U.S. patent number 3,789,350 [Application Number 05/297,574] was granted by the patent office on 1974-01-29 for reduced bandwidth processing for ultrasonic image conversion.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Navy. Invention is credited to Albert L. Rolle.
United States Patent |
3,789,350 |
Rolle |
January 29, 1974 |
REDUCED BANDWIDTH PROCESSING FOR ULTRASONIC IMAGE CONVERSION
Abstract
Disclosed is an ultrasonic, image conversion, high definition
sonar having multitude of transducer channels employing improved
signal processing in each channel to reduce video bandwidth and
switching speed requirements. Signal processing is characterized in
each of the multitude of channels by detecting and holding the peak
return from a transmit pulse for the remainder of the pulse project
period, then holding that peak value for the subsequent pulse
project period, during which time the value may be multiplexed for
conversion to video signals for a CRT display, or may be applied to
elements of an LED array.
Inventors: |
Rolle; Albert L. (Lynn Haven,
FL) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (Washington,
DC)
|
Family
ID: |
23146872 |
Appl.
No.: |
05/297,574 |
Filed: |
October 13, 1972 |
Current U.S.
Class: |
367/11; 367/113;
367/903 |
Current CPC
Class: |
G01S
7/527 (20130101); Y10S 367/903 (20130101) |
Current International
Class: |
G01S
7/523 (20060101); G01S 7/527 (20060101); G01s
009/66 () |
Field of
Search: |
;340/5H,5MP,1R,3R,6R
;343/16R,17 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3717843 |
February 1973 |
Farrah et al. |
|
Primary Examiner: Farley; Richard A.
Attorney, Agent or Firm: Sciascia; Richard S. Doty; Don D.
David; Harvey A.
Claims
What is claimed is:
1. An ultrasonic, image conversion, high definition sonar system
comprising in combination:
function generator means for providing control signals including
clock signals, each representing a pulse project period, and reset
signals;
transducer means, comprising an array including a plurality of
individual transducer elements, for periodically projecting
ultrasonic energy pulses of predetermined width and responsive to
ultrasonic energy reflected from a target within a predetermined
range of interest to generate electrical echo signals corresponding
thereto;
receiver means for detecting said echo signals, and comprising a
plurality of channels for generating envelope signals corresponding
to echo signals from each of said transducer elements
signal processing means comprising a plurality of channels, each
connected to receive the output of one of said receiver channels,
for generating, from said envelope signals, output signal
levels;
each channel of said signal processing means comprising peak detect
and hold means for detecting the peak value of an envelope signal
occurring in a particular pulse project period and for holding said
peak value during the remainder of that pulse project period,
sample and hold means, responsive to said clock signals, for
sampling said peak value at the beginning of the next pulse project
period and for holding said peak value as one of said output signal
levels until the beginning of the following pulse project period,
and means for resetting said peak detect and hold means after said
sampling of said peak value; and
visual display means responsive to said output signal levels to
produce corresponding emissions of eye stimulating light.
2. A sonar system as defined in claim 1, and wherein: said display
means comprises cathode ray tube means.
3. A sonar system as defined in claim 2 and further comprising:
video amplifier means for driving said cathode ray tube means;
and
multiplexer means including logic means and multiplexer gate means
responsive to said logic means for coupling said output signal
levels of said signal processor channels to said video amplifier
means in accordance with a predetermined program.
4. A sonar system as defined in claim 1 and wherein:
said peak detect and hold means of each signal processor channel
comprises an operational amplifier, capacitor, and diode
combination, wherein the peak input signal is stored on said
capacitor, and transistor means for discharging said capacitor to
reset said peak detect and hold means; and
said function generator means comprises means for generating a
reset pulse following each of said clock pulses, said transistor
means being rendered conductive by said reset pulse.
5. A sonar system as defined in claim 4, and wherein:
said sample and hold means of each signal processor circuit
comprises a switching transistor, capacitor, and operational
amplifier combination, and buffer amplifier means coupling said
peak detect and hold means to said sample and hold means; and
said switching transistor being operative in response to said clock
signals to apply the output of said buffer amplifier means to said
capacitor and operational amplifier of said sample and hold
means.
6. A sonar system as defined in claim 5, and wherein said display
means comprises cathode ray tube means.
