Georgios N. Lilis

Sound Field Reproduction using the Lasso

Reproducing a sampled sound field using an array of loudspeakers is a problem with well-appreciated applications to acoustics and ultrasound treatment. Loudspeaker signal design has traditionally relied on (possibly regularized) least-squares (LS) criteria. In many cases however, the desired sound field can be reproduced using only a few loudspeakers, which are sparsely distributed in space. To exploit this feature, the fresh look advocated here permeates benefits from advances in variable selection and compressive sampling to sound field synthesis by formulating a sparse linear regression problem that is solved using the least-absolute shrinkage and selection operator (Lasso). An efficient implementation of the Lasso for the problem at hand is developed based on a coordinate descent iteration. Analysis and simulations demonstrate that Lasso-based sound field reproduction yields better performance than LS especially at high frequencies and for reproduction of under-sampled sound fields. In addition, Lasso-based synthesis enables judicious placement of loudspeaker arrays.

Harmonic Generation Using Nonlinear LC Lattices

Nonlinear LC lattices have shown promise for high-power high-frequency signal generation. Here we offer the first detailed study of the frequency response of these lattices, as well as a method designed to find input excitation frequencies that result in intense harmonic generation. The crux of the method is to locate regions in frequency space where the spectral norm of the lattice response matrix is large. When the fundamental excitation frequency (or one of its multiples) is located in these regions, the lattice harmonic response is intensified. These findings are supported by extensive numerical simulations and experimental measurements. We deal chiefly with a first-order dependency of capacitance (C) on voltage (V); however, it is also shown that lattices with higher order C-V dependencies achieve proportionally higher harmonic generation. Simulations using a 0.13-μm CMOS process indicate harmonic generation at 400 GHz (three times the cutoff frequency of the fastest active device in this process), suggesting potential applications of this lattice topology in terahertz range devices.

Steady-state perturbative theory for nonlinear circuits

We study the steady-state behavior of a damped, driven nonlinear LRC oscillator, where the nonlinearity arises due to voltage-dependent capacitance. The driving or input signal is assumed to be a pure tone. Using an iterative, perturbative solution technique combined with an energy conservation argument, we show that the oscillator transfers energy from the fundamental to higher harmonics. We determine a series expansion of the two-norm of the steady-state output signal and show that in a large region of parameter space, the two-norm depends superlinearly on the input amplitude. We also use the two-norm calculation to devise a performance goal that the infinity-norm of the steady-state output signal should satisfy, in order for the nonlinear system to have a genuine boost over the corresponding linear system. Taken together, these results are a step toward the automatic design of nonlinear systems that have an optimal boost over corresponding linear systems.

Parsimonious sound field synthesis using compressive sampling

Reproducing a sampled sound field over a two-dimensional area using an array of loudspeakers is a problem with well-appreciated applications to acoustics and ultrasound treatement. Loudspeaker signal design has traditionally relied on a (possibly regularized) least-squares criterion. The fresh look advocated here, permeates benefits from advances in variable selection and compressive sampling by casting the sound field synthesis as a sparse linear regression problem that is solved by the least absolute shrinkage and selection operator (Lasso). Analysis and simulations demonstrate that the novel approach exhibits superb performance even for under-sampled sound fields, where least-squares methods yield inconsistent field reproduction. In addition, Lasso-based synthesis enables judicious placement of parsimonious loudspeaker arrays.

Inverse Acoustic Wave Field Synthesis

Acoustic wave field synthesis is a method of sound reproduction of a primary sound source with the use of secondary sources, implemented as arrays of micro‐speakers. This method is based on wave field theory. We have developed a finite element based scheme to solve this problem posed in an inverse setting. Huygens principle has been used to validate the method for a few simple problems.Huygen’s principle suffers from the drawback that incorporation of secondary sources at desired locations is rather difficult. We present a method for inverse acoustic wave field synthesis which overcomes the above limitation in the context of Two‐Dimensional problems and show that incorporation of any geometric or material non linearities is relatively straight forward. This has significant implications for problems in geophysics or biological medium where material inhomogeneities are quite prevalent. Numerical results are presented for sample problems in noise cancellation and wave field synthesis for inhomogeneous media....

A Cloud-Based Platform for IFC File Enrichment with Second-Level Space Boundary Topology

To facilitate the automatic generation of building energy performance simulation models from BIM data sources and support multiple building designs almost simultaneously in a district environment, a cloud-based platform which uses containerized micro-services for the generation of the required buildings second level space boundary topology from IFC geometric data, is introduced.

dWFS: Distributedwave Field Synthesis

In this paper we consider the problem of using a network of sensor and actuator nodes, to synthesize a given desired wave field, in a given medium we refer to mis problem as the distributed wave field synthesis problem (dubbed dWFS). We formulate this problem as one of minimization of a quadratic function, subject to linear (and very sparse) constraints. This formulation results from a finite-element approximation of the underlying wave equation, which constraints the values that a field and the source that induces that field can take. We present a complete solution for a 1D vibration, although our solution method cart be readily extended to any number of dimensions. Numerical simulations are included