Overview of Challa, V. R., Prasad, M. G., Shi, Y., and Fisher, F. T.’s 2008 Paper on a Vibration Energy Harvesting Device with Bidirectional Resonance Frequency Tunability

Overview of Challa, V. R., Prasad, M. G., Shi, Y., and Fisher, F. T.’s 2008 Paper on a Vibration Energy Harvesting Device with Bidirectional Resonance Frequency Tunability

Warmstarting the Constrained Optimal Filter Design Problem for Active Noise Control Systems in Conic Formulation

In practical active noise control (ANC) systems, constraints such as stability, need to be considered in the controller design process. The optimal control filters can be obtained by solving a constrained optimization problem, which requires a significant computational effort. Recently, a convex formulation in conic form was proposed for ANC applications which was shown to result in a computational time reduction by several orders. It is desirable to further improve its efficiency so that the optimal filter design process can be continuously repeated to achieve adaptive control for slow varying operating conditions. One potential way is to introduce a warmstart technique where the filter solution of a similar system or environment is used as the starting point of the optimization algorithm. However, the conic formulation should be solved by the interior-point method which, in general, is challenging for applying warm start techniques. In the current work, modifications are proposed to the original ANC filter design formulation so that the warmstart techniques can be applicable. The performance of warmstarting technique is investigated. Results show that an appropriate choice of warmstart strategy can significantly reduce the number of iterations required for solving the proposed conic formulation of ANC filter design problem

A Constrained Adaptive Active Noise Control Filter Design Method Via Online Convex Optimization

In practical active noise control (ANC) applications, various types of constraints may need to be satisfied, e.g., robust stability, disturbance enhancement, and filter output power constraint. Some adaptive filters such as leaky LMS have been developed to apply required constraints indirectly. However, when multiple constraints are required simultaneously, satisfactory noise performance is difficult to achieve by tuning only one leaky factor. Another filter design approach that may achieve better noise control performance is to solve a constrained optimization problem. But the computational complexity of solving such a constrained optimization problem for ANC applications is usually too high even for offline design. Recently, a convex optimization reformulation is proposed which significantly reduces the required computational effort in solving constrained optimization problems for active noise control applications. In the current work, a constrained adaptive ANC filter design method is proposed. The previously proposed convex formulation is improved so that it can be implemented in real-time. The optimal filter coefficients are then redesigned continuously using online convex optimization when the environment is time-varying

A Constrained Optimal Hear-Through Filter Design Approach for Earphones

Signal characteristics can be altered when sound from environment transmits through earphones to the ear canal. A hear-through filter is usually implemented in an earphone to create a more natural hearing experience. Hear-through filter is also important in augmented reality audio applications. In this paper, a constrained optimal hear-through filter design approach is proposed, where the hear-through filter is designed using a formulation similar to that for a constrained active noise control filter design. One advantage of such a filter design approach is that, compared with the commonly used direct plant response inversion method, the leakage sound around and through earphone will be attenuated in the proposed method, so that the comb-filtering effect is alleviated. Another advantage of the proposed method is that multiple practical constraints can be applied conveniently by formulating a constrained optimization problem and it can be solved efficiently. The proposed design approach can specify the desired delays of reproduced sound in each earphone channel, if a spatial sound impression is desired. The designed hear-through filter can be directly implemented in an active noise control system framework so that the requirement for additional electronic hardware and software components can be minimal for an active noise control earphone

Study on theCone Programming Reformulation of Active Noise Control Filter Design in the Frequency Domain

In the practice of active noise control, the control filter can be designed in either the time domain or the frequency domain. Compared with the former method category, it is more convenient to use frequency-domain methods to apply constraints such as stability, robustness, disturbance enhancement, input limit of loudspeakers, etc. Better noise reduction performance can usually be achieved by frequency-domain design as well. However, the computational complexity of designing a filter in the frequency domain is usually significant, especially for multichannel systems with multiple constraints. This is one of the challenges of using frequency-domain design in practical applications. In this paper, the traditional optimization problem used in frequency-domain filter design was modified and reformulated to a cone programming problem, where the inequality constraints were reformulated as second-order cones and positive semidefinite cones. Because of its convex nature, the global minimum solution to the problem can always be found. Another advantage of this cone programming reformulation is that algorithms with high computational efficiency can be used. It was demonstrated that, compared with using the traditional sequential quadratic programming method, the calculation is more efficient if the filter design problem is reformulated to cone programming and solved by the primal-dual interior-point method

Development and Application of Dual Form Conic Formulation of Multichannel Active Noise Control Filter Design Problem in Frequency Domain

