`(12) Patent Application Publication (10) Pub. No.: US 2006/0264756 A1
`(43) Pub. Date:
`NOV. 23, 2006
`Lo et al.
`
`US 20060264756A1
`
`(54) ULTRASONIC MONITOR WITH A
`BIOCOMPATIBLE OIL BASED
`TRANSMISSION MEDIUM
`
`(76) Inventors: Thomas Ying-Ching Lo, Fremont, CA
`(US); Rong Jong Chang, Fremont, CA
`(Us)
`Correspondence Address:
`VIERRA MAGEN MARCUS & DENIRO LLP
`575 MARKET STREET SUITE 2500
`SAN FRANCISCO, CA 94105 (US)
`
`(21) Appl. No.:
`
`11/124,707
`
`(22) Filed:
`
`May 9, 2005
`
`Publication Classi?cation
`
`(51) Int. Cl.
`A61B 8/14
`
`(2006.01)
`
`(52) US. Cl. ............................................................ .. 600/459
`
`(57)
`
`ABSTRACT
`
`An ultrasonic monitor implemented on a PCB includes a
`transmission medium. The transmission medium may be
`biocompatible and implemented as an oil-based transmis
`sion medium, a gel pad, or a combination thereof. Ultrasonic
`signals are transmitted between the ultrasonic monitor and a
`living subject through the transmission medium. An air gap
`is formed in the PCB underneath transducer elements to
`provide for more ef?cient signal transmission. The entire
`ultrasonic monitor may be encapsulated in plastic, a trans
`mission medium, or both to provide Water resistant proper
`ties.
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`300
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`Remote Display
`&
`
`T
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`Wireless
`_
`—> Transmitter '’ Recelver
`£2
`
`l
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`l
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`T1 4
`T2
`m 29
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`Mirco
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`Controller
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`-_-——————> Local Display
`i
`@
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`Band Pass
`Filter
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`LQ
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`——> RF Ampli?er
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`m
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`Audio
`> Mixer —> Frequency
`Ampli?er
`E
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`350
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`Figure 3
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`@
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`Transmit Ultrasonic Signal
`
`?g
`
`l
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`Receive Re?ected Signal
`
`Q
`
`l
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`Amplifv Received Signal m
`
`l
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`Retrieve Modulated Signal m
`
`V
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`Amplify DeModulated Signal @
`
`l
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`Filter Demodulated Signal
`
`_@_Q
`
`l
`
`Perform Additional Processing m
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`Figure 4
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`5 of 30
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`Q
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`Convert Analog to Digital
`
`w
`
`i
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`Determine Absolute Value @
`
`i
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`Filter with LPF
`
`m
`
`i
`
`Derive Heart Rate Information
`
`_54_O
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`Figure 5
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`ULTRASONIC MONITOR WITH A
`BIOCOMPATIBLE OIL BASED TRANSMISSION
`MEDIUM
`
`CROSS REFERENCE TO RELATED
`INVENTION
`
`[0001] The instant non-provisional application is related
`to the following patent applications, all of Which are hereby
`incorporated by reference in their entirety:
`
`[0002] US. Pat. No. 6,843,771, ?led on Jan. 15, 2003,
`entitled “ULTRASONIC MONITOR FOR MEASURING
`HEART RATE and BLOOD FLOW RATE,” having inven
`tors Thomas Ying-Ching Lo, Tolentino Escorcio, Rong Jong
`Chang;
`[0003] US. patent application Ser. No. 10/990,794, ?led
`on Nov. 17, 2004, entitled “ULTRASONIC MONITOR
`FOR MEASURING BLOOD FLOW AND PULSE
`RATES”, having inventor Thomas Ying-Ching Lo, attorney
`docket number SALU-0l002USO; and
`[0004] US. patent application Ser. No. l0/99l,ll5, ?led
`on Nov. 17, 2004, entitled “GEL PAD FOR USE WITH AN
`ULTRASONIC MONITOR”, having inventors Thomas
`Ying-Ching Lo, Rong Jong Chang, attorney docket number
`SALU-0l002USO.
`
`BACKGROUND OF THE INVENTION
`
`[0005] 1. Field of the Invention
`
`[0006] The present invention relates to ultrasonic monitors
`for measuring heart rates and pulse rates in living subjects.
