CA1065045A - Pulse-mode parametric transmitter - Google Patents
Pulse-mode parametric transmitterInfo
- Publication number
- CA1065045A CA1065045A CA253,098A CA253098A CA1065045A CA 1065045 A CA1065045 A CA 1065045A CA 253098 A CA253098 A CA 253098A CA 1065045 A CA1065045 A CA 1065045A
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- CA
- Canada
- Prior art keywords
- signal
- pulse
- medium
- transmitter
- frequency
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
- G01S15/06—Systems determining the position data of a target
- G01S15/08—Systems for measuring distance only
- G01S15/10—Systems for measuring distance only using transmission of interrupted, pulse-modulated waves
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Acoustics & Sound (AREA)
- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A parametric sound transmitter in which a secondary signal having highly directional and penetrating characteristics is produced. A primary frequency acoustic carrier signal is pulse modulated and is of such level as to cause distortion thereof by the medium. The pulse frequency is the same as that of the secondary signal or a sub multiple thereof.
A parametric sound transmitter in which a secondary signal having highly directional and penetrating characteristics is produced. A primary frequency acoustic carrier signal is pulse modulated and is of such level as to cause distortion thereof by the medium. The pulse frequency is the same as that of the secondary signal or a sub multiple thereof.
Description
10~50~5 . PULSE--MODE PARAMETRIC TRANSMITTER
This invention relates to a parametric sound trans-mitter which has improved conversio~ efficiency.
The transmission of sound is utilized in a variety of applications, for instance in sonar systems, ultra-sonic control systems, etc. Previously thPse types of systems in the main utilized single source transmitters, which provided output signals at desired frequencies, and which were received in a rather straightforward manner. It had been considered that distortion of the transmitted signal was to be avoided in order to obtain proper representation of the transmitted frequency.
However, it was discovered by Westervelt (Journal of Acoustical Society of America 35, page 535[1963]), that a parametric function based on a combination of signals in a distorting medium could enhance the distance of transmission of a signal.
U.S. Patent 3,613,069 dated October 12th, 1971 to Cary et al describes a parametric sonar system which utilizes the interaction of two sound waves of differing frequency, in a sLmilar manner as that described by Westervelt.
Basically, the enhancement effect is based on the distortion of sound waves upon travelling through media whether gas, liquid, or solid. Westervelt points out that two single frequency sound waves travelling in the same direction through the same matter would necessarily interact ~o as to produce secondary or "scattered" sound waves at frequencies equal to the sum and difference of the original frequencies.
The characteristic of the different frequencies so produced was particularly interesting. If the two original waves were launched from a single transducer, or from two ,~ .
lO~O~S
-- closely spaced transducers, the difference wave produced (1) would be highly directional and (2) would suffer less - at~enuation in the medium than the original waves. It has been found practical to utilize this interaction to generate highly directional sound waves while keeping the transducer dimensions small.
It had been found that the secondary wave produced by a single modulated sound wave could be evaluated and is the second time derivative of the square of the amplitude of the primary or carrier wave. Upon this analysis having been made, I-found that I could improve the parametric sound ¦ transmitter by a design which is up to four times as efficient as Westervelt's.
In my structure, a single frequency primary carrier wave, instead of being modulated as described in the afore-noted U.S. Patent 3,613,069, by a sine wave, is pulse modu-lated at a repetition frequency equal to the frequency of the desiréd secondary wave or a sub multiple thereof. The carrier ` wave may also be simultaneously phase modulated so as to reduce the frequency bandwidth of the carrier wave.
¦ In speaking of pulse modulation, it is also intended that the equivalent of pulse modulation can be effected by i combining the outputs of several separate oscillators of the appropriate frequencies and phases, to combine in a Fourier manner, and thereby produce a similar modulation effect.
An average improvement over the two frequency method over several experiments has been found to be approx-imately 2dB, but up to 6dB improvement has been measured.
