Development and characteristics of solid state acoustic variable time delay line using direct current voltage and radio frequency pulse

Fitzgerald, T. M.

English

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[72] Inventor Tho d 
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[21) Appl. No. 757,857 
333130, 
..................................................... 333!_72 Q3h 9/16, 
H03h 9/30 
............ 333130, 72, 
2800 
UNITED STATES PATENTS 
3,185,935 511965 White ........................... 333130 
3,25423 1 511 966 Gandhi ......................... 333/30X 
3,45 1,046 611969 Cohler .......................... 333130X 
Primary Examiner- Eli Liberman 
Attorneys-John R. Manning, Herbert E. Farmer and Garland 
T. McCoy 
ACT: This disclosure describes a solid-state variable 
time delay line. A DC voltage applied to the longitudinal axis 
of piezoelectric material creates a high field domain that 
propagates along said axis from one end of the material to the 
other end. An RF pulse is applied to the end of the material 
toward which the high field domain is traveling. The RF pulse 
generates an acoustic wave that travels toward the high field 
domain. When the acoustic wave reaches the high field 
domain, it is reflected by the moving high field domain back 
toward the end of the material to which the RF pulse is ap- 
plied. The total time delay is the time it takes for the acoustic 
wave to reach the high field domain and be reflected back to 
the RF input end of the material. Hence, by varying the time 
relationship between the creation of the moving high field 
domain by the DC voltage and the application of the RF pulse, 
a variable time delay is provided. 
0 A S  
Y 
3 3  
A SOLD STATE ACOUSTIC VARIABL 
BACKGROUND OF THE INVENTION 
Delay lines have found widespread use in various electronic 
circuits and systems, particularly in microwave electronic cir- 
cuits and systems. Many solid state delay lines of a fixed na- 
ture have been developed for use in these circuits. However, 
because the time delay of these lines is fixed, they must be 
precisely formed under rigorous conditions if a precise time 
delay is desired. Therefore, they are expensive. In addition, 
because the time delay of these lines is fixed, they are not 
suitable for use in circuits that require a variable time delay 
line. 
Some prior art solid-state variable time delay lines have 
been developed. One group of such prior art devices relies on 
a mechanical means for changing the delay of the delay line. 
More specifically, a sliding transducer is moved along the 
delay line so that the application of the received signal can be 
applied to different points on the delay line depending upon 
the amount of delay desired. More recently, variable time 
delays have been achieved using the magnetoelastic properties 
of certain materials such as YIG (Yttrium-Iron-Garnet). 
While prior art variable time delay lines are suitable for use 
in some circuit and system applications, they have certain dis- 
advantages making them unsuitable for use in other applica- 
tions. For example, mechanical motion is not desirable in elec- 
tronic systems where rapid changes in delay times are necessa- 
ry. That is, a mechanical movement time delay line is in- 
herently slow acting with respect to making changes in the 
length of delay to be provided and this slow change is un- 
desirable. The major disadvantage of delay lines that use. 
materials having magnetoelastic is that they require a mag- 
netic field, and, in some environments, it is undesirable to 
generate a magnetic field. For example, it is undesirable to 
generate a magnetic field onboard a spacecraft when the 
spacecraft is designed to measure the earth’s magnetic proper- 
ties. 
Therefore, it is an object of this invention to provide a varia- 
ble time delay line that overcomes the disadvantages of prior 
art devices of a similar nature. 
It is also an object of this invention to provide a variable 
time delay line that does not require mechanically moving 
components. 
It is another object of this invention to provide a variable 
time delay line that does not require the use of a magnetic 
field to control a time delay. 
It is also an object of this invention to provide a variable 
time delay line that is structurally uncomplicated and, there- 
fore, inexpensive to manufacture. 
It is another object of this invention to provide a solid state 
variable time delay line that requires a minimum of elements. 
It is a still further object of this invention to provide a solid- 
state variable time delay line that has amplification properties 
as well as time delay properties. 
