Continuous Wave RF Research Articles

Novel Handheld Diffuse Optical Spectroscopy Probe for Breast Cancer Assessment: Clinical Study

Diffuse optical spectroscopy (DOS) and diffuse optical tomography (DOT) are non-invasive breast cancer assessment modalities which employ near-infrared (NIR) light to measure optical properties of biological tissue. These properties cannot be measured by other methods including X-ray mammography, ultrasound (US) and magnetic resonance imaging (MRI) which are main breast cancer diagnosis tools. The objective of this paper is to test and validate a recently designed and developed hand-held continuous-wave radio-frequency modulated diffuse optical spectroscopy probe in a clinical trial performed on patients who diagnosed to have breast cancer. The probe has an encapsulated light emitting diode (eLED) including four wavelengths (690 nm, 750 nm, 800 nm and 850 nm) and two photodiodes located in reflectance geometry. The direct approach method has been used to extract concentration of two main chronophers in the breast tissue including deoxy-hemoglobin (Hb) and oxy-hemoglobin (HbO2). The results of the clinical trial, which included fourteen patients, show that the RF-DOS probe can correctly classify the cancerous lesion from healthy tissue in the breast. The results prove that the absorption coefficient of the breast tumor is higher than normal tissue due to higher vascularization level in four mentioned wavelengths. Conclusively, the results show 92 percent sensitivity for the extracted absorption coefficient.

Design of an 81.25 MHz continuous-wave radio-frequency quadrupole accelerator for Low Energy Accelerator Facility

An 81.25MHz continuous wave (CW) radio frequency quadrupole (RFQ) accelerator has been designed for the Low Energy Accelerator Facility (LEAF) at the Institute of Modern Physics (IMP) of the Chinese Academy of Science (CAS). In the CW operating mode, the proposed RFQ design adopted the conventional four-vane structure. The main design goals are providing high shunt impendence with low power losses. In the electromagnetic (EM) design, the π-mode stabilizing loops (PISLs) were optimized to produce a good mode separation. The tuners were also designed and optimized to tune the frequency and field flatness of the operating mode. The vane undercuts were optimized to provide a flat field along the RFQ cavity. Additionally, a full length model with modulations was set up for the final EM simulations. Following the EM design, thermal analysis of the structure was carried out. In this paper, detailed EM design and thermal simulations of the LEAF-RFQ will be presented and discussed. Structure error analysis was also studied.

Alpha to Gamma Mode Transitions in Pulse-Modulated Radio Frequency Atmospheric Pressure Glow Discharges

In pulse-modulated (PM) radio frequency (RF) atmospheric pressure glow discharges (APGDs), the alpha–gamma mode transition is analyzed and confirmed with $I$ – $V$ characteristic curve. The behaviors of alpha–gamma mode transition in PM RF APGDs are more complicated than that in continuous wave (CW) RF APGDs. In terms of amplitude of applied RF voltage just before a pulse falling edge ( $V_{\mathrm {appls}}$ ), the critical $V_{\mathrm {appls}}$ at the alpha–gamma mode transition in a PM RF APGD increases with the decreasing duty ratio and is higher than that of a CW RF APGD. The feature of the alpha–gamma mode transition in a PM RF APGD is attributed to the gas temperature rise depending on both the RF voltage and duty ratio. The alpha–gamma mode transition is verified to occur at the initial phase of a PM RF APGD and the onset is earlier at a higher transient RF voltage. As the mode transition occurs, a RF voltage spike is formed in the pulse waveform.

