JP3156117B2 - Underwater telemetry device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underwater telemetry device for acquiring a signal from a signal source moving underwater for the purpose of medicine, biology, engineering, etc. Underwater communication device.

[0002]

2. Description of the Related Art Underwater signal sources, such as fish, dolphins,
A wireless telemeter system is required to collect signals obtained from sensors or transducers such as bioelectrodes attached to whales, turtles, and sensors such as temperature, pressure, speed, and position while freely moving them. . Conventionally, electromagnetic waves that propagate as waves in water are considered to be unsuitable as a signal carrier because of their large attenuation, and electromagnetic coupling or electrostatic coupling or a shunt of conductive current instead is used as purely electric signal means. However, they are not suitable for medium- or long-distance transmissions that greatly exceed the order of the wavelength because the receiving sensitivity decreases in inverse proportion to the square or the cube of the distance. On the other hand, ultrasound and some wavelength bands of visible light have been successfully used for this purpose, and in particular, ultrasound has even been used for transmission over considerable long distances. The use of electromagnetic waves for this purpose has not been put to practical use other than in systems where the test organism, and thus the transmitter, aims at the moment the transmitter comes to the surface.

However, in consideration of the size and weight of the transmitter, the life of the battery, and the like, these purely electric transmitters are far more advantageous than those that emit ultrasonic waves or light.
If you roughly consider that you need the same transmitter output to get the same receiver input, then the efficiency of the conversion of electrical energy to these other energies, such as light, ultrasound, etc., is generally not a favorable value. Because telemeter transmitters using them generally require an order of magnitude higher power consumption. The increase in power consumption necessarily leads to an increase in battery capacity or a shortened useful life, so that unrestricted biometric measurement can be performed for several days or weeks with a transmitter attached to a fish that is not so small, such as rainbow trout. This is a serious problem.

It is very preferable that the transmitter side use the electromagnetic wave system in such circumstances, so that it is exclusively used. However, conventionally, for example, 10
A radio wave having a frequency near 0 MHz was received in the vicinity of the water surface as an airwave. It has been empirically said that this method is used, but it can reach only a few meters at most in the horizontal direction from the water surface directly above the source. Also, it reaches only about one wavelength in the vertical direction. This is because the wavelength of electromagnetic waves in water is significantly different from air as described later, and the wave impedance of water is also significantly different from air, resulting in significant attenuation at the stage of electromagnetic waves emerging into the air, or even more effective propagation. It is because it does not come out as an electromagnetic wave that can be obtained. In other words, on the water surface, the state of total reflection is mostly from the inside to the outside, and the component leaking to the vicinity is exclusively an evanescent wave (Evan
e.g., e.g. In addition, the difficulty increases as the source adds depth, as this tendency becomes more pronounced.

[0005]

SUMMARY OF THE INVENTION The present invention is to solve practically the difficulty in the reach of electromagnetic wave telemetry from an underwater transmission source. That is, in the electromagnetic wave telemetry from the conventional underwater transmission source, the electromagnetic wave energy emitted from the transmitter is not utilized so as to be effectively used as the input to the receiver even if the electromagnetic wave energy propagates in the water.

[0006]

An underwater electromagnetic wave telemetry system according to the present invention is configured to receive an electromagnetic wave signal from a transmission source that freely moves in water, underwater.
It is also characterized by having an underwater antenna optimized for underwater reception, particularly in such a form that a large number of such underwater antennas are distributed and effectively coordinated.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment, the source is mounted on its back to receive an electrode implanted in its head for collecting rainbow trout brain waves, and has a transmission frequency of about 9 Hz.
This is a 5MHz PFM / FM type telemeter transmitter designed and manufactured by a known general-purpose method. Substantially acting as an antenna is a tank coil which is a frequency determining element of a Colpitts transmission circuit using one general-purpose transistor as a main carrier generating means, is about 8 mm in length, about 4 mm in diameter, and has an average thickness of about 3 mm around the periphery. Is exposed to water with the silicon rubber interposed as an insulating material.

[0008] The radiation from the source into the water, apart from the electrostatic and electromagnetic fields at close distances, is a vertically polarized wave that can propagate as long as the fish normally swims or stops. is there. This is within the design freedom because it can be set depending on the direction of the coil of the radiation source, but it is empirically stated that vertical polarization is the least affected by the turning movement of fish, etc. Is most preferably employed.

The self-weight (= mass) of the transmitter in the air is about 4 g
However, it weighs 1.6 g in water. Rainbow trout equipped with this weighs about 800 g, and the weight of this transmitter can be ignored. The built-in power supply of the transmitter is two CR2032 type coin-type lithium primary batteries and can withstand continuous operation for about 50 hours. The rainbow trout equipped with the transmitter is released again to a limited section of a free water channel (natural river) with a depth of about 1 m, a width of about 3 m and a length of about 30 m, and is left to free action, during which brain waves are continuously transmitted for 22 hours Observed over the above.