Thus according to one aspect this invention provides a transmitter for transmitting a directional acoustic secondary - signal of predetermined frequency through a medium, comprising:
means for generating ~ primary signal for application to sàid .~
. - ~
~ S045 medium at a level such as to cause distortion of the signal by the medium; means for generating a pulse signal having a pulse ...
repetition frequency equal to the predetermined frequency or a ' sub multiple thereof; and means for producing the secondary signal in the medium by pulse modulation of the ~rimary signal by the pulse signal.
According to another aspect this invention provides a method of transmitting a directional acoustic secondary signal of predetermined frequency through a medium, comprising the steps of: generating a primary signal for aPPlication to said medium at a level such as to cause distortion of the signal by the medium; generating a pulse signal having a pulse repetition ~i frequency equal to the predetermined frequency or a sub multiple 1 thereof; and producing the secondary ~ignal in the medium by -I pulse modulation of the primary signal by the pulse signal.
f ' -- : ............................. .. = ~
t It should be noted that while in the prior a`rt the modulating signal is such as to provide a difference freguency ¦ between the two frequency components of the carrier wave which is equal to the secondary signal frequency, in the present ; 20 invention the carrier wave is pulse modulated at a pulse repetition frequency equal to the desired secondary signal frequency or a sub multiple thereof.
, A better understanding of the invention will be -I obtained by reference to the more detailed description ~i below, and to the following drawings in which:
Figure 1 is a block schematic of a transmitter according to the invention, Figure 2 shows the pulse envelope and resulting wave form in the medium, Figure 3 is a sectional view of a transducer -suitable for use in the invention, .
,~ ~ '.... .
~ _ 3 _ :
. . ; , ' .
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~ Figure 4 is a schematic of a matching network which can be used to interface with the transducer, Figure 5 is a schematic of a portion of the trans-mitter according to a second embodiment, and Figure 6 is a block schematic of a portion of the ` transmitter according to a third embodiment.
Turning to Figure 1, a block schematic is shown of a transmitter according to the first or preferred embodiment.
An oscillator 1 provides a source of carrier signal. For ' 10 use as a sonar transmitter, a typical frequency which can usefully be employed, and which was used in a first experi-. I ~
1 . .
- ' , ''~
. ~ ~:
, , ' ' , ~ .
' .
- 3a -, 10~04S
ment was 8.75 megahertz.
A pulse generator 2 provides a source of pulses at a repetition frequency corresponding to the desired secon~ary wave. Typical secondary wave frequencies, and the ones which were used during the first experimental models of the invention were 100 kilohertz, 150 kilohertz, and 300 kilohertz.
The carrier signal and the pulse signal are each applied to inputs of modulator 3. The output waveform of modulator 3 is shown as a pulsed carrier signal 4.
While the pulsed signal can be continuously trans-mitted, in a sonar system it may be desired to transmit successively spaced bursts of pulsed carrier signal, whereby a return echo can be received between the bursts. In order to provide each burst, a second pulse generator 5 provides a sequence of pulses sufficient to include a multiplicity of pulses of the pulse modulated carrier signal. The output sig~a~l ~rom~t-he-~econd-.~}~e gene~ator 5 is shown as waveform 6.
The output of modulator 3 and the output of pulse generator 5 are each connected to separate inputs of a second modulator 7. The resulting output of the second modulator 7, at the point marked "A" is a repeating sequence of bursts of pulse modulated carrier signal.
The signal at ~" is applied to the input of amplifier 8, the output of which is applied to the input of power amplifier 9. It should be noted that due to the nature of the signal, power amplifier 9 can be of type class A, B, C or D.
The output of power amplifier 9 is applied to transducer 10 through a matching network 11. Transducer 10 applies the bursts of pulse modulated carrier signal to the medium, such as water.
It should be noted that for continuous acoustic transmission pulse generator 5 and modulator 7 can be deleted, and the output of modulator 3 applied directly to the input of amplifier 8~
It has been found that with the type of pulse modulated signal provided, the non-linearity of the trans-mitting medium produces a secondary signal having a much greater penetrating effect than the primary carrier wave.
The pulse generation rate of the pulse generator 2 determines the frequency of the secondary signal caused by the distortion of the acoustic signal by the medium.
