JPH01109897A - Underwater acoustic data transmitter - Google Patents

Abstract

PURPOSE:To widen a band width or a data transmission band width by making the resonance frequency of the piezoelectric ceramic single member of a wave transmitter and a wave receiver equal and composing 1/4 wave length acoustic matching layers disposed in the front face of the piezoelectric ceramic respectively of a material having the characteristic acoustic impedance of a constant value. CONSTITUTION:An underwater ultrasonic wave transmitter and receiver is provided with the disk shape piezoelectric ceramic 11, a cork rubber 12, a cable 13, the disk shape 1/4 wave length acoustic matching layer 14 and a flange 15 and the piezoelectric ceramic 11, the cork rubber 12, the cable 13 and the 1/4 wavelength acoustic matching layer 14 and the flange 15 are integrally molded by a resin material such as urethane. The 1/4 wave length acoustic matching layer 14 is made of the material having the intermediate characteristic impedance of the piezoelectric ceramic 11 and water to make the acoustic impedance of the 1/4 wave length acoustic matching layer of the wave receiver side substantially equal to (Zw<2>Zc)<3/2> (Zw: acoustic impedance of water, Zc: acoustic impedance of piezoelectric ceramic) or lower than it and make the acoustic impedance of the 1/4 wave length acoustic matching layer 14 of the wave transmitter side higher than (Zw<2>Zc)<3/2>.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to an underwater acoustic data transmission device using an electroacoustic transducer that utilizes an underwater acoustic wave propagation path as a data transmission path.

[Prior art]

FIG. 8 is a functional block diagram showing a typical underwater acoustic data transmission device used for this type of data transmission, and a data transmission method using this device will be described below.

In FIG. 8, an electric signal generated from an electric signal generator 1 of a transmission system is modulated by a modulator 3 based on underwater data measured by a sensor 2, and the modulated electric signal is amplified by an amplifier 4. Thereafter, this electrical signal is converted into an acoustic signal by the transmitter 5 and radiated into the water as a sound wave.

The sound waves radiated as described above propagate through the water and enter the receiver 6 of the receiving system, where they are converted into electrical signals.
The demodulator 7 demodulates the signal, and the display/recording device 8 displays and records the signal as predetermined data.

In this underwater data transmission method that uses an underwater acoustic wave propagation path as a data transmission path, an electroacoustic transducer, that is, a transmitter 5 and a receiver 6, converts an electric signal and an acoustic signal for transmitting and receiving data. are used, but the bandwidth of data that can be transmitted is limited by the performance of these transmitters 5 and receivers 6. As an example, FIG. 9 shows the sensitivity product, that is, the sensitivity characteristic between the transmitter and the receiver when an underwater ultrasonic transmitter and receiver using piezomagnetic resonance are used.

Note that rL in the figure is the lower limit frequency of the transmission band, and fU is the upper limit frequency of the transmission band.

Underwater ultrasonic transmitters and receivers that utilize the resonance of piezoelectric ceramics are commonly used in this type of underwater data transmission, but the resonance sharpness Q is often around Q = 10 to 20. , If the bandwidth of the data transmission characteristic at the sensitivity edge is set to the center frequency of 500KH2, then it is 25KH2 to 50KH.
Limited to a range narrower than 2.

Therefore, a 1/4 wavelength acoustic matching layer is installed on the front surface of the piezoelectric ceramics of the transmitter 5 and the receiver 6 to widen the resonance characteristics of the transmitting and receiving sensitivity characteristics to approximately Q-4. A device that performs data transmission and widens the transmission bandwidth is conceivable.

[Problem that the invention seeks to solve]

However, as in the past, a 1/4 wavelength acoustic matching layer is provided on the front surface of the piezoelectric ceramic of the transmitter 5 and the receiver 6, and the sensitivity characteristics of the transmitter and receiver are equally wideband. When used as a transmission transceiver, there is a problem in that the bandwidth of the sensitivity product (data transmission characteristics) is considerably narrower than the sensitivity characteristics of the individual transducers. For example, transmitter 5
And the resonance characteristics of the receiver 6 are centered around 500KH2, Q-4 (
If the bandwidth is 125KH2), the bandwidth (-3dB) is approximately 80K as a sensitivity product, which is the product of transmitting sensitivity and receiving sensitivity.
It becomes H2.

