Papers by Daniel Noreland
arXiv (Cornell University), Mar 14, 2024
The compression driver, the standard sound source for midrange acoustic horns, contains a cylindr... more The compression driver, the standard sound source for midrange acoustic horns, contains a cylindrical compression chamber connected to the horn throat through a system of channels known as a phase plug. The main challenge in the design of the phase plug is to avoid resonance and interference phenomena. The complexity of these phenomena makes it difficult to carry out this design task manually, particularly when the phase-plug channels are radially oriented. Therefore, we employ an algorithmic technique that combines numerical solutions of the governing equations with a gradient-based optimization algorithm that can deform the walls of the phase plug. A particular modeling challenge here is that viscothermal losses cannot be ignored, due to narrow chambers and slits in the device. Fortunately, a recently developed, accurate, but computationally inexpensive boundary-layer model is applicable. We use this model, a level-set geometry description, and the Cut Finite Element technique to avoid mesh changes when the geometry is modified by the optimization algorithm. Moreover, the shape calculus needed to compute derivatives for the optimization algorithm is carried out in the fully discrete case. Applying these techniques, the algorithm was able to successfully design the shape of a set of radially-directed phase plugs so that the final frequency response surprisingly closely matches the ideal response, derived by a lumped circuit model where wave interference effects are not accounted for. This result may serve to resuscitate the radial phase plug design, rarely used in today's commercial compression drivers.
Scientific Reports, Nov 30, 2023
Using material distribution-based topology optimization, we optimize the bandpass design of a lou... more Using material distribution-based topology optimization, we optimize the bandpass design of a loudspeaker cabinet targeting low frequencies. The objective is to maximize the loudspeaker's output power for a single frequency as well as a range of frequencies. To model the loudspeaker's performance, we combine a linear electromechanical transducer model with a computationally efficient hybrid 2D-3D model for sound propagation. The adjoint variable approach computes the gradients of the objective function with respect to the design variables, and the Method of Moving Asymptotes (MMA) solves the topology optimization problem. To manage intermediate values of the material indicator function, a quadratic penalty is added to the objective function, and a non-linear filter is used to obtain a mesh independent design. By carefully selecting the target frequency range, we can guide the optimization algorithm to successfully generate a loudspeaker design with the required bandpass character. To the best of our knowledge, this study constitutes the first successful attempt to design the interior structure of a loudspeaker cabinet using topology optimization. Loudspeaker systems 1,2 are designed to reproduce sound within the range of human hearing. However, it is difficult to design a single loudspeaker that can efficiently reproduce the whole frequency range. Therefore, separate loudspeakers are often used to cover different parts of the sound spectrum. The loudspeaker aimed at the lowest frequencies is referred to as a subwoofer. Public address systems, movie theaters, home theaters, and car audio systems all use subwoofers. Here, we optimize a so-called bandpass 3,4 design of a subwoofer loudspeaker, in which a transducer is mounted in a sealed back chamber and radiates into a ported front chamber. The back chamber serves as a high pass filter, while the front chamber and port serve as a low pass filter, jointly forming an acoustic bandpass filter. The high pass filter restricts the movement of the transducer's membrane and protects it from exceeding excursion limits. The low pass filter hampers the transmission of high frequencies, including spurious ones caused by distortion in the transducer, an effect not possible to achieve with mere signal processing at the source. This type of loudspeaker can be designed for a narrow frequency band with high efficiency or a wider frequency band that also includes the low frequencies at the expense of efficiency. In this study, we use a material distribution based topology optimization method to design the loudspeaker cabinet. This method seeks to the optimal placement of material inside a design domain. This domain is divided into pixels (or voxels in 3D), and an optimization algorithm finds for each pixel whether or not it should be occupied by material to extremize an objective function. Initial work by Bendsøe and Kikuchi 5 laid the foundation for material distribution based topology optimization. Bendsøe and Sigmund 6 comprehensively summarize early research on topology optimization techniques and their applications. This concept has been successfully employed for optimizing modern automotive 7 and aircraft structures . Moreover, the method has also proven successful for other applications, such as fluid flow 10 , heat transfer 11 , optics 12 , electromagnetics , and acoustics ; however, techniques for design optimization are still maturing in these fields. The methods in acoustics focus on optimizing individual components, such as loudspeaker horns 15 and sound mufflers , under idealized conditions. However, real-life acoustic systems consist of many components that interact and affect each other's performance. Separate optimization of each system component under idealized conditions will most likely yield a sub-optimal design. In recent studies, topology optimization has been used to optimize phase plugs 20 , waveguides 21 , as well as material properties of a transducer 22 . In this study, we do not aim to optimize a transducer or elements of loudspeaker. Instead, we employ topology optimization to optimize the loudspeaker cabinet by using a model that takes into account the transducer's effects within the linear regime.