SUMMARY OF THE INVENTION 
In accordance with a principle of this invention, a solid-state 
variable time delay line is provided. A DC voltage is applied to 
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In accordance with a further principle of this invention, the 
time relationship between the application of the RF pulse and 
the application of the D.C. voltage is controlled by a control 
means so that the interaction between the high field domain 
and the acoustic wave can occur at different points along the 
longitudinal axis of the piezoelectric material. Hence, a con- 
trollable variable time delay line is provided by the invention. 
In accordance with an alternative principle of the invention, 
the variable time delay is provided by varying the magnitude 
of the DC voltage applied to the piezoelectric material. The 
variation in magnitude controls the rate of travel of the high 
field domain so that the point of interaction between the 
acoustic wave and the high field domain is varied. 
In accordance with a still further principle of this invention, 
electric field means are provided for amplifying the traveling 
acoustic wave after it enters the piezoelectric material prior to 
its being reflected by the high field domain. Hence, the inven- 
tive device can amplify as well as delay the acoustic wave. Al- 
ternatively, if the domain is moving at an appropriate velocity, 
the acoustic wave is amplified upon reflection because of an 
interaction between the acoustic wave and drifting electrons 
in the domain. 
It will be appreciated from the foregoing description that 
the invention is an uncomplicated solid-state device that pro- 
vides a variable time delay. The application DC an RF pulse to 
a piezoelectric material creates an acoustic wave that travels 
along the longitudinal axis of the material and the application 
of a DC voltage along said axis creates a high field domain that 
travels in the opposite direction to the direction of movement 
of the acoustic wave. When the high field domain meets the 
acoustic wave, the acoustic wave is reflected back toward its 
point of entry. A variable time delay is created by varying the 
time between the application of the RF pulse and the applica- 
tion of the DC voltage. Alternatively, the magnitude of the 
D.C. voltage can be varied to create a variable time delay. In 
addition, the invention provides a means for amplifying as well 
as delaying the acoustic wave. 
BRIEF DESCRIPTION OF THE DRAWINGS 40 
The foregoing objects and many of the attendant ad- 
vantages of this invention will become more readily ap- 
preciated as the same becomes better understood by reference 
45 to the following detailed description when taken in conjunc- 
tion with the accompanying drawings wherein: 
FIG. 1 is a schematic diagram illustrating one embodiment 
of the invention; 
FIG. 2 is a schematic diagram illustrating a second embodi- 
50 ment of the invention; 
FIG. 3 is a schematic diagram illustrating a third embodi- 
.FIG. 4 is a timing diagram for FIG. 3. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
ment of the invention; and 
55 
A schematic diagram of one embodiment of the invention is 
illustrated in FIG. 1 and comprises a body of piezoelectric 
, a DC source 13 and a switch 15. the piezoelectric 
6o material may be formed of cadmium sulfide (CdS), for exam- 
ple. For purposes of illustration, the body of piezoelectric 
material B 1 has a longitudinal axis and a rectangular cross sec- 
tion. However, any other generally regular form of piezoelec- 
tric material can be used, i.e., one having a round, triangular 
65 or trapezoidal cross section, for example. The DC source 13 is 
connected in series with the switch 15 across the ends of the 
the longitudinal axis of the material when the 
material. ?‘he acousiic wave travels. toward the%- 
domain and, when it reaches the high field domain, It is 70 domain 19 propagates from the negative end of the marerial to 
reflected by the moving high field domain. The reflected the positive end of the material, i.e., in the Vo direction illus- 
acoustic wave travels out the end of the material to which the trated in FIG. 1. 
RF pulse is applied. The total time delay is equal to the time it A transducer 17 adapted to receive and RF pulse is 
takes for the acoustic wave to travel to the high field domain mounted on the “positive” end of the body of piezoelectric 
and to return to its point of origin. 75 material. When an RF pulse 21 is applied to the transducer 17 
an acoustic wave is generated that propagates through the through one of the end transducers 31 to one end of the 
material toward the high field domain 19, i.e., in the V,, piezoelectric material 11 so that an RF pulse can be applied to 
direction. Upon reaching the high field domain, the acoustic the material in the mahner illustrated and described with 
wave is reflected because the elastic properties of the domain respect to FIG. 1. A further line 41 connects the RF source 39 
are different than the elastic properties of the bulk of material. 5 to a control 43 so that a control signal can be applied to the 
control 43. The control 43 controls the closure of switches $5 The reflected signal propagates back through the material to 
the transducer and from the transducer out of the material. 
