Continuous-wave Applications Research Articles

A Compact Broadband Power Combiner for High-Power, Continuous-Wave Applications.

A compact broadband combiner with a high power capacity and a low insertion loss, which is especially useful for solid-state power sources where multi-way power synthesis is needed, was designed and experimentally investigated. The combiner could combine the microwave signals of sixteen terminals into a single one and was based on a radial-line waveguide whose circumferential symmetry benefited the amplitude and phase consistency of the combiner. Simulation and experimental results showed that the prototype device, designed for S-band applications, exhibited a reflection coefficient S1,1 < -20 dB in the range of 2.06-2.93 GHz, which corresponds to a relative bandwidth of approximately 34.6%. At 2.45 GHz, the phase imbalance was ±4.5° and the 16-way transmission coefficient was concentrated around -12.0~-12.3 dB. The insertion loss of the device at ambient and elevated temperatures was simulated and experimentally verified, which is of importance for the design of similar high-power microwave combiners. High-power tests proved that even without enforced wind or liquid cooling, the device can handle continuous power (CW) of at least 3.9 kW, which can be much enhanced by taking regular cooling measures. The combined features of the designed combiner suggest promising applications for power synthesis in high-power, solid-state RF sources.

A 28V NMOS power switch and bootstrap driver with integrated PA gate driver

For low power dissipation and area reasons, achieving a small size driver circuit for high power amplifiers (HPAs) is critical. Performing high-voltage driving and control technology based on NMOS power transistor is very important to achieve high efficiency. This paper proposes a fully integrated NMOS transistor driving circuit with an integrated on-chip NMOS power LDMOS transistor, and a CMOS gate driver for the HPA is also integrated capable of handling 1 μF capacitor and dozens of mA loads. This strategy ensures that the drain supply of HPA is modulated and gate power supply is supported simultaneously. The bootstrap driver circuit proposed in this work is suitable for continuous wave applications, and has faster response speed and smaller chip area. Measurements from a test chip in 180 nm high voltage BCD technology confirm the proposed strategy achieved in this paper.

Maximizing the applicability of continuous wave (CW) Electron Paramagnetic Resonance (EPR): what more can we do after a century?

Electron Paramagnetic Resonance/Electron Spin Resonance (EPR/ESR) spectroscopy is a powerful experimental approach solving challenging problems that are inaccessible to other experimental techniques. While pulsed EPR techniques and their applications have been the central focus of the field nowadays, methodology development and application of continuous wave (CW) EPR have never been undervalued. Although the importance of EPR in research has been recognized in many areas as indicated by the increasing number of EPR research articles published every year, the growth in the number of EPR research teams seems to not match the former, likely caused by the relatively high cost of modern pulsed EPR spectrometers. In this perspective, we aim to discuss the new areas and new directions of the application of CW EPR in combination with spin labeling that are slightly different from the classic/traditional applications of the CW EPR technique. Based on our experience, we show example applications of CW EPR on the interfaces of protein-confinement materials, protein-inorganic crystal lattices, protein-nanoparticles, and protein-polymers. Various structure and dynamics information can be resolved from the data analysis of CW EPR, leading to enhanced understanding of protein biophysics upon interaction with the synthetic nanostructures as well as possible guidance of hybrid materials development based on the combination of proteins and nanostructures. We also discussed the possibilities of even broadening the application spectrum of EPR spectroscopy. The relatively high affordability of CW EPR spectrometers (as compared to the pulsed ones) also facilitates the growth in EPR research groups worldwide.

Study of Possible Frequency Dependence of Small AC Fields on Magnetic Flux Trapping in Niobium by Polarized Neutron Imaging

Reducing the size of ambient magnetic flux trapping during cooldown in superconducting radio-frequency niobium cavities is essential to reaching the lowest power dissipation as required for continuous wave application. Here, it is suggested that applying an alternating magnetic field superimposed to the external DC field can potentially reduce the size of trapped flux by supporting flux line movement. This hypothesis is tested for the first time systematically on a buffered chemically polished (BCP) niobium sample before and after high temperature annealing, a procedure which is known to reduce flux pinning. External low-frequency (Hz-range) magnetic fields were applied to the samples during their superconducting transition and the effect of varying their amplitude, frequency and offset was investigated. A few results can be highlighted: The influence of the frequency and magnitude of the AC fields on the flux trapping in the untreated Nb sample cannot be neglected. The trapped flux seems to be homogeneously distributed, unlike the flux trapping in, e.g., lead (Pb), which is a type I superconductor. After annealing, the Nb sample shows practically no dependency of flux trapping on external AC fields. The trapped magnetic flux was measured by polarized neutron imaging, and calculations of trapped fields show good agreement with experimental results.