`
`[0007] 2. Description of the Related Art
`[0008] Measuring heart and pulse rates in living subjects
`has become a valuable tool during physical exercise and for
`health monitoring. The heart rate and pulse rate of a subject
`are related. Heart rate may be de?ned as the number of heart
`contractions over a speci?c time period, usually de?ned in
`beats per minute. A pulse is de?ned as the rhythmical
`dilation of a vessel produced by the increased volume of
`blood forced through the vessel by the contraction of the
`heart. Since heart contractions normally produce a volume
`of blood that can be measured as a pulse, heart rate and pulse
`rate are ideally the same. HoWever, a pulse rate may differ
`from the heart rate during irregular heart beats or premature
`heart beats. In this case, a heart contraction may not force
`enough blood through a blood vessel to be measured as a
`pulse.
`[0009] A pulse rate is measured by counting the rate of
`pulsation of a subject’s artery. The heart rate is measured by
`sensing the electrical activity of the heart based on electro
`cardiograms (for example EKG or ECG). Individuals Who
`Want to increase their endurance or performance may Wish
`to exercise While maintaining target heart rates. Conversely,
`subjects With a history of heart disease or other heart related
`condition should avoid exceeding a certain heart or pulse
`rate to reduce unnecessary strain on their heart.
`[0010] Most subjects that require continuous heart rate
`readings choose a monitor that requires a chest strap.
`Though they provide heart rates continuously, chest straps
`are cumbersome and generally undesirable to Wear. In
`addition to chest strap solutions, portable patient monitors
`
`(e.g., vital signs monitors, fetal monitors) can perform
`measuring functions on subjects such as arrhythmia analy
`sis, drug dose calculation, ECG Waveforms cascades, and
`others. HoWever, such monitors are usually fairly large and
`are attached to the subject through uncomfortable Wires.
`
`[0011] Pulse rate can be measured at the Wrist. The shal
`loW depth of the radial artery in the Wrist offers a number of
`advantages for achieving continuous pulse detection at the
`Wrist. Prior sensors that monitor pressure pulses in the Wrist
`have not been effective. Pressure pulses are attenuated by the
`tissues betWeen the artery and the sensor. Most of the high
`frequency signal components are lost because of the attenu
`ation. Additionally, muscle movement may create substan
`tial noise at the pressure sensors. The loW frequency noise
`signals make it very di?icult to reliably identify loW fre
`quency blood pressure pulses.
`
`[0012] Ultrasonic monitors using sonar technology Were
`developed to overcome noise signal problems. Ultrasonic
`monitors transmit ultrasonic energy as a pulse signal. When
`a poWer source drives a transducer element, such as a
`pieZoelectric crystal, to generate the pulse signal, the ultra
`sonic pulse signal is generated in all directions, including the
`direction of the object to be measured such as a blood vessel.
`The portion of the ultrasonic pulse signal reaching the vessel
`is then re?ected by the vessel. When the blood vessel
`experiences movement, such as an expansion due to blood
`?oW from a heart contraction, the re?ected pulse signal
`experiences a frequency shift, also knoWn as the Doppler
`shift.
`
`[0013] When either the source of an ultrasonic signal or
`the observer of the sonar signal is in motion, an apparent
`shift in frequency Will result. This is knoWn as the Doppler
`effect. If R is the distance from the ultrasonic monitor to the
`blood vessel, the total number of Wavelengths 7» contained in
`the tWo-Way path betWeen the ultrasonic monitor and the
`target is 2RD». The distance R and the wavelength 7» are
`assumed to be measured in the same units. Since one
`Wavelength corresponds to an angular excursion of 2st
`radians, the total angular excursion 4) made by the ultrasound
`Wave during its transit to and from the blood vessel is 4J'cR/7t
`radians. When the blood vessel experiences movement, R
`and the phase 4) are continually changing. A change in q) With
`respect to time is equal to a frequency. This is the Doppler
`angular frequency Wd, given by
`
`Where f‘,1 is the Doppler frequency shift and VI is the relative
`(or radial) velocity of target With respect to the ultrasonic
`monitor.
`
`[0014] The amount of the frequency shift is thus related to
`the speed of the moving object from Which the signal
`re?ects. Thus, for heart rate monitor applications, the ?oW
`rate or ?oW velocity of blood through a blood vessel is
`related to the amount of Doppler shift in the re?ected signal.
`
`[0015] A pieZoelectric crystal may be used both as the
`poWer generator and the signal detector. In this case, the
`ultrasonic energy is emitted in a pulsed mode. The re?ected
`signal is then received by the same crystal after the output
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`power source is turned off. The time required to receive the
`re?ected signal depends upon the distance betWeen the
`source and the object. Using a single crystal to measure heart
`rates requires high speed poWer sWitching due to the short
`distance betWeen source and object. In addition, muscle
`movement generates re?ections that compromise the signal
`to-noise-ratio in the system. The muscle movement noise
`has a frequency range similar to the frequency shift detected
`from blood vessel Wall motion. Therefore, it is very di?icult
`to determine heart rates With this method. The advantage of
`this approach, hoWever, is loW cost and loW poWer con
`sumption.
