| United States Patent |
5,539,705 |
| Akerman , et al. |
July 23, 1996 |
Ultrasonic speech translator and communications system
Abstract
A wireless communication system undetectable by radio frequency methods for
converting audio signals, including human voice, to electronic signals in the
ultrasonic frequency range, transmitting the ultrasonic signal by way of
acoustical pressure waves across a carrier medium, including gases, liquids, or
solids, and reconverting the ultrasonic acoustical pressure waves back to the
original audio signal. The ultrasonic speech translator and communication system
(20) includes an ultrasonic transmitting device (100) and an ultrasonic
receiving device (200). The ultrasonic transmitting device (100) accepts as
input (115) an audio signal such as human voice input from a microphone (114) or
tape deck. The ultrasonic transmitting device (100) frequency modulates an
ultrasonic carrier signal with the audio signal producing a frequency modulated
ultrasonic carrier signal, which is transmitted via acoustical pressure waves
across a carrier medium such as gases, liquids or solids. The ultrasonic
receiving device (200) converts the frequency modulated ultrasonic acoustical
pressure waves to a frequency modulated electronic signal, demodulates the audio
signal from the ultrasonic carrier signal, and conditions the demodulated audio
signal to reproduce the original audio signal at its output (250).
| Inventors: |
Akerman; M. Alfred (Knoxville, TN);
Ayers; Curtis W. (Clinton, TN); Haynes; Howard D.
(Knoxville, TN) |
| Assignee: |
Martin Marietta Energy Systems, Inc.
(Oak Ridge, TN) |
| Appl. No.: |
329889 |
| Filed: |
October 27, 1994 |
| Current U.S. Class: |
367/132 |
| Intern'l Class: |
H04B 011/00 |
| Field of Search: |
367/132,131,133,134,7
|
References Cited
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Primary
Examiner: Pihulic; Daniel T.
Attorney, Agent or Firm: Spicer; J.
S., Neely; A. S., Adams; H. W.
Goverment Interests
This invention was made with Government support under Contract
DE-AC05-840R21400 awarded by the U.S. Department of Energy to Martin Marietta
Energy Systems Inc., the Government has certain rights to this invention.
Claims
What is claimed is:
1. A wireless communication system for
transmitting and receiving audio signals via ultrasonic acoustical pressure
waves comprising an ultrasonic transmitting device and an ultrasonic receiving
device; wherein the ultrasonic transmitting device further comprises:
a source for producing audio signals; a voltage controlled
oscillator for receiving the audio signal, producing a carrier signal in the
ultrasonic frequency range, frequency modulating the carrier signal with the
audio signals, and producing a frequency modulated carrier signal; a
transmitting converter for receiving a frequency modulated carrier signal and
transforming the frequency modulated carrier signal to produce a frequency
modulated acoustic pressure wave signal; and wherein the ultrasonic
receiving device further comprises: a receiving converter for receiving
frequency modulated acoustic pressure wave signals and transforming the
frequency modulated acoustic pressure wave signals to produce a frequency
modulated electronic carrier signal; a demodulator for receiving a
frequency modulated electronic carrier signal, demodulating the modulating audio
signal from the ultrasonic carrier signal, and producing a demodulated audio
signal; and an output device for receiving the demodulated audio signal.
2. A wireless communication system in accordance with claim 1, wherein
the ultrasonic receiving device further comprises a signal conditioner for
receiving a frequency modulated electronic carrier signal, conditioning the
frequency modulated electronic carrier signal for frequency demodulation, and
producing a conditioned frequency modulated carrier signal that is received by
the demodulator.
3. A wireless communication system in accordance with
claim 1, wherein the ultrasonic receiving device further comprises a filter for
receiving a demodulated audio signal, removing unwanted electronic noise and
producing a filtered audio signal that is received by the output device.
4. A wireless communication system in accordance with claim 1, wherein
the ultrasonic receiving device further comprises an audio amplifier for
receiving a demodulated audio signal and amplifying the demodulated audio signal
to produce a final audio signal that is received by the output device.
5. A wireless communication system in accordance with claim 1, wherein
the demodulator for receiving a conditioned modulated carrier signal on the
ultrasonic receiving device comprises an integrated circuit phase-locked loop
further comprising: a phase detector for receiving the conditioned
frequency modulated carrier signal and a control signal, and for comparing the
frequency of the conditioned frequency modulated carrier signal with the
frequency of the control signal to produce a phase error signal, such that the
phase error signal is the frequency difference between the two input signals;
a low-pass filter for receiving said phase error signal and filtering
out the high frequency noise components to produce a filtered phase error
signal; an amplifier for receiving the filtered phase error signal and
amplifying it to produce both the demodulated audio signal output of the
demodulator and a feedback control voltage; and a voltage controlled
oscillator for receiving the feedback control voltage, adjusting the frequency
of the voltage controlled oscillator in the direction of the incoming
conditioned frequency modulated carrier signal of the phase detector to produce
the control signal input to the phase detector.
