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DESCRIPTION JPH03182200

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DESCRIPTION JPH03182200
[0001]
<Industrial field of application> The present invention relates to an acoustic path receiver for
obtaining a constant directivity pattern in a wide frequency range. <Prior Art> In general, in a
disk-like vibrator, the directivity characteristic of the sound obtained at the point pre-separated
from the sound source is given by the following equation of directivity function D (?). D (?)-2 J
+ (k-a-sin ?) / (k-a-sin ?) (1) where Jl is the first-order Bessel function of the first order, k-? /
V% ? is the frequency, Is the velocity of sound, a is the radius of the transducer, and ? is the
azimuth. The polar coordinates of the relationship between D (?) and the azimuth angle ? are
as shown in FIG. It should be noted in equation (1) that D (?) is not only a function of the
azimuth angle ? but also a function of the frequency ?. Therefore, even at the same azimuth
angle ?, the gain of the signal is different due to the difference in the frequency ?. By the way,
when ultrasonic waves are emitted continuously at a single frequency, ka-constant and D (?) is a
function of only the azimuth angle ?, so a single directivity pattern independent of ? With On
the other hand, in order to improve the distance resolution, it is necessary to add a short pulse
signal to the vibrator as shown in FIG. 8 (a), but such short pulse signal has many frequency
components. Contains. For this reason, when a short pulse signal is added, so-called frequency
dispersion occurs which has different directional characteristics depending on the frequency
component, and the pulse waveform is not accurately reproduced in the sound field. That is, as
shown in (b) of the figure, the on-axis of the vibrator (the pulse waveform does not change at
??0, but at a location far from the azimuth angle ? from this axis Since the gains of the signals
are different, as shown in FIG. 6C, as a result, the pulse waveform spreads and the distance
resolution decreases. For this reason, in a fish finder, for example, such a problem occurs that the
exact position of the fish school at a position inclined by the azimuth angle ? can not be known.
This is a particular problem when using an ideal beam transducer composed of circular
transducers as described in Japanese Patent Application Laid-Open No. 61-186878. That is, as
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shown in FIG. 9, in this ideal beam transducer, the weighting function in the direction of the
radius a of the drive voltage applied to the transducer is also Fourier transformed with the itit
function W (a) and the directivity function D (?) Focusing on the pair, azimuth angle ▒ ?
described by Bessel function in the radial direction of the oscillator. The sensitivity is constant
within the range of .beta., And has directivity characteristics (see (b) in the figure) such that there
is no sensitivity at azimuth angles outside the range of. ▒ .00.
Therefore, in order to obtain such an ideal beam transducer, the directivity needs to be
dependent only on the azimuth angle ?, and must not change with the frequency ?. <Problems
to be Solved by the Invention> By the way, in the prior art, measures for avoiding the
phenomenon of dispersion of directivity characteristics when a short pulse signal is added are
not sufficiently considered. The azimuthal dependence of the dispersion of the short pulse signal
is large, and there is a limit in itself in terms of enhancing the distance resolution. <Means for
Solving the Problems> The present invention has been made in view of such circumstances.
Therefore, the present invention aims to obtain an acoustic path receiver that avoids the
phenomenon of dispersion of directivity characteristics and in which the directivity gain does not
depend on frequency at any azimuth angle. In the acoustic path receiver including the diskshaped vibrator having the drive electrodes divided into the following, the following
configuration is adopted. That is, in the acoustic path receiver according to the present invention,
assuming that the short pulse input signal s (t: for t) is ?i (i = 0.1, 2) when the short pulse for
excitation driving to be applied to the vibrator is The radius ai from the center-side drive
electrode to the simultaneous peristaltic target to the drive electrode on the outer layer side is ai
= c / ?i (here, C is the minimum frequency component ?). Are set so as to satisfy the relation of
constants determined by unambiguous fishing), and on the basis of the input signal S (t), a signal
S 1 (t) having the frequency component ? i of the signal S (t) as each central frequency ..), And
each signal Si (t) output from the signal generation circuit according to the frequency .omega.i of
the signal S1 (t). And a signal distribution circuit that applies and distributes to each drive
electrode from the center to the radius ai. In the above configuration, the signal generation
circuit generates a signal S 1 (t) having the frequency component ? i of the signal S (t) as the
center frequency based on the input signal S (t) of the short pulse applied to the vibrator.
Generate (i = Oll, 2, ...). Next, the signal distribution circuit applies and distributes each signal S1
(t) output from the signal generation circuit to each drive electrode from the center to the radius
aj according to the frequency ?i of the signal 510). Then, for the drive electrodes driven
simultaneously, ai и ? i = c (constant). For this reason, the directivity function D (.theta.) Shown
by the equation (1) depends only on the azimuth angle .theta., And the directivity characteristic
shows a single directivity pattern independent of the frequency .omega.i. Therefore, the
dispersion of directivity is avoided. EXAMPLES To describe the present invention in detail, first,
the principle of the present invention will be described.
