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TECHNICAL FIELD The present invention relates to a transducer, and more particularly to a
biomedical device that monitors the acoustic output from the heart or respiratory system of a
living body, etc., with high blocking properties to block external acoustic noise and false
electromagnetic signals. It relates to a transducer. In clinical situations, such as experiments on
the function of the prior art heart, it is often necessary to monitor the acoustic output from the
heart on the outer surface of the thoracic cavity of a living being using a biomedical transducer
or the like. However, since the cardiac acoustic signal generated from the heart is very weak in
this way, its measurement is generally considered to be difficult, and the acoustic signal
generated due to the body movement of the living body and the noise propagating in the air
(noise There is a problem that it often becomes complicated by the interference generated due to
Furthermore, external electromagnetic noise collected by the skin of the living body or by the
indirect vtil line may generate an erroneous signal that interferes with the operation of the
transducer. Biomedical transducers are also used to monitor the respiratory system of the body.
At this time, the transducer is placed between the sternum or at a portion of the clavicle to detect
an acoustic signal corresponding to the respiration of the living body. This type of transducer is
substantially the same as that used to monitor a circulatory system, and is likely to suffer from
the same problems as described above. The above problems have not been effectively solved by
conventional transducers that monitor acoustic signals in relation to cardiac function and
respiration. In a conventional transducer, in connection with the relatively light weight, an
operation for preventing an error in detecting an circulatory movement of a chest of a living
body, that is, an acoustic signal corresponding to a function of a heart or a respiratory system.
The stability can not be obtained sufficiently. In addition, in such a conventional transducer,
subtle movements of the operator's hand may be erroneously detected as an acoustic signal from
the heart or respiratory system. Furthermore, there is a risk that an external acoustic signal
transmitted from the rear of the transducer body may be detected. In order to effectively solve
the problems as described above, the transducer has a very high sensitivity in a wide frequency
band to the acoustic signal propagating in the tissue, while the movement of the living body or
the air The sensitivity to other acoustic signals resulting from propagation noise etc. and
electromagnetic interference must be lowered. It is also important that such transducers be easy
to clean and disinfect.
The above-mentioned requirements have not been fulfilled by the conventional transducers.
SUMMARY OF THE INVENTION The biomedical transducer of the present invention is highly
sensitive to tissue-borne acoustic signals, but sensitive to body movement of the living body and
airborne and electromagnetic noise from the outside. By solving the problem, the abovementioned conventional problems are solved. The transducer of the present invention is provided
with an acoustically sensitive thin acoustic diaphragm device mounted on a rigid and easy to
operate metal housing. The acoustic diaphragm system includes a circular plate-shaped
deformable piezoelectric diaphragm that provides electrical polarization and electrode placement
such that the phase of the output signal from the transducer is different in relation to its origin.
In the housing, an acoustic diaphragm device is arranged such that the output signal is
completely isolated from the external electromagnetic field. In addition, since the housing of the
transducer is relatively heavy, the stability of the operation necessary to prevent accidental
detection of body movement is obtained. In addition, the flexible handle attached to the housing
places the transducer in the desired position, thus preventing vibration from being applied to the
acoustic diaphragm device due to the caretaker's carelessness during transducer movement. Ru.
The housing of the transducer is preferably made of metal such as stainless steel which is easy to
clean and disinfect. The biomedical transducer 10 of this embodiment is shown in FIGS. 1 to 4.
FIG. The transducer 10 includes a diaphragm device 12 described later, and a housing 14 having
a hole for receiving the diaphragm device 12 and accommodating an electrical wiring connected
to the diaphragm device 12. The housing 14 is a generally cylindrical metal part, the upper part
of which is fixed to the lower surface of a relatively heavy metal disc 16. The diaphragm
mounting device 12 is provided at the lower portion of the housing 14 as shown in FIG. 1, and
the electrical components thereof are accommodated in the holes formed in the housing 14. A
flexible handle (knob) 18 is attached to the upper surface of the metal disk 16 as shown in FIGS.
1 and 2 so that the vibration caused by the operator's carelessness when operating the
transducer 10 is erroneous. Detection as an acoustic signal is prevented. The housing 14 and the
metal disc 16 are made of metal suitable for disinfection, such as stainless steel.