7. A sonar system as defined in claim 6, and further
comprising:
video amplifier means for driving said cathode ray tube means;
and
multiplexer means, including logic means and multiplexer gate means
responsive to said logic means, for coupling said output signal
levels of said signal processor channels to said video amplifier
means in accordance with a predetermined program.
8. In an ultrasonic, image conversion sonar system of the type
including a source of clock signals representing the end of one
pulse project period and the start of another, a plurality of
transducers, and receiver means having a plurality of corresponding
channels for generating echo envelope signals, reduced bandwidth
signal processing and display apparatus comprising:
a plurality of echo envelope peak detection and holding means for
providing a peak voltage level representative of the peak return
signal in each of said channels during a first predetermined period
in which echoes may be received from a given pulse transmission,
said peak detection and holding means each comprising a storage
capacitor connected to receive and store said peak voltage level
and transistor means connected to said capacitor for discharging
thereof in response to reset signals;
reset signal generating means connected to said transistor means
and responsive to said clock signals for generating said reset
signals;
a plurality of sample and hold means, each connected by a buffer
amplifier means to one of said peak detection and holding means,
for sampling the voltage level stored on said storage capacitors in
response to said clock signals, and for providing corresponding
voltage levels for a second predetermined period following said
first predetermined period, said sample and hold means each
comprising a switching transistor, capacitor, and operational
amplifier combination;
cathode ray tube means for generating a visible display of said
peak return signals;
sweep generating means, connected to said cathode ray tube means,
for causing a raster to be traced thereby;
video amplifier means connected to the cathode of said cathode ray
tube means and responsive to said corresponding voltage levels from
said sample and hold means, when applied thereto, to modulate the
intensity of said visible display; and
multiplexer means, including logic means and multiplexer gate
means, said multiplexer means being connected between said sample
and hold means and said video amplifier means so as to apply said
corresponding voltage levels to said video amplifier means in
accordance with a predetermined program.
Description
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or
for the Government of the United States of America for governmental
purposes without the payment of any royalties thereon or
therefor.
BACKGROUND OF THE INVENTION
This invention relates to ultrasonic image conversion as used in
high definition sonar systems, and more particularly, to
improvements in video processing therein which permit cathode ray
tube visual displays and brighter light emitting diode displays,
when used.
The carrying out of various underwater tasks by divers is often
hindered by turbid water conditions which render a diver
effectively blind if he must rely on an unaided view through his
faceplate or mask. Lights and other optical aids are ineffective in
a turbid environment because of backscatter from particulate
matter. Chemicals and mechanical envelopes can be effective to
clarify turbid water, but are subject to various limitations which
restrict their use.
Because ultrasonic energy propagation is relatively unaffected by
turbid conditions of water, efforts have been directed to
development of ultrasonic means of generating or enhancing images
of objects within the working range of a diver to enable him to
carry on tasks such as hull inspection and repair, detection of
various objects, rescue, and the like.
Patent application Ser. No. 296,500, filed in the U. S. Pat. Office
on Oct. 4, 1972, and entitled Sonar Image Converter, by A. L. Rolle
describes in considerable detail a diver or swimmer carried
ultrasonic image-conversion visual display system which goes far
toward overcoming the problems of viewing objects in turbid water.
In that system, pulsed untrasonic energy is transmitted and target
reflected energy is focused on an array of transducer elements
located at the focal plane of an ultrasonic lens. The output of
each element of the transducer array is amplified, band limited,
and envelope detected in a separate channel. The detected output
signal of each transducer element channel is processed and used to
control energization of an LED (light emitting diode) in an array
of LED's corresponding in number and arrangement to the transducer
array. The transducer and LED arrays are mounted on a common shaft
for synchronized rotation and scanning of a viewing zone. The
resulting visual display is an image of the target of interest
rather than an indication of bearing and range, as in conventional
sonar.
For successful direct viewing of the LED array, it is necessary
that energization of the individual LED's be for a long enough
period, say 500 .mu.sec or longer, to provide adequate light to
stimulate the eye. The envelope-detector output in the above system
is approximately equal to the width of the projected pulse and
typically ranges from 50 to 300 .mu.sec. Accordingly, the mentioned
signal processing following the envelope detector of each channel
serves to detect the peak value of the envelope and hold it for a
period inversely proportional to the range of the target of
interest or at least for some minimum period which would assure
visual stimulation by the LED.