Figure 2 shows graphically (but not to scale) the correspondence between the envelope of the carrier signal after modulation by the pulse generator 2, and the resulting waveform produced in the medium. The pulse modulated enve-lope 12 shown as power level Po with respect to time t is located above waveform 13, which is the resulting secondary ;( ~ signal Ps in the medium. It can be seen that the rising and falling slopes of the pulses correspond to peaks in the waveform as transmitted. The peaks are believed to be produced due to parametric self-modulation effects caused by non-linearity in the medium, resulting from what is believed to be the production of shock fronts, as opposed to linear compressions and rarefactions of the medium. The spikey nature of the secondary waveform indicates that substantial acoustic energy is also radiated at frequencies which are integer multiples (harmonies) of the pulse repetition frequency. The ;~ -8econdary signal has been found to have substantially increased penetrating power and is highly directional.
Figure 3 shows a section of a transducer suitable for use in this invention. A brass plate 14 is attached to a housing by suitable means such as the unreferenced screws shown. A piezoelectric ceramic 15 such as type PZT-5A made ,___, _ _ _, , , ,, , ,, , ~ . ,, .,,, . , .,, . ,. ,,, ._, .. . _ _ i5~45 by ~levite Corporation has its bottom embedded in epoxy 16 such as araldite. Electrical connections (not shown) are made to the ceramic by conventional means, such as by soldering to the front and rear thereof.
In one experiment, the piezoelectric ceramic plate 15 was one centimeter square by about .009 inches thick. At this thickness the ceramic was resonant at about 9 megahertz, which closely matches the frequency of the carrier signal produced by oscillator 1 noted earlier.
Figure 4 is a schematic of the matching network 11 connected to the transducer shown in Figure 3. For best results the matching network should be designed to reject frequency components in the region of the pulse generation frequency of pulse generator 2.
~ The input signal from amplifier 9 is applied via a - coaxial cable inner conductor to inductor 17~ which applies - it to one terminal af transducer 18. The other terminal oftransducer la is connected to the shield of the aforenoted coaxial cable.
Connected to the junction of the inner conductor of the cable and inductor 17 is a capacitor 19, which has its other terminal connected to the shield of the coaxial cable.
, A suitable inductor for the experimental system noted had an inductance of 0.33 microhenry, and a suitable capacitor 19 had a capacitance of 539 picofarads.
With the system described, the ascoustic radiation i5 gradually transformed by the medium, by a combination of ~ -non-linear and thermoviscous effects, into a highly direc-tional wave of frequency corresponding to the pulse generation frequency of pulse generator 2 and of waveform 13. ~armonics of this frequency are also present to a degree depending on the width of the pulses and ~y the bandwidth of the amplifier, mat~hing network, and transducer combination.
It should be noted that rather than electrically ' .' :' '''''' ' ' , . .: ~ , .
10~504S
modulating the signal by a pulse generator, a sLmilar effect can be obtained by providing a multiplicity of oscillators and transducers, closely spaced, so as to produce a Fourier type combination of effective pulses in the medium by para-metric combination. These pulses parametrically modulate the carrier signal, and produce a similar effect in the medi~m as with the earlier described electrical pulse modulation of the carrier.
Figure 5 shows in block schematic form another embodiment of the invention. As before, oscillator 1 produces a carrier frequency signal. Pulse generator 2 produces a pulse signal at the secondary signal repetition frequency.
Pulse generator 5 produces long pulses which establish repetitive burst rate of the pulse modulated carrier signal.
The output of pulse generator 5 is applied to one input of modulator 20 with the output of pulse generator 2 applied to a second input. The output of modulator 20 is a series of bursts of pulse signals of the frequency from pulse generator
This invention relates to a parametric sound trans-mitter which has improved conversio~ efficiency.
The transmission of sound is utilized in a variety of applications, for instance in sonar systems, ultra-sonic control systems, etc. Previously thPse types of systems in the main utilized single source transmitters, which provided output signals at desired frequencies, and which were received in a rather straightforward manner. It had been considered that distortion of the transmitted signal was to be avoided in order to obtain proper representation of the transmitted frequency.
