The present application relates to an underwater locator beacon with a pressure sensor for a flight recorder.

Most underwater location beacons or pingers, when activated, emit periodic acoustic pulses. Hand-held, towed, or ship- mounted underwater location beacon receivers receive these acoustic pulses to determine positions of these pingers.

These acoustic pulses have a limited range, due to energy lost and to attenuation as these pulses travel in water. In addition, the sea has background acoustic noise, which prevents these acoustic pulses from being detected when energy of these acoustic pulses falls below a pre-determined value

In use, the underwater location beacons are intended for attaching to aircraft flight recorders for providing location signals of these flight recorders, in an event of aircraft accident. Search teams can use the location signals for locating the fallen flight recorders. These underwater location beacons can also be placed on torpedoes, when the torpedoes are undergoing underwater test and practice during development of the torpedoes. Sometimes, the torpedoes are lost during such testing. This can be a serious problem and the underwater location beacons, which are attached to the torpedoes, assist in recovery of these torpedoes.

It is an object of the application to provide an improved underwater locator beacon (ULB) . It is believed that the underwater locator beacon can be im- proved by including an integrated pressure sensor to extend battery life of the underwater locator beacon.

The application provides an underwater locator beacon (ULB) . The ULB includes a pressure sensor, a battery, an acoustic pulse transmitter, a water button, and a processor.

In use, the underwater locator beacon is intended for attaching to a flight recorder, which is installed in an airplane. The flight recorder is also called a black box.

In an event of an airplane accident, if the flight recorder with the underwater locator beacon drops into the sea, river, or lake, the water of the sea, river, or lake would activate the water button such that the battery provides electrical power to the pulse generator for emitting acoustic pulse signals in a periodic manner. The acoustic pulse signals are also called beacon signals.

When an acoustic pinger receiver is located in the vicinity of the operational ULB, the acoustic pinger receiver can receive these acoustic pulse signals, which enable search teams to locate the fallen flight recorder.

The pressure sensor is used to measure water pressure of the fallen ULB. Since water pressure of the ULB is proportional to underwater depth of the ULB, this water pressure measurement can be used to estimate the underwater depth of the flight recorder.

The processor then adjusts the pulse generator according to the said water pressure measurement in a manner that extends the operational time of the battery while allowing the pinger receiver to detect the acoustic signal. The adjustment relates to power as well as to pulse repetition rate of the acoustic signals.

The extended battery life has a benefit of allowing the search team a longer time to locate the fallen flight recorder. This is especially important when the search time extends to months due to the vastness and weather conditions of the search area.

For example, the search for the black box of the crashed Air France Flight AF447 in 2009 went through four search phases, which lasted almost 2 years. Normally, the battery of ULB, which is attached to the black box, is designed to operate for about one month. When the black box could not be located one month after the crash, the search process became more difficult as the search teams cannot depend on the signals of the ULB to locate the black box. Instead, the search teams had to employ complicated tools, such as submarine, underwater vehicle, sonar radar, for locating the black boxes. This is why the search process took such very long time. If the battery life of ULB were longer, the search time could have been shorter. Hence, it is desirable to extend the battery life of ULB.

The application provides an underwater locator beacon device for a flight recorder of an aircraft. The locator beacon de- vice includes a wet button, a power source, a pressure sen- sor, a processor, and an acoustic transmitter.

Operationally, the wet button is actuated when it is wet. The button is often wet in the event of an aircraft accident, wherein the locator beacon device falls into a body of water, which can be a lake, river, or sea. The actuated wet button enables the power source to provide electrical energy to other parts of the locator beacon device.

The energized pressure sensor then provides a water pressure measurement data of the underwater locator beacon device. The energised processor later receives the water pressure measurement data from the pressure sensor and provides a control signal according to the water pressure measurement data.

The acoustic transmitter, receiving the energy from the power supply source, provides an acoustic pulse signal for search teams to locate the fallen locator beacon device. The acoustic transmitter provides the acoustic pulse signal according to the control signal such that the operating time of the power source is extended while maintaining the probability of locating the locator beacon device. In other words, the extending of battery life does not reduce chances of locating the locator beacon device.

