Richard Mett, Ph.D.
Professor
- Milwaukee WI UNITED STATES
- Allen Bradley Hall of Science: S241
- Physics and Chemistry
Dr. Richard Mett is an expert in electrodynamics, magnetic resonance and plasma physics
Education, Licensure and Certification
Ph.D.
Electrical Engineering
University of Wisconsin-Madison
1990
M.S.
Electrical Engineering
University of California-Berkeley
1985
B.S.
Electrical Engineering
Milwaukee School of Engineering
1982
Biography
Areas of Expertise
Accomplishments
Karl O. Werwath Engineering Research Award, MSOE
2005
Honorarium, Institute of Physical and Theoretical Chemistry, Johann Wolfgang Goethe-Universitat Frankfurt/Main, Germany
2006
Magnetic Fusion Energy Technology Fellowship, U. S. Department of Energy
1982-1984
Affiliations
- American Society for Engineering Education (ASEE) : Member
- International EPR (ESR) Society : Member
Event and Speaking Appearances
Simulations of Electromagetic Fields in the Dielectric Loop-gap Resonator (dLGR)
EPR Workshop
2015-08-22
Hyperbolic-Cosine Waveguide Tapers and Oversize Rectangular Waveguide for Reduced Broadband Insertion Loss in W-band EPR II: Implementation
EPR Workshop
2015-08-22
C1903 Planar dual surface coil element
Technology Evaluation Committee at the Medical College of Wisconsin
2016-04-26
C1805 High Quality Factor Metamaterial Distributed-Gap Loop-Gap Resonator Surface Coil
Office of Technology Development at The Medical College of Wisconsin for Provisional Patent
2014-10-08
Metametallic Coils and Resonators
National Biomedical EPR Center Scientific Advisory Board Meeting at the Medical College of Wisconsin
2015-05-01
Patents
Strongly coupled fourth-order resonance coil systems for enhanced signal detection
PCT/US17/52045
Filed on September 18, 2017, priority date September 19, 2016
High q-factor magnetic resonance imaging radio frequency coil device and methods
US20180340991A1
2015
High Q-value radio frequency (RF] coils are described. In general, the RF coils include multiple conductor layers that at least partially overlap to define a capacitive region that equalizes current flowing in each conductor. In some instances, the RF coil includes sets of layered conductors, where each set of layered conductors overlaps in an overlap region. In some other instances, the RF coil includes a spiraled conductor coupled to a dielectric material, where the number of turns of the spiral defines the overlap area. Multiple spiraled conductors can be interleaved. An equalization coil can also be provided to equalize currents along an axial dimension of each conductor in such RF coils. The thickness of the conductors is less than three skin depths, and preferably less than one skin depth, to overcome skin-depth limitations.
Aqueous sample holder for EPR and MR spectroscopy
US7088101B2
2006
A sample holder for use in an EPR spectrometer is extruded using a material having a low dielectric constant. The extruded sample holder has a plurality of channels formed in it for holding sample material for testing. The shape and orientation of these channels are such that losses due to the high dielectric constant of the sample are minimized. Sample holders for cylindrical and rectangular cavity resonators and uniform field cavity resonators are disclosed, as well as for two-gap and four-gap loop-gap resonators.
Distributed inductively-coupled plasma source
US6273022B1
2003
Apparatus and method for inductively coupling electrical power to a plasma in a semiconductor process chamber. In a first aspect, an array of induction coils is distributed over a geometric surface having a circular transverse section. Each coil has a transverse section which is wedge-shaped so that the adjacent sides of any two adjacent coils in the array are approximately parallel to a radius of the circular transverse section of the geometric surface. The sides of adjacent coils being parallel enhances the radial uniformity of the magnetic field produced by the coil array. In a second aspect, electrostatic coupling between the induction coils and the plasma is minimized by connecting each induction coil to the power supply so that the turn of wire of the coil which is nearest to the plasma is near electrical ground potential. In one embodiment, the near end of each coil connects directly to electrical ground. In second and third embodiments, two coils are connected in series at the near end of each coil. In the second embodiment, the opposite (“RF hot”) end of each coil is connected to a respective balanced output of an RF power supply. In the third embodiment, the hot end of one coil is connected to the unbalanced output of an RF power supply, and the hot end of the other coil is connected to electrical ground through a capacitor which resonates with the latter coil at the frequency of the RF power supply.
