 eV. Above this range, a deterioration in material quality is observed, presumably due to more effective bulk atomic displacements induced by the silicon-containing ions. These results are consistent with the performance of single-junction µc-Si:H solar cell devices using these materials as active layers. Optimum performance is obtained for devices with an absorber layer deposited using a plasma excitation resulting in IBEmax in the range of ~45–55 eV. The variation in device performance is mainly due to changes in the open circuit voltage.

Electrical manipulation of semiconductor spin qubits within the g -matrix formalism

We discuss the modeling of the electrical manipulation of spin qubits in the linear-response regime where the Rabi frequency is proportional to the magnetic field and to the radio-frequency electric field excitation. We show that the Rabi frequency can be obtained from a generalized g-tensor magnetic resonance formula featuring a g-matrix and its derivative g' with respect to the electric field (or gate voltage) as inputs. These matrices can be easily calculated from the wave functions of the qubit at zero magnetic field. The g-matrix formalism therefore provides the complete dependence of the Larmor and Rabi frequencies on the orientation of the magnetic field at very low computational cost. It also provides a compact model for the control of the qubit, and a simple framework for the analysis of the effects of symmetries on the anisotropy of the Larmor and Rabi frequencies. The g-matrix formalism applies to a wide variety of electron and hole qubits, and we focus on a hole qubit in a silicon-on-insulator nanowire as an illustration. We show that the Rabi frequency of this qubit shows a complex dependence on the orientation of the magnetic field, and on the gate voltages that control the symmetry of the hole wave functions. We point out that the qubit may be advantageously switched between two bias points, one where it can be manipulated efficiently, and one where it is largely decoupled from the gate field but presumably longer lived. We also discuss the role of residual strains in such devices in relation to recent experiments.

Blood vessel imaging using radiofrequency-induced second harmonic acoustic response

We introduce a contrast mechanism for visualizing blood vessels based on radiofrequency-induced second harmonic acoustic (RISHA) signals sensing blood conductivity. We develop a novel imaging system using commonly available inexpensive components, and demonstrate in vivo RISHA visualization of blood vessels based on low-power quasi-continuous radiofrequency excitation of tissue at frequencies of a few MHz. We show how the novel approach also implicitly enables radiofrequency-induced passive ultrasound imaging and can be readily applied to non-invasive imaging of blood vessels ex vivo and in vivo. We discuss the implications of non-invasive conductivity measurements in the context of biomedical applications.

Simultaneous fat-free isotropic 3D anatomical imaging and T2 mapping of knee cartilage with lipid-insensitive binomial off-resonant RF excitation (LIBRE) pulses.

Improved knee cartilage morphological delineation and T2 mapping precision necessitates isotropic 3D high-resolution and efficient fat suppression. To develop and assess an isotropic 3D lipid-insensitive T2 mapping technique of the knee for improved cartilage delineation and precise measurement of T2 relaxation times. Prospective. Phantoms (n = 6) used in this study were designed to mimic the T1 and T2 relaxation times of cartilage and fat. The study cohort comprised healthy volunteers (n = 7) for morphometry and T2 relaxation time measurements. A high-resolution isotropic 3D T2 mapping technique that uses sequential T2 -prepared segmented gradient-recalled echo (Iso3DGRE) images and lipid-insensitive binomial off-resonant radiofrequency (RF) excitation (LIBRE) at 3T. Numerical simulations and phantom experiments were performed to optimize the LIBRE pulse. Phantom studies were carried out to test the accuracy of the technique against reference standard spin-echo (SE) T2 mapping. Subsequently, T2 maps with and without LIBRE pulses were acquired in knees of healthy volunteers and the T2 relaxation time values in different cartilage compartments were compared. A two-tailed paired Student's t-test was used to compare the average T2 values and the relative standard deviations (inverse measurement of the precision) obtained with and without LIBRE pulses. A LIBRE pulse of 1 msec suppressed fat with an RF excitation frequency offset of 1560 Hz and optimal RF excitation angle of 35°. These results were corroborated by phantom and knee experiments. Robust and homogeneous fat suppression was obtained (a fat signal-to-noise ratio (SNR) decrease of 86.4 ± 2.4%). In phantoms, T2 values were found in good agreement when comparing LIBRE-Iso3DGRE with SE (slope 0.93 ± 0.04, intercept 0.11 ± 1.6 msec, R2 >0.99). In vivo, LIBRE excitation resulted in more precise T2 estimation (23.7 ± 7.4%) than normal excitation (30.5 ± 9.9%, P < 0.0001). Homogeneous LIBRE fat signal suppression was achieved with a total RF pulse duration of 1 msec, allowing for the removal of chemical shift artifacts and resulting in improved cartilage delineation and precise T2 values. 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:1275-1284.

