Dissipation alone can produce counterintuitive topological wave transport that is otherwise absent in a non-dissipative system. This work demonstrates the influence of dissipation on degeneracies that arise in the context of elastic wave transport. The conditions on the parameters necessary to observe non-Hermitian degeneracies in the Bloch spectrum are precisely derived. It will be shown—contrary to the expectation from singularity theory of a linear eigenvalue problem—that a proportionally damped system with commutative damping does not exhibit non-Hermitian degeneracies. The necessity of a non-commutative and non-proportional dissipation model to observe non-Hermitian degeneracies (or exceptional points) is emphasized. Non-proportional dissipation is used to induce a non-Hermitian degeneracy in a local resonance sub-Bragg bandgap of a linear chain, without using negative damping. While Bloch waves are chosen to illustrate the influence of dissipation, the results readily extend to waves in non-periodic media as well as other wave and vibration transport problems.

1.
M. V.
Berry
, “
Anticipations of the geometric phase
,”
Phys. Today
43
(
12
),
34
40
(
1990
).
2.
F.
Wilczek
and
A.
Shapere
,
Geometric Phases in Physics
(
World Scientific
,
1989
).
3.
D.
Vanderbilt
,
Berry Phases in Electronic Structure Theory: Electric Polarization, Orbital Magnetization and Topological Insulators
, 1st ed. (
Cambridge University Press
,
Cambridge
,
2018
).
4.
R. A.
Horn
and
C. R.
Johnson
,
Matrix Analysis
(
Cambridge University Press
,
Cambridge
,
1985
).
5.
M. V.
Berry
, “
Physics of non-Hermitian degeneracies
,”
Czech. J. Phys.
54
,
1039
1047
(
2004
).
6.
W. D.
Heiss
, “
Exceptional points—Their universal occurrence and their physical significance
,”
Czech. J. Phys.
54
,
1091
1099
(
2004
).
7.
C. M.
Bender
, “
Making sense of non-Hermitian Hamiltonians
,”
Rep. Prog. Phys.
70
,
947
1018
(
2007
).
8.
M. V.
Berry
, “
Aspects of degeneracy
,” in
Chaotic Behavior in Quantum Systems: Theory and Applications
, edited by
G.
Casati
(
Springer US
,
Boston, MA
,
1985
), pp.
123
140
.
9.
A. P.
Seyranian
,
O. N.
Kirillov
, and
A. A.
Mailybaev
, “
Coupling of eigenvalues of complex matrices at diabolic and exceptional points
,”
J. Phys. A
38
,
1723
1740
(
2005
).
10.
E.
Teller
, “
The crossing of potential surfaces
,”
J. Phys. Chem.
41
,
109
116
(
1937
).
11.
J.
Von Neumann
and
E.
Wigner
, “
On some peculiar discrete eigenvalues
,”
Z. Phys.
30
,
465
467
(
1929
).
12.
J.
Von Neumann
and
E.
Wigner
, “
No crossing rule
,”
Z. Phys.
30
,
467
470
(
1929
).
13.
V. I.
Arnol'd
,
Mathematical Methods of Classical Mechanics
(
Springer Science & Business Media
,
2013
), Vol.
60
.
14.
T.
Kato
,
Perturbation Theory for Linear Operators
(
Springer Science & Business Media
,
2013
), Vol.
132
.
15.
C. M.
Bender
and
S.
Boettcher
, “
Real spectra in non-Hermitian Hamiltonians having PT symmetry
,”
Phys. Rev. Lett.
80
,
5243
(
1998
).
16.
R.
El-Ganainy
,
K. G.
Makris
,
M.
Khajavikhan
,
Z. H.
Musslimani
,
S.
Rotter
, and
D. N.
Christodoulides
, “
Non-Hermitian physics and PT symmetry
,”
Nat. Phys.
14
,
11
19
(
2018
).
17.
P.
Nair
and
S.
Durvasula
, “
On quasi-degeneracies in plate vibration problems
,”
Int. J. Mech. Sci.
15
,
975
986
(
1973
).
18.
N.
Perkins
and
C.
Mote
, Jr.
, “
Comment on curve veering in eigenvalue problems
,”
J. Sound Vib.
106
,
451
463
(
1986
).
19.
A. S.
Phani
,
J.