However, it was discovered by Westervelt (Journal of Acoustical Society of America 35, page 535[1963]), that a parametric function based on a combination of signals in a distorting medium could enhance the distance of transmission of a signal.
U.S. Patent 3,613,069 dated October 12th, 1971 to Cary et al describes a parametric sonar system which utilizes the interaction of two sound waves of differing frequency, in a sLmilar manner as that described by Westervelt.
Basically, the enhancement effect is based on the distortion of sound waves upon travelling through media whether gas, liquid, or solid. Westervelt points out that two single frequency sound waves travelling in the same direction through the same matter would necessarily interact ~o as to produce secondary or "scattered" sound waves at frequencies equal to the sum and difference of the original frequencies.
The characteristic of the different frequencies so produced was particularly interesting. If the two original waves were launched from a single transducer, or from two ,~ .
lO~O~S
-- closely spaced transducers, the difference wave produced (1) would be highly directional and (2) would suffer less - at~enuation in the medium than the original waves. It has been found practical to utilize this interaction to generate highly directional sound waves while keeping the transducer dimensions small.
It had been found that the secondary wave produced by a single modulated sound wave could be evaluated and is the second time derivative of the square of the amplitude of the primary or carrier wave. Upon this analysis having been made, I-found that I could improve the parametric sound ¦ transmitter by a design which is up to four times as efficient as Westervelt's.
In my structure, a single frequency primary carrier wave, instead of being modulated as described in the afore-noted U.S. Patent 3,613,069, by a sine wave, is pulse modu-lated at a repetition frequency equal to the frequency of the desiréd secondary wave or a sub multiple thereof. The carrier ` wave may also be simultaneously phase modulated so as to reduce the frequency bandwidth of the carrier wave.
¦ In speaking of pulse modulation, it is also intended that the equivalent of pulse modulation can be effected by i combining the outputs of several separate oscillators of the appropriate frequencies and phases, to combine in a Fourier manner, and thereby produce a similar modulation effect.
An average improvement over the two frequency method over several experiments has been found to be approx-imately 2dB, but up to 6dB improvement has been measured.
Thus according to one aspect this invention provides a transmitter for transmitting a directional acoustic secondary - signal of predetermined frequency through a medium, comprising:
means for generating ~ primary signal for application to sàid .~
. - ~
~ S045 medium at a level such as to cause distortion of the signal by the medium; means for generating a pulse signal having a pulse ...
repetition frequency equal to the predetermined frequency or a ' sub multiple thereof; and means for producing the secondary signal in the medium by pulse modulation of the ~rimary signal by the pulse signal.
According to another aspect this invention provides a method of transmitting a directional acoustic secondary signal of predetermined frequency through a medium, comprising the steps of: generating a primary signal for aPPlication to said medium at a level such as to cause distortion of the signal by the medium; generating a pulse signal having a pulse repetition ~i frequency equal to the predetermined frequency or a sub multiple 1 thereof; and producing the secondary ~ignal in the medium by -I pulse modulation of the primary signal by the pulse signal.
f ' -- : ............................. .. = ~
t It should be noted that while in the prior a`rt the modulating signal is such as to provide a difference freguency ¦ between the two frequency components of the carrier wave which is equal to the secondary signal frequency, in the present ; 20 invention the carrier wave is pulse modulated at a pulse repetition frequency equal to the desired secondary signal frequency or a sub multiple thereof.
, A better understanding of the invention will be -I obtained by reference to the more detailed description ~i below, and to the following drawings in which:
Figure 1 is a block schematic of a transmitter according to the invention, Figure 2 shows the pulse envelope and resulting wave form in the medium, Figure 3 is a sectional view of a transducer -suitable for use in the invention, .
,~ ~ '.... .
~ _ 3 _ :
. . ; , ' .
~0~[)4~
~ Figure 4 is a schematic of a matching network which can be used to interface with the transducer, Figure 5 is a schematic of a portion of the trans-mitter according to a second embodiment, and Figure 6 is a block schematic of a portion of the ` transmitter according to a third embodiment.
