JPS6227696B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for ensuring high time or position resolution by time-compressing an input ultrasonic signal with a small amplitude intensity and a large time width to obtain a sharp signal. This invention relates to a method of ultrasonic time axis compression.

Conventionally, there is a technology called pulse compression in radar, etc., but its principle is to first extend the pulse width of the original pulse signal using a delay circuit with frequency characteristics and then transmit it to the receiving side. In this method, the received pulse signal was compressed to its original pulse width in a process that was the reverse of that during transmission. In this case, the complexity of the mechanism limits the miniaturization of the device, and its characteristics limit its application to high-frequency pulse signals.
Furthermore, since the pulse width after compression is defined by the original pulse width, there is a drawback that there is a limit to the time (position) accuracy.

The present invention has been devised to eliminate these drawbacks, and its purpose is to provide an ultrasonic time axis compression method for use in a relatively low frequency range from several tens of KHz to several MHz. It is in.

The gist of this invention, which was made to achieve this object, is as follows.

(b) Realize time axis compression of ultrasound using the principle of acousto-optic light correlation calculation.

(b) Use an input ultrasound signal that is an ultrasound spatial phase grating forming signal to obtain an acousto-optic optical correlation.

First, the structure of the ultrasonic spatial phase grating forming signal, which forms one of the fundamentals of the present invention, will be specifically explained using FIG. Ultrasonic propagation velocity v ₁ , v ₂ ,..., v _o (n
2) ratio v _k /v _k - ₁ (k=2, 3,..., n)
At least two types of ultrasonic propagation media are prepared such that R is a constant value R (0<R<1). FIG. 1 is an example of the configuration of the ultrasonic spatial phase grating forming signal 1 when the ratio R is determined, and the ultrasonic spatial phase grating forming signal 1 is shown when the horizontal axis represents time and the vertical axis represents amplitude. signal 1
This shows the waveform over time. As time t progresses, the waveform moves from right to left in the figure. This ultrasonic spatial phase grating forming signal 1 consists of consecutive r pieces (r
2), each of which is composed of signals of different time frequencies. First, the temporal frequency ₁ = of the first segment 2 and the duration time t ₁ =T during which this temporal frequency continues to be emitted are set to arbitrary values. Next, set the time frequency ₂ of the second segment 3 to /
R, the duration t ₂ is T・R, the time frequency ₃ of the third segment 4 is /R ² , the duration t ₃ is T・R ² ,...
The r segments are sequentially switched and emitted in succession. This produces an ultrasound spatial phase grating-forming signal 1 in which the duration of each segment decreases by a factor R and the temporal frequency increases by a factor 1/R. In other words, based on the time frequency and duration T of the first segment 2, the i-th segment (i=
1, 2, _{..., r) time frequency i =}・R ¹
If each segment is configured and emitted continuously so that the duration time t _i is t ⁱ = _T ·R ⁱ − ¹ , an ultrasonic spatial phase grating forming signal 1 can be obtained.

Next, FIG. 2a shows a structural diagram of an embodiment of a liquid cell for acousto-optic electrical signal processing necessary to realize ultrasonic time axis compression using the ultrasonic spatial phase grating forming signal 1. , b. An ultrasonic transducer 6 and an ultrasonic absorbing member 7 are provided on one set of opposing wall surfaces of the rectangular parallelepiped cell 5, and a pair of light transmission windows 8a and 8b are provided on the other opposing wall surface of the rectangular parallelepiped. It is being Monochromatic plane wave light outside the cell is allowed to pass through the cell through this window. Further, the inside of the cell is divided into two chambers by a single transparent partition plate 9, and the portion where the partition plate 9 and the vibrator 6 come into contact, that is, the edge of the partition plate 9, is exposed to the vibration of the vibrator 6. In order to prevent this from being obstructed, a liquid-tight elastic member 10 is used to separate the two chambers in a liquid-tight manner. These two chambers are filled with ultrasonic propagation media (liquid substances) 11a and 11b having different ultrasonic propagation velocities. An input terminal 12 for supplying an electrical signal is connected to the ultrasonic transducer 6.

