JP2872396B2 - Ultrasonic signal processor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting or inspecting an object using ultrasonic waves, and particularly to a phasing process for phasing received signals from a plurality of ultrasonic transducer elements.

[Conventional technology]

The azimuth resolution is improved by adding delays to the received wave signals of the ultrasonic waves detected by the arrayed transducer elements to make the ultrasonic waves from the desired azimuth or distance in phase, and adding them together. Is used in various fields such as inspection of a flaw of an object, sonar or imaging of an ultrasonic tomographic image of a living body.

Also, JP-A-52-20857, and U.S. Pat.
In the figure, a device is shown in which a received signal is frequency-shifted to a low-frequency signal by mixing a reference signal whose phase is controlled respectively with each received signal, and thereafter each is delayed and added. In these devices, it can be said that the frequency shift phasing method is performed.

[Problems to be solved by the invention]

In any of the devices employing the above phasing method, it is necessary to change the amount of delay to each signal in accordance with the change in the azimuth or distance to be matched. In order to achieve this with limited equipment cost, the delay unit to give a delay,
Generally, a configuration is adopted in which a delay time that can approximate the theoretical value of the delay time of the received signal is selected from a plurality of delay times having a limited value and executed. That is, the delay time is selected from values that are integral multiples of a certain quantization unit.

In the above-described frequency shift phasing method, a sufficient azimuth resolution can be obtained even if the quantization unit of the delay time of the delay unit is made larger than that of the simple phasing method. For example, in one example described in Japanese Patent Application Laid-Open No. 52-20857, each received signal frequency-shifted by mixing is sampled at a predetermined cycle, and a delay amount that is an integral multiple of the sampling cycle is realized. But,
The sampling period can be made relatively large. However, the phase control of the reference signal mixed with each received signal needs to be performed with sufficient precision in accordance with the wavefront to be phased, and it has been difficult to configure such a frequency shifter.

[Means for solving the problem]

After a minute delay, the present invention uses a reference signal common to a plurality of received signals, that is, a reference signal having a common phase, as a reference signal to be mixed for frequency shift. For this purpose, a minute delay circuit is inserted before the mixing, and a phase shifter for shifting the mixed output by a predetermined phase is used.

[Action]

The azimuth resolution is formed by adjusting the phases of the signals received by the plurality of receiving elements and adding them. Although the conventional configuration is that shown in Figure 2, where Figure 2 a) is a simple construction, is delayed by a minute delay circuits each signal from the receiver elements TR ₁ to Tr _N, sufficiently small delay Quantization delay circuit that can set delay time in units of time τ '
Only the target signal is received by delaying and adding by QD. According to this configuration, since τ ′ is small, the configuration of the quantization delay circuit becomes difficult. FIG. 2 (b) shows a frequency shift method according to the inventor's inventor, which performs a mixing process such as multiplication of a signal from the TR and a reference signal R whose time is precisely controlled to convert the signal into a low-frequency signal. Quantization delay circuit that can be set in units of large delay time τ ″
This is a configuration for simplifying a quantization delay circuit by delaying and adding by QD. According to this configuration, the configuration of the mixing section becomes difficult. In addition, there is deterioration of the waveform.

In the configuration of the present invention, since the mixing process with the reference signal having the same phase is performed after each of the small delays, the configuration of the mixing unit is simplified, and the frequency shifts to a low frequency at the same time. In addition, requirements on the frequency characteristics of the main delay section are relaxed, and the configuration of this section is simplified.

〔Example〕

Hereinafter, embodiments will be described in detail with reference to the drawings. In FIG. 1, TR _{1 to} TR _N are arranged ultrasonic transducers (transducer elements), SD is a minute delay circuit, M is a mixer, and MD is each delay time in a quantization unit of delay time τ _Mn. Is a quantizing delay circuit that can be set, and AD is an adder.

Transmitting signals from the circuit for transmission, not shown in the part of the element TR ₁ to Tr _N is applied, the ultrasonic pulses are transmit toward the target with. Reflective wave element TR ₁ to Tr _N Thereby resulting
Is detected in each of the. Each received signal is a minute delay circuit SD
After each delay at the mixer M, the reference signal generator
Each is mixed with a common reference signal from RG. The low-frequency components generated by the mixing are respectively subjected to a specific phase shift by the phase shifter PS, then delayed by the quantization delay circuit MD, added by the adder AD, and phase-adjusted to obtain the received signal ω.
_n (t).

