Power Attenuator Research Articles

Frequency-segmented power amplification using multi-band radio frequency amplifiers to produce a high-voltage pulse.

A method of frequency-segmented power amplification using multiband radio frequency (RF) amplifiers was proposed to generate stable and arbitrary high-voltage pulses. The concept behind this method is that an arbitrary pulse with a specified duration and sharp edges can be reconstructed using only several frequencies, and most of the power is concentrated on the fundamental frequency. The high-voltage pulse can, therefore, be obtained by amplifying each segmented frequency and then combining it with the RF power combiners. To correct the frequency-dependent group delays and gain of the amplifier circuit and to perform fine-tuning of the pulse structure, a seed pulse is divided into several lines that have bandpass filters, variable delay lines, variable power attenuators, and main RF amplifiers. A prototype pulse amplifier was designed and fabricated based on this method to generate rectangular pulses for the electron beam chopper of an x-ray free-electron laser injector. Flat and stable pulses with a 2ns width of 0.2kV height, peak-to-peak flat top of 0.8%, and route-mean-squared peak jitter of less than 0.2% were successively generated in both single- and multi-bunch structures. In the future, this type of pulse generator will play an important role in accelerators that require complicated and precise beam handling at high repetition rates of kHz or MHz.

Exploitation of response surface method for the optimization of RF-MEMS reconfigurable devices in view of future beyond-5G, 6G and super-IoT applications

The emerging paradigms of the Beyond-5G, 6G and Super-IoT will demand for high-performance Radio Frequency (RF) passive components, and RF-MEMS technology, i.e. Microsystems-based RF passives, is a good candidate to meet such a challenge. As known, RF-MEMS have a complex behavior, that crosses different physical domains (mechanical; electrical; electromagnetic), making the whole design optimization and trimming phases particularly articulated and time consuming. In this work, we propose a novel design optimization approach based on the Response Surface Method (RSM) statistical methodology, focusing on a class of RF-MEMS-based programmable step power attenuators. The proposed method is validated both against physical simulations, performed with Finite Element Method (FEM) commercial software tools, as well as experimental measurements of physical devices. The case study here discussed features 3 DoFs (Degrees of Freedom), comprising both geometrical and material parameters, and aims to optimize the RF performances of the MEMS attenuator in terms of attenuation (S21 Scattering parameter) and reflection (VSWR—Voltage Standing Wave Ratio). When validated, the proposed RSM-based method allows avoiding physical FEM simulations, thus making the design optimization considerably faster and less complex, both in terms of time and computational load.

Design and realization of a single klystron-based radio frequency system for a radio frequency quadrupole and a drift tube linac

This work describes the design and realization of a radio frequency (RF) system with a single klystron to power two conjunct independent cavities, namely, an RF quadrupole (RFQ) and a drift tube linac (DTL). In contrast with a two-klystron scheme, an RF system that adopts a single-klystron scheme for two accelerating cavities exhibits simpler configuration, smaller occupation area, and lower cost. However, the low intrinsic flexibility of the single-klystron scheme needs to be compensated by independent adjustment of RF field phases and amplitudes inside the two cavities. A proposed RF system design based on the single-klystron scheme includes a 4.77 dB power divider, an adjustable power attenuator, and a phase shifter. The power attenuator and phase shifter are set in different branches of the RF power transmission line. This design is used to power an RFQ and a downstream DTL in the Compact Pulsed Hadron Source (CPHS) at Tsinghua University. During commissioning, the amplitudes inside the RFQ and DTL and the relative phase difference between them can be adjusted independently. The 13 MeV proton beam commissioning result verifies the design parameters and effectiveness of the single-klystron-based RF system. A proton beam energy of 12.92 MeV and a beam peak current of 41.2 mA at the exit of DTL were achieved, and the beam transmission from the entrance of RFQ to the exit of DTL reached 88.6%.

