JPH04581Y2 - - Google Patents

Description

[Detailed description of the invention] This invention consists of two solid-state ultrasonic delay elements, a coil,
The present invention relates to an ultrasonic delay circuit constituted by circuit elements such as transistors, and relates to an ultrasonic delay circuit with improved unnecessary signal characteristics.

As shown in Fig. 1, a solid-state ultrasonic delay element consists of a delay medium 1 made of a solid material such as metal, crystal, glass, ceramics, etc., which propagates ultrasonic waves, and a crystal mounted on an appropriately selected surface of this medium. Alternatively, it consists of an input transducer 2 made of a piezoelectric material such as lead zirconate titanate, which converts an electrical signal into a mechanical signal, and an output transducer 3, which converts the mechanical signal into an electrical signal.
When an electrical signal is applied to input transducer 2, this signal is converted into a mechanical signal and travels through delay medium 1 as indicated by arrow 4. The mechanical signal reaching the output transducer 3 is converted into an electrical signal.

Conventionally, when constructing a delay circuit having a certain delay time using one ultrasonic delay element, it has been difficult to downsize the delay circuit because the unnecessary signal characteristics shown in FIG. 2 deteriorate. In other words, in order to miniaturize an ultrasonic delay element, it is necessary to use a multiple reflection type in which the ultrasonic wave is reflected many times in the delay medium, and as a result, it is reflected and scattered away from the main signal path at the reflecting surface. As the number of components increases, the level of unnecessary signal components increases, and the distance between the input transducer and the output transducer becomes smaller, causing problems such as unnecessary signals reaching the output transducer without being sufficiently attenuated. Ta.

In FIG. 2, the horizontal axis is the time axis, and the vertical axis is the amplitude intensity of the signal. Note that if the signal is shown using a wavelength near the pass signal band of the delay element, the signal will be very fine compared to the scale of the horizontal axis in the figure.
The signals in the figure are shown by their envelopes. Unnecessary signals 6 and 7 having different delay times are generated with respect to the main signal 5. This is due to the fact that sound waves are diffracted and scattered in the delay medium, and some sound waves reach the output transducer from the input transducer through a path different from that of the main signal. For example, the unnecessary signal 6 is a signal that is output as an ultrasonic wave that is reflected and scattered on a different path from the main signal in a delay medium, and the unnecessary signal 7 is a signal that is output because it goes back and forth several times along the same path as the main signal. A signal output with a delay time that is an odd multiple of the main signal delay time, i.e. 3τ spurious (third-order reflected signal)
etc. signals.

As a delay circuit that eliminates this drawback, two ultrasonic delay elements each having a delay time of 1/2 of the required delay time are used, and one of the electrodes of the output transducer of the first ultrasonic delay element is connected to the second ultrasonic delay element. A delay circuit has been proposed in which one of the input transducers of an ultrasonic delay element is conductively connected, and the other of the first output transducer is conductively connected to the other of the second input transducer, that is, the delay circuit is continuously connected.

However, it has been found that unnecessary signal characteristics are degraded even in a delay circuit having such a structure.

In view of this, the present inventor has made various experimental and theoretical studies, and has found that the unnecessary signals 6 and 7 generated after passing through one element are changed to the main signal 5 after passing through two elements, as shown in FIGS. It has been found that the unnecessary signal characteristics are deteriorated by overlapping in the same phase with the unnecessary signal generated by newly passing through the second element.

FIG. 3a shows the signal after passing through the first element, and FIG. 3b shows the signal after passing through the second element. In b, in addition to the unnecessary signals 6 and 7 of a that have passed through the second element, the unnecessary signal shown by the broken line that is newly generated due to the main signal 5 passing through the second element overlaps in the same phase. . Therefore, as shown in the figure, the unnecessary signals 6' and 7' after passing through the second element become about twice as large as the unnecessary signals after passing through the first element.

As a result of further repeated experiments based on the above knowledge, the inventor of the present invention determined that the delay time of the first element and the delay time of the second element are each Θ ₁ , When Θ ₂ is specified, 45° + m × 180° ≦ | Θ ₁ − Θ ₂ | ≦ 135° + m
By setting ×180° (m is an integer greater than or equal to 0),
A signal in which two unnecessary signals with phase differences Θ ₁ +3Θ ₂ and 3Θ ₁ +Θ ₂ that pass through one of the two solid-state ultrasonic delay elements as a main signal and the other as a tertiary reflected signal are superimposed, It has been found that it can be effectively attenuated.