The extension of battery life is useful, especially when a long time is needed to located the beacon device due to the water and weather conditions.

The control signals can be used in different ways to extend the battery life.

The control signal can be used to adjust a power of the acoustic pulse signal. When the locator beacon device has fallen in shallow waters, rather than deep waters, the processor can reduce the power of the acoustic pulse signal via the control signal without reducing probability of locating the locator beacon device.

Alternatively, the control signal can be used to adjust a pulse repetition rate of the acoustic pulse signal. A reduced pulse repetition rate would result in reduced power consumption and in longer battery life.

The pressure sensor can deactivated such that the pressure sensor does not consume power or energy after the pressure measurement data have stabilised to further reduce power consumption. The pressure measurement data are often stabilised when the locator beacon device has reached bottom of the water .

The application also provides a flight recorder of an aircraft. The flight recorder comprises a flight recorder module and the above underwater locator beacon device. The flight recorder module is used for recording flight information of the aircraft while the underwater locator beacon device is attached to the flight recorder module for providing location signal of the underwater flight recorder module in an event of an aircraft accident.

Fig. 1 illustrates an improved underwater locator beacon

(ULB) with an integrated pressure sensor, Fig. 2 illustrates a block diagram of the ULB of Fig. 1, Fig. 3 illustrates a locating of a flight recorder with the ULB of Fig. 1,

Fig. 4 illustrates a transmission of an acoustic beacon signal of the ULB of Fig. 1, and

Fig. 5 illustrates 3 dB (decibel) zones of the acoustic beacon signal of Fig. 3 on the surface of water. In the following description, details are provided to describe the embodiments of the application. It shall be apparent to one skilled in the art, however, that the embodiments may be practised without such details.

Figs, below have similar parts. The similar parts have the same names or similar part numbers. The description of the similar parts is hereby incorporated by reference, where ap- propriate, thereby reducing repetition of text without limiting the disclosure.

Fig. 1 shows an improved underwater locator beacon (ULB) 10 with an integrated pressure sensor 12. The ULB is also called an underwater locator device or a pinger.

As better seen in Fig. 2, the ULB 10 includes a plurality of parts, namely a water button 14, a battery 15, an acoustic transmitter 17, a pressure sensor 18, and a control part 20. These components are placed in a single rugged housing 22.

In use, the housing 22 is intended for attaching to a flight recorder of an aircraft. The housing 22 protects parts within the housing 22 from harm.

Fig. 3 shows an accident of an aircraft 30, wherein the aircraft 30 has a flight recorder that is attached to the ULB 10. The aircraft 30 is submerged in water. The water activates the water button 14 such that the battery 15 to provide electrical power to the acoustic transmitter 17, and to the control part 20. The control part 20 then activates automatically the acoustic transmitter 17 to send acoustic beacon signals 28. Search teams use pinger receivers 32 to receive these transmitted acoustic beacon signals 28 for locating the submerged ULB 10, as seen in Fig. 3.

The pressure sensor 18 is used to measure water pressure of the ULB 10. Since this water pressure is proportional to the water depth of the submerged ULB 10, the measured pressure data can be used to estimate the depth of the ULB 10.

Moreover, the operation of pressure sensor 18 is controlled by the control part 20. When necessary, the control part 20 activates the pressure sensor 18 to take pressure measurement. Similarly, when unnecessary, the control part 20 deactivates the pressure sensor 18 to save power. Often, the pressure sensor 18 is operational for very short time after the ULB 10 is switched on. When the ULB 10 reaches the sea floor, the reading of the pressure sensor 18 becomes stable in that the pressure reading does not change and the pressure sensor 18 is then shut off to save power. In this manner, the integrated pressure sensor 18 consumes very little power.

The acoustic beacon signals 28 are attenuated along its propagation direction. The longer the beacon signals 28 travel, the more weak or more attenuated the beacon signals 28 becomes due mainly to spreading and energy absorption of the beacon signals 28 by water.