Turning to Figure 1, a block schematic is shown of a transmitter according to the first or preferred embodiment.
An oscillator 1 provides a source of carrier signal. For ' 10 use as a sonar transmitter, a typical frequency which can usefully be employed, and which was used in a first experi-. I ~
1 . .
- ' , ''~
. ~ ~:
, , ' ' , ~ .
' .
- 3a -, 10~04S
ment was 8.75 megahertz.
A pulse generator 2 provides a source of pulses at a repetition frequency corresponding to the desired secon~ary wave. Typical secondary wave frequencies, and the ones which were used during the first experimental models of the invention were 100 kilohertz, 150 kilohertz, and 300 kilohertz.
The carrier signal and the pulse signal are each applied to inputs of modulator 3. The output waveform of modulator 3 is shown as a pulsed carrier signal 4.
While the pulsed signal can be continuously trans-mitted, in a sonar system it may be desired to transmit successively spaced bursts of pulsed carrier signal, whereby a return echo can be received between the bursts. In order to provide each burst, a second pulse generator 5 provides a sequence of pulses sufficient to include a multiplicity of pulses of the pulse modulated carrier signal. The output sig~a~l ~rom~t-he-~econd-.~}~e gene~ator 5 is shown as waveform 6.
The output of modulator 3 and the output of pulse generator 5 are each connected to separate inputs of a second modulator 7. The resulting output of the second modulator 7, at the point marked "A" is a repeating sequence of bursts of pulse modulated carrier signal.
The signal at ~" is applied to the input of amplifier 8, the output of which is applied to the input of power amplifier 9. It should be noted that due to the nature of the signal, power amplifier 9 can be of type class A, B, C or D.
The output of power amplifier 9 is applied to transducer 10 through a matching network 11. Transducer 10 applies the bursts of pulse modulated carrier signal to the medium, such as water.
It should be noted that for continuous acoustic transmission pulse generator 5 and modulator 7 can be deleted, and the output of modulator 3 applied directly to the input of amplifier 8~
It has been found that with the type of pulse modulated signal provided, the non-linearity of the trans-mitting medium produces a secondary signal having a much greater penetrating effect than the primary carrier wave.
The pulse generation rate of the pulse generator 2 determines the frequency of the secondary signal caused by the distortion of the acoustic signal by the medium.
Figure 2 shows graphically (but not to scale) the correspondence between the envelope of the carrier signal after modulation by the pulse generator 2, and the resulting waveform produced in the medium. The pulse modulated enve-lope 12 shown as power level Po with respect to time t is located above waveform 13, which is the resulting secondary ;( ~ signal Ps in the medium. It can be seen that the rising and falling slopes of the pulses correspond to peaks in the waveform as transmitted. The peaks are believed to be produced due to parametric self-modulation effects caused by non-linearity in the medium, resulting from what is believed to be the production of shock fronts, as opposed to linear compressions and rarefactions of the medium. The spikey nature of the secondary waveform indicates that substantial acoustic energy is also radiated at frequencies which are integer multiples (harmonies) of the pulse repetition frequency. The ;~ -8econdary signal has been found to have substantially increased penetrating power and is highly directional.
Figure 3 shows a section of a transducer suitable for use in this invention. A brass plate 14 is attached to a housing by suitable means such as the unreferenced screws shown. A piezoelectric ceramic 15 such as type PZT-5A made ,___, _ _ _, , , ,, , ,, , ~ . ,, .,,, . , .,, . ,. ,,, ._, .. . _ _ i5~45 by ~levite Corporation has its bottom embedded in epoxy 16 such as araldite. Electrical connections (not shown) are made to the ceramic by conventional means, such as by soldering to the front and rear thereof.
In one experiment, the piezoelectric ceramic plate 15 was one centimeter square by about .009 inches thick. At this thickness the ceramic was resonant at about 9 megahertz, which closely matches the frequency of the carrier signal produced by oscillator 1 noted earlier.
Figure 4 is a schematic of the matching network 11 connected to the transducer shown in Figure 3. For best results the matching network should be designed to reject frequency components in the region of the pulse generation frequency of pulse generator 2.