6. A wireless
communication system in accordance with claim 1, wherein the source for
producing audio signals on the ultrasonic transmitting device comprises a
microphone.
7. A wireless communication system in accordance with claim
1, wherein the source for producing audio signals on the ultrasonic transmitting
device comprises a recording tape deck.
8. A wireless communication
system in accordance with claim 1, wherein the converter on the ultrasonic
transmitting device for receiving a frequency modulated carrier signal and
producing a frequency modulated acoustic pressure wave signal further comprises:
a power amplifier; and an electroacoustic transducer.
9.
A wireless communication system in accordance with claim 1, wherein the
converter on the ultrasonic receiving device for receiving frequency modulated
acoustic pressure wave signals and producing a frequency modulated electronic
carrier signal further comprises an electroacoustic-transducer.
10. A
wireless communication system in accordance with claim 1, further comprising a
signal conditioner on the ultrasonic receiving device for producing a
conditioned frequency modulated carrier signal that is received by the
demodulator, said signal conditioner comprising: a filter for receiving
a frequency modulated electronic carrier signal, filtering unwanted ambient
acoustic noise from the carrier medium producing a filtered frequency modulated
carrier signal; and a pre-amplifier for receiving the filtered frequency
modulated carrier signal and amplifying the filtered frequency modulated carrier
signal to produce a conditioned frequency modulated carrier signal.
11.
A wireless communication system in accordance with claim 10, wherein the filter
for receiving a frequency modulated electronic carrier signal and producing a
filtered frequency modulated carrier signal comprises a band-pass filter.
12. A wireless communication system in accordance with claim 10, wherein
the filter for receiving a frequency modulated electronic carrier signal and
producing a filtered frequency modulated carrier signal comprises a high-pass
filter.
13. A wireless communication system in accordance with claim 1,
further comprising a filter for receiving the demodulated audio signal to
produce a filtered audio signal that is received by the output device, said
filter comprising a low-pass filter.
14. A wireless communication system
in accordance with claim 1, wherein the output device for receiving the final
audio signal comprises an audio speaker.
15. A wireless communication
system in accordance with claim 1, wherein the output device for receiving the
final audio signal comprises a set of headphones.
16. A wireless two-way
ultrasonic communication system comprising two or more matching devices each
further comprising both an ultrasonic transmitting device and an ultrasonic
receiving device in accordance with claim 1, whereby each device both transmits
signals to and receives signals from the matching device.
17. A wireless
communication system in accordance with claim 1, wherein the ultrasonic
transmitting device further comprises an adjustable tuner for altering the
ultrasonic carrier frequency to create a multi-channel transmitting device such
that a signal may be transmitted on various channels to reach variously tuned
ultrasonic receiving devices.
18. A wireless communication system in
accordance with claim 1, wherein the source for producing audio signals on the
ultrasonic transmitting device comprises: a digital-to-analog converter
for receiving digital electronic signals and converting the digital electronic
signals to analog to produce the audio signal input; and wherein the
output device on the ultrasonic receiving device comprises: an
analog-to-digital converter for receiving the final audio signal and converting
said final audio signal to digital electronic signals; such that the
system may be used as a wireless computer network.
19. A wireless
communication system for transmitting and receiving audio signals via ultrasonic
acoustical pressure waves comprising an ultrasonic transmitting device and an
ultrasonic receiving device; wherein the ultrasonic transmitting device
further comprises: a source for producing audio signals; a
pre-amplifier for receiving the audio signals and amplifying the audio signals
to produce an amplified audio signal; a frequency modulator for
receiving the amplified audio signal, frequency modulating an ultrasonic carrier
signal with the amplified audio signal, and producing a frequency modulated
carrier signal; a converter for receiving a frequency modulated carrier
signal and transforming the frequency modulated carrier signal to produce a
frequency modulated acoustic pressure wave signal; and wherein the
ultrasonic receiving device further comprises: a converter for receiving
frequency modulated acoustic pressure wave signals and transforming the
frequency modulated acoustic pressure wave signals to produce a frequency
modulated electronic carrier signal; a signal conditioner for receiving
a frequency modulated electronic carrier signal, conditioning the frequency
modulated electronic carrier signal for frequency demodulation, and producing a
conditioned frequency modulated carrier signal; a phase-locked loop
demodulator for receiving a conditioned frequency modulated carrier signal,
demodulating the modulating audio signal from the ultrasonic carrier signal, and
producing a demodulated audio signal; a filter for receiving a
demodulated audio signal, removing unwanted electronic noise and producing a
filtered audio signal; an audio amplifier for receiving a filtered audio
signal and amplifying the filtered audio signal to produce a final audio signal;
and an output device for receiving the final audio signal.
