Acoustic wave imaging apparatus and method

Abstract

An acoustic imaging apparatus and method that achieves desired delays with coded signals. Linear, curved linear and sector scanning is provided in 1-D arrays and planar, curved planar and sector scanning is provided in 2-D arrays. Composite and non-linear implementations are presented. Dynamic and discrete dynamic focusing is disclosed for the relevant arrays. The 2-D array makes possible 3-D imaging.

Description

FIELD OF THE INVENTION

The present invention relates to acoustic wave imaging systems.

BACKGROUND OF THE INVENTION

Conventional acoustic wave imaging systems use a one dimensional (1-D) array of electro-acoustic transducers, for example, a 1×100 array, and have been configured to achieve linear, curved linear and sector scanninga

The paraxial approximation allows one to decompose a 2-D lens into two, orthogonal, 1-D lenses, one immediately in front of the other. At each point on the aperture, the phase delay from one lens adds to that of the other to produce the same phase delay as would result from a single 2-D lens. This means that a 2-D array can be used to synthesize a 2-D lens by phasing the rows with a phase relationship that will create a 1-D focus in the X-axis and the columns with one that will create a 1-D focus in the Y-axis. Such phasing is now discussed in more detail, first in a general continuous wave context and then in a context for broadband operation using coded signals.

In general operation, the row signals are used to produce a 1-D focus in the X direction while the columns signals are used to produce a 1-D focus along the Y axis. To achieve the desired 2-D focus, the row and column signals are combined in a manner such as that achieved by mixing (or multiplying) the signals together. Such mixing allows one to synthesize a 2-D focus using only as many control signals are there are rows and columns in array 100. In other words, this permits the effective control of M×N transducers by M+N control signals. Thus, the exemplary 10,000 transducers in array 100 (with M=N=100) can be controlled by 200 processing channels.

FIG. 2 shows several cells and transducers of the active 2-D array 100. Here each array element is connected to the output of its own electronic mixing circuit. One input of
$\begin{array}{cc}\begin{array}{c}\Delta \left(X,Y\right)\cong \left(X^2/2R+Y^2/2R-X\theta -Y\varphi \right)/V\\ \cong \Delta \left(X\right)+\Delta \left(Y\right)\end{array}& \mathrm{Eq}.3\end{array}$
Sr(X)=cos(ωr*(t−Δ(X))+α*r²/2−2α*Δ(X)*t+α*Δ(X)²)   Eq. 4
Sc(Y)=cos(ωc*(t−Δ(Y))+α*r²/2−2α*Δ(Y)*t+α*Δ(Y)²)   Eq. 4

In receive, the purpose of the control signals which have the characteristics of continuous wave signals, is to shift the frequency and phase of each signal so that, as that signal occurs, it coherently adds with all the other signals as they progress in their time sequence. The net result is, for a single point source, a single output chirp whose length in time and frequency corresponds to the total time over which the acoustic energy is insonifing the array aperture. For a point source located at a large angle away from array 100, the resulting output chirp can last over 20 microseconds even though the chirp coming from the point source or target lasted only 10 microseconds.

Mathematically, this requirement to achieve coherence can be established by changing the phase and amplitude of every chirp so that the summed output produces a single chirp centered in time with the chirp signal arriving at the center element of the array. Equation 6 provides the condition for coherence (ωa is the base frequency of the received chirp). Solving for the frequency shift ‘ωs*t’, and the phase shift ‘ψ’, gives the frequency and phase shift for each array element to ensure a coherent sum, Equation 7. Separating this equation into its row and column components gives rise to the row and column control signals, Equations 8 and 9 respectively, for receive (ωlor and ωloc are the rows and column local oscillator frequencies and tz is the transit time from the center of the array 100 to the target).
cos(ωa*(t−tz)+α*(t−tz)²)=cos(ωΔ*(t−Δ(X,Y))+α*(t−Δ(X,Y))²+ωr*t+ψ)   Eq. 6
ωs=2*α*Δ(X,Y)
ψ=ωa*Δ(X,Y)−α*(Δ(X,Y))²   Eq. 7
Sr=cos(ωlor*t+2*α*Δ(X)*t+ωa*Δ(X)−α*(Δ(X)²))   Eq. 8
Sc=cos(ωloc*t+2*α*Δ(Y)*t+ωa*Δ(Y)−α*(Δ(Y)²))   Eq. 9
Dynamic Focusing

In current pulsed array imaging systems, a single pulse of acoustic energy is transmitted from an array for every line of range data that is collected. As that pulse travels away from the aperture it interacts with progressively deeper objects (targets). For best resolution, the focal length of the system is dynamically changed to follow the pulse as it interacts with objects at ever increasing ranges. This process is known as dynamic focusing and is one of the main advantages of array technology. Furthermore, dynamic focusing and discrete dynamic focusing, discussed below for sector scanning, permit the generation of real time images.

