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JP2010212826

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DESCRIPTION JP2010212826
An electro-acoustic transducer having desired directivity characteristics and easy to manufacture,
and a control parameter optimization method thereof. An electro-acoustic transducer for
converting between electrical and acoustic signals, comprising m (m is an integer of 2 or more)
transducers on each side of a regular n-face (n is an integer of 4 or more) , And n faces of a
regular n-surface form a transducer array. [Selected figure] Figure 3
Electro-acoustic transducer, control parameter optimization method for electro-acoustic
transducer
[0001]
The present invention relates to an electro-acoustic transducer that converts an electrical signal
to an acoustic signal or converts an acoustic signal to an electrical signal, and a control
parameter optimization method for the electro-acoustic transducer.
[0002]
In order to transmit and receive sound waves in water, a hydrophone (underwater sound wave
transceiver) having excellent directivity characteristics is used.
There is a technology for realizing nondirectionality in a wide frequency band by using a hollow
spherical piezoelectric ceramic (see, for example, Non-Patent Document 1 and Non-Patent
Document 2).
04-05-2019
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[0003]
O. M. Al-Bataineh, R. J. Meyer, R. E. Newham, N. B. Smith, "Utilization of the High-Frequency
Piezoelectric Ceramic Hollow Spheres for Exposimetry and Tissue Ablation," Proceedings of IEEE
International Ultrasonics Symposium, Munich, Germany, October 2002. R. Newnham, J. Zhang, S.
Alkoy, R. Meyer, W. Hughes, A. Hladkey-Hennion, J. Cochran, and D. Markley, "Cymbal and BB
underwater transducers and arrays," Material Research Innovations, Vol. .6, No. 3, pp. 89-91,
Springer Berlin, September 2002.
[0004]
However, hollow spherical piezoelectric ceramics are difficult to develop and manufacture, and
difficult to maintain a certain quality.
[0005]
The present invention has been made to solve the above-mentioned problems, and it is an object
of the present invention to provide an electroacoustic transducer having desired directivity
characteristics and which is easy to manufacture, and a control parameter optimization method
thereof. .
[0006]
In order to solve the problems described above, one aspect of the present invention is an
electroacoustic transducer that performs conversion between an electrical signal and an acoustic
signal, wherein m is provided on each face of a regular n-face (n is an integer of 4 or more).
There are n (m is an integer of 2 or more) transducers, and n faces of a regular n-face form a
transducer array.
[0007]
Further, one aspect of the present invention is a control parameter optimization method for
optimizing a control parameter of an electro-acoustic transducer that performs conversion
between an electrical signal and an acoustic signal, the electro-acoustic transducer comprising n
(m is an integer of 2 or more) transducers are provided on each surface of n (an integer of 4 or
more), and n surfaces of a regular n-face form a transducer array, and (m × n) The amplitude
and phase of the signal transmitted or received by each of the (m × n) transducers are
determined using a genetic algorithm such that the directivity characteristics by all the
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transducers satisfy the predetermined directivity characteristics. Use and optimize.
[0008]
According to the present invention, it is possible to provide an electroacoustic transducer having
desired directivity characteristics and easy to manufacture, and a control parameter optimization
method thereof.
[0009]
It is an external view which shows an example of the external appearance of the hydrophone in
this Embodiment.
It is a structural drawing which shows an example of the structure of the inner wall face of flat
plate piezoelectric ceramic.
It is a layout showing an example of layout of a transducer.
It is a flowchart which shows an example of a parameter optimization process.
[0010]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0011]
In the following embodiments, a hydrophone to which the electroacoustic transducer of the
present invention is applied will be described.
[0012]
In the present embodiment, a flat plate piezoelectric ceramic is used to realize a hydrophone
having a matrix-like array.
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In addition, Genetic Algorithms (GA) are used to control the directional properties of the array.
[0013]
In the present embodiment, a regular hexahedron is used as the structure of the hydrophone.
The structure of the hydrophone may be a regular polyhedron such as a regular tetrahedron, a
regular dodecahedron, and a regular icosahedron (a regular n-hedron: n is an integer of 4 or
more), instead of the regular hexahedron.