When measuring the delay time between the input signal and the output signal of a delay element, it is known to use a phase difference meter to measure the phase difference (phase delay time) between the input and output signals. In this case, the phase difference between the input signal and the output signal is Θ=n×360°+θ (n is an integer, 0
≦θ<360°). In reality, only θ is measured by the phase difference meter, and n is determined by another method. The delay time from this phase difference is as follows: Delay time (T)=n×360°+θ/360°× However, indicates the frequency at which the phase difference was measured.

From this equation, it can be seen that the phase difference corresponds to the delay time.

For example, the phase difference between the input and output signals of a delay element with a delay time of 63.5556μS and a center frequency of the passband of ^3.579545MHz ; ×3.579545×10 ⁶ = 81900° = 227×360° + 180°. That is, n=227 and θ=180°.

Unlike the delay time, the phase difference between the input and output signals has no meaning unless the measurement frequency is specified, and the delay time cannot be calculated from this phase difference unless the frequency is specified. In the present invention, this measurement frequency is the center frequency of the pass signal band of the delay element,
When the bands are different between two elements, the average frequency of both center frequencies is used.

In the present invention, when the delay time of two delay elements is defined by the phase difference Θ ₁ and Θ ₂ of the input and output signals, the phase difference Θ ₁ corresponding to the delay time of the input and output signal of the first delay element, that is Θ ₁ =T ₁ ×360°×. The phase difference Θ ₂ corresponding to the delay time of the input and output signals of the second delay element, that is, Θ ₂ = T ₂ × 360° × (T ₁ , T ₂ ...delay time expressed in time), is 45 °＋m×180°≦｜Θ ₁ −Θ ₂ ｜≦135°＋
The relationship should be m x 180° (m is an integer greater than or equal to 0).

FIG. 4a shows the signal after passing through the first element, and FIG. 4b shows the signal after passing through the second element. For example, the operation of the present invention will be explained when the signal 7 is an unnecessary signal occurring at three times the predetermined delay time, that is, a spurious signal (third-order reflected signal) at 3τ. First, the main signal 5 is output from the first element after Θ ₁ has elapsed from its input to the first element, and the unnecessary signal 7 is output from the first element after 3Θ ₁ has elapsed. These two signals are input to the second element at approximately the same time as the output. Then, the main signal 5'' is output after Θ ₂ elapses from the input of the main signal 5 to the second element, and the unnecessary signal associated with the input of the main signal 5 is output after 3Θ ₂ elapses.The latter is shown in Fig. 4b. This is shown by a broken line in the following,
It is called unnecessary signal A. That is, the unnecessary signal A is output from the second element after Θ ₁ +3Θ ₂ has elapsed after being input to the first element. On the other hand, due to _the input of the unnecessary signal 7 to the second element, there is an output from the second element after the predetermined delay time Θ ₂ has elapsed, and this is because the _second It will be output from the element. (Hereinafter, this will be referred to as unnecessary signal B.)
The unnecessary signal A and the unnecessary signal B are output at close times, and the time difference between them is a phase difference of 2|Θ ₁ -Θ ₂ |. In this case, the phase difference that is most attenuated when the two waveform signals cancel each other out is 180° + m × 360° (m
is an integer greater than or equal to 0), so 2|Θ ₁ −Θ ₂ |=
From 180° + m x 360° | Θ ₁ - Θ ₂ | = 90° + m x 180°
They are attenuated the most and do not strengthen each other. It is desirable to have a phase difference such that the two unnecessary signals cancel each other out, but the value differs depending on how many times the unnecessary signal occurs at a predetermined delay time. Therefore, in practice, it is preferable to select the most convenient phase difference |Θ ₁ −Θ ₂ | depending on the characteristics of the delay element.

Note that when the phase difference |Θ ₁ −Θ ₂ | between the two elements is smaller than 45°, the phase shift between the two unnecessary signals is not large, so the cancellation effect is small. ｜Θ ₁ −
The preferred range of Θ ₂ | is 45° + m × 180° ≦ | Θ ₁ − Θ ₂ | ≦ 135°, centered on the phase difference of 90° + m × 180°.
A range of +m×180° (m is an integer of 0 or more) is preferable.