Apparatus and method for actively controlling the DC potential of a cathode pedestal
US5737177A
2001
A method and apparatus for actively controlling the DC cathode potential of a wafer support pedestal within a semiconductor wafer processing system. The apparatus contains a variable DC power supply coupled through an RF filter to a cathode pedestal. The variable DC power supply is actively controlled by a control signal generated by a cathode bias control unit, e.g., a computer or other control circuitry. The cathode bias control unit can be as simple as an operator adjustable control signal, e.g., a rheostat. However, for more accurate control of the DC power supply, a feedback circuit is used that generates a control signal that is proportional to the peak-to-peak voltage on a cathode pedestal. The application of the DC bias to the pedestal reduces the DC potential difference between the wafer and the cathode and, thereby avoids arcing from the wafer to the pedestal.
Research Grants
Modeling In Aqueous Biological Samples
EPR
The goal of this proposal is to improve sensitivity in electron paramagnetic resonance (EPR) spectroscopy of aqueous fluid phase samples.
Role: Co Investigator
Development of Biomedical EPR Instrumentation
EPR
An electron paramagnetic resonance (EPR) saturation recovery (SR) and pulse electron double resonance (ELDOR) capability will be developed at W-band (94 GHz) that is tailored for application to nitroxide spin-labeled biomolecules in the aqueous
phase.
Role: Engineer
National Biomedical EPR Center
EPR
This Research Resource is broadly based with unique instrumentation in many branches of EPR spectroscopy. The mission of the Resource is to serve the community of EPR spectroscopists with emphasis on development of advanced EPR instruments and new EPR methodology.
Role: Co-Investigator
Selected Publications
Rutile dielectric loop-gap resonator for X-band EPR spectroscopy of small aqueous samples
Journal of Magnetic ResonanceMett, R.R., Sidabras, J.W., Anderson, J.R., Klug, C.S., Hyde, J.S.
2019
The performance of a metallic microwave resonator that contains a dielectric depends on the separation between metallic and dielectric surfaces, which affects radio frequency currents, evanescent waves, and polarization charges. The problem has previously been discussed for an X-band TE011 cylindrical cavity resonator that contains an axial dielectric tube (Hyde and Mett, 2017). Here, a short rutile dielectric tube inserted into a loop-gap resonator (LGR) at X-band, which is called a dielectric LGR (dLGR), is considered. The theory is developed and experimental results are presented. It was found that a central sample loop surrounded by four “flux-return” loops (i.e., 5-loop–4-gap) is preferable to a 3-loop–2-gap configuration. For sufficiently small samples (less than 1 µL), a rutile dLGR is preferred relative to an LGR both at constant Λ () and at constant incident power. Introduction of LGR technology to X-band EPR was a significant advance for site-directed spin labeling because of small sample size and high Λ. The rutile dLGR introduced in this work offers further extension to samples that can be as small as 50 nL when using typical EPR acquisition times.
Uniform Field Resonators for EPR Spectroscopy: A Review
Cell Biochemistry and BiophysicsHyde, J.S., Sidabras, J.W., Mett, R.R.
2019
Cavity resonators are often used for electron paramagnetic resonance (EPR). Rectangular TE102 and cylindrical TE011 are common modes at X-band even though the field varies cosinusoidally along the Z-axis. The authors found a way to create a uniform field (UF) in these modes. A length of waveguide at cut-off was introduced for the sample region, and tailored end sections were developed that supported the microwave resonant mode. This work is reviewed here. The radio frequency (RF) magnetic field in loop-gap resonators (LGR) at X-band is uniform along the Z-axis of the sample, which is a benefit of LGR technology. The LGR is a preferred structure for EPR of small samples. At Q-band and W-band, the LGR often exhibits nonuniformity along the Z-axis. Methods to trim out this nonuniformity, which are closely related to the methods used for UF cavity resonators, are reviewed. In addition, two transmission lines that are new to EPR, dielectric tube waveguide and circular ridge waveguide, were recently used in UF cavity designs that are reviewed. A further benefit of UF resonators is that cuvettes for aqueous samples can be optimum in cross section along the full sample axis, which improves quantification in EPR spectroscopy of biological samples.
Broadband W-band Rapid Frequency Sweep Considerations for Fourier Transform EPR
Cell Biochemistry and BiophysicsStrangeway, R.A., Hyde, J.S., Camenisch, T.G., Sidabras, J.W., Mett, R.R., Anderson, J.R., Ratke, J.J., Subczynski, W.K.