20. A
wireless communication system in accordance with claim 19 wherein the source for
producing audio signals on the ultrasonic transmitting device comprises a
microphone.
21. A wireless communication system in accordance with claim
19, wherein the source for producing audio signals on the ultrasonic
transmitting device comprises a recording tape deck.
22. A wireless
communication system in accordance with claim 19, wherein the converter on the
ultrasonic transmitting device for receiving a frequency modulated carrier
signal and producing a frequency modulated acoustic pressure wave signal further
comprises: a power amplifier; and an electroacoustic transducer.
23. A wireless communication system in accordance with claim 19, wherein
the converter on the ultrasonic receiving device for receiving frequency
modulated acoustic pressure wave signals and producing a frequency modulated
electronic carrier signal further comprises an electroacoustic transducer.
24. A wireless communication system in accordance with claim 19, wherein
the signal conditioner on the ultrasonic receiving device for producing a
conditioned frequency modulated carrier signal further comprises: a
filter for receiving a frequency modulated electronic carrier signal, filtering
unwanted ambient acoustic noise from the carrier medium producing a filtered
frequency modulated carrier signal; and a pre-amplifier for receiving
the filtered frequency modulated carrier signal and amplifying the filtered
frequency modulated carrier signal to produce a conditioned frequency modulated
carrier signal.
25. A wireless communication system in accordance with
claim 24, wherein the filter for receiving a frequency modulated electronic
carrier signal and producing a filtered frequency modulated carrier signal
comprises a band-pass filter.
26. A wireless communication system in
accordance with claim 24, wherein the filter for receiving a frequency modulated
electronic carrier signal and producing a filtered frequency modulated carrier
signal comprises a high-pass filter.
27. A wireless communication system
in accordance with claim 19, wherein the filter for receiving the demodulated
audio signal to produce the filtered audio signal further comprises a low-pass
filter.
28. A wireless communication system in accordance with claim 19,
wherein the output device for receiving the final audio signal comprises an
audio speaker.
29. A wireless communication system in accordance with
claim 19, wherein the output device for receiving the final audio signal
comprises a set of headphones.
30. A wireless two-way ultrasonic
communication system comprising two or more matching devices each further
comprising both an ultrasonic transmitting device and an ultrasonic receiving
device in accordance with claim 19, whereby each device both transmits signals
to and receives signals from the matching device.
31. A wireless
communication system in accordance with claim 19, wherein the ultrasonic
transmitting device further comprises an adjustable tuner for altering the
ultrasonic carrier frequency to create a multi-channel transmitting device such
that a signal may be transmitted on various channels to reach variously tuned
ultrasonic receiving devices.
32. A wireless communication system in
accordance with claim 19, wherein the source for producing audio signals on the
ultrasonic transmitting device comprises: a digital-to-analog converter
for receiving digital electronic signals and converting the digital electronic
signals to analog to produce the audio signal input; and wherein the
output device on the ultrasonic receiving device comprises: an
analog-to-digital converter for receiving the final audio signal and converting
said final audio signal to digital electronic signals; such that the
system may be used as a wireless computer network.
Description
BACKGROUND OF THE INVENTION
The present invention relates
generally to the art of wireless communication and, more particularly, to a
system which utilizes ultrasonic acoustical pressure waves to transmit and
receive audio signals across a medium such as gas, liquid, or solid material.
The invention further relates to the art of modulation of audio signals to the
ultrasonic frequency range, and to the art of demodulation of audio signals from
frequency modulated ultrasonic carrier signals. The invention further relates to
the art of inaudible communication, whereby the information contained in the
signals is secure and undetectable by radio frequency monitoring.
Radio
frequency waves , or electromagnetic radiation in the frequency range of
approximately 10 kilohertz to 100 gigahertz, has been utilized for wireless
communication systems by civilian and military personnel for decades. Numerous
applications of radio frequency communication methods include, to name a few,
radio broadcasting, air traffic control, and cellular telecommunications. Radio
frequency communication is limited, for practical purposes, to operation within
mediums such as air and space. Furthermore, radio frequency methods are
inappropriate in some circumstances where communication is required, such as
within blasting zones where explosives may be susceptible to unplanned
detonation due to radio interference. In addition, radio frequency methods are
limited in their ability to provide a secure system to ensure confidentiality of
information, which is required by many applications for communication.
