Biomedical subjects

Karl Grosh

Publications and source records attributed to Karl Grosh.

6 recordsLinked to original sources

PubMed2003

Effect of current stimulus on in vivo cochlear mechanics.

In this paper, the influence of direct current stimulation on the acoustic impulse response of the basilar membrane (BM) is studied. A positive current applied in the scala vestibuli relative to a ground electrode in the scala tympani is found to enhance gain and increase the best frequency at a given location on the BM. An opposite effect is found for a negative current. Also, the amplitude of low-frequency cochlear microphonic at high sound levels is found to change with the concurrent application of direct current stimulus. BM vibrations in response to pure tone acoustic excitation are found to possess harmonics whose levels relative to the fundamental increase with the application of positive current and decrease with the application of negative current. A model for outer hair cell activity that couples changes in length and stiffness to transmembrane potential is used to interpret the results of these experiments and others in the literature. The importance of the in vivo mechanical and electrical loading is emphasized. Simulation results show the somewhat paradoxical finding that for outer hair cells under tension, hyperpolarization causes shortening of the cell length due to the dominance of voltage dependent stiffness changes.

Acoustic Stimulation↗

PubMed2002

Design of ultrasonic array elements for acoustic power considerations.

In sound-transmitting applications such as therapeutic ultrasound, the acoustic power at a particular operating frequency is a critical figure of merit for transducer/array design. A design methodology for enhancing the acoustic power radiated from fluid-loaded piezoelectric array elements at a fixed frequency is developed in this paper. A gradient-based optimization algorithm is integrated within the finite element framework to guide the determination of the two design variables, the piezoelectric element thickness and the matching layer thickness, to optimize the acoustic power output. A method for avoiding explicit remeshing in the optimization iteration is presented. Optimized designs are determined numerically, and the effectiveness of the design method is confirmed by experimental measurements. The validated numerical analysis also shows that conventional design strategies using one-dimensional transducer analysis and rule-of-thumb matching layer or protection layer sizing rules may not give the best design for array elements in acoustic power applications.

Acoustics↗

PubMed2002

Maximum likelihood estimation of structural wave components from noisy data.

In this paper, a general framework is developed for determining the underlying parameters of general signal models through the application of maximum likelihood estimation theory for functions whose variables separate. This method extends previous work in sinusoidal and exponential estimation to include models with other functional bases, such as exponential functions with nonconstant amplitudes and Bessel functions. Nonuniform spatial sampling is also possible with this technique. The maximum likelihood method is applied to the identification of wave components along one-dimensional structural elements. Results are given which demonstrate the viability and accuracy of the technique estimating exponential and Bessel function model parameters from noisy simulation data.

Journal Article↗

PubMed2002

A theoretical study of structural acoustic silencers for hydraulic systems.

Theoretical studies show that the introduction of an in-line structural acoustic silencer into a hydraulic system can achieve broadband quieting (i.e., high transmission loss). Strategies for using structural acoustic filters for simultaneously reducing reflection and transmission by tailoring the material properties are studied. A structural acoustic silencer consists of a flexible layer inserted into nominally rigid hydraulic piping. Transmission loss is achieved by two mechanisms--reflection of energy due to an impedance mismatch, and coupling of the incoming acoustic fluctuations to structural vibrations thereby allowing for the extraction of energy through losses in the structure. Structural acoustic finite element simulations are used to determine the transmission loss and evaluate designs. Results based on the interaction of orthotropic and isotropic plates with variable geometry, operating in heavy fluids like water and oil, are presented.

Acoustics↗

PubMed2002

Topology optimization of the kerf fillings in linear phased arrays for therapy.

Cross talk in ultrasonic arrays is an important problem that affects the array performance. For therapy arrays, cross talk decreases the acoustic power efficiency and array steering capabilities. Since arrays used for therapy are generally air-backed, structure-borne cross talk from the kerf fillings that connect the elements is predominant. In this paper, design strategies are developed to reduce the cross talk in linear phased arrays by optimizing the topology of kerf fillings. Two topology optimization schemes, an element-by-element design and layer-by-layer design, are developed. Sequential linear programming is used to solve the nonlinear optimization problem. Using an array subset technique as the basis for the design, an objective function based on maximizing the normal velocity response of the wet surface of an electrically driven element is shown to improve both the power output and steering of the array.

Acoustics↗

PubMedDate not supplied

In vivo micromechanical measurements of the organ of Corti in the basal cochlear turn.

Cochlear mechanical measurements of organ of Corti motion are generally accomplished in the apical or basal turn as in vivo or in vitro studies. In the apex it is possible to observe and measure tectorial membrane vibration as well as vibrations of structures such as the reticular lamina or the basilar membrane (BM). However, compared to the basal turn, cochlear amplification and nonlinearity are not strong in the apex. Basal turn studies have typically been limited to point location measurements of the BM but improved technology for laser interferometry is now making possible the spatial mapping of BM motion. The 'complexity' of BM motion in the radial direction (particularly the phase variation) is important to new models of cochlear wave amplification. In future work it may be possible to learn about vibration of structures within the organ of Corti.

Animals↗