RF-MEMS for 5G applications: a reconfigurable 8-bit power attenuator working up to 110 GHz. Part 2—Experimental characterisation of the RF behaviour

RF-MEMS technology is indicated as a key enabling solution to realise the high-performance and highly-reconfigurable passive components that future 5G communication standards will demand for. In this work, divided in the previous Part 1 and the current Part 2, a novel design concept of an 8-bit reconfigurable power attenuator manufactured in the RF-MEMS technology available at the CMM-FBK, in Italy, is presented, tested and discussed. As reported in Part 1, the device features electrostatically controlled MEMS ohmic switches, in order to select/deselect resistive loads (both in series and shunt configuration) that attenuate the RF signal, and comprises eight cascaded stages (i.e. 8-bit), thus implementing 256 different network configurations. In the current Part 2, fabricated samples are measured (S-parameters) from 10 MHz to 110 GHz in a wide range of different configurations, and modelled/simulated in a full 3D Finite Element Method (FEM) environment. Despite the attenuator complexity, the simulation approach leads to accurate prediction of the experimental behaviour. The device exhibits attenuation levels (S21) in the range from − 10 to − 60 dB, up to 110 GHz. In particular, the S21 shows flatness from 15 down to 3–5 dB, from 10 MHz to 50 GHz, while less linear traces up to 110 GHz. A comprehensive discussion is developed around the voltage standing wave ratio (VSWR), employed as quality indicator for the attenuation levels. Finally, margins of improvement at design level are also discussed, in order to overcome the limitations of the presented RF-MEMS device.

RF-MEMS for 5G applications: a reconfigurable 8-bit power attenuator working up to 110 GHz. Part 1: design concept, technology and working principles

RF-MEMS technology is indicated as a key enabling solution to realise the high-performance and highly-reconfigurable passive components that future 5G communication standards will demand for. In this work, a novel design concept of an 8-bit reconfigurable power attenuator manufactured in the RF-MEMS technology available at the CMM-FBK, in Italy, is tested and discussed. In the current Part 1 of the contribution, the RF-MEMS power attenuator design concept is discussed. The device features electrostatically controlled MEMS ohmic switches, in order to select/deselect resistive loads (both in series and shunt configuration) that attenuate the RF signal, and comprises eight cascaded stages (i.e. 8-bit), thus implementing 256 different network configurations. In Part 2 of the article, fabricated samples are measured (S-parameters) from 10 MHz to 110 GHz in a wide range of different configurations, and modelled/simulated in with a Finite Element Method software tool. Despite the attenuator complexity, the simulation approach leads to accurate prediction of the experimental behaviour. The device exhibits attenuation levels (S21) in the range from − 10 to − 60 dB, up to 110 GHz. In particular, the S21 shows flatness from 15 dB down to 3–5 dB, from 10 MHz to 50 GHz, while less linear traces up to 110 GHz. A comprehensive discussion is developed around the voltage standing wave ratio, employed as quality indicator for the attenuation levels. Finally, margins of improvement at design level are also discussed, in order to overcome the limitations of the presented RF-MEMS device.

Sub-Kelvin (100 mK) time resolved electron paramagnetic resonance spectroscopy for studies of quantum dynamics of low-dimensional spin systems at low frequencies and magnetic fields.

This article presents a time-resolved electron paramagnetic resonance spectrometry setup designed to work at frequencies below 20 GHz and temperatures down to 50 mK. The setup consists of an on-chip microstrip resonator (Q < 100) placed in a dilution cryostat located within a superconducting 3D vector magnet. A housemade spin echo circuitry controlled by a microwave network analyzer, a pulse pattern generator, and an oscilloscope connects to the microstrip through a series of copper, stainless steel, and superconducting semirigid coaxial lines which are thermally anchored to the different cooling stages of the fridge by means of power attenuators, circulators, and a cryogenic amplifier. Spin echo experiments were performed at a 0.5-T magnetic field on a spin 1 2 paramagnetic coal marker sample mounted on a 15 GHz microstrip resonator at temperatures ranging from 100 to 800 mK. The results show an increase in echo signal intensity as temperature is decreased until saturation as theoretically expected in reaching 99% spin polarization at 100 mK. Our technique allows tuning of the spin system in the pure-state regime and minimizing dipolar fluctuations, which are the main contribution to decoherence in solid-state samples of single-molecule magnets (SMMs) - molecular spin systems that are currently being tested for applications in quantum computation. The achievement of full spin polarization at 100 mK will allow for coherent control over the time evolution of spin systems without the need for large magnetic fields (commonly used to polarize the dipolar bath at higher temperatures) and high frequencies.