In addition, if the acoustic matching layer is multilayered, it is possible to further widen the transmitting and receiving sensitivity characteristics, but the structure becomes complex, making the characteristics unstable and reducing environmental resistance. There was a fear that it would.

The present invention has been developed in view of the above-mentioned points, and is directed to a transducer for underwater data transmission in which a single 1/4 wavelength acoustic matching layer is provided on the front surface of the piezoelectric ceramic of the transmitter and receiver. Another object of the present invention is to provide an underwater acoustic data transmission device with excellent data transmission characteristics by eliminating the problem that the data transmission bandwidth is considerably narrower than the individual sensitivity characteristic bandwidths of a transmitter and a receiver.

[Means for solving problems]

In order to solve the above problems, the present invention provides an underwater acoustic data transmission device that uses an underwater acoustic wave propagation path as a transmission path. , let the specific acoustic impedance zI of one acoustic matching layer be Z s > ” JT.

! z, the sensitivity characteristic has two resonances, and the specific acoustic impedance zI of the other acoustic matching layer is 21*”f7.
By setting it to 77π, the bandwidth of the sensitivity characteristic, that is, the data transmission characteristic is widened.

However, here, z: acoustic impedance of water lZe: acoustic impedance of piezoelectric ceramic.

[Effect]

By configuring the 1/4 wavelength acoustic matching layer in front of the piezoelectric ceramic of the transmitter and receiver of the underwater acoustic data transmission device as described above, the sensitivity product (transmitter → ocean →
It becomes possible to widen the bandwidth of the receiver (sensitivity characteristics), that is, the data transmission bandwidth.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.
7 is a structural diagram showing an example of an underwater ultrasonic wave transmitter/receiver provided with a 1/4 wavelength acoustic matching layer. In Figure 7,
The underwater ultrasonic wave transmitter/receiver includes a disk-shaped piezoelectric ceramic 11, Kirk rubber 12, a cable 13, a disk-shaped 1/4 wavelength acoustic matching layer 14, and a flange 15.
1. Kirk rubber 12, cable 13. It has a structure in which the 1/4 wavelength acoustic matching layer 14 and flange 15 are integrally molded with a resin material such as urethane.

The 1/4 wavelength acoustic matching layer 14 is made of a material with an inherent impedance between that of the piezoelectric ceramic 11 and water, and its inherent acoustic impedance 2 is expressed as z, -3, /'-muT'
...When (1) is set, the widest sensitivity characteristic can be obtained.

Here, 2° is the specific acoustic impedance of the piezoelectric ceramic 11,
z, is the specific acoustic impedance of water. Furthermore, the sensitivity characteristics with 2°>8th edition exhibit two resonance characteristics as shown in FIG.

In the above formula (1), Z, -1, 5X 10'kg
/ m”see, Z, !30 X 10'kg/
m"sec, 2o=-4, IX 10'
kg/m"sec. Materials with a specific acoustic impedance close to this value include epoxy resin containing metal powder.

The characteristic acoustic impedance 2□ of the 1/4 wavelength acoustic layer 14 provided on the front surface of the piezoelectric ceramic 11 of the transmitter is 4.1 k.
g/m ”see: Z, the wave transmission sensitivity characteristics of the closed one are shown in Figure 4.Here, the piezoelectric ceramic 1 of the transmitter and receiver
The resonant frequencies of the single unit of 1. If it is 7.0 x 10'kg/m"see (1.77,), the sensitivity characteristics will be as shown in Figure 2. Using this as receiver A, the transmitting sensitivity characteristics shown in Figure 4 above will be as follows. When combined with a transmitter of
If it is 00KH2, it will be about 190KH2.

Also, the characteristic acoustic impedance of the acoustic matching layer on the receiver side 2. 15, OX 10'kg/m"5ec(
*2.6Z,), the receiving sensitivity characteristics will be as shown in Figure 3. When this receiver is combined with a transmitter having the characteristics shown in FIG. 4, the transmission characteristics will be as shown by the solid line in FIG. 1, and the bandwidth will be 260 KH2.

