Spherical Diode Research Articles

Wrap-like transfer printing for three-dimensional curvy electronics.

Three-dimensional (3D) curvy electronics has wide-ranging application in biomedical health care, soft machine, and high-density curved imager. Limited by material properties, complex procedures, and coverage ability of existing fabrication techniques, the development of high-performance 3D curvy electronics remains challenging. Here, we propose an automated wrap-like transfer printing prototype for fabricating 3D curvy electronics. Assisted by a gentle and uniform pressure field, the prefabricated planar circuits on the petal-like stamp are integrated onto the target surface intactly with full coverage. The driving pressure for the wrapping is provided by the strain recovery of a prestrained elastic film triggered by the air pressure control. The wrapping configuration and strain distribution of the stamp are simulated by finite element analysis, and the pattern and thickness of the stamps are optimized. Demonstration of this strategy including spherical meander antenna, spherical light-emitting diode array, and spherical solar cell array illustrates its feasibility in the development of complex 3D curvy electronics.

In Vivo Dosimetry in the Urethra During Prostate Carbon Ion Radiotherapy.

In vivo dosimetry can prevent dose delivery errors by directly measuring the dose of radiation administered to a patient. However, a method for in vivo dosimetry during carbon ion radiotherapy (CIRT) has not been established. Therefore, we investigated data from in vivo dosimetry of the urethra during CIRT for prostate cancer using small spherical diode dosimeters (SSDDs). This study included five patients enrolled in a clinical trial (jRCT identifier: jRCTs032190180) on which the use of four-fraction CIRT for prostate cancer was examined. The urethral dose during CIRT for prostate cancer was measured using the SSDDs inserted into the ureteral catheter. The relative error between the in vivo and calculated doses obtained using the Xio-N treatment planning system was determined. Additionally, a dose-response stability test for the in vivo dosimeter was performed under clinical conditions. The relative error between the in vivo and calculated urethral doses ranged from 6 to 12%. The dose-response stability under clinical conditions of the measured dose was ≤1%. Therefore, an error >1% would be due to an interfractional patient setup error in the large dose gradient in the urethra. The usefulness of in vivo dosimetry using SSDDs in CIRT and SSDDs' potential for detecting dose delivery errors during CIRT is herein highlighted.

A coordinate system invariant formulation for space-charge limited current with nonzero injection velocity

Recent studies have extended the classical space-charge limited current (SCLC) solution in a non-magnetic, planar diode with zero injection velocity to other geometries using variational calculus (VC). We further extend VC to solve for SCLC with a non-relativistic, monoenergetic injection velocity from first principles for nonplanar diodes. By extremizing either the current or a functional of the electric field (and not its derivative), we demonstrate that VC can find either the bifurcation or the SCLC solution, respectively. The bifurcation solution is characterized by the onset of particle reflection, resulting in a singularity in the derivative of the electric field at the virtual cathode, physically analogous to the singularity at the cathode in SCLC for zero injection velocity. Alternatively, using VC to extremize a functional of the potential and its gradient (electric field) yields the maximum current SCLC result. We then derive the SCLC solutions in cylindrical and spherical diodes; additionally, we develop a method to determine SCLC numerically and the bifurcation solution exactly for any orthogonal geometry. Implications for the potential profile and virtual cathode are discussed, especially the behavior for other geometries.

Large-scale planar and spherical light-emitting diodes based on arrays of perovskite quantum wires

Large-scale planar and spherical light-emitting diodes based on arrays of perovskite quantum wires

Temporally-adjustable radiative thermal diode based on metal-insulator phase change

