Note: Descriptions are shown in the official language in which they were submitted.
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Sp~ifi~li 11
This invention }elates to devices used to summon u..~ divers from a distance.
Common devices used to summon underwater divers produce audible sound in the water by
rn~h ~ l or ek,~ v..~ ' i means. They rely on the ears of divers to detect the sound. The
distance over which they are effective depends on the level of interfering noise from breathing
apparatus, ocean surf, boats, and other sources. It is typically under 30 meters. In cold water diving,
divers wear a protective hood made of foam rubber which blocks sound, so that the effective distance
is less than 3 meters. As a result, such sound generators are seldom used by cold water divers.
We have invented an ~.dc;~ g (paging) device that operates by ~
and receiving modulated ultrasonic acoustic ~vaves in the water. It transmits when a push-button
switch is pressed. When it receives an ultrasonic signal, it produces a audible sound that can be heard
easily by the diver who carries the device. It is superior to audible sound generators in three ways.
First, the device is effective over a greater distance because it's receiver is more sensitive than the
human ear. Second, it's range is not reduced by sources of audible noise or by the use of a foam
rubber diving hood. Third, a number of different waveforms can be used to modulate the carrier
wave. These different waveforms are used to convey simple messages between divers by causing the
receiving device to produce various different sounds. Different ~ i"" waveforms are also used
to achieve separate operating channels, so that a number of I, ~ groups of divers can use
these devices within range of each other.
Such ~ devices are required because vocal and visual ~.,"." .~ .., between
divers is difficult. It is not possible to speak clearly with commonly used breathing apparatus, and
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vocal~y produced sounds can typically be heard less than 10 meters away. Peripheral vision is poor
through a scuba diving mask, so that two divers do not always see each other for visual
,~ f~n Visibility can be limited by suspended particles in the water. As a result of these
fliffif.-lltif c a diver who stops to make O~a~l v~lLivl-~ or has an emergency situation is oflen lefl behind
by his partners.
Following is a list of the drawings which illustrate one ., . i ,ofl;, .. .1 of this invention. These
drawings specifically illustrate the uu~ u~,lioll and function of a prototype device which we have
built.
Figures I, 2, and 3 are views that show the major ~.,..1,~,....~t~
Figure 4 shows how the device may be carried by a diver.
Figure 5 is a block diagram of the electronic circuitry.
Figure 6 illustrates the ultrasonic acoustic signal.
Figure 7 lists the set of mflf~ stif~n signal rlt;4..~,.1ci~ ~.
Figures 8, 9, and 10 are views that show the acoustic transducem;u~ l u~,liu~.
Figure 11 shows the radiation pattem of the acoustic transducer.
The device illustrated in Figures I, 2, and 3 consists of a ~vaterproof housing I that contains
electronic circuitry on a printed circuit board 2 which is powered by a battery 3. A speaker ~,
mounted in a recess beneath the printed circuit board, vibrates the housing to create sound that can be
heard by the diver who carries the device. Two ~ ,lc pushbutton switches 5, labeled "page"
and "emergency," are used to activate the transmitter. A transducer 6, which transmits and receives
the ultrasonic acoustic waves, is mounted on the outside of the housing. A large stainless steel clip 7
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is used to mount this device to the strap of a diver's mask as shown in Figure 4. The device can also
be mounted on other straps on various pieces of the diver's equipment.
Figure S shows, in the form of a block diagram, the electronic circuits that comprise the
device's transmitter and receiver. The transmitter is activated when one of the push-button switches I
is pressed. The mor~ tjnn generator 2 produces a different frequency of square wave "c ' ' on
signal in response to each push-button switch. A carrier oscillator 3 generates the carrier wave at an
ultrasonic frequency (200 ki'~z). This car ier is modulated by the amplitude modulator 4 and then
appiied to a power amplifier 5 which increases it's amplitude to a high voltage. This electrical signal
is applied to the p;~.~.U~ l iC transducer 6, which generates ultrasonic acoustic waves in the water.
The receiver operates if no switch is pressed. An electrical signal from the transducer 6,
produced in response to acoustic waves in the water, is applied to a bandpass filter 7 which passes
oniy signals near the ultrasonic carrier frequency. The signal's amplitude is increased by an amplifier
8 before it is applied to the i~ ' ' 9, which recovers the m~ lqti(m signal. This signal is
applied to a detector 10 which detects the presence of one of the expected modulation signals and
triggers the sound generator 11 to produce an .~",.~",, ;~L~ signal at audible r.~,u~l.ci~ (800-1100 Hz
in this example~. The speaker 12 then produces a sound that the diver can hear. Different sounds are
produced depending on which m~ lqtjl~n signal is detected.
