CROSS REFERENCE TO RELATED APPLICATIONS
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.
FIELD OF THE INVENTION
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.
BACKGROUND OF THE INVENTION
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.
SUMMARY OF THE INVENTION
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.
A feature of the invention is that the diaphragm, being the same element that makes contact with the body, is primarily sensitive to sounds emanating from the body, rather than sound transmitted through the air from ambient noise. By making contact with the body, the acoustic impedance of the sensor becomes matched to that of the body, rather than the surrounding air. Therefore, the capacitance change due to diaphragm motion is primarily due to body sounds, rather than overall ambient noise.
While a number of means are available for converting the capacitance variation to an electrical signal, the preferred embodiment performs this conversion by charging the capacitance formed by the diaphragm-plate combination to a high DC voltage, via a high resistance. This produces a somewhat constant charge on the capacitor. Movement of the diaphragm then produces a variation in the capacitance. If the capacitor charge is fixed, and the capacitance varies with time, a small AC variation in capacitance voltage is produced. This is sensed by a high-impedance amplifier, which is designed to detect the AC changes in capacitance voltage while avoiding rapid discharge of the capacitor.
A second method for detecting capacitance change is to employ the same diaphragm-plate capacitance in a high-frequency resonant or oscillation circuit, and detect changes in oscillation frequency produced by changes in the time constant of the capacitive circuit.
A third method of constructing a capacitive sensor, and sensing capacitance variation is via the use of an electret technique. This method requires that one or both of the plates of the capacitor formed by the diaphragm-plate be coated with a permanently charged material, such as an electret material, to create a permanent electric field between the plates. Since the plate, or plates, have a permanent electric field between them, the production of a high DC charge voltage is obviated, and voltage changes can be produced due to movement without the need for a DC charge voltage produced via a circuit.
A fourth method of constructing a capacitive sensor is to build the capacitive elements on a semiconductor substrate. In this case, the diaphragm contacts the body, there is a spacing for diaphragm motion, and the rear capacitive plate comprises the aluminum, copper or polysilicon conductive material as one of the layers of a semiconductor process. The fundamental principle of the invention still applies in that a diaphragm in contact with a body forms a movable capacitive electrode.
Any method of detecting capacitance change and converting such change to an electrical signal is encompassed by this invention. This invention therefore covers all such methods for detecting capacitance changes due to diaphragm motion.
It should be noted that while the preferred embodiment comprises a fixed plate behind the diaphragm, the invention includes methods whereby both plates are flexible and form a capacitance. In such a case, the basic principle applies whereby the capacitance varies due to sound pressure from the body, but the second plate is not necessarily rigid.
In the preferred embodiment, the fixed plate is mounted behind the diaphragm. In order to ensure acoustic isolation from external sounds, the fixed plate should preferably be mounted through a means which acoustically isolates it from the housing, or uses a means intended to prevent the fixed plate from vibrating. This is an important improvement which enhances noise isolation.
A variation of the basic principle of operation is to create two capacitors, by having the conductive diaphragm as described, with a conductive plate behind the diaphragm forming one capacitor, and a third plate behind the second, forming a second capacitor. The diaphragm and second plates are charged, while the third, rear plate is connected to an amplifier circuit. This two-capacitor method operates on essentially the same principle, whereby voltage across a charged capacitor varies in response to distance between plates, one plate being formed by the diaphragm. A further feature of the invention, is the method for constructing and producing the diaphragm. The diaphragm material must be flexible, and conduct electricity, in order to perform as a variable capacitor plate sensitive to sound pressure. This electrically conductive surface is preferably, but not necessarily, electrically insulated from the surface of the diaphragm that touches the body, for both safety and interference-prevention purposes.
A further feature of the preferred embodiment is the capacitive sensing circuitry connected to the diaphragm-plate capacitor. In the preferred embodiment, the circuit comprises two critical elements: (1) a high voltage DC bias generator with very high impedance, and (2) an AC amplifier with very high impedance to sense AC voltage changes without discharging the capacitor.
The invention also includes methods for signal amplitude control, DC charge voltage control to preserve battery power, and construction and manufacture of the capacitive sensor.
The first magnetic sensor embodiment of the invention comprises a diaphragm with permanently magnetized material adhered to or integral to the diaphragm, such that diaphragm movement results in changes in the magnetic field in the space behind the diaphragm. A magnetic field sensor is than placed at a distance from the diaphragm, but sufficiently close to detect changes in magnetic field due to diaphragm motion. The field sensor then converts magnetic field changes to an electrical signal. The diaphragm is housed such that it can be placed in direct contact with the body for body sound detection.
