An amplitude correlation synthesis processing (ACSP) method is proposed for ultrasonic underground imaging, in order to reduce the error image reconstructed with the low-frequency signal received by linear array receivers. In contrast to the previous method of special polarity correlation processing (SPCP), the amplitudes of received signals corresponding to a processing point, in every subarray group, is multiplied according to polarity condition, and all the conditional multiplication outputs are synthesized, in the ACSP method. For the experiment, an electromagnetic induction type sound source is employed as a powerful impulse incident ultrasound. A comparison of the imaging results of bodies buried 1 m underground, derived both by the ACSP and SPCP methods shows that the new method eliminates most of the error images, and hence its efficiency for imaging with a low signal-to-noise ratio (SNR) signal is verified.

The dynamics of the n = 25 shell of Li atoms in weak electric, E, and magnetic, B, fields was studied experimentally as a function of the rate of change of the electric field strength, = |dE/dt|, the strength, B, of a constant magnetic field and the angle between the two fixed field directions, ϕ. Prior to the variation of E, it was held constant at E = E 0 with E 0 strong enough to dominate the Stark-Zeeman manifold for the shell. The uppermost state, which is a coherent elliptic state (CES), was populated selectively by pulsed laser excitation. The field was subsequently varied without rotation from +E 0 to −E 0 at the constant rate . It is shown experimentally, in accordance with theory, that the dynamics is described by a single dimensionless parameter ζ given by ζ = (sin ϕ/ √ n )B in atomic units. When ζ 5 the variation of E is so slow that the electron has time to adjust and the population then remains in the uppermost state of the manifold (adiabatic transformation), for smaller ζ ( 2) the population shifts to an interval of states centred near the middle of the manifold and at ζ 0.6 the wavefunction is almost frozen and the lowermost part of the manifold populated (diabatic transformation). The experimental findings for near-adiabatic evolution of the CES (ζ 4) agree with theoretical results obtained in a non-relativistic, hydrogenic model but discrepancies are seen when non-hydrogenic states are populated for ζ < 4.The eccentricity and orientation of a CES is given by the vectors L and A , where L is the angular momentum and A the Runge-Lenz vector [1] †. The CES remain eigenstates of the † Eccentricity e = | A |/ | L | 2 + | A | 2 . Orbital plane perpendicular to L and major axis parallel to A .

The lateral resolution of the three-dimensional (3D) amplitude correlation synthesis processing (ACSP) method for imaging objects buried underground is studied by computational simulation and experimental measurement. An electromagneticinduction sound source is employed for radiating a powerful impulsive elastic wave into the ground. Twelve receivers at identical intervals are placed symmetrically to form a cross-shaped array with its center at the sound source. The 12 signals reflected from underground objects are calculated by the 3D ACSP method. Two neighboring objects buried at an identical depth underground are imaged using signals acquired from both the computational simulation and the experimental measurement. The comparison of imaging results derived from different apertures of the array of receivers and different intervals of objects buried underground shows that two objects with a lateral interval of 0.9 m (over 1) buried at a depth of 1.5 m (about 2) can be imaged separately, using the echo signals of receivers in an array with an aperture of 2.4 m (about 3).

A new approach of frequency-modulated pulse compression for target ranging using ultrasonic pulse-echo is discussed. To acquire a receiving signal with a broader bandwidth, a flatter spectrum, and a higher signal-to-noise ratio, the use of a sensitivity-compensated transmitting signal is proposed. To compensate for the uneven and narrow bandwidth of the receiving signal brought forth by the sensitivities of ultrasonic transducers, the sensitivity-compensated signal is calculated by inversing the spectrum of the response function majorly composed of the sensitivities of transmitters and receivers. Moreover, instead of the transmitting signal, a reference receiving signal with an expanded flat spectrum measured priorly is employed for cross-correlation calculation with the receiving signal. The efficiency of the proposed method, compared with both the inverse and matched filtering methods using a chirp wave as the transmitting signal, is studied by a target ranging experiment in air. The results show that the spectrum of the receiving signal is compensated for and expanded using the sensitivity-compensated signal, and that unevenness of less than À20 dB in the spectrum of the receiving signal of the chirp wave is compensated for efficiently. Furthermore, the results of pulse compression show that, using the proposed method, the signalto-noise ratio of the compressed pulse can be expected to be improved by more than that derived by the inverse filtering method, while the pulse width is shortened and the resolution is improved up to about 1/3 of that acquired by the matched filtering method with a chirp wave.

In this paper, we describe a method of evaluating the strength of concrete by the quality factor of the resonant peak of multireflected elastic waves propagating inside the concrete. An electromagnetic-induction-type sound source and a piezoelectric transducer are employed as an elastic wave transmitter and a receiver, respectively. Linear predictive coefficient processing and resonant analysis methods are employed for spectrum derivation and quality factor calculation, respectively. Three types of concrete specimen with the same dimensions but different strengths are measured, with variations in the geometrical arrangement of the sound source and receiver. Although it is difficult to distinguish the differences in strength from the time domain signals, the quality factors of the resonant peaks of multireflected elastic waves corresponding to different types of concrete show stable results, and this tendency agrees well with that of the concrete strengths.