Vibrophonocardiograph comprising low weight and small volume piezoelectric microphone with amplifier having high imput impedance for high sensitivity and low frequency respons

Barker, P.

Wright, L. N.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE AOMlNlStAAtlON . 
1 %  Wauocro~oa* 0.C. 2094 
 scientific 61 Technical Information Divimion 
Attention# 'US.@ Winnir W. Morgan 
FROM: G~/Office of Aeeiqtar)t General Couneel for 
Patent Mattexe 
SUBJECT: ' Announcement of NASA-Owned U, 8 .  Patents i n  STAR 
Sn accordance with the procedures agreed upon by Code GP 
and Code USI ,  the attached NASA-owned~U. Sme'Patent is beAng 
forwarded fo r  abetracting, and announcement Ln'mA @*AIR. 
. . t 
U. 8. Patent No. 
. Government or 
' Corporate Employee 
Supplementary Corporate 
Source ( i f  applicable ) 
NASA Patent Caee NO, s - XFRL.67/,ZZ- 
NOTE - t f  this  patent c w e r r  an invention made by a corporatq, 
employee of a NASA Contractor, the follawing is applicable8 
yes @- NO CJ 
. Pursuant t o  Section 305(a) of the National ~ e r o n i u t i c s  and 
'.Space Act. the name of the Administrator of NASA appears on 
the first page of the patent; however, the name of the actual 
inventor (author) appear8 at the heading oC C o l r a n  No. 1 of 
the specification, following tho word8 .: with rommct to 
- 
I 
- - . 
Copy of Patent aited above I . < 
I i,, 
(CATEGORY) , , , I "{l I 
https://ntrs.nasa.gov/search.jsp?R=19710017758 2020-03-17T03:12:47+00:00Z
PATENTED FEE 1 6 1971 
FIG 2 
FIG 3 INVE,'NTO$? 
LESTER N. WRIGb1T 
Ulaited States Bateat rw 3,563,232 
1721 lnvewtoas James FVebb 
Administrator ofthe National Aeronautics 
and Space .Qdmimi&ration with respect to 
an invention of: 
Lester N. Wright, Long Beach; Peter R. 
Barker, Lawndale, Calif. 
121 1 AppE. No. 720,041 
[221 Filed Apr. 10, 1368 
1451 Patented Feb. 16,1971 
References Cited 
UNITED STATES PATEN'TS 
811 964 Sikorra ......................... 
10/1964 Grindheim etai .  ........... 
411 945 Smith ................... ........ 
611965 Farrar et  aI. .................. 
811966 Davis et  al. .................. 
1 111964 Johanson ...................... 
10/196S Dittrich ........................ 
Primary Examiner - William E .  Kar;,m 
Attorneys-D. E .  Leslie, J .  H. Wardcn and G T blcCov 
-- 
[541 VPBROPIEONOCAIRDHbPGWAPH 
3 Claims, 3 Drawing Figs. ABSTRACT: Apparatus is disclosed far r n ~ ~ i t o r i n g  cardiac dynamics comprising an extremely :ow weight and small 
I 521  U+S.Ci ........................................................ P28/2.05 volume piezoelectric microphone with ar? a~nplifier having 
[5 1 1 b b .  CI ......................................................... A6Pb 5/02 high input impedance for high sensitivity and low frequency 
1501 Field oPSearcL ............................................ 12812.05; response in a dynamic range of from about 2 to 2.006; cycies 
179llst.; 330/28, 104 per second. 