2017
A multi-arm W-band (94 GHz) electron paramagnetic resonance spectrometer that incorporates a loop-gap resonator with high bandwidth is described. A goal of the instrumental development is detection of free induction decay following rapid sweep of the microwave frequency across the spectrum of a nitroxide radical at physiological temperature, which is expected to lead to a capability for Fourier transform electron paramagnetic resonance. Progress toward this goal is a theme of the paper. Because of the low Q-value of the loop-gap resonator, it was found necessary to develop a new type of automatic frequency control, which is described in an appendix. Path-length equalization, which is accomplished at the intermediate frequency of 59 GHz, is analyzed. A directional coupler is favored for separation of incident and reflected power between the bridge and the loop-gap resonator. Microwave leakage of this coupler is analyzed. An oversize waveguide with hyperbolic-cosine tapers couples the bridge to the loop-gap resonator, which results in reduced microwave power and signal loss. Benchmark sensitivity data are provided. The most extensive application of the instrument to date has been the measurement of T1 values using pulse saturation recovery. An overview of that work is provided.
EPR Uniform Field Signal Enhancement by Dielectric Tubes in Cavities
Applied Magnetic ResonanceHyde, J.S., Mett, R.R.
2017
The dielectric tube resonator (DTR) for electron paramagnetic resonance spectroscopy is introduced. It is defined as a metallic cylindrical TE011 microwave cavity that contains a dielectric tube centered on the axis of the cylinder. Contour plots of dimensions of the metallic cylinder to achieve resonance at 9.5 GHz are shown for quartz, sapphire, and rutile tubes as a function of wall thickness and average radius. These contour plots were developed using analytical equations and confirmed by finite-element modeling. They can be used in two ways: design of the metallic cylinder for use at 9.5 GHz that incorporates a readily available tube such as a sapphire tube intended for NMR and design of a custom procured tube for optimized performance for specific sample-size constraints. The charts extend to the limiting condition where the dielectric fills the tube. However, the structure at this limit is not a dielectric resonator due to the metal wall and does not radiate. In addition, the uniform field (UF) DTR is introduced. Development of the UF resonator starting with a DTR is shown. The diameter of the tube remains constant along the cavity axis, and the diameter of the cylindrical metallic enclosure increases at the ends of the cavity to satisfy the uniform field condition. This structure has advantages over the previously developed UF TE011 resonators: higher resonator efficiency parameter Λ, convenient overall size when using sapphire tubes, and higher quality data for small samples. The DTR and UF DTR structures fill the gap between free space and dielectric resonator limits in a continuous manner.
Uniform field loop-gap resonator and rectangular TEU02 for aqueous sample EPR at 94 GHz
Journal of Magnetic ResonanceSidabras, J.W., Sarna, T., Mett, R.R., Hyde, J.S.
2017
In this work we present the design and implementation of two uniform-field resonators: a seven-loop–six-gap loop-gap resonator (LGR) and a rectangular TEU02 cavity resonator. Each resonator has uniform-field-producing end-sections. These resonators have been designed for electron paramagnetic resonance (EPR) of aqueous samples at 94 GHz. The LGR geometry employs low-loss Rexolite end-sections to improve the field homogeneity over a 3 mm sample region-of-interest from near-cosine distribution to 90% uniform. The LGR was designed to accommodate large degassable Polytetrafluorethylen (PTFE) tubes (0.81 mm O.D.; 0.25 mm I.D.) for aqueous samples. Additionally, field modulation slots are designed for uniform 100 kHz field modulation incident at the sample. Experiments using a point sample of lithium phthalocyanine (LiPC) were performed to measure both the uniformity of the microwave magnetic field and 100 kHz field modulation, and confirm simulations. The rectangular TEU02 cavity resonator employs over-sized end-sections with sample shielding to provide an 87% uniform field for a 0.1 × 2 × 6 mm3 sample geometry. An evanescent slotted window was designed for light access to irradiate 90% of the sample volume. A novel dual-slot iris was used to minimize microwave magnetic field perturbations and maintain cross-sectional uniformity. Practical EPR experiments using the application of light irradiated rose bengal (4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein) were performed in the TEU02 cavity. The implementation of these geometries providing a practical designs for uniform field resonators that continue resonator advancements towards quantitative EPR spectroscopy.
Extruded dielectric sample tubes of complex cross section for EPR signal enhancement of aqueous samples
Journal of Magnetic ResonanceSidabras, J.W., Mett, R.R., Hyde, J.S.