Woodhouse
, and
N. A.
Fleck
, “
Wave propagation in two-dimensional periodic lattices
,”
J. Acoust. Soc. Am.
119
,
1995
2005
(
2006
).
20.
B. R.
Mace
and
E.
Manconi
, “
Wave motion and dispersion phenomena: Veering, locking and strong coupling effects
,”
J. Acoust. Soc. Am.
131
,
1015
1028
(
2012
).
21.
P. B.
Allen
and
W. E.
Pickett
, “
Accidental degeneracy in k-space, geometrical phase, and the perturbation of π by spin-orbit interactions
,”
Physica C
549
,
102
106
(
2018
).
22.
J.
Cha
,
K. W.
Kim
, and
C.
Daraio
, “
Experimental realization of on-chip topological nanoelectromechanical metamaterials
,”
Nature
564
,
229
233
(
2018
).
23.
P.
Wang
,
L.
Lu
, and
K.
Bertoldi
, “
Topological phononic crystals with one-way elastic edge waves
,”
Phys. Rev. Lett.
115
,
104302
(
2015
).
24.
T.
Stehmann
,
W.
Heiss
, and
F.
Scholtz
, “
Observation of exceptional points in electronic circuits
,”
J. Phys. A
37
,
7813
(
2004
).
25.
M.
Manav
,
G.
Reynen
,
M.
Sharma
,
E.
Cretu
, and
A.
Phani
, “
Ultrasensitive resonant MEMS transducers with tuneable coupling
,”
J. Micromech. Microeng.
24
,
055005
(
2014
).
26.
M.
Manav
,
A. S.
Phani
, and
E.
Cretu
, “
Mode localization and sensitivity in weakly coupled resonators
,”
IEEE Sens. J.
19
,
2999
3007
(
2019
).
27.
R.
Kononchuk
,
J.
Cai
,
F.
Ellis
,
R.
Thevamaran
, and
T.
Kottos
, “
Exceptional-point-based accelerometers with enhanced signal-to-noise ratio
,”
Nature
607
,
697
702
(
2022
).
28.
J.
Wiersig
, “
Prospects and fundamental limits in exceptional point-based sensing
,”
Nat. Commun.
11
,
2454
(
2020
).
29.
C.
Dembowski
,
H.-D.
Gräf
,
H.
Harney
,
A.
Heine
,
W.
Heiss
,
H.
Rehfeld
, and
A.
Richter
, “
Experimental observation of the topological structure of exceptional points
,”
Phys. Rev. Lett.
86
,
787
(
2001
).
30.
S. A. H.
Gangaraj
and
F.
Monticone
, “
Topological waveguiding near an exceptional point: Defect-immune, slow-light, and loss-immune propagation
,”
Phys. Rev. Lett.
121
,
093901
(
2018
).
31.
M.
Xiao
,
G.
Ma
,
Z.
Yang
,
P.
Sheng
,
Z. Q.
Zhang
, and
C. T.
Chan
, “
Geometric phase and band inversion in periodic acoustic systems
,”
Nat. Phys.
11
,
240
244
(
2015
).
32.
A.
Alù
,
C.
Daraio
,
P. A.
Deymier
, and
M.
Ruzzene
, “
Topological acoustics
,”
Acoust. Today
17
(
3
),
13
(
2021
).
33.
M.-A.
Miri
and
A.
Alù
, “
Exceptional points in optics and photonics
,”
Science
363
,
eaar7709
(
2019
).
34.
A.
Shapere
and
F.
Wilczek
, “
Self-propulsion at low Reynolds number
,”
Phys. Rev. Lett.
58
,
2051
(
1987
).
35.
A.
Shapere
and
F.
Wilczek
, “
Geometry of self-propulsion at low Reynolds number
,”
J. Fluid Mech.
198
,
557
585
(
1989
).
36.
J.
Wisdom
, “
Swimming in spacetime: Motion by cyclic changes in body shape
,”
Science
299
,
1865
1869
(
2003
).
37.
R. L.
Hatton
,
Y.
Ding
,
H.
Choset
, and
D. I.
Goldman
, “
Geometric visualization of self-propulsion in a complex medium
,”
Phys. Rev. Lett.
110
,
078101
(
2013
).
38.
W.