Preface. When H. Bouasse published his Instrumentsà Vent in two volumes in 1929-30, he set the st... more Preface. When H. Bouasse published his Instrumentsà Vent in two volumes in 1929-30, he set the starting point for what can be regarded as modern research on musical acoustics. Some 40 years later, the stock of published papers could be counted in their hundreds. However, it is only during the last two or three decades that our physical understanding, in combination with the development of computers, has made it possible to analyse wind instruments with the precision necessary, not only to explain the basic principles of their function, but also to be of practical use for instrument makers. This thesis deals with numerical methods and procedures for the analysis and design of acoustic horns of the kind found in brass instruments. The same models are applicable also to loudspeaker horns, with which one part of the thesis is concerned. Although the properties and merits of different systems for sound reproduction, such as loudspeakers, are sometimes debated lively, it is at least possible to define an ideal system, in the sense that the sound at the position of the listener's ears should be in as good agreement as possible with the sound at the position of the microphone in the concert hall during the recording. When speaking about optimisation of musical instruments, one has to be much more careful. The instruments of the modern western orchestra are the result of centuries of evolution, where tradition, musical ideals, performance techniques, and acoustical considerations have been inextricably intertwined with each other. Our judgement about a certain instrument is dependent on a preconception about how the instrument should sound [13], and this preconception may vary between individuals, different musical settings and different times. It is important to bear in mind that the term "quality" for the sound of a musical instrument lacks sense, unless one also places the instrument in its musical context. Nevertheless, research on musical acoustics is of more than constructional interest. Firstly, it gives the possibility to quantify the differences between instruments, and to answer the question why one instrument is considered to be better than another. Secondly, once we have a clear-cut idea about what we expect from an instrument, we can apply the mathematical tools in order to make instruments that comply with our standards as far as possible.
Acoustic horns are used in musical instruments and loudspeakers in order to provide an impedance ... more Acoustic horns are used in musical instruments and loudspeakers in order to provide an impedance match between an acoustic source and the surrounding air. The aim of this study is to develop numerical tools for the analysis and optimisation of such horns, with respect to their input impedance spectra. Important effects such as visco-thermal damping and modal conversion are shown to be localised to different parts of a typical brass instrument. This makes it possible to construct hybrid methods that apply different numerical techniques in different parts of the instrument. Narrow and slowly flaring parts are modelled using a one-dimensional transmission line analogy, and the rapidly flaring bell is modelled using a two-dimensional finite-difference method. The connection between the different regions is done by the aid of impedance boundary conditions. The use of such boundary conditions is investigated with respect to the required number of degrees of freedom. Numerical shape optimisation is employed in order to design horns with desired impedance characteristics throughout a design frequency band. A loudspeaker horn is optimised with respect to its sound power output, and a brass instrument is optimised with respect to its intonation. The horns are modelled using the finite-element method and a transmission line analogy. In order to achieve rapid convergence of the optimisation, gradient based minimisation algorithms are used. A prerequisite for success is the ability to accurately and inexpensively compute the gradient of the objective function. The gradient for the finite-element method is computed by an adjoint equation technique, whereas for the transmission line analogy, it is derived by formal differentiation of the model. In order to find smooth solutions, a smoothing technique is used, where optimisation is done with respect to the right hand side of a Poisson type equation.