The surface area of the wave front of the acoustic beacon signals 28 becomes larger as the transmission distance T of the beacon signals 28 becomes longer. This is because this surface area is geometrically proportional to the square of the transmission distance T. In effect, the energy of the beacon signals 28 is spreader over a larger area as the bea- con signals 28 travel further away. If the square of the transmission distance T is denoted by D ² , the power dissipation of acoustic beacon signals 28, which is due to the spreading, is proportional to D ² .

In contrast, the absorption of beacon signals 28 by water depends on many parameters, such as water temperature, water salinity, water depth, and signal acoustic frequency. The control part 20 uses the water pressure measurements of the pressure sensor 18 to adjust the power and the pulse repetition rate of the beacon signals 28 of the acoustic transmitter 17 in order to extend the operating life of the battery 15 while allowing the pinger receivers 32 to detect the beacon signals 28. Put differently, the pinger receivers 32 are still able to detect the transmitted beacon signals 28 even though these beacon signals 28 may have reduced energy and reduce repetition rate for prolonging or extending the operating life of the battery 15.

The operating life of a battery 15 can be extended by optimizing and adjusting the transmission power and the pulse repetition rate of the acoustic beacon signals 28 since most energy of the battery 15 is consumed for generating the bea- con signals 28.

In one implementation, when the transmission power of the beacon signal is at 162 dB and the pulse repetition rate of the beacon signal is at 1 pulse per 2 seconds, a 9 volt alka- line battery of the underwater locator beacon would have an operating life of 26 days while a 9 volt lithium battery of the underwater locator beacon would have an operating life of 60 days.

When the transmission power of the beacon signal is at 162 dB and the pulse repetition rate of the beacon signal is at 2 pulses per 1 second, a 9 volt alkaline battery of the underwater locator beacon would have an operating life of 20 days while a 9 volt lithium battery of the underwater locator beacon would have an operating life of 45 days.

When the transmission power of the beacon signal is at 168 dB and the pulse repetition rate of the beacon signal is at 1 pulse per 2 seconds, a 9 volt alkaline battery of the underwater locator beacon would have an operating life of 20 days while a 9 volt lithium battery of the underwater locator beacon would have an operating life of 45 days.

When the transmission power of the beacon signal is at 168 dB and the pulse repetition rate of the beacon signal is at 2 pulses per 1 second, a 9 volt alkaline battery of the underwater locator beacon would have an operating life of 10 days while a 9 volt lithium battery of the underwater locator beacon would have an operating life of 20 days.

The extended battery life is of benefit as it may take some time for search teams to locate the fallen ULB 10. This is especially important when the location of the fallen ULB is not precise and the water, in which the aircraft has fallen, is deep.

Considering properties of water, water pressure increases by about 14.7 psi (pound per square inches), which is about 1 atmospheric pressure, when the water depth increases by 33 feet, which is about 10 meters. The absorption r. water for a beacon signal with pulse rate of 37. tween about 2 clB (decibel) /km (kilometre) and ab> The absorption rate is often lower in deeper wat that the average seawater absorption rate is 9 d depth of 1 km and is 7.5 dB/km at the depth of 4 difference of signal loss, due to absorption los spreading loss, between the depth of 1 km and th> km is

The shortest transmission distance T from the UL: surface is often equal to the underwater depth o even though the ULB 10 may be tilted in the wate in Fig. 4. This is because the beam-width of the transmitter 17 is often is quite wide. In one ca width is about 80 percent of sphere.

On the surface of water, the strength of the bea 28 peaks at a certain area that is located verti the ULB 10. This area is called here as a peak p> signal strength at surface areas weakens, as the as are placed further away from the peak point. . distance S on the water surface from the peak po con signals 28 become so weak that the pinger re cannot detect them due to acoustic noise in the ^" on this, an effective coverage area of the beaco: is defined here as an area, where the pinger re detect the beacon signals 28.

Furthermore, the deeper the ULB 10 is located in weaker the beacon signals 28 at the water surfac comes since the beacon signals 28 have to travel for a longer distance from the ULB 10 to the wafer surface.