The receiver itself is a known general-purpose communication type receiver.
The receiving operation is performed in the narrow-band FM mode, and a subcarrier obtained by demodulating the main carrier of the radio frequency is supplied to the subcarrier demodulator at the subsequent stage. The subcarrier demodulator and thereafter are also provided by a well-known general-purpose system and configuration for direct recording of continuous EEG data, recording by a data recorder, etc., and real-time waveform observation and analysis. There is no characteristic point in the configuration of the present invention in the above transmitter and receiving system.

The features of the present embodiment of the present invention are as follows.
FIG. 1 shows that a number of underwater antennas were arranged in a free water channel in which rainbow trout equipped with the transmitter could swim.
Shown in That is, a large number of unit receiving antennas (1a to 1k) are provided along the direction of the flow at the center of the water bottom of the free-swimming water area of the rainbow trout equipped with the transmitter serving as the signal source (S) Are arranged, and a drop-in cable (3) for picking up the signals to be received is arranged.

That is, a total of 11 unit receiving antennas (1a to 1a) are provided every 2 m from the underwater end of the pull-in cable.
k) is arranged. The unit receiving antennas are separated from each other by one or several wavelengths in water. As will be described later, since the wavelength shortening rate in water is very large, 1/9, several wavelengths in water are much shorter than one wavelength on a coaxial cable, and therefore, the pull-in cable (3) is located between the joining points of each unit receiving antenna. In some cases, it is arranged in a meandering manner to take the length of its own one wavelength.

Individual unit receiving antennas (1a to 1k)
Is a monopole structure in which a conductor rod having a length of about 16.5 cm and a thickness of about 6 mm covered with a thin polyethylene insulating film is vertically erected in water so that vertical polarization is sensed.
The buffer amplifiers (2a to 2k) pick up the potentials at the respective lower ends and pass them through to the cable (3) in one direction. FIG. 2 shows an example of this buffer amplifier.
ET amplifier. For this reason, the monopole underwater antenna is allowed to resonate at about a half wavelength, and exhibits gentle frequency selectivity.

For the feedthrough cable (3) to which the drain of each FET is connected, since the output impedance of the drain is high, the loading impedance at the point of addition can be ignored. Each FET performs voltage-current conversion of a signal received at the gate in accordance with the transfer conductance of a half value (37.5Ω) of the characteristic impedance (75Ω) of the coaxial cable (5C-2V in this case) at each joining point. To join. The FET used here is
If 2SK291 is used as an example, the transfer conductance is about 45 ms, so that one or more gains can be obtained with respect to the load impedance of 37.5Ω. At this stage, it is a preferred embodiment to have one or more gains for each buffer amplifier from the viewpoint of securing the noise figure of the system.

The added signals propagate in both directions from each point of addition, but there is no reflection because the underwater end is ac-coupled to the matching termination (4). The end that is drawn out of the water is coupled to the input terminal of the receiver (6) via the antenna coupler (5), and takes over to the receiver (6) in a form in which all the added signals are added. The antenna coupler (5) has a separate DC branch as shown in the figure, and supplies operating power to a source grounded buffer amplifier that directly connects the drain to each junction through this. The operation of the receiver and the following is well-known, and the description is omitted.

According to this embodiment, the width 3 m and the depth 1
The signal was received without interruption even if the rainbow trout (S) to be observed was free to move over the entire area of the natural river section less than 30 m long and 30 m or longer.

When the unit antennas are arranged on a straight line and the interval between them is one wavelength of the underwater wavelength, the effective sensitivity is set to the farthest in the direction of flow, that is, in the direction on both extensions of the straight line formed by the antenna array. I could have it. As an example, effective sensitivity was obtained up to a point about 22 m further from the end of the array. In this case, it is clear that the array is operating as an endfire array having sensitivity in both the forward and reverse directions. This reaching distance corresponds to a propagation distance of about 70 wavelengths in terms of the wavelength in water, and it is clear that transmission is by electromagnetic waves.

In another embodiment, only one underwater antenna on the receiving side was used, and when underwater electromagnetic waves transmitted by the same transmitter were received, effective sensitivity was obtained up to a radius of about 15 m from the antenna. This corresponds to a propagation distance of 40 to 45 wavelengths in terms of wavelength in water. It is clear that this is also transmission by electromagnetic waves.