When using a transmitter with the sensitivity characteristics shown in Figure 3, the relationship between the characteristic acoustic impedance 2 of the matching layer on the receiver side and the transmission characteristic bandwidth is as shown in Figure 5. Yes, the transmission bandwidth increases as the specific acoustic impedance increases by 2°. However, the value of the sensitivity result at the center frequency r, is the characteristic acoustic impedance 2. decreases as the value increases.

The relationship is shown in FIG.

The relationship between the characteristic acoustic impedance 2° and the transmission characteristic bandwidth shown in FIG. 5 and the characteristic acoustic impedance 2.degree. shown in FIG. Based on the relationship between the frequency and the sensitivity performance at the center frequency f0, the characteristic acoustic impedance of the acoustic matching layer on the receiver side can be set to an optimal value according to the bandwidth and sensitivity performance required by the system. That is, in the present invention, the acoustic impedance of the 1/4 wavelength acoustic layer on the receiver side is 8.01w Ze (Zv:
The acoustic impedance of water (#ZC: acoustic impedance of piezoelectric ceramic) is set to be approximately equal to or lower than that, and the acoustic impedance of the 1/4 wavelength acoustic layer 14 on the transmitter side is set to be larger than s1ρT fur.

The above holds true even if the transmitter and receiver are replaced.

〔Effect of the invention〕

As explained above, according to the present invention, in an underwater data transmission device, the resonant frequencies of the single piezoelectric ceramics of the transmitter and the receiver are made equal, and the 1/4 wavelength acoustic layer provided in front of the piezoelectric ceramic is placed on one side. has a specific acoustic impedance of s7ργ2
] Since the material was made of material approximately equal to or less than τ, and the other material was made of material larger than 1f77zc, the bandwidth of the sensitivity characteristic (transmitter→ocean→receiver sensitivity characteristic), that is, the data transmission. An excellent effect can be obtained in that the bandwidth can be widened.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the transmission characteristics of a receiver used in the underwater acoustic data transmission device according to the present invention, Fig. 2 is a diagram showing the sensitivity characteristics of receiver A, and Fig. 3 is a diagram showing the sensitivity of receiver B. Figure 4 is a diagram showing the sensitivity characteristics of the transmitter, Figure 5 is a diagram showing the relationship between the characteristic acoustic impedance of the matching layer on the receiver side and the transmission bandwidth, and Figure 6 is a diagram showing the relationship between the transmitter side matching layer and the transmission bandwidth. Figure 7 shows the relationship between the characteristic acoustic impedance of the side matching layer and the sensitivity at the center frequency; Figure 8 is a functional block diagram showing a typical underwater data transmission device used for this type of data transmission, and Figure 9 shows the sensitivity results of a conventional underwater acoustic data transmission device (
FIG. 3 is a diagram showing transmission characteristics. In the figure, 1... electric signal generator, 2... sensor,
3...Modulator, 4...Amplifier, 5...Transmitter, 6...Receiver, 7...Demodulator, 8...
Display recording device, 11...piezoelectric ceramic, 12...kirk rubber, 13...cable, 14...1/4
wavelength wavelength acoustic layer, 15... flange, 16...
Urethane mold.

Claims (1)

[Claims] The resonant frequency of the piezoelectric ceramics of the plurality of transducers used in an underwater acoustic data transmission device that uses an underwater acoustic wave propagation path as a transmission path is the same, and the piezoelectric ceramics in either the transducer for wave transmission or for wave reception are There are acoustic impedance ▲ mathematical formulas, chemical formulas, tables, etc. ▼ (Z_w
: Acoustic impedance of water, Z_c: Acoustic impedance of piezoelectric ceramic) A 1/4 wavelength acoustic matching layer is provided which is approximately equal to or less than the acoustic impedance of the piezoelectric ceramic in the other transducer, and the acoustic impedance is set to the formula ▲ above, There are chemical formulas, tables, etc. An underwater acoustic data transmission device characterized by providing a 1/4 wavelength acoustic matching layer larger than ▼.