Quadrupole mass filter operation with dipole direct current and quadrupole radiofrequency excitation.

For mass analysis, a quadrupole mass filter (QMF) usually operates at the upper tip of the first stability region. We introduce a new mode of QMF operation with dipole direct current (dc) and with auxiliary quadrupole excitation. Before experimental investigation of this mode, we have carried out numerical simulations of this process. Based on the analytical description of the equations of ion motion and mapping of stability islands, ion trajectory calculations are used to calculate peak shapes or mass filter transmission contours. Ions are given Gaussian distributions of initial positions in x and y, and thermal initial velocity distributions. The effects of the dipole dc in the y direction and auxiliary quadrupole excitation in the x and y directions are modeled. We find that, with dipole dc excitation, the working area of the first stability region decreases and a new y stability boundary follows a βy line. This allows control of the resolution with the removal of the low-mass tail of a peak thereby improving the isotopic abundance sensitivity by about two orders of magnitude. The operation of a QMF with high resolution (about 5000) and high transmission (20-25%) and with a relatively short sorting time of ions n = 150 radiofrequency (rf) cycles based on the use of dipole dc and quadrupole excitation is shown. A new mode of QMF operation with dipole direct current (dc) and with an auxiliary quadrupole is discussed. Using dc excitation allows control of the resolution with the removal of the low-mass tail of a peak. The method of operation of a quadrupole mass filter with high resolution (about 5000) and high transmission (20-25%) and a relatively short sorting time (150 rf cycles) based on the use of dipole dc and on quadrupole excitation is shown.

Integrated Cooperative Ambient Power Harvester Collecting Ubiquitous Radio Frequency and Kinetic Energy

An integrated cooperative harvester capable of collecting both electromagnetic [(principally radio frequency (RF)] and kinetic energy simultaneously is proposed and studied in this paper. One single substrate board is demonstrated to accommodate and integrate an electromagnetic kinetic generator, an F-shaped antenna, and a rectifying circuit, having a compact credit-card size. Cooperative harvesting mode enables a significant enhancement of the diode’s power conversion efficiency (PCE) and also greatly strengthening the resilience of harvester at the same time. Measured results suggest that SMS7630 and HSMS-2850-based cooperative harvesters can increase dc output power by 50% to around 100% when both injecting power sources exhibit below −37 dBm with reference to the total added amount of dc power harvested directly from separate RF and kinetic excitation modes. A closed-form method is proposed and used to predict the enhanced efficiency performance of the cooperative harvester within a low power range of interest (from −50 to −30 dBm). Our analysis highlights the roles of the diode’s nonlinear junction resistance and capacitance. Good agreements are observed when comparing the analysis results with harmonic balance simulations by ADS. Furthermore, this method is carefully verified by measured results of two different diode-based harvesters. Measured dc output power rectified from cooperative harvesting mode is reported to be 1.16 and 1.97 times larger with SMS7630 and HSMS-2850, respectively, when both power sources are −40 dBm, compared to the conventional single RF harvesting mode. The proposed cooperative harvester with its strong resilience is highly suitable for ambient power harvesting in an ever-changing environment.

Low-rank magnetic resonance fingerprinting.