FIG. 5 shows the entire delay circuit according to the present invention, where 11 is a first delay element, 12 and 13 are input transducers and output transducers, respectively, 14 is a second delay element, and 15 and 16 indicate input transformer and output transformer, respectively. Output converter 1 of the first delay element
3 and the input transducer 15 of the second delay element are connected by a lead wire 18 provided with a coil 17, which is a passive impedance element, thereby achieving impedance matching between the two delay elements. Instead of the coil 17, an active circuit element such as a transistor may be provided. 19 is an input terminal, 20 is an input matching resistor, 21 is an input matching coil, 22 is an output matching coil, 23 is an output matching resistor, and 24 is an output terminal.

Example The phase difference Θ ₁ between the input and output signals of a delay element with a passband center frequency of 4.43362 MHz and a delay time of 63.973 μS is Θ ₁ = 63.973 × 10 ^-6 × 360° × 4.43362 × 10 ⁶ =
It is 102108°.

In addition to this element, a delay element with a delay time of 63.913μS (center frequency 4.43362MHz, input/output phase difference Θ ₂ =
102012°) is continuously connected through the coil as shown in Figure 5, the strength of the 3τ spurious signal (third reflected signal) is -50dB relative to the main signal.
The strength of other unnecessary signals was -32 dB. still,
The phase difference between the center frequencies of both elements is Θ ₁ −Θ ₂ =96°.

For comparison, two delay elements with a delay time of 93.943 μS were used.
When connected continuously (the delay time difference defined by the phase between both elements is 0°), the strength of the 3τ spurious signal was -34 dB with respect to the main signal, and the strength of other unnecessary signals was -27 dB. Here, FIG. 6 shows the relationship between the intensity (vertical axis) and phase difference (horizontal axis) of the signal in which unnecessary signals A and B are superimposed at frequencies of 3.9, 4.2, 4.43,
A specific example of measurement for 5 different frequencies of 4.6 and 4.9 MHz will be shown below.

The horizontal axis is the delay time T (ns) and its phase difference Θ ₁ −
The unit is the value converted to Θ ₂ , and T = (Θ ₁ −
Θ ₂ )/(360°×) (where frequency is). In this example, 4.43 MHz is the reference unit on the horizontal axis, and 360° corresponds to approximately 226 ns. The vertical axis shows the relative signal strength when the main signal is 600. At any frequency, the signal strength is lowest and attenuated when the phase difference is around 90° and around 270°.

According to the present invention, a delay circuit that is small in size and has good unnecessary signal characteristics is realized.

[Brief explanation of the drawing]

FIG. 1 shows a plan view of an example of a solid-state ultrasonic delay element. Fig. 2 shows the state of the output signal of one conventional delay element, Fig. 3 shows the state of the output signal of the conventional delay element with two connected delay elements, and Fig. 4 shows the state of the output signal of the conventional delay element with two connected delay elements. The states of the output signals of the elements are shown respectively. FIG. 5 is a circuit diagram showing an entire example of the ultrasonic delay circuit of the present invention. FIG. 6 is a graph obtained by measuring the phase difference and signal strength of a superimposed signal of unnecessary signals A and B of the present invention at five frequencies.

Claims (1)

[Claims for Utility Model Registration] (1) For two solid-state ultrasonic delay elements, when the delay time is defined by the phase difference Θ ₁ and Θ ₂ between the input and output at the center frequency of the respective passbands, the delay time is 45°.
+m×180°≦｜ _Θ1 , _Θ2 ｜≦135°＋m×180°(m
is an integer greater than or equal to 0), two solid-state ultrasonic delay elements are connected in cascade, and one of the two solid-state ultrasonic delay elements is passed as a main signal, and the other is passed as a tertiary reflected signal. An ultrasonic delay circuit characterized by attenuating a signal in which two unnecessary signals having phase differences Θ ₁ +3Θ ₂ and 3Θ ₁ +Θ ₂ overlap. (2) Claims for utility model registration in which a circuit element consisting of a passive impedance element such as a coil is connected in parallel between two solid-state ultrasonic delay elements, and the two solid-state ultrasonic delay elements are connected in cascade. 1st
The ultrasonic delay circuit described in Section 1. (3) If the center frequencies of the two delay elements are different, the utility model registration claim 1 stipulates the delay time based on the phase difference between input and output using the average frequency of the center frequencies of both elements. 1st or 2nd
The ultrasonic delay circuit described in Section 1.