An important point in this embodiment of the present invention is that
Each receiving antenna is placed on the cable through the antenna so that each receiving antenna is spatially separated by one or more wavelengths in the underwater wavelength, so that they contribute in phase and amplitude. Taking the wavelength shortening rate into account, the distance should be one wavelength or an integral multiple of the wavelength. The reason will be described below.

Consider the behavior of electromagnetic waves in water. Water looks like an insulator or a dielectric or a conductor or a resistor depending on its salinity or conductivity and frequency. In the medium having the angular frequency ω, the conductivity κ, and the dielectric constant ε of the electromagnetic wave, whether the value of κ / εω is larger or smaller than 1 is a boundary between a conductor and a dielectric. For example, considering freshwater having a κ of 1.0 × 10 ⁻² S / m (this is a typical value in a clean inland lake such as Lake Chuzenji), the frequency f is 100 MHz and ω Is 2π × 10 ⁸ rad / s, and ε of water is 7.1 × 10 ⁻¹⁰ F / m at 80 times the air.
Substituting these gives

[0021]

(Equation 1)

At this frequency, such fresh water is completely dielectric. Then, when the loss term is further considered and the attenuation constant α is obtained, α is proportional to κ, and is given by the following equation under the same condition of κ / εω << 1.

[0023]

(Equation 2)

Assuming that the permeability of fresh water is the same as that of air, μ
= 1.257 × 10 ⁻⁶ H / m is substituted, and the other values are also substituted with the above values.

[0025]

(Equation 3)

This is a moderate value. This value is not necessarily decisively large, and may be considered to be in a region where consideration with a lossless medium is still valid.

After all, in freshwater, a scale factor of 80 times, μ is invariable, wave impedance is 1/9, and wavelength reduction ratio is also 1/9 is applied in terms of the ratio to the air. The only simplistic understanding is that they differ only in points.

Therefore, the wavelength of an electromagnetic wave of 100 MHz in water is 33 cm at 3 m in the air, the wave impedance of the space is 40 Ω at 370 Ω in the air, a half-wave dipole antenna or a monopole antenna with a 波長 wavelength ground plane. The driving point impedance of 50 to 70Ω in the air is several ohms at most, so it is easy to handle it electrically. Rather, the driving of the half-wave antenna is disadvantageous because the driving point impedance is too high in the air. In the preferred embodiment described herein, such a design is employed as described above.

However, since there is considerable attenuation in water unlike in the air, the range that one antenna can cover is limited to a radius of at most several tens of wavelengths as described above. Also, when there are two or more receiving antennas, even if the distance from the transmission source is one wavelength, the one that is short will obtain an overwhelmingly strong reception level. Therefore, when innumerable antennas are distributed with a distance of more than a wavelength, about several wavelengths to about several tens of wavelengths, the reception outputs of those antennas are all in-phase summed uniformly through one-way coupling means. However, due to the property that even one wavelength is closer, the receiving level is overwhelmingly strong, there is no coherence sensitivity distribution at the boundary of the sharing area of the antenna.

Therefore, in this embodiment, the outputs of all the unit receiving antennas are substantially the same by the same amplifier at the position of an integral multiple of one electric wavelength as a unit on the feedthrough coaxial cable to be added. The addition by phase and amplitude (ignoring integer multiples of 360 degrees can be neglected) prevents the occurrence of coherent dead spots at the boundaries of the sharing area of each antenna.

[0031]

As described above, according to the present invention, it is possible to perform telemetry which allows free movement of a signal source over a wide range in relatively clean fresh water having a sufficiently low salinity or conductivity. The place that contributes to the above is great.

Further, this technology is not limited to biotelemetry as described above, and it can be used for underwater electromagnetic communication in a similar position regardless of the signal source. It is self-evident to the experts. Further, as a preferred embodiment, it has been described that unit underwater antennas are arranged on the bottom of the water, and in some cases, endfire arrays are formed on a straight line at equal intervals, but this is merely an example, and Does not restrict the gist of the present invention described in (1).

If there is a reason that the water depth is deep, the unit underwater antennas may be hung like a buoy from the water surface in some cases and may be arranged in a row, and a weight may be pulled from the buoy so as to have an appropriate depth. It may be hung in the middle of it.

Although the operation in the horizontal plane has been described only as an array, an array in a vertical plane may be used in some cases. In that case, a configuration may be adopted in which monopoles or dipoles oriented in the horizontal direction are sequentially arranged in the vertical direction on the ropes hanging from at most one buoy. It can be listed on the side walls of ships and underwater structures. In this case, if the configuration of the end fire array is adopted, the main task is to monitor the downward direction in the vertical direction, but if the configuration of the side fire array or the ordinary phased array is adopted, the main task has a horizontal direction or a slight depression angle. It is a thing to monitor in the direction. In this case, furthermore, the reception focal point is set at the transmission source, and the reception output of each reception antenna is given a phase or delay distribution and combined and received so as to selectively receive the diffuse wavefront generated therefrom. Is also possible.

