DEVELOPMENT OF A MOMENT ECHOGRAPHY SYSTEM WITH A SINGLE ULTRASOUND SENSOR

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In the research, we have tested the feasibility of a new acoustical sensor which have an spatial resolving ability based on a new concept. In the sensor, a single signal channel is connected to a transducer whose sensitivity is spatially modulated on an aperture. If the spatial modulating function is so designed to have an impulse response from which we can distinguish the direction and delay of propagated wavefront, we can control the directivity using the detected waveforms. We have called the aperture of the sensor "Encoding Aperture". This sensor can steer a directivity without any mechanical and/or electrical scanning. Beam-forming can be performed with an entirely digital ans indirect manner. Furthermore, the sensor can acquire data with only a single transmitting and receiving process.We proposed three implementations for the apertures. The first one uses a piezoelectric film with an electrode whose pattern is designed according to a spatial modulating function. The second and the third use an inclined 1-D or 2-D arrays coded with binary sequences. We also proposed an discriminating operator using a pseudo-inversion of the propagation matrix of the sensing system.Experimental systems using 5MHz ultrasound in water or 50KHz one in air were constructed. The relative levels of undesired peaks emerges in PSF of the systems were less than -40dB when the developed operator was used. The results demonstrate the feasibility of the sensor to the 2-D echography.