For linear or curved linear scanning or planar or curved planar scanning as taught herein, the direction cosines are zero. Without correction, the response of the system will fall away from the chosen focal range. To correct for this problem, the control signals must change in time in such a way as to keep all points in range in focus as they are sequentially insonified by the transmit chirp. Since the acoustic energy must travel from the array to some target and back again, the effective rate at which the targets are insonified is ½ the speed of sound. Thus to keep targets at different ranges in focus, the system must increase its focal distance at ½ the speed of sound.

Due to the time dependence of the focal changes, simply substituting R=½*V*t into the control signals gives rise to a DC signal and is not adequate. Appropriate delay, δ(t), is determined by the frequency of the control signals, Equation 10. The phase evolution of the control signals can be found by integrating this frequency shift, ωs(t), as demonstrated in Equations 11 and 12. To determine the constants of integration, some time ‘Tm’ is chosen to be the beginning point of the dynamic focusing process. The constant of integration is found by setting equations equal to Equations 11 and 12 at the time Tm. The result, for dynamic focusing is the control signals described by Equations 13 and 14.
δ(t)=ωs/(2*a)
ωs(t)=2*a*(X²/(V*t)+Y²/(V*t))   Eq. 10
$\begin{array}{cc}\begin{array}{c}\mathrm{Phase}\left(x\right)=\mathrm{integral}\left(2*\alpha *\Delta \left(X,t\right)\mathrm{dt}\right)\\ =2*\alpha *X^2*\mathrm{in}\left(t\right)+K1\end{array}& \mathrm{Eq}.11\end{array}$ $\begin{array}{cc}\begin{array}{c}\mathrm{Phase}\left(y\right)=\mathrm{integral}\left(2*\alpha *\Delta \left(Y,t\right)\mathrm{dt}\right)\\ =2*\alpha *Y^2*\mathrm{in}\left(t\right)+K2\end{array}& \mathrm{Eq}.12\end{array}$
Sr=cos(ωlor*t−2*α*X²*In(t/Tm)+2*α*Δ(X,Tm)+ωa*Δ(X,Tm)−α*Δ(X, Tm)²)   Eq. 13
Sc=cos(ωlor*t−2*α*Y²*In(t/Tm)+2*α*Δ(Y,Tm)+ωa*Δ(Y,Tm)−α*Δ(X, Tm)²)   Eq. 14

It should be noted that at scan angles more than a few degree, continuous dynamic focusing is not possible. This is due to the 2XRθ and 2YRΦ terms in Equation 2. The rate of change in the focal length causes these terms to introduce a frequency shift that significantly degrades the output signal.

Planar Array

Referring to FIG. 5, a diagram of a planar array 505 in accordance with the present invention is shown.

Row control lines 35 and column control lines 45 are connected to the planar array 505 to deliver the appropriate control signals discussed herein and the collective output signal from transducers (not shown) in array 505 is propagated on line 65 to the interface circuit 20.

Planar scanning is achieved by setting the direction cosines to zero in Eq. 2 and electrically translating a sub-aperture 510 across the array 505. Electrically translating a sub-aperture is generally known and its implementation in system 10 would be apparent to one skilled in the art given the teachings herein. Similar scanning in either an X or Y direction in 1-D arrays has been termed “linear” scanning. The term “planar” scanning is used herein to denote scanning a sub-aperture in both the X and Y directions in a 2-D array. Though the array 505 and sub-aperture 510 may have any practical dimension, in one practical embodiment the X and Y dimensions of the array 505 are approximately each 4″ and the dimensions of the X and Y sub-aperture 510 are approximately each ¾″.

Curved Planar Array

Referring to FIG. 6a, a convex curved planar array 550 and a less 555 therefor in accordance with the present invention are shown. The control lines and processing circuitry (not shown) for the array 550 are as taught herein.