Sound waves, or acoustical pressure waves, have likewise been
successfully employed as a method of wireless ultrasonic communication across
various mediums. Ultrasonic communication is most often utilized in underwater
applications because the physical properties of solids and liquids tend to allow
waves traveling via molecular vibrations to cover relatively long distances, on
the order of the kilometer range. It has been similarly employed for
communication over structural matter such as beams or pipes. Ultrasonic
communication has generally not been utilized in air for long range
communication because radio frequency methods are particularly suitable in air
for long range communication, offering suitable and efficient means for most
applications.
Some applications, however, require security and
inaudibility by radio detectors. Examples of these applications include
undercover operations where it is necessary not only that the communication be
uninterpretable, but also that the communication be undetectable so as not to
alert the presence of such communication. Other applications requiring
inaudibility include situations where radio frequency methods are inappropriate,
such as, for example, in a blasting zone where the presence of radio frequency
waves could unexpectedly set off a detonator or in a factory with sensitive
electronics or other components sensitive to electromagnetic radiations.
In applications requiring confidentiality and a high degree of security,
numerous schemes have been employed to minimize detection and eavesdropping.
These schemes often include scrambling a signal prior to broadcasting and then
unscrambling the signal after reception, as well as continual switching from
frequency to frequency. The main problem with these existing techniques is that
the simple detection of any radio frequency transmission whatsoever, even if the
transmitted signals are not decoded or interpreted, indicates the presence of
existing communication. Thus, such schemes may not provide sufficient security
in operations requiring complete inaudibility. It is desirable, therefore, to
provide a communication system which is inaudible by radio frequency detectors.
The invention is disclosed herein in the context of utilizing ultrasonic
waves for relatively long range, secure, wireless communication through air.
However, by way of example, and not limitation, the disclosed invention is
useful in a variety of applications including undercover operations, industrial
applications, and many commercial uses in various media.
Prior art
ultrasonic communication systems involving the conversion of audio signals to
ultrasonic acoustical pressure waves encompass a variety of methods and
applications. In the context of the present invention, it may be noted that
there are no known prior art communication systems which employ ultrasonic
acoustical pressure waves for signal transmission through air for relatively
long distances.
Prior art ultrasonic communication systems employ a
means of carrying a modulated ultrasonic frequency signal from a transmitter to
a receiver. One approach has been disclosed for use in electrical power
networks, whereby a two-tone control signal frequency modulates an ultrasonic
subcarrier which is then used to frequency modulate the broadcast of a local FM
station. The frequency modulated ultrasonic signal is demodulated from the FM
broadcast program on the receiving end by receiver circuitry. In this particular
approach, however, communication is entirely through radio frequency waves and
telephone lines, whereby although a signal is used to modulate an ultrasonic
subcarrier, the modulated ultrasonic subcarrier is never transformed from radio
frequency signals to acoustical pressure waves. The communication thus remains
detectable by radio frequency detectors. It is desirable to employ an alternate
communication carrier other than radio frequency waves such that the system is
not limited to the use of radio facilities or wire lines.
Another prior
art approach for transmitting a modulated ultrasonic frequency signal across a
medium is through the conversion of the electronic audio signals to acoustical
pressure waves. This technique is employed in many communication systems where
radio waves cannot travel useful distances due to the attenuation caused by the
properties of the carrier medium, as in underwater communication.
Prior
art ultrasonic communication systems employ a means of modulating an ultrasonic
frequency signal with an audio frequency signal. Methods utilized have included
both amplitude modulation and angle modulation, which encompasses both frequency
and phase modulation.
The amplitude modulation techniques used in prior
art have encountered the inherent limitation that medium disturbance, e.g. air
or water currents, causes additional amplitude modulation of a carrier signal.
Thus, unwanted signals from medium disturbance become superimposed on the
amplitude modulated carrier, which often results in difficulty recovering a
clean original audio signal. Furthermore, amplitude modulation, even when
superimposed on a carrier of ultrasonic frequency, may still be audible.
Another prior art approach for modulating an ultrasonic frequency signal
with an audio signal is through frequency modulation. One prior art technique
feeds an audio signal through a modulator to produce a frequency modulated (FM)
radio frequency signal at a predetermined intermediate center frequency. The FM
radio frequency signal is then fed into one input of a balanced modulator having
a second input of fixed frequency from a local oscillator. The balanced
modulator produces two outputs including the sum and the difference of the two
input signals, whereby proper selection of the fixed intermediate frequency for
the first input and the fixed frequency for the second input produces at the
difference output the frequency modulated signal in the ultrasonic range. It
would be desirable to eliminate the additional intermediate carrier frequency
step.
