JPH0580200B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of 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 transmitted to a sensor 2 by a modulator 3.
After the modulated electrical signal is amplified by an amplifier 4, the electrical signal is converted into an acoustic signal by a 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, demodulated by the demodulator 7, and displayed and recorded as predetermined data. The information is displayed and recorded by the device 8.

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. However, the bandwidth of data that can be transmitted is limited by the performance of the transmitter 5 and receiver 6. As an example, when an underwater ultrasonic transmitter and a receiver using piezomagnetic resonance are used, the sensitivity characteristic between the transmitter, the ocean, and the receiver is shown in FIG.

Note that f _I in the figure is the lower limit frequency of the transmission band, and f _U 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 sharpness of the resonance is Q.
= 10 to 20 in most cases, and the sensitivity product, that is, the bandwidth of data transmission characteristics is limited to a range narrower than 25 KHz to 50 KHz when the center frequency is 500 KHz.

Therefore, a 1/4 wavelength acoustic matching layer is provided on the front surface of the piezoelectric ceramics of the transmitter 5 and the receiver 6, and the resonance characteristics of the transmitting and receiving sensitivity characteristics are widened to about Q = 4. A device that performs 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 receiver 6, and the sensitivity characteristics of the transmitter and receiver are equally wideband. When used as a transmission transceiver, there was a problem in that the bandwidth of the sensitivity product (data transmission characteristics) was considerably narrower than the sensitivity characteristics of the individual transducers. For example, the resonance characteristics of the transmitter 5 and receiver 6 are centered at 500KHz, Q = 4 (bandwidth
125KHz), the bandwidth (-3dB) is approximately 80KHz as a sensitivity product, which is the product of transmitting sensitivity and receiving sensitivity.
become.

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 happen.

The present invention has been made in view of the above points, and is a transducer for underwater data transmission in which an acoustic matching layer of 1/4 wavelength is provided on the front surface of the piezoelectric ceramic of the transmitter and receiver. It is an object of the present invention to provide an underwater acoustic data transmission device with excellent data transmission characteristics by eliminating the problem that the 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. , the specific acoustic impedance Z ₁ of one acoustic matching layer is Z ₁ > ³ √ _W ² _C , the sensitivity characteristic has two resonances, and the specific acoustic impedance Z ₁ of the other acoustic matching layer is Z ₁ ≒ ³ √ _W ²
By setting Z _C , the sensitivity characteristic, that is, the bandwidth of the data transmission characteristic is widened. However, here
Z _W : Acoustic impedance of water, Z _C : 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.

FIG. 7 is a structural diagram showing an example of an underwater ultrasonic transmitter/receiver provided with a 1/4 wavelength acoustic matching layer. 7th
In the figure, the underwater ultrasonic wave transmitter/receiver includes a disc-shaped piezoelectric ceramic 11, a Kirk rubber 12, a cable 13,
Disc-shaped 1/4 wavelength acoustic matching layer 14 and flange 1
5, these piezoelectric ceramics 11, Kirk rubber 1
2. It has a structure in which the cable 13, the 1/4 wavelength acoustic matching layer 14, and the 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 when its inherent acoustic impedance Z is Z ₀ = ³ √ _W ² _C ... (1) , the widest sensitivity characteristics can be obtained.
Here, Z _C is the specific acoustic impedance of the piezoelectric ceramic 11, and Z _W is the specific acoustic impedance of water.
Furthermore, the sensitivity characteristic with Z _O ³ √ _W ² _C exhibits two resonance characteristics as shown in FIG.

In the above equation (1), Z _W = 1.5×10 ⁶ Kg/m ² sec,
Let Z _C = 30×10 ⁶ Kg/m ² sec, Z ₀ = 4.1×10 ⁶ Kg/
m ² sec. Materials with a specific acoustic impedance close to this value include epoxy resin containing metal powder.