`[0016] In some ultrasonic signal systems, tWo pieZoelec
`tric elements are used to continuously measure a pulse. The
`tWo elements can be positioned on a base plate at an angle
`to the direction of the blood. In continuous pulse rate
`measurement, the Doppler shift due to blood ?oW has a
`higher frequency than the shifts due to muscle artifacts or
`tissue movement. Therefore, even if the muscle motion
`induced signals have larger amplitudes, they can be removed
`by a high pass ?lter to retain the higher frequency blood ?oW
`signals. The disadvantages of continuous mode over pulsed
`mode are higher cost and more poWer consumption
`
`[0017] Several Wrist mounted ultrasonic monitor devices
`are knoWn in the art. HoWever, ultrasonic signals are prone
`to diffraction and attenuation at the interface of tWo media
`of different densities. Thus, air in the media or betWeen the
`monitor and the subject’s skin make ultrasonic energy
`transmission unreliable. Prior ultrasonic monitors require
`applying Water or an aqueous gel betWeen the transducer
`module and the living subject to eliminate any air gap.
`Because Water and aqueous gels both evaporate quickly in
`open air, they are not practical solutions.
`
`[0018] US. Pat. No. 6,843,771 disclosed the use of ther
`moplastic and thermoset gels as the transmission medium
`for ultrasonic signals to overcome the problems associated
`With Water and aqueous gel solutions. In US. Pat. No.
`6,716,169, Muramatsu et al. disclosed a soft contact layer
`based on silicone gel, a type ofthermoset gel, as the medium
`for the ultrasonic signal transmission. These gels mainly
`consist of a large quantity of non-evaporating (at ambient
`condition) liquid diluents entrapped in a lightly cross-linked
`elastomeric netWork. These cross-linked netWorks can be
`either physical in nature, such as in the thermoplastic gels,
`or chemical in nature, such as the thermoset gels.
`[0019] Synthetic thermoset and thermoplastic gels have
`disadvantages. The liquid diluents, though entrapped in the
`elastomeric netWork, can still diffuse into the skin of a user
`upon contact over a period of time. Since silicone gels use
`silicone oil as diluents, diffusion of silicone oil is an impor
`tant health concern, Diffusion of these oils into body tissues
`can cause biological problems. Synthetic thermoset and
`thermoplastic gels also tend to be soft gels. Though a softer
`gel alloWs better contact With the skin and results in better
`ultrasonic transmission, soft gels are Weak, di?icult to
`handle and di?icult to attach to ultrasonic transmitters.
`
`[0020] E?iciency of the transmitting transducer is an
`important feature in Wrist Worn and other small heart rate
`monitors. Transmission of an ultrasonic signal by a trans
`mitting transducer can be made more e?icient by use of a
`re?ector. Transmission signals generated aWay from target
`can be re?ected using a re?ector on one or more sides of the
`
`transducer. Some heart rate monitors include a foam sub
`stance having air voids underneath the pieZoelectric crystals.
`As illustrated in FIG. 1, a foam layer 120 may be placed
`Within ultrasonic module 110 underneath transducers 130
`and 140. The foam material air voids partially inhibit
`ultrasound energy penetration and provide fairly e?fective
`re?ection of ultrasound signals. With this foam backing,
`some of the ultrasonic signals directed toWards the foam are
`re?ected toWard the desired direction. The disadvantage to
`incorporating foam layers is that they are manually installed
`during manufacture. Other prior systems increase e?iciency
`by separating the tWo pieZoelectric crystals by a channel on
`a base plate. This reduces crosstalk betWeen the transducers
`to some degree but does not eliminate the loading or
`dampening effect caused by the base plate.
`
`[0021] Heart rate monitors that provide continuous heart
`rate readings through a transmission media are useful. The
`transmission media should be biocompatible and not dry out
`during the monitoring, leave an uncomfortable Wet ?lm, or
`be di?icult to generate and apply.
`
`SUMMARY OF THE INVENTION
`
`[0022] The present invention, roughly described, pertains
`to ultrasonic monitors. The ultrasonic monitor uses ultra
`sonic signals to measure movement inside the body of a
`living subject. The movement may be a heart contraction,
`?oWing blood or movement of the blood vessel itself. From
`information collected from these movements, electronics
`Within the monitor may determine blood ?oW rate, heart
`rate, or pulse rate of the living subject.
