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arxiv: 1906.09099 · v1 · pith:IG5Q6P2Xnew · submitted 2019-06-20 · ⚛️ physics.app-ph

Broadband nonreciprocal acoustic propagation using programmable boundary conditions: from analytical modelling to experimental implementation

Sami Karkar , Emanuele De Bono , Manuel Collet , Ga\"el Matten , Morvan Ouisse , Etienne Rivet This is my paper

Pith reviewed 2026-05-25 19:07 UTC · model grok-4.3

classification ⚛️ physics.app-ph
keywords nonreciprocal acousticsacoustic isolatorprogrammable boundaries1D waveguideactive acoustic controlscattering matrixpassivity
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The pith

Direction-dependent programmable boundary conditions in a 1D waveguide produce broadband acoustic isolation.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that acoustic waves can be made to propagate differently in opposite directions within a straight tube by imposing boundary conditions that depend on the direction of travel. A theoretical model derives the nonreciprocity from these controlled boundaries. Numerical checks confirm that the device remains passive while blocking sound in one direction over a broad frequency range. Experiments then implement the idea and observe the predicted isolation effect.

Core claim

We theoretically, numerically and experimentally demonstrate the acoustic isolator effect in a 1D waveguide with direction dependent controlled boundary conditions. A theoretical model explains the principle of non reciprocal propagation. Numerical simulations on a reduced model show the non-reciprocity as well as the passivity through the scattering matrix and power balance. An experimental implementation validates the approach.

What carries the argument

Direction-dependent controlled boundary conditions applied to a 1D acoustic waveguide.

Load-bearing premise

Programmable boundary conditions can be implemented in an experiment without introducing unmodeled losses or instabilities that would prevent broadband isolation.

What would settle it

Observation of equal transmission coefficients in both directions or violation of energy conservation in the experimental measurements would disprove the claimed nonreciprocity and passivity.

Figures

Figures reproduced from arXiv: 1906.09099 by Emanuele De Bono, Etienne Rivet, Ga\"el Matten, Manuel Collet, Morvan Ouisse, Sami Karkar.

Figure 1
Figure 1. Figure 1: A cylindrical waveguide along coordinate x, with cross section of arbitrary shape Ω. Left: overview of the waveguide. Right: detail of the cross-section and its contour ∂Ω parametrized by a curvilinear coordinate s. ~n is the local exterior normal at each point of the contour. its scattering matrix. Finally, we show experimental results obtained by applying a non-local boundary control on an acoustic waveg… view at source ↗
Figure 2
Figure 2. Figure 2: A finite-sized acoustic isolator connected to semi-infinite waveg￾uides at both ends. Ingoing and outgoing waves are shown on both sides. separately from the backward wave. Even though backward waves alone do not contribute to the source term, it does have an incidence on the power balance in case of a superposition of both forward and backward waves, as it contributes to the pressure term of the product i… view at source ↗
Figure 3
Figure 3. Figure 3: Scattering matrix coefficients magnitude (dimensionless) of the proposed acoustic isolator as a function of frequency (in Hz), for different parameter values d. Top-left: |S11|, top-right: |S12|, bottom-left: |S21|, and bottom-right: |S22|. ingoing waves in the left (subscript 1) and right (subscript 2) regions outside the device (see [PITH_FULL_IMAGE:figures/full_fig_p008_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Isolation (in dB) as a function of frequency, for different values of the parameter d. The calculation of the Isolation Index, IS = 20 log10(|S12/S21|), is straightforward and its plot is in [PITH_FULL_IMAGE:figures/full_fig_p009_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Acoustic power injected by the isolator into the acoustic domain, as a function of frequency, for different values of the parameter d, in case of an incident wave of 1Pa RMS in the positive x direction [PITH_FULL_IMAGE:figures/full_fig_p010_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Sound pressure level (in dB ref.20µ Pa) along the system for different frequencies, in case of an incident wave of 1 Pa RMS in the positive x direction. Parameter d = 0.14 m. The isolator is located between x = 0 and x = 0.33 m 10 [PITH_FULL_IMAGE:figures/full_fig_p010_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Left: Unit cell. Right: Prespective of the lined waveguide, with upstream and downstream microphones for the TL evaluation through the transfer matrix method. The synthesized algorithm for the implementation of the control law was able to invert the dynamics of the loudspeaker after its first resonance (see Appendix A) which is between 500 and 550 Hz for all loudspeakers, that is why the plot is limited to… view at source ↗
Figure 8
Figure 8. Figure 8: Left: 2D sketch of the lined waveguide. Right: Insertion Loss measurements relative to incident waves directed towards the positive x (forward), and towards the negative x (backward). 1000 1500 2000 2500 3000 freq (Hz) 0 5 10 15 20 25 IS (dB) Measurements Simulations with d eq = 0.14 m [PITH_FULL_IMAGE:figures/full_fig_p013_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Isolation index: measurements compared to 1D reduced model simulation with d equivalent to the experimental application. 13 [PITH_FULL_IMAGE:figures/full_fig_p013_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: View of the waveguide interior. The layers of foam, in pink color applied in front of the loudspeakers, do not interfere with the diaphragms mechanical vibration. The ”flush” condition of the liner is maintained. and 18. Clearly, this is not true in a real application, where delay and model incertitudes are inevitably present in the controller. Above all, the time delay is responsible of the loss of acous… view at source ↗
read the original abstract