In another magnetic sensor embodiment, the diaphragm can be placed against the body, and has an electrical conductor on the rear side of the diaphragm such as a wire coil or printed circuit attached to the diaphragm or printed onto the diaphragm. A current in the coil sets up a magnetic field, or senses changes in a magnetic field produced by another coil or permanent magnet that is fixed behind the moving diaphragm. The diaphragm coil, or another magnetic field sensing means, converts changes in the magnetic field due to diaphragm motion to an electrical signal. Thus the coil can either produced the magnetic field and another circuit perform field detection, or the field can be produced by a separate magnet or circuit, and the diaphragm coil can perform field detection.
An optical sensor embodiment of the invention comprises a diaphragm which has optical elements, such as a reflective or transmissive plane integral to the diaphragm structure. A light transmitter, such as a laser or visible or infrared emitter is placed behind the diaphragm. A light sensor such as a photodiode or phototransistor is also placed behind the diaphragm such that it can detect the reflected light signal being modified by diaphragm motion. The sensor then converts the changing light signal to an electrical signal.
In one embodiment of the optical diaphragm structure, light from the emitter strikes the rear diaphragm surface. The surface or an underlying layer has a reflective pattern that produces either a pulsating or variable analog reflection signal that is then sensed by the optical detector and converted to an electrical signal.
In a second embodiment of the optical transducer, an optical structure such as a film is placed normal to the diaphragm plane, on the rear side of the diaphragm. The emitter and detector are placed such that the optical structure is within the light path between emitter and detector. The light path might be transmissive or reflective. In either case, diaphragm motion produces motion in the optical structure attached to the diaphragm, and the light signal is modified by mechanical movement of the diaphragm. This light signal is then converted to an electrical signal.
In all of the above embodiments, and others suggested by the invention, the diaphragm is physically separated from the conversion mechanism so that diaphragm movement is unimpeded. At the same time, the sensing means directly detects diaphragm motion in the form of a changing electric field, magnetic field, or optical signal. Thus the advantages of direct diaphragm sensing are achieved without the mechanical resistance of a mechanical sensor compromising acoustic characteristics of the diaphragm.
Improvements in the present invention provide for mitigation of ambient noise effects. Stethoscopes and body sound transducers in general are affected by ambient noise being picked up by the transducer. The present invention provides for a transducer housing that can be opened to reduce or eliminate standing waves and resonant effects that tend to create ambient noise reverberations in closed body sound transducer housings. This is a novel modification of existing transducer housings since a sealed cavity placed against the body is essential to the operation of pneumatic/acoustic and microphone-based electronic stethoscopes. Opening the housing allows more ambient noise into the transducer housing yet improves the perceived sound quality. This is a surprising and counterintuitive result. Since the present invention does not rely on a sealed cavity, this change in cavity acoustics can be exploited to improve response to ambient noise.
The dynamics of the diaphragm are critical to the performance of the body sound detector. The present invention provides for an adjustable diaphragm dynamic so that users can set the dynamics of the diaphragm to a preferred response characteristic.
Another noise mitigation technique provided in this invention is the use of noise canceling at the front-end input of the capacitive transducer. An anti-noise signal drives the electrode(s) of the capacitance used for body sound detection. This signal nulls the signal produced by displacement of the conductive diaphragm. This results in noise cancellation within the transducer capacitor itself prior to any amplification or electronic processing. This is a unique benefit of the present invention, providing for very effective noise cancellation techniques.
Capacitive transducers detect changes in electric field or voltage. In the case of vibrational transducers, this change is produced by displacement of a diaphragm and the changing space between electrodes of a capacitance. This invention provides for modification of the transducer so that the transducer can detect changes in voltage on an external electrode, when the transducer is placed in capacitive or conductive contact with said external electrode or multiple electrodes. Such external electrodes can be driven by a signal source and placed on the surface of a body or object. This scheme can be applied to the construction of educational models or manikins, or clothing that can be worn, whereby the body sound detector, modified to detect electric fields, can be used for educational or recreational purposes. Specifically, a manikin can be constructed with multiple electrodes, driven by a multi-channel signal source. A student can then place the body sound detector, preferably as part of a stethoscope, on the manikin at various sites, and hear the sound that would be emitted at that site on a patient. The sounds can be selected from a library of pathologies to simulate numerous pathologies. Similar methods can be adopted for the magnetic and optical transducers, however the capacitive method is the preferred embodiment.