The total time delay is the time it takes for the acoustic wave 
to travel from the transducer to the domain and back to the 
transducer. In addition to delaying the acoustic wave, the 
wave is Doppler shifted in frequency (either positively or 
negatively) depending on the direction of travel of moving 
domain. 
The total time delay is varied by varying the point of in- 
teraction between the high field domain and the acoustic 
wave. The point is varied by varying the time of creation of the 
high field domain relative to the time of application of the RF 
pulse. This time variation is created by controlling the time of 
and 35 as illustrated by the dotted lines. 
The device illustrated in FIG. 3 operates in the manner 
hereinafter described; at time to (FIG. 4) the RF source 
0 generates an RF pulse that is applied through the transducer 
to one end of the body of piezoelectric material B I. The XF 
pulse creates an acoustic wave inside of the body which travels 
from left to right as illustrated in FIG. 3. Simultaneously, or 
within a desired time relationship to the application of the RF 
5 pulse, a control pulse is applied along the line 41 to the control 
43. The control 43 immediately closes the second switch 35 so 
that an amplifying field is created between the pair of transdu- 
cers 31 and 33. This field amplifies the acoustic wave traveling 
Elosure ofthe switch 15. The variation in application time will, along the longitudinal axis of the piezoelectric material in a 
of course, vary in accordance with the material forming the 2o manner well known in the prior art. After a predetermined 
body of piezoelectric material since the velocity of movement Period of time ( t l ) ,  the control opens the second witch 35 
of an acoustic wave in a material is determined by the material and closes the first switch 15. The opening of the second 
and its orientation, i.e., the acoustic wave can be a fast Or slow switch prevents further amplification of the acoustic wave 
shear Wave or a longitudinal wave depending on the material 25 while the closing of the first switch creates a high field domain 
and its crystal orientation. In addition, the time of interaction l9 that propagates toward the acoustic wave. When the 
which is also dependent upon the material parameters. acoustic wave is reflected back to the transducer 31 in the 
manner heretofor described with respect to the operation of 
the invention is a rather uncomp~icated solid-state device 3o the embodiment of the invention illustrated in FIG. 1. The 
of application ofan R~ pulse to a body of piezoelectric line 40 to the RF source 39 where it k detected and used by an 
al and the time of the electronic circuit or system (not shown) connected to the RF 
longitudinal axis of the body, a variable time delay is provided. source. 
be eliminated because certain materials of a piezoelectric na- illustrated in FIG. 3 amplifies as well as time delays an RF 
pulse signal. It will also be appreciated that there are other ture form their own transducers. 
FIG. a illustrates an alternative embodiment of the inven- amplification methods which can be used prior to the acoustic 
tion the body of piezoelectric material 23 is formed of wave interacting with the high field domain. For example, as 
gallium arsenide, for example. A variable DC power 25 40 the acoustic wave travels down the piezoelectric material, an electric field can be applied to amplify the wave. At a critical 
field level, a high field domain will form and reflect the wave. is connected in series with a switch 27 across the piezoelectric material so as to create a high field domain when the switch is The reflected wave will have an atmarent gain. Alternatively. 
is also dependent upon the velocity of the high field domain acoustic wave and the high field domain meet ( r 2 ) l  the 
It will be appreciated from the foregoing description that 
suitable for time delaying an RF pulse. By controlling the time reflected wave passes through the transducer and passes 
of an electric field 
It should be noted in Some devices that the transducer 17 can 35 It be appreciated that the embodiment Of the invention 
1 ,  
when the acoustic wave reaches'the high- field domain, the ciosea. The primary difference between the embodiment illustrated 
in FIG. is that the 45 acoustic wave can penetrate the domain to a certain extent and then be reflected. During the penetration period, the velocity of movement of the high field domain can be con- acoustic wave will see some carriers with a drift velocity ap- trolled in gallium arsenide or similar materials by controlling proximately equal to or greater than acoustic velocity. These 
the magnitude Of the Dc "Itage creating the high field carriers will couple energy to the reflected acoustic wave to 
velocity in materials such as cadmium sulfide. Hence, there depends, to extent, upon the shape of the domain and 
are two methods of control provided in the FIG. 2 embodi- the velocity distribution of the carriers within the domain. 