Providing that the curved planar array 550 is not excessively curved relative to its active sub-aperture, for example for a sub-aperture of 1.5 cm a curved planar array with a curvature of r=4 cm is suitable, dynamic focusing can be achieved at a large angle by electronically translating a sub-aperture over array 550. Electrically translating a sub-aperture across a curved array is generally known. By the curvature of the array 550, the sub-aperture is able to scan an angle with the direction cosines equal to zero.

The less 555 provides focal point adjustment. For example, without the acoustic lens 550, an electronic focal length of 3 cm would correspond to an acoustic length of 6 cm due to a 4 cm convex curvature of array 550. Using a lens 550 having an acoustic velocity 0.8 that of water, the acoustic focal length is reduce to 4 cm. The convex shape of array 550 acts as a diverging lens. The acoustically slow convex covering 550 acts as a diverging lens that removes some of the diverging curvature of the wavefront. The array curvature has a significantly less pronounced affect at a 9 cm focal length. It should be recognized that although a diverging lens 555 is shown, a converging lens or no lens at all may be utilized.

Referring to FIG. 6b, a concave curved planar array 570 in accordance with the present invention is shown. An acoustic lens 575 is also provided for focusing acoustic energy from array 570.

Curved planar scanning can be achieved in both the composite and non-linear implementations.

Sector Scanning

As noted above, continuous dynamic focusing is achievable when angular or sector scanning is not performed. Discontinuous or discrete focusing however, can be achieved in angular scanning systems at a level that approximates continuous focusing if additional electronic componentry (discussed below) is added to system 10. The additional electronic componentry is implemented in the semiconductor material of the composite implementation, but the functions it provides are not properties of non-linear electro-acoustic material. Accordingly, sector scanning can be achieved only in the composite implementation.

Sector scanning requires that the transmit and receive beams be scanned over a predefined angle, normally +/−45 degrees (direction cosines +/−0.5 and +/−0.5, azimuth and elevation, i.e., X and Y). Increasing the pointing angle to 45 degrees in both azimuth and elevation significantly degrades the response. To correct for this distortion, an additional cross term is required and it is:
Err=(X*Y(θ*Φ)/(R*V)   Eq. 16
As this term contains information unique to the X and Y position of a given, it cannot be incorporated into row and column control signals. This is why the non-linear array is not effective at large angles.

Referring to FIG. 7, a schematic diagram of two transducer cells with phase adjustment for angular scanning in accordance with present invention is shown. The two cells 610 and 640 are analogous to cells 110 and 140, for example, of FIG. 2.

Referring to cell 610, the first mixer 611, buffer 612, T/R switch 613, amplifier 617 and second mixer 618 are analogous to their counterparts in cell 110. Cells 610, 640 each include a phase shifter 614, 644 and a voltage divider 616, 646. A DC signal source 605 for generating a common DC control signal is connected to the voltage divider. It is controlled by an additional processing channel (not shown).

The limitations imposed by Eq. 15 are removed by the addition of the phase shifters 614, 644 as programmed by the voltage divider outputs. The voltage dividers 616, 646 essentially comprise two resistors that can be precisely selected to divide the common DC signal to a unique voltage level. This voltage level or ratio of input to output voltage is chosen for each cell to be proportional to its XY position in the array (100 of FIG. 2). Eq. 16 shows the relationship of the DC control signal and Eq. 17 shows the actual phase shift introduced by each phase shifter in array 100 (FIG. 2), represented in FIG. 7 by phase shifters 614 and 644.
Scorr=(θ+Φ)*(ωa+2*a*R/V)/(2*R*V)   Eq. 16
C=X*Y*Scorr   Eq. 17

The immediately preceding discussion illustrated a way of achieving unique phase correction for each transducer for achieving angular scan in transmit. A way of angularly focusing in receive is now discussed.

Prior art acoustic imaging systems sample the output image at discrete ranges. For this reason, a continuous output, in range, is not required. One can use a sequence of range outputs, in other words, discontinuous or discrete dynamic focusing, without any loss in image quality that is detectable by the human eye.