Whether to use a monopole or a dipole as described above, or to use a unitary receiving antenna having a specific structure for a more specific purpose is completely included in the degree of freedom in the implementation of the present invention. . With respect to reception of electromagnetic waves in water in which the wave impedance of the medium is extremely different from that in the air, there may be various unit receiving antennas having a specific structure suitable for the use and having completely different design concepts from those in the air.

As described above, in the preferred embodiment, a half-wavelength monopole is used in which the ends are terminated with high impedance and a signal is obtained in the form of a voltage output. However, this may be optimized for a buffer amplifier with moderate to low input impedance, or a monopole of appropriate length less than half a wavelength if the input has a specific matched termination. Here, it does not make much sense that the unit receiving antenna itself has a sharper directivity in the direction in which the unit receiving antennas are arranged. This is because, when such a property is particularly necessary, these unit receiving antenna groups can be sufficiently output while being handled as an array.

In the preferred embodiment, a monopole landed on the bottom of the water is used. Therefore, no special consideration is required for the ground plane to be opposed to the monopole. However, in the case where the unit receiving antenna is raised without landing in water, a vertical dipole is used rather than a monopole having a ground plane, that is, according to the same high impedance termination design concept as described above, the total length is one wavelength or less. It is simpler and more convenient to use the following vertical dipole in terms of structure. However, this is also a degree of freedom in implementing the present invention.

If there is no problem in operation even if each unit receiving antenna floats in the water randomly or orderly, each unit receiving antenna is given a float such that buoyancy is balanced and released into the water. Or towing at the end of the ship. There are countless other applications.

Also, in the embodiment described above, one through-coaxial cable is used as the means for in-phase addition. However, this can be done individually for each antenna as long as mutual phase and amplitude are considered. It is obvious that the antennas may be separately installed for each group of antennas. An optical fiber may be used instead of the coaxial cable.

Also, here, the configuration is described in which the transmitting source operates freely and the receiving system is distributed and fixed. On the contrary, it is said that the recipient operates freely and the transmitting system is distributed and fixed. The configuration can also be realized by exactly the same technical idea.

[Brief description of the drawings]

FIG. 1 illustrates a preferred embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a buffer amplifier in the embodiment.

[Explanation of symbols]

 S Signal source (rainbow trout with transmitter) 1a-1k Unit receiving antenna 2a-2k Buffer amplifier 3 Pass-through cable 4 Matching termination 5 Antenna coupler 6 Receiver

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-67904 (JP, A) JP-A-63-269635 (JP, A) JP-A-50-139605 (JP, A) JP-A 54-67605 102906 (JP, A) JP-A-62-289022 (JP, A) JP-A-6-504660 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 7/00 H04B 7 / 02-7/12 H04B 13/02 H04L 1/02-1/06

Claims (6)

(57) [Claims] 1. An underwater telemetry device for continuously receiving an electromagnetic wave signal from a signal source that freely moves in freshwater having a sufficiently low conductivity, wherein a plurality of unit receiving antennas are generally provided in the water. It is characterized by being arranged so as to be distributed at a distance equal to or longer than the wavelength, and to add the received signals obtained from each of these multiple unit receiving antennas with substantially the same amplitude and the same phase and to input the receiver. The underwater telemetry device. 2. A vertical surface wave is used as a wavefront of an electromagnetic wave to be adopted, and the unit receiving antenna has a vertical monopole of approximately half a wavelength or less or a vertical dipole of approximately a wavelength or less, and these unit receiving antennas are used. The underwater telemetry device according to claim 1, further comprising at least one coaxial cable arranged so as to be connected while being connected. 3. A buffer amplifier is arranged between each of said unit receiving antennas and a corresponding addition point of said feed-through coaxial cable so as to cause one-way coupling from the former to the latter. The underwater telemetry device according to claim 2, wherein: 4. A method according to claim 1, wherein each of said adding points is electrically disposed at a distance of approximately one wavelength or an integral multiple thereof in consideration of a wavelength shortening rate of said coaxial cable. 4. The underwater telemetry device according to 3. 5. The underwater telemetry device according to claim 3, wherein the coaxial cable is configured to also be used as a means for supplying operating power to the buffer amplifier. 6. The underwater telemetry apparatus according to claim 1, wherein the unit receiving antenna is arranged along a flow of water, wherein the underwater telemetry apparatus uses a river or an elongated waterway as a freshwater area to be observed. The underwater telemetry, characterized in that the through-coaxial cables run in substantially the same direction and the receiving antennas are arranged in an endfire array in a direction parallel to the flow. apparatus.