Ultrasonic Phase Conjugator Research Articles

Measuring the acoustic absorption coefficient in biological tissue specimens using ultrasonic phase conjugation

Acoustic absorption has been measured in a series of biological tissue specimens—porcine muscle, renal and fat tissues—by the standard insert-substitution method, as well as by ultrasonic phase conjugation. Comparison of the experimental results and revealed differences confirm the promise of using phase conjugate waves to measure acoustic losses in biological objects. It is demonstrated that in inhomogeneous tissues, the phase conjugation method makes it possible to obtain a more reliable estimate of dissipative losses.

Diagnostics and doppler tomography of liquid flows with ultrasonic phase conjugation

The potential of ultrasonic velocimetry and mapping for liquid flows in a model and real biological media is demonstrated experimentally and theoretically using the technique of parametric phase conjugation of sound. The basis of the proposed method is violation of invariance of an acoustic field with respect to time reversal in a moving medium that leads to an uncompensated phase shift of a phase-conjugate wave at a transmitter-receiver array. The principles for application of nonlinear acoustic effects for improving the reconstruction precision for the field of flow velocities are discussed.

Observation of living samples in a C-mode configuration with an ultrasonic phase conjugator

Ultrasonic images of living samples have been obtained in a C-mode configuration with phase conjugation (time-reversal) processes. A phase conjugator for 10-MHz ultrasound was realized by the field-mixing in a PZT block pumped with 20-MHz electric fields. Samples, relatively thick (mm to cm) living materials, were placed between an ultrasonic transmitting/receiving transducer and the phase conjugator and were scanned to form C-mode transmission images. Ultrasonic tone-burst pulses radiated onto the sample were led into the PZT block and were converted to their phase conjugate waves, which, for their time-reversing nature, acted to cancel the wavefront deformation introduced by the thick living samples. In the experiment, images were obtained at a frequency of 10 MHz for several samples such as chicken liver, poke meat, and some model samples made of agarose gel, both by the phase conjugate method and by the conventional one. Images by the phase conjugate method showed relatively good accordance with the real ultrasonic attenuation distribution, while those by the conventional method were very sensitive to the shapes or the discontinuities of samples.

Reflection-Type Ultrasonic Phase Conjugate Imaging System with a Waveguide

A reflection-type ultrasonic C-mode imaging system with an ultrasonic phase conjugator and a waveguide has been built, and images at 10 MHz have been obtained for metal samples with surface undulations. Surface or sub-surface elastic properties were visualized with a small influence of the surface roughness. The waveguide worked to enlarge the effective aperture of the phase conjugator, to smooth the incident-angle dependence of the phase conjugate reflectivity, and to improve the signal-to-noise ratio of the phase conjugate signals. Schlieren images of the ultrasonic fields in the system are also presented.

Detection of Moving Objects and Flows in Liquids by Ultrasonic Phase Conjugation

The possibility for the application of the method of parametric phase conjugation of ultrasonic waves in measuring the velocity of moving objects and flows is investigated. Results of experimental measurements of the Doppler frequency shift are presented for a low-frequency wave (1 MHz) generated by phase-conjugate waves (10 MHz and 11 MHz) propagating in opposite directions in the presence of a moving scatterer. The super high sensitivity of the phase of the low-frequency wave to variations in the spatial position of the scatterer is used to measure the velocity of the object. The presence of flows in the region of propagation of phase-conjugate waves returned leads to an uncompensated Doppler shift of the phase of the phase-conjugate wave at the primary radiation source. The implementation of this feature of ultrasonic phase conjugation for the detection and measurement of the flow velocities in a liquid is demonstrated experimentally.

Ultrasonic phase conjugation

A real-time ultrasonic phase conjugator is reported. The scheme is based on sampling the wave front in space by means of a transducer array and mixing the signal from each array element with a second harmonic signal using nonlinear circuit components. The same array then retransmits the phase conjugated wave front into the medium. The technique is demonstrated at 300 kHz using a 20-element transducer array, and it is shown that efficient phase conjugation is possible up to spatial frequencies of ±80°.

Ultrasonic phase conjugator using a microparticle suspended cell and novelty imaging: T. Sato, T. Nakayama, Y. Yamakoshi and Y. Kataoka, The Graduate School at Nagatsuta, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama-shi 227, Japan

Ultrasonic phase conjugator using a microparticle suspended cell and novelty imaging: T. Sato, T. Nakayama, Y. Yamakoshi and Y. Kataoka, The Graduate School at Nagatsuta, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama-shi 227, Japan