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Transducer for sensing actual or simulated body sounds

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Transducer for sensing actual or simulated body sounds

A transducer system is disclosed for detecting actual or simulated body sounds. An audio signal generation and detection system is disclosed for the purposes of simulating the medical examination of a patient or simulating the listening of sounds seeming to emanate from a live or inanimate body. A signal generator sets up a voltage potential at an electrode physically attached to the body, or electrically connected to a body, thereby setting up a voltage potential on a surface area of the body. An electric field potential sensor or a capacitive electrical sensor placed in proximity to the electrode or body surface then detects the voltage potential. The signals produced by the signal generator can represent heart, lung, bowel or other sounds and the electrical sensor can take the physical form of a listening device such as a stethoscope, thereby creating a simulation of listening to body sounds for medical diagnostic purposes.
Related Terms: Audio Bowel Electrode Stethoscope Transducer Animate Simulation

USPTO Applicaton #: #20130028433 - Class: 381 67 (USPTO) - 01/31/13 - Class 381 
Electrical Audio Signal Processing Systems And Devices > Stethoscopes, Electrical

Inventors: Clive Smith

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The Patent Description & Claims data below is from USPTO Patent Application 20130028433, Transducer for sensing actual or simulated body sounds.

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This application is a continuation-in-part of U.S. patent application Ser. No. 10/747,863 filed Dec. 23, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 10/730,750 filed Dec. 8, 2003, which is a continuation of U.S. patent application Ser. No. 10/328,768 filed Dec. 23, 2002, now U.S. Pat. No. 6,661,897, which is a continuation in part of U.S. patent application Ser. No. 09/431,717 filed Oct. 28, 1999, now U.S. Pat. No. 6,498,854, all of which are incorporated herein by reference in their entirety.


The present invention relates to sensing body sounds and simulated body sounds, and to acoustic-to-electrical and electrical transducers used for sensing body sounds or simulated body sounds, especially in stethoscopes.


Stethoscopes are widely used by health professionals to aid in the detection of body sounds. The procedures for listening to and analyzing body sounds, called auscultation, is often difficult to learn due to the typically low sound volume produced by an acoustic stethoscope. Electronic stethoscopes have been developed which amplify the faint sounds from the body. However, such devices suffer from distortion and ambient noise pickup. The distortion and noise are largely due to the performance of the acoustic-to-electrical transducers, which differ in operation from the mechanical diaphragms used in acoustic stethoscopes.

Acoustic stethoscopes have been the reference by which stethoscope sound quality has been measured. Acoustic stethoscopes convert the movement of the stethoscope diaphragm into air pressure, which is directly transferred via tubing to the listener\'s ears. The listener therefore hears the direct vibration of the diaphragm via air tubes.

Existing electrical stethoscope transducers are typically one of three types: (1) microphones mounted behind the stethoscope diaphragm, or (2) piezo-electric sensors mounted on, or physically connected to, the diaphragm, or (3) other sensors which operate on the basis of electro-mechanical sensing of vibration via a sensing mechanism in mechanical contact with the diaphragm placed against the body

Microphones mounted behind the stethoscope diaphragm pick up the sound pressure created by the stethoscope diaphragm, and convert it to electrical signals. The microphone itself has a diaphragm, and thus the acoustic transmission path comprises stethoscope diaphragm, air inside the stethoscope housing, and finally microphone diaphragm. The existence of two diaphragms, and the intervening air path, result in excess ambient noise pickup by the microphone, as well as inefficient acoustic energy transfer. Various inventions have been disclosed to counteract this fundamentally inferior sensing technique, such as adaptive noise canceling, and various mechanical isolation mountings for the microphone. However, these methods are often just compensations for the fundamental inadequacies of the acoustic-to-electrical transducers.

The piezo-electric sensors operate on a somewhat different principle than merely sensing diaphragm sound pressure. Piezo-electric sensors produce electrical energy by deformation of a crystal substance. In one case, the diaphragm motion deforms a piezoelectric sensor crystal which is mechanically coupled to the stethoscope diaphragm, and an electrical signal results. The problem with this sensor is that the conversion mechanism produces signal distortion compared with sensing the pure motion of the diaphragm. The resulting sound is thus somewhat different in tone, and distorted compared with an acoustic stethoscope.

