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The present invention relates to an ultrasonic transducer used in a sonar, a fish finder, etc., and
more particularly to an array structure of vibrating elements. In general, a transducer used for a
sonar, a fish finder, etc. has a large number of vibration elements arranged in order in the
longitudinal and lateral directions on a flat or cylindrical surface, and has an amplitude 9 phase
suitable for these. It is configured to provide an electrical signal to obtain desired sound wave
directivity characteristics, sound pressure and the like. By the way, in general, it is difficult to
achieve a wide band (since Q is high) for these vibrating elements. Therefore, in most cases, the
operating frequency of the transducer is used at a single frequency which is the resonant
frequency of the vibrating element. However, since it is extremely inconvenient that the
operating frequency is only a single frequency, some devices have been devised so that
ultrasonic waves can be transmitted and received even at the 2nd harmonic or 3rd harmonic
frequency of each transducer. Also, in general, the radiation surface dimension of the vibrating
element is λ / 2 (λ is the wavelength of the sound wave at the frequency f) in order to suppress
the sound wave beam (hereinafter referred to as a side rope) other than the target direction of
the transmitted and received ultrasonic waves. Is selected. For example, the resonance frequency
is f. Consider the case of a transducer that can be used at two and two nine frequencies. The
sound wave radiation surface dimension of the vibration element is constant regardless of the
resonance frequency. Now, if the radiation surface dimension is selected to be λo / 2 which is a
half wavelength of the above frequency fo, the dimension when used at a frequency of 2fo Is
equivalent to the length of one wavelength of the used frequency, which is inconvenient due to
insufficient side rope suppression. In this case, the frequency f is as shown in the conventional
example of FIG. In addition to the transmitter / receiver 1 consisting of the vibration element
group 3 whose radiation surface dimension is λV / ′ 2 at one frequency 2fo, the dimension λ
is a half wavelength. Since it is necessary to have both of the transducers 2 composed of the / 4
vibration element group 4, there is a disadvantage not only in the form surface to be enlarged
but also in the suppression of the side ropes. The present invention overcomes the drawbacks of
the prior art by connecting in parallel a plurality of oscillating elements used for the resonant
frequency. The transducer elements can also be used for other resonant frequencies, and the
external dimensions of the transducer can be made smaller by sharing the transducer elements at
a plurality of resonant frequencies. An ultrasonic transducer for multiple frequencies is provided.
The present invention will be described in detail below with reference to the drawings. FIG. 2
shows an embodiment of the present invention, and FIG. 2 (a) shows a transmitter / receiver 4
comprising a large number of vibration elements whose dimension of one side of the radiation
surface is b.
Now, it is assumed that the resonance frequency of this vibration element is f, and the resonance
frequency is also present in this double harmonic 2f. When such an oscillating element is used at
frequency 2f, the radiation surface dimension is set to λ / 2 = C / 4f which is 1/2 of wavelength
λ = O / 2f (where C is the speed of sound) at frequency 2f, By providing an electric signal with
an appropriate amplitude 1 phase to each vibration element, it is possible to form a transmission
sound beam with few side lobes, and conversely, the reception sound pressure of each vibration
element is an appropriate electric signal level It is possible to form a receive beam by performing
phase control to the On the other hand, when using at the resonance frequency f, it is sufficient
to determine the radiation surface dimension with the half wavelength at the working frequency
as the length of one side of the vibrating element, for example, as shown in FIG. A vibration
element with a side of 0 / 2f can be obtained by connecting two (two in total) vibration elements
each having a side length of C / 4 / in both vertical and horizontal directions. Thus, one side of
the vibrating element 3 in which four vibrating elements 4 each having a side length b are
connected in parallel has a side which is twice as large as b, and the frequency f of half the
frequency 2f used in the vibrating element 4 is It becomes possible to use. In this way, a
transducer with few side lobes at any of the two types of frequencies can be realized without
increasing the external dimensions. If it is desired to have a transducer having a resonance
frequency at the frequency 3f, which is the triple frequency f in addition to the fundamental
frequency f, FIG. 2 (the vibration of one side b (−, 7ρ as shown by the mouth j) Instead of the
element 40, it is realized by arranging elements of C / 6f in a row and three each in the
longitudinal and lateral directions, that is, by connecting a total of nine oscillating elements 4 in
parallel. It is well known that the width (beam width) of an acoustic beam to be transmitted /
received is uniquely determined from the frequency, the size of one vibrating element, the
element spacing (element center spacing) and the number of elements. Also, in the present
invention, the element size is 172 wavelengths of the used frequency. Since the element spacing
has been described as being set to a half wavelength of the operating frequency, in order to make
the beam width of the sound wave the same at the operating frequency f and 2fC or 3f), the
number of elements used at each frequency must be the same. You must. To meet the
requirement that the sound wave beam width be the same at a plurality of frequencies, as shown
in FIG. 3, 2f (or 3f) may be provided at the center (or end) of the entire transducer. The vibration
element 4 having a resonance frequency and one side of C / 4f (or C / 6f) may be disposed.
In this case, it goes without saying that the number of elements used for one history and the
number of elements used at 2fC or 3f) are equal to each other at the resonance frequency f. In
the above description, the vibrating elements are described as being arranged in one plane, but
the present invention is not limited to this, and it is possible to arrange all on the 9 cylindrical
surfaces or spherical surfaces. In addition, f, 2f and 3f are merely exemplified for the resonance
frequency. According to the present invention according to the above-described 45 Je, the
present invention provides a transceiving frequency that can be used at a plurality of resonance
frequencies without increasing the size of the ultrasonic transducer and can obtain an ultrasonic
beam with few side lobes. Also, it has the advantage of being able to easily configure a transducer
capable of making the acoustic beam of 11] identical at the plurality of operating frequencies.
Brief description of the drawings
FIG. 1 is a plan view showing a transducer array of a conventional transducer, and FIGS. 2 (a) and
2 (b) show an embodiment of the present invention in a plan view showing a transducer array, B)
is a plan view showing a part of the same in an enlarged manner, and FIG. 3 is a plan view
showing another embodiment of the present invention.
1: Transmitter and receiver consisting of a group of transducers having a radiation surface size of
1⁄2 wavelength 2. Transmitter and receiver comprising a group of transducers having a radiation
surface size of 1⁄4 wavelength 3. Radiation surface Vibration element with dimensions 172
wavelength, 4 ... applicant vibration element with radiation surface dimension 1/4 wavelength
Japan Radio Co., Ltd.