Underwater Sonar Communication Using Small Hardware with Space Savings

Abstract

The present invention relates to a quasi-miniature underwater communication device that uses sonar ultrasonic signals for voice and data communication between divers.

Description

Technical Field

[0001] The present invention relates to underwater sonar communication that can be embedded in a micro transmitter, a micro receiver, and a quasi-miniature wearable device or other devices using a low overhead modulation algorithm.

Background Art

[0002] 1. Background Ultrasonic sonars are widely used for underwater communication of voice and data. In the case of voice communication, the audio frequency is up-converted to the ultrasonic frequency, transmitted underwater, and finally down-converted to the audio frequency at the destination. In the case of data communication, data bits are modulated to the ultrasonic frequency using modulation techniques such as FSK (Frequency Shift Keying) and PSK (Phase Shift Keying). The modulated ultrasonic frequency is transmitted underwater and demodulated to data bits at the destination. Such communication systems are typically medium to large in size, equipped with a large transmitter, a large receiver, and complex processing hardware. Such large systems are not convenient for individual divers who want to minimize the load of diving equipment. They are also expensive due to the complex hardware required for extensive signal processing.

[0003] A quasi-miniature underwater sonar communication system using a micro transmitter, a micro receiver, and lightweight processing hardware has been proposed. Using the proposed system architecture, users can communicate underwater with space-saving devices such as wearable diving watches or diving masks. The proposed solution uses a smart signaling algorithm to minimize the need for expensive processing hardware. The small transmitter and receiver are implemented using low-cost commercially available components. The resulting communication device is extremely small, convenient to use, and also low-cost.

Summary of the Invention

[0004] 2. System Overview The sonar ultrasonic communication system includes modulation hardware for converting voice or data into ultrasonic waves, a transmitter for transmitting ultrasonic waves, a receiver for detecting the transmitted ultrasonic waves, and demodulation hardware for inverse-converting the signal into voice or data.

[0005] On the transmitter side, voice or digital data is modulated using a carrier ultrasonic frequency. This signal is further transmitted underwater using a piezo bender / transducer attached to the body of the device. This low-cost piezo bender, which has a typical thickness of 0.5 mm, is embedded in a slot within the plastic surface, and the additional volume within the device is zero.

[0006] On the receiver side, the system includes a micro MEMS piezo microphone receiver with a waterproof membrane. This MEMS receiver is typically designed to detect ultrasonic frequencies used for modulation in the range of 20 kHz to 100 kHz. The receiver converts the ultrasonic frequency into an electrical signal. This signal is filtered and further demodulated to be converted into voice or digital data. The MEMS microphone receiver is a low-cost device manufactured by a semiconductor process and is extremely small in the range of 3×2×1 mm.

[0007] For low-cost and low-bandwidth communication, dual-tone multi-frequency (DTMF)-type modulation has been proposed. This technology is widely used in telephone push buttons and can operate with a low-cost hardware modulator. The two audio tone systems used to generate 16 different digits in a telephone system are adopted together with two ultrasonic tones for representing 16 different digits. When higher bandwidth and performance are required, standard techniques such as frequency modulation like FSK modulation and phase shift modulation like PSK modulation can be used (Figure 7).

[0008] 3. System Details In this section, the three main components of the proposed sonar communication system, namely the transmitter, receiver, and modulator, will be described in detail.

[0009] 3.1 Piezo surface vibrator transmitter Conventional sonar transmitters use piezo transducers that cannot be integrated into small enclosures such as wearable wristwatches. In these transducers, the stacked piezo layers and the vibrating surface that generate ultrasonic signals occupy the internal volume. Another requirement for a diving communication system is that the signal needs to be omnidirectional, i.e., transmitted in all directions. This additional requirement requires an additional reflector and thus adds further bulk to the transmitter.