Potential CCP Pulsed Plasma Application at Beol AIO Etch Process

Plasma etching has been extensively used for more than 30 years in semiconductor manufacturing industry [1]. Typically, plasma reactor RF power sources have constant average power to excite the plasma in a vacuum chamber. Such mode of operation is termed as continuous-wave (CW) RF mode [2]. As COMS is being scaled down to 28nm node and beyond, CW plasmas etching processes are reaching their limits to satisfy the multiply stringent requirements, such as better uniformity, higher selectivity, less plasma induced damage, tighter critical dimension and profile control. The RF pulsed plasma is one of promising knobs to increase the flexibility of plasma processing by enlarging the range of operating conditions [3-5]. There are two main parameters characterizing the RF pulse: one is the pulsed frequency at which the RF power is turned on and off per second; the other is the pulse duty cycle, which is defined as the ratio between the pulse on time and the total pulse duration. As the multiple-frequency RF powers have been introduced for the better control plasma flux and energy in CCP system, the effect of different RF power pulsing varies, bias only, source only and synchronized pulsed plasmas also shows quite different performances. In this work, self-aligned via (SAV) based all-in-one (AIO) etch processes were performed in one commercial etcher, and the effects of pulsed plasmas on the etch process were analyzed. The different pulsed mode, pulsed duty cycle, pulsed frequency on CCP chamber were tested on the SAV based AIO etching process in BEOL copper interconnect system. We compared the bias only, source only and synchronized pulsed plasma performances, checked the duty cycle effects, which varies from 10% to 90%. The Physical performances were analyzed by CDSEM, SEM, TEM, and TK. Compared with conventional CW plasmas, the performances of AIO etching process could be significantly improved via pulsed plasma, such as more rounding chamfer profile, via bottom CD control, and better SAC process with higher selectivity to metal hard mask. Acknowledgement This work is sponsored by Shanghai Rising-Star Program (B type). REFERENCES [1] S. Banna, A. Agarwal, G. Cunge, M. Darnon, E. Pargon, and O. Joubert. J. Vac. Sci. Technol. A, vol. 30, 2012, pp. 040801. [2] S. Banna, A. Agarwal, K. Tokashiki, H. Cho, S. Rauf, V. Todorow, K. Ramaswamy, K. Collins, P. Stout, J. Y. Lee, J. Yoon, K. Shin, S. J. Choi, H. S. Cho, H. J. Kim, C. H. Lee, and D. Lymberopoulos. IEEE Trans. Plasma Sci., vol. 37, 2009, pp. 1730-1746. [3] R. W. Boswell and D. Henry. Appl. Phys. Lett., vol. 47, 1985, pp. 1095-1097. [4] P. Subramonium and M. J. Kushner. Appl. Phys. Lett., vol. 79, 2001, pp. 2145-2147. [5] A. Rousseau, E. Teboul, N. Lang, M. Hannemann, and J. Ropcke. J. Appl. Phys., vol. 92, 2002, pp. 3463-3471.

Continuous-Wave RF Plasma Polymerization of Furfuryl Methacrylate: Correlation Between Plasma and Surface Chemistry

The plasma phase of furfuryl methacrylate (FMA) and its relationship to the surface chemistry of the generated plasma coatings was investigated utilizing mass spectrometry. Positive ion mass spectra from plasma phase and plasma coatings of FMA revealed that furanylmethyl fragment (FM, 81 m/z) has high stability and form oligomers with itself and other species in the plasma phase and on the surface. Combined with ion flux and deposition rate data, the correlation between the normalized intensities of positive fragments from the mass spectra of the neutrals and plasma coatings suggests that neutrals were a major contributor to the plasma film growth. These findings highlight the potential of plasma phase diagnostic tools to predict the chemistry of neutral and positive species, and their role in thin film deposition.