merit whereas there was Only One method Of control in the Moreover, the body of material 11 can be formed of gallium 
FIG. 1 edxxfiment.  Specifically, the time relationship arsenide or the like and the first DC source 83 can be variable. 
between the application ofthe RF pulse and the c h a m  ofthe 5 5  f t  will be appreciated from the foregoing description that switch controls the time of generation of the high field domain the invention provides an uncomplicated and, therefore, inex- 
relative to the time of application of the RF pulse. Hence, one pensive solid-state of providing a variable tirne delay 
control is provided. In addition, controlling the magnitude of line. The basic inventive device is a block of semjconductor 
the DC voltage Source 25 controls the of ~ O v ~ m e n t  material of a piezoelectric nature connected to a DC voltage 
of the high field domain. Hence, a second control is provided. 60 and the 
FIG. 3 illustrates yet another embodiment of the invention switch means are connected in series the longitudinal 
wherein the acoustic wave is amplified as well as delayed. FIG. axis of the material SO as to create a high field domain that 
3 also ilhstrates a Control for COntrOlling the time Of aPptiCa- propagates down the material when the switch is closed. The 
tion Of various voltages to the body Of piezoelectric material DC voltage Source may be variable depending upon the 
SO that the body Provides a desired time delay and a desired 65 material to be used, i.e., gallium arsenide, for example, as op- 
amount of amplification. FIG. 4 is a timing diagram for the posed to cadmium sulfide. If the voltage source is variable the 
embodiment of the invention illustrated in FIG. 3. velocity of the high field domain is controllable. The switch 
means may be a solid-state switch such as a transistor or the 
FIG. 9, i.e., a body of Piezoelectric material $1, a DC voltage like, a conventional switch, or a relay switch depending upon 
source 13 and a switch E5. Also illustrated in FIG. 3 are a pair 70 the use of the invention. In addition to creating a time delay, 
of transducers 31 and 33 located at opposite ends of the the invention also provides a rather uncomplicated device for 
piezoelectric material. The pair of transducers are connected both amplifying and delaying a signal. 
together through a switch 35 connected in series with a second 
DC source 37 of opposite polarity to the first DC source 13. 
An RF source 39 is illustrated as connected by a line 40 75 
and the embodiment illustrated in FIG. 
domain whereas the magnitude Of the "Itage has no effect On 50 cause an apparent gain. This latter method of amplification 
by a switch means. The DC voltage 
9 
FIG. 3 comprises a basic circuit of the type illustrated in 
I claim: 
1. A variable time delay line comprising: 
a body of piezoelectric material having a longitudinal axis, 
3,568,103 
a pair of transducers, one transducer connected to one end 
of said body of piezoelectric material and the second 
transducer connected to the other end of said body of 
said piezoelectric material; 
first means for applying a DC voltage to said longitudinal 
axis to create a high field domain that propagates along 
said longitudinal axis; 
a second DC voltage source connected in series with a 
switch between said pair of transducers, said second 
source connected in opposite polarity to said first means; 
and 
second means comprising an RF pulse source electrically 
connected to one end of said body of piezoelectric 
material for applying a pulse to the end of said body of 
said piezoelectric material toward which said high field 
domain is traveling so that an acoustic wave is created in 
said body of said piezoelectric material and is reflected 
when said high field domain and said acoustic wave meet. 
2. A variable time delay line as claimed in claim 1 wherein 
said first means includes a fixed DC source connected in series 
with a switch across the ends of said body of piezoelectric 
3. A variable time delay line as claimed in claim 2 including 
a control electrically connected to said RF source and adapted 
to close said first and second switches in a predetermined 
manner. 
4. A variable time delay line as claimed in claim 3 wherein 
said body of piezoelectric material is formed of cadmium sul- 
fide. 
5. A variable time delay line as claimed in claim 3 wherein 
15 said body of said piezoelectric material is formed of gallium 
5 material. 
lo  
arsenide. 
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A solid state acoustic variable time delay line Patent

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