The specific acoustic impedance Z ₁ of the 1/4 wavelength acoustic matching layer 14 provided on the front surface of the piezoelectric ceramic 11 of the transmitter is
Figure 4 shows the transmission sensitivity characteristics when 4.1Kg/m ² sec≒Z ₀ . Here, the resonant frequencies of the piezoelectric ceramics 11 of the transmitter and receiver are both equal to f ₀ , and the specific acoustic impedance Z ₂ of the 1/4 wavelength acoustic matching layer 14 on the receiver side is 7.0×10 ⁶ Kg/ ^m2 esc (≒
1.7Z ₀ ), the sensitivity characteristics will be as shown in Figure 2. When this is combined as receiver A with a transmitter having the transmission sensitivity characteristics shown in Figure 4 above, the transmission characteristics will be as shown by the broken line in Figure 1, and the bandwidth will be approximately 500KHz with a center frequency of 500KHz. It becomes 190KHz.

Further, when the characteristic acoustic impedance Z ₂ of the acoustic matching layer on the receiver side is set to 15.0×10 ⁶ Kg/m ² sec (≈2.6Z ₀ ), the receiving sensitivity characteristics are as shown in FIG. 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 KHz.

When using a transmitter with the sensitivity characteristics shown in Figure 3, the specific acoustic impedance of the matching layer on the receiver side
There is a relationship between Z ₂ and the transmission characteristic bandwidth as shown in FIG. 5, and as the specific acoustic impedance Z ₂ is increased, the transmission bandwidth becomes wider. However, the value of the sensitivity product at the center frequency f ₀ decreases as the specific acoustic impedance Z ₂ increases. The relationship is shown in FIG.

From the relationship between the characteristic acoustic impedance Z ₂ and the transmission characteristic bandwidth shown in Figure 5 above, and the relationship between the characteristic acoustic impedance Z ₂ and the sensitivity product at the center frequency f ₀ shown in Figure 6, it is clear that the acoustic matching layer on the receiver side The characteristic acoustic impedance can be set to an optimal value according to the bandwidth and sensitivity product required by the system. That is, in the present invention, the acoustic impedance of the 1/4 wavelength acoustic matching layer on the receiver side is approximately equal to or less than ³ √ _W ² _C (Z _W : acoustic impedance of water, Z _C : acoustic impedance of piezoelectric ceramic). The acoustic impedance of the 1/4 wavelength acoustic matching layer 14 on the transmitter side is ³ √ _W ² as follows.
Make Z larger than _C.

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 individual piezoelectric ceramics of a transmitter and a receiver are equalized, and a 1/4 wavelength acoustic matching layer provided on the front side of the piezoelectric ceramic is applied to one side. Since one is made of a material with a specific acoustic impedance approximately equal to or less than ³ √ _W ² _C , and the other is made of a material larger than ³ √ _W ² _C , the sensitivity product (transmitter→ocean→receiver) is An excellent effect can be obtained in that it becomes possible to widen the bandwidth of the wave transmitter (sensitivity characteristics), that is, the data transmission bandwidth.

[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. A diagram showing the relationship between the characteristic acoustic impedance of the side matching layer and the sensitivity product at the center frequency, FIG. 7 is a structural diagram showing an example of an underwater ultrasonic transducer equipped with a 1/4 wavelength acoustic matching layer, FIG. 8 is a functional block diagram showing a typical underwater data transmission device used for this type of data transmission, and FIG. 9 is a diagram showing the sensitivity product (transmission characteristics) of a conventional underwater acoustic data transmission device. In the figure, 1...electric signal generator, 2...sensor,
3...Modulator, 4...Amplifier, 5...Transmitter, 6
... Wave receiver, 7 ... Demodulator, 8 ... Display and recording device, 11 ... Piezoelectric ceramic, 12 ... Kirk rubber, 1
3... Cable, 14... 1/4 wavelength acoustic matching layer,
15...flange, 16...urethane mold.

Claims (1)

[Claims] 1 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 ceramic in either the transducer for wave transmission or for wave reception The acoustic impedance in front of the porcelain is ³ √ _W ² _C
(Z _W : Acoustic impedance of water, Z _C : Acoustic impedance of piezoelectric ceramic) A 1/4 wavelength acoustic matching layer approximately equal to or less than that is provided, and the acoustic impedance is set in front of the piezoelectric ceramic in the other transducer. An underwater acoustic data transmission device characterized by providing a 1/4 wavelength acoustic matching layer larger than ³ √ _W ² _C.