3,563,232 
1 2 
VIBROPWONOCARDIOGRABW DESCRIPTlON OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, a low mass, srnali: volbme 
ORIGIN OF INVENTION piezoelectric microphone 10 is shown coupled to a reco~ de* 
5 11 by an amplifier comprising an N-channel field-effect 
The invention described herein was made in the per- transistor Q, for high input impedance, a PNP jucctaon 
formance of work under a NASA contract and is subject to the transistor Qe for voltage amplification and an NPR*! gu:icteun 
provisions of section 305 of the National Aeronautics and transistor Q for coupling into a low rlapue rrnpet'ance an the 
Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 recorder 11. The piezoelectric microphone 10 rs z type C45W 
U.S.C. 2457). 10 manufactured by Shure Bros., Inc., of Chlcaga, IIE Howeve* 
other low mass,small volume piezoelectric iacrophones r n q  
BACKGROUND OF THE INVENTION be used to equal advantage in accordance wsth the feschv:~cs 
1. PieEd of the Invention of the present invention. - 
This invelltion relates an apparatus for monitoring car- The source electrode of transistor Q,! is biased by a resssror 
disc dynamics referred to herein after as a vibrophonocardio- 15 12 connected to ground while the drain electrode is biased by 
graph (vPC), and more particularly to such apparatus using a resistor 13 connected to a source of positive potential (16  tc 
an low weight and small volume piezoelectric 9 DC). The gate electrode is then biased by a pair of sesismss 
microphone with an amplifier having high input impedance 14 and 1s connected in series to the source of positive paten- tial. The output signal of the microphone 10 is coupled by 1; for high sensitivity and low frequency response in a dynamic 20 
capacitor 16 to the gate electrode of the transistor Q,. A iow 
range of from about 2 to 2,000 cycles per second. 
2. Description of the Prior Art noise coaxial cable about 2 feet long is employed between the 
microphone 10 and the capacitor 16 for convenience, but Various vibrophonocardiographic sensors have been 
other lengths may be used. The amplified and phase-invertcri devised in the past using such transducers as capacitive 
output of the transistor Q, is taken from the drain eirctrode 
transducers and 25 thereof and connected directly to the $ase electrode 0f the Whereas the capacitive transducer has been found to have a p ~ p  transistor Q* which has its connected directly ti) 
good range and for use in a vibro~honocar- the source of positive poten&], and i~ collector connected to 
diograph, such a transducer may be used to advantage only in the ground through a resistor 17 in series with the resistor 12. 
a laboratory environment because of its weight and size. A 30 Accordingly, the transistor Q, is collnected in a comms.i7 
crystal transducer has been found to have an acceptable emitter configuration for voltage amplification. 
dynamic range but, although it is smaller and therefore more The amplified voltage signal derived from the coSlectc,r 01 
adaprable to monitoring a subject in a dynamic environment the transistor Q2 is coupled to the base of the NPN transisti~r 
than a capacitive transducer, the mass was found to be too Q, when has its collector biased by a resistor 68 cunncctcd to 
large for best results. Crystal microphones suggested by the 35 the source of positive potential, its ernittea biased to ground 
general disclosure in U.S. Pat. No. 3,030,946 relating to a car- through a resistor 19, and its base biased by voltage-dividing 
diac diagnostic method would also give acceptable results, but resistors 20 and 21 connected between the source of positivr: 
again only with a mic, ophone having relatively large mass and potential and ground. 
volume. F[,: monitoring cardiac mechanical of an ac- The output signal of the amplifier is coupled from :he 
tive who may also be in a dynamic environment, it is 40 emitter of transistor Q3 to the recorder I I  by a capacitor 22 
irnpOfiant to reduce the inass and volume without sacrificing Thus, the transistor Qa functions as an emitter Co!?ower fo r  
performance, particularly low frequency response. matching the low input impedance of the recorder 1 8 .  if tht: 
recorder does not have low input impedance, the ccnfigura- 
OBJECTS AND SUhaMARY OF THE INVENTION tion of the transistor Q, may be modifiecl or eliminated. 
45 To increase the input impedance of the first stage, transistor 
A primary object of the Present invention is to provide an Q,, to about 1,000 x 106 ohms, regenel-aeiuir feed!-jack is 
improved vibropho~!ocardiograph. vided from the collector of the second stage, t:;:,nsi.stor Q,, 
Another ol-?iect of the invention is to provide a through the resistor 17 and a capacitor 29 conalccted to a 
vibrophonocardiographic sensor of low weight and small junction between resistors 14 and 15. A resistor 26 fcpnneclod 
vo~ume without sacrifice to sensitivity and frequency respon:r 50 between that junction and ground reduces the feedback s i g ~ a :  
in the dynamic range of interest. being applied to the gate of the transistor Q, to the desire? 