In the composite implementation, discrete focusing is achieved by at least the two following approaches or a combination thereof. A first approach is to use as many processing electronic cells per transducer as the number of range increments desired. The control signals only have to be in existence for the duration over which the energy from a particular range point insonifies the array. This concept is illustrated in FIG. 8, wherein dashed line 681 represents a ray or line emanating from the center of array 100 on which range points for focusing lie. The ray 681 is defined by certain elevation and azimuth angles. Segment 683 represents one process period which is essentially the time over which energy from a focused range point insonifies the array. The range focus along ray 681 is sequential extended a distance equal to the speed of sound in the relevant medium times the period of insonification, up to a distance that is no longer practical or desirable for scanning. For a practical design for use in medical ultrasound imaging, the process period is on the order of 20 microseconds. This means that every 20 microseconds, the control signals can change to focus on a new range point. Having 40 processing cells for every array element would permit one range sample every 0.5 microseconds; approximately what is used for current imaging systems when displaying 16 cm of range.

A second approach to obtain multiple range samples is to use the high electronic bandwiths of current integrated electronic circuits. Assuming a bandwidth requirement of 10 MHz per range channel, a 400 MHz electronic bandwidth would permit 40 simultaneous range channels. Implementation of this approach in the imaging system 10 described herein is now presented.

Referring to FIG. 9, a range versus frequency band diagram for implementing discrete focusing is shown. A plurality of range points are defined, point 1, point 2, . . . point j, that sufficiently approximate the range overwhich focusing is desired along a particular ray (681 of FIG. 8). A specific frequency band, band 1, band 2, . . . band j, is defined for each range point.

Referring to FIG. 10, a phase accumulator 691 is provided either in or in communication with the interface circuit 20. The phase accumulator 691 preferably receives a digital signal, ν(t), from signal generating circuitry (not shown, but generally known), in system control circuitry that includes components for each of the j frequency bands of FIG. 9. Thus,
ν(t)=ν(t)₂′+ν(t)₂′+. . . +ν(t)_j′  Eq. 19
where ωlor₁+ωloc₁=band ν(t)₁ center frequency and ωlor₂+ωloc₂=band ν(t)₂ center frequency, etc.

The phase accumulator 691 preferably includes a digital to analog converter (not shown) or one is placed downstream thereof. The output of accumulator 691 is the Scorr signal which is delivered to the voltage dividers (616,646 of FIG. 7). The output of each voltage divider is the control signal, C, which is propagated to the phase shifters (614, 644 of FIG. 7) to uniquely code the receive focusing signal for each cell. In the exemplary embodiment, mentioned immediately above, each band or frequency component ν(t)′ differs by 10 MHz from the adjacent band. Thus, for 40 range channels, ν(t) has a band width of 40×10 MHz=400 MHz.

Referring to FIG. 11, a modification in the interface circuit 20 to appropriately process a multi frequency component signal in accordance with the present invention is shown.

In contrast to the singular receive channel 305 of the embodiment of FIG. 3, the embodiment of FIG. 11 includes j receive channels 705 (705₁, 705₂, 705_j) which contain matched filters 720₁, 720₂, 720_j that are specifically configured for their corresponding frequency component ν(t)₁′, ν(t)₂′, ν(t)_j′, respectively. Continuing with the current example of 40 range points and 40 frequency components, there are 40 receive channels 705 in the modification to the interface circuit 20 illustrated in FIG. 11. It should be recognized that one can combine multiple cells per transducer, for example 6 cells per transducer (with appropriate frequency multiplexing and phase shifting as taught herein), with larger bandwidth signals, for example 6 frequencies in the bandwidth and 6 receive channels, to achieve the desired number of range samples, in this example, 6×6=36.

1-D Implementation and Annular Array

Referring to FIG. 12, a 1-D array 800 for an acoustic scanning system in accordance with the present invention is shown. The array 800 is integrated into the system 10 of FIG. 1, replacing array 100. Since array 800 is one dimensional, control lines are only implemented in one dimension, either row or column control. The row control circuiting 30 is shown in FIG. 12 and hence in integrating array 800 into system 10, the column circuit 40 and related electronics are removed. Each cell 810,840,870 does not contain a first mixer, such as mixer 111 and the like of FIG. 2 because of the absence of column control lines, but does include a buffer 812,842,872, a T/R switch 813,843, 873 receive amplifier 817,847,877 and a second mixer 818, 848,878. Each cell is connected to a transducer 815,845, 875. Cells 810,840,870 are otherwise generally analogous to cells 110,140,170 of FIG. 2. Accordingly, they may be implemented as a composite array or non-linear array and be configured in embodiments for linear and curved linear scanning in both implementations, and for sector scanning in the composite implementation. In addition, the 1-D array can be implemented as a discrete array coupled to discrete electronics. The 1-D array 800 operates under the same signal generating and processing aspects taught herein, with the exception of those aspects specific to the mixing of row and column signals.

