Transducer has thin piezoelectric sensing element of 0.051-cm-thick lead zirconate titanate crystal which is cut as a conical frustum. Sensing crystal and titanium wire are protected from mechanical shock and vibration. Transducer is insensitive to mechanical vibrations of instrument plug on which it is mounted

Raman, K. R.

English

NASA Technical Reports Server

May 1971	 Brief 71-10114 
NASA TECH BRIEF 
Ames Research Center
	
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Subminiature Transducer Measures Unsteady Pressures 
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A subminiature transducer measures hypersonic 
boundary-layer fluctuating pressures having frequency 
components ranging from 1 to 500 kHz. The sen-
sing element of the transducer is a thin, piezoelectric 
Thin-Film	 Piezoelectric 
Electrodes	 Crystal
Conductive 
Titanium Backing 
Wire 
RTC-Si I icon
Aluminum 
ict i ye 
wafer in the shape of a conical frustum. The overall 
transducer is approximately 032 cm (1/8 in.) in 
diameter and 3.81 cm (1.5 in.) in length. The 
piezoelectric sensing element, a 0.051-cm (0.020-in.)-
thick crystal of lead zirconate titanate, is cut as 
a conical frustum having base angles of 1.31 radians 
(750) This geometry was selected in order to ensure
that the plane pressure-wave energy incident on 
the small-diameter face of the crystal would travel 
in an optimal path through the crystal and back-
ing material, which is a titanium wire with a 
sharpened point. The pressure-wave energy propagates 
through the titanium wire by multiple reflections 
from its lateral surfaces to the sharpened point, 
where the energy is mostly dissipated as heat. Ti-
tanium was selected as the backing material because 
it closely matches this piezoelectric crystal in 
acoustic impedance, thus ensuring maximum energy 
transfer. 
The sensing crystal and the titanium wire are 
embedded in a room-temperature-curing (RTC) 
silicone to protect them from mechanical shock and 
vibration. Thin-film electrodes of silver, 5 to 10 nm 
(50 to 100 A) thick, deposited by sputtering on 
the parallel faces of the crystal, are of such small 
mass that their effect on the natural frequency of 
the crystal is negligible. Electrically conductive epoxy 
resin is used to cement the silvered base of the 
crystal to the large-diameter end of the titanium 
wire and also to cement the pointed end of the 
wire to the central pin of the miniature coaxial 
connector at the base of the transducer. The thin 
film of silver on the small-diameter face of the 
crystal extends to the outer diameter of the alu-
minum cylinder to form one of the conductors for 
the piezoelectric signal generated by the crystal. 
The other conductor is the central pin of the minia-
ture coaxial connector. 
To use the transducer for unsteady-pressure meas-
urement, the unit is connected directly to a field 
effect transistor • (FET) emitter follower and the 
output terminals of the emitter follower are con-
nected to a high-gain, low-noise amplifier. The volt-
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000113 2020-03-17T02:23:14+00:00Z
3. Requests for further information may be directed 
to:
Technology Utilization Officer	 0 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP71-101 14 
Patent status: 
No patent action is contemplated by NASA. 
Source: K. R. Raman
Ames Research Center
(ARC-10349) 
age output from the amplifier, corresponding to the 
pressures sensed by the transducer, is fed to a re-
cording system having adequate frequency response. 
In preliminary experiments, the unamplified output 
from the transducer ranged from 4 to 10 mV for 
a pressure of 5.3 N/m (0.04 torr). The measured. 
time rise of the instrument was approximately 0.8zs. 
The transducer was found to be insensitive to me-
chanical vibrations of the instrument plug on which 
it was mounted. 
Notes: 
1. For better acoustic matching, the sputtered thin-
film electrodes on the crystal can be titanium 
instead of silver. 
2. Other metals (e.g., brass, silver, aluminum) can be 
used for the backing wire, though they would be 
less efficient than titanium. A ceramic tube with 
an elastomer-filled core and a conductive-material 
surface coating can also be used in place of the 
titanium backing wire.
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Brief 71-10114	 Category 01,03


Subminiature transducer measures unsteady pressures

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