Still another object is to provide a vibrophonocardio~aph level. 
with low voltage therein for safe use on human subjects. Since the collector of the transistor Q, is biased through rhe 
These and orber objects are achieved in apparatus for moni- 55 resistor 17 connected to the source electrode of the tratzsiseo,* 
toring cardiac dynamics and other cardiovascular activity by Q , ,  it should be appreciated that feedback current is aiso 
the use of a low weight and small volume piezoelectric being conducted through the resistor 12. However, that feel- 
microphone with an amplifier having high input impedance. A back current is a t  a higher AC level than the AC currcni 
fieldeeffect transistor (FET) in the input stage of the amplifier through the transistor 0,. In that manner, degenerative f e d -  
provides very high input impedance. Even higher impedance 60 back is also provided to the first stage, transistor Q, for  stabili.. 
is realized through regenerative feedback. For stability, 'y. 
degenerative feedback is also provided. Although the primary function of the second sta,se, 
~h~ novel features of the invention are set forth with par- transistor Q,, is to provide feedback to the first stage, its 
ticularity i n  :he claims, The invention will best be secondary function is to provide voltage ampiifleation, bile 
from the description when read in con- 65 since the piezoelectric microphone 10 provides a signal of E:I/_ 
junc",on with the accompanying drawings. ficient amplitude for the recorder EL 1 which may be, for exam- 
ple, a magnetic recorder or an oscillogsaphic ?ecc.rder which 
5 R E F  OESCRIPTlON OF THE DRAWlNGS is normally provided with a high gain preamplifier, vc~l tsgc  
ampiification is not important. hcoiplrasg capa;n:~r i l - L 
FIG. 1 is a schematic diagram of a preferred embodiment of 70 the DC component of the signal transmstted Crom tllr ~ e c r , ~  
the anbentlon stage, transistor Q,, to the emltter-follt>wea stapt, t r a?sAs i~ r  
FlG. 2 iq a typical recording of a cardlac cycle produced Q,. 
with a \.ibrophonocardiograph as shown In FIG I. In practice, the microphone 10 1s b o d e d  to ar aiumanmm 
FIG. 3 is a Gongltudinal section of a p~ezoelectric mounting plane 28 (shown partially brokr;aa away n FIG P~ 
mmcrophone in the preferred embodiment on FIG. 1. 75 The assembly is then placed externally isn the cheat of z s ~ b  
3,563,232 
3 4 
jbcr 3 ~ 7  ZT wedl t>e pomt ofmaxnmum ~rnpulse created by the zerconate-titanate ceramic bar and the total weight of the 
-I- r , i  rn- :ktr'!:31 1~ I ~ I F ~ ,  using a suntable adhesive between mtcrophone is less than 2.8 grams. However, it should be un- 
thi: -12 y1 X ~ L  piate rrid Pie subject. or an adhesive in the same derstood that any piezoelectric element in a suitable enclosure 
-..xnne- iiih ail eqa.;:zc bandage or rubber strap, or wtth only may be employed. This particular, commercially available, 
,- e a*r ,ac 'A~c U- rubber strap For best results however, 5 piezoelectric microphone is here described in some deta~l only 
I 9 - .,7 3 ines 112 !co?tact ccment) and rubber strap or elastic to provide a more complete understanding of the embodiment 
i d r  J d h ~ ~  c be used Wash that attachment of the low lllustrated in FIG. li actually reduced to practlce with com- 
- ,sL ri,i ioliipre rn~crophone to the subject, and the high ponents of the follow~ng types and values 
J* ,rnd>eadi.cc ~inplifier couplang the microphone to a 
yb< r ;: 3 (1.1e i.e~liencj response (iB db) Rom about 2 cy- Resistor 12 1 K 
L~ ;er $ COI f i  0 ~ b o u t  2,000 cycles per second IS achieved 
b Gi s r i ~ 1  / >jib Inysabency response wath a p~ezoelectric Resistor 13 2K 
7~( '3- 3~ '? ,~,JIT> low frequency response down to only 
&r:,~t 4" ctcies pea .iecond with a 140 megohm load ns made 
Resistor 14 560M 
- >  s blc 5) 1116 hlgner lnput impedance (about 1,000 15 Reslstor 15 5M 
n~:~cS-,ras) o" the amplifier coripllng the output of the 
n e7oc?e; rzc agacs,avaone BO to the recorder 11. The rnounl- Resistor 17 1K 
&re -Sale feeor, the transducer properly ortented for maximum 
$1 s v  1'5 cr 3 F I P  - urn nonse (response to artifacts) Resistor 18 100 
e *.si.; -g acv rb hL1G 2, a facssamile of a recording of a car- 20 
a a& c y h  rronlto*cd by the apparatus ~llustrated ln FIG. 1 Res~stor 19 16K 
~12aaiy 0'1 i ce- ponnts of Interest such as onset of Res~stor 20 130K 
1.0 olu~etrs ,  cor,rraciaon at poant 31, openlng of sern~lunar 
i e I 11 32, 7;ipld ejectaon between polnts 32 and 33, 25 Resistor 21 220K 
rc t l ~ s e d  ,jel:lon i ~ t w e e n  points 33 and 34, and closure of 
sd orlaunaF vaives zr posnt 35. FOP better analysts of the func- Res~stor 26 5 1 K 
r t i - ,  and acadll!mn of the heart, an electrocard~ogram may be 
r i~,)rde,* S I ~ ~ ~ ~ ~ I S ~ P ~ ~ O U S B ~ ,  as may other parameters Slnce Capacator 16 2.2mf. 
