Quick test of ultrasonic transducer arrays radiating in air using B-mode-images.

This paper describes a statistical procedure working on ultrasound B-mode images that were recorded with the transducer array radiating in air. From the digital image data, a gray value profile was generated using a computer program. A statistical procedure was developed to examine if there are significant deviations from the mean. They occur, for example, when single piezoelements are severely damaged or completely out of function. The entire technique was tested using an ultrasonic imaging system (SonixTouch, Ultrasonix Medical Corporation, Richmond, Canada) in which individual elements or groups of elements can be turned off via firmware. A failure of as large as two out of 128 elements was detectable.

Modal parameters of two incomplete and complete guitars differing in the bracing pattern of the soundboard.

Similarities and differences in vibrational behavior of two guitars having a symmetric Torres bracing pattern and an asymmetric pattern forming a lattice on a soundboard are investigated by means of the modal analysis technique and laser Doppler vibrometry (LDV) measurements. Instruments are investigated before and after a bridge and strings assembling (i.e., they are incomplete or complete). The bracing pattern and the absence/presence of the bridge and strings have some effect on modal frequencies and mode shapes. The bracing pattern does not affect the sequence of at least first three low frequency mode shapes of incomplete/complete instruments but affects their modal frequencies. Depending on frequency, the bridge behaves either as a rigid or a flexible structure.

Mechanical and optical investigation of dynamic behavior of violins at modal frequencies.

Two main aims of our investigation are to show differences in natural vibrations between two violins that differ in the thickness of the back plate and to determine whether they are linear systems. Two experiments were performed on the top and back plates. The first experiment was a mechanical modal analysis in a version with a fixed response point. In the second experiment optical measurements of the plate's velocities in modal frequencies obtained from the first experiment were performed by use of laser Doppler vibrometry. The second experiment was a simplified modal analysis experiment with a fixed excitation point. Changes in the thickness of the back plate caused changes in certain modal frequencies of both plates. However, no important differences in mode shapes were found in both experiments. Thus, violins can be treated as linear systems but with great care.