~ The input signal from amplifier 9 is applied via a - coaxial cable inner conductor to inductor 17~ which applies - it to one terminal af transducer 18. The other terminal oftransducer la is connected to the shield of the aforenoted coaxial cable.
Connected to the junction of the inner conductor of the cable and inductor 17 is a capacitor 19, which has its other terminal connected to the shield of the coaxial cable.
, A suitable inductor for the experimental system noted had an inductance of 0.33 microhenry, and a suitable capacitor 19 had a capacitance of 539 picofarads.
With the system described, the ascoustic radiation i5 gradually transformed by the medium, by a combination of ~ -non-linear and thermoviscous effects, into a highly direc-tional wave of frequency corresponding to the pulse generation frequency of pulse generator 2 and of waveform 13. ~armonics of this frequency are also present to a degree depending on the width of the pulses and ~y the bandwidth of the amplifier, mat~hing network, and transducer combination.
It should be noted that rather than electrically ' .' :' '''''' ' ' , . .: ~ , .
10~504S
modulating the signal by a pulse generator, a sLmilar effect can be obtained by providing a multiplicity of oscillators and transducers, closely spaced, so as to produce a Fourier type combination of effective pulses in the medium by para-metric combination. These pulses parametrically modulate the carrier signal, and produce a similar effect in the medi~m as with the earlier described electrical pulse modulation of the carrier.
Figure 5 shows in block schematic form another embodiment of the invention. As before, oscillator 1 produces a carrier frequency signal. Pulse generator 2 produces a pulse signal at the secondary signal repetition frequency.
Pulse generator 5 produces long pulses which establish repetitive burst rate of the pulse modulated carrier signal.
The output of pulse generator 5 is applied to one input of modulator 20 with the output of pulse generator 2 applied to a second input. The output of modulator 20 is a series of bursts of pulse signals of the frequency from pulse generator
2, at a burst rate determined by pulse generator 5.
The output of modulator 20 is applied to one input of modulator 3, and the output of oscillator 1 is applied to a second input. The output of modulator 3 at point "A" is sLmilar to that at point "A" of the em~odiment of Figure 1.
The signal is then amplified and applied to the transducer, which applies it to the medium in a similar manner as in Figure 1.
Figure 6 shows a further embodiment in block schematic form. As in Figure 1, the output signals of pulse generator 2 and of oscillator 1 are applied to respec-tive inputs of modulator 3.
The signal from pulse generator 2 in this case is also applied via a Hilbert transformer 21 to the input of a phase , ... . . ..
-- - - --- --- , ,,, ~ ,, . ~ ",, . , - ~ , .
modulator 22. ~ second input of the phase modulator 22 has the output of modulator 3 applied thereto. The output of phase modulator 22 is applied to amplitude modulator 7, to which the output of pulse generator 5 is also connected, resulting in an output signal at point "A", as in Figure 1. The pulse modulated carrier signal is thus modulated by the Hilbert trans-formed signal from the pulse generator 2 prior to transmission, resulting in a reduction in bandwidth. Pulse generator 5 and modulator 7 can be deleted if a continuous pulsing signal is desired, rather than bursts of pulsed carried signal.
It has been found that for all the above embodiments - the amount of power in the transmission medium at the secondary signal frequency is greater than if the same amount of power had been transmitted using the two-sine-wave frequency method of the prior art. Harmonics also add to the amount of power coupled to the medium.
In a further embodiment, the structure is similar ~-to that of Figure 1, but the pulse generator 2 is replaced by a sine wave generator having frequency one half the frequency of the desired secondary signal. The output signal of modulator 3, therefore contains the sum and difference of the carrier frequency with respect to one half the secondary frequency, the difference between the aforenoted sum and - difference being equal to the secondary signal frequency.
This signal is then modulated, if desired, by the output of pulse generator 5 to obtain bursts of signal as described earlier with respect to Figure 1. However in this case the power amplifier should be type Class A or B.
,It is also desirable to provide for controls in the pulse generator 2 whereby the mark-space ratio of the output pulses thereof can be adjusted for maximum system output, or efficiency, as the case may be.
