Passive Modulation Research Articles

Modeling scatter through sides of island blocks used for intensity-modulated bolus electron conformal therapy.

Passive Radiotherapy Intensity Modulators for Electrons (PRIME) devices are comprised of cylindrical tungsten island blocks imbedded in a machinable foam slab within the patient's cutout. Intensity-modulated bolus electron conformal therapy (IM-BECT) uses PRIME devices to reduce dose heterogeneity caused by the irregular bolus surface. Heretofore, IM-BECT dose calculations used the pencil beam redefinition algorithm (PBRA) assuming perfect collimation. This study investigates modeling electron scatter into and out the sides of island blocks. Dose distributions were measured in a water phantom at 7, 13, and 20 MeV for devices having nominal intensity reduction factors of 1.000 (foam only), 0.937, 0.812, and 0.688, corresponding to nominal island block diameters (dnom ) of 0.158, 0.273, and 0.352cm, respectively. Pencil beam theory derived an effective diameter (dIS ) to account for in-scattered electrons as a function of dnom and beam energy (Ep,0 ). However, for out-scattered electrons, an effective diameter (dmod ) was estimated by best fitting measured data. In the modulated region (under island blocks, depth<R90 ), modified PBRA-calculated dose distributions showed 2%/2mm passing rates for dnom =0.158, 0.273, and 0.352cm of (100%, 100%, 100%) at 7 MeV, (100%, 100%, 93.5%) at 13 MeV, and (99.8%, 85.4%, and 71.5%) at 20 MeV. The largest dose differences (≤6%) occurred at the highest energy (20 MeV), largest dnom , shallowest depths (≤2cm), and on central axis. An equation for modeling island block scatter, dmod (dnom , Ep,0 ), has been developed for use in the PBRA, insignificantly impacting calculation time. Although inaccuracy sometimes exceeded our 2%/2mm criteria, it could be clinically acceptable, as superficial dose differences often fall inside the bolus. Also, patient PRIME devices are expected to have fewer large diameter island blocks than did test devices. Inaccuracies are attributed to out-scattered electrons having energy spectra different than the primary beams.

A 3.6 GHz Polar Reflection-Type Vector Modulator Phase Shifter With Amplitude Control Capability

This paper presents a new passive vector modulator phase shifter (VMPS) based on a polar architecture suitable for use in advanced beamforming feeding networks. The cascaded structure of a reflection-type bi-phase variable attenuator (RTBVA) and a reflection-type phase shifter (RTPS) allows great flexibility regarding phase and amplitude control, and reduces amplitude errors in phase shifting. A printed circuit operating at a central frequency of 3.6 GHz with 5-bit phase resolution was designed and implemented to validate the proposed concept. The measured results showed a 360° phase shift range, an average insertion loss of 2.4 dB at 3.6 GHz, a root-mean-square phase, and a gain error of 1.3° and 0.06 dB, respectively. This VMPS also allows an amplitude control range of ~25 dB and an operational bandwidth of 0.7 GHz (19.4%).

Reference-frame-independent quantum key distribution based on passive light source monitoring

In quantum key distribution (QKD), the users need to share the same reference frame. If their reference frames are inconsistent, the QKD system will not function properly. The most widely used method today is the active real-time calibration of both communication reference frames by using classical communication. In order to get rid of the real-time calibration operation of the reference frames, a QKD protocol independent of reference frame is proposed, called reference-frame-independent QKD (RFI-QKD). The RFI-QKD protocol is immune to the effects of slowly changing reference frame drift, requiring that only one set of bases should be aligned by Alice and Bob, and the remaining two sets of bases can slowly change in the channel. In the real QKD system, a set of basis vectors can always be found to maintain a stable alignment. However, some assumptions are made for the sources in most reported researches, i.e. with a trusted and fixed photon-number distribution (PND), which usually cannot be satisfied in practical implementations. Those unreasonable assumptions will inevitably compromise the security of practical QKD systems. To solve the problem, in this work, we present a passive light source monitoring (PLSM) scheme for RFI-QKD, which is accomplished by a passive monitoring module consisting of a beam splitter and two detectors on the source side. Through the PLSM module, we can have four monitoring events by using two local detectors and then precisely estimate the bounds of source distributions. Specifically, we take the three-intensity decoy-state-based RFI-QKD for example for illustraing the events. Compared with the original RFI-QKD, our PLSM method can passively monitor the PND and has many advantages, with light source fluctuations, finite-size effects and reference frame deflection angles taken into account.