Kinetic Inductance Detectors and readout electronics for the OLIMPO experiment

Kinetic Inductance Detectors (KIDs) are superconductive low–temperature detectors useful for astrophysics and particle physics. We have developed arrays of lumped elements KIDs (LEKIDs) sensitive to microwave photons, optimized for the four horn–coupled focal planes of the OLIMPO balloon–borne telescope, working in the spectral bands centered at 150 GHz, 250 GHz, 350 GHz, and 460 GHz. This is aimed at measuring the spectrum of the Sunyaev–Zel’dovich effect for a number of galaxy clusters, and will validate LEKIDs technology in a space–like environment. Our detectors are optimized for an intermediate background level, due to the presence of residual atmosphere and room–temperature optical system and they operate at a temperature of 0.3 K. The LEKID planar superconducting circuits are designed to resonate between 100 and 600 MHz, and to match the impedance of the feeding waveguides; the measured quality factors of the resonators are in the 104 – 105 range, and they have been tuned to obtain the needed dynamic range. The readout electronics is composed of a cold part, which includes a low noise amplifier, a dc–block, coaxial cables, and power attenuators; and a room–temperature part, FPGA–based, including up and down-conversion microwave components (IQ modulator, IQ demodulator, amplifiers, bias tees, attenuators). In this contribution, we describe the optimization, fabrication, characterization and validation of the OLIMPO detector system.

RF MEMS packaged switch evaluation tests up to 25 GHz

This article presents the results of the series of experimental tests of a packaged RF MEMS switch manufactured as a chip on a silicon substrate in the Center for Materials and Microsystems of Fondazione Bruno Kessler. Experiments have been performed up to 25 GHz and included S-parameters check in different operation and environmental conditions, including variation of input power, ambient temperature and number of switching cycles. Presented RF MEMS SPST switch is a basic element of more complex reconfigurable networks such as SPxT switches, phase shifters, power attenuators etc.

All-polarization-maintaining figure-eight Er-fiber ultrafast laser with a bidirectional output coupler in the loss-imbalanced nonlinear optical loop mirror

In this Letter, we report on a novel architecture for a self-starting mode-locked figure-eight erbium-doped fiber laser using a loss-imbalanced nonlinear optical loop mirror (NOLM) with a bidirectional output coupler. An all-polarization-maintaining structure is adopted. A 2 × 2 optical coupler with a splitting ratio of 50:50 is used at the junction to form an NOLM. Another coupler with a splitting ratio of 10:90 is introduced at one end of the fiber loop. The 10:90 coupler plays two roles: power attenuator and bidirectional output coupler. This architecture can achieve both large modulation depth and good self-starting ability simultaneously. With this architecture, the self-starting mode-locking operation is achieved easily with pump power above the threshold. The clockwise and counter-clockwise mode-locked output powers are 10.1 and 10.3 mW, respectively, with the repetition rate of 3.63 MHz. The spectral bandwidths of the clockwise and counter-clockwise mode-locked output pulses are 7.4 and 2.9 nm, and the corresponding pulse widths of the direct outputs are 530.6 fs and 1.55 ps, respectively.