As was noted earlier, the secondary signal is . ,, . .. .- .......... : . .
~O~i504~
found to have an extremely narrow beamwidth, and even though a single transducer is utilized, the equivalent of an endfire array has been produced. Typical beamwidths measured in various experiments varied between about 10.5 degrees and 18.5 degrees.
A suitable modulator for use as modulators 3 or 7 is the type MDS, from Hatfield Instruments Limited, Plymouth, England. The remaining amplifiers, oscillators, and pulse generators are well known in the art and since their specific design is not part of this invention, they will not be described further. However, it should be noted that the electro-acoustic transducer used should have a bandwidth greater than the repetition frequency of pulse generator 2 or the frequency of the desired secondary signal.
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.~
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~ - _g_ , . .
.
. . .
The output of modulator 20 is applied to one input of modulator 3, and the output of oscillator 1 is applied to a second input. The output of modulator 3 at point "A" is sLmilar to that at point "A" of the em~odiment of Figure 1.
The signal is then amplified and applied to the transducer, which applies it to the medium in a similar manner as in Figure 1.
Figure 6 shows a further embodiment in block schematic form. As in Figure 1, the output signals of pulse generator 2 and of oscillator 1 are applied to respec-tive inputs of modulator 3.
The signal from pulse generator 2 in this case is also applied via a Hilbert transformer 21 to the input of a phase , ... . . ..
-- - - --- --- , ,,, ~ ,, . ~ ",, . , - ~ , .
modulator 22. ~ second input of the phase modulator 22 has the output of modulator 3 applied thereto. The output of phase modulator 22 is applied to amplitude modulator 7, to which the output of pulse generator 5 is also connected, resulting in an output signal at point "A", as in Figure 1. The pulse modulated carrier signal is thus modulated by the Hilbert trans-formed signal from the pulse generator 2 prior to transmission, resulting in a reduction in bandwidth. Pulse generator 5 and modulator 7 can be deleted if a continuous pulsing signal is desired, rather than bursts of pulsed carried signal.
It has been found that for all the above embodiments - the amount of power in the transmission medium at the secondary signal frequency is greater than if the same amount of power had been transmitted using the two-sine-wave frequency method of the prior art. Harmonics also add to the amount of power coupled to the medium.
In a further embodiment, the structure is similar ~-to that of Figure 1, but the pulse generator 2 is replaced by a sine wave generator having frequency one half the frequency of the desired secondary signal. The output signal of modulator 3, therefore contains the sum and difference of the carrier frequency with respect to one half the secondary frequency, the difference between the aforenoted sum and - difference being equal to the secondary signal frequency.
This signal is then modulated, if desired, by the output of pulse generator 5 to obtain bursts of signal as described earlier with respect to Figure 1. However in this case the power amplifier should be type Class A or B.
,It is also desirable to provide for controls in the pulse generator 2 whereby the mark-space ratio of the output pulses thereof can be adjusted for maximum system output, or efficiency, as the case may be.
As was noted earlier, the secondary signal is . ,, . .. .- .......... : . .
~O~i504~
found to have an extremely narrow beamwidth, and even though a single transducer is utilized, the equivalent of an endfire array has been produced. Typical beamwidths measured in various experiments varied between about 10.5 degrees and 18.5 degrees.
A suitable modulator for use as modulators 3 or 7 is the type MDS, from Hatfield Instruments Limited, Plymouth, England. The remaining amplifiers, oscillators, and pulse generators are well known in the art and since their specific design is not part of this invention, they will not be described further. However, it should be noted that the electro-acoustic transducer used should have a bandwidth greater than the repetition frequency of pulse generator 2 or the frequency of the desired secondary signal.