Passive intensity modulation of a pattern for fabricating near-net shaped features in microscale metal additive manufacturing

A large variation in part size across the projection area of the microscale selective laser sintering process is caused by non-uniform intensity projected onto the substrate by the digital micromirror device (DMD). A corrective gray scale mask with varying intensities was mapped according to a sintered array of parts. The variance in part size across the area was reduced by as much as 45% by using this technique. This approach can be extended to in real-time process control to create a more uniform distribution of heat and in turn better near net shape parts across the projection area.

Reconfigurable Intelligent Surface-Assisted Backscatter Communication: A New Frontier for Enabling 6G IoT Networks

Backscatter Communication (BackCom), which is based on passive reflection and modulation of an incident radio-frequency (RF) wave, has emerged as a cutting-edge technological paradigm for self-sustainable Internet-of-things (IoT). Nevertheless, contemporary BackCom systems are limited to short-range and low data rate applications only, rendering them insufficient on their own to support pervasive connectivity among the massive number of IoT devices. Meanwhile, wireless networks are rapidly evolving toward the smart radio paradigm. In this regard, reconfigurable intelligent surfaces (RISs) have come to the forefront to transform the wireless propagation environment into a fully controllable and customizable space in a cost-effective and energy-efficient manner. Targeting the sixth-generation (6G) horizon, we anticipate the integration of RISs into BackCom systems as a new frontier for enabling 6G IoT networks. In this article, for the first time in the open literature, we provide a tutorial overview of RIS-assisted BackCom (RIS-BackCom) systems. Specifically, we introduce the three different variants of RIS-BackCom and identify the potential improvements that can be achieved by incorporating RISs into BackCom systems. In addition, owing to the unrivaled effectiveness of non-orthogonal multiple access (NOMA), we present a case study on a RIS-assisted NOMA-enhanced BackCom system. Finally, we outline the way forward for translating this disruptive concept into real-world applications.

Scalable and all-season passive thermal modulation enabled by radiative cooling, selective solar absorption, and thermal retention

Temperature regulation of infrastructures by active heating and cooling approaches consumes about 20% of the total energy across the world, intensifying the energy crisis and exacerbating global warming by greenhouse gas emissions. In this work, we demonstrate a strategy for the all-season passive thermal modulation enabled by its three-mode functionality of radiative cooling, selective solar absorption, and thermal retention in a scalable manner. The radiative cooler consists of a 50μm thick Polydimethylsiloxane (PDMS) film with its back coated by broadband reflective silver (Ag) thin film (200 nm in thickness). The high solar reflectance (Rsolar, 0.95) and thermal emittance (ϵIR, 0.9) of the PDMS-derived radiative cooler facilitate the subambient cooling effect during the hot summer. The selective solar absorber is derived by selective leaching the aluminum (Al) element in the aluminum alloy by the hot alkaline solution to form the solar absorption copper (Cu) nanostructures over the all-wavelength reflective alloy substrate. The high solar absorptance (αsolar, 0.95) and low ϵIR (0.05) of the selective solar absorber assist the efficient solar harvesting during the daytime of the cold winter, meanwhile, its low ϵIR suppresses the radiative heat dissipation helping the thermal retention during the cold nighttime of the winter. The fabrication of the radiative cooler is derived by roll-to-roll casting, while the selective solar absorber can be manufactured by the solution process, which allows the all-season passive temperature regulation in a scalable manner.

