Experimental tests of compact broadband high power microwave sources and amplifiers based on meta material interaction circuits
Abstract
Metamaterials are composed of unit cells in repeating lattices typically in 2 or 3 dimensions. The building block is a detailed geometrical element of conductors designed to have subtle variation in their response as a function of frequency, presenting small, localised capacitances and inductances controlled by the layout of the conducting material. Often these conducting elements are supported by dielectrics. Where the size of these units are of order of the wavelength, �, they may be referred to as photonic bandgap materials. When the structure size is ≪� the term meta-material is used. Due to the complicated electrical spectral response of these unit cells, they can be designed to control the dispersion of electromagnetic waves in hitherto unprecedented manner. They can also be used to define allowed solutions to Maxwells equations that have attractive polarisation and propagation properties for a range of applications. One application for these new materials is their potential to revolutionise slow wave vacuum electronics. In such systems an energetic (kV to ~100 kV) electron beam is decelerated by synchronous interaction with an electromagnetic wave. Typically the vacuum electronic approach to microwave source and amplifiers allows two orders of magnitude uplift on the power capability at a given frequency compared to solid state techniques. Moreover it may be possible to also take advantage of these structures in fast wave electronics (e.g. gyro devices where the beam s cyclotron motion provides the energy source) which can achieve a further one to two orders of magnitude uplift in peak and average power (e.g. 1MW CW at 170GHz). One of the limitations for slow wave devices is that the device size scales with the wavelength, and the power hence scales as the wavelength squared. The use of meta materials has the potential to break the direct association of the transverse size with the wavelength, enhancing power capacity. Issues may however arise with the use of such structures in high power vacuum electronics. Firstly the use of dielectrics in the presence of charged particle streams has the risk of charging the dielectric leading to deceleration of the beam and breakdown across the dielectric. The same may be said of any isolated metallic elements that have no drain for accumulated charge. Moreover the detailed localised elements may cause field enhancement, leading to breakdown risk, and are thermally as well as electrically isolated. The University of Huddersfield have developed a new approach to implementing metamaterial control of the interaction volume of the source that offers substantial advantages. The Huddersfield approach is based on the use of Complementary Split Ring Resonators (CSSR) on a cylindrical pipe, machined using laser cutting. This geometry does not require dielectrics at all, the CSSRs are not excessively close to the electron beam, there are no thermally or electrically isolated elements and the cylindrical form is convenient for integration in the magnetic fields and vacuum envelopes required for an electron beam and accelerator system. Huddersfield have achieved promising initial experimental results at lower voltage and current, and have simulations indicating higher performance with higher voltage and current beams. This project will enable the testing of this potential using facilities at Strathclyde in conjunction with expertise at Huddersfield. Metamaterials are composed of unit cells in repeating lattices typically in 2 or 3 dimensions. The building block is a detailed geometrical element of conductors designed to have subtle variation in their response as a function of frequency, presenting small, localised capacitances and inductances controlled by the layout of the conducting material. Often these conducting elements are supported by dielectrics. Where the size of these units are of order of the wavelength, �, they may be referred to as photonic bandgap materials.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 05, 2025
- Source ID
- FA86552417387
Entities
People
- Kevin Ronald
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of Strathclyde