Now in some circumstances it would be desirable to utilize a CRT
(cathrode ray tube) display in an ultrasonic image conversion sonar
rather than an LED array. These circumstances would include
situations where power and weight factors are not as restrictive as
in the case of swimmer/diver use, for example, when mounted on a
submersible vessel. With a CRT display, the output of each envelope
detector would be sequentially gated to a single video amplifier by
an analog multiplexer. The video amplifier would drive the Z or
amplitude axis of the CRT. The number N of transducer elements can
vary from approximately 30, as in the mechanically scanned array of
the copending application, to possibly 10,000 elements in an
extensive electronically scanned array. For use with a CRT it is
desirable to sample all of the envelope detector outputs at least
once for each projected pulse. If done in a period corresponding to
a projected pulse width PW, the sampling time per sample then would
be PW/N. For even small transducer arrays, the sampling time per
sample would be extremely short and would require high power,
wide-band sampling gates, drive logic, and CRTs. Sampling at high
speeds also introduces significant errors due to the spikes
generated in the signal channel by the rapidly changing drive logic
voltages.
For extensive arrays with thousands of transducer elements, signal
processing as used heretofore would require long projected pulse
widths to facilitate within pulse scanning. Long pulse widths are
undesireable in turbid water, where the need for ultrasonic imaging
is the greatest, as the contrast between the target echo and volume
reverberation decreases as PW increases.
SUMMARY OF THE INVENTION
With the foregoing in mind, it is a principal object of this
invention to provide an improved ultrasonic image conversion sonar
which is particularly useful in turbid water conditions.
Another object of the invention is to provide an image conversion
sonar, wherein a cathode ray tube can be utilized as the visual
display means.
Still another object is the provision of a high definition sonar
having a transducer array in which the transducer elements may
number in the thousands.
Yet another object is to provide an improved image conversion sonar
employing signal processing means, such that elements of an LED
display will be excited for a period which is independent of the
range to the target, thereby increasing the apparent brightness of
the display for very short pulse width projections.
As another object, the invention aims to provide an improved sonar
system having one or more of the foregoing characteristics and
which utilizes improved signal processing in each transducer
channel whereby weight, power, and most importantly, bandwidth
requirements are substantially reduced in the generation of images
from relatively short pulse width ultrasonic projections.
Other objects and many of the attendant advantages will be readily
appreciated as the subject invention becomes better understood by
reference to the following detailed description, when considered in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic illustration in block form of an
ultrasonic, image conversion, high definition sonar system
embodying the invention; and
FIG. 2 is a diagrammatic illustration, in greater detail, of the
signal processing portion of the system of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, the general organization of an exemplary
ultrasonic image conversion sonar system employing the invention
comprises a transducer array 10, including a number of transducer
elements 12. The transducers 12, which may number from
approximately 30 to 10,000 or more depending upon the use to which
the system is put, are connected as shown by lines 14 to transmit
and receive switches 16. The latter serve in the usual manner to
direct transmission pulses received via lines 18 from a transmitter
20 to the elements 12, and to direct return signals detected by the
elements 12 to appropriate channels of a multi-channel receiver 22
via corresponding lines 24.
The transmitter 16 and the receiver 22 are under the control of a
system function generator 28 for transmission, range gate, and gain
control functions as indicated by lines 30, 32, and 34,
respectively. The operation of the system as described thus far may
be regarded as the same as in the above mentioned application, to
which reference may be had for further details.
The outputs of the channels of the receiver 22, indicated by lines
36 are in the form of signal envelopes 38, each representative of
the return from a corresponding transducer element within the
reception time dictated by the range gate.
The receiver outputs on lines 36 are applied to corresponding
channels of a reduced bandwidth signal processor 40, the
construction, purposes and functions of which will be described in
more detail with reference to FIG. 2, as this specification
proceeds. Suffice it to say for the moment that the envelope
detected signals 38 are processed in the processor 40, under the
control of signals represented by lines 42 and 44 from the function
generator, to generate for each channel a signal level
representative of the peak response of the associated transducer,
which signal levels are available at the outputs 46 of the
processor for sufficient time to be individually sampled by
multiplexer gates 48 in accordance with an order of succession
determined by a multiplexer logic 50. The latter may take various
forms but conveniently comprises shift register means having
outputs 52 under the program control of the function generator 28,
as shown by line 54.
The sampled outputs of the multiplexer gates 48 are summed on line
56 for application as the input to a video amplifier 58, the output
of which on line 60 drives the Z axis (brightness) of a cathode ray
tube display 62. Sweep generators 64 are provided for developing a
suitable raster on the CRT display at a frame rate determined by a
sync signal output 66 of the function generator 28.