A Novel MEMS Capacitor with a Side Wall for High Tuning Ranges

These days, the market of wireless communications has developed dramatically. Thus, demand increased with respect to wireless communication terminals that consume less power. Consequently, integration technology for passive elements and circuit module development with respect to ‘Radio frequency systems’ using ‘Micro electro mechanical system’ is becoming a focused topic. Many researchers focused various perspectives in this field. The development of ultra-low operating voltage elements is required in voltage-tunable MEMS-type capacitors, but development for satisfying demands has not occurred. Among many studies, a capacitor with a high tuning range using carrier beams has been proposed by Barki-Kassem and others in 2006. In the proposed study, a high tuning range was generated using a carrier beam when the voltage was applied, passing through the pull-in point and exceeding the controllable range. However, these carrier beams are relatively inefficient because these are applied only in one location and not in several air gaps. Therefore, this study dealt with the optimization of a new MEMS capacitor concept, such as using a total of four beams and by applying a side wall instead of a single carrier beam compared to the previous study. Therefore, in this study, further steps were applied to existing research findings to optimize a new concept MEMS capacitor by applying the side wall instead of a carrier beam. The side wall is the same as the one used in the four-beam example.

A compact 90–96 GHz 6‐bit passive vector modulator phase shifter in 28‐nm CMOS for phase array applications

AbstractThis letter presents a 90–96 GHz 6‐bit digital control passive vector modulator phase shifter (PS) in a 28‐nm complementary metal–oxide–semiconductor for phase array application. In PS, a full differential directional coupler as a quadrature generator (QG) is proposed, which achieves wide bandwidth and a high‐performance orthogonal network by introducing more pole‐zero pairs. In the vector modulator, two 6‐bit binary‐weighted vector modulators, respectively scale the quadrature signal generated by QG to achieve a high‐resolution vector phase. The measured PS cover and the minimal root mean square (RMS) phase error is and RMS gain error 0.3 dB at 93 GHz, respectively. The fabricated PS occupies excluding pads with no power consumption.

A 32–40 GHz 7-bit Bi-Directional Phase Shifter With 0.36 dB/1.6° RMS Magnitude/Phase Errors for Phased Array Systems

This paper presents a digitally programmable bi-directional 7-bit passive phase shifter in a 65 nm CMOS technology. The core of this passive vector-synthesized phase shifter is a hybrid quadrature generator (HQG), an interstage matching network, and a passive vector modulator (PVM). This work proposes a high coupling-factor-based quadrature generator design methodology and demonstrates it with a compact vertical transformer. The interstage matching network between HQG and PVM is proposed to release the bandwidth bottleneck and achieve a 34% fractional frequency bandwidth. Two 6-bit X-type attenuators in the I and Q path form a high-resolution 12-bit controlling word. In 32–40 GHz, this 7-bit 360° phase shifter achieves a measured 2.8° step with 0.45-1.6° RMS phase error and 0.2-0.36 dB RMS magnitude error. With the broadband technique, its 3-dB bandwidth reaches 30.2-42.7 GHz with a 2.8° RMS phase error. Its in-band 1-dB compression point is 10.2 dBm. With the proposed compact HQG and PVM, this mm-wave passive phase shifter only occupies <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$220\times 630\,\,\mu \text{m}^{2}$ </tex-math></inline-formula> and has no power consumption.

A Mechanophotonic Approach toward an Organic, Flexible Crystal Optical Interferometer

AbstractOrganic crystals are poised to be a potential alternative to conventional silicon and its derivatives due to their utilization as microscale photonic components like active and passive waveguides, ring‐resonators, modulators, directional couplers, add‐on filters, interferometers (IMs), and reconfigurable circuits. Among these, IMs are important for flexible organic photonic integrated circuits. Here, the design and synthesis of extremely flexible (E)‐1‐(((5‐bromopyridin‐2‐yl)imino)methyl)naphthalen‐2‐ol (BPyIN) crystals are demonstrated. The interactions stabilizing the crystal packing and crystal‐substrate adhesion dictate the elasticity and pseudo‐plasticity, respectively. The extremely flexible BPyIN crystals disclose bending geometry‐dependent optical modes in the fluorescence spectra. This understanding is extended for fabricating a fiber loop mirror (FLM)‐like geometry using a BPyIN single crystal. Mechanophotonics approach facilitates the integration of FLM‐like crystal with a doubly bent waveguide to construct a first‐of‐its‐kind IM. The light propagating path‐length‐dependent optical interference within the IM is established. These proof‐of‐principle experiments illustrate the usefulness of mechanophotonics to fabricate miniature photonic devices beyond the traditional fabrication approach.