Magnetic resonance fingerprinting (MRF) is a relatively new approach that provides quantitative MRI measures using randomized acquisition. Extraction of physical quantitative tissue parameters is performed offline, without the need of patient presence, based on acquisition with varying parameters and a dictionary generated according to the Bloch equationsimulations. MRF uses hundreds of radio frequency (RF) excitation pulses for acquisition, and therefore, a high undersampling ratio in the sampling domain (k-space) is required for reasonable scanning time. This undersampling causes spatial artifacts that hamper the ability to accurately estimate the tissue's quantitative values. In this work, we introduce a new approach for quantitative MRI using MRF, called magnetic resonance fingerprinting with low rank (FLOR). We exploit the low-rank property of the concatenated temporal imaging contrasts, on top of the fact that the MRF signal is sparsely represented in the generated dictionary domain. We present an iterative recovery scheme that consists of a gradient step followed by a low-rank projection using the singular value decomposition. Experimental results consist of retrospective sampling that allows comparison to a well defined reference, and prospective sampling that shows the performance of FLOR for a real-data sampling scenario. Both experiments demonstrate improved parameter accuracy compared to other compressed-sensing and low-rank based methods for MRF at 5% and 9% sampling ratios for the retrospective and prospective experiments, respectively. We have shown through retrospective and prospective experiments that by exploiting the low-rank nature of the MRF signal, FLOR recovers the MRF temporal undersampled images and provides more accurate parameter maps compared to previous iterative approaches.

Low-temperature helium plasma generated at atmospheric pressures by non-standard field applicator

Low-temperature helium plasmas were sustained using radio frequency excitation waveforms in a cylindrical glass tube, both in steady state and flowing conditions.

14N overtone nuclear magnetic resonance of rotating solids.

By irradiating and observing at twice the 14N Larmor frequency, overtone (OT) nuclear magnetic resonance (NMR) is capable of obtaining 14NOT spectra without first-order quadrupolar broadening. Direct excitation and detection of the usually "forbidden" double-quantum transition is mediated by the perturbation from the large quadrupole interaction to the spin states quantized by the Zeeman interaction. A recent study [L. A. O'Dell and C. I. Ratcliffe, Chem. Phys. Lett. 514, 168 (2011)] has shown that 14NOT NMR under magic-angle spinning (MAS) can yield high-resolution spectra with typical second-order quadrupolar line shapes allowing the measurement of 14N chemical shift and quadrupolar coupling parameters. This article has also shown that under MAS the main 14NOT peak is shifted by twice the sample spinning frequency with respect to its static position. We present the theory of 14NOT NMR of static or rotating samples and the physical picture of the intriguing spinning-induced shift in the second case. We use perturbation theory for the case of static samples and Floquet theory for rotating samples. In both cases, the results can be described by a so-called OT parameter that scales down the 14NOT radio-frequency (rf) excitation and signal detection. This OT parameter shows that the components of the rf field, which are transverse and longitudinal with respect to the magnetic field, are both effective for 14NOTrf excitation and signal detection. In the case of MAS at angular frequency ωr , the superposition of the excitation and detection components in the OT parameter makes either the +2ωr or -2ωr term the dominant 14NOT signal, depending on the sense of sample spinning with respect to the magnetic field. This leads to an apparent 14NOT signal shifted at twice the spinning frequency. The features of 14NOT NMR spectra for both static and rotating samples are illustrated with simulations. The spinning induced shift and its dependence on the spinning direction are confirmed experimentally by reversing the spinning direction and the field of the 36 T series-connected hybrid magnet at the US National High Magnetic Field Laboratory.

OA043] A new signal-to-noise ratio (SNR) measurement method based on low-pass filtering for magnetic resonance imaging (MRI) quality control (QC) purposes

