Steering of directional sound beams

• US 20040264707A1
• Filed: 02/28/2004
• Published: 12/30/2004
• Est. Priority Date: 08/31/2001
• Status: Active Grant

• Current Assignee: Nanyang Technology University
• Original Assignee: Nanyang Technology University
• Inventors: Yang, Jun, Wang, Yi, Tan, Khim Sia, Karnapi, Furi Andi, Er, Meng Hwa, Gan, Woon Seng, Liew, Yew Hin, Lee, Chee Mun Kelvin, Sha, Kan
• Granted Patent: US 7,146,011 B2
• Time in Patent Office: Days
• US Class Current: 381/77
• CPC Class Codes: G01N 2291/02491 Materials with nonlinear acoustic properties
• CPC Class Codes: G10K 11/26 Sound-focusing or directing, e.g. scanning
• CPC Class Codes: G10K 15/02 Synthesis of acoustic waves synthesis of speech G10L13/00
• CPC Class Codes: H04R 2217/03 Parametric transducers where sound is generated or captured by the acoustic demodulation of amplitude modulated ultrasonic waves

Abstract

Apparatus is disclosed for steering a directional audio beam that is self-demodulated from an ultrasound carrier. The apparatus includes means for modulating a carrier signal with an audio signal and means for adjusting the amplitude and phase of at least one of the audio signal and/or the carrier signal to steer the audio beam to a desired direction. The apparatus also includes means for generating an ultrasound beam in the desired direction driven by the modulated carrier signal. The apparatus may include means for weighting the audio and/or carrier signal by a zeroth order Bessel function to synthesize a Bessel distribution source. A corresponding method for steering a directional audio beam is also disclosed. A harmonic generator may be used to generate harmonics of low frequencies in the audio signal. The harmonics may provide (upon demodulation) a psycho-acoustic impression of improved perception of low frequencies. Further, a modulated ultrasonic signal or an unmodulated audio signal may be band-passed into two or more different band-limited signals. The band-limited signals may be amplified and transmitted by ultrasonic transducers having mechanical resonance frequencies substantially equal to a characteristic frequency of the band-limited signals. Ultrasonic processing of the audio signal may include square root methods without generating large numbers of harmonics.

Claims

1-85. -85. Canceled

86. Method for steering a directional audio beam that is self-demodulated from an ultrasound carrier, said method including the steps of:

generating an audio signal;

generating an ultrasound carrier signal;

modulating said carrier signal with said audio signal;

adjusting both amplitude and phase of at least one of said audio signal and said carrier signal to steer said audio beam to a desired direction; and

generating an ultrasound beam driven in said direction by said modulated carrier signal.

87. The method according to claim 86 including suppressing a sidelobe of the ultrasound beam.

88. The method according to claim 86 including weighting said audio and/or carrier signal by a zeroth order Bessel function to synthesize a Bessel distribution source.

89. Method according to claim 88 wherein said step of generating an ultrasound beam includes driving a plurality of ultrasound transducer elements with said modulated carrier signal and said step of weighting includes adjusting gain and delay of said audio and/or carrier signal prior to driving each transducer element.

90. Method according to claim 86 wherein said step of generating an ultrasound beam includes driving a plurality of ultrasound transducer elements via a corresponding plurality of matching filters adapted to adjust the phase of the modulated carrier signal to the resonant frequency of the associated transducer element.

91. Method according to claim 86 including detecting the location of a potential listener and adjusting said means for generating to steer said audio beam towards said location.

92. Method according to claim 86 including reflecting said audio beam from an intermediate surface such as a billboard panel.

93. A method of processing an audio signal, including:

performing a square root operation on the audio signal to generate a square rooted signal;

alternating the gain of the square rooted signal between positive and negative gain values at selected locations to generate a flipped signal, wherein the selected locations of the signal are minimum turning points of the signal;

modulating the flipped signal onto a first ultrasonic carrier wave; and

offsetting the audio signal by a predetermined amount prior to performing the square root operation to ensure that the square root operation only results in real values.

