Sound zones are typically created using Acoustic Contrast Control (ACC), Pressure Matching (PM), or variations of the two. ACC maximizes the acoustic potential energy contrast between a listening zone and a quiet zone. Although the contrast is maximized, the phase is not controlled. To control both the amplitude and the phase, PM instead minimizes the difference between the reproduced sound field and the desired sound field in all zones. On the surface, ACC and PM seem to control sound fields differently, but we here demonstrate they are actually extreme special cases of a much more general framework. The framework is inspired by the variable span linear filtering framework for speech enhancement. Using this framework, we demonstrate that 1) ACC gives the best contrast, but the highest signal distortion in the bright zone, and 2) PM gives the smallest signal distortion in the bright zone, but the worst contrast. Aside from showing this mathematically, we also demonstrate this via a small toy example.

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The design of so-called sound zones is a fairly old idea which has recently gained some research attention. The idea is to control a loudspeaker array to reproduce a desired sound field in certain regions. In this paper, we show how the sound zone control problem can be solved using techniques from speech enhancement. Specifically, we first describe in detail the recently introduced variable span linear filtering (VSLF) framework which unifies the popular optimal filtering and subspace-based approaches to speech enhancement. We then show how the sound zone control problem can be solved using the VSLF framework and how a number of well-known sound zone control methods can be viewed as special cases of this solution. We also discuss in detail the differences between the speech enhancement problem and the sound zone control problem and argue that the VSLF framework is actually even better suited for controlling sound zones than for enhancing speech.

We investigated graphene-oxide-(GO-) coupled surface plasmon resonance (SPR) detection sensitivity for sandwiched antigen-antibody interaction between human and antihuman immunoglobulin G molecules. GO was prepared in a Langmuir-Blodgett solution on gold and dielectric surfaces. Theoretical and experimental data suggest that an increased dielectric spacer thickness reduces resonance shifts for GO-coupled SPR detection as dielectric properties of GO appear to prevail. In general, a metal-enhanced structure was shown to provide a larger resonance shift by plasmonic field enhancement. The far-field properties were described in terms of near-field overlap. The peak resonance shift that was obtained with GO-coupled SPR detection was enhanced to 113% of the resonance shift obtained by conventional thin-film-based SPR detection and may further be improved by GO stacking.

The creation of sound zones with frequency-domain variable span trade-off filters (VAST) is investigated herein. Both narrowband and broadband discrete Fourier transform (DFT)-domain VAST approaches are proposed, and we discuss their relationship to the existing time-domain VAST approach. The core idea in VAST is to apply a generalized eigenvalue decomposition to the spatial statistics to control the trade-off between acoustic contrast and signal distortion. Moreover, a method for determining the optimal Lagrange multiplier that controls this trade-off is also considered in terms of physical, meaningful parameters. Through analysis and experiments, a performance comparison using measured room impulse responses is conducted not only between the two proposed methods but also between the two proposed methods and the existing time-domain approach. The results confirm that the broadband approach is able to transfer the acoustic contrast from one frequency bin to another, which is not the case for the narrowband approach. Furthermore, the results also show that the proposed DFTdomain VAST approach can be considered to be a special case of the time-domain VAST approach.