Resonance enhancement stimulated Raman scattering of O–H stretching vibration in water molecule

Stimulated Raman scattering (SRS) of water molecules excited by 532 nm laser is greatly enhanced by the application of CW (continuous-wave) seeding laser with 650 nm. When the CW laser power is 1 mW, the normalized SRS intensity of O–H stretching vibration at 3405 cm−1 is increased by ten orders of magnitude. Two new lower frequency shoulder peaks are also observed after adding CW seeding laser, which shift to the low-wavenumber due to the pulse heating of water molecules in the laser focused volume. The CW seeding laser not only lowers the threshold of SRS, but also increases the intensity of SRS. The mechanism of enhancement is attributed to the frequency difference between pump laser (532 nm) and CW seeding laser (650 nm) matching the O–H stretching vibrational frequency of water molecule, which provides the possibility of using resonance methods to enhance weak Raman vibration modes.

连续波与脉冲激光器在三重态-三重态湮灭上转换中的应用（特邀）

连续波与脉冲激光器在三重态-三重态湮灭上转换中的应用（特邀）

Continuous Wave Operation of SiO2 Sandwiched Colloidal CdSe/ZnS Quantum-Dot Microdisk Lasers

We report continuous wave operation of SiO2 sandwiched colloidal CdSe/ZnS quantum-dot microdisk lasers at room temperature. The SiO2 sandwiched quantum dot structure is formed first and then the disk patterns are defined by e-beam lithography. The benefits of introducing the sandwich structure are two folds: one to increase the confinement factor and the other to reduce the photo-oxidation of quantum dots. The luminescence stability of CdSe/ZnS quantum dots is much improved after they are sandwiched in silicon dioxide. We observe whispering gallery modes spatially and spectrally in the microdisks. We also fabricated Si3N4 microdisks for comparison. The result shows that Si3N4 microdisks are severely damaged when operating under continuous wave excitation while SiO2 microdisks demonstrate stable lasing behavior at the same excitation condition. Therefore, SiO2 microdisks are more suitable for high excitation and/or continuous wave applications such as lasers. This device structure shows great potentials to be applied to other wavelength in the visible range.

Spin Labeling Studies of Transmembrane Signaling and Transport: Applications to Phototaxis, ABC Transporters and Symporters.

Membrane proteins still represent a major challenge for structural biologists. This chapter will focus on the application of continuous wave and pulsed EPR spectroscopy on spin-labeled membrane proteins. Site-directed spin labeling EPR spectroscopy has evolved as a powerful tool to study the structure and dynamics of proteins, especially membrane proteins, as this method works largely independently of the size and complexity of the biological system under investigation. This chapter describes applications of this technique to three different systems: the archaeal photoreceptor/-transducer complex SRII/HtrII as an example for transmembrane signaling and two transport systems, the histidine ATP-binding cassette transporter HisQMP, and the sodium-proline symporter PutP.

Irregular particle sizing using speckle pattern for continuous wave laser applications

A technique to retrieve the size of irregular particles using the speckle pattern produced from the scattering of laser light is presented. A sizing algorithm based on the maximum curvature peak detection of the Fourier transform of the speckle pattern is introduced, and its application to sand particles with and without motion is studied, using a continuous wave laser. The sizes obtained with this algorithm are in good agreement with the sizes resulting from shadowgraph measurements. It was also observed that the properties of the speckle pattern are independent on the scattering angle. When using a continuous wave laser, special attention is paid to the exposure time while recording the speckle pattern. This special care avoids the images to be blurred as a consequence of the speckle pattern displacement and reshaping due to particle rotation. Finally, further recommendations to define the setup parameters are given in order to apply the technique, focusing on a continuous wave application.

GaN Switches in Pulsed Power: A Comparative Study

Present research in widebandgap semiconductors is concentrated predominantly in continuous-wave applications. While their applicability for pulsed power is recognized, little work has been done in taking advantage of the individual characteristics, such as the large drift velocities, of the candidate materials. Analysis of the relative merits of the key semiconductor technologies - Si, GaAs, SiC, and GaN - in the pulsed-power regime is presented, including limitations associated with majority carrier operation and thermal transients. We will also discuss a GaN photoconductor with a vertical topology, which is particularly well suited to higher current applications and also is geometrically more applicable for integration to transmission lines without degrading the high blocking field (2 MV/cm) now available. The relation between the blocking voltage and conduction current typical of majority carrier operation is analyzed and we will show how optical carrier generation provides the much higher switching power associated with bipolar operation.