these ,s \ubstantiaiiy no delay ~n the production of the 30 Capacitor 22 100mf. 
~b-np!,orocdsa~apr~irn relattve to the electrocardiogram, 
d r ~ e t  C( ~,pa r s~or  and correlatnon can be made of the Capacitor 25 100mf. 
-r .rde, ugnnis 
Jeairizd, the vabrophonocardiographic signal may be fil- Capacntor 27 5mf 
I ~ ~ : h :  provide only a record of the frequency range of in- 35 
se--st, go: instance 3 no 20 cycles per second. If so, a sl~ght Transistor Q, FE 202 
i ~ - , - y  :P ~ r s a l u c ~ ~ g  the record of the filtered vnbrophonocar- 
B, ojrapbi .. signal miiy be lwtroduced as described In a paper Transistor Q, 2N 1 132 
. - I ze rcce,-ct w h x h  led to the present invention tltled "- Transnstor Q, 2N 697 
" rg?t Ro.,ear:"I Pro :ram - V l l l  Study of Vibrophonocar- 40 
o;-apb 1 Technlgbes for ~~~i~~~~~~ cardiac It should of course, be apprectated that many modifications 
^ 4 -  2 r L , : ,  ~n rnc F i~ ~t Er3vsronment" pubinshed by the inven- may be made without departrng from the true spirit of the tn- 
.$ ,n Loope* .,: oq .vr Il,h .I Cejeneano, D. and D M. wa~-  ventmn For instance, an insulated gate, field-effect transistors 
r 1% In ~ s r c \ ~ > ~ c i ;  Wed~cane, iiol 38, No 6 (June, 1967) at (commonly referred to as the MOS type) may be found to 
; ipcs 5 -?c to 5 3 45 have a sufficiently h~gh  input tmpedance for the pxezoelectr~c 
-- ,I: 11; crophoai  10 ~llustrated In a longitudinal section in microphone selected If not, feedback may be employed to In- 
F I ,  3 z-na,s:s 3s n. metal enclosure &) about 1 inch long, a crease its rnput ampedance, in addition, any other utll~zatlon 
- ,, &c- 3 at I F C ~  iilde and a tenth of an inch th~ck,  it has a means may be employed instead of a recorder, such as a com- 
, ?* o a , ~  sss 4, i ~ ( ~  a back vent $2 The front of the enclo- puter In the event on-l~ne analysls of the cardiac dynamics is 
s r 211' 7)s por:-an urroundang the openlng 41 raised suffi- 50 des~red. 
