A method and system for providing electrical stimulation to tissue includes implanting one or more battery-free microtransponders having spiral antennas into tissue. Energy is provided wirelessly to the plurality of microtransponders. Tissue is stimulated using the energy.

Implantable Transponder Systems and Methods

Dielectric window breakdown is a serious challenge in high-power microwave (HPM) transmission and radiation. Breakdown at the vacuum/dielectric interface is triggered by multipactor and finally realized by plasma avalanche in the ambient desorbed or evaporated gas layer above the dielectric. Methods of improving breakdown thresholds are key challenges in HPM systems. First, the main theoretical and experimental progress is reviewed. Next, the mechanisms of multipactor suppression for periodic rectangular and triangular surface profiles by dynamic analysis and particle-in-cell simulations are surveyed. Improved HPM breakdown thresholds are demonstrated by proof-of-principle and multigigawatt experiments. The current theories and experiments of using dc magnetic field to resonantly accelerate electrons to suppress multipactor are also synthesized. These methods of periodic profiles and magnetic field may solve the key issues of HPM vacuum dielectric breakdown.

Review of recent theories and experiments for improving high-power microwave window breakdown thresholdsa)

We review recent progress in the physics and technology of cold cathode electron emitters. The characteristics of emission from field emitter arrays, photocathodes, and ferroelectrics are presented, together with a summary of the understanding of the physics involved. The paper concludes with a description of L-band micropulse gun, based on secondary emission in an RF cavity. Emphasis is placed on cathode development for electron guns to drive microwave tubes and RF accelerators.

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Advances in cold cathode physics and technology

The behavior of multipactoring electrons in an S-band pillbox RF window used in the KEK electron linac was investigated. The electric field distributions in the pillbox were calculated using the MAFIA code. The trajectory of emitted electrons to the surface of an alumina window disk in the calculated electric field was simulated. The energy deposition distribution of electrons impinging on the alumina disk was also obtained. The results agree well with the discoloring patterns observed for alumina disks after RF operation. This shows that the discoloring can be explained in terms of the bombardment of single-surface multipactoring electrons. Knowledge concerning the electric field distribution and the behavior of multipactoring electrons in the pillbox RF window will be useful in designing RF windows from an electrical point of view. >

Trajectory simulation of multipactoring electrons in an S-band pillbox RF window

The breakdown of RF windows used in high-power klystrons is one of the most serious problems in the development of klystrons. The durability of several dielectric materials used for RF windows is discussed in terms of secondary electron emission (SEE), cathodoluminescence, and dielectric loss. High-power tests of these materials with TiN coatings, thus having low SEE, were also carried out using a traveling wave resonant ring. The results show that alumina ceramics are superior to sapphire and aluminum nitride. The origin of breakdown is investigated, and the requirements for RF window materials are presented. >

Dielectric materials for use as output window in high-power klystrons

Thin films of TiN having low secondary electron emission (SEE) yields are coated on alumina rf windows in order to suppress the occurrence of multipactor. It is necessary to form films with a proper thickness in order to obtain a sufficient reduction of SEE as well as to avoid any excessive ohmic loss in conductive TiN films. For an optimization of the film thickness on an alumina surface, measurements of the SEE coefficients, and ohmic losses in the rf (S‐band) field were carried out. High‐power examinations of the coated windows were also performed. The results show that TiN films with a thickness of 0.5 nm or greater on alumina ceramics have SEE coefficients of less than unity at an incident energy of 10 keV. High‐power tests have revealed that the ‘‘going away’’ of TiN films is probably due to excessive ohmic losses taking place when the thickness is greater than 1.5 nm. It is concluded that optimized film thickness for window coatings is 0.5–1.5 nm.

TiN film coatings on alumina radio frequency windows

The breakdown mechanism of RF windows has been investigated. The localized multipactor electron bombardment, accompanied by rapidly growing alumina luminescence leading to the surface melting, were observed by the resonant ring test. The puncture is found to be induced by surface melting. TiN coating on the alumina disk was confirmed to suppress secondary electron emission and to prevent multipactor bombardment. >

Breakdown of alumina RF windows

The breakdown of alumina rf windows being used in high‐power rf systems of accelerators has been investigated. The puncture and the thermal fracture often taking place in s‐band pulsed rf systems and in UHF cw rf systems, respectively, are found to be induced by alumina surface heating due to an electron multipactor bombardment accompanied by a luminescence of alumina. It is ascertained that TiN coatings on the alumina window suppress the multipactor, and that the window duration for breakdown is dependent on the microstruture of the alumina ceramic.

Namio Matuda

Papers

Dielectric materials for use as output window in high-power klystrons

TiN film coatings on alumina radio frequency windows

Breakdown of alumina RF windows

Breakdown of alumina rf windows

Breakdown of Alumina RF Windows and its Inhibition