Microwave attenuators for use with quantum devices below 100 mK

To reduce the level of thermally generated electrical noise transmitted to superconducting quantum devices operating at 20 mK, we have developed thin-film microwave power attenuators operating from 1 to 10 GHz. The 20 and 30 dB attenuators are built on a quartz substrate and use 75 nm thick films of nichrome for dissipative components and 1 μm thick silver films as hot electron heat sinks. The noise temperature of the attenuators was quantified by connecting the output to a 3D cavity containing a transmon qubit and extracting the dephasing rate of the qubit as a function of temperature and dissipated power Pd in the attenuator. The minimum noise temperature Tn of the output from the 20 dB attenuator was Tn≤53 mK for no additional applied power and Tn≈120 mK when dissipating 30 nW. In the limit of large dissipated power (Pd&amp;gt;1 nW), we find Tn∝Pd1/5.4, consistent with detailed thermal modeling of heat flow in the attenuators.

RF-MEMS for future mobile applications: experimental verification of a reconfigurable 8-bit power attenuator up to 110 GHz

RF-MEMS technology is proposed as a key enabling solution for realising the high-performance and highly reconfigurable passive components that future communication standards will demand. In this work, we present, test and discuss a novel design concept for an 8-bit reconfigurable power attenuator, manufactured using the RF-MEMS technology available at the CMM-FBK, in Italy. The device features electrostatically controlled MEMS ohmic switches in order to select/deselect the resistive loads (both in series and shunt configuration) that attenuate the RF signal, and comprises eight cascaded stages (i.e. 8-bit), thus implementing 256 different network configurations. The fabricated samples are measured (S-parameters) from 10 MHz to 110 GHz in a wide range of different configurations, and modelled/simulated with Ansys HFSS. The device exhibits attenuation levels (S21) in the range from −10 dB to −60 dB, up to 110 GHz. In particular, S21 shows flatness from 15 dB down to 3–5 dB and from 10 MHz to 50 GHz, as well as fewer linear traces up to 110 GHz. A comprehensive discussion is developed regarding the voltage standing wave ratio, which is employed as a quality indicator for the attenuation levels. The margins of improvement at design level which are needed to overcome the limitations of the presented RF-MEMS device are also discussed.

RF-MEMS Technology for Future Mobile and High-Frequency Applications: Reconfigurable 8-Bit Power Attenuator Tested up to 110 GHz

In this letter, we present and test—to the best of our knowledge, for the first time—, an 8-bit (256-state) reconfigurable RF-MEMS attenuator, from 10 MHz up to 110 GHz, realized in the CMM-FBK technology. Resistive loads, in series and shunt configuration, are selectively inserted on the RF line by means of electrostatic MEMS ohmic switches. The network exhibits several attenuation levels in the range of −10/−45 dB that are rather flat up to 50 GHz, and a certain number of configurations with VSWR smaller than 4 from nearly dc up to 110 GHz, and better than 2 on a frequency span of ~80 GHz.

Experimental implementation of array-compressed parallel transmission at 7 tesla.

To implement and validate a hardware-based array-compressed parallel transmission (acpTx) system. In array-compressed parallel transmission, a small number of transmit channels drive a larger number of transmit coils, which are connected via an array compression network that implements optimized coil-to-channel combinations. A two channel-to-eight coil array compression network was developed using power splitters, attenuators and phase shifters, and a simulation was performed to investigate the effects of coil coupling on power dissipation in a simplified network. An eight coil transmit array was constructed using induced current elimination decoupling, and the coil and network were validated in benchtop measurements, B1+ mapping scans, and an accelerated spiral excitation experiment. The developed attenuators came within 0.08 dB of the desired attenuations, and reflection coefficients were -22 dB or better. The simulation demonstrated that up to 3× more power was dissipated in the network when coils were poorly isolated (-9.6 dB), versus well-isolated (-31 dB). Compared to split circularly-polarized coil combinations, the additional degrees of freedom provided by the array compression network led to 54% lower squared excitation error in the spiral experiment. Array-compressed parallel transmission was successfully implemented in a hardware system. Further work is needed to develop remote network tuning and to minimize network power dissipation. Magn Reson Med 75:2545-2552, 2016. © 2016 Wiley Periodicals, Inc.