`
`[0023] In some embodiments, a biocompatible oil-based
`transmission medium is used to transmit ultrasonic signals
`betWeen an ultrasonic monitor module and a subject. The
`biocompatible oil-based transmission medium is positioned
`in contact With the ultrasonic monitor module and the
`subject, and provides transmission of ultrasonic signals
`betWeen the ultrasonic monitor module and the subject.
`
`[0024] In some embodiments, an ultrasonic monitor may
`include a transmission transducer, a receiving transducer, a
`housing and biocompatible oil-based transmission medium.
`The transmission transducer can be con?gured to transmit an
`ultrasonic signal and the receiving transducer can be con
`?gured to receive a re?ected ultrasonic signal. The housing
`may contain the transmission transducer and the receiving
`transducer. The biocompatible oil-based transmission
`medium is in contact With the housing. The ultrasonic signal
`and re?ected ultrasonic signal are transmitted through the
`biocompatible oil-based transmission medium betWeen the
`transducers and a subject.
`
`[0025] A heart rate may be monitored by applying a
`biocompatible oil-based transmission medium betWeen an
`ultrasonic monitor module and a subject. The ultrasonic
`monitor module transmits an ultrasonic signal through the
`biocompatible oil-based transmission medium to the subject.
`A re?ected ultrasonic signal is received by the ultrasonic
`monitor module through the biocompatible oil-based trans
`mission medium from the subject. The received ultrasonic
`signal is then processed.
`
`[0026] In some embodiments, a monitor system may
`include an ultrasonic monitor and an oil-based transmission
`medium. The ultrasonic monitor may be positioned in prox
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`imity to a subj ect’s blood vessel. The oil-based transmission
`medium may be positioned between the ultrasonic monitor
`and the subject’s blood vessel. The oil-based transmission
`medium may comprise a Wax component and an oil com
`ponent and be able to transmit ultrasonic signals betWeen the
`ultrasonic monitor and the subject When positioned betWeen
`the ultrasonic monitor and the subject.
`
`[0027] In some embodiments, an ultrasonic monitor may
`include an ultrasonic monitor module, a gel pad, and a
`biocompatible oil based transmission medium. The gel pad
`may be in contact With the ultrasonic monitor module. The
`biocompatible oil based transmission medium may be in
`contact With the gel pad and a subject. The gel pad and
`biocompatible oil based transmission medium may provide
`transmission of ultrasonic signals betWeen the ultrasonic
`monitor module and the subject.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0028] FIG. 1 illustrates a cross section of an ultrasonic
`monitor of the prior art.
`
`[0029] FIG. 2A illustrates one embodiment of an ultra
`sonic monitor With a physical connection to a display device.
`
`[0030] FIG. 2B illustrates one embodiment of an ultra
`sonic monitor With a Wireless connection to a display device.
`
`[0031] FIG. 3 illustrates one embodiment of a block
`diagram of an ultrasonic monitor.
`
`[0032] FIG. 4 illustrates one embodiment of a method of
`operation of an ultrasonic monitor.
`
`[0033] FIG. 5 illustrates one embodiment of a method for
`performing additional processing by an ultrasonic monitor.
`
`[0034] FIG. 6 illustrates one embodiment of a perspective
`vieW of an ultrasonic monitor on a PCB having an air gap.
`
`[0035] FIG. 7 illustrates one embodiment of a side vieW
`of an ultrasonic monitor on a PCB having an air gap.
`
`[0036] FIG. 8A illustrates one embodiment of a perspec
`tive vieW of an ultrasonic monitor on a PCB having an air
`gap With a supporting member.
`
`[0037] FIG. 8B illustrates one embodiment of a side vieW
`of an ultrasonic monitor on a PCB having an air gap With a
`supporting member.
`
`[0038] FIG. 9A illustrates one embodiment of a perspec
`tive vieW of an ultrasonic monitor on a PCB having one air
`gap shared by tWo transducers.
`
`[0039] FIG. 9B illustrates one embodiment of a side vieW
`of an ultrasonic monitor on a PCB having one air gap shared
`by tWo transducers.
`
`[0040] FIG. 9C illustrates one embodiment of a front
`vieW of an ultrasonic monitor on a PCB having one air gap
`shared by tWo transducers.
`
`[0041] FIG. 10A illustrates one embodiment of a biocom
`patible oil-based transmission medium applicator.
`
`[0042] FIG. 10B illustrates one embodiment of a gel pad.
`
`[0043] FIG. 11A illustrates one embodiment of a perspec
`tive vieW of a oil-based transmission medium component.