Thermochromic Fenestration Elements Based on the Dispersion of Functionalized VO2 Nanocrystals within a Polyvinyl Butyral Laminate.

The energy required to heat, cool, and illuminate buildings continues to increase with growing urbanization, engendering a substantial global carbon footprint for the built environment. Passive modulation of the solar heat gain of buildings through the design of spectrally selective thermochromic fenestration elements holds promise for substantially alleviating energy consumed for climate control and lighting. The binary vanadium(IV) oxide VO2 manifests a robust metal-insulator transition that brings about a pronounced modulation of its near-infrared transmittance in response to thermal activation. As such, VO2 nanocrystals are potentially useful as the active elements of transparent thermochromic films and coatings. Practical applications in retrofitting existing buildings requires the design of workflows to embed thermochromic fillers within industrially viable resins. Here, we describe the dispersion of VO2 nanocrystals within a polyvinyl butyral laminate commonly used in the laminated glass industry as a result of its high optical clarity, toughness, ductility, and strong adhesion to glass. To form high-optical-clarity nanocomposite films, VO2 nanocrystals are encased in a silica shell and functionalized with 3-methacryloxypropyltrimethoxysilane, enabling excellent dispersion of the nanocrystals in PVB through the formation of siloxane linkages and miscibility of the methacrylate group with the random copolymer. Encapsulation, functionalization, and dispersion of the core-shell VO2@SiO2 nanocrystals mitigates both Mie scattering and light scattering from refractive index discontinuities. The nanocomposite laminates exhibit a 22.3% modulation of NIR transmittance with the functionalizing moiety engendering a 77% increase of visible light transmittance as compared to unfunctionalized core-shell particles. The functionalization scheme and workflow demonstrated, here, illustrates a viable approach for integrating thermochromic functionality within laminated glass used for retrofitting buildings.

Comprehensive evaluation of file systems robustness with SPIN model checking

SummaryIn existing computer systems, file systems are indispensable for organizing user data and system codes. However, several studies have reported certain file system errors that cause significant data loss or system crashes. Most of these errors are due to external failures, such as an unexpected power outage. However, comprehensively evaluating file system robustness to detect these errors is challenging. The various types of file systems use different data structures and algorithms for various applications. Moreover, file system errors may be triggered by an unpredictable external condition. In addition, a file system works in an operating system's kernel layer as a passive module and runs in a multi‐thread mode, which makes file system testing time‐intensive. Furthermore, the large number of states in file systems leads to greedy checking, which results in a state explosion. In this study, we comprehensively evaluated the robustness expected in multiple properties of file systems using a model checking approach. The evaluation covered the majority of the mainstream file system types and included both single‐thread and multi‐thread modes. We developed Promela models that abstracted the real file systems and subsequently checked them using a SPIN model checker. Our model was optimized to avoid state explosion during model checking. Using the model checking, we successfully detected corner‐case errors during an unexpected power outage. By analysing counterexamples generated by model checking, we determined an improved file system model capable of preventing errors in most mainstream file system types. Finally, we rechecked the improved file system model and verified the absence of all critical errors.