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Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A transmitter for transmitting a directional acoustic secondary signal of predetermined frequency through a medium, comprising:
means for generating a primary signal for applica-tion to said medium at a level such as to cause distortion of the signal by the medium;
means for generating a pulse signal having a pulse repetition frequency equal to the predetermined frequency or a sub multiple thereof; and means for producing the secondary signal in the medium by pulse modulation of the primary signal by the pulse signal.
means for generating a primary signal for applica-tion to said medium at a level such as to cause distortion of the signal by the medium;
means for generating a pulse signal having a pulse repetition frequency equal to the predetermined frequency or a sub multiple thereof; and means for producing the secondary signal in the medium by pulse modulation of the primary signal by the pulse signal.
2. A transmitter as defined in claim 1 wherein the means for producing the secondary signal in the medium includes means for pulse modulating the primary signal by the pulse signal and an electroacoustic transducer for applying the pulse modu-lated signal to the medium.
3. A transmitter as defined in claim 1 wherein the means for generating the pulse signal comprises means for genera-ting a multiplicity of signals and the means for producing the secondary signal in the medium comprises means for applying the primary signal to the medium and means for applying the multi-plicity of signals to the medium so as to add in said medium and pulse modulate the primary signal.
4. A transmitter as defined in claim 3 wherein the means for producing the secondary signal in the medium comprises a plurality of electroacoustic transducers, individually provided for each of the multiplicity of signals and the primary signal, all of which transducers are closely spaced and individually coupled to the medium.
5. A transmitter as defined in claim 2, including filter means for substantially preventing signals from passing to the transducer at the pulse repetition frequency.
6. A transmitter as defined in claim 5 further including means for Hilbert transforming the pulse signal and for phase modulating the pulse modulated signal by the Hilbert transformed pulse signal prior to application of the pulse modulated signal to the electroacoustic transducer.
7. A transmitter as defined in claim 2, 5 or 6 further including means for generating a further pulse signal with a pulse repetition frequency which is an integral divisor of the pulse repetition frequency of the first mentioned pulse signal, and means for modulating the pulse modulated signal by said further pulse signal prior to application of the pulse modulated signal to the transducer.
8. A transmitter as defined in claim 2 or 5 further including means for generating a further pulse signal with a pulse repetition frequency which is an integral divisor of the pulse repetition frequency of the first mentioned pulse signal, and means for modulating the first mentioned pulse signal by the further pulse signal prior to modulation of the primary signal.
9. A method of transmitting a directional acoustic secondary signal of predetermined frequency through a medium, comprising the steps of:
generating a primary signal for application to said medium at a level such as to cause distortion of the signal by the medium;
generating a pulse signal having a pulse repetition frequency equal to the predetermined frequency or a sub multiple thereof; and producing the secondary signal in the medium by pulse modulation of the primarv signal by the pulse signal.
generating a primary signal for application to said medium at a level such as to cause distortion of the signal by the medium;
generating a pulse signal having a pulse repetition frequency equal to the predetermined frequency or a sub multiple thereof; and producing the secondary signal in the medium by pulse modulation of the primarv signal by the pulse signal.
10. A method as defined in claim 9 wherein the primary signal is electrically pulse modulated by the pulse signal and the pulse modulated signal is applied to the medium via an elec-troacoustic transducer.
11. A method as defined in claim 9 wherein the primary signal and a multiplicity of signals for producing the pulse signal by addition in said medium are applied to the medium via individual closely spaced electroacoustic transducers whereby the primary signal is pulse modulated in the medium to produce the secondary signal.
12. A method as defined in claim 9, 10 or 11 wherein the pulse repetition frequency is equal to the predetermined frequency.
13. A method as defined in claim 9, 10 or 11 wherein the pulse repetition frequency is equal to a sub multiple of the predetermined frequency.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA253,098A CA1065045A (en) | 1976-05-21 | 1976-05-21 | Pulse-mode parametric transmitter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA253,098A CA1065045A (en) | 1976-05-21 | 1976-05-21 | Pulse-mode parametric transmitter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1065045A true CA1065045A (en) | 1979-10-23 |
Family
ID=4106021
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA253,098A Expired CA1065045A (en) | 1976-05-21 | 1976-05-21 | Pulse-mode parametric transmitter |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1065045A (en) |
-
1976
- 1976-05-21 CA CA253,098A patent/CA1065045A/en not_active Expired
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