Purposes Signal-to-noise ratio (SNR) is a prominent metric to assess scanners performances. SNR measurement in MRI is challenging because of the difficulty to quantify noise level from images. A gold-standard consist in pixel-by-pixel variance calculation on several images (>100) scanned in identical conditions. This method is accurate but cannot be practically implemented because of time constraints. Another gold-standard consists in scanning images without radiofrequency excitation hence collecting noise-only. This latter is also unpractical because it requires a specific and generally not-granted access to the hardware. Consequently, there is a need for designing alternative methods for accurate and precise noise quantification. This work aims to introduce a new noise level quantification method for SNR measurement. Methods Our method (Noisefilt) quantifies noise level by combining these operations: (1) subtraction of two images subsequently scanned in identical conditions, (2) Low-pass filtering to extract and suppress low-frequency remaining information, (3) (Noisefilt = standard deviation of pixels. Using a dataset of 30 exams of a head phantom scanned on a 3T MR unit with an 8-channel phased-array brain coil, we compared our method with three others from the literature: noise level quantified using one image-background region-of-interest (ROI) (Noisebgd), several background ROIs (Noisebgd+), and from the subtraction of two images (Noisediff) [6]. By means of Bland–Altman analysis, we assessed the agreement between all these methods and the noise-only standard method (NoisenoRF). We also assessed their correlation with NoisenoRF (Pearson’s correlation coefficient r, p Results Bland–Altman analysis showed that Noisefilt agrees more with the standard than the three other methods. Correlation of our Noisefilt method with the gold-standard (rfilt =0.80, p Conclusion We demonstrated that our method produces accurate measurement, is simple to implement, and is usable for instance for quality control (QC) purposes. This new metric is being tested with additional scans in QC monitoring of different MR scanners. Download : Download high-res image (87KB) Download : Download full-size image Download : Download high-res image (159KB) Download : Download full-size image

Design and Evaluation of “BTTN”: A Backscattering Tag-to-Tag Network

Radio frequency (RF)-powered backscatter communication between passive tags holds tremendous potential as an enabling technology for a ubiquitous “Internet of Things.” We develop a backscattering tag-to-tag network (BTTN), comprised of passive tags capable of large-scale, passive, and multihop communication with each other via backscatter modulation of an external RF excitation signal. The low sensitivity and lack of active demodulator on passive tags present significant challenges to the communication, including a unique phase cancellation problem, which significantly affects the range and robustness of a passive tag-to-tag link. We overcome these challenges using innovative tag architecture and also develop a novel multiphase backscatter modulation technique with a learning mechanism that overcomes the phase cancellation problem. This improves the link performance bringing passive tag-to-tag communication closer to practical use. The additional hardware compared to the conventional radio frequency identification tag architecture includes one more terminating impedance in the modulator. The data rate is reduced due to backscatter at two different phases while the increase in the power consumption is negligible. We develop prototype BTTN tag hardware and firmware and evaluate its performance. The prototype achieves link ranges of up to 3 m at 5 kb/s with an excitation power level of only -20 dBm while successfully overcoming phase cancellation. We further extend BTTN operation to a multihop network where we demonstrate a four hop link capable of communicating over 12 m under similar conditions.

In vivo MRI with Concurrent Excitation and Acquisition using Automated Active Analog Cancellation

Magnetic resonance imaging (MRI) provides excellent cross-sectional images of the soft tissues in patients. Unfortunately, MRI is intrinsically slow, it exposes patients to severe acoustic noise levels, and is limited in the visualization of certain tissues such as bone. These limitations are partly caused by the timing structure of the MRI exam which first generates the MR signal by a strong radio-frequency excitation and later acquires the weak MRI signal. Concurrent excitation and acquisition (CEA) can overcome these limitations, but is extremely challenging due to the huge intensity difference between transmit and receive signal (up to 100 dB). To suppress the strong transmit signals during signal reception, a fully automated analog cancellation unit was designed. On a 3 Tesla clinical MRI system we achieved an on-resonance analog isolation of 90 dB between the transmit and receive path, so that CEA images of the head and the extremities could be acquired with an acquisition efficiency of higher than 90% at sound pressure levels close to background noise. CEA with analog cancellation might provide new opportunities for MRI in tissues with very short T2 relaxation times, and it offers a silent and time-efficient MRI acquisition.

Transverse relaxation determination based on light polarization modulation for spin-exchange relaxation free atomic magnetometer**Project supported by the National Natural Science Foundation of China (Grant No. 61227902), the National Key R&D Program of China (Grant No. 2017YFB0503100), and the Natural Science Foundation of Beijing Municipality, China (Grant No. 4162038).

A transverse relaxation determination of spin-exchange relaxation free (SERF) magnetometer based on polarization modulation technique is proposed. Compared with the radio-frequency (RF) excitation and light intensity excitation methods used in SERF magnetometer, the light polarization modulation method has a high stability in low-frequency range, which indicates a more accurate transverse relaxation measurement.

