Variable time delay line does not require use of a magnetic field to control a time delay, and can both amplify and delay a signal. Device is inexpensive and space saving, it does not require mecanically moving components, eliminating detrimental vibrations in a sensitive environment

Fitzgerald, T. M.

English

NASA Technical Reports Server

November 1970	 Brief 70-10492 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
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be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Solid State Variable Time Delay 
Piezoelectric Material
CdS 
rf Pulse
Domain 
VD 
Piezoelectric Material 
rf Pulse 
B 
7^^ VA
VD High Field 
Domain	 Piezoelectric 
-,Material 
Source
Transducer 
Transducer	 I	 High Field 
LI ControlJ	 Domain 
Figure 1. Representations of. Pulse Delay Process 
This device is designed for use in electronic circuits 
wherever a fast reacting variable time delay is required, 
and should prove valuable for application in the 
communications industry; and to technical personnel 
involved in the design and development of microwave 
components and systems. The solid state variable time 
delay line offers the following advantages: (1) is in-
expensive and space saving, eliminating the need for 
extra equipment to utilize the delay time; (2) does not 
require mechanically moving components, elimina-
ting vibrations which could prove detrimental in a sen-
sitive environment; (3) does not require the use of a 
magnetic field to control a time delay; and (4) features 
the capability for both amplifying and delaying a 
signal. 
Fixed and variable delay lines are widely used in 
microwave electronic circuits and systems. However, 
the fixed lines have had the disadvantages of being 
expensive and limited in scope. Some solid state 
variable time delay lines have been developed, but they 
rely primarily on a mechanical means for changing 
the delay of the delay line. Recently, variable time de-
lays have been designed using the magnetoelastic pro-
perties of certain materials such as YIG (yttrium-iron-
garnet). The major disadvantage of these materials is 
that they require a magnetic field, which may be unde-
sirable in specific environments. 
Using cadmium sulfide (Figure 1A) as the piezo-
electric material, the magnitude of the voltage had no 
effect on velocity. In Figure 1B, with gallium arsenide 
as the piezoelectric material (similar materials will 
serve), the velocity of movement of the high field do-
main can be varied by controlling the magnitude of the 
dc voltage creating the high field domain, thus offering 
an additional method of control. 
An electric source is applied across the ends of the 
crystal (Fig. 1A). A high field domain then propagates 
from the negative to the positive end of the material (in 
the VD direction). A transducer adapted to receive an 
rf pulse is mounted on the positive end of the piezoelec-
tric material. When an rf pulse is applied to the trans-
ducer, an acoustic wave is generated that propagates 
through the material toward the high field domain (in 
the VA direction). The acoustic wave is then reflected 
because the elastic properties of the high field domain 
and the bulk of the material differ. The reflected signal 
(coouiflUCd overleaf) 
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	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
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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 high field domain 
and back to the transducer. By varying the point of 
interaction between the high field domain and the 
acoustic wave, the total time delay can be varied. The 
point is controlled by varying the time of creation of 
the high field domain relative to the time of application 
of the rf pulse. The variation in application time is 
determined by the nature of the piezoelectric material. 
In some devices, the transducer can be eliminated be-
cause certain piezoelectric materials form their own 
transducers. 
Figure 1C shows how the acoustic wave is amplified 
as well as delayed. It also illustrates a means for con-
trolling time of application of various voltages to the 
body of piezoelectric material, thus providing variable 
time delay and degree of amplification.
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Headquarters 
National Aeronautics 
and Space Administration 
Washington, D.C. 20546 
Reference: TSP70- 10492 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, nonexclusive
licenses for its commercial use will be granted by

NASA. Inquiries concerning license rights should be 
made to NASA, Code GP, Washington, D.C., 20546. 
Source: T. M. Fitzgerald 
Electronics Research Center
(ERC- 10032) 
Brief 70-10492	 Category 01


Solid state variable time delay

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