At the water surface level, the strength of the beacon sig- nals 28 decreases as the distance S from the peak point increases. The decaying rate of signal is dependent on the depth of the ULB 10. If the depth of fallen ULB 10 were small, the transmission distance T between the beacon signal at the water surface and the ULB 10 changes fast as the dis- tance S between the beacon signals at the water surface and the peak point increases. Because of this, the decay of signal is also fast. The opposite of this is also true. Because of this, a 3 dB (decibel) zone for the beacon signals 28 is larger when the ULB 10 is deeper, as illustrated in Fig. 5. The 3 dB zone denotes an area when signal power at its rim area is half of the signal power at its central area.

Consider an example where absorption loss and spreading loss is taken into account. If the ULB 10 is located at a distance of 1000 meters below sea level and the average water absorption rate at that level is about 9 dB/km, then the radius of its 3 dB zone is about 650 meters. On the hand, if the ULB 10 is located at a distance of 4000 meters below sea level and the average water absorption rate at that level is about 7.5 dB/km, then the radius of its 3 dB zone is about 1.7 km. As compared to the former 3 dB zone area, the latter 3 dB zone area increases by π 21.5 times.

If the power loss caused by the incident angle to the pinger receiver is taken into account, the difference of 3 dB area between a ULB, which is shallow water and a ULB, which is in deep water, is even bigger. When the power of the acoustic transmitter 17 is configured for deep-water usage, this power can be reduced for shallow water usage without affecting probability of detecting the ULB 10. Similarly, the pulse repetition rate of the beacon signals 28 can also be adjusted without affecting probability of detecting the ULB 10. When both a first ULB at deep water and a second ULB at shallow water provide the same peak power at the water surface level, the first ULB would provide an effective coverage area that is larger the effective coverage area of the second ULB. In this case, the pulse rate of the first ULB can be reduced without affecting the probability of the locating the said ULB. Based on the preceding calculation, if the ULB 10 is located at 1000 m under water and the output power of the acoustic transmitter 17 is lowered by 15 dB, then the battery 15 can last about 3 to 4 times longer. On the hand, if the ULB 10 is located at 4000 m under water and the pulse repetition rate is reduced by about 5 times, then the battery 15 can last about 3 to 4 times longer.

In one implementation, the output power of ULB 10 is about 160 dB ref 1μΡ3@ΐΓη. The pulse repetition rate of the beacon signals 28 is about 1 pulse/second. The pressure sensor measures water pressure at one measurement per hour.

In another implementation, the pressure sensor 18 measures up to a pressure of 20,000 psi. Such a pressure sensor 18 can be used to a water depth of 10,000 meters, which is about 14,700 psi. The pressure sensor 18 can be produced using MEMS (Micro-Electro-Mechanical Systems) pressure sensor technology, which allows the pressure sensor 18 to have a small size. This pressure sensor 18 can then be integrated with the ULB 10 without increasing much the size of the ULB 10.

In short, the pressure sensor 18 can determine the water depth of the ULB 10. The ULB 10 can then employ the depth information to optimize or improve its output power and its pulse repetition rate so as to prolong the life of its battery 15. With the longer battery life, the search teams are allowed to have more time to locate the ULB 10 together with the flight recorder. In this manner, the probability of finding out the flight recorder in water is enhanced and search efforts can be saved.

Although the above description contains much specificity, this should not be construed as limiting the scope of the embodiments but merely providing illustration of the foreseeable embodiments. The above stated advantages of the embodiments should not be construed especially as limiting the scope of the embodiments but merely to explain possible achievements if the described embodiments are put into practice. Thus, the scope of the embodiments should be determined by the claims and their equivalents, rather than by the examples given.

Reference

10 underwater locator beacon

12 pressure sensor

14 water button

15 battery

17 acoustic transmitter

18 pressure sensor

20 control part

22 housing

28 beacon signal

30 aircraft

32 pinger receiver

S distance on the water surface from the peak point

T transmission distance