Other sensors are designed to transfer mechanical movement of the diaphragm, or other surface in contact with the body, via some fluid or physical coupling to an electromechanical sensing element. The problem with such sensors is that they restrict the mechanical movement of the diaphragm by imposing a mechanical load on the diaphragm. Acoustic stethoscopes have diaphragms that are constrained at the edges or circumference, but do not have any constraints within their surface area, other than the inherent elasticity imposed by the diaphragm material itself. Thus placing sensors in contact with the diaphragm restrict its movement and change its acoustic properties and hence the sounds quality. Capacitive acoustic sensors have been disclosed and are in common use in high performance microphones and hydrophones. A capacitive microphone utilizes the variable capacitance produced by a vibrating capacitive plate to perform acoustic-to-electrical conversion. Dynamic microphones that operate on the principle of a changing magnetic field are well-known. These devices typically operate by having a coil move through a static magnetic field, thereby inducing a current in the coil. Optical microphones have been disclosed, which operate on the principle that a reflected light beam is modified by the movement of a diaphragm.

A capacitive, magnetic or optical microphone placed behind a stethoscope diaphragm would suffer from the same ambient noise and energy transfer problems that occur with any other microphone mounted behind a stethoscope diaphragm. A unique aspect of the present invention is that the stethoscope diaphragm is the only diaphragm in the structure, whereas existing microphone-based solutions comprise a stethoscope diaphragm plus a microphone diaphragm, resulting in the inefficient noise-prone methods described previously.

The present invention provides both direct sensing of the diaphragm movement, with the diaphragm making direct contact with the body, while at the same time avoids any change in acoustic characteristics of the diaphragm compared with that of an acoustic stethoscope, since the sensing means does not mechanically load the diaphragm. This results in efficient energy transfer, and hence reduced noise, with acoustic characteristics that are faithful to that of an acoustic stethoscope diaphragm. The present invention discloses three basic embodiments: (a) A capacitive sensor, (b) a magnetic sensor, and (c) an optical sensor.

Body sound transducers and stethoscopes in particular have been plagued by pickup of ambient noise in addition to body sounds. The chestpieces of acoustic and electronic stethoscopes must typically be sealed so that air does not leak to the outside atmosphere. Thus stethoscope chestpieces have closed cavities, which result in standing waves and acoustic resonance within the cavity. Such acoustics tend to exacerbate the effects of ambient noise which reverberates in the chestpiece. The present invention provides openings in the transducer to mitigate this problem. Diaphragm dynamics and tension also affect transducer response and the present invention provides a means to make such dynamics adjustable.

Noise canceling methods have also been applied to body sound detectors and capacitive transducers in general. Noise canceling must be applied to signals received from the transducer. The present invention provides for the cancellation of noise signals at the capacitive transducer electrodes prior to electronic amplification.

Learning auscultation has always been a difficult process. Body sound simulators have been developed, such as “Harvey”, which have acoustic and mechanical sound sources within a manikin so that students can learn sounds and the locations at which they are typically found. The present invention provides for the simple adaptation of the body sound transducers herein and the capacitive transducer in particular, to be used in conjunction with a body sound simulator that has no moving parts, and does not require acoustic signal generation which is subject to dispersion and signal loss within the manikin body. Such simulation techniques can be applied to other applications in education and entertainment wherein electrodes placed on a body or object produce signals which can be detected by minimally-modified body sound transducers.



According to one aspect of the invention, there is provided a acoustic-to-electrical transducer for detecting body sounds, the transducer comprising (a) a capacitive to electrical conversion means, or (b) a magnetic to electrical conversion means, or (c) an optical (light) to electrical conversion means.

The capacitive to electrical conversion means comprises: a diaphragm having an electrically conductive surface, the diaphragm being mounted in a housing such that the diaphragm can contact a body for body sound detection; a conductive plate substantially parallel to the diaphragm, mounted within the housing, the conductive plate being positioned behind and spaced from the diaphragm to allow diaphragm motion, the diaphragm and conductive plate being connected in the form of an electrical capacitance to electrical circuitry; and a capacitance-to-electrical signal conversion means to convert capacitance changes to electrical signals.