Also, the flexible handle 18 is composed of a spring covered with a soft synthetic resin, a flexible
metal, or a rubber material. In the present embodiment, since the metal disk 16 has a weight of
about 1 kg and has a weight that can sufficiently function as a mechanical low pass filter by
itself, the filter means of the present embodiment is used. Function. In addition, the handle 18
also functions as a mechanical filter because it blocks the propagation of inappropriate acoustic
signals generated when the operator holds the transducer 10 in contact with the living body. The
weight of the metal disk 16 according to the present embodiment is set so as to obtain excellent
operational stability and not to cause excessive discomfort to the living body. If the transducer
10 is located at the chest of a living being, its resonant frequency is well below the lowest
frequency in the response curve of the transducer 10. Therefore, the heavy metal disk 16
suppresses movement of the transducer 10 and stabilizes the mechanical positional relationship,
so that the signal in the desired frequency range increases in the output signal of the transducer
10. Further, the metal disk 16 has a function of reducing the sensitivity of the transducer 10 to
the acoustic signal from the living body transmitted through the rear end (upper end) of the
housing 14 by its weight. That is, since the acoustic signal transmitted through the housing 14 is
suppressed by the relatively large weight of the metal disk 16, the vibration of the diaphragm
device 12 generated due to the acoustic signal is suppressed. Furthermore, the metal disc 16
prevents the vibration due to the contact of the operator's hand from being transmitted to the
transducer 10. Again, the combination of the weight of the metal disk 16 and the handle 18
forms a mechanical low pass filter that removes the acoustic signal from the handle 18. In FIG. 3
and FIG. 4, the diaphragm device 12 of the zero embodiment in which the diaphragm device 12
is shown in detail is a substantially circular metal plate provided with a circular thin plate-shaped
ceramic disc 22 made of ceramic. 20 are provided. When the plate 20 vibrates in response to the
acoustic signal, the vibrational motion is converted by the piezoelectric disc 22 into an electrical
output signal corresponding to the acoustic signal. The transducer 10 to which the piezoelectric
disk 22 is applied in this manner is generally known as a flat transducer generally sold under the
trade name "Biomorph @", and the configuration of such a transducer is generally known.
belongs to.
However, in the present embodiment, a novel device is provided in which an electrode is formed
on the piezoelectric disk 22 so as to function as a transducer having a differential signal output.
The transducer 10 is totally shielded from an external electromagnetic field as described later. A
pair of semicircular electrodes 24 and 26 are fixed to the upper surface of the piezoelectric disk
22 as shown in FIG. 3, while a circular electrode 28 is formed on substantially the entire lower
surface as shown in FIG. Is fixed. The pair of electrodes 24 and 26 have opposite polarities to
each other, for example, the electrode 24 is an anode and the electrode 8i 26 is a cathode, and
the piezoelectric disk 22 is a portion located directly under the electrodes 24 and 26. Are
configured to polarize with different polarities. The direction of the polarization characteristic of
the piezoelectric disk 22 is indicated by an arrow in FIG. プレート20. The plate-like members
constituting the diaphragm device 12 such as the piezoelectric disk 22 are usually adhered to
each other by an epoxy adhesive. The circular electrode 28 located inside the diaphragm device
12 is electrically bonded to the plate 20 via the conductive epoxy layer 30. Here, a typical shape
of the plate 20 is that its thickness dimension is about 0.10 inch and its diameter dimension is
about 1.25 inch, and the piezoelectric disk 22 is, for example, 0.01 inch in thickness dimension
and The diameter dimension is 1.0 inch. Further, in the present embodiment, the electrodes 24
and 26 and the circular electrode 28 have a thickness dimension of about 0.. (14) A 1-inch silver
printing electrode. Since the resonant frequency of the output signal from the transducer 10 is
influenced by the dimensions of the parts set as described above, the bandwidth of the spectrum
of the output signal is also changed by the dimension. Therefore, by setting each part to a
specific size, a specific resonant frequency corresponding to that size can be obtained.
Incidentally, in the diaphragm device 12 set to the above-mentioned size, a high resonance
frequency of about 7 ratio can be obtained. FIGS. 5a and 5 schematically show the electrical
connection of the diaphragm device, and FIG. 5a shows the circuit configuration of a general
conventional transducer, and FIG. The circuit structure of the transducer 10 of an Example is
shown. The dashed lines in FIGS. 5a and 5 represent the electrical shields generated by a suitable
housing, such as the housing 14 in FIGS. 1 and 2, respectively.