2017
This paper builds on the work of Mett and Hyde (2003) and Sidabras et al. (2005) where multiple flat aqueous sample cells placed perpendicular to electric fields in microwave cavities were used to reduce the RF losses and increase the EPR signal. In this work, we present three novel sample holders for loop-gap resonators (LGRs) and cylindrical cavity geometries. Two sample holders have been commissioned and built by polytetrafluoroethylene (PTFE) extrusion techniques: a 1 mm O.D. capillary with a septum down the middle, named DoubleDee, and a 3.5 mm O.D. star shaped sample holder, named AquaStar. Simulations and experimental results at X-band show that the EPR signal intensity increases by factors of 1.43 and 3.87 in the DoubleDee and AquaStar respectively, over the current TPX 0.9 mm O.D. sample tube in a two-loop–one-gap LGR. Finally, combining the insight gained from the constructed sample holders and finite-element solutions, a third multi-lumen sample holder for a cylindrical TE011 cavity is optimized, named AquaSun, where simulations show an EPR signal intensity increase by a factor of 8.2 over a standard 1 mm capillary.
MRI surface-coil pair with strong inductive coupling
Review of Scientific InstrumentsMett, R.R., Sidabras, J.W., Hyde, J.S.
2016
A novel inductively coupled coil pair was used to obtain magnetic resonance phantom images. Rationale for using such a structure is described in R. R. Mett et al. [Rev. Sci. Instrum. 87, 084703 (2016)]. The original rationale was to increase the Q-value of a small diameter surface coil in order to achieve dominant loading by the sample. A significant improvement in the vector reception field (VRF) is also seen. The coil assembly consists of a 3-turn 10 mm tall meta-metallic self-resonant spiral (SRS) of inner diameter 10.4 mm and outer diameter 15.1 mm and a single-loop equalization coil of 25 mm diameter and 2 mm tall. The low-frequency parallel mode was used in which the rf currents on each coil produce magnetic fields that add constructively. The SRS coil assembly was fabricated and data were collected using a tissue-equivalent 30% polyacrylamide phantom. The large inductive coupling of the coils produces phase-coherency of the rf currents and magnetic fields. Finite-element simulations indicate that the VRF of the coil pair is about 4.4 times larger than for a single-loop coil of 15 mm diameter. The mutual coupling between coils influences the current ratio between the coils, which in turn influences the VRF and the signal-to-noise ratio (SNR). Data on a tissue-equivalent phantom at 9.4 T show a total SNR increase of 8.8 over the 15 mm loop averaged over a 25 mm depth and diameter. The experimental results are shown to be consistent with the magnetic resonance theory of the emf induced by spins in a coil, the theory of inductively coupled resonant circuits, and the superposition principle. The methods are general for magnetic resonance and other types of signal detection and can be used over a wide range of operating frequencies.
Meta-metallic coils and resonators: Methods for high Q-value resonant geometries
Review of Scientific InstrumentsMett, R.R., Sidabras, J.W. and Hyde, J.S.
2016
A novel method of decreasing ohmic losses and increasing Q-value in metallic resonators at high frequencies is presented. The method overcomes the skin-depth limitation of rf current flow cross section. The method uses layers of conductive foil of thickness less than a skin depth and capacitive gaps between layers. The capacitive gaps can substantially equalize the rf current flowing in each layer, resulting in a total cross-sectional dimension for rf current flow many times larger than a skin depth. Analytic theory and finite-element simulations indicate that, for a variety of structures, the Q-value enhancement over a single thick conductor approaches the ratio of total conductor thickness to skin depth if the total number of layers is greater than one-third the square of the ratio of total conductor thickness to skin depth. The layer number requirement is due to counter-currents in each foil layer caused by the surrounding rf magnetic fields. We call structures that exhibit this type of Q-enhancement “meta-metallic.” In addition, end effects due to rf magnetic fields wrapping around the ends of the foils can substantially reduce the Q-value for some classes of structures. Foil structures with Q-values that are substantially influenced by such end effects are discussed as are five classes of structures that are not. We focus particularly on 400 MHz, which is the resonant frequency of protons at 9.4 T. Simulations at 400 MHz are shown with comparison to measurements on fabricated structures. The methods and geometries described here are general for magnetic resonance and can be used at frequencies much higher than 400 MHz.
Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization
Review of Scientific InstrumentsSidabras, J.W., Strangeway, R.A., Mett, R.R., Anderson, J.R., Mainali, L., Hyde, J.S.
2016
Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE10 mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in millimeter-wave EPR bridges.
A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces
Review of Scientific InstrumentsSidabras, J.W., Varanasi, S.K., Mett, R.R., Swarts, S.G., Swartz, H.M., Hyde, J.S.
2014
A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.