Thermal diode, which allows heat transfer between two terminals in one direction but blocks it in the opposite direction, has attracted extensive attention in recent years because of its potential applications in thermal management, energy systems, information processing and so on. Compared to the conductive thermal diode, the photon-based radiative thermal diode can break the performance limitations and achieve better thermal rectification effect. In this study, a temporally-adjustable radiative thermal diode consisting of vanadium dioxide (VO2) and blackbody is proposed. Based on the metal-insulator phase change of vanadium dioxide, the thermal rectification could be modulated with time, thus enabling time-dependent heat flow control. The influence of shape factors on the thermal rectification is specifically investigated, revealing that the thermal rectification effect is positively correlated with the ratios of inner and outer radius of cylindrical and spherical radiative thermal diodes, and the thermal rectification effect of planar diode is stronger than that of cylindrical or spherical diode under the same settings. The temporally-adjustable photon-based thermal diode is demonstrated to be more powerful with large thermal rectification ratio, precise control of heat, and configuration adjustability.

A multi-dimensional Child–Langmuir law for any diode geometry

While prior theoretical studies of multi-dimensional space-charge limited current (SCLC) assumed emission from a small patch on infinite electrodes, none have considered emission from an entire finite electrode. In this paper, we apply variational calculus (VC) and conformal mapping, which have previously been used to derive analytic solutions for SCLC density (SCLCD) for nonplanar one-dimensional geometries, to obtain mathematical relationships for any multi-dimensional macroscopic diode with finite cathode and anode. We first derive a universal mathematical relationship between space-charge limited potential and vacuum potential for any diode and apply this technique to determine SCLCD for an eccentric spherical diode. We then apply VC and the Schwartz–Christoffel transformation to derive an exact equation for SCLCD in a general two-dimensional planar geometry with emission from a finite emitter. Particle-in-cell simulations using VSim agreed within 4%–13% for a range of ratios of emitter width to gap distance using the thinnest electrodes practical for the memory constraints of our hardware, with the difference partially attributed to the theory's assumption of infinitesimally thin electrodes. After generalizing this approach to determine SCLCD for any orthogonal diode as a function of only the vacuum capacitance and vacuum potential, we derive an analytical formulation of the three-dimensional Child–Langmuir law for finite parallel rectangular and disk geometries. These results demonstrate the utility for calculating SCLCD for any diode geometry using vacuum capacitance and vacuum potential, which are readily obtainable for many diode geometries, to guide experiment and simulation development.

Spherical and cylindrical conductive thermal diodes based on two phase-change materials

Abstract We theoretically studied and optimized the thermal rectification of spherical and cylindrical conductive thermal diodes operating with two phase-change materials (PCMs), whose thermal conductivities significantly changes in a narrow interval of temperatures. This is done by deriving simple analytical expressions for the heat flows, temperature profiles and rectification factors of both diodes. It is shown that diode geometry has a significant impact on the heat flows and temperature profiles, but not so much on the thermal diode rectification factor. Optimal rectification factors of 63.5 and 63.2% are obtained for the spherical and cylindrical thermal diodes operating between the terminals of VO2 and polyethylene with a temperature difference of 150 K spanning the metal–insulator transition of both PCMs. These similar rectification factors could be enhanced even more with a phase-change material exhibiting higher contrast thermal conductivity than the ones in the present study. The obtained results can thus be useful to guide the development of PCMs capable of optimizing the rectification of conductive heat flows with different geometries.

Optimization of the rectification factor of radiative thermal diodes based on two phase-change materials

We have theoretically studied and optimized the thermal rectification of plane, cylindrical and spherical radiative thermal diodes operating with terminals of two phase-change materials, whose emissivities significantly change within a narrow interval of temperatures. Analytical expressions for the optimal rectification factors of these three diodes are derived and analyzed comparatively. Optimal rectification factors of 82%, 86% and 90.5% are obtained for the plane, cylindrical and spherical diodes made up with terminals of Ge2Sb2Te5 and VO2 operating with a temperature difference of 450−300=150 K, respectively. The spherical geometry thus represents a suitable shape to optimize the rectification of radiative heat currents. Furthermore, it is shown that higher rectification factors can potentially be achieved by using phase-change materials with emissivities contrasts higher than those of Ge2Sb2Te5 and VO2. We demonstrate that radiative thermal diodes based on two phase-change materials are able to operate with rectification factors higher than the corresponding ones of diodes involving a single phase-change material. The obtained results thus shed light on the phase-change materials required for optimizing the rectification factor of radiative thermal diodes with different geometries.