Analysis of gene expression in mouse brain regions after exposure to 1.9 GHz radiofrequency fields

Purpose: To assess 1.9 GHz radiofrequency (RF) field exposure on gene expression within a variety of discrete mouse brain regions using whole genome microarray analysis. Materials and methods: Adult male C57BL/6 mice were exposed to 1.9 GHz pulse-modulated or continuous-wave RF fields for 4 h/day for 5 consecutive days at whole body average (WBA) specific absorption rates of 0 (sham), ∼0.2 W/kg and ∼1.4 W/kg. Total RNA was isolated from the auditory cortex, amygdala, caudate, cerebellum, hippocampus, hypothalamus, and medial prefrontal cortex and differential gene expression was assessed using Illumina MouseWG-6 (v2) BeadChip arrays. Validation of potentially responding genes was conducted by RT-PCR. Results: When analysis of gene expression was conducted within individual brain regions when controlling the false discovery rate (FDR), no differentially expressed genes were identified relative to the sham control. However, it must be noted that most fold changes among groups were observed to be less than 1.5-fold and this study had limited ability to detect such small changes. While some genes were differentially expressed without correction for multiple-comparisons testing, no consistent pattern of response was observed among different RF-exposure levels or among different RF-modulations. Conclusions: The current study provides the most comprehensive analysis of potential gene expression changes in the rodent brain in response to RF field exposure conducted to date. Within the exposure conditions and limitations of this study, no convincing evidence of consistent changes in gene expression was found in response to 1.9 GHz RF field exposure.

High-power dual-fed traveling wave photodetector circuits in silicon photonics

We introduce the concept of dual-illuminated photodetectors for high-power applications. Illuminating the photodetector on both sides doubles the number of optical channels, boosting DC and RF power handling capability. This concept is demonstrated utilizing multiple-stage dual-illuminated traveling wave photodetector circuits in silicon photonics, showing a maximum DC photocurrent of 112 mA and a 3-dB bandwidth of 40 GHz at 0.3 mA. Peak continuous-wave RF power is generated up to 12.3 dBm at 2 GHz and 5.3 dBm at 40 GHz, at a DC photocurrent of 55 mA. High speed broadband data signals are detected with eye amplitudes of 2.2 V and 1.3 V at 10 Gb/s and 40 Gb/s, respectively. A theoretical analysis is presented illustrating design tradeoffs for the multiple-stage photodetector circuits based on the bandwidth and power requirements.

Cuffless blood pressure estimation from the carotid pulse arrival time using continuous wave radar.

Ambulatory blood pressure monitors based on pulse transit time are limited by the challenge of changing vascular tone. This study focuses on the use of the carotid artery as an alternative location for arterial pulse acquisition. We use continuous wave radio frequency (RF) radar coupled directly to the body to detect the pulse wave signal. We have shown that the blood pressure-pulse transit time calibration using the carotid pulse is as accurate as that of the radial arterial pulse. The results of this investigation may be useful in developing wearable sensors for long-term monitoring of the pulse wave signal at the carotid artery.

The mechanical structure of the WEST Ion Cyclotron Resonant Heating launchers

The WEST ICRH system has to deal with two challenging issues that no other ICRH system before ITER has faced simultaneously so far, i.e. ELMs resilience and Continuous Wave (CW) RF operation. The technical solution chosen to meet the requests imposed by the WEST scenarios is to build three new launchers based on the RF structure successfully tested in short pulses in 2007 on Tore Supra prototype launcher. This paper gives an overview of the mechanical structure of the CW ELMs resilient WEST ICRH launchers. The technical solutions chosen to drive the mechanical design are presented, in regard of the past experience on the 2007 TS prototype, together with the significant work carried out on the mechanical design to improve the launcher structure. The thermal and electro-mechanical analyses conducted and their impact on the launcher design are also presented. These three new CW ELMs resilient ICRH launchers are foreseen to be installed on WEST in 2016, and operational for the first plasmas.

Optimized power simulation of AlGaN/GaN HEMT for continuous wave and pulse applications**Project supported by the National Natural Science Foundation of China (No. 61204086).

An optimized modeling method of 8 × 100 μm AlGaN/GaN-based high electron mobility transistor (HEMT) for accurate continuous wave (CW) and pulsed power simulations is proposed. Since the self-heating effect can occur during the continuous operation, the power gain from the continuous operation significantly decreases when compared to a pulsed power operation. This paper extracts power performances of different device models from different quiescent biases of pulsed current–voltage (I–V) measurements and compared them in order to determine the most suitable device model for CW and pulse RF microwave power amplifier design. The simulated output power and gain results of the models at Vgs = −3.5 V, Vds = 30 V with a frequency of 9.6 GHz are presented.

