Master's Thesis

Nonlinear spin-wave power limiter for RF applications

Author of thesis: Ing. Kristýna Davídková

Acad. year: 2022/2023

Supervisor: Ing. Michal Urbánek, Ph.D.

Reviewer: dr. Sebastian Wintz

Abstract:

Power limiters are essential devices for protecting RF electronics from large input signals causing overload and potential destruction. So far, only macroscopic power limiters based on nonlinear spin-wave transmission and multi-magnon scattering in ferrites have been manufactured and used. These were later replaced by semiconductor limiters, which allowed device miniaturisation. However, semiconductor-based limiters have significant drawbacks, such as high electrical noise as they approach the GHz range, low output power and design complexity. This makes them unsuitable for many practical applications. Ferrite-based power limiters are passive, low cost, simple to design and allow operation in the GHz range. In this work, we experimentally study the power-limiting effects in nanoscale yttrium iron garnet (YIG) thin films and lithographically fabricated nanowaveguides and compare them with the power-limiting effects in macroscale YIG stripes. The investigations are performed for various magnetic fields and spin-wave modes with all electric measurements using a vector network analyser (VNA).

Keywords:

Power limiter, multi-magnon scattering, nonlinear spin waves, magnonics, dispersion relations, vector network analyzer, YIG, nanofabrication, magnetism, microwaves.

Date of defence

19.06.2023

Date of publish

18.06.2026

Result of the defence

Defended (thesis was successfully defended)

znamkaAznamka

Grading

A

Process of defence

Po otázkách oponenta bylo dále diskutováno: Magnetické materiály vhodné pro vysoké frekvence. Problémy s vícemagnonovým rozptylem. Studentka na otázky odpověděla velmi obsáhle.

Language of thesis

English

Faculty

Fakulta strojního inženýrství

Department

Institute of Physical Engineering

Study programme

Physical Engineering and Nanotechnology (N-FIN-P)

Composition of Committee

prof. RNDr. Tomáš Šikola, CSc. (předseda)
prof. RNDr. Jiří Spousta, Ph.D. (místopředseda)
prof. Mgr. Dominik Munzar, Dr. (člen)
doc. Mgr. Adam Dubroka, Ph.D. (člen)
prof. RNDr. Petr Dub, CSc. (člen)
prof. RNDr. Bohumila Lencová, CSc. (člen)
prof. RNDr. Jiří Petráček, Dr. (člen)
prof. RNDr. Radim Chmelík, Ph.D. (člen)
doc. Ing. Radek Kalousek, Ph.D. (člen)
prof. Ing. Miroslav Kolíbal, Ph.D. (člen)
doc. Ing. Stanislav Průša, Ph.D. (člen)
RNDr. Antonín Fejfar, CSc. (člen)

Supervisor’s report
Ing. Michal Urbánek, Ph.D.

Ms. Kristyna Davidkova's thesis focused on investigating power-limiting effects in ferrites at different scales, aiming to develop a miniaturized power-limiting device using magnonic nano-waveguides. Although the initial approach did not yield desired results, her research produced valuable findings for the field. Her recognition with the Best Poster Award at the recent INTERMAG conference attests to the significance of her work. Unfortunately, the fact that the original idea did not work as we initially thought negatively influenced Kristyna's attitude towards writing her thesis. I know that she is capable of better output. On the other hand, her contributions to other projects (she is already a co-author of five research papers) demonstrate her commitment and competence. Considering these achievements and the potential value of her findings, Ms. Davidkova deserves a grade A for her thesis.
Evaluation criteria Grade
Splnění požadavků a cílů zadání A
Postup a rozsah řešení, adekvátnost použitých metod A
Vlastní přínos a originalita A
Schopnost interpretovat dosažené výsledky a vyvozovat z nich závěry B
Využitelnost výsledků v praxi nebo teorii A
Logické uspořádání práce a formální náležitosti A
Grafická, stylistická úprava a pravopis A
Práce s literaturou včetně citací A
Samostatnost studenta při zpracování tématu B

Grade proposed by supervisor: A

Reviewer’s report
dr. Sebastian Wintz

ln her Master thesis, Mrs. Bc. Kristýna Davídková investigated "Nonlinear spin-wave power limiter for RF applications", covering both macro- and nanoscale devices made ofyttrium iron gamet. This subject is highly topical since there is a strong demand for compact, passive limiters in mobile communication technologies (5G+). ln my view, throughout the thesis, referencing, experiments, calculations and analysis are conducted rigorously. The thesis is clearly written and well structured. The conclusions drawn and the results reported are scientifically sound. By means of this thesis, Mrs. Davídková makes a valuable contribution to the fields of applied spin dynamics and magnonics, and the results presented are of high quality and novelty.
Evaluation criteria Grade
Splnění požadavků a cílů zadání A
Postup a rozsah řešení, adekvátnost použitých metod A
Vlastní přínos a originalita A
Schopnost interpretovat dosaž. výsledky a vyvozovat z nich závěry A
Využitelnost výsledků v praxi nebo teorii B
Logické uspořádání práce a formální náležitosti A
Grafická, stylistická úprava a pravopis B
Práce s literaturou včetně citací B
Topics for thesis defence:
  1. 1) ln 1.2, the design of a power limiter based on a mm-sized YIG sphere in a microwave resonator is presented (Spencer and Sansalone 1961). What is the actual working principie of this device and in particular, why does it have a ost no transmission losses in the linear regime (Fig. 1.2b), as compared to other ferrite limiter designs?
  2. 2) ln 4.3, the results from macroscale spin-wave power limiter experiments are discussed for different magnitudes of the external magnetic field. For small fields (30 mT), there was no linear regime observed for input powers above -30dBm as a consequence of 3-magnon scattering. Would there be any linear regime expected for lower input powers and would it be possible to perform measurements at such low powers?
  3. 3) ln 6.3, it is mentioned that 5G communications systems require operation frequencies up to 28 GHz and that standard magnetic materials exhibit rather high resonance fields at such frequencies. Apart from an increase in saturation magnetization, are there other potential magnetic property modifications that would allow for higher intrinsic resonance frequencies, or=-equivalently-lower resonance fields at a given frequency?

Grade proposed by reviewer: A

Reasons for publication postponement

Publication of the final thesis has been postponed in compliance with the provisions of Section 47b (4) of Act No. 111/1998 Coll., on the Higher Education Institutions and on amendments and supplements to other acts, as amended.

Responsibility: Mgr. et Mgr. Hana Odstrčilová