Spherical and cylindrical conductive thermal diodes based on VO2

We theoretically and comparatively study the performance of spherical and cylindrical conductive thermal diodes operating with a phase-change material, whose thermal conductivity significantly changes in a narrow interval of temperatures. Simple analytical expressions are derived for the temperature profiles, heat flows and optimal rectification factors of both diodes. It is shown that the diode geometry has a strong impact on the temperatures and heat flows, but not so much on the diode rectification factor. Optimal rectification factors of 20.8% and 20.7% are obtained for the spherical and cylindrical diodes operating with a temperature difference of 376−300 = 76 K and 376.5-300 = 76.5 K between the terminals of VO2 and a phase invariant material, respectively. These similar rectification factors could be enhanced with a material thermal conductivity exhibiting a higher contrast than that of VO2 . The obtained results can thus be useful to guide the development of phase-change materials able to optimize the rectification of conductive thermal diodes with different geometries.

Miniature spherical silicon diode as a dosimeter during carbon-ion beam therapy

Abstract As the best use of the Bragg curve nature, hypofractionated ion-beam therapy is being actively explored for therapeutic applications in various cancer treatments. In the case of prostate cancer treatment, radical hypofractionation has been performed by selectively reducing the urethral dose located at the center of the prostate tumor. Establishing an in-vivo dosimeter to confirm if the dose to the urethra is surely reduced during therapeutic irradiation is strongly needed. This study investigated the application of miniature spherical silicon diode as an in-vivo dosimeter candidate for therapeutic carbon-ion beam. The spherical geometry of silicon caused a slight broadening of pristine Bragg peak of the carbon-ion beam; however, for practical therapeutic carbon-ion beam applications, it showed a superior dosimetric response, free from LET (linear energy transfer) dependency, and almost comparable to those measured using an ionization chamber . The spherical diode caused minor field perturbations, and displayed a gradual decrease in sensitivity as a function of integral dose from radiation damage. However, output linearity on dose, subtle incident angular dependence, compactness, and safeness of the silicon diode make the diode a good candidate for an in-vivo dosimeter during ion-beam therapy.

Analytical and exact solutions of the spherical and cylindrical diodes of Langmuir–Blodgett law

This paper discloses the exact solutions of a mathematical model that describes the cylindrical and spherical electron current emissions within the context of a physics approximation method. The solution involves analyzing the 1D nonlinear Poisson equation, for the radial component. Although an asymptotic solution has been previously obtained, we present a theoretical solution that satisfies arbitrary boundary conditions. The solution is found in its parametric form (i.e., φ(r)=φ(r(τ))) and is valid when the electric field at the cathode surface is non-zero. Furthermore, the non-stationary spatial solution of the electric potential between the anode and the cathode is also presented. In this work, the particle–beam interface is considered to be at the end of the plasma sheath as described by Sutherland et al. [Phys. Plasmas 12, 033103 2005]. Three regimes of space charge effects—no space charge saturation, space charge limited, and space charge saturation—are also considered.

Mimebot: spherical robot visually imitating a rolling sphere

PurposeWhen designing a performance involving people and mobile robots, the required functions and shape of the robot must be considered. However, it can be difficult to account for all of the requirements. The purpose of this paper is to discuss a mobile robot in the shape of a ball that is used in theatrical performances.Design/methodology/approachThe paper proposes a mobile robot that can give the audience the optical illusion of the unique movements of a sphere by mounting a spherical light-emitting diode (LED) display on a high-agility wheeled robot.FindingsIt was found that movements that are difficult to implement with existing mechanisms can nonetheless be visualized through the use of light.Originality/valueThe paper proposes the concept of using pseudo-physical movements in performances with robots. The authors built a robot that visually reproduces the movements of a rolling sphere and is capable of faster movements and easier position estimations in comparison with previous spherical robots.