Pulsed radio frequency characterisation on 28 nm complementary metal–oxide semiconductor technology

The influence of electrothermal behaviour on radio frequency (RF) performances of 28 nm bulk complementary metal–oxide semiconductor technology is examined. Biased continuous-wave RF and pulsed RF (applying different DC pulse and RF pulse width combinations) characterisations are performed within the 1–30 GHz frequency domain at room temperature and the transit frequency (f T) is extracted at 15 GHz frequency. It has been found that the degradation in f T on I/O devices is about 3 GHz because of the self-heating effect.

Effect of source frequency and pulsing on the SiO2 etching characteristics of dual-frequency capacitive coupled plasma

A SiO2 layer masked with an amorphous carbon layer (ACL) has been etched in an Ar/C4F8 gas mixture with dual frequency capacitively coupled plasmas under variable frequency (13.56–60 MHz)/pulsed rf source power and 2 MHz continuous wave (CW) rf bias power, the effects of the frequency and pulsing of the source rf power on the SiO2 etch characteristics were investigated. By pulsing the rf power, an increased SiO2 etch selectivity was observed with decreasing SiO2 etch rate. However, when the rf power frequency was increased, not only a higher SiO2 etch rate but also higher SiO2 etch selectivity was observed for both CW and pulse modes. A higher CF2/F ratio and lower electron temperature were observed for both a higher source frequency mode and a pulsed plasma mode. Therefore, when the C 1s binding states of the etched SiO2 surfaces were investigated using X-ray photoelectron spectroscopy (XPS), the increase of C–Fx bonding on the SiO2 surface was observed for a higher source frequency operation similar to a pulsed plasma condition indicating the increase of SiO2 etch selectivity over the ACL. The increase of the SiO2 etch rate with increasing etch selectivity for the higher source frequency operation appears to be related to the increase of the total plasma density with increasing CF2/F ratio in the plasma. The SiO2 etch profile was also improved not only by using the pulsed plasma but also by increasing the source frequency.

Isothermal Electrical Characteristic Extraction for mmWave HBTs

In this brief, we demonstrate a straightforward approach to obtain isothermal electrical characteristics of state-of-the-art SiGe:C BiCMOS heterojunction bipolar transistors designed for mmWave applications. DC and conventional continuous-wave RF measurements are performed at different chuck temperatures ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\rm chuck}$ </tex-math></inline-formula> ). Knowing the thermal resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R} _{\rm {TH}}$ </tex-math></inline-formula> ) of the device, all the isothermal dc and ac (above thermal cutoff frequency) data can be determined. The validation of the methodology is demonstrated by comparing the results with the pulsed dc and pulsed RF measurements, which are found to be in good agreements. This method could be applied with a standard measurement equipment.

Impedance matching network systems using stub-lines of 20 kW CW RF amplifier for SKKUCY-9 compact cyclotron

The SKKUCY-9 is a compact cyclotron for radioactive isotopes (RI) production of positron emission tomography (PET). Charged particles such as H-ions are accelerated azimuthally within a high intensity electric field (E-field) generated from a radio frequency (RF) system in cyclotron. A high power RF signal is transmitted from an RF amplifier to an RF resonating cavity. The RF system of the SKKUCY-9 operates in continuous wave (CW) mode. If an ion beam were accelerated in the cyclotron, the vacuum level and permittivity would be changed because of beam loading. It causes an impedance shift of the RF resonating cavity. This impedance mismatch generates reflected power that decreases the RF transmitting power. To prevent this situation, an impedance matching system is necessary.This paper describes the impedance matching system of a 20kW RF amplifier in an SKKUCY-9 compact cyclotron. The impedance matching circuit was designed using both an input stage and output stage, which are divided between the cathode and anode in a vacuum tube that is used as an amplifying device. The equivalent circuit of the matching system is made of passive elements. The characteristic results of designed circuit were calculated using a Smith chart. In assembling, the inductors were replaced by movable stub-line structures. The dimensions of the stub-line structures were optimized with equations and the measurement results. The experiment was performed to find the result values of matching circuit impedance and RF power amplitude.