Heiss
, “
Exceptional points of non-Hermitian operators
,”
J. Phys. A
37
,
2455
(
2004
).
39.
C.
Gordon
,
D. L.
Webb
, and
S.
Wolpert
, “
One cannot hear the shape of a drum
,”
Bull. Am. Math. Soc.
27
,
134
138
(
1992
).
40.
M. I.
Hussein
, “
Theory of damped Bloch waves in elastic media
,”
Phys. Rev. B
80
,
212301
(
2009
).
41.
M. I.
Hussein
and
M. J.
Frazier
, “
Band structure of phononic crystals with general damping
,”
J. Appl. Phys.
108
,
093506
(
2010
).
42.
A. S.
Phani
and
M. I.
Hussein
, “
Analysis of damped Bloch waves by the Rayleigh perturbation method
,”
J. Vib. Acoust.
135
,
041014
(
2013
).
43.
A. S.
Phani
and
M. I.
Hussein
,
Dynamics of Lattice Materials
(
John Wiley & Sons
,
2017
).
44.
C. L.
Bacquet
,
H.
Al Ba'ba'a
,
M. J.
Frazier
,
M.
Nouh
, and
M. I.
Hussein
, “
Metadamping: Dissipation emergence in elastic metamaterials
,”
Adv. Appl. Mech.
51
,
115
164
(
2018
).
45.
J. W.
Rayleigh
,
The Theory of Sound
(
Dover
,
New York
,
1894
), Vol.
1
.
46.
H.
Goldstein
,
Classical Mechanics
(
Addison-Wesley
,
1980
).
47.
J.
Woodhouse
, “
Linear damping models for structural vibration
,”
J. Sound Vib.
215
,
547
569
(
1998
).
48.
S.
Adhikari
and
J.
Woodhouse
, “
Identification of damping, part 1: Viscous damping
,”
J. Sound Vib.
243
,
43
61
(
2001
).
49.
A. S.
Phani
and
J.
Woodhouse
, “
Experimental identification of viscous damping in linear vibration
,”
J. Sound Vib.
319
,
832
849
(
2009
).
50.
T. K.
Caughey
and
M. E. J.
O'Kelly
, “
Classical normal modes in damped linear dynamic systems
,”
J. Appl. Mech.
32
,
583
588
(
1965
).
51.
A. S.
Phani
, “
On the necessary and sufficient conditions for the existence of classical normal modes in damped linear dynamic systems
,”
J. Sound Vib.
264
,
741
745
(
2003
).
52.
D. E.
Newland
,
Mechanical Vibration Analysis and Computation
(
Dover Publications
,
New York
,
2006
).
53.
S.
Adhikari
and
A. S.
Phani
, “
Experimental identification of generalized proportional viscous damping matrix
,”
J. Vib. Acoust.
131
,
011008
(
2009
).
54.
K.
Uhlenbeck
, “
Generic properties of eigenfunctions
,”
Am. J. Math.
98
,
1059
1078
(
1976
).
55.
M. I.
Hussein
,
M. J.
Leamy
, and
M.
Ruzzene
, “
Dynamics of phononic materials and structures: Historical origins, recent progress, and future outlook
,”
Appl. Mech. Rev.
66
,
040802
(
2014
).
56.
R.
Langley
,
N.
Bardell
, and
H. M.
Ruivo
, “
The response of two-dimensional periodic structures to harmonic point loading: A theoretical and experimental study of a beam grillage
,”
J. Sound Vib.
207
,
521
535
(
1997
).
57.
R. M.
Orris
and
M.
Petyt
, “
A finite element study of harmonic wave propagation in periodic structures
,”
J. Sound Vib.
33
,
223
236
(
1974
).
58.
L.
Raghavan
and
A. S.
Phani
, “
Local resonance bandgaps in periodic media: Theory and experiment
,”
J. Acoust. Soc. Am.
134
,
1950
1959
(
2013
).
59.
The polynomial form C=αMn=0p1an(M1K)n is one general proportional damping: the first two terms of this series give the Rayleigh damping C=αM+βK. Even more general forms of proportional damping exist, for example, C=Mβ1(M1K)+Kβ2(K1M), where β1(·) and β2(·) are smooth analytic functions in the neighborhood of the eigenvalues of their argument matrices.53 
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