[0010] The proposed design for the transmitter uses a thin piezo plate (also called a piezo bender) that is attached to the body of the enclosure. The piezo bender is designed to have a resonant frequency within the ultrasonic range. The vibrations from the piezo bender are transmitted to the surface of the enclosure, further vibrating the plastic or metal body of the enclosure. The vibrations on the larger surface of the enclosure generate ultrasonic signals and transmit them into the water. This concept is similar to a vibrating speaker where a small transducer is attached to a large surface to generate audio from surface vibrations.

[0011] Piezo bender These piezo plates can be made as small as about 10 mm in diameter and 0.5 mm thick, and the space they occupy is negligible (Figure 8). By embedding these plates in slots on the inner surface of the enclosure, they are designed to have zero volume inside the device. By arranging these plates on multiple surfaces of the enclosure, ultrasonic waves can be radiated in multiple directions. The surface thickness of the enclosure is designed to transmit ultrasonic vibrations into the water.

[0012] Piezo bender on the inner surface of the enclosure (Figure 9)

[0013] 3.2 MEMS microphone receiver Conventional ultrasonic receivers, also known as hydrophones, use piezoelectric transducers. They convert ultrasonic vibrations from the environment into electrical pulses. These are typically medium to large-sized devices and cannot be integrated into a quasi-miniature housing such as a wristwatch due to their bulk.

[0014] The proposed solution is to use semiconductor MEMS (Micro-Electro-Mechanical Systems) receiver microphones. They are designed to be sensitive to ultrasonic frequencies in the range of 20 kHz to 100 kHz. These devices can be designed to be as small as about 3×2×1 mm and can be easily integrated into a quasi-miniature wearable type of device. Multiple receivers can be integrated within the housing to detect signals from multiple directions. Using multiple receivers also helps in detecting the direction of the ultrasonic signal.

[0015] Using multiple receivers and beamforming microphone technology, the system can detect the direction of the source signal. By using the time delay and phase shift of the ultrasonic signal between different microphones, the direction of the sound can be perceived. One application of this technology is the boat finder function that guides a diver towards a boat. The boat will emit an ultrasonic beacon towards the diver. The device worn by the diver detects the direction of the signal coming from the boat, and the diver is navigated towards the boat.

[0016] The MEMS receiver is protected by a waterproof membrane that can transmit ultrasonic frequencies without loss. This protected MEMS receiver is exposed to the environment by an audio port within the housing. The gasket around the MEMS receiver seals the housing from water.

[0017] MEMS Ultrasonic Microphone Receiver (Figure 10)

[0018] 3.3 DTMF-Based Modulation Conventional sonar communication systems use standard modulation techniques such as frequency shift keying (FSK) to convert digital data into ultrasonic signals. These techniques provide good speed and bandwidth, but require complex and expensive hardware for modulation and environmental ultrasonic noise filtering.

[0019] The proposed design uses dual-tone multi-frequency (DTMF) signaling for simple low-bandwidth modulation of data into ultrasonic signals. This system is similar to the DTMF tones used in telephones where each digit pressed on the phone dial is transmitted as a two-tone frequency. The destination detects the two frequencies in the signal and converts them into the transmitted digit. By using four frequencies for the first tone and four other frequencies for the second tone, a total of 16 digits can be represented for signaling. In the solution proposed by the inventors, the audio frequencies used in telephone signaling are replaced by ultrasonic frequencies for underwater signaling.

[0020] In one embodiment, the range of 20 - 21 kHz is used for the first frequency and the range of 22 - 23 kHz is used for the second frequency. Using 16 possible combinations of the signals, 10 digits (0 - 9), start / end commands, and four additional commands can be represented. With a tone duration of 50 milliseconds, data at 20 bytes per second can be transmitted. [Table 1] Two-tone frequencies for representing 16 signals

[0021] Dual-tone frequencies (Figure 11).

[0022] The use of DTMF technology in ultrasonic communication eliminates the need for expensive hardware used in complex modulation and false signal filtering. This method may not be suitable for high-speed communication, but may be sufficient for low-speed communication. This solution can be effectively embedded with low-cost and simple hardware.