Characterization of deep energy level defects in α-Al2O3:C using thermally assisted OSL

Abstract Commercially available α-Al2O3:C powder was studied for deep energy level defects by a newly suggested method using thermally assisted optically stimulated luminescence (TA-OSL) phenomenon. The method involves simultaneous application of continuous wave optically stimulated luminescence (CW-OSL) as well as thermal stimulation up to 400 °C, using a linear heating rate of 4 K/s. By using this method, two well-defined peaks at 121 °C and 232 °C were observed. These TA-OSL peaks have been correlated to two different types of deeper defects which can be bleached at 650 °C and 900 °C respectively on thermal treatment. These deeper defects, having larger thermal trap depth and relatively lower photoionization cross-section at room temperature for stimulation with blue LED (470 nm), are stable up to 500 °C, so they can store absorbed dose information even if the sample is inadvertently exposed to light or temperature. As only a fraction of signal is bleached during TA-OSL readout, multiple readouts could be performed on an exposed sample using this technique. The dose vs TA-OSL response from deep traps of α-Al2O3:C was found to be linear up to 10 kGy, thus extending its application for high dose dosimetry. The value of thermally assisted energy (EA) associated with these traps in α-Al2O3:C has been determined to be 0.268 eV and 0.485 eV respectively and the corresponding values of photoionization cross-section at room temperature (25 °C), for optical stimulation with blue light (470 nm), are 5.82 × 10−20 and 3.70 × 10−22 cm2, respectively. The process of thermally assisted OSL has been formulated analytically as well as theoretically for describing the temperature dependence of optical cross-section and evaluation of thermally assisted energy associated with deep traps.

Characterization of Acoustic Cavitation Bubbles in Different Sound Fields

Various fundamental properties of acoustic cavitation bubbles have been investigated in single- and dual-frequency sound fields. It was found that the relative extent of bubble coalescence in the dual-frequency field correlated strongly with the synergistic enhancement of the sonochemical reaction rates. Both the relative extent of coalescence and the sonochemical synergy observed were enhanced through the addition of coalescence-inhibiting solutes. This was attributed to greater nucleation in the dual-frequency mode compared with the single-frequency modes, producing a very localized and high-density bubble field. The acoustic bubble size, compared with that measured at 355 kHz alone, was found to increase upon the application of synchronous 20 kHz pulses but was reduced dramatically when the low frequency was applied as a continuous wave. This trend is consistent with previous reports indicating that the bubble density and cavitation activity are relatively higher in the pulsed system and that the continuous wave application exerts a strong cancellation effect. The changes in bubble density and coalescence rates are proposed to govern the acoustic bubble size. The bubble lifetime was found to be longer in the dual-frequency field (>0.30 ms; >6 low-frequency oscillations, >100 high-frequency oscillations) compared with both single-frequency fields (0.26 ms and 5 oscillations for the low frequency; 0.22 ms and 75 oscillations for the high frequency). The confluence of a longer bubble lifetime and more asymmetric collapse conditions, the latter inferred from a more pronounced sodium atom emission in the sonoluminescence spectrum, resulted in a lower bubble collapse temperature measured in the dual-frequency system.

Doppler echocardiography.

We describe concepts important in the clinical application of continuous wave, pulsed wave, and color Doppler flow imaging. In the second half of this manuscript, the application of these tools in pediatric echocardiography is addressed.

EPR analysis of radicals generated in ultrasound-assisted lipoplasty simulated environment

The generation of various radicals by application of continuous wave (CW) high-intensity ultrasound energy (HIUE) to an aqueous biologic medium containing spin traps, under conditions simulating ultrasound-assisted lipoplasty (UAL), was demonstrated by EPR spectroscopy. The addition of water- soluble antioxidants, ascorbic acid and glutathione to the wetting solution substantially reduces the levels of hydroxyl radicals in the sonicated medium. These findings provide direct evidence for the generation of cavitation in the simulated intercellular environment, corroborating previous data, and pointing out that generation of transient cavitation in clinical UAL and other therapeutic and surgical applications of ultrasound is possible. The findings indicate that the effect of transient cavitation in aqueous biologic media may be similar to the effects of ionizing radiation, and raise the question of the long-term biosafety of the use of CW HIUE in UAL. The introduction of biocompatible water-soluble antioxidants to the sonicated medium may be utilized to suppress accumulation of radicals and reduce their possible adverse effects. (E-mail: topazmd@netvision.net.il)

Novel design concepts of widely tunable germanium terahertz lasers

We explore the full parameter space for laser operation and compile guidelines for building improved Ge lasers, especially for continuous wave applications. We present laser emission from p-type Ge lasers with small volumes at high repetition rates and with inter-contact distances as low as 750 μm. The emission is analyzed as a function of the current–voltage characteristic. The Poisson equation is solved to determine the electric field distribution and two new laser designs are presented.