It should also be recognized herein that the teachings herein apply to annular arrays and they could, accordingly, be fabricated in the same embodiments of a 1-D array discussed immediately above.

Aberration Correction

The various tissues of the body have differing speeds of sound. Not correcting the beamforming process for this fact may degrade the acuity of the resulting acoustic images. To date, modest improvement in image quality has been achieved by aberration correction techniques on 1-D phased arrays. It is generally accepted, however, that these methods would produce a significant increase in image quality if they could be applied to large 2-D apertures. Thus, perhaps the most significant impediment to aberration correction has been the expense and complexity of building a 2-D array imaging system.

Use of the present invention makes practical a 2-D scanning system and hence makes possible aberration correction techniques. The required delay perturbations are achieved by suitable modification of the row and column control signals. In a relatively basal embodiment, the system can implement any delay profile that is separable into X and Y components. Since the present system has been shown to correct the large first and second order delays required to produce an image in homogeneous media, the constraints of separability upon the improvement in image quality and general system performance should not be significant.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims.

Claims

1. An acoustic imaging apparatus, comprising:

control logic;

a plurality of transducer elements arranged in an array, each coupled to said control logic and capable of transmitting an acoustic signal representative of an electrical transmit control signal propagated from said control logic and generating an electrical receive signal representative of an incident acoustic signal;

means within said control logic for generating an electrical transmit control signal for each transducer element such that the electrical transmit control signal for each transducer element contains a coded signal;

means within said control logic for generating an electrical receive control signal for each transducer element such that the electrical receive control signal for each transducer element contains a frequency and phase shift than when combined with the transducer element's electrical receive signal modifies the frequency and phase of that electrical receive signal in such a manner as to permit the coherent combination of the modified electrical receive signals from all of said plurality of transducer elements;

means for combining the electrical receive control signal of each transducer element with an electrical receive signal generated by that transducer;

means coupled to each of said transducer elements for combining the modified electrical receive signals from said transducer elements so as to form a coherently combined array output signal;

means coupled to said transducer output combining means for decoding a combined reflected coded signal in the coherently combined array output signal to produce a decoding means output signal; and means coupled to said decoding means for generating image data from said decoding means output signal.

2. The apparatus of claim 1, wherein said coded signal is a chirp.

3. The apparatus of claim 2, wherein said decoding means comprises at least one matched filter for coded signal decoding.

4. The apparatus of claim 1, wherein said chirp is a linear FM chirp.

5. The apparatus of claim 1, wherein said array has a size of M rows and N columns and said electrical transmit control signal generating means comprises means for generating individual row and column transmit control signals for each of said rows and columns, the electrical transmit control signal for each transducer element being a combination of the transmit row and column control signals for that transducer.

6. The apparatus of claim 5, wherein at least one of said row and column transmit control signals for a given transducer element contains a frequency based coded signal.

7. The apparatus of claim 5, wherein said electrical receive control signal generating means comprises means for generating individual row and column receive control signals for each of said rows and columns, the electrical receive control signal for each transducer being a combination of the receive row and column control signals for that transducer.

8. The apparatus of claim 1, wherein said coded signal includes a frequency based code.

9. The apparatus of claim 1, wherein said array is a one dimensional array with a plurality of rows and one column.

10. The apparatus of claim 1, wherein said array of transducer elements comprises M rows and N columns, where M and N are positive integers and at least one of M and N is greater than 1;

at least one of said transmit control signal generating means and said receive control signal generating means includes means for generating row and column control signal components; and

wherein each transducer element includes an active electronic device for combining said row and column control signal components for that transducer element.

11. The apparatus of claim 1, wherein each transducer element includes a transducer comprised of a non-linear electro-acoustic, non-linear dielectric material.