[0023] The operating frequency can be in the range of 20 kHz to 100 kHz. The lower the frequency, the stronger the single directivity and the wider the transmission range. However, the data rate will be lower. Since it causes audible sound that can be heard by the diver, it cannot be below 20 kHz. The higher the frequency, the better the data rate, but the attenuation loss increases and the range becomes shorter. They also have strong directivity.

[0024] Due to these diverse frequency transmission characteristics of the sonar frequency, the system can use the range of 20 - 30 kHz for communication between the boat and the diver within a distance range of several miles. Diver team communication can use the range of 30 - 40 kHz to cover a medium distance range of 100 meters. This higher frequency also provides a faster data rate. Communication between the diver's devices can use the range of 40 - 50 kHz for a short distance range of 2 meters.

[0025] The present invention is shown in the following figures.

Brief Description of the Drawings

[0026]

Figure 1

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Figure 6

Embodiments for Carrying Out the Invention

[0027] Beamforming Microphone Array for Detecting Sound Direction Sound (audible and ultrasonic) beamforming is a technique used to detect sound from a single direction or to detect the directivity of sound using an array of microphones. At a very basic level, this technique involves detecting which microphone receives the signal first. The distance between the microphones is known, and thus the time (and signal phase difference) it takes for sound to reach from one microphone to the next is known. This phase difference is used to detect the direction of the sound. In the case of a 2x2 microphone array, the direction of the sound is calculated by looking at the phase differences between all four microphones using the phase differences between the four microphones.

[0028] To detect sound from only one direction, the signal is phase-shifted at each microphone with a phase shift estimated according to the required direction of the sound. After this shift, the signals from the desired direction are added and amplified. Signals from any other direction are negated and the amplification is reduced. This process can be repeated in all directions to detect the peak sound direction.

[0029] A 1D array is used to detect sound from the direction of the array. A 2D array can be used to detect sound in two axial directions. A 3D array can detect directions from all three axes.

Claims

1. A sub-miniature underwater communication device that uses sonar ultrasonic signals for voice and data communication between divers.

2. The underwater communication device according to claim 1, wherein the underwater communication function can be integrated into a wearable such as a diving wristwatch or a diving eyewear mask.

3. The sub-miniature underwater communication device according to claim 1, wherein the ultrasonic signal is generated using a surface vibration device such as a piezo bender or a piezo plate.

4. The sub-miniature underwater communication device according to claim 3, wherein the piezo bender is disposed in a slot on the inner surface of the device without consuming the internal volume space of the device.

5. The sub-miniature underwater communication device according to claim 1, wherein the ultrasonic signal is received and converted into an electrical signal using a microelectromechanical system (MEMS) device.

6. The sub-miniature underwater communication device according to claim 5, wherein the MEMS device is protected by a waterproof membrane capable of transmitting ultrasonic signals without attenuation.

7. The sub-miniature underwater communication device according to claim 6, wherein the waterproof MEMS device is exposed to ambient ultrasonic waves using an audio port and a gasket around the port.

8. The sub-miniature underwater communication device according to claim 5, wherein a plurality of MEMS receivers are used to detect omnidirectional signals.

9. The sub-miniature underwater communication device according to claim 8, wherein a plurality of MEMS receivers equipped with beamforming technology provide the direction of the signal, and this information can be used for boat detection or navigation of other divers.

10. The sub-miniature underwater communication device according to claim 1, wherein the voice and digital data are modulated to an ultrasonic frequency at the source using surface vibration and demodulated to voice and digital data at the destination using a MEMS microphone.

11. The sub-miniature underwater communication device according to claim 8, wherein voice or data is modulated to ultrasonic waves using dual-tone multi-frequency (DTMF) signaling and demodulated back to voice and data.

12. The sub-miniature underwater communication device according to claim 9, wherein binary data is modulated using two-frequency signaling, or hexadecimal data (or 16-level data) is modulated using eight-frequency signaling.

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