Costing models for roundwood transports have been developed by NB Nord co-operation with Road and... more Costing models for roundwood transports have been developed by NB Nord co-operation with Road and Transport group, coordinated by Pirjo Venäläinen of Metsäteho, and consisting of transport researchers from all member institutes including: Dag Fjeld, NIBIO, Kari Väätäinen, Luke, Henrik von Hofsten and Daniel Noreland, Skogforsk, Ingeborg Callesen, IGN KU and Andis Lazdins, Silava. In general, the NB Nord costing models follow classical cost assessments for material transportations with specialities of each transport mode. Models are aimed at calculating the operating costs of roundwood transports either on a yearly basis as for road and rail transports or on a voyage basis as for sea transports. In addition, models can be used for calculating performance indicators of transports such as annual working hours, loads, transported tons of timber, transport distances etc. As an output, key performance indicators for costing include costs per metric ton, per km, per tkm, per load, per hour and per year. The models enable sensitivity analysis and direct comparison of transport costs between e.g. alternative supply chains, transport modes and countries of interest. “A common Nordic-Baltic costing framework for road, rail and sea transport of roundwood” -handbook guides using the costing models and it is available at https://hdl.handle.net/11250/2723839</a
This paper treats the use of numerically computed impedance boundary conditions for acoustic simu... more This paper treats the use of numerically computed impedance boundary conditions for acoustic simulations. Such boundary conditions may be used to combine different methods on different parts of the computational domain. Impedance boundary conditions may be computed for each subproblem independently of each other. In order to develop insight into this approach, wave propagation in a rectangular waveguide with a step discontinuity is studied.
Acta Acustica United With Acustica, 2002
ABSTRACT A hybrid method for computing the impedance of an axisymmetric acoustic horn is presente... more ABSTRACT A hybrid method for computing the impedance of an axisymmetric acoustic horn is presented. The slowly flaring part of the horn is analyzed with a transmission-line model, whereas the rapidly flaring mouth and the space surrounding the horn are modeled with a two-dimensional finite difference time-domain method. In this way, the effect of higher modes that are excited near the mouth of the horn is considered. The computed impedance spectrum shows good agreement with measured data.
Journal of the Acoustical Society of America, 2010
This paper presents how the shape of a brass instrument can be optimized with respect to its into... more This paper presents how the shape of a brass instrument can be optimized with respect to its intonation properties. The instrument is modeled using a hybrid method between a lossy one-dimensional transmission line analogy for the slowly flaring part of the instrument, and a two-dimensional finite element model for the rapidly flaring part. The optimization employs gradient-based algorithms, and allows for a large number of design variables. Through the use of an appropriate choice of design variables, the algorithm is capable of rapidly finding horn profiles that are optimal subject to various geometric constraints, such as increasing or convex bell flares. It is found that under a convexity constraint, brass wind bells that are optimal with respect to an intonation condition can be constructed of piecewise conical sections.
This paper presents how the shape of a brass instrument can be optimised with respect to its into... more This paper presents how the shape of a brass instrument can be optimised with respect to its intonation and impedance peak magnitudes. The instrument is modelled using a one-dimensional transmission line analogy with truncated cones. The optimisation employs the Levenberg-Marquardt method, with the gradient of the objective function obtained by analytic manipulation. Through the use of an appropriate choice of design variables, the optimisation is capable of rapidly finding smooth horn profiles.
IEEE journal of electromagnetics, RF and microwaves in medicine and biology, Dec 1, 2017
This is the accepted version of a paper published in. This paper has been peer-reviewed but does ... more This is the accepted version of a paper published in. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.
Recently, the human fat tissue has been proposed as a microwave channel for intra-body sensor app... more Recently, the human fat tissue has been proposed as a microwave channel for intra-body sensor applications. In this work, we assess how disturbances can prevent reliable microwave propagation through the fat channel. Perturbants of different sizes are considered. The simulation and experimental results show that efficient communication through the fat channel is possible even in the presence of perturbants such as embedded muscle layers and blood vessels. We show that the communication channel is not affected by perturbants that are smaller than 15 mm cube.