Prior art techniques for demodulating audio signals from frequency
modulated ultrasonic carrier signals in ultrasonic communication systems have
utilized digital integrated circuit techniques.
The present invention
reveals a technique for inaudible, long range communication through air, as well
as other media such as water or solid pipes and beams. Prior art techniques have
involved limitation to liquid or solid media or to very short ranges in air.
The present invention also reveals a technique for simple, direct
modulation of audio signals onto ultrasonic frequency carrier signals for use in
ultrasonic communication systems. Prior art techniques have always involved
indirect techniques resulting from the high cost of quality components required
to build systems with high noise immunity operating at high frequency with a
wide bandwidth.
Similarly, the present invention reveals a technique for
simple, direct demodulation of audio signals from ultrasonic frequency carrier
signals for use in ultrasonic communication systems. Again, prior art techniques
have involved more complicated, indirect techniques for demodulation.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the
invention to provide a transmitting device capable of converting audio signals
to frequency modulated ultrasonic acoustical pressure waves using a simple,
direct method of frequency modulation.
It is another object of the
invention to provide a receiving device capable of converting frequency
modulated ultrasonic acoustical pressure waves into audio signals using a
simple, direct method of signal demodulation.
It is yet another object
of the invention to provide a wireless communication system which may be
employed where radio frequency is prohibited.
It is yet another object
of the invention to provide a secure communication system to protect
confidential information against eavesdropping.
It is yet another object
of the invention to provide a system for communicating in a noisy environment.
It is yet another object of the invention to provide a portable
convenient method of wireless communication.
Briefly, in accordance with
one aspect of the invention, there is provided an ultrasonic transmitting device
which includes an input device such as a microphone which converts audio
acoustical pressure waves to electronic audio signals, or an audio input for
accepting electronic audio signals such as from a tape deck. A pre-amplifier
raises the audio signal to an acceptable power level without significant
degradation in the signal-to-noise ratio. The amplified audio signal produced by
the pre-amplifier feeds into the input of a voltage controlled oscillator,
having a fixed carrier frequency set in the ultrasonic range and producing at
its output an ultrasonic carrier signal which is frequency modulated by the
audio signal. A power amplifier amplifies the frequency modulated carrier signal
to a sufficient power level to produce an amplified frequency modulated Carrier
signal. The amplified frequency modulated carrier signal drives an
electroacoustic transducer, which converts the amplified frequency modulated
carrier signal to frequency modulated acoustical pressure waves for transmission
across a carrier medium, such as air, water, or pipes and beams. Preferably, the
transducer is designed to unique size and performance specifications such that
it contains linear characteristics in the desired ultrasonic frequency range, as
well as sufficient power for the desired application.
In accordance with
another aspect of the invention, there is provided an ultrasonic receiving
device which includes an electroacoustic transducer to convert the frequency
modulated acoustical pressure waves to a frequency modulated electronic carrier
signal. Preferably, the linear frequency and power characteristics of the
receiving transducer match the characteristics of the transmitting transducer. A
signal conditioner receives the frequency modulated electronic carrier signal
for conditioning to produce a conditioned frequency modulated carrier signal.
Preferably this includes an amplifier which receives the frequency modulated
electronic carrier signal and amplifies it to produce an amplified frequency
modulated carrier signal of a suitable level for filtering without degradation
of the signal-to-noise ratio. The amplified frequency modulated carrier signal
may contain amplitude modulated noise due to natural carrier medium disturbance
such as wind in air or currents in water. Preferably, a bandpass filter removes
the unwanted ambient acoustic noise from the amplified frequency modulated
carrier signal to produce a filtered frequency modulated carrier signal.
Preferably, a main signal amplifier device receives the filtered frequency
modulated carrier signal, amplifying it in preparation for demodulation, to
produce a conditioned frequency modulated carrier signal. A phase-locked loop
demodulator performs the actual direct demodulation of the audio signal from the
ultrasonic carrier signal. Complicated phase-locked loop techniques were
impractical or uneconomical in the past. However, in accordance with one aspect
of the invention, a direct method of demodulation is used, whereby the input of
the phase-locked loop is a conditioned frequency modulated carrier signal, and
the output is the recovered audio signal. An audio signal conditioner device,
preferably including a low-pass filter, removes unwanted noise from the receiver
electronics to produce a conditioned audio signal. A power amplifier amplifies
the conditioned audio signal to the appropriate level to drive the desired
output device such as a speaker or headphone set.
The ultrasonic speech
translator and communication system provides an elegant solution for secure,
long-range, inaudible, and wireless communication through air and various other
mediums. The invention may be applicable in a wide variety of applications.