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The directivity function D (?) represented by the above equation (1) is not only the azimuth
angle ? but also a function of the frequency ? and the radius a of the oscillator. Can be offset
by a. That is, the short pulse human force signal S (t) is ?i (i = 0. If there is a frequency
component of I, 2,...) And if a virtual oscillator having a radius ai (i = 0,?, 2, ...) corresponding to
each frequency component? I is prepared, then the old? = C (constant) (2) As a result, D (?)
exhibits a directivity pattern that depends only on the azimuth ftJ? regardless of the frequency
component ?i. Therefore, in order to always satisfy the above equation (2), (i) creating a virtual
oscillator and a mover having a radius ai according to the frequency component ?i, and (11) a
frequency component of the input signal S (?) generate a signal S 1 (t) (i = O 1 s 2,...) with ? i as
each center frequency, and add each signal S i (t) to a virtual oscillator with radius ai Can be
realized by two points. In order to create a virtual oscillator having a radius at according to the
frequency component ?i of the human horn signal S (t), the following is performed. Now, let ?0
be the center frequency of the smallest frequency band, and this frequency ?. The radius of the
virtual vibrator corresponding to is set to ao according to the production specification, aO?. It
becomes -C (constant). If C is determined, the radius al corresponding to ?i is a, = C / ?i from
equation (2), ?. The radius ai corresponding to is a, = c / ?, and so on, and so on, each radius ai
can be determined by ai = c / ?i. On the other hand, in order to generate each signal S 1 (t) (i =
0, 1, 2,...) Having the frequency component ?i of the human power signal S as the center
frequency, for example, the input shown in FIG. The signal S (t) is Fourier-transformed and
divided into each frequency component ?i (three frequency components in FIG. 1) as shown in
the frequency spectrum of FIG. Inverse Fourier transform produces each signal s 1 (L)
corresponding to the center frequency ? i, but instead, each signal S can be similarly obtained
by passing through a frequency filter having a bandwidth and gain appropriately set. It is
possible to obtain 1 (t). Then, if each signal S 1 (t) is applied to each drive electrode from the
center to the radius ai according to the frequency ? i, the equation (2) is always satisfied.
Basically, according to the above principle, an acoustic path receiver can be obtained in which
dispersion of directional characteristics is avoided. However, in the case of obtaining the above
ideal thermal transducer (refer to FIG. 9), a vibrator As shown in FIG. 1 (C), it is necessary to
weight the signal Si (t) in order to give the vibration distribution according to the predetermined
? ? function W (и) in the 0 radial direction.
Next, an embodiment of the acoustic path receiver embodied based on the above principle will be
described. FIG. 3 is a plan view of a 4 '' 'transducer used in the acoustic path receiver according
to this embodiment. The vibrator I includes a disk-shaped piezoelectric substrate 2, and on the
surface side of the piezoelectric substrate 2, driving is divided concentrically into multiple layers
(in this example, n layers up to numbers ?o? -n ?). An electrode 4 is formed, and a ground
electrode (not shown) is formed on the entire back surface of the piezoelectric substrate 2. Then,
when the frequency component of the short pulse input signal S for excitation drive is ?i (in this
example, j?0, 112), the minimum frequency component ?. The radius a from the center to the
simultaneous peristaltic target to the drive electrode of the outermost layer. , ? i are preset such
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that that of radius ai, ? is radius a. The radius a. Other radius alSa with ?! The ratio is! : (?. /
?,) (?. / ?t). FIG. 4 is a circuit diagram for generating a signal for simulated driving to be
applied to the vibrator 1. In the same figure, 6 is a signal S 1 (t) (t) (wherein the central
component is the frequency component ? i (i = 0, 1, 2 in this example) of the signal S <t> based
on the input signal S (t). This is a signal generation circuit that generates + = 0, ?, 2), and in this
example, is configured by a frequency filter in which the bandwidth and gain are appropriately
set. A signal distribution circuit 8 applies and distributes each signal Si (t) output from the
frequency filter 6 to each drive electrode 4 from the center to the radius and 1 according to the
frequency ?i of the signal Si (t). is there. Then, this signal distribution circuit 8 is a variable
resistor that performs predetermined weighting on each signal S 1 (t) in order to give a vibration
distribution according to a predetermined vt function W (a) in the radial direction of the vibrator
1 The weighting which consists of the circuit 9. .About.9n, weighted circuit 9. .About.9 n to each
of the drive electrodes 4 from the center to the radius ai according to the frequency .omega.j.
