Experimental findings of non invasive in-vivo monitoring are essential to study the diversity and evolution of
musculoskeletal kinematics. In this paper, results obtained from the uni-axial monitoring of the quasi-static
dynamics of the biceps muscle-belly are reported. Monitoring of the belly diameter is based on a custom
developed ultrasonic caliper combined with the synchronously recorded applied external force and joint angle
variations detected with a custom build ultrasonic force sensor and a resistive angle decoder respectively. The
monitored muscle action includes the processes of active muscle contraction and relaxation in a closed path
starting with an initial isotonic contraction followed by eccentric (spring like) stretching. The technology
applied here allows for observations of those processes and registration of their paths in the length-forceangle
parameter space. That way of presentation reveals that at some conditions the closed-loop human cycles
follow in close approximation characteristic lines of well identifiable elementary processes. The presentation
of these processes in the length-force parameters space allows for discussion of the mechanical energy
expenditure during different muscle actions. Comparative studies of identical closed-loop muscle actions and
the joint angle-force-length relationships of the muscle-tendon complex are presented. This synchronous
monitoring also allows quantifying the joint torques and positions with high accuracy for living person.
Based on the lattice dynamics approach the dependence of the time-of-flight (TOF) on stress has been modeled for
transversal polarized acoustic waves. The relevant dispersion relation is derived from the appropriate mass-spring model
together with the dependencies on the restoring forces including the effect of externally applied stress. The lattice
dynamics approach can also be interpreted as a discrete and strictly periodic lumped circuit. In that case the modeling
represents a finite element approach. In both cases the properties relevant for wavelengths large with respect to the
periodic structure can be derived from the respective limit relating also to low frequencies. The model representing a
linear chain with stiffness to shear and additional stiffness introduced by extensional stress is presented and compared to
existing models, which so far represent each only one of the effects treated here in combination. For a string this effect is
well known from musical instruments. The counteracting effects are discussed and compared to experimental results.
Acoustic bulk waves were excited by local electric field probe in an anisotropic piezo-electric crystal Lithium Niobate
(X-cut). A narrow pulse with a width of 25 ns was used for excitation to obtain wide frequency content in the Fourier
domain. A wide spectrum ensures metamorphosis of bulk waves into Lamb waves for scan lengths comparable to the
involved wavelengths. The low frequency content experiences multiple reflections from the two surfaces of the plate and
disperses along the propagation direction. Acoustic bulk wave's evolution and transformation to Lamb waves are
illustrated and explained with the aid of the Lamb wave dispersion phenomenon. The holographic images in the Fourier
domain exemplify the metamorphosis of waves during propagation following the excitation at an approximate point
source.
In this work, the Foucault knife-edge test, which has traditionally been known as the classic test for optical imaging
devices, is used to characterize an acoustic lens for operation at 1.2 GHz. A confocal laser scanning microscope (CLSM)
was used as the illumination and detection device utilizing its pinhole instead of the classical knife edge that is normally
employed in the Foucault test. Information about the geometrical characteristics, such as the half opening angle of the
acoustic lens, were determined as well as the quality of the calotte of the lens used for focusing. The smallest focal spot
size that could be achieved with the examined lens employed as a spherical reflector was found to be about 1 μm. By
comparison to the idealized resolution a degradation of about a factor of 2 can be deduced. This limits the actual quality
of the acoustic focus.
Excitation and detection of acoustic waves in piezoelectric materials relies on a gradient in the piezoelectric properties
respectively a gradient in the electric field. The relatively weak coupling is usually enhanced for established practical
applications by mechanical, geometrical and electrical resonances. The geometrical resonances, as present for the
commonly used inter digital transducer (IDT), lead to limitations concerning the spatial and temporal resolution that can
be achieved with such devices. Concentration of the electric field by geometrical means and point like conversion at the surface of piezoelectric materials is the basis for the novel scheme presented here. The principles of the developed method together with instrumental details are discussed. Applications involving two dimensional imaging with time resolved recording for each pixel of the image for phase and magnitude of the transfer and echo signals are presented.
Due to the dependence on a limited amount of parameters, the dispersion relations of Lamb waves can be presented in a generalized way. This is exemplified for the different established typical representations. Special attention is given to the representation of the momentum on energy, which is well suited to discuss basic features since energy as well as momentum is the properties which are strictly conserved in loss free homogeneous materials. Representations involving the phase and group velocity are discussed. Features related to level crossing of interacting modes and relations to basic mechanical properties especially relevant to Lamb waves are included in the presentation and discussion.