`
`[0044] FIG. 11B illustrates one embodiment of a side
`vieW of a oil-based transmission medium component.
`
`[0045] FIG. 12A illustrates one embodiment of a trans
`mission medium con?guration.
`
`[0046] FIG. 12B illustrates one embodiment of a trans
`mission medium con?guration.
`
`[0047] FIG. 12C illustrates one embodiment of a trans
`mission medium con?guration.
`
`[0048] FIG. 13A illustrates one embodiment of a perspec
`tive vieW of an ultrasonic monitor on a PCB With a mold.
`
`[0049] FIG. 13B illustrates one embodiment of a side
`vieW of an ultrasonic monitor on a PCB With a mold.
`
`[0050] FIG. 14A illustrates one embodiment of a side
`vieW of an encapsulated PCB board.
`
`[0051] FIG. 14B illustrates one embodiment of a side
`vieW of an encapsulated PCB board.
`
`[0052] FIG. 14C illustrates one embodiment of a side
`vieW of an encapsulated PCB board.
`
`[0053] FIG. 15A illustrates an embodiment of an ultra
`sonic monitor system With an encapsulated transmission
`medium.
`
`[0054] FIG. 15B illustrates an embodiment of an ultra
`sonic monitor system With an attached transmission
`medium.
`
`DETAILED DESCRIPTION
`
`[0055] The present invention, roughly described, pertains
`to ultrasonic monitors. The ultrasonic monitor uses ultra
`sonic signals to measure movement inside the body of a
`living subject. The movement may be a heart contraction,
`?oWing blood or movement of the blood vessel itself. From
`information collected from these movements, electronics
`Within the monitor may determine blood ?oW rate, heart
`rate, or pulse rate of the living subject.
`
`[0056] In one embodiment, the ultrasonic monitor mea
`sures blood ?oW through an artery of a person. The ultra
`sound signals re?ected by blood vessel expansion (expan
`sion due to blood moving through the vessel) have a
`frequency range similar to that of noise caused by muscle
`artifacts and tissue movement. The ultrasound signals
`re?ected by the ?oWing blood itself have a frequency range
`higher than muscle and tissue related noise. As a result, the
`signals re?ected by ?oWing blood are easier to process to
`?nd the rate values than those re?ected by expansion of the
`blood vessel itself.
`
`[0057] The terms ultrasonic and ultrasound are used inter
`changeably herein and refer to a sound Wave having a
`frequency betWeen about 30 KHZ and about 30 MHZ. An
`ultrasonic transducer, or transducer element, as used herein
`is a device used to introduce sonic energy into and detect
`re?ected signals from a living subject. Ultrasonic transduc
`ers respond to electric pulses from a driving device and
`ultrasonic pulses re?ected by a subject.
`
`[0058] The ultrasonic monitor is comprised of an elec
`tronics portion and a transmission portion. The electronics
`portion includes the electrical components required to trans
`mit, receive, and process the ultrasonic signals as discussed
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`with respect to FIGS. 3-5. Processing may include ampli-
`fying, filtering, demodulating, digitizing, squaring, and other
`functions typically signal processing functions. Processing
`may be performed all or in part by digital circuitry. For
`example, the received ultrasonic signal can be digitized. The
`processing described herein to the received signal can then
`be performed by digital circuitry. The transmission portion,
`or transmission medium, may include a biocompatible oil-
`based transmission medium, gel pad, or combination of the
`two between the monitor and the subject. In some embodi-
`ments, the oil—based transmission medium can be positioned
`in direct contact with the living subject and the ultrasonic
`monitor. In some embodiments, the oil based transmission
`medium is in contact with the gel pad, and the oil based
`transmission medium and gel pad provide transmission of
`ultrasonic signals between an ultrasonic monitor and a
`subject. Both oil based transmission mediums and gel pads
`are discussed in more detail below.
`
`In one embodiment, an oil—based transmission
`[0059]
`medium used to transmit ultrasonic signals between the
`ultrasonic monitor and the subject may be biocompatible. A
`biocompatible transmission medium is one that can be in
`contact with a user’s skin without being toxic, being inju-
`rious, causing immunological rejection or otherwise result-
`ing in undesirable health effects, such as those caused by
`typical therrnoset and thermoplastic gels. In one embodi-
`ment, a biocompatible oil—based transmission medium can
`include an oil component and a wax component. Both the oil
`and wax components may be natural rather than synthetic.
`Additional components may be included as well, including
`one or more “essential oils” and water. An essential oil is a
`natural oil that provides