As one example of an application for the ultrasonic speech translator
and communication system, directional receivers in the form of a small button
may be mounted on a hat which feeds to earphones, whereby the user can detect
which direction the signal is coming from as well as what the person is saying.
As another example, the reception and transmission could be in a plane
just above the ground.
As yet another example, multiple sets may be
utilized, where each user transmits at a different frequency and receives one or
more frequencies at a time.
As another example, communication may occur
throughout a rigid structure by connecting the transmitter and receiver to it,
said rigid structures including, but not limited to, piping, concreted beams or
floors, and building steel, as in a house or building or the space station or
shuttle.
As another example, in communicating data signals rather than
voice signals, the system may operate as a wireless computer network within a
building.
As another example, the ultrasonic speech translator and
communication system may be very portable, taking the form of quick temporary
hookups at numerous suitable locations in an office building, industrial
facility, and others. This concept may be applied to areas such as space shuttle
or space station internal communication through the vessel structural members.
As yet a further example, the invention may be employed in circumstances
where radio interference is prohibited but close communication is necessary,
such as in a blasting site containing explosive detonators.
As another
example, in areas where high audible noise levels are present, this system may
operate as a wireless voice communicator between personnel working in the area.
As another example, the invention may provide secure and discrete
communication for military, security, and law enforcement applications.
Applications of this technique include communication through air when radio
frequencies are monitored and communication must be secure and undetected.
As another example, this communication scheme may be miniaturized and
integrated for use in binoculars or rifles or concealed in clothing. An
inexpensive toy based on this ultrasonic communication technique may be designed
and mass marketed as a non-radio based walkie-talkie, allowing discrete
communication through air, water pipes, or solid walls, without detection by
radio frequency scanners.
BRIEF DESCRIPTION OF THE DRAWINGS
While the novel features of the invention are set forth with
particularity in the appended claims, the invention, both as to organization and
content, will be better understood and appreciated, along with other objects and
features thereof, from the following detailed description of a preferred
embodiment, taken in conjunction with the drawings, in which:
FIG. 1
depicts a block diagram of the ultrasonic speech translator and communication
system in accordance with the invention;
FIG. 2 depicts a block diagram
of the ultrasonic transmitting device along with the corresponding output signal
waveforms for each device.
FIG. 3 depicts a block diagram of the
ultrasonic receiving device along with the corresponding output signal waveforms
for each device.
FIG. 4 depicts example uses for the ultrasonic speech
translator and communication system.
FIG. 5 depicts a the circuit
diagram for the specific embodiment of the ultrasonic transmitting device herein
described.
FIG. 6 depicts a the circuit diagram for the specific
embodiment of the ultrasonic receiving device herein described.
FIG. 7
depicts a graph of transmitted power level versus distance actually achieved by
the specific embodiment herein described.
DETAILED DESCRIPTION
Turning now to the drawings in greater detail, there is illustrated in
FIG. 1 an ultrasonic speech translator and communication system 20 embodying the
invention. The embodiment herein described is particularly well-suited for
focused directional communication through air for distances of approximately 100
to 150 feet. However, it will be understood that the ultrasonic communication
system 20 may be utilized in other carrier media as well as in applications in
air with broader directional requirements such as for transmitting throughout a
closed room among several people with receiving devices 200. Accordingly, the
principles of the present invention may be variously applied.
FIG. 1 is
a block diagram of the ultrasonic speech translator and communication system 20
comprising an ultrasonic transmitting unit 100 and an ultrasonic receiving unit
200.
With references to FIG. 1, FIG. 2, and FIG. 5, the ultrasonic
transmitting unit may be constructed in any suitable form or in any container
110, with provisions for acceptable power input 111 provided by a source of
power including but not limited to a power supply or battery pack 112. The
ultrasonic transmitting device described in this specific embodiment utilizes a
metal chassis the approximate volume of a cigarette pack.
Included in
the ultrasonic transmitting device 100 is an input device 115 capable of
receiving electronic audio signals in the range 20 hertz to 20 kilohertz. The
audio signals may be derived from an external device such as a tape deck or a
microphone 114 which converts sound such as voice to electronic audio signals.
Alternatively, a device for converting sound to electronic audio signals such as
a microphone 114 may be built into the system.
Also included in the
ultrasonic transmitting device is a pre-amplification device 120 which
preferably includes a variable gain microphone control switch 116. The
pre-amplification device 120 may be constructed using any suitable operational
amplifier designed for the desired output gain. In the specific embodiment, said
pre-amplifier consists of a 741-type operational amplifier with a variable input
gain of approximately 100.