MR-compatibility assessment of MADPET4: a study of interferences between an SiPM-based PET insert and a 7 T MRI system

Compromises in the design of a positron emission tomography (PET) insert for a magnetic resonance imaging (MRI) system should minimize the deterioration of image quality in both modalities, particularly when simultaneous demanding acquisitions are performed. In this work, the advantages of using individually read-out crystals with high-gain silicon photomultipliers (SiPMs) were studied with a small animal PET insert for a 7 T MRI system, in which the SiPM charge was transferred to outside the MRI scanner using coaxial cables. The interferences between the two systems were studied with three radio-frequency (RF) coil configurations. The effects of PET on the static magnetic field, flip angle distribution, RF noise, and image quality of various MRI sequences (gradient echo, spin echo, and echo planar imaging (EPI) at 1H frequency, and chemical shift imaging at 13C frequency) were investigated. The effects of fast-switching gradient fields and RF pulses on PET count rate were studied, while the PET insert and the readout electronics were not shielded. Operating the insert inside a 1H volume coil, used for RF transmission and reception, limited the MRI to T1-weighted imaging, due to coil detuning and RF attenuation, and resulted in significant PET count loss. Using a surface receive coil allowed all tested MR sequences to be used with the insert, with 45–59% signal-to-noise ratio (SNR) degradation, compared to without PET. With a 1H/13C volume coil inside the insert and shielded by a copper tube, the SNR degradation was limited to 23–30% with all tested sequences. The insert did not introduce any discernible distortions into images of two tested EPI sequences. Use of truncated sinc shaped RF excitation pulses and gradient field switching had negligible effects on PET count rate. However, PET count rate was substantially affected by high-power RF block pulses and temperature variations due to high gradient duty cycles.

Homodyne detection of ferromagnetic resonance by a non-uniform radio-frequency excitation current

Ferromagnetic resonance (FMR) is one of the most popular techniques to characterize dynamic properties of ferromagnetic materials. Among various FMR measurement techniques, the homodyne FMR detection has been frequently used to characterize thin-film ferromagnetic multilayers owing to its high sensitivity. However, a drawback of this technique was considered to be the requirement for a structural inversion asymmetry, which makes it unsuitable to characterize a single layer of ferromagnet. In this study, we demonstrate a homodyne FMR detection of the Kittel’s mode FMR dynamics of a single layer of FeNi by creating a non-uniform radio-frequency excitation current.

Simultaneous Recording of NMR Signals from Nuclei with Different Gyromagnetic Ratios Using Undersampling Technique

The article describes experiments on the simultaneous recording nuclear magnetic resonance signals from two nuclei with different gyromagnetic ratios—1H and 19F, 13C and 23Na. It is shown that large frequency detunings or/and low sampling rates are not an obstacle to their realization even in a relatively weak (0.5 T) field. We use undersampling technique when registering the response of the spin system. In this case, the sampling frequency is much less than the distance between the Larmor frequencies for the indicated nuclear pairs. It gives the effect of multiple aliasing. Fourier processing of the response produces a spectrum consisting of two subspectra, each of which corresponds to specific nucleus of the investigated pair. The subordination of the spectral peaks in each subspectrum is the same as the spectrum obtained by the usual way. Two variants of the radio-frequency excitation of the spin system (single and double pulse) are considered. A formula for calculating the excitation frequency and sampling rate, which ensures a rational distribution of the lines in the hybrid spectrum, is proposed.

Resonant heating of Fe3O4 and hemozoin nanoparticles dispersed in D2O by RF excitation of transitions between Zeeman components

Presently we evaluated the natural relaxation frequency of the spin angular momentum of Fe3O4 and hemozoin superparamagnetic (SP) nanoparticles in D2O solutions in function of the sample temperature. The sample was composed of 1% H2O in D2O with dispersed Fe3O4 or hemozoin nanoparticles at variable number density. The natural relaxation frequencies are in the sub-MHz and MHz range for the Fe3O4 and hemozoin nanoparticles, respectively. We studied resonance heating of the same samples. We found that scanning the external magnetic field strength in a constant-frequency radio-frequency (RF) electromagnetic field, with its magnetic field component perpendicular to the external magnetic field, we obtain resonant heating at the magnetic field strength of 50 or 100 Gs for the RF excitation at 150 or 300 MHz, respectively. The measured resonance line has a Lorentzian form, with the heating amplitude dependent on the number density of SP nanoparticles, RF power and time. The resonance width correlates with the natural relaxation frequency of the spin angular momentum of the SP nanoparticles. We describe a theoretical model explaining the experimental results. As the achievable heating rate is directly proportional to the spin relaxation rate of the SP nanoparticles, we expect two orders of magnitude higher heating rates in suspensions based on water with natural isotopic composition.