Design and multiphysics analysis of a 176 MHz continuous-wave radio-frequency quadrupole

We have developed a new design for a 176 MHz cw radio-frequency quadrupole (RFQ) for the SARAF upgrade project. At this frequency, the proposed design is a conventional four-vane structure. The main design goals are to provide the highest possible shunt impedance while limiting the required rf power to about 120 kW for reliable cw operation, and the length to about 4 meters. If built as designed, the proposed RFQ will be the first four-vane cw RFQ built as a single cavity (no resonant coupling required) that does not require π -mode stabilizing loops or dipole rods. For this, we rely on very detailed 3D simulations of all aspects of the structure and the level of machining precision achieved on the recently developed ATLAS upgrade RFQ. A full 3D model of the structure including vane modulation was developed. The design was optimized using electromagnetic and multiphysics simulations. Following the choice of the vane type and geometry, the vane undercuts were optimized to produce a flat field along the structure. The final design has good mode separation and should not need dipole rods if built as designed, but their effect was studied in the case of manufacturing errors. The tuners were also designed and optimized to tune the main mode without affecting the field flatness. Following the electromagnetic (EM) design optimization, a multiphysics engineering analysis of the structure was performed. The multiphysics analysis is a coupled electromagnetic, thermal and mechanical analysis. The cooling channels, including their paths and sizes, were optimized based on the limiting temperature and deformation requirements. The frequency sensitivity to the RFQ body and vane cooling water temperatures was carefully studied in order to use it for frequency fine-tuning. Finally, an inductive rf power coupler design based on the ATLAS RFQ coupler was developed and simulated. The EM design optimization was performed using cst Microwave Studio and the results were verified using both hfss and ansys . The engineering analysis was performed using hfss and ansys and most of the results were verified using the newly developed cst Multiphysics package.

Evaluation of liver fibrosis with T1ρ MR imaging.

Chronic liver disease is a major public health problem worldwide. Liver fibrosis, a common feature of almost all chronic liver diseases, involves the accumulation of collagen, proteoglycans, and other macromolecules in the extracellular matrix. The accumulation of proteins in the extracellular matrix promotes the formation of scars that bridge together adjacent portal triads and central veins. Ultimately, progressive hepatic fibrosis leads to cirrhosis, a characteristic of all end-stage liver disease. Clinically, liver fibrosis usually has an insidious onset and progresses slowly over decades. Patients remain asymptomatic or have only mild, nonspecific symptoms until the development of cirrhosis (1). To date, the conventional imaging diagnostic tests available in clinical practice are not sensitive or specific enough to function as screening tests for detecting liver fibrosis. In patients with precirrhotic stages of liver fibrosis, as well as patients with early cirrhosis, the liver parenchyma usually has a normal appearance or may exhibit only subtle, nonspecific heterogeneity on conventional MR images. A number of MR imaging techniques have been investigated to identify or to assign a grade to liver cirrhosis. These include double contrast material-enhanced MR imaging (2), MR elastography (3-5), and diffusion weighted imaging (3,5,6). The reproducibility and intersite variability of these techniques have not been well established. A mechanism for magnetic resonance (MR) tissue contrast, spin-lattice relaxation time in the rotating frame (T1ρ), has been investigated in biomedical applications. In T1ρ imaging, the equilibrium magnetization, M0, established by the static magnetic field, B0, is flipped into the transverse plane first. This magnetization in the transverse plane relaxes like a normal free induction decay but in the presence of an onresonant continuous wave radiofrequency pulse, which is much weaker than B0 and is called spin-lock radiofrequency pulse. The relaxation rate constant of this transverse magnetization