A further improvement in auscultation education embodied in this invention is a method for driving a human, animal or inanimate body with a signal source, such as an audio signal source, thereby creating a surface electric field or skin voltage potential across a substantial surface area of the body. This field can then be detected by a transducer designed to detect voltage or electric field potentials. The capacitance to electrical transducer disclosed in this invention, normally built to detect diaphragm vibration, can also detect surface potential voltage or electric field variations, making it possible to use essentially the same transducer, or entire stethoscope, for detecting acoustic vibrations as well as electric fields or voltages (simulations of acoustic vibrations). Thus simulation and actual patient listening can be achieved with the same transducer or stethoscope, creating an entirely realistic embodiment of patient simulation. The same methods can be applied to toys and other devices.
Improvements in the transducer therefore include noise reduction, performance, and modification of the sensor to detect not just sound but other phenomena, and simulate patient examination.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the basic mechanical structure of the invention in one preferred embodiment;
FIG. 2 shows a second embodiment of the sensor capacitive elements of the invention, whereby a double-capacitance is formed;
FIG. 3 shows another embodiment of a mounting means for the diaphragm for the capacitive sensor;
FIG. 4 shows means of ambient sound isolation for the capacitive plate in further detail;
FIG. 5 shows the overall circuit topology of the capacitive sensor when used with a DC-DC charging circuit and associated function;
FIG. 6 shows a triple plate capacitance form of the sensor;
FIG. 7 shows the sensor used in a generalized capacitive sensing circuit;
FIG. 8 shows the capacitive sensor wherein the diaphragm, plate, or both are permanently charged such that an electric field exists between the plates obviating the need for a capacitive charging circuit; and
FIG. 9 shows in schematic form and not to scale a stethoscope including the capacitive sensor of the invention.
FIG. 10 shows a magnetic sensor embodiment wherein a magnetic material is adhered to or an integral part of a diaphragm.
FIG. 11 shows a magnetic sensor embodiment wherein the diaphragm has a coil or printed circuit coil as part of the diaphragm and magnetic assembly.
FIG. 12 shows a magnetic sensor embodiment wherein a coil is mounted normal to the diaphragm and a permanent magnet is placed behind the diaphragm to form a dynamic microphone structure.
FIG. 13 shows a magnetic sensor embodiment wherein a magnet is mounted normal to the diaphragm with a stationary coil used to sense diaphragm motion.
FIG. 14 shows an optical sensor embodiment wherein a light beam is reflected from the back of the diaphragm, and changes reflected light are converted to an electrical signal.
FIG. 15 shows various diaphragm optical reflection patterns that produce changes in the reflected light signal as the diaphragm position changes, and the point of reflection changes.
FIG. 16 shows a optical sensor embodiment wherein an optical film or other structure is mounted normal to the diaphragm, such that the structure interferes with a transmitted light source in order to produce an electrical signal that measures diaphragm motion.
FIG. 17 shows the transmissive light patterns that are applicable to the transmissive reflector shown in FIG. 16.
FIG. 18 shows a capacitive transducer housing modified to provide air and sound transmission into the transducer housing inner cavity and specifically to the space behind the diaphragm.
FIG. 19 shows a general transducer housing modified to provide air and sound transmission into the transducer housing cavity, as well as means to close the cavity to moisture while maintaining transmission of sound into the cavity.
FIG. 20 shows a transducer housing with multiple cavities in which a small cavity behind the diaphragm is sealed to ambient sound while other cavity(ies) in the housing are open to external sound.
FIG. 21 shows a diaphragm that can be separated from the main transducer housing, and attached to a body.
FIG. 22 shows a separate flexible diaphragm assembly that can be adhered or attached to a body.
FIG. 23 shows the conventional topology of a noise-canceling system.
FIG. 24 shows the topology and details of a noise canceling capacitive transducer.
FIG. 25 shows the storage and transmission of both signal and noise for further processing.
FIG. 26 shows an active noise canceling method wherein a speaker mounted in the transducer housing produces anti-noise in order to reduce the noise level inside the transducer housing.
FIG. 27 shows an externally-driven electrode arrangement for the capacitive coupling of signals into the capacitive transducer.
FIG. 28 shows modifications of the diaphragm in connection with use of an external electrode.
FIG. 29 shows modifications of the transducer to provide flexibility in the application of the capacitive transducer for voltage and biopotential detection, and for use with external electrodes for simulation.
FIG. 30 shows a multi-electrode system, such as could be used on a manikin, to be used in connection with a capacitive transducer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments are divided into three categories —(a) Capacitive Sensor embodiments, (b) Magnetic Sensor embodiments, and (c) Optical Sensor embodiments. These are all discussed separately below.
A fundamental aspect of the invention, covering all embodiments, is (a) that the diaphragm makes direct contact with the body for sound sensing, (b) the diaphragm is an integral part of the acoustic-to-electric transducer mechanism rather than simply transmitting sound waves via air to a second acoustic-to-electrical transducer i.e. in this invention the diaphragm motion itself is converted to an electrical signal and (c) the mechanical structure of transducer elements other than the diaphragm do not make direct contact with the diaphragm and hence the conversion means does not impede diaphragm motion or place a mechanical load on the diaphragm.