Each output of the mixing circuits 10 to 10n is individually connected to each drive electrode 4
of numbers "0" to "n". Therefore, in the above configuration, when the short pulse input signal S
(t) is applied to the frequency filter 6, the frequency component ? i (i = OlI, 2) of the input signal
S (L) Signals S1 (t) (i = O1, 2) having frequency are generated, and each signal Sin is applied to
the signal distribution circuit 8 at the next stage. Each signal SiQ output to the signal distribution
circuit 8 has a predetermined vibration distribution W by the circuits 91 to 9 n.
After weighting so as to give (a), W, (a), Wy (a) (see FIG. 1 (c)), the mixing circuit 10. It is applied
to each drive electrode 4 by -1 on. Then, for the drive electrodes 4 driven simultaneously, ai и ? i
= c (constant). Therefore, the directivity function D (0) represented by the equation (1) depends
only on the azimuth angle ?, and the directivity characteristic exhibits a single directivity
pattern independent of the frequency ?i. Therefore, the dispersion of directivity is avoided. In
this embodiment, although the case where the frequency component ?i of the input signal S (t)
is divided into three has been described, it is needless to say that the present invention is not
limited to this. FIGS. 5 and 6 show a modification, wherein FIG. 5 is a plan view of the vibrator
and FIG. 6 is a circuit diagram for generating a signal to be applied to the vibrator of FIG. The
vibrator 1 ? ? in this case is the same as the above embodiment in that the drive electrodes 4
? are formed concentrically with the numbers ?O to? n ?, but in the present embodiment
each individual drive electrode is further included. 4 is radially divided into partial electrodes A,
B, C corresponding to the frequency ?j to be driven. And, a partial electrode ASB in each interlayer. C are connected in parallel, respectively. On the other hand, after the signal distribution
circuit 8 'performs predetermined weighting according to the vibration distribution to each
output signal S + (t) of the frequency filter 6, each drive electrode 41 from the center to the
radius ai according to the frequency ?i. Weight transformer T with tap to distribute. , T1, T, and
each tap of each weight transformer T0, T1, T is connected to the drive electrode 4 of the
corresponding layer. Therefore, also in this case, as in the case of the above-described
embodiment, al и ? i = c (constant) for the drive electrodes 4 driven simultaneously. For this
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reason, the directivity function D (.theta.) Shown by the equation (1) depends only on the azimuth
angle .theta., And the directivity characteristic shows a single directivity no. Turn independent of
the frequency .omega.i. Therefore, the dispersion of directivity is avoided. In each of the above
embodiments, in order to obtain the ideal beam transducer, the vibration distribution according
to the predetermined sacrificial function W (a) is given in the radial direction of the transducer,
but in the vibration plane Even in the case of a normal vibrator for applying such a weight
voltage, or for a vibrator having any vibration distribution, if the present invention is applied, one
having no dispersion of directivity characteristics can be obtained. Of course. According to the
present invention, the following effects can be obtained. (I) When the vibrator of the present
invention is used, ai и ?i = c (constant) that determines the directivity function D (?), the
directivity function D (?) depends only on the azimuth angle ?.
Therefore, the directivity exhibits a single directivity pattern independent of the frequency ?,
and the dispersion of the directivity is avoided. Therefore, it is possible to obtain an acoustic path
receiver in which the directional gain does not depend on the frequency at any azimuth angle ?,
and the pulse reproducibility is excellent. This is particularly effective when obtaining an ideal
beam transducer. (11) The high frequency component drives only the central portion of the
vibrator, which is substantially equivalent to the fact that the diameter of the vibrator becomes
smaller at a high frequency. Therefore, since the resonance frequency of the radial mode is
increased, the frequency response of the vibrator itself is also improved.
[0002]
Brief description of the drawings
[0003]
1 to 6 show an embodiment of the present invention, FIG. 1 is an explanatory view of the
principle of the present invention, FIG. 2 is a directivity characteristic diagram showing a single
directivity pattern obtained by the present invention, FIG. The figure is a plan view of the
transducer used in the ultrasonic wave transmitting and receiving i2 & device based on the
principle of the present invention, FIG. 4 is a circuit diagram for generating a signal applied to
the transducer of FIG. FIG. 6 is a circuit diagram for generating a signal applied to the vibrator of
FIG. 5.
Fig. 7 is an explanatory view of dispersion of directivity characteristics, Fig. 8 is an explanatory
view of reproducibility of short pulses accompanying dispersion of directivity characteristics, and
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Fig. 9 is a weight function W (a) for obtaining an ideal pattern transducer. And a directivity
function D (?). 1.1 ? иии Vibrator, 4.4 ? ? иии Drive electrode, 6 иии Signal generation circuit
(frequency filter), 8.8 ? иии Signal distribution circuit. Fig.5 Fig.5 Fig.11- "
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