On relativistic space charge limited current in planar, cylindrical, and spherical diodes

This paper revisits the relativistic limiting current in planar, cylindrical, and spherical diodes, with alternative analytic and numerical treatments which are easy to implement. Convenient, approximate expressions for the limited current are presented for gap voltages up to 10 MV. They are accurate to within 1% for planar diode, and to within 4% for both cylindrical and spherical diode in the range 10−5<rc/ra<500, where ra and rc are, respectively, the anode and cathode radius.

Bipolar diodes with divergent electron beam

Cylindrical and spherical bipolar diodes with divergent electron beams are analyzed. A tendency related to the application of plasma structures in the classical devices of vacuum electronics working in the steady-state and pulsed regimes is discussed.

Rol' pryanodnykh protsesiv v enerhetytsi zhevriyuchoho rozryadu

The role of anode processes in the formation of self-organized glow discharge (GD) structure is analyzed in the case of spherical diode, the latter, as well as a short plane diode, being characterized by the absence of a positive column. The results of numerical calculations are compared with the experimental GD current-voltage characteristics and the electric field strength distributions measured by the probe method. It is shown that the boundary conditions at the anode should be formulated with regard for a possibility of a potential drop at the anode. In this case, the calculated diode potential decreases significantly and corresponds to experimentally observed results.

Application of spherical diodes for megavoltage photon beams dosimetry

External beam radiation therapy (EBRT) usually uses heterogeneous dose distributions in a given volume. Designing detectors for quality control of these treatments is still a developing subject. The size of the detectors should be small to enhance spatial resolution and ensure low perturbation of the beam. A high uniformity in angular response is also a very important feature in a detector, because it has to measure radiation coming from all the directions of the space. It is also convenient that detectors are inexpensive and robust, especially to perform in vivo measurements. The purpose of this work is to introduce a new detector for measuring megavoltage photon beams and to assess its performance to measure relative dose in EBRT. The detector studied in this work was designed as a spherical photodiode (1.8 mm in diameter). The change in response of the spherical diodes is measured regarding the angle of incidence, cumulated irradiation, and instantaneous dose rate (or dose per pulse). Additionally, total scatter factors for large and small fields (between 1 × 1 cm(2) and 20 × 20 cm(2)) are evaluated and compared with the results obtained from some commercially available ionization chambers and planar diodes. Additionally, the over-response to low energy scattered photons in large fields is investigated using a shielding layer. The spherical diode studied in this work produces a high signal (150 nC/Gy for photons of nominal energy of 15 MV and 160 for 6 MV, after 12 kGy) and its angular dependence is lower than that of planar diodes: less than 5% between maximum and minimum in all directions, and 2% around one of the axis. It also has a moderated variation with accumulated dose (about 1.5%/kGy for 15 MV photons and 0.7%/kGy for 6 MV, after 12 kGy) and a low variation with dose per pulse (± 0.4%), and its behavior is similar to commercial diodes in total scatter factor measurements. The measurements of relative dose using the spherical diode described in this work show its feasibility for the dosimetry of megavoltage photon beams. A particularly important feature is its good angular response in the MV range. They would be good candidates for in vivo dosimetry, and quality assurance of VMAT and tomotherapy, and other modalities with beams irradiating from multiple orientations, such as Cyberknife and ViewRay, with minor modifications.

