Abstract:   As a result of frequency congestion and data demands, wireless communications and sensing systems alike require higher frequency operation across larger bandwidths. At the antenna level, these applications typically require high gain to overcome the greater path loss. However, these applications also require spatial/angular   flexibility and relevant antenna systems must be able to scan highly directive beams. This burgeoning wireless landscape is very diverse and though it is unlikely that all relevant antenna systems will require extreme performance in both bandwidth and scannability, it is expected that the antenna environment of the future will be dominated by antenna systems with substantial degrees of both. Furthermore, many applications - such as low Earth orbit satellite communications and 5G terrestrial communications - require that the system hardware be small, lightweight, cheap, and with low power consumption (ie, low SWaP-C: size, weight, power and cost).
 

Abstract:  Spin waves are modes that exist in magnetic media due to Maxwellian fields and quantum mechanical fields (exchange interaction) between magnetic moments. These waves exist at frequencies between 1 and 100 GHz and can couple to microwave and millimeter-wave circuits, yet they have propagation velocities as slow as 100 to 1000 m/s. As a result, wavelengths tend to be 1-100 micrometers when propagation is dominated by Maxwellian dipole forces (magnetostatic waves) and less than a micrometer in wavelength when dominated by exchange forces (spin waves). Spin waves can also behave non-linearly due to the fact that magnetic materials have finite saturation magnetization. These two intrinsic qualities make spin waves incredibly useful for a variety of applications, including frequency and amplitude filtering, true-time delays, tunable circuits, non-reciprocal devices, attenuators, and boolean and wave-based computing.

Nonetheless, these devices and applications require conversion from electromagnetic signals to spin waves and vice versa. This transduction is inefficient, partly due to the difference in wavelength scale and partly due to the lack of fully-coupled cross-domain simulation tools. Most numerical simulation approaches for linear spin waves typically apply some simplifying assumptions to solve the coupled problem. Some analytical solutions with approximations do exist for simple structures and almost exclusively magnetostatic waves. For exchange regime waves, there has been little work done to quantify transducer and system efficiency.

The purpose of this work is to study the efficiency of EM-to-spin-wave transducers in both the dipole and exchange regime, and will be both theoretical and experimental in nature. In this work, the intrinsic radiation impedance of spin waves in the magnetostatic and exchange regime are studied theoretically, followed by several practical transducer examples, one of which is suitable for wide-band transduction of spin waves. A discussion on spin wave bandwidth and an appropriate definition for transduction bandwidth is proposed. The future work proposed in this candidacy is to design and build a calibrated time-resolved Magneto-optic Kerr Effect (MOKE) that will enable the experimental validation of various transducer designs, including investigation of transducer efficiency, bandwidth, localization of spin-wave launch sites, and system-level figures of merit.

Abstract: We present an automated design procedure for the rapid realization of wideband millimeter-wave lens antennas. The design method is based upon the creation of a library of matched unit-cells which comprise wideband impedance matching sections on either side of a phase-delaying core section. The phase accumulation and impedance match of each unit-cell is characterized over frequency and incident angle. The lens is divided into rings, each of which is assigned an optimal unit-cell based on incident angle and required local phase correction given that the lens must collimate the incident wavefront. A unit-cell library for a given realizable permittivity range, lens thickness, and unit-cell stack-up can be used to design a wide variety of flat wideband lenses for various diameters, feed elements, and focal distances. A demonstration GRIN lens antenna is designed, fabricated, and measured in both far-field and near-field chambers. The antenna functions as intended from 14GHz to 40GHz and is therefore suitable for all proposed 5G MMW bands, Ku- and Ka-band fixed satellite services. The use of intrinsically matched unitcells results in aperture efficiency ranging from 31% to 72% over the 2.9:1 bandwidth which is the highest aperture efficiency demonstrated across such a wide operating band.

Abtract: Next-generation wireless communications systems are looking to exploit an abundance of spectrum at millimeterwave (mmW) frequencies as well as the benefits of spectral efficiency promised by massive MIMO systems. The current 5G solution employs traditional high-order modulation and phased-array beamsteering for mobile wireless, which at mmW consumes significant power per RF chain. Because of the high number of transceivers required to realize the benefits of massive MIMO, much research effort has gone into increasing the energy efficiency of the RF chains. One potential solution is the use of low-resolution, even 1-bit, architectures. This approach has been investigated by both information theorists and hardware designers. Circuit design strategies such as noncoherent detection and reduction in linearity requirements can reduce per-receiver power consumption. Yet the vast majority of 1-bit massive MIMO system analysis employs linear models which do not reflect the hardware realities of this low-resolution paradigm. This work aims to establish accurate receiver models for use in information-theoretic simulations that expose key hardware quantities and enable transceiver/system codesign in massive MIMO deployment scenarios. In this candidacy proposal, we describe a 1-bit on-off-keying (OOK) receive circuit at 39 GHz, for which a nonlinear noise model is developed and verified. This model is used to optimize the receiver design and predict massive MIMO system performance. BPSK and QPSK receive circuits at 39 GHz are also proposed based upon the 1-bit OOK unit cell.

“Spin” is a property of electrons that makes them act like tiny bar magnets (or compass needles) the size of individual atoms.

Just about every modern electronic device – such as computers, printers, smart TVs and, of course, cell phones – has the built-in capability to communicate wirelessly. Today, nearly all electronics are based on electrical, rather than magnetic, interactions. The Notre Dame team is pioneering the use of magnetic phenomena for information processing, exploiting the unique properties of spin waves.

Magnetic materials are like a room full of closely spaced bar magnets. If a magnetic field changes on one edge of the room, the effect is felt throughout the room in the form of a “spin wave.”
 

Spin waves operate at the same frequencies as the electrical interactions used for wireless communications, and they employ much less space than would be required for conventional electronics. This offers the possibility of very compact devices, low-energy processing, and high signal integrity. Initial results indicate that this new technology could enable the replacement of today’s bulky passive electromagnetic systems with smaller [chip-scale], lower-power, higher performance devices.

An article in the most recent issue of Scientific Reports describes the Notre Dame team’s design of a nanoscale spectrum analyzer based on spin-wave interference. The results of simulation studies of that design suggest that all performance figures of the team’s magnetoelectric device (speed, area, and power consumption) are potentially order(s) of magnitude better than what is achievable in a purely electrical system at room temperature.

Based upon this proposed device concept, the team has been awarded a $690,000 grant from the National Science Foundation (NSF) to build a prototype micromagnetics-based real-time spectrum sensor that is low-cost, high-performance, and chip-scale. This experimental team includes Gary Bernstein, the Frank M. Freimann Professor of Electrical Engineering and Research Professor Alexei Orlov and Assistant Professor Jonathan Chisum, also in the Department of Electrical Engineering.

In addition to the research, the NSF award will support the training of students in this new technology and graduate students exploring commercialization through University of Notre Dame’s Innovation Park and the Engineering Science and Technology Entrepreneurship Excellence Master’s Program. Local high-school teachers and faculty from the South Bend campus of Ivy Tech Community College will also participate in the work through an NSF Research Experiences for Teachers program.

While much of this work will occur on campus, this project is being conducted in collaboration with Professor György Csaba at the Pázmány Péter Catholic University in Budapest, Hungary, and is based on the doctoral thesis of Adam Papp, a Hungarian student who is the first in a new joint Ph.D. program between the Notre Dame and the Pázmány Péter Catholic University.

Originally published by Nina Welding at conductorshare.nd.edu on September 27, 2017.