1: L 3 .y a r B >w : h ~  lyiomtnng plate 28 to be bonded to the face The piezoelectric microphone illustrated ~n FIG 3 IS suffi- 
-" -- - -7oqTi.sre ? plate 0 0: 56 rnches th~ck  pernits a Wush ciently ~nexpensive to warrant d~sposlng of ~t after use In a 
. r ; suclj t.pia~ r h r n  the rno:Enrilr\g piate is attached to the contaminated environment, and the entlre apparatus IS suffi- 
q-ia*cas hc *en\~tj e  :<ice of the mscrophone enclosure 40 sur- 55 clently inexpensive to be considered d~sposable It 1s also 
.i, ; ' e opening 4 1 wsl\ be against the subject suitable for use in extreme environments, such as In flight at  
qe v LC 2 apra agm 43 rs attached lnslde the front face of altitudes as high as, say, 40,000 feet. 
cib. t ~: lc . ,~ ie  aind .. a frce enii of an elongated piezoeiecrrlc Although partxcular embod~ments of the invention have 
e e-.Gat .4, j r  b: 7 a*op 45 of epoxy resnn The base of the been described and illustrated herein, ~t 1s recognized that 
P 44 f i r d  attached to a deelectrmc block 45 ce- 60 mod~ficatlons and var~at~ons may readily occur to those skilled 
- I C V ~ G  0 t k  enci :ag r.: s0 Thus, both ends of the element 44 an the art and consequently it is intended that the claims be In- 
& ~ I Z C ~ ; I C Z ' I ~ I  s ~ ' ~  ted so that as it 1s subjected to stress and terpreted to cover such modifications and equivalents 
++i.i~l- n cipcr c tc moaann of the daagram, an electrostatic We clam 
~ 3 ~ ~ 2 : ~  ~lc/etopetl  across it an a manner known to those 1 Apparatus for monltor~ng cardiac dynamics of a subject 
r tL  I d a*  1 . i ~  a%+ rhe vent 42 allows free lnotnon of the d ~ a -  65 comprising: 
,ran .; pieveil", the pressure in back of the dilaphragm a piezoelectric microphone of a total we~ght of the order of 
""3-1 llrcreas i ~ g  2s he dnaphragrn nroves toward the back). To 1.8 grams having an enclosure of a total volume of the 
e-,li,*ice %e 3 3 ~ ~ 2 ~ 4  nqd stram in response to a given displace- order 25X1CP cubic inches w~th  an opening In one face 
me- 01 : 16 ~ t 1 i p b r 3 p  43, a depressed portaon 46 is provided for receiving acoustlc energy In the form of air pressure 
s i . ~  i"J * laik o; tPe cnclesure 40. The element is suibbPe 70 waves and adapted to be placed externally on the chest of 
w*itcd w +B i dw /ec t~~c  rnaterjal to prevent shorting she electro- said subject with said openlng agaanst sand subject, said 
s*a c dyagz  ~ e ~ t l o p e d  ehsrenn at the poant of contact mncroghone havrng. 
(~irresse"Jnr\ion 46) with the enclosure 4BB Leads 47 and a paezeelectric element lnside of said enclosure and away 
dd  arc ea-neciera ;c- :hc eIen1c3nt 44 through the dielectric from any contact with said subject through s a ~ d  open- 
bract " '1  , p~o;.oelectasc eiement 44 as preferable a lead- 75 ~ n g ,  said element having one end secured to said enclo- 
3,563,232 
5 6 
sure and another end free to move relative to said en- input terminal of said utilization means. 
closure; 2. Apparatus as defined in claim 1 including means Birr 
a flexible diaphragm attached inside said enclosure to maintaining said piezoelectric microphorie stable ooi said sub-  
separate said element from said opening; ject in a position oriented for rnaximum response :c cardiac 
means anaching an area of said diaphragm directly over 5 activity. 
said hole to said free end of said element; and 3. Apparatus as defined in claim 2 wtnerein s a i ~  microphone 
an output terminal connected to said element to &bin enclosure has a raised portion around said opecl:.ig, and said 
piezoelectric signals in response to air pressure waves means for rnaintainlng said piezoelest?-ic rnicrru~!>:>ne stable 
against said diaphragm; on said subject conaprises a mounting plate surrounding said 
u.hil&al:lon means having an input terminal adapted to 10 raised portion, said plate being bonded ao said riiicrtiphanc in 
signals which vary as a function of said a position substantialEy flush with the top :3f said raised por- 
cardizc activity; and tion, whereby a maximum of energy prodcced by cardiac zc- 
an amplifier having an input stage with a very high input im- tivity is coupled into said piezcslectric rnicrophcre throaigii 
pedarnce of the order of 1,000 megohms coupling said said opening whed said plate is secured against said sribfect. 
output terminal of said piezoelectric microphone to said j5 


Vibrophonocardiograph Patent

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