The circuit shown in FIG. 5a constitutes a flat transducer having a pair of electrodes 24 'and 26'
adhered to the upper and lower surfaces of the piezoelectric disc 221, respectively. The anode
side electrode 24 'is connected to a coaxial cable 32' which is an internal conductor connected to
an amplifier 34 '. In the transducer 10 of this embodiment, as shown in FIG. 5, the first and
second electrodes 24 and 26 are bonded on one side of the piezoelectric disk 22, and the third
electrode 28 is bonded on the other side. ing. As described above, portions of the piezoelectric
disk 22 located directly below the electrodes 24 and 26 are configured to be polarized in
opposite directions when subjected to the same strain. Thus, each electrode outputs a signal
having a unique phase, which is used to block electromagnetic noise as described later. The
circuit shown in FIG. 5a is provided with the same sensitivity as the circuit shown in FIG. 5, but
the function to remove the collected electrical noise by each component of the transducer is not
prepared. The shield formed by the housing surrounding the piezoelectric disk 221 and the
coaxial cable 32 'may lower the amplitude of the radiation noise captured by the signal
electrodes and the signal leads connected thereto but may not eliminate them sufficiently. On the
other hand, in the transducer 10 of this embodiment, two signals having a phase difference of
180 degrees from each other are generated. These two signals are shielded by the housing 14 of
the transducer 10 and the shielded two-wire cable, and their phase difference is 180 degrees
while the phase difference of the incorporated radiation noise is zero. is there. Therefore, when
the above two signals are supplied to the differential input amplifier 34 which functions as the
amplification means of the present embodiment, the desired signal is amplified and unnecessary
noise is removed. The operation of the transducer 10 will be described with reference to FIGS. 3
and 4. When the transducer 10 is in close contact with the tissue of the chest of a living body, an
acoustic wave from the heart of the living body strikes the plate 20 to generate a minute force in
a direction orthogonal to one surface of the diaphragm device 12. It is Since the peripheral
portion of the diaphragm device 12 is clamped within the housing 14, the above-described force
generated due to the acoustic wave causes the central portion of the diaphragm device 12 to be
on the inner and outer peripheral sides with respect to the peripheral portion. Because the micro
displacement of the diaphragm device 12 causes bending of the metal-ceramic layer, the
piezoelectric disk 22 is alternately stretched and compressed in its radial direction.
Here, since the piezoelectric disc 22 is of the piezoelectric type, an electrical signal generated by
radial force is collected by the electrodes 24.26 and supplied to the differential input amplifier
34 via a suitable intermediate connection cable. . As mentioned above, since the portions of the
piezoelectric disk 22 located directly below the electrodes 24 and 26 are polarized in opposite
directions, respectively, the signals generated by the electrodes 24 and 26 have the same
amplitude and Because it has a 180 degree phase difference, a differential output is generated
and used to block unwanted electromagnetic interference. That is, in the present embodiment,
the plate 20 functions as an acoustic signal transmission means, and the piezoelectric disk 22
functions as a piezoelectric diaphragm. As described above, according to the present
embodiment, the sensitivity to an acoustic signal transmitted through tissue is very high, and the
sensitivity to an inappropriate acoustic signal and electromagnetic interference is An effective
biomedical transducer IO can be provided with the property of being very low. The above
description is merely an example of the present invention, and the present invention can be
variously modified without departing from the spirit of the present invention.
Brief description of the drawings
FIG. 1 is a perspective view showing a transducer according to an embodiment of the present
FIG. 2 is a side view of FIG. FIG. 3 is a perspective view showing the diaphragm device of FIG. FIG.
4 is a side cross-sectional view showing in detail the positional relationship with the electrodes
on the piezoelectric disk in the diaphragm device of FIG. 3; FIG. 5a is a schematic diagram
showing the circuit configuration of a conventional transducer. FIG. 5 is a schematic view
showing a circuit configuration of a transducer according to an embodiment of the present
invention. 10 Nd lance sensor 12: diaphragm device (acoustic diaphragm device) 14: housing 16:
metal disk (filter means) 18: handle 20 nibrate (acoustic signal transmission means) 22:
piezoelectric disk (piezoelectric diaphragm) 24: electrode (first) Electrode: 26: Electrode (second
electrode) 28: Circular electrode (third electrode) 30: Conductive epoxy layer 34: Differential
input amplifier (amplifying means) Applicant: Chorin Electronics Co., Ltd. FIG.
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description, jps63125244
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