Active noise control filter design methods can be categorized as time-domain or frequency-domain methods. When multiple frequency-dependent constraints need to be specified, such as the enhancement constraint, stability constraint, and robustness constraint, the optimal filter coefficients can be obtained more conveniently by solving a constrained optimization problem formulated using frequency-domain methods. However, the computational load for searching the global optimal solution is significantly high, if the number of channels, filter coefficients, or constraints is large. To improve computational efficiency, some previous work relaxed the traditional formulation to a convex problem, and then reformulated it to a cone programming problem. After this reformulation, efficient algorithms for cone programming problem, e.g., the primal-dual interior-point methods, can be applied to solve the filter design problem. However, some numerical issues may occur when solving the reformulated standard conic form directly. In this paper, the numerical instability issue for active noise control filter design problem is investigated. The original conic form was rearranged via dual formulation and different treatments of free variables are discussed. It is demonstrated that the proposed approach result is equivalent to the standard conic form but numerically more stable

A Sub-band Filter Design Approach for Sound Field Reproduction

The purpose of sound field reproduction is to use loudspeakers to produce desired sound at particular locations in a given environment, which has a wide range of applications such as virtual reality, etc. The computational load required to design and implement filters involved in sound reproduction systems can be significant, especially when the desired sound has rich information over a wide frequency band. To reduce the computational load, sub-band filtering approaches are usually used in sound reproduction systems. In the present work, an approach is proposed to design the sub-band filters used in sound reproduction systems in a more convenient way, where the filter design problem is formulated into a convex optimization problem. Detailed analysis has been conducted on how to specify the response characteristics of each sub-band and how different sub-band filters can be combined into one full band filter in the design and implementation of the system. Results also show that even if the sub-band filter structure is not necessary, this approach can also be applied to reduce the computational load in designing inverse filters when the plant responses involve relatively large differences in delay time among different frequency bands

Singular Vector Filtering Method for Disturbance Enhancement Mitigation in Active Noise Control Systems

In multichannel active noise control systems, when reference signals are correlated, the disturbance enhancement phenomenon is likely to occur, i.e., the resulting sound is enhanced instead of being reduced in some frequency bands, if the filter is designed to minimize the total energy for all frequencies. In previous works, a truncated singular value decomposition method was applied to the system autocorrelation matrix to mitigate the disturbance enhancement due to the correlation of reference signals. Some small singular values and the associated singular vectors are removed, if they are responsible for unwanted disturbance enhancement in some frequency bands. However, some of these removed singular vectors may still contribute to noise control performance in other frequency bands, thus a direct truncation will degrade the noise control performance. In the present work, through an additional filtering process, the set of singular vectors that cause the disturbance enhancement are replaced by a set of new singular vectors whose frequency responses are attenuated in the frequency band where disturbance enhancement occurs, while the frequency responses in other frequency bands are unchanged. Compared with truncation, the proposed method can maintain the performance in the noise reduction bands, while mitigating the influence in disturbance enhancement bands

Parkinson’s Disease Motor Subtypes Show Different Responses to Long-Term Subthalamic Nucleus Stimulation

Background and purpose: Subthalamic nucleus deep brain stimulation (STN DBS) is well established for the treatment of advanced Parkinson’s disease (PD), substantially improving motor symptoms, quality of life, and reducing the long-term need for dopaminergic medication. However, whether chronic STN DBS produces different effects on PD motor subtypes is unknown. This retrospective study aimed to evaluate the long-term effects of STN DBS on the PD motor subtypes.Methods: Eighty patients undergoing STN DBS were included. The Unified Parkinson’s Disease Rating Scale (UPDRS) analysis was performed in “On” and “Off” medication/“On” and “Off” stimulation conditions. The patients were classified as akinetic-rigid type (ART), tremor-dominant type (TDT), and mixed type (MT) based on the preoperative UPDRS III subscores in the “Off” medication state. Preoperative and postoperative comparisons were performed.Results: After 4.9 years, STN DBS produced significant improvement in the UPDRS III total scores and subscores of tremor, rigidity, and bradykinesia in the “Off” medication state in the ART group, less improvement in the MT group, and the least improvement in the TDT group. The UPDRS II and III total scores and other subscores failed to improve during the “On” medication state. However, all groups improved substantially, and the improvement in tremor was sustained for both the “On” and “Off” medication states after years. Long-term STN DBS failed to improve swallowing and speech in all the subtypes.Conclusion: The data confirms that PD is heterogeneous. Long-term STN DBS produced the best effects on bradykinesia/rigidity in the “Off” medication state and on tremor in the “On” and “Off” medication states. There were differences in the response by each group, but some of the differences could be explained by the fact that more severe symptoms at baseline tend to have greater improvement. The findings support the idea that ART mainly involves the basal ganglia-thalamo-cortical pathway, whereas TDT involves a different circuit, likely the cerebellar-thalamo-cortical pathway