Conducting micro-spheres approximating point probes have been employed to piezoelectrically excite and detect
ultrasonic wave packages in anisotropic single crystals. Imaging based on the detection of magnitude and phase is
performed in transmission. The experimental data can be used for the determination of the elastic constants of the
material. Here we compare this approach with imaging using conventional ultrasonic lenses and water as a coupling
fluid. The large bandwidth and the absence of internal lens echoes in the Coulomb excitation and detection scheme
permit unperturbed monitoring of multiple echoes in plane-parallel samples and the detailed investigation of mode
conversion processes of longitudinal and transverse waves at the surfaces of the crystal. Due to differences in the
coupling between the probes and the ultrasound in the sample, excitation of ultrasound by an acoustic lens or an
electrical point contact, respectively, result in noticeably different phonon focusing patterns. This is illustrated for
lithium niobate single crystals.
Narrowband excitation at 86 MHz with vector detection and wideband excitation in the range of 2 to 20 MHz have both
been used for tomographic imaging in transmission. A line-shaped point spread function has been realized by temporal
apodization selecting from a pulsed signal observed in transmission only the contribution traveling the path connecting
the transducer foci. By this method a pair of scanned focusing transducers mounted in a defocused arrangement was
employed for tomographic imaging. The technique relates to shadowing of a point source in transmission as used in X-ray
tomography, but, in addition, variations of the time-of-flight are measured else by phase contrast or a cross-correlation
procedure with high resolution. From these data an image with velocity contrast can be derived in addition to
the conventional image representing the extinction in the samples under investigation. Examples presented include
resolution test samples and biomedically relevant materials. It is also demonstrated that the coherent detection scheme
can be used to enhance the resolution by the synthesis of an enlarged aperture. Respective procedures are implemented
for image reconstruction.
Electric surface excitation of ultrasound in the Coulomb field of scanned electrically conductive spherical local probes and similar detection has been employed for imaging of the transport properties of acoustic waves in piezoelectric materials including singlecrystalline wafers. The employed Coulomb scheme leads to a fully predictable and almost ideal point excitation and detection. In combination with two-channel quadrature transient detection it allows high precision spatially and temporally resolved holographic imaging. Via modeling of the excitation and propagation properties, the effective elastic tensor and the piezoelectric properties of the observed materials can be determined with high resolution from a single measurement. The generation and detection scheme as well as the theoretical background are demonstrated and applications are exemplified.
Numerical modeling of wave propagation in anisotropic single crystal is based on the angular spectrum technique. The decomposition of initial acoustic signal distribution into its angular spectrum is performed by the calculation of 2D Fourier transformation. Phase shift of each harmonic plane wave component depends on the distance between initial and observation planes and the normal component of the wave phase slowness vector. In anisotropic media slowness depends on direction of propagation vector and on polarization. In acoustics directionally depending phase velocities are calculated from Christoffel equation. Decomposition of initial distribution and superposition of plane waves in observation plane is performed by the use of FFT algorithm. One may use this procedure in forward or back propagation. Here we use this technique for reconstruction of point source and a structure located inside of a single crystal. The complex data sets of synthetic aperture type were measured by scanning ultrasonic microscope with phase contrast.
The paper presents prototypes of ultrasonic sensors for fingerprint pattern recognition. Their principle of operation is based on the amplitude measurements taken in selected points of acoustic field of ultrasonic wave diffracted from subsurface finger structure. Examples of sensor construction and measured data are presented. Fingerprint structure recognition from pulse echo shows the possible use of the sensor as a synthetic aperture microscope.
The setup for reconstruction of 2D quasi periodical structures from the measurements of its ultrasonic diffractive field is presented. Construction of the ultrasonic head is based on the prototype of our ultrasonic sensor for fingerprint pattern recognition. An example of the measured and reconstructed acoustic image of a fingerprint is compared with an optical picture.
This paper presents an analytical method for determining the grating vector distribution of holographic Fourier transform lens (FTL) recorded on a curved substrate. The design method is based on analytic ray-tracing procedure that exploits the minimization of the mean-squared difference of the propagation vectors between the actual output and desired output rays. This minimization yields an analytic solution for the optimal grating vector. The simulation of spot diagrams has allowed us to state that the designed grating vector distribution is optimal for a sufficiently wide spatial frequency range.
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