Optimizing spherical light-emitting diode array for highly uniform illumination distribution by employing genetic algorithm

A numerical optimization method (genetic algorithm) is employed to design the spherical light-emitting diode (LED) array for highly uniform illumination distribution. An evaluation function related to the nonuniformity is constructed for the numerical optimization. With the minimum of evaluation function, the LED array produces the best uniformity. The genetic algorithm is used to seek the minimum of evaluation function. By this method, we design two LED arrays. In one case, LEDs are positioned symmetrically on the sphere and the illuminated target surface is a plane. However, in the other case, LEDs are positioned nonsymmetrically with a spherical target surface. Both the symmetrical and nonsymmetrical spherical LED arrays generate good uniform illumination distribution with calculated nonuniformities of 6 and 8%, respectively.

Novel Scaling Laws for the Langmuir-Blodgett Solutions in Cylindrical and Spherical Diodes

It is found that the Langmuir-Blodgett solutions for the space charge limited current density, for both cylindrical and spherical diodes, may be approximated by Japp=(4/9)ε0sqrt[(2e/m)](Ec3/2/sqrt[D]) over a wide range of parameters, where Ec is the surface electric field on the cathode of the vacuum diode and D is the anode-cathode spacing. This dependence is valid whether Ra/Rc is greater than or less than unity, where Ra and Rc are, respectively, the anode and cathode radius. Minor empirical corrections to the above scaling yield fitting formulas that are accurate to within 5% for 3×10(-5)<Rc/Ra<500. An explanation of this scaling is given. An accurate transit time model yields the Langmuir-Blodgett solutions even in the Coulomb blockade regime for a nanogap, where the electron number may be in the single digits, and the transit time frequency is in the THz range.

Application of spherical diodes for megavoltage photon beams dosimetry

Purpose: External beam radiation therapy (EBRT) usually uses heterogeneous dose distributions in a given volume. Designing detectors for quality control of these treatments is still a developing subject. The size of the detectors should be small to enhance spatial resolution and ensure low perturbation of the beam. A high uniformity in angular response is also a very important feature in a detector, because it has to measure radiation coming from all the directions of the space. It is also convenient that detectors are inexpensive and robust, especially to performin vivo measurements. The purpose of this work is to introduce a new detector for measuring megavoltage photon beams and to assess its performance to measure relative dose in EBRT. Methods: The detector studied in this work was designed as a spherical photodiode (1.8 mm in diameter). The change in response of the spherical diodes is measured regarding the angle of incidence, cumulated irradiation, and instantaneous dose rate (or dose per pulse). Additionally, total scatter factors for large and small fields (between 1 × 1 cm{sup 2} and 20 × 20 cm{sup 2}) are evaluated and compared with the results obtained from some commercially available ionization chambers and planar diodes. Additionally, themore » over-response to low energy scattered photons in large fields is investigated using a shielding layer. Results: The spherical diode studied in this work produces a high signal (150 nC/Gy for photons of nominal energy of 15 MV and 160 for 6 MV, after 12 kGy) and its angular dependence is lower than that of planar diodes: less than 5% between maximum and minimum in all directions, and 2% around one of the axis. It also has a moderated variation with accumulated dose (about 1.5%/kGy for 15 MV photons and 0.7%/kGy for 6 MV, after 12 kGy) and a low variation with dose per pulse (±0.4%), and its behavior is similar to commercial diodes in total scatter factor measurements. Conclusions: The measurements of relative dose using the spherical diode described in this work show its feasibility for the dosimetry of megavoltage photon beams. A particularly important feature is its good angular response in the MV range. They would be good candidates forin vivo dosimetry, and quality assurance of VMAT and tomotherapy, and other modalities with beams irradiating from multiple orientations, such as Cyberknife and ViewRay, with minor modifications.« less

A Paraxial approximation of the problem of formation of nonparaxial conical and toroidal electron beams of an arbitrary cross section

A paraxial solution is constructed for the problem of calculation of forming electrodes for non-paraxial cuts from converging and diverging flows in a spherical diode and a Meltzer flow with circular paths. The solution is expressed in elementary functions for the case of a cone. For example, computations for a square on a sphere (the first approximation of the approximation of a contour) and a toroid with a circular cross section are presented.