12. An acoustic imaging apparatus, comprising:

a plurality of electro-acoustic transducer elements arranged in an array, each capable of transmitting an acoustic signal and generating an electrical signal representative of an incident acoustic wave;

control means having a plurality of control channels coupled to each of said plurality of transducer elements, said control channels being fewer in number than said transducer elements;

wherein said control means generates control signals for each transducer element that when combined with the electrical receive signal of that transducer element modifies the electrical receive signal in such a manner as to permit the simultaneous processing of the modified electrical receive signals from said plurality of transducer elements;

means for combining the modified electrical receive signals of each of said transducer elements to form an array output signal; and

means coupled to said combining means for generating image data from said array output signal.

13. The apparatus of claim 12, wherein said array has a plurality of rows and a plurality of columns each having one of said plurality of control channels associated therewith;

said control signal generating means further including means for generating row and column control signal components; and

wherein said transducer element is uniquely and simultaneously controlled by a combination of the row and column control signal components for that transducer element.

14. The apparatus of claim 12, wherein said control signal generating means further includes means for generating a transmit control signal for each transducer element that contains a frequency based coded signal for transmission by each transducer element.

15. The apparatus of claim 14,

further comprising means for decoding a reflected frequency based coded signal.

16. An acoustic imaging system, comprising:

an array of electro-acoustic transducer elements having M rows and N columns, where M and N are positive integers and at least one of M and N is greater than one;

M row control lines, each coupled to the transducer elements in one of said M rows;

N column control lines, each coupled to the transducer elements in one of said N columns;

control means coupled to each of said M row and N column control lines for generating row control signals for each of said row control lines and column control signals for each of said column control lines, a control signal for each transducer being a combination of one of said row control signals and one of said column control signals;

a plurality of active devices, each coupled to one of said transducer elements for combining the row control signal and the column control signal of that transducer element;

means for combining the output of each transducer element to produce an array output signal; and

means coupled to said transducer output combining means for generating image data from said array output signal.

17. The apparatus of claim 16, wherein said active device is an active electronic device.

18. The apparatus of claim 17, wherein said control means includes means for generating a transmit control signal that contains a frequency based coded signal for each transducer element; and

wherein said apparatus further comprises means in communication with each of said transducer elements for modifying a reflected coded signal received thereby to achieve a delay encoded in the coded signal, said delay for each transducer element being based on the relative position of that transducer element in the array.

19. The apparatus of claim 16, wherein said active device includes a non-linear electro-acoustic material.

20. The apparatus of claim 16, wherein said active device includes a non-linear electro-acoustic material for combining row and column control signal on transmit and an active electronic device for combining row and column control signal on receive.

21. The apparatus of claim 16, wherein said active device includes a non-linear electro-acoustic, nonlinear dielectric material.

22. A method for acoustic imaging, comprising the steps of:

providing control logic;

providing a plurality of transducer elements arranged in an array, each coupled to said control logic and capable of transmitting an acoustic signal representative of an electrical transmit control signal propagated from said control logic and generating an electrical receive signal representative of an incident acoustic signal;

generating an electrical transmit control signal for each transducer element such that the electrical transmit control signal for each transducer element contains a coded signal;

generating an electrical receive control signal for each transducer element that contains an appropriate frequency and phase shift that when combined with that transducer element's electrical receive signal permits the coherent combination of the electrical receive signals of each of the plurality of transducer elements;

combining the coherent output signals from said transducer elements so as to form a coherently combined array output signal;

decoding a combined reflected coded signal in the coherently combined array output signal to produce a decoded output signal; and

generating image data from the decoded output signal.

23. An acoustic imaging apparatus, comprising:

control logic;

a plurality of transducer elements arranged in an array, each coupled to said control logic and capable of transmitting an acoustic signal representative of an electrical transmit control signal propagated from said control logic and generating an electrical receive signal representative of an incident acoustic signal;

means within said control logic for generating an electrical transmit control signal for each transducer element that contains a frequency based coded signal and cause causing each transducer to emit an acoustic signal representative of said coded signal;

means for modifying the frequency and chase phase of an electrical receive signal of each transducer element for coherently combining reflected coded signals within the electrical receive signals thereof;

means coupled to said modifying means for decoding the combined reflected coded signals to achieve a time delay based on that coded signal; and

means coupled to said decoding means for generating image data from an output signal therefrom.