Figure 6 illustrates the amplitude-modulated ultrasonic acoustic wave that is transmitted
through the water. Since the ~"0 ~ ; -, signal in this case is a square wave, the 200 kHz acoustic
carrier wave is simply tumed on and offat the frequency ofthe ",.~.1.,1.~;.." signal. Nine different
""~ ;, .., L~ ,.c;.,, are used for different purposes, as listed in Figure 7. Eight modulation
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~IG.~u.,.~G;-.~ are used by different groups of divers to page only the other divers of the same group.
These are used when the push-button labeled "page" is pressed. Each device transmits and receives
only one of these eight ~of~ otif n .',~ ,.,. The ninth ~ ' ' " frequency is used when the
push-button labeled "~ ,y" is pressed. This is used by any diver to indicate to all other divers
that there is an emergency situation. All of the paging devices can transmit and receive with this
modulation frequency.
The acoustic signal illustrated in Figures 6 and 7 is that used by our prototype device. Other
carrier Gc~4~ may be used, and many other types of modulation are possible. The carrier wave
may be frequency-modulated rather than amplitude--~ ~(' ' ' 1 Modulation waveforms other than a
square-wave Gan be used, and messages other than 'page" or C'~ ""_y" can be conveyed.
Figures 8, 9, and 10 show the construction of the ultrasonic transducer assembly. A smgle
transducer is used for both frs~omiooi~n and reception of the ultrasorlic acoustic waves. It consists of
a cylinder of l.: " ~ ceramic material I which is ~ ,.lly resonant at the ultrasonic carrier
frequency. Each circular end of the ceramic cylinder is plated with metal to serve as an electrode. A
cylinder of cork 2 surrounds the ceramic to prevent acoustic waves from escaping from it's sides. A
sleeve of heat-shrink plastic tubing 3 surrounds the cork to hold it tightly to the ceramic cylinder.
Glue secures these three ,v ~ ~I .v~, ,1. to a metal bracket 4 which is fastened to one of the two
mounting screws 5. A thin wire G is connected, using solder, between each of the mourlting scre~vs
and one of the metal-plated end surfaces of the ceramic cylinder. All of the ~, , are then
encased in molded epoxy plastic 7. The plastic protects the ~UIII,UU ' yet conducts the acoustic
waves well between the water and the two circular faces of the ceramic cylinder. The two screws 5
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erve to mount the assembly to the housing of the paging device. They also serve as the electrical
to the l.~ . ,r crystal.
E1igure 11 shows the acoustic radiation pattern of the transducer for a 0.4 inch diameter
ceramic cylinder which is resonant at 200 kHz. It radiates wide beams from both the front and rear
surfaces. It therefore transmits and receives well in many directions. This is essential for successful
operation of the paging device.
We have d~lllUII~ I that our prototypes operate reliably to distances over 30 meters when
randomly oriented, and to over 130 meters when the acoustic transducer points at another diver.
Transmitter power is ~ 200 milliwatts. The receiver circuitry detects signals as small as
3 microvolts RMS from the transducer. The circuitry is designed for low power . , so that
a common 9 volt battery lasts for 12 hours of normal operation.
A carrier frequency of 200 kHz was selected for our prototype. Ultrasorlic &~4..~,.1GiC~ from
10 kHz to ~ lo 'y 2000 kHz can be used for these devices. Higher OEequency waves suffer
more attenuation as they pass through the water, and a wide beam is mote difficult to achieve.
Greatest operating range is therefore achieved at lower carrier fi~l~u.,.~;.,;,. However, ~ du~,~,,s for
r,~ .,c.~,s below 100 kHz require large ceramic cylinders and additional c....~ , and so are
more expensive to construct.
A frequency range of 800-1100 Hz was selected for the sounds ptoduced by the speaker. This
is near the resonant frequency of the ~ o~ lic speaker that we used. We have found that a foam
rubber diving hood attenuates r,~4u.,..c.~, . higher than 1500 Hz, and it is desirable to use low
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cics for best ~ . through the rubber. However, r.c4 ~lc;~ below 800 Hz are
difficult to generate at sufficient amplitude with a small speaker.
Ultrasonic diver pagers may be used in ~U~ liUIl with a similar device located on a boat
tbat is serving as a diving tender. From the boat, it is possible to page a group of divers, monitor for
emergency situations, recall divers to the boat, etc A boat-based device is functionally similar to the
UIA~ . ;t~,l diver devices, but can be powered from a boat's electrical system and need not be
. Powem;~ iv - and size are not critical, so higher transmitter power and receiver
sensitivity can be achieved to give greater range The ultrasonic transducer can be dropped into the
water or mounted on the boat's hull, and connected to the device by a cable.
