Piotr Pruchnicki

Theory of piezoelectric axisymmetric bimorph

Abstract A theory of a piezoelectric axisymmetric bimorph is presented in this paper. Bimorphs are often used as electroacoustic transducers, but their use is much wider. A piezoelectic bimorph consists of two or more layers which are placed asymmetrically to the middle surface of the structure. When voltage is supplied to the bimorph, a bending moment is produced which causes transversal deflections of the structure. Average elastic parameters are calculated. Equations for the calculation of bending moments and stretching forces produced by voltage are derived. When the bimorph is a shell of revolution with any shape of meridian, the derived equations can be solved by numerical methods. The finite-element method (FEM) is applied to solve this problem. The bimorph can also be used as a sensor. A theory of such a sensor is also presented. The results obtained by means of the described theory and numerical methods have been verified experimentally or by comparing them with results obtained analytically for a simple structure. It has been proved theoretically that the electric signal produced by a circular transducer clamped on the outer rim of a piezoelectric disc is equal to zero.

Imaging results of multi-modal ultrasound computerized tomography system designed for breast diagnosis

Nowadays, in the era of common computerization, transmission and reflection methods are intensively developed in addition to improving classical ultrasound methods (US) for imaging of tissue structure, in particular ultrasound transmission tomography UTT (analogous to computed tomography CT which uses X-rays) and reflection tomography URT (based on the synthetic aperture method used in radar imaging techniques). This paper presents and analyses the results of ultrasound transmission tomography imaging of the internal structure of the female breast biopsy phantom CIRS Model 052A and the results of the ultrasound reflection tomography imaging of a wire sample. Imaging was performed using a multi-modal ultrasound computerized tomography system developed with the participation of a private investor. The results were compared with the results of imaging obtained using dual energy CT, MR mammography and conventional US method. The obtained results indicate that the developed UTT and URT methods, after the acceleration of the scanning process, thus enabling in vivo examination, may be successfully used for detection and detailed characterization of breast lesions in women.

The effect of crosstalk in a circular transducer array on ultrasound transmission tomography of breast

Various types of undesirable crosstalk can occur in ultrasonic arrays consisting of a number of elementary piezoelectric transducers. Crosstalk is a result of deficiency in electrical or mechanical isolation between array elements. It is a function of proximity between piezoelectric transducers of the array or between connections. Small piezoceramic transducers tightly located inside of a circle (cylinder or sphere in 3-D systems) are mostly used for in vivo ultrasound tomography imaging of breast tissue. This means that proper switching of transducers makes it possible to quickly acquire tomographic transmission and reflection data for all directions around the object. A problem with such arrangements is the occurrence of crosstalk, which introduce specific errors to measurement data. Transmission and reflection tomographic images reconstructed based on ultrasonic measurements with crosstalk are distorted in a characteristic way. This work analyzes the effect of crosstalk in a circular transducer array on ultrasound transmission tomography imaging—especially, when used for examination of breast tissue.

Breast Ultrasound Tomography: Preliminary In Vivo Results

The paper presents the preliminary results of examinations of biological structures and healthy breast tissue in vivo obtained with the developed ultrasound tomography model. This device uses an innovative combination of ultrasound transmission tomography (UTT) and ultrasound reflection tomography (URT) which enable to obtain three-dimensional images in the same way as in the classical computer tomography (CT). The huge advantage of these methods is not exposing the patient to ionizing radiation. Compared to conventional breast ultrasonic echography (US), UTT and URT methods enable to acquire a much larger amount of information whose clinical significance has not been well documented yet. Based on the preliminary results, it is anticipated that the ultrasound tomography may contribute to the creation of a new standard of diagnosis and treatment of breast cancer. Currently, a Polish manufacturer of ultrasound scanners aims at getting an ultrasonic tomography device for examining women’s breasts to market.

Silent Speech Recognition by Surface Electromyography

For some time, new methods based on a different than acoustic signal analysis are used for speech recognition. The purpose of nonacoustic signals is to allow silent communi‐ cation. One of these methods based on the electromyography signal is generated by the human speech articulation system. This article presents a device for electromyographic (EMG) signal acquisition and the first measurements from its use.

Breast Phantom Imaging Results from an Ultrasound Computer Tomography Research System

Today, in the age of computerization, experts not only strive to perfect methods of ultrasonographic (US) imaging of tissue structure, but also intensively develop transmission methods, focusing especially on ultrasound transmission tomography (UTT) (analogous to X-ray computed tomography - CT) and ultrasound reflection tomography (URT) based on synthetic aperture method used in radar imaging. The following paper presents and analyses the results of ultrasound transmission tomography of the internal structure of a biopsy CIRS Model 052A breast phantom. The imaging was performed with an internally designed ultrasound computer tomography research system. The obtained results were compared to the imaging results from dual energy CT, MR mammography and traditional US.

System for High Speed Measurement of Head-Related Transfer Function

Recently surround-sound systems have become popular. The effect of “surrounding“ the listener in sound is achieved by employing acoustic phenomena which influence localizing the source of the sound. Similarly to stereophony system the time, volume and phase interrelations in signals coming from each sound source are taken into account. Additionally the influence of the acoustic system created by the pinna, head and torso on the frequency characteristic of the sound is taken into consideration. This influence is described by the Head-Related Transfer Function (HRTF). The knowledge of the human physical body characteristics’ influence on the perception of the sound source location in space is being more and more frequently applied to building sound systems.

2-D directional ultrasonic passive matrix of 512 elementary transducers for projection imaging of biological structures

The following paper presents an idea of minimising the number of connections of individual piezoelectric transducers in a row-column multielement passive matrix system used for imaging of biological media structure by means of ultrasonic projection method. Elementary transducers of a passive matrix are connected to one common electrode in rows and to another common electrode in columns. There are two groups of switches in this type of matrix, one for a selected active column and the other for a selected active row. When the transducer situated at the point of intersection of the selected row and column is activated, the activating signal in the passive matrix can travel through inactive transducers to other column and row lines despite their switches being opened (crosstalk). This phenomenon is advantageous in the context of achieving a directional beam of ultrasonic wave and reducing matrix input impedance.

Determination of structure of the NARMAX model for dynamic loudspeaker using the orthogonal algorithm

NARMAX is a general method for modeling of nonlinear systems. In the paper, an application of this method for modeling of nonlinearities in dynamic loudspeakers is presented. In most cases, a polynomial representation of the NARMAX model causes an ill‐conditioned equation system which indicates that the use of orthogonalization is necessary to solve the system. The high number of coefficients is the main disadvantage of the NARMAX method, and it results in an erroneous model, and an algorithm for identification of coefficients that is noneffective. A modification of the orthogonal algorithm (classical Gram–Schmidt) is presented. It is based on the premise that the coefficient providing the highest error reduction ratio is chosen in every step of the algorithm. The creation of the model stops when the given accuracy is achieved. This way leads to the choice of only the most significant coefficients. The work and effectiveness of this modified algorithm for systems with given nonlinearities at different lev...