Referring now to FIG. 2, the signal processor construction and
operation will be described in more detail, the description being
confined to the operation of one channel with the understanding
that it applies as well to the numerous parallel channels which
would be employed. The incoming detected envelope on line 36 is
applied to an operational amplifier 70 having its reference side
connected through a capacitor 72 to ground, and having its output
74 connected through a diode 76 and line 78 to the reference side,
as well as to the input of a buffer amplifier 80. This amplifier
70, capacitor, diode configuration will be recognized as a peak
detection and hold circuit.
A transistor 82 has its emitter-collector circuit connected across
the capacitor 72, and its base connected to receive a reset pulse
84 via line 42. In this regard, the reset pulse 84 is conveniently
generated within the function generator 28 by a delay means in the
form of a single shot multivibrator, or one-shot, 86. The one-shot
86 is triggered by the negative going characteristic of each of a
train of clock pulses 88 on line 90.
The clock pulses 88 are also applied via line 44 to a gate means,
conveniently in the form of a field effect transistor 92 which,
when rendered conductive by the positive clock pulses, transfers
the output of the buffer amplifier 80 to the input of an
operational amplifier 94 and to a capacitor 96. The gate 92,
amplifier 94, and capacitor 96 will be recognized as constituting a
sample and hold circuit.
The output signal level line 46 from the sample and hold circuit is
gated by a transistor 100 to the video amplifier input line 56 in
response to a control pulse 102 from the multiplexer logic 50. In
this regard, it should be noted that transistor 100 is only one of
the plurality of gating transistors corresponding to the plurality
of channels in the system and that point 104 is a summing node for
the plurality of channel sample and hold levels gated by these
transistors.
MODE OF OPERATION
In the operation of the system, an isonifying pulse having a width
of say 10 .mu.sec to 100 .mu.sec is projected every T seconds, the
period T being referred to as the project pulse period. The pulse
projection is conveniently under the control of clock signals 88,
which clock signals are also applied as shown by lines 90 and 44 to
the one-shot 86 and to the gating transistor 92. Consider the pulse
project period T to be equal to twice the maximum range of interest
in feed divided by the velocity of sound c in the medium concerned,
usually sea water. For example, if the maximum range of interest
for a particular application is 10 ft., T is approximately 4
msec.
At a time during the period T, depending upon the range of a target
of interest within 10 feet, a detected envelope will arrive on line
36 and will be peak detected and held by the action of amplifier
70, capacitor 72, and diode 76. At the end of the period T, the
gating transistor 92 is rendered conductive for a period sufficient
to sample the voltage level of buffer amplifier 80 which, of
course, represents the peak detected and held value, and store it
in the hold circuit formed by capacitor 96 and amplifier 94. As the
last mentioned clock pulse 88 goes negative, the one-shot 86 is
fired causing it to provide the pulse 84 which resets the peak
detect and hold circuit in readiness for the next return signal.
The response time of the one-shot 86 conveniently introduces
sufficient delay to assure that the signal stored on capacitor 72
is not discharged until after the output level of buffer amplifier
80 has been transferred to the capacitor 96.
The capacitor 96 and amplifier 94 hold the sampled value for the
following period T, during which time the multiplexer gate
transistor 100 will be called upon to release that value to the
video amplifier input line 56.
Keeping in mind that the preferred projected pulse width is on the
order of 10 .mu.sec and that the project pulse period T is on the
order of 4 msec in the example given, the described processing
gives an increase in time by a factor of 400 during which N
channels can be sampled by the multiplex logic for CRT
presentation. Accordingly, this allows employing of microwatt logic
and analog gates and, because of the relatively low switching
speeds, feed through of the logic switching voltages into the
signal channels is significantly reduced.
If an LED display is desired where the brightness of the display is
assured for all ranges, rather than having the brightness inversely
proportional to range as in the aforementioned application, the
output of each channel on line 46 may be applied to the
corresponding LED.
Obviously, other embodiments and modifications of the subject
invention will readily come to the mind of one skilled in the art
having the benefit of the teachings presented in the foregoing
description and the drawing. It is, therefore, to be understood
that this invention is not to be limited thereto and that said
modifications and embodiments are intended to be included within
the scope of the appended claims.
* * * * *