Healthcare technology letters, May 23, 2017
The human body can act as a medium for the transmission of electromagnetic waves in the wireless ... more The human body can act as a medium for the transmission of electromagnetic waves in the wireless body sensor networks context. However, there are transmission losses in biological tissues due to the presence of water and salts. This Letter focuses on lateral intra-body microwave communication through different biological tissue layers and demonstrates the effect of the tissue thicknesses by comparing signal coupling in the channel. For this work, the authors utilise the R-band frequencies since it overlaps the industrial, scientific and medical radio (ISM) band. The channel model in human tissues is proposed based on electromagnetic simulations, validated using equivalent phantom and ex-vivo measurements. The phantom and ex-vivo measurements are compared with simulation modelling. The results show that electromagnetic communication is feasible in the adipose tissue layer with a low attenuation of ∼2 dB per 20 mm for phantom measurements and 4 dB per 20 mm for ex-vivo measurements at 2 GHz. Since the dielectric losses of human adipose tissues are almost half of ex-vivo tissue, an attenuation of around 3 dB per 20 mm is expected. The results show that human adipose tissue can be used as an intra-body communication channel.
Scientific Reports, Jan 8, 2021
A subwoofer generates the lowest frequency range in loudspeaker systems. Subwoofers are used in a... more A subwoofer generates the lowest frequency range in loudspeaker systems. Subwoofers are used in audio systems for live concerts, movie theatres, home theatres, gaming consoles, cars, etc. During the last decades, numerical simulations have emerged as a cost-and time-efficient complement to traditional experiments in the design process of different products. The aim of this study is to reduce the computational time of simulating the average response for a given subwoofer design. To this end, we propose a hybrid 2D-3D model that reduces the computational time significantly compared to a full 3D model. The hybrid model describes the interaction between different subwoofer components as interacting modules whose acoustic properties can partly be pre-computed. This allows us to efficiently compute the performance of different subwoofer design layouts. The results of the hybrid model are validated against both a lumped element model and a full 3D model over a frequency band of interest. The hybrid model is found to be both accurate and computationally efficient.
Publisher Summary Shape optimization is increasingly being used as a tool to optimize structural ... more Publisher Summary Shape optimization is increasingly being used as a tool to optimize structural or aerodynamic performances. This chapter applies numerical shape optimization to alter the transmission properties of an acoustic horn. A finite-element approximation of the Helmholtz equation models wave propagations, and a quasi-Newton algorithm can solve the optimization problem. The adjoint-equation approach provides gradients, while a smoothing technique enforces smooth design updates. Single-frequency optimization yields convex horns narrowly optimized only for design frequency. Multiple-frequency optimization yields horns with a slightly wavy shape and with good transmission properties throughout the considered frequency band. A convexity constraint in the optimization inhibits waviness and produces a horn with smooth comers. The constraint causes only marginal performance degradation at the design frequencies but yields improved performance in a region above the design frequencies.
In this paper, we present an approach for communication through human body tissue in the R-band f... more In this paper, we present an approach for communication through human body tissue in the R-band frequency range. This study examines the ranges of microwave frequencies suitable for intra-body communication. The human body tissues are characterized with respect to their transmission properties using simulation modeling and phantom measurements. The variations in signal coupling with respect to different tissue thicknesses are studied. The simulation and phantom measurement results show that electromagnetic communication in the fat layer is viable with attenuation of approximately 2 dB per 20 mm.
Scientific Reports, Mar 23, 2017
To maximize the matching between a coaxial cable and rectangular waveguides, we present a computa... more To maximize the matching between a coaxial cable and rectangular waveguides, we present a computational topology optimisation approach that decides for each point in a given domain whether to hold a good conductor or a good dielectric. The conductivity is determined by a gradient-based optimisation method that relies on finite-difference time-domain solutions to the 3D Maxwell's equations. Unlike previously reported results in the literature for this kind of problems, our design algorithm can efficiently handle tens of thousands of design variables that can allow novel conceptual waveguide designs. We demonstrate the effectiveness of the approach by presenting optimised transitions with reflection coefficients lower than −15 dB over more than a 60% bandwidth, both for right-angle and end-launcher configurations. The performance of the proposed transitions is crossverified with a commercial software, and one design case is validated experimentally.