Optimization of Cyclopropylamine Plasma Polymerization toward Enhanced Layer Stability in Contact with Water

The present investigation of cyclopropylamine (CPA) plasma polymerization in pulsed and continuous wave radio frequency (RF) discharges leads to the proposition of conditions at which amine‐rich films exhibit a good stability in contact with water. The analyses reveal complex structure of CPA plasma polymers containing hydrocarbon chains, primary and secondary amines, nitriles and possibly imines. The decomposition of the monomer in plasma is progressing with the composite parameter W/F (RF power over monomer flow rate) but, in pulsed discharges, it is possible to deposit the films with N/C ratio above 0.24 using higher monomer flow rate. At the optimized monomer flow rate the 280 nm thick film exhibits only 20% thickness loss after 48 h immersion in water and still contains about 5 at% of the NHx environment.

Regulated High-Voltage Power Supply (RHVPS): Integration, Operation, and Test Results With LHCD System of SST-1

A regulated high-voltage power supply (RHVPS) and its results are presented for its initial integration and operation with lower hybrid current drive (LHCD) system. Experimental results are shown to show the ability of RHVPS as a practical source of electrical power for LHCD. Klystron is operated at 3.7 GHz. with a continuous wave RF power level of 500 kW with various subsystems. RHVPS has proven its capability for feeding power to klystron with a safe and good level of required quality. Up to 65 kV and a load current in excess of 18 A was imparted to klystron with a trapezoidal pulse of voltage. Repeatability of operation is shown by successive shot results. RHVPS is explained with its scheme and control system. Basic parameters are fulfilled with a dummy load testing of RHVPS. Test results are illustrated for basic parameters with resistive dummy load. LHCD system operation parameters and experimental parameters of RHVPS for its operation are discussed. A regulation on flat top level of voltage is as per the requirement of LHCD system. Initial integration of RHVPS has been successful and future plans are mentioned for full-fledged SST-1 operation.

Characterization of low-pressure microwave and radio frequency discharges in oxygen applying optical emission spectroscopy and multipole resonance probe

Optical emission spectroscopy (OES) and multipole resonance probe (MRP) are adopted to characterize low-pressure microwave (MW) and radio frequency (RF) discharges in oxygen. In this context, both discharges are usually applied for the deposition of permeation barrier SiOx films on plastic foils or the inner surface of plastic bottles. For technological reasons the MW excitation is modulated and a continuous wave (cw) RF bias is used. The RF voltage produces a stationary low-density plasma, whereas the high-density MW discharge is pulsed. For the optimization of deposition process and the quality of the deposited barrier films, plasma conditions are characterized using OES and MRP. To simplify the comparison of applied diagnostics, both MW and RF discharges are studied separately in cw mode. The OES and MRP diagnostic methods complement each other and provide reliable information about electron density and electron temperature. In the MW case, electron density amounts to ne = (1.25 ± 0.26) × 1017 m−3, and kTe to 1.93 ± 0.20 eV, in the RF case ne = (6.8 ± 1.8)×1015 m−3 and kTe = 2.6 ± 0.35 eV. The corresponding gas temperatures are 760±40 K and 440±20 K.

Second harmonic acoustic responses induced in matter by quasi continuous radiofrequency fields

We subjected conductive matter and tissue to intermittent continuous-wave radiofrequency fields and investigated whether acoustic responses could be recorded. By placing samples in the near-field of the excitation, we observed frequency-domain acoustic responses from tissues responding to CW radiofrequency excitation. Frequency analysis revealed the generation of 2nd harmonic mechanical waves. This discovery of non-linear responses can lead to alternative measurement concepts of CW radiofrequency deposition in matter and tissues. We offer the theoretical mainframe and discuss sensing applications involving the direct measurement of second harmonic responses representative of CW RF energy deposition in matter.