FIG. 3 shows an embodiment of an acousto-optic ultrasonic time-base compressor constructed using the acousto-optic liquid cell shown in FIG. 2. In the Fourier transform optical system that combines the liquid cell 5, lens 13, optical filter 14, and photodetector 15, the ultrasonic transducer 6 in the cell has the above-described period and frequency in a specific relationship. When a sinusoidal signal that changes with time is applied, the monochromatic plane wave light incident on the liquid cell undergoes phase modulation due to the spatial phase grating of two ultrasonic waves generated by this sinusoidal signal, and the monochromatic plane wave light incident on the liquid cell undergoes phase modulation. 13 and is focused to produce a diffraction image on the focal plane of the lens 13. Of this diffraction image, only specific diffraction bright spots that have passed through the two spatial phase gratings are filtered out by an optical spatial filter 1.
4 and converts the intensity of the bright spot at that position into an electrical signal by the photodetector 15, the time of the electrical signal applied to the transducer 6 is determined by the principle of ultrasonic time axis compression described later. A compressed signal can be obtained. For this understanding, a spatial phase grating formed in a cell will be explained. That is, the propagation velocity v
_o (n2) ratio v _k /v _k - ₁ (k=2, 3,...,
When the ultrasonic spatial phase grating forming signal 1 is simultaneously emitted in the same direction into at least two types of ultrasonic propagation media such that n) becomes a constant value R (0<R<1), the ultrasonic propagation The shape and movement of an ultrasonic spatial phase grating formed in a medium will be explained using one example. FIG. 4 is an explanatory diagram when forming an ultrasonic spatial phase grating in a liquid cell for acousto-optic electrical signal processing. For simplicity, an example using two types of media will be described. propagation velocity v ₁ and
Two types of ultrasonic propagation media 11a and 11b, such that the ratio _{v 2 /} v ₁ of v 2 is a constant value R (0<R<1), are liquid-tightly separated by a light-transparent partition plate 9. The ultrasonic waves filled in each of the chambers and emitted simultaneously in the same direction by one ultrasonic transducer 6 excited by the electric signal input from the electric signal input terminal 12 travel through the mediums 11a and 11b in different ways. speed
Propagates with v ₁ and v ₂ , respectively. If the ultrasonic spatial phase grating forming signal 1 inputted at this time is composed of, for example, five segments, the ultrasonic spatial phase grating 16a moves at a speed v ₁ in the medium 11a.
Each segment of has a length given by l _i =T・R ⁱ − ¹・v ₁ , l ₁ =T・v ₁ , l ₂ =T・R・v ₁ , l ₃ =T・
R ²・v ₁ , l ₄ = T・R ³・v ₁ , l ₅ = T・R ⁴・v ₁ , each of which has a spatial frequency given by k _i =・R ¹ − ⁱ /v _i k ₁ =/v ₁ , k ₂ =/R・v ₁ , k ₃
=/R ²・v ₁ , k ₄ =/R ³・v ₁ , k ₅ =/R ⁴・
Consists of v ₁ . Similarly, each segment of the ultrasonic spatial phase grating 16b moving in the medium 11b at a velocity v ₂ has a length l′ ₁ =T·v ₂ , l′ ₂ =T·R·
v ₂ , l′ ₃ = T・R ² v ₂ , l′ ₄ = T・R ³・v ₂ , l′ ₅ = T・
R ⁴ · v ₂ , each of which has a spatial frequency k′ ₁ =
/v ₂ ,k′ ₂ =/R・v ₂ ,k′ ₃ =/R ²・v ₂ ,k′ ₄
It consists of =/R ³・v ₂ , k′ ₅ =/R ⁴・v ₂ . By the way, since R=v ₂ /v ₁ , the length of each segment of the ultrasonic spatial phase grating 16b is l' _i
=T・R ⁱ - ¹・v ₂ =T・R ⁱ・R ^-1・v ₂ =T・R ⁱ・
(v ₁ /v ₂ )・v ₂ = T・R ⁱ・v ₁ , and the spatial frequency is
k′ _i =・R ¹ ― ⁱ /v ₂ =・R ^-i・(v ₂ /v ₁ )/v ₂ =
It can be rewritten as /R ⁱ・v ₁ . In other words,
The length of each segment of the ultrasonic spatial phase grating 16b is l' ₁ =T・R・v ₁ , l′ ₂ =T・R ²・v ₁ , l′ ₃ =T・
R ³・v ₁ , l′ ₄ = T・R ⁴・v ₁ , l′ ₅ = T・R ⁵・v ₁ ,
Also, the spatial frequency is k′ ₁ =/R・v ₁ , k′ ₂ =/
R ²・v ₁ , k′ ₃ =/R ³・v ₁ , k′ ₄ =/R ₄・v ₁ , k′ ₅
It can be written as =/R ⁵・v ₁ . In other words, the ultrasonic spatial phase grating 16 moving in the medium 11a
The waveforms of the second to fifth segments of a are
The waveforms are completely equal to the respective waveforms of the first to fourth segments of the ultrasonic spatial phase grating 16b that moves at a speed R times R in the other medium 11b.
Next, the movements of two types of ultrasonic spatial phase gratings 16a and 16b that are simultaneously emitted by one ultrasonic transducer 6 into two types of media 11a and 11b having different propagation velocities will be described. When the top of the spatial phase grating 16b moves to a position x from the ultrasonic transducer 6, the top of the other spatial phase grating 16a is ahead by a distance x(1-R)/R, and the difference is gradually It moves through the medium while increasing in size. Therefore, the beginning of the spatial phase grating 16b is x
(1-R)/R=l When the distance x reaches ₁ , the i-th segment of the spatial phase grating 16b (i=1, 2,
3 and 4) overlap the i+1th segment of the spatial phase grating 16a, and the spatial phase grating waveforms of these overlapping segments are completely equal. In other words, after T/(1-R) time has elapsed after the ultrasonic spatial phase grating forming signal 1 is input to the ultrasonic transducer 6, the two spatial phase gratings 16a and 16b are shifted by one segment and overlap with equal dimensions. At this time, the spatial frequencies of opposing segments are also equal. The cross-correlation of such states takes its maximum value.