IEEE Transactions on Antennas and Propagation, Sep 1, 2015
We present an approach to design from scratch planar microwave antennas for the purpose of ultra-... more We present an approach to design from scratch planar microwave antennas for the purpose of ultra-wideband near-field sensing. Up to about 120,000 design variables associated with square grids on planar substrates are subject to design, and a numerical optimization algorithm decides, after around 200 iterations, for each edge in the grid whether it should consist of metal or a dielectric. The antenna layouts produced with this approach show ultra-wideband impedance matching properties and near-field coupling coefficients that are flat over a much wider frequency range than a standard ultrawideband antenna. The properties of the optimized antennas are successfully cross-verified with a commercial software and, for one of the designs, also validated experimentally. We demonstrate that an antenna optimized in this way shows a high sensitivity when used for near-field detection of a phantom with dielectric properties representative of muscle tissue.
This thesis introduces a topology optimization approach to design, from scratch, efficient microw... more This thesis introduces a topology optimization approach to design, from scratch, efficient microwave devices, such as antennas and waveguide transitions. The design of these devices is formulated as a general optimization problem that aims to build the whole layout of the device in order to extremize a chosen objective function. The objective function quantifies some required performance and is evaluated using numerical solutions to the 3D~Maxwell's equations by the finite-difference time-domain (FDTD) method. The design variables are the local conductivity at each Yee~edge in a given design domain, and a gradient-based optimization method is used to solve the optimization problem. In all design problems, objective function gradients are computed based on solutions to adjoint-field problems, which are also FDTD discretization of Maxwell's equations but solved with different source excitations. For any number of design variables, the computation of the objective function gradient requires one solution to the original field problem and one solution to the associated adjoint-field problem. The optimization problem is solved iteratively using the globally convergent Method of Moving Asymptotes (GCMMA).By the proposed approach, various design problems, including tens of thousands of design variables, are formulated and solved in a few hundred iterations. Examples of solved design problems are the design of wideband antennas, dual-band microstrip antennas, wideband directive antennas, and wideband coaxial-to-waveguide transitions. The fact that the proposed approach allows a fine-grained control over the whole layout of such devices results in novel devices with favourable performance. The optimization results are successfully verified with a commercial software package. Moreover, some devices are fabricated and their performance is successfully validated by experiments.
Journal of the Acoustical Society of America, Oct 1, 2020
The compression driver, used to feed midrange horns, consists of a compression chamber whose outl... more The compression driver, used to feed midrange horns, consists of a compression chamber whose outlets are connected to the horn throat through a phase plug. The main challenge in the design of the phase plug is to avoid resonance and interference phenomena. The complexity of these phenomena makes it difficult to accomplish this design task manually. Therefore, we employ an algorithmic technique that combines numerical solutions of the governing equations with a gradient-based optimization algorithm that almost arbitrarily can deform the walls of the phase plug. A particular modeling challenge here is that visco–thermal losses cannot be ignored, due to the presence of narrow chambers and slits in the driver. Fortunately, a recent accurate but computationally inexpensive boundary-layer model is applicable and is here successfully used within the optimization loop. We use this model together with the so-called Cut Finite Element technique to avoid mesh changes when the geometry is modified by the optimization algorithm. Applying these techniques, the algorithm was able to successfully design the shape of a set of radially-directed phase plugs so that the final frequency response closely matches an ideal response, that is, one that is obtained by a lumped circuit model, ignoring wave effects.
We have developed and investigated a 1D-model for the interaction between a stack of wood and an ... more We have developed and investigated a 1D-model for the interaction between a stack of wood and an impinging electromagnetic field. Maxwell's equations are used to model the electromagnetic interaction and each layer in a stack of boards has been modeled as a homogenous lossy dielectric slab. The main reason for developing this model has been to investigate the possibility of measuring the moisture content of wood inside a drying kiln using electromagnetic waves. Our investigations show that it is in principle possible to measure the moisture content, since the electromagnetic field is sensitive to changes in the moisture content of the wood. We also show that it might be possible to measure the average moisture content, without detailed knowledge of the distribution of moisture content between different boards.
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Papers by Daniel Noreland