Optically Controlled Coupled Microstripline Microwave Power Attenuator

This paper presents an optically controlled coupled microstripline microwave powerattenuator on a high resistivity silicon substrate in the 3GHz-7GHz frequency band. The structure is based on the10dB microstrip directional coupler. Attenuation control is performed by optical control of the open end resistances. The open end act as a variable resistance under sufficient optical illumination conditions. The attenuator has been designed for 10dB and 25dB attenuation control for one-port and two port optical illuminations respectively. The analysis has been carried out for one port illumination using a 30mW, 850nm laser diode and two ports illumination using two 20mW, 650nm laser diode. The attenuator has been modeled by the Computer Simulation Technique's Micro Wave Studio (CST MWS) 3D EM simulator. At 5GHz, the structure provides a continuous variation of S41 between 0 and 25dB with both open end illumination.

Tunable Microring Resonator Based on Dielectric-Loaded Surface Plasmon Polariton Waveguides

Integrated optical ring resonators are essential elemental components for integrated optical circuits. An ultrasmall thermo-optical microring resonator with two bus waveguide-configuration based on surface plasmon polariton waveguide is theoretically analyzed. The thermo-optical coefficient, the temperature-dependent amplitude attenuation coefficient and the temperature distribution properties of the waveguide are investigated numerically by finite element method. The critical resonant conditions of the microring resonator are discussed by considering the propagation losses in the plasmonic ring cavity. The transmission characteristics and the tunability of the ring resonator with different structural parameters are investigated. The results show that the proposed ring resonator with a low driving power and high efficient tunability has potential to develop nano-scope wavelength tunable channel drop filters, low power optical switches, attenuators, and other high compact integrated optical devices.

Muscle power attenuation by tendon during energy dissipation

An important function of skeletal muscle is deceleration via active muscle fascicle lengthening, which dissipates movement energy. The mechanical interplay between muscle contraction and tendon elasticity is critical when muscles produce energy. However, the role of tendon elasticity during muscular energy dissipation remains unknown. We tested the hypothesis that tendon elasticity functions as a mechanical buffer, preventing high (and probably damaging) velocities and powers during active muscle fascicle lengthening. We directly measured lateral gastrocnemius muscle force and length in wild turkeys during controlled landings requiring rapid energy dissipation. Muscle-tendon unit (MTU) strain was measured via video kinematics, independent of muscle fascicle strain (measured via sonomicrometry). We found that rapid MTU lengthening immediately following impact involved little or no muscle fascicle lengthening. Therefore, joint flexion had to be accommodated by tendon stretch. After the early contact period, muscle fascicles lengthened and absorbed energy. This late lengthening occurred after most of the joint flexion, and was thus mainly driven by tendon recoil. Temporary tendon energy storage led to a significant reduction in muscle fascicle lengthening velocity and the rate of energy absorption. We conclude that tendons function as power attenuators that probably protect muscles against damage from rapid and forceful lengthening during energy dissipation.

Tendons as power attenuators

Tendons as power attenuators

Focus on Lasers and Optics

Focus on Lasers and Optics

Photoinduced Phenomena in Conjugated Organic Systems Doped with Fullerenes

ABSTRACT Optical limiting properties of C60 and C70-doped organic thin films (polyimide, 2-cyclooctylamino-5-nitropyridine) under a laser irradiation at wavelengths of 532, 1047, and 1315 nm have been studied. The films can be applied as laser power attenuators at a laser energy density of more than 2 J·cm−2 and at a laser energy density up to 0.8–1 J·cm−2 in the visible and near infrared spectral ranges, respectively. Reverse saturable absorption and the complex formation have been discussed to explain optical limiting results. The place of the materials studied can be predicted among other nonlinear optical systems attenuating high energy density in the near infrared.

Microstructure Damage in Thermal Absorbers Induced by High Energy Synchrotron Light Irradiation

Aluminium plates are used as power attenuators in beamline ID15 at the ESRF. They absorb the low-energy part of the synchrotron light to reduce the heat-load on the following beamline components. Despite of many proposed design criteria, the high hea