In this paper, we theoretically, numerically and experimentally demonstrate the acoustic isolator effect in a 1D waveguide with direction dependent controlled boundary conditions. A theoretical model is used to explain the principle of non reciprocal propagation in boundary controlled waveguides. Numerical simulations are carried out on a reduced model to show the non-reciprocity as well as the passivity of the system, through the computation of the scattering matrix and the power delivered by the system. Finally, an experimental implementation validate the potential of programmable boundary conditions for non reciprocal propagation.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The paper claims to theoretically model, numerically simulate (via scattering matrix and power-balance calculations on a reduced model), and experimentally implement nonreciprocal acoustic propagation in a 1D waveguide by imposing direction-dependent programmable boundary conditions, thereby realizing a passive acoustic isolator.

Significance. If the experimental demonstration confirms that the programmable boundaries achieve broadband isolation while remaining passive (no net acoustic power supplied by the control hardware), the result would provide a concrete route to nonreciprocal acoustic devices without relying on nonlinear media or external bias fields.

major comments (1)
  1. [Experimental implementation] Experimental implementation section: the abstract states that the experiment validates the isolator effect, yet no data or analysis is presented showing that the actuators/sensors deliver zero net acoustic power (or that any supplied power is accounted for in the power-balance calculation). The numerical passivity result on the reduced model does not automatically transfer to the physical controller; without this measurement the observed nonreciprocity could be active rather than the passive effect claimed.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the detailed review and the emphasis placed on confirming passivity in the experimental implementation. We address the single major comment below.

read point-by-point responses

  1. Referee: [Experimental implementation] Experimental implementation section: the abstract states that the experiment validates the isolator effect, yet no data or analysis is presented showing that the actuators/sensors deliver zero net acoustic power (or that any supplied power is accounted for in the power-balance calculation). The numerical passivity result on the reduced model does not automatically transfer to the physical controller; without this measurement the observed nonreciprocity could be active rather than the passive effect claimed.

    Authors: We agree that the manuscript reports power-balance calculations demonstrating passivity only on the numerical reduced model and does not present corresponding experimental measurements of net acoustic power delivered by the actuators or sensors. The experimental results validate the nonreciprocal propagation but do not directly confirm that the physical controller supplies zero net power. In the revised manuscript we will add experimental power measurements (or an explicit accounting of supplied power) to demonstrate that the observed isolation remains passive. revision: yes

Circularity Check

0 steps flagged

No circularity: derivation chain is independent and self-contained

full rationale

The paper derives a theoretical model for direction-dependent boundary conditions in a 1D waveguide, computes the scattering matrix and power balance on a reduced numerical model to demonstrate non-reciprocity and passivity, then reports separate experimental validation. No load-bearing step reduces by construction to fitted inputs, self-citations, or ansatzes imported from prior author work; the central claims rest on explicit computation and physical implementation rather than renaming or self-definition. This is the normal non-circular outcome for a modeling-plus-experiment paper.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Abstract provides insufficient detail to enumerate specific free parameters or invented entities; the core modeling assumption is direction-dependent boundary control.

axioms (1)
  • domain assumption Direction-dependent controlled boundary conditions can produce nonreciprocal propagation in a 1D waveguide
    This premise underpins the theoretical model and is required for the isolator effect to hold.

pith-pipeline@v0.9.0 · 5630 in / 1023 out tokens · 23443 ms · 2026-05-25T19:07:41.217263+00:00 · methodology

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Reference graph

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