Tunable Electromagnetically Induced Transparent Window of Terahertz Metamaterials and Its Sensing Performance

The electromagnetically induced transparency effect of terahertz metamaterials exhibits excellent modulation and sensing properties, and it is critical to investigate the modulation effect of the transparent window by optimizing structural parameters. In this work, a unilateral symmetrical metamaterial structure based on the cut-wire resonator and the U-shaped split ring resonator is demonstrated to achieve electromagnetically induced transparency-like (EIT-like) effect. Based on the symmetrical structure, by changing the structural parameters of the split ring, an asymmetric structure metamaterial is also studied to obtain better tuning and sensing characteristics. The parameters for controlling the transparent window of the metamaterial are investigated in both passive and active modulation modes. In addition, the metamaterial structure based on the cut-wire resonator, unilateral symmetric and asymmetric configurations are investigated for high performance refractive index sensing purposes, and it is found that the first two metamaterial structures can achieve sensitivity responses of 63.6 GHz/RIU and 84.4 GHz/RIU, respectively, while the asymmetric metamaterial is up to 102.3 GHz/RIU. The high sensitivity frequency response of the proposed metamaterial structures makes them good candidates for various chemical and biomedical sensing applications.

Joint EURADOS WG9-WG11 rem-counter intercomparison in a Mevion S250i proton therapy facility with Hyperscan pulsed synchrocyclotron

Objective. Proton therapy is gaining popularity because of the improved dose delivery over conventional radiation therapy. The secondary dose to healthy tissues is dominated by secondary neutrons. Commercial rem-counters are valuable instruments for the on-line assessment of neutron ambient dose equivalent (H*(10)). In general, however, a priori knowledge of the type of facility and of the radiation field is required for the proper choice of any survey meter. The novel Mevion S250i Hyperscan synchrocyclotron mounts the accelerator directly on the gantry. It provides a scanned 227 MeV proton beam, delivered in pulses with a pulse width of 10 μs at 750 Hz frequency, which is afterwards degraded in energy by a range shifter modulator system. This environment is particularly challenging for commercial rem-counters; therefore, we tested the reliability of some of the most widespread rem-counters to understand their limits in the Mevion S250i stray neutron field. Approach. This work, promoted by the European Radiation Dosimetry Group (EURADOS), describes a rem-counter intercomparison at the Maastro Proton Therapy centre in the Netherlands, which houses the novel Mevion S250i Hyperscan system. Several rem-counters were employed in the intercomparison (LUPIN, LINUS, WENDI-II, LB6411, NM2B-458, NM2B-495Pb), which included simulation of a patient treatment protocol employing a water tank phantom. The outcomes of the experiment were compared with models and data from the literature. Main results. We found that only the LUPIN allowed for a correct assessment of H*(10) within a 20% uncertainty. All other rem-counters underestimated the reference H*(10) by factors from 2 to more than 10, depending on the detector model and on the neutron dose per pulse. In pulsed fields, the neutron dose per pulse is a fundamental parameter, while the average neutron dose rate is a secondary quantity. An average 150–200 μSv/GyRBE neutron H*(10) at various positions around the phantom and at distances between 186 cm and 300 cm from it was measured per unit therapeutic dose delivered to the target. Significance. Our results are partially in line with results obtained at similar Mevion facilities employing passive energy modulation. Comparisons with facilities employing active energy modulation confirmed that the neutron H*(10) can increase up to more than a factor of 10 when passive energy modulation is employed. The challenging environment of the Mevion stray neutron field requires the use of specific rem-counters sensitive to high-energy neutrons (up to a few hundred MeV) and specifically designed to withstand pulsed neutron fields.

Passive PV module cooling under free convection through vortex generators

High operating temperatures have a negative impact on photovoltaic (PV) modules. Hence, lowering the temperature of commercial crystalline silicon modules during their operation becomes increasingly interesting, as it increases the system's energy yield and prolongs the module's lifespan. In this work, we experimentally and numerically investigated a potentially cost-effective passive cooling method for PV modules, using vortex generators (VGs) optimised for free convection conditions (in the absence of wind). The VGs are attached to the rear surface of the module and arranged in an array. Infrared thermography was employed to assess the cooling ability of the VGs with different spacing. It is found that the thermally non-conductive VGs can reduce the operating temperatures of a module by up to 2 °C under free convection and by 3 °C with the use of conductive materials. To better understand the flow behaviour around the VGs, computational fluid dynamics simulations were undertaken, along with particle image velocimetry (PIV) measurements. The VG-induced mixing in the boundary layer is responsible for enhancing the convective flux on the rear module surface. We observed both that the formation of vortices is strongly dependent on the aerodynamic shape of the VG and that the placement of the VGs is crucial.