Or it may be a polyhedron other than a regular polyhedron.
[0014]
Here, in the genetic algorithm, selection of genes is roulette selection and crossover of genes is
two-point crossover.
Instead of roulette selection, ranking selection, tournament selection, or elite selection may be
used. Instead of the two-point crossing, one-point crossing or multi-point crossing may be used.
[0015]
Also, here, a piezoelectric ceramic is used as a vibrator that constitutes an array. A giant
magnetostrictive vibrator or the like may be used instead of the piezoelectric ceramic.
[0016]
The structure of the hydrophone in the present embodiment will be described below.
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[0017]
FIG. 1 is an external view showing an example of the external appearance of the hydrophone in
the present embodiment.
This figure shows the x-axis, y-axis, z-axis, and the hydrophone 1 in the present embodiment. The
shape of the hydrophone 1 is a regular hexahedron. Each face of the regular hexahedron in this
hydrophone 1 is a square planar transducer array 2. In the planar transducer array 2, the surface
forming the outer wall of the hydrophone 1 is an outer wall surface, and the surface forming the
inner wall of the hydrophone 1 is an inner wall surface.
[0018]
FIG. 2 is a structural view showing an example of the structure of the inner wall surface of the
planar transducer array 2. The planar transducer array 2 comprises a flat piezoelectric ceramic 5.
On the inner wall surface of the flat plate piezoelectric ceramic 5, m (m is an integer of 2 or
more) electrodes 7 are provided. Here, m is 9 and nine square electrodes 7 are provided on the
inner wall surface of the flat plate piezoelectric ceramic 5 in a matrix of 3 rows and 3 columns.
[0019]
As shown in FIG. 1, one electrode 6 is provided on a square region covering all the regions of the
inner wall facing the nine electrodes 7 on the outer wall of the planar transducer array 2.
[0020]
FIG. 3 is a layout diagram showing an example of the layout of the transducers 3.
In this figure, the positional relationship between the x axis, the y axis, the z axis, and the
hydrophone 1 is the same as in FIG. Hereinafter, in the planar transducer array 2, a portion
covered by one electrode 7 of the inner wall surface is referred to as one transducer (vibrator) 3.
This figure further shows an angle φ from the x axis on the xy plane for use in calculation of
directivity characteristics described later.
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[0021]
This figure further shows a signal processing device 4 that performs signal processing on the
transmission signal or reception signal of the hydrophone 1. Each of the electrodes 7 is
connected to the signal processing device 4 independently. The electrode 6 is connected to a
reference potential (ground) in the signal processing device 4. The signal processing device 4
has, for example, a digital signal processor (DSP), a storage unit, and a central processing unit
(CPU). At the time of transmission, the transmission signal from the signal processing unit 4 to
each transducer 3 is independently signal processed by the signal processing unit 4. At the time
of wave reception, the received signal from each transducer 3 to the signal processing device 4 is
independently signal processed by the signal processing device 4.
[0022]
As described above, one planar transducer array 2 has nine transducers 3, and the hydrophone 1
has six planar transducer arrays 2. Thus, the hydrophone 1 operates as a 54 element transducer
array. Assuming that the number of transducers in one planar transducer array is m and the
number of planar transducer arrays in the hydrophone is n, m = 9 and n = 6 in this embodiment.
[0023]
At the time of wave transmission, each transducer 3 vibrates in thickness by the voltage applied
between the electrodes 6 and 7 from the signal processing device 4. At the time of wave
reception, each transducer 3 sends the voltage generated between the electrodes 6 and 7 by the
thickness vibration to the signal processing device 4.
[0024]
The control method of the hydrophone 1 is demonstrated below.
[0025]
A common omnidirectional hydrophone achieves omnidirectionality in a band of several tens of
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MHz.
Such an omnidirectional hydrophone is realized by vibrating a sphere-shaped piezoelectric
ceramic on a breathing sphere. In the present embodiment, respiratory sphere vibration is
simulated in a pseudo manner by array control. In theory, the reproduction accuracy of the
respiratory sphere vibration is improved in proportion to the number of elements of the array.