The actual modulation of the ultrasonic
carrier by the audio signal is performed by a voltage controlled oscillator 130.
Any suitable voltage controlled oscillator which operates in the ultrasonic
range may be utilized to perform the modulation. Suggested voltage controlled
oscillators include model number 566 or equivalents, as well as any suitable
newer voltage controlled oscillators. The specific embodiment utilizes a NE 566
voltage controlled oscillator integrated circuit with the ultrasonic carrier
frequency set at approximately 21.8 kilohertz, but it may be set at any desired
ultrasonic carrier frequency that the specific voltage controlled oscillator 130
is capable of producing. Thus, the practical ultrasonic carrier frequency ranges
from 20 kilohertz to 100 kilohertz in air, and 20 kilohertz to 1000 kilohertz in
liquids and solids. In the specific embodiment, the 21.8 kilohertz carrier
signal is frequency modulated by the amplified audio input signal from the audio
input 115, and appears at the output of the voltage controlled oscillator 130.
The output of the voltage controlled oscillator 130 is connected
directly to the input of the power amplifier 140. The power rating of the power
amplifier 140 is application specific, depending on the load rating of the
electroacoustic transducer 150 and the desired output power in watts.
The output of the power amplifier 140 drives the electroacoustic
transducer 150 to transmit the frequency modulated ultrasonic carrier signal
across the carrier medium via acoustical pressure waves. Through a careful
selection of transmitter and receiver subcomponents, voice and music have been
transmitted over 100 feet in air using less than 1 mW of electrical power. FIG.
7 illustrates the distances actually achieved using the specific embodiment,
along with predicted distances with more applied power. Subcomponents in the
specific embodiment include signal translation and detection circuits based on
frequency-modulation (FM) where carrier is 21.8 kHz, efficient electroacoustic
transducers 152, specially-designed parabolic dish reflectors 151, parabolic
dish collectors 216, and sensitive microphone element 217. Analytical models
predict a useful range of 250 ft can be achieved with less than 5 watts input
power. The application for the specific embodiment was to achieve distance with
small output power. The transducer chosen was of piezoelectric material with a
linear response in the range of 21.8 kilohertz, modified by increasing the gain
in the linear response band, and narrowing the parabolic dish elements 216, 151
for a more focused directional sensitivity. Additional engineering may be
carried out to optimize the transducer, collector, and frequency combination for
specific applications having unique requirements. For example, higher power with
an optimized collector dish may be employed to achieve extended distance;
miniaturization of transmitter and receiver devices may be accomplished for
concealment in clothes, or for integration in other equipment such as binoculars
or rifles. Each application may utilize transducers specially-designed to unique
size and performance specifications. The transducers may be made of any suitable
material including, by way of example and not limitation, piezoelectric
material. The output of the transducer 150 is the frequency modulated ultrasonic
carrier signal converted to acoustical pressure waves which travel across the
medium.
With references to FIG. 1, FIG. 3, and FIG. 6, the ultrasonic
receiving device 200 may be constructed in any suitable form or in any container
210, with provisions for acceptable power input 211 provided by a source of
power including but not limited to a power supply or battery pack 212. The
ultrasonic receiving device described in this specific embodiment utilizes a
metal chassis.
The ultrasonic receiving device 200 includes an receiving
transducer 215, which receives the frequency modulated acoustical pressure waves
transmitted across the carrier medium. In the preferred embodiment, the linear
frequency and power characteristics match that of the electroacoustic transducer
150 of the ultrasonic transmitting unit 100. In the specific embodiment, the
receiving transducer 215 matched the transmitting transducer 150 with its linear
frequency range near 21.8 kilohertz and its specially-designed narrow parabolic
collector dish 216 and sensitive microphone element 217. The frequency modulated
acoustical pressure waves are converted by the receiving transducer 215 to a
frequency modulated electronic carrier signal.
The frequency modulated
electronic carrier signal from the receiving transducer 215 feeds directly into
a signal conditioner 220 depicted in FIG. 1. The frequency modulated electronic
carrier signal at this stage may contain unwanted amplitude modulation generated
by disturbance in the carrier medium, and it may contain added ambient noise.
Disturbance may be caused by natural air currents, water currents, or unrelated
vibration in solids. Preferably, the signal conditioner 220 includes a
pre-amplifier 221, a band-pass filter 222, and a main signal amplifier 223.
In the preferred embodiment, the frequency modulated carrier signal from
the receiving transducer 215 connects directly to the pre-amplifier 221, which
increases the power without changing the signal-to-noise ratio in preparation
for filtering the unwanted noise caused by carrier medium disturbance. The
preferred embodiment utilizes a variable-gain operational amplifier, preferably
with means of adjusting the gain via a gain control knob 213. In the specific
embodiment, the preamplifier 221 utilized a 741-type operational amplifier with
a variable gain of approximately 100.