Dynamic and wave propagation analysis of periodic smart beams coupled with resonant shunt circuits: passive property modulation

Dynamic and wave propagation analysis of periodic smart beams coupled with resonant shunt circuits: passive property modulation

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)

Quasi-Bessel Acoustic-Vortex Beams Constructed by the Line-Focused Phase Modulation for a Ring Array of Sectorial Planar Transducers.

Acoustic Bessel beams are commonly used as ideal sources to study the characteristics for acoustic-vortex (AV) beams, exhibiting prosperous perspectives in contactless object manipulations and acoustic communications. However, accurate Bessel beams are difficult to construct using 2-D arrays in practical applications. By integrating active phase control and passive phase modulation to a ring array of sectorial planar transducers, quasi-Bessel AV (QB-AV) beams of arbitrary order are built by the line focus of AV fields in the current study. Based on Snell's refraction law, a circular sawtooth lens of phase modulation is designed to converge incident waves toward the beam axis at the same deflection angle. QB-AV beams constructed by the main lobes of the sectorial sources are demonstrated by theoretical derivations, numerical simulations, and quality evaluations, while those created by the sidelobes are neglected to avoid the pressure fluctuations in the near field. Experimental measurements for AV beams of different orders coincide basically with the simulations, demonstrating that line-focused QB-AV beams can be generated along the beam axis across the pressure peak. With the increase of the topological charge, the peak pressure of the beam decreases accordingly with a reduced effective axial range. The favorable results prove that, as a special kind of diffraction sources, the adjustable QB-AV beams may enable more important biomedical applications where Bessel beams are necessary, especially for the line-focused manipulation of biological and drug particles.

A wireless "Janus" soft gripper with multiple tactile sensors.

Biomimetic properties allow soft robots to complexly interact with the environment. As the bridge between the robot and the operating object, the gripping hand is an important organ for its connection with the outside world, which requires the ability to provide feedback from the grasped object, similar to the human sensory and nervous system. In this work, to cope with the difficulty of integrating complex sensing and communication systems into flexible soft grippers, we propose a GO/PI composite bilayer film-based gripper with two types of tactile sensors and a LC passive wireless transmission module to obtain the grip information and transmit it to the processor. The bilayer film structure demonstrates good photothermal driving performance. Pressure and material sensors are located at the tips of the gripper's fingers to acquire tactile information which is wirelessly transmitted to the processor for analysis via the LC circuit. The grasping and feedback of the gripper are presented through an intelligent display system, realizing the wireless interconnection between the robot terminal and processing system, exhibiting broad application potential.

The Yb3+:LuAlO3 crystal as an active medium for picosecond mode-locked lasers

Herein, we report on the mathematical modelling and experimental study of the regime of nonsoliton mode locking in a laser based on the Yb3+:LuAlO3 (Yb:LuAP) crystal with longitudinal pumping by laser diode radiation. Simulation based on the Haus master equation permitted to determine the requirements for the parameters of a saturable absorber (SA), the level of the average output power, the size of the TEM00 mode of the cavity in the active element and on the gate to obtain a stable regime of generation of picosecond laser pulses. Laser experiments were carried out in a fourmirror X-shaped resonator using a semiconductor saturable mirror (SESAM) as a passive modulator and a laser diode with a fiber output of a maximum power up to 30 W at a wavelength of 978.5 nm as a pump source. We obtained a stable passive mode locking with a maximum average output power of up to 12 W and an ultrashort pulse duration of about 2 ps at an optical conversion efficiency of pump radiation into lasing radiation of about 38 %. Laser pulses were obtained at a central wavelength of about 999 nm with a minimum Stokes shift (about 2 %) with respect to the pump radiation, which significantly reduced the thermal load on the active element. Additionally, the preliminary results on the second harmonic generation and synchronous pumping of a parametric light generator using a Yb3+ : LuAlO3 crystal laser as a pump source are presented.