Rotation relaxation splitting for optimizing parallel RF excitation pulses with [formula omitted]- and [formula omitted]-relaxations in MRI

Exact solutions of the Bloch equations with T1- and T2-relaxation terms for piecewise constant magnetic fields are numerically challenging. We therefore investigate an approximation for the achieved magnetization in which rotations and relaxations are split into separate operations. We develop an estimate for its accuracy and explicit first and second order derivatives with respect to the complex excitation radio frequency voltages. In practice, the deviation between an exact solution of the Bloch equations and this rotation relaxation splitting approximation seems negligible. Its computation times are similar to exact solutions without relaxation terms. We apply the developed theory to numerically optimize radio frequency excitation waveforms with T1- and T2-relaxations in several examples.

In vivo self-gated 23 Na MRI at 7 T using an oval-shaped body resonator.

PurposeThis work faces three challenges of sodium (23Na) torso MRI on the way to quantitative 23Na MRI: Development of a 23Na radiofrequency transmit and receive coil covering a large part of the human body in width and length for 23Na MRI at 7 T; reduction of blurring due to respiration in free‐breathing 23Na MRI using a self‐gating approach; and reduction of image noise using a compressed‐sensing reconstruction.MethodsAn oval‐shaped birdcage resonator with a large field of view of (400 mm)3 and a homogeneous transmit and receive field distribution was designed, simulated, and implemented on a 7T MR system. In free‐breathing 3‐dimensional radial 23Na MRI (acquisition time ≈ 30 minutes), retrospective respiratory self‐gating was applied, which sorts the acquired projections into two respiratory states based on the intrinsic respiration‐dependent signal changes. Furthermore, a 3‐dimensional dictionary‐learning compressed‐sensing reconstruction was applied.ResultsThe developed body coil provided homogeneous radiofrequency excitation (flip angle error of 4.9% in central region of interest of 23 × 13 × 10 cm3) and homogeneous signal reception. The self‐gating approach allowed for separation of the full data set into two subsets associated with different respiratory states (inhaled and exhaled), and thereby reduced blurring due to respiration in the separated images. Image noise was markedly reduced by the compressed‐sensing algorithm.ConclusionThe presented body coil enables full body width 23Na MRI with long z‐axis coverage at 7 T for the first time. Additionally, the retrospective respiratory self‐gating performance is demonstrated for free‐breathing lung and abdominal 23Na MRI in 3 subjects.

Development of High-Density Radio Frequency Plasma Sources With Very Small Diameter for Propulsion

Radio frequency (RF) plasma sources, especially helicon ones, are very useful in many fields, because of the high-density (up to $\sim 10^{13}$ cm -3 ) and low electron temperature (from a few to several electronvolts) available, using an RF frequency range. Here, we develop and characterize very small-area (from 2-cm down to 0.1-0.3 cm in diameter) RF sources that are useful for a space propulsion system with an advanced concept of an electrodeless condition (no direct contact between the plasma and electrodes), leading to a longer operation lifetime. Measurements by using electrostatic probes as well as by a spectrometer based on the collisional radiative model in a small plasma region were employed to estimate the electron density $n_{\mathrm{ e}}$ and its temperature. Here, $n_{\mathrm{ e}}$ was measured as a function of the input RF power and RF excitation frequency, especially in a higher frequency range than the usual one of ~14 MHz, under the mirror magnetic-field configuration. The electron cyclotron resonance effect in the divergent field was examined under a weaker magnetic field with the RF frequency lower than those generally employed. The particle production efficiency, even in this small source, showed an excellent performance, based on classical diffusion discussions. In addition, applying these sources were applied to a space propulsion system with the concept of the m (azimuthal mode number) = 0 half-cycle acceleration, which was operated under all electrodeless conditions in both the plasma generation and electromagnetic acceleration phases.