Amplitude modulation systems for underwater communication have a number of disadvantages. For example, with a number of divers attempting to communicate simultaneously, intolerable cross-talk occurs. Variable tuning is necessary to overcome this problem. However, the invention disclosed herein uses angle modulation (phase or frequency modulation) which inherently has fewer noise problems and, because of the "capture effect" reduces any cross-talk problems. In an exemplary embodiment an audio transducer feeds a modulator to produce frequency modulated radio frequency signals which are fed to a balanced modulator together with a fixed frequency radio frequency signal from a local oscillator. The output of the balanced modulator comprises ultrasonic frequency signals which are frequency modulated in accordance with the audio signals. Also disclosed is a receiver for such ultrasonic frequency signals. By the use of integrated circuits, a combined ultrasonic transmitter and receiver may be provided in a compact unit adapted to be strapped on the head of a diver.
A portable and hand-held device for making humanly audible sounds responsive to the detecting of ultrasonic sounds. The device includes a hand-held housing and circuitry that is contained in the housing. The circuitry includes a microphone that receives the ultrasonic sound, a first low voltage audio power amplifier that strengthens the signal from the microphone, a second low voltage audio power amplifier that further strengthens the signal from the first low voltage audio power amplifier, a 7-stage ripple carry binary counter that lowers the frequency of the signal from the second low voltage audio power amplifier so as to be humanly audible, a third low voltage audio power amplifier that strengthens the signal from the 7-stage ripple carry binary counter, and a speaker that generates a humanly audible sound from the third low voltage audio power amplifier.
A system for two way communication under shallow water or between a swimmer and observer comprising a transceiver, a wire for conducting electrical signals connected to the transceiver, a watertight transducer housing that curvedly conforms to human heads incorporating a speaker/microphone transducer in watertight connection with the wire, an adjustable strap connected to the transducer housing so that it may be attached to a portion of a human body, and a hollow acoustic transmission tube in watertight connection with the transducer housing for sound transmission to an earplug which is inserted into a human ear.
An underwater audio communication system to be worn by a diver is connected with and carried by a conventional face mask such that bone conduction occurs through the mastoid bone of the diver (i.e., behind the ear of the diver). The underwater audio communication system includes a face mask with a head strap for placement behind the head of the diver. A transceiver which is connected with and carried by the head strap is configured for receiving and transmitting ultrasonic signals in the water. At least one bone conduction transducer assembly is connected with and carried by the head strap at a location for placement against a mastoid bone of the diver. Each bone conduction transducer assembly is electrically connected with the transceiver.
An apparatus and improved method for transmitting an information signal. According to the improved method, an information signal is transmitted under water from a transmitter located at a first place to a receiver located distant therefrom at a second place. In performing the signal transmission, a modulated ultrasound carrier signal is delivered to the water and is formed with a fixed amplitude value in the transmitter. The modulation is performed by pulse duration modulating (with an information signal) the ultrasound carrier signal which, in turn, has a given frequency. The modulated ultrasound carrier signal is then picked up from the water and is demodulated in the receiver in order to recover the information signal. The improvement resides in performing the pulse duration modulation so that the modulated ultrasound carrier signal is modulated in the form of ultrasound pulses having the pulse leading edges thereof modulated with the information signal and having a fixed pulse amplitude below the cavitation limit of the transmission medium. The apparatus performs the improved method.
The conversation device of an MR imaging apparatus including a magnet for generating a static magnetic field, a gradient field coil disposed between pole pieces of the magnet and used for endowing an NMR signal with positional information, a high-frequency coil disposed in the gradient field coil for transmitting an electromagnetic wave and for detecting the NMR signal, and a bed disposed in the high-frequency coil for holding a person to be inspected, is disclosed. In this conversation device, a bone conduction microphone insensitive to a magnetic field and surrounding noise is mounted on an auxiliary member (which is used for placing the to-be-inspected person at a predetermined position on the bed) so that the bone conduction microphone can be kept in contact with that part of the to-be-inspected person which can conduct the voice of the to-be-inspected person by a bone.