24. An acoustic energy transmitting apparatus, comprising:

a plurality of electro-acoustic transducer elements arranged in an M row by N column array, where M and N are positive integers and at least one of M and N is greater than one;

control circuit for propagating row and column control signals for each of said M rows and said N columns, each control signal having a frequency and a phase component; and

wherein each transducer element is configured to function as an active device so as to achieve a combining at each transducer element of the frequency and phase components of the row and column control signals for that transducer element in such a manner as to provide a focused acoustic signal at a given focal distance and direction from said array.

25. The apparatus of claim 24, wherein the electric signal to acoustic signal relationship and vice versa of each transducer element is non-linear.

26. The apparatus of claim 24, wherein said control circuit includes a control channel for each of said M rows and a control channel for each of said N columns, and wherein the number of control channels is fewer than the number of transducer elements.

27. The apparatus of claim 24, wherein said control circuit is configured such that the row and column signals for at least some of the transducer elements includes a coded signal.

28. The apparatus of claim 27, wherein M equals one.

29. An acoustic energy transmitting apparatus, comprising:

a plurality of electro-acoustic transducer elements arranged in an M row by N column array, where M and N are positive integers and at least one of M and N is greater than one;

M row control lines, each coupled to the transducer elements in one of said M rows;

N column control lines, each coupled to the transducer elements in one of said N columns;

control circuit for propagating row and column control signals for each of said M rows and said N columns, a control signal for each transducer element being a combination of one of said row control signals and one of said column control signals;

a plurality of active devices, each coupled to one of said transducer elements for combining the row control signal and the column control signal of that transducer element;

wherein said transducer elements, control circuit and active devices are configured so as to achieve a combining at each transducer element of the row and column control signals for that transducer element in such a manner as to provide a focused acoustic signal at a given focal distance and direction from said array; and

wherein each of said electro-acoustic transducer elements is configured within said apparatus to function in a non-linear manner in operation.

30. An acoustic energy receiving apparatus, comprising:

a plurality of electro-acoustic transducer elements arranged in an M row by N column array;

control circuit for propagating row and column control signals for each of said M rows and said N columns, each row and column control signal having a frequency and a phase component; and

wherein said transducer elements and said control circuit are configured so as to achieve a combining at each transducer element of the frequency and phase components of the row and column control signals for that transducer element with a resultant electrical receive signal, corresponding to an acoustic signal incident on that transducer element, in such a manner as to modify the frequency and phase of the transducer element's electrical receive signal so as to achieve the coherent combination of the modified electrical receive signals from all of said plurality of transducer elements; and

a filter that filters spurious frequencies output from the transducer elements;

wherein said transducer elements, control circuit and filter are configured to achieve focused acoustic signal reception at a given distance and direction from said array.

31. The apparatus of claim 30, wherein said transducer elements and said control circuit are configured to achieve dynamic focused acoustic signal reception.

32. The apparatus of claim 31, wherein the electric signal to acoustic signal relationship and vice versa of each transducer element is non-linear.

33. The apparatus of claim 30, wherein said filter includes a matched filter.

34. The apparatus of claim 33, wherein said matched filter includes a conjugate of a coded signal.

35. The apparatus of claim 29, wherein M equals one.

36. The apparatus of claim 30, further comprising a circuit that generates image data from the coherent combination of transducer element receive signals.

37. The apparatus of claim 30, wherein said control circuit includes a control channel for each of said M rows and a control channel for each of said N columns, and wherein the number of control channels is fewer than the number of transducer elements.

38. An acoustic energy receiving apparatus, comprising:

a plurality of electro-acoustic transducer elements each capable of generating an electrical receive signal in response to an incident acoustic wave and arranged in an M row by N column array, where M and N are positive integers and at least one of M and N is greater than one;

control circuit for propagating row and column control signals for each of said M rows and said N columns, the control signal for each transducer element being a combination of the row and column control signals for that transducer element;

wherein said row and column control signals are configured, for each transducer element, such that when combined with the electrical receive signal of that transducer element the electrical receive signal is modified in such a manner as to permit the simultaneous processing of the modified electrical receive signals from said plurality of transducer elements;

a first circuit that combines the modified electrical receive signals of each of said transducer elements to form an array output signal; and

a second circuit coupled to said first circuit that generates image data from said array output signal.

39. The apparatus of claim 38, wherein M equals one.

40. The apparatus of claim 24, wherein each transducer element includes non-linear electro-acoustic material.