[0026]
An array composed of a plurality of transducers 3 constitutes the sound field of the entire
hydrophone 1. Here, the calculation of the sound field of the hydrophone 1 can not be performed
using a directivity function that assumes an infinite rigid baffle. In addition, it is necessary to
calculate the sound field of the hydrophone 1 in consideration of the influence of diffraction. In
the hydrophone 1, since a plurality of rectangular piston sound sources are disposed on the
surface of a regular hexahedron, it is necessary to consider the directivity of the rectangular
piston sound source.
[0027]
Here, each of the N transducers 3 on the hydrophone 1 is a transducer k (k = 1, 2,... N)とする。
The sound field when a signal based on the reference signal is input to the transducer k will be
described. Here, let Pk be the measured complex sound pressure (representing amplitude and
phase) observed at an angle φ from the x axis on the xz plane. Pk is determined by the
directivity characteristic of the transducer 3 alone, and is a function of φ. Further, with respect
to the reference signal, the amplitude ratio of the signal input to the transducer k is Rk, and the
phase difference is Sk. At this time, P is a complex sound pressure (directivity characteristic) of
the entire hydrophone 1 observed at an angle φ from the x axis on the xz plane, and P, which is
a function of φ, is given by the following equation (1) Be
[0028]
[0029]
Thereafter, RN and SN are used as array control parameters.
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[0030]
The hydrophone 1 is connected to the signal processing device 4.
When transmitting by the hydrophone 1, the signal processing device 4 adjusts the transmission
signal of each transducer 3 based on the array control parameter and supplies the transmission
signal to each transducer 3.
When performing reception by the hydrophone 1, the signal processing device 4 obtains a
reception signal from each transducer 3 and combines the reception signals of each transducer 3
based on the array control parameter.
[0031]
Here, since RN and SN are an amplitude ratio and a phase difference, respectively, the number of
combinations of these values is infinite, and it is not practical to calculate the optimal solution of
the array control parameter by the brute force method. Not only does the directivity
characteristic change with the amplitude and phase of each element of the array, there are
multiple optimal solutions of the array control parameters and they are not mathematically
closed.
[0032]
Generally, control of the array is performed by actively changing the amplitude and phase of the
signal input to each transducer constituting the array, but the problem that the characteristics of
the array are due to the characteristics and shape of the transducer, There is a problem that it is
difficult to evaluate the directivity characteristics of the array by calculation. Therefore, in the
present embodiment, parameter optimization processing using a genetic algorithm is provided in
order to obtain the optimum solution from a wide variety of combinations of amplitude and
phase.
[0033]
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The parameter optimization process of the present embodiment is realized by the parameter
optimization program being executed by the parameter optimization device. The parameter
optimization device is realized by, for example, a computer having a CPU, a storage unit, and a
medium reading unit. The parameter optimization program is recorded on a computer readable
recording medium, read from the recording medium by the medium reading unit, expanded in
the storage unit, and executed by the CPU.
[0034]
The array control parameters optimized by the parameter optimization device are set in the
signal processing device 4, and the signal processing device 4 performs signal processing in
accordance with the array control parameters. The signal processing device 4 and the parameter
optimization device may be provided in one device.
[0035]
The parameter optimization process may obtain array control parameters of all the transducers 3
as N = 54. Here, due to the symmetry of the arrangement of the transducers 3, it is possible to
reduce the number of calculations of the array control parameter of the transducer 3 which is
the same array control parameter. In this case, the transducers 3 can be classified into three
types: the transducer 3 located at the center of each surface (planar transducer array 2), the
transducer 3 in contact with each vertex of the hydrophone 1, and the other transducers 3.
Therefore, in the parameter optimization process, three types of array control parameters may be
calculated with N = 3.
[0036]
In the parameter optimization process, the parameter optimization device sets RN and SN as
binary codes (binary values), and sets the gene G as [R1R2 ... RNS1S2 ... SN].
[0037]
FIG. 4 is a flowchart showing an example of the parameter optimization process.
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First, the parameter optimization device randomly generates M genes, and sets the generated set
of genes [G1G2... GM] as an initial group (S11).