The output of the pre-amplifier
221 ideally electrically connects directly to a band-pass filter 222, which
actually removes the unwanted noise. Alternatively, a high-pass filter with a
cutoff frequency passing only ultrasonic frequency signals may be used. The
specific embodiment actually utilizes a high-pass filter built from 741-type
operational amplifiers designed with a cutoff frequency of approximately 20
kilohertz. The output of the filter 222 contains the filtered frequency
modulated ultrasonic carrier signal having the desired frequency bandwidth.
Amplitude modulations will still be present in the signal at this stage.
The output from the band-pass filter 222 electrically connects directly
into the main signal amplifier 223 for pre-demodulation conditioning. The
specific embodiment utilizes a 741-type operational amplifier with a gain of
100, producing the conditioned frequency modulated carrier signal at its output.
Demodulation of the audio signal from the ultrasonic carrier signal is
performed via a phase-locked loop. The phase-locked loop, an electronic servo
system, attempts to maintain a fixed phase relationship with the input signal.
Typically, a phase-locked loop contains a phase detector, a low-pass filter, and
a voltage controlled oscillator. The phase detector compares the frequency of an
input signal with the frequency of the voltage controlled oscillator. The
voltage output from the phase detector is the measure of their phase difference,
called the phase error signal. The phase error signal feeds into a low-pass
filter and is amplified to adjust the control voltage of the voltage controlled
oscillator, which feeds into the second input of the phase detector. In this
manner, the voltage controlled oscillator attempts to "lock" to the input
carrier frequency signal. It will be noted that the output of the low-pass
filter is the desired demodulated audio signal. Phase locked loops built with
discrete components are complex to build and fairly unreliable. Phase-locked
loops built as integrated circuits are easy to use due to small packaging, have
high immunity to amplitude modulations, and are reliable when utilized properly
in a design. Typical general purpose phase-locked loops available from many
manufacturers provide two outputs. One output is a square wave oscillator
output, which is equal to the incoming carrier frequency when the signals are
locked. The other output is a voltage proportional to the frequency of the
incoming signal. This is the modulating signal output of the demodulator, which,
in this application, is the desired recovered original audio signal. The
preferred embodiment of the ultrasonic receiving device 200 utilizes any
integrated circuit phase-locked loop which accepts at its input a carrier signal
in the anticipated ultrasonic range, and produces the output of the low-pass
filter at one of its outputs.
The phase-locked loop 230 receives the
frequency modulated ultrasonic carrier signal from the main signal amplifier
223. The specific embodiment utilizes a Signetics LM 565 phase-locked loop 230,
and locks on to the carrier signal frequency of 21.8 kilohertz. The phase-locked
loop 230 low-pass filter output is the demodulated audio signal.
The
output of the phase-locked loop 230 electrically connects directly to the input
of the final signal conditioning unit 240. Included in the final signal
conditioning unit 240 is a filter 241 which filters out unwanted receiver noise,
and an audio amplifier 242 which amplifies the final audio signal to a suitable
power level to drive the output device.
The filter 241 receives the
demodulated audio signal from the phase-locked loop demodulator 230. In the
preferred embodiment, the unwanted electronics circuitry noise is filtered using
a low-pass filter. The specific embodiment implements a low-pass filter
employing a 741-type operational amplifier. The output of the filter 241
contains a reproduction of the original audio input signal. This output is fed
directly into the audio amplifier 242 which increases the power of the audio
signal while maintaining the signal-to-noise ratio. The specific embodiment
utilizes a 741-type operational buffer amplifier circuit with a gain of 10,
feeding to the output 250, which drives a set of headphones 251 or a powered
speaker 252.
Considering now exemplary uses by which the ultrasonic
speech translator and communication system 20 may be employed, FIG. 4
illustrates several applications. These include by way of example and not
limitation communication between two people, between two cars, between a person
and a car, between two buildings, between a car and a building, between a person
and a building, and between locations within the same building. Furthermore, the
system may be designed for use with various carrier media, including air,
liquids, and solids.
From the foregoing description of the invention, it
will be appreciated that the ultrasonic speech translator and communication
system encompasses a wide range of desirable and useful applications. While
specific embodiments of the invention have been illustrated and described
herein, it is realized that numerous modifications and changes will occur to
those skilled in the art. It is therefore to be understood that the appended
claims are intended to cover all such modifications and changes as fall within
the true spirit and scope of the invention.
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