Microphone used as a phonocardiograph transducer monitors small amplitude audio signals in the presence of large shock loads and high humidity. It contains a lead zirconate-lead titanate piezoelectric plate encapsulated in a flexible polyurethane resin. The resin is contained in a sealed nylon case having a diameter of less than one inch

Young, W. J.

English

NASA Technical Reports Server

Flexible
Potting Comr'-' 
July 1966
	 Brief 66-10314 
NASA TECH BRIEF
	
at'' 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Phonocardiograph Microphone Is Rugged and Moistureproof 
The problem: 
To design a microphone to be used as a phono-
cardiograph transducer under conditions such as 
experienced by an astronaut. The microphone must 
be capable of monitoring small amplitude audio signals 
in the presence of large shock loads, accelerations of 
up to 40g, temperatures from 30° to 200° F, and 
high humidity. 
The solution: 
A microphone incorporating a lead zirconate—lead 
titanate piezoelectric plate encapsulated in a flexible 
polyurethane resin contained in a sealed nylon* case 
having a diameter of less than 1 inch. 
How it's done: 
A square plate (approximately 0.4 inch on a side) 
of the piezoelectric ceramic with a silver coating on 
opposite faces, to permit soldering of lead wires to 
the plate, is supported at diagonally opposite corners 
on a flange at the bottom of the nylon case. The
lead wires are soldered to the plate surfaces as shown 
in the illustration. A 470 Kohm (0.1 watt) carbon 
resistor, soldered in parallel with the terminals of the 
piezoelectric plate, serves to provide the required low 
frequency response of the transducer. The plate is 
secured to the support points on the flange by means 
of a suitable adhesive coating. This adhesive material 
is also used to seal the joints between the case and 
the cable. 
The space directly above the plate is partially filled 
with a polyurethane resin, which, when cured, re-
mains sufficiently flexible so as not to interfere with 
the piezoelectric characteristics of the plate. The 
polyurethane resin also holds the resistor in flied 
relation to the plate and effectively seals the internal 
circuit against moisture in the atmosphere and from 
perspiration from the body to which the transducer 
is attached. The remainder of the cavity is filled with 
an epoxy resin, which, when cured, serves as an 
(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=19660000313 2020-03-11T17:39:07+00:00Z
electrical and thermal insulator and exhibits high re-
sistance to mechanical shock. This epoxy resin is 
also applied as a seal to the interface junction be-
tween the piezoelectric plate and the opening at the 
base of the transducer. 
Notes: 
1. In use, the base of the microphone is secured to 
the skin over the area to be monitored with a 
piece of double-backed surgical tape.
2. Inquiries concerning this invention may be di-
rected to: 
Technology Utilization Officer 
Manned Spacecraft Center 
Houston, Texas 77058 
Reference: B66-10314 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: William J. Young 
(MSC-212) 
Brief 66-10314	 Category 04


Phonocardiograph microphone is rugged and moistureproof

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