The magnetic to electrical conversion means comprises a diaphragm that is placed against the body, the diaphragm having magnetic elements such as a permanent magnetic surface or electrically-induced magnetic field due to a wire or printed-circuit coil, so that a magnetic field is set up that is subject to change by motion of the diaphragm. The conversion means additionally comprises a magnetic field sensing means to convert the magnetic field changes to an electrical signal. Thus diaphragm motion affects the magnetic field, the magnetic field changes an electrical signal, and acoustic to electrical conversion is achieved.

The optical to electrical conversion means comprises a diaphragm placed against the body, with a light path that can be modified by motion of the diaphragm. A light source transmits visible or infrared light to the diaphragm. The diaphragm reflects the light, which is then detected by an optical detector, and changes in the reflected light signal due to diaphragm motion are then converted to an electrical signal. Another embodiment of the optical method is transmissive, with the light beam passing through an optical element that moves with the diaphragm, the motion of the optical element causing changes in the light beam received by the optical detector.

The present invention provides an acoustic-to-electrical transducer means for the detection of body sounds, such as for use in a stethoscope. The term “body” in this specification may include living or inanimate bodies. Living bodies may include humans and animals, while inanimate bodies may include, by example only, buildings, machinery, containers, conduits, vibrating objects and the like. The sensor detects stethoscope diaphragm movement directly, converting the diaphragm movement to an electrical signal which is a measure of the diaphragm motion. Further amplification or processing of the electrical signal facilitates the production of an amplified sound with characteristics closely resembling the acoustic stethoscope sound, but with increased amplification, while maintaining low distortion. This is a significant improvement over the more indirect diaphragm sound sensing produced by the existing microphonic or piezoelectric methods described above. Since the diaphragm motion is sensed directly, the sensor is less sensitive to outside noise than the other methods described, and the signal is a more accurate measure of the diaphragm movement. In the case of the acoustic stethoscope, diaphragm movement produces the acoustic pressure waves sensed by the listener\'s ears, and in the case of the present invention, that same diaphragm movement produces the electrical signal in a direct manner, the signal eventually being used to drive an acoustic output transducer such as headphones, to set up the same acoustic pressure waves impinging on the listener\'s ears.

A fundamental advantage of the present invention is that diaphragm movement is not impeded by the acoustic-to-electrical conversion means, since there is a spacing between the diaphragm and other transducer elements. Therefore, the acoustic characteristics of the diaphragm are maintained, and the sound more closely resembles an acoustic stethoscope sound, which is familiar to the current user base of doctors, nurses and others. This is a unique aspect of this invention, in that other acoustic sensors do not require the amount of diaphragm motion required for a contact-type sensing device such as a stethoscope. Thus while other applications require only tens of microns of spacing, and the diaphragms typically move only a few microns when in use, this invention allows for movement of the diaphragm of more than 0.1 mm. Depending on the stiffness of the diaphragm, pressure against the body can result in 0.1 mm, 0.2 mm, 0.5 mm or even 1 mm of diaphragm displacement due to pressure.

The present invention discloses three sensing methods.

The first embodiment utilizes a capacitive sensing method. Capacitive acoustic sensors have been disclosed and are in common use in high performance microphones and hydrophones. However, the present invention uses the stethoscope diaphragm itself as one plate of the capacitive sensor which touches the body surface directly. This method of direct contact capacitive sensing of body sounds as described, is unique.

The sensor comprises a movable diaphragm with a conductive plane or surface, and a co-planar conductive surface (electrode or plate) placed behind the diaphragm, with a space or electrolyte between the two elements. The diaphragm\'s conductive surface, in conjunction with the second conductive plate, form a capacitor. Movement of the diaphragm due to motion or sound pressure modulates the distance between the diaphragm and plate, producing a change in capacitance. One unique aspect of the invention lies in the fact that the stethoscope diaphragm forms one plate of the capacitor.

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stats Patent Info
Application #
US 20130028433 A1
Publish Date
Document #
File Date
381 67
Other USPTO Classes
International Class


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