FIG. 5 is a graph showing an example of a temporal change in the intensity of a specific diffraction bright spot detected by the acousto-optic ultrasonic time-base compressor (FIG. 3). The nonlinear FM signal shown at the bottom of the graph is the ultrasonic spatial phase grating forming signal 1 input to this ultrasonic time axis compressor, and is
The ultrasonic wave propagates through different ultrasonic propagation media 11a and 11b. These two spatial phase gratings 16a and 16b moving parallel to each other
When these overlap, the intensity of the diffraction bright spot reaches its maximum value. That is, in Figure 5, the time is approximately 13.0
(μ seconds) band pulse is approximately 0.3 around time t=7.
(μsec) pulse.

In the above explanation, the ultrasonic spatial phase grating forming signal 1 is a discontinuous nonlinear signal as shown in FIG.
Although FM signals are used, this is to make it easier to understand the technical idea of the invention, and other developments are also possible. That is, it is also possible to create an ultrasonic spatial phase grating forming signal in which the temporal frequency changes along a continuous, smooth nonlinear curve by making the discontinuous sections fine. In the figure, by changing the time frequency along a curve 17 indicated by a broken line, continuous FM that can be used in the same liquid cell as the ultrasonic spatial phase grating forming signal using the discontinuous FM signal shown in the embodiment of the present invention. A method of generating an ultrasonic spatial phase grating forming signal by a signal is possible. In other words, the time frequency is continuously changed so that the spatial phase gratings in each ultrasonic propagation medium due to the ultrasonic spatial phase grating forming signal overlap equally in a finite interval due to the parallel movement of these spatial phase gratings.
Moreover, it is also possible to change it nonlinearly.

The present invention exhibits its characteristics particularly in pulse compression in the low frequency ultrasonic band, and can be used for radar, sonar, etc.
This is an ultrasonic time axis compression method that can be applied in a wide range of fields such as biological measurement.

In the example, the case where there are two ultrasonic propagation media has been explained, but in the case where there are two or more ultrasonic propagation media, the diffraction bright spot intensity waveform in Fig. 5 can be made even sharper in a certain local part, and the time The effect of axial compression can be enhanced.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of an ultrasonic spatial phase grating forming signal, and Fig. 2 is a structural diagram of an embodiment of a liquid cell for acousto-optic electrical signal processing, where a is a perspective view and b is a view from above. , Fig. 3 is a diagram showing the configuration of an acousto-optic ultrasonic time-base compressor, Fig. 4 is a diagram for explaining the formation of an ultrasonic spatial phase grating, and Fig. 5 is a diagram showing the ultrasonic time-base compressor of the present invention. FIG. 6 is a diagram showing an example of an ultrasonic spatial phase grating forming signal. In the figure, 1
are ultrasonic spatial phase grating forming signals, 11a, 11b
are ultrasonic propagation media with different propagation velocities, 13
is a lens, 14 is a spatial filter, 16a, 16b
indicate the ultrasonic spatial phase grating, respectively.

Claims (1)

[Claims] 1 Ratio of sound velocity v _o (n2) v _k /v _k − ₁ (k=
11 in at least two types of ultrasonic propagation media such that 2, 3, ..., n) is a constant value R (0<R<1)
A, 11b are ultrasonic signals of time frequency T time, and the following sequentially ultrasonic signals of time frequency/R.
RT time, time frequency/R ² ultrasound signal R ² T
Ultrasonic spatial phase grating forming signals 1 are emitted simultaneously in the same direction while continuously switching over time... (T is an arbitrary time) to form ultrasonic spatial phase gratings 16a and 16b in each medium. A monochromatic plane wave light is passed in a direction perpendicular to the ultrasonic spatial phase grating; it is focused by a lens 13 to create a diffraction image; the bright spot intensity of the diffraction image is detected at a predetermined position by a spatial filter 14; Method of ultrasonic time axis compression.