When the transmission signal center frequency is omega _S and s (t) can be approximated by s (t) = A (t ) exp (jω S t). Here, A (t) is the envelope shape of the transmission signal. Received signal u _n by the n-th element of the reflected signal by the transmission signal (t) u _n is by the propagation time of the sound wave and _{τ n (t) = s (} t-τ n) = A (t-τ n ) Exp {jω _S (t−τ _n )}. In this method, the time tau _Sn by SD this u _n (t)
And delay by f _n (t). This signal f _n (t) is M
To be in phase by D, f _n (t) = A (t + τ _Mn ) exp ｛jω _S (t +
τ _Mn )｝. Here, τ _Sn + τ _Mn = τ _n . This signal is multiplied by a reference signal h (t). here,
In this method, h (t) is common to all element channels, and h (t) = exp {jω _d t)}. Therefore, _assuming that the multiplication result is g _n (t), g _n (t) = f _n (t) h (t) = A (t + τ _Mn ) · exp [j ｛(ω _S −ω _d ) t + ω _S τ _Mn ｝] = A (t + τ _Mn ) · exp [j ｛ω′t−ω _S τ _Mn ｝] = A (t + τ _Mn ) · exp [j ｛ω′t + (ω ′ + ω _d ) τ _Mn ｝] = A ( t + τ _Mn ) · exp [j ｛ω ′ (t + τ _Mn ) + ω _d τ _Mn }]. Here, ω ′ corresponds to the frequency after the movement, and ω _S −ω ′ = ω _d . The signal v _n (t) obtained by subjecting this waveform to a time delay of τ _Mn by the MD is v _n (t) = g _n (t−τ _Mn ) = A (t) exp [jω′t + ω _d τ _Mn ] = A (t) exp [jω't + 2πτ _Mn / τ _d ]. Here, τ _d is the period of the reference signal, and ω _d = 2π / τ _d . In this signal, τ _Mn differs depending on n, and is the result of adding these. In general, the phases do not match, and the amplitude of the reflected signal from the desired position does not grow at the output of the adder circuit AD. Therefore the phase shifter shown in the first diagram PS of the present method rotates only mixer output of the phase the phase phi _n. Here, by setting φ _n = −2πτ _Mn / τ _d , v _n ″ (t) has the same waveform as v _n ″ (t) = A (t) exp [jω′t], and the addition result of these W ″ (t)
To And can grow big.

Here, since the fixed phase angle is linear, by rotating the phase of f _n (t) by φ _n by PS as in the configuration shown in FIG. 3, similarly, v _n ″ (t) Has the same waveform as v _n ″ (t) = A (t) exp [jω′t], and the result of addition of these is w ″ (t)
Can be greatly grown.

Here, the I and L is an integer, when the tau _Mn is set to _{τ Mn = (I / L)} τ d, the signal v _n (t) is _{v n (t) = g n} (t-τ Mn) = A (t) becomes _{exp [jω't + 2πτ Mn / τ} d] = a (t) exp [jω't + 2πI / L]. For this reason, the phase shift amount of the PS is always φ _n ≡0 when L = 1, φ _n is 0 or π when L = 2, and L types of phases when L = L. The amount of rotation is limited, and PS is not required or can be configured with a phase inversion circuit, thereby simplifying the device.

Here, as the configuration of the PS, a delay line can be used in addition to a normal phase shifter.

Although the above has been treated as a complex signal for the sake of simplicity, the present invention is not limited to this configuration, and a configuration using only a real part or an imaginary part is naturally possible as a simple configuration.

〔The invention's effect〕

This method has the feature of not being affected by waveform deterioration. Further, ω ′ is a signal frequency after moving to a low frequency,
The MD configuration is simplified. Further, the reference signal h (t) is common to all signals, and the configuration of the mixing unit is greatly simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a basic configuration of an embodiment of the present invention. FIG. 2 is a configuration explanatory view of a conventional system. FIG. 3 is a block diagram illustrating the configuration of another embodiment of the present invention. TR: Transceiver, SD: Micro delay circuit, M: Mixer,
MD: Quantization delay circuit, AD: Adder, RG: Reference signal generator, PS: Phase rotator, PC: Phase control circuit.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Kondo 1-280 Higashi Koikebo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-4-194770 (JP, A) JP-A-4 JP-A-94771 (JP, A) JP-A-3-94738 (JP, A) JP-A-3-291580 (JP, A) JP-A-4-38940 (JP, A) JP-A-63-209632 (JP, A) JP-A-58-141142 (JP, A) JP-A-55-158706 (JP, U) JP-B 5-32709 (JP, B2) JP-B 1-227394 (JP, B2) (58) Field (Int.Cl. ⁶ , DB name) G01S 15/89 G01S 7/52 G01N 29/22 A61B 8/00

Claims (4)

(57) [Claims] An ultrasonic signal processing apparatus for processing a plurality of received signals to form an image by performing signal processing, wherein a plurality of first delay means for giving a short delay time to each of the received signals; Mixing means for mixing a common reference signal with the output of the delay means, a plurality of phase shift means for changing the phase of the output of the mixing means, and second delay means for delaying the output of each phase shift means And an adding means for adding the outputs delayed by the second delay means. 2. The ultrasonic signal processing apparatus according to claim 1, wherein a ratio of a period of said reference signal to a delay time of said second delay means is an integer ratio. 3. An ultrasonic signal processing apparatus for processing a plurality of received signals to form an image by performing signal processing, wherein a plurality of first delay means for giving a short delay time to each of the received signals; A plurality of phase shifting means for changing the phase of the output of the delay means, a mixing means for mixing a common reference signal with the output of each of the phase shifting means, and a second means for delaying each output mixed by the mixing means. 2. An ultrasonic signal processing apparatus comprising: a second delay unit; and an adding unit that adds each output delayed by the second delay unit. 4. The ultrasonic signal processing apparatus according to claim 3, wherein a ratio between a period of said reference signal and a delay time of said second delay means is an integer ratio.