This article presents an original method of B/A measurement with a single plane transducer used in pulse-echo mode. To determine the best conditions of measurement, we use an ideal model with a new solution for the second harmonic. We take into account the phenomena of attenuation and diffraction. Experiments validate simulations in the case of comparative method measurement. Then we present a device to improve the detection of the second harmonic. Thus measurement of the B/A parameter of ethanol and glycerol validates this device and we also show the possibility of its use in nonlinear imaging with a weak excitation.

In biomedical ultrasound imaging, many studies show the advantages of harmonics to obtain a better quality of image; this is particularly true in echography and diffraction tomography. Recent work confirms that lateral resolution can be improved by the use of the harmonics generated by a nonlinear distortion in the medium. In this study, the enhancement made by the use of the second harmonic in ultrasound reflection tomography is shown. A focused transducer containing both concentric 2.5 and 5 MHz elements composes the experimental device. They are, respectively, the transmitter/receiver of the fundamental field and the receiver of the second harmonic field. The tests are carried out with PVC tubes. The first object is a single tube whereas the second one is an asymmetrical structure made up of two tubes. The image reconstruction is made from the measurements of the fundamental and second harmonics of the reflected fields using the back-projection method. This technique of relying on higher harmonics seems to provide a better resolution of tomographic images.

The ultrasonic wave propagation is affected by absorption and diffraction. The transmission line is used to simulate the propagation media in PSpice model. To take into account diffraction effects we used the model proposed by J. Johansson [11]. A set of Gaussian beam is used to simulate the radiated field allowing us to deduce the exact diffraction loss. The diffraction loss is incorporated into the transmission line model using the attenuation parameter G. Measurements have been performed using a pulse echo system transmitting in water. The measurements show good agreement with the simulation results.

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We present a procedure for measurement of the non linear BIA parameter using a simple comparative method . A theoretical model of the measurement system is proposed. A function sensitivity of the system is derived in order to connect the electric and acoustic magnitudes. Thus the optimal conditions in order to avoid complex calculation of the transducers sensitivities were carried out. We showed that the sensitivity function of the measurement system can be kept close to the unit by making a good choice of the fundamental frequency. Indeed if the frequency of the source transducer is chosen less than the resonance frequency we can avoid determining the sensitivities. Measurements had been carried out to validate the procedure and the theoretical aspects.