The benefit of this method is that the acoustic properties of the diaphragm are essentially the same as those of an acoustic stethoscope due to the freedom of movement of the diaphragm, and the direct conversion of diaphragm motion that ensures efficient energy conversion from acoustic to electrical energy. Further, the direct conversion method decreases or eliminates the insertion of ambient noise into the conversion process, since ambient noise usually enters the system between the diaphragm and any secondary transducer.
Another unique aspect of the invention is the operation of the diaphragm in this invention compared with diaphragms in conventional microphones. In a conventional microphone, the diaphragm does not make physical contact with any body, the sound being coupled from the source via air, or fluid in the case of a hydrophone. The diaphragm displacement is therefore very limited, typically less than 5 microns displacement. The diaphragms are therefore designed to be displaced a few microns, and the spacing of the diaphragm to other elements behind the diaphragm is typically on the order of tens of microns. In most cases, the goal of conventional microphone design is to minimize such diaphragm spacing in order to optimize performance and sensitivity. It is thus counterintuitive to (a) place a diaphragm directly against the body, (b) allow the diaphragm to withstand the large displacements produced by pressure against a body, and (c) to construct a sensor that increases, rather than decreases, the displacement capability of the diaphragm. Thus in stethoscope applications, the prior art either includes placement of a microphone (with its own diaphragm) behind the stethoscope diaphragm, ensuring that the microphone diaphragm cannot contact the body as well as making the system susceptible to noise, or a mechanical coupling is used that loads the diaphragm thereby limiting its ability to move with any substantial displacement as well as modifying the diaphragm\'s acoustic characteristics. This invention resolves both problems simultaneously.
In the present invention, the spacing between the diaphragm and any other element of the transducer placed behind the diaphragm typically exceeds 0.1 mm, 0.25 mm, 0.5 mm or 1 mm, subject to the stiffness and radius of the diaphragm, and the mounting means. The present invention, addresses stethoscope diaphragms which are typically in excess of 25 mm diameter, although smaller diaphragms are also covered by the invention. If the diaphragm mounting means allows substantial diaphragm displacement, the spacing is increased. If the mounting is more rigid, and the diaphragm material sufficiently stiff to withstand pressure, the spacing can be reduced. In the case of an embodiment that is produced by semiconductor processing means, such that the transducer forms part of a semiconductor integrated circuit, the spacing can be made substantially smaller than 0.1 mm, since the diaphragm diameter is then significantly smaller than a conventional stethoscope diaphragm.
All embodiments of this invention include considerations of spacing and diaphragm displacement, and the numerical values defined above cover all embodiments.
Another aspect of the displacement characteristic of the diaphragm in this invention is the capability to allow static pressure from a body to change the steady-state position of the diaphragm about which vibrations occur due to sound. Thus when the diaphragm is pressed against a body for listening, the diaphragm moves from its unpressured position to a new displacement due to pressure. This is referred to as the static displacement. Then acoustic waves produce smaller dynamic displacement or vibration from sub-sonic (5 Hz-20 Hz) through audio frequency range (20 Hz to 20 KHz). In this case, most sounds of interest do not cover the entire audio range, but are limited to approximately 10 Hz to 2000 Hz. In the present invention, the static and dynamic displacements are used to control the sound characteristics of the transducer in a novel way. The static displacement influences the gain or amplitude of the transducer. The static displacement also affects the frequency response of the transducer. Thus the user can control amplitude and frequency characteristics by applying different static pressures to the diaphragm as it is pressed against the body. The prior art seeks to establish uniform amplitude and frequency characteristics for electronic transducers, so that there is no user-to-user variability. This invention exploits the inherent feedback loop that allows a user to hear the amplitude and frequency characteristics, and adjust pressure on the diaphragm to control for the optimal sound characteristics. While acoustic stethoscopes do provide for modification of sound characteristics with pressure, these effects have not been implemented in electronic stethoscope transducers. Further, the acoustic diaphragms that facilitate this effect do so by modification of the effective diameter of the diaphragm. This invention is novel in that diaphragm displacement is used as the controlling parameter, and the means for effecting this acoustic change have not been achieved with electronic transducers in this application.
This invention includes three primary embodiments of the fundamental inventive steps described above—capacitive, magnetic and optical sensing embodiments.
Capacitive embodiments are presented in FIGS. 1 to 9, Magnetic embodiments are presented in FIGS. 10 to 13, and optical embodiments are presented in FIGS. 14 to 17.