94. The method of claim 93 further including the step of:

dividing the audio signal into a plurality of frames;

determining, after the offsetting step;

a minimum value of a portion of the audio signal in a particular frame;

subtracting the minimum value from the portion of the audio signal in the particular frame; and

compensating the flipped signal in adjacent frames for discontinuities resulting from subtracting different minimum amounts in adjacent frames.

95. The method of claim 93 further including the steps of:

determining a first modulation envelope for the processed audio signal;

determining a second modulation envelope for an ideal square rooted signal;

determining the difference between the first and second modulation envelopes; and

modulating the difference between the first and second modulation envelopes onto a second ultrasonic carrier wave.

96. A method for processing an audio signal received from an audio source, including:

processing the audio signal into a first processed audio signal;

processing the audio signal into a second processed audio signal;

modulating the first processed audio signal onto a first ultrasonic carrier wave; and

modulating the second processed audio signal onto a second ultrasonic carrier wave;

wherein the first and second ultrasonic carrier waves have different phases.

97. The method of claim 96 wherein the first ultrasonic carrier wave is orthogonal to the second ultrasonic carrier wave.

98. A method of processing an audio signal, including:

separating a low frequency component from the audio signal;

generating harmonics of the low frequency component using a psycho acoustic model to create a preprocessed signal; and

modulating the preprocessed signal onto an ultrasonic carrier wave.

99. The method of claim 98 further including the steps of:

combining the low frequency component with the preprocessed signal prior to the modulating step;

combining other frequency components of the audio signal with the preprocessed signal prior the modulating step; and

processing the other frequency components of the audio signal using a psycho acoustic model prior to combining the other frequency components of the audio signal with the preprocessed signal.

100. The method of claim 99 further including the steps of:

transmitting the preprocessed signal from a first ultrasonic emitter after the modulation step;

modulating other frequency components of the audio signal onto an ultrasonic carrier wave; and

transmitting the modulated other frequency components of the audio signal using the first ultrasonic emitter or a second ultrasonic emitter.

101. The method of claim 100 wherein the preprocessed signal is modulated using a first ultrasonic carrier wave and the other frequency components are modulated using a second ultrasonic carrier wave orthogonal to said first ultrasonic carrier wave.

102. A method of processing an audio signal including the steps of:

separating the audio signal into a plurality of band-limited signals;

modulating each of the band-limited signals onto ultrasonic carrier waves having either the same or different carrier frequencies thereby to create a plurality of modulated signals; and

transmitting each of the modulated signals from separate ultrasonic emitters.

103. The method of claim 102 further comprising the steps of:

preprocessing at least one of the band-limited signals prior to the modulating step;

generating harmonics of the at least one band-limited signal; and

combining the harmonics with the at least one band-limited signal.

104. A method of processing an audio signal including the steps of:

modulating the audio signal onto an ultrasonic carrier wave to provide a modulated audio signal;

separating the modulated audio signal into a plurality of band-limited signals; and

transmitting each of the plurality of band-limited signals from separate ultrasonic transmitters.

105. The method of claim 104 wherein the ultrasonic transmitters are matched to a corresponding characteristic frequency of the respective band-limited signals.

106. The method of claim 105 wherein the separating step is conducted by passing the audio signal through N filter banks having passbands centered at frequencies f₁ to f_N, and the band-limited signals are transmitted from N ultrasonic transmitters having mechanical resonance frequencies equal to f₁ to f_N respectively.

107. Method for steering a directional audio beam that is self-demodulated from an ultrasound carrier, said method including the steps of:

generating an audio signal;

generating an ultrasound carrier signal;

modulating said carrier signal with said audio signal;

generating an ultrasound beam driven by said modulated carrier signal; and

adjusting said means for generating to steer said audio beam to a desired direction,

wherein said step of generating is performed by means of a plurality of transducer elements and said step of adjusting is performed by means of a stepper motor for rotating said transducer elements relative to at least one axis.

108. Method according to claim 107 including detecting the location of a potential listener and adjusting said means for generating to steer said audio beam towards said location.

109. Method according to claim 107 including reflecting said audio beam from an intermediate surface such as a billboard panel.