[0038]
Next, the parameter optimization device calculates the fitness fi of each group obtained, (i = 1, 2,.
M) is evaluated (S12). Here, the parameter optimization device calculates the directivity
characteristic P from each gene, calculates fi based on this P, and which directivity characteristic
(predetermined directivity characteristic) is required according to the value of fi Evaluate only
close. For example, fi is expressed by the following formula (2).
[0039]
[0040]
Here, the required directivity characteristic is omnidirectional, that is, a uniform sound pressure
level with respect to an angle.
DG is a directivity function calculated by equation (1) and gene G. As this fi is closer to 0, the
difference in sound pressure level in gene G is smaller and closer to the required directivity
function. Here, the fitness function f is used in which the fitness is lower as the required
directivity function is approached, but a fitness function may be used in which the fitness is
higher as the required directivity function is approached.
[0041]
Next, the parameter optimization device performs a selection operation to select a gene to be left
in the next generation (S13). In this selection operation, a gene with lower fitness (the gene
closer to the required directivity characteristic) has a higher probability of being selected.
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[0042]
Next, the parameter optimization device crosses the selected genes (S14). Here, the parameter
optimization device determines from what bit of the gene to what bit to cross using random
numbers.
[0043]
Next, the parameter optimization device generates a mutation in the gene with a predetermined
mutation probability (S15). Here, the mutation probability is very low.
[0044]
Next, the parameter optimization device determines whether the termination condition is
satisfied (S16). The termination condition is, for example, that the change of the maximum value
of fitness falls within a predetermined range over a predetermined number of generations (the
maximum value of fitness converges).
[0045]
If the termination condition is not satisfied (S16, N), the parameter optimization device shifts this
flow to S12. If the termination condition is satisfied (S16, Y), the parameter optimization device
performs termination processing (S17) and terminates this flow. The termination process outputs
the final gene as an optimal solution of the combination of array control parameters.
[0046]
According to this parameter optimization process, it is possible to calculate an array control
parameter for realizing a desired directivity characteristic in a short time.
[0047]
According to the present embodiment, in the low frequency region of several tens of MHz or less,
omnidirectionality can be realized without using a hollow shape structure.
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[0048]
The stable measurement can be realized at low cost by constructing a flat-plate piezoelectric
ceramic which is easy to develop and manufacture and stable in quality and in the form of a
regular polyhedron and array controlling them.
Since array control can realize not only nondirectionality but also various directional
characteristics, it is possible to provide a versatile hydrophone that does not depend on the
shape.
[0049]
In underwater acoustic measurement, a hydrophone is used as a means of transmission and
reception of sound waves.
In conventional hydrophones, the shape of the piezoelectric ceramic determines the directivity
characteristics. Depending on the location of the measurement, such as the presence of a quay
behind it, a hydrophone is required to suppress unwanted reflected waves. According to the
hydrophone of the present embodiment, precise acoustic measurement under any environment
becomes possible with one hydrophone.
[0050]
Moreover, the performance of underwater acoustic communication can be improved by applying
the hydrophone of this Embodiment to acoustic communication.
[0051]
According to the present embodiment, it is possible to realize directivity characteristics optimum
for various environments with a single device.
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Therefore, the temperature, the flow velocity, etc. in any place can be measured with high
accuracy. The present invention can also contribute to analysis of complex flow fields in an
estuary or the like, measurement of temperature and wind direction in the air, and clarification of
flow fields in multiphase flow.
[0052]
The piezoelectric element corresponds to the flat plate piezoelectric ceramic 5 in the
embodiment.
[0053]
The present invention can be embodied in other various forms without departing from the spirit
or main features thereof.
Therefore, the above-described embodiment is merely illustrative in every point and should not
be interpreted in a limited manner. The scope of the present invention is indicated by the claims,
and is not restricted at all by the text of the specification. Moreover, all variations, improvements,
alternatives and modifications that fall within the equivalent scope of the claims are all within the
scope of the present invention.
[0054]
Reference Signs List 1 hydrophone 2 plane transducer array 3 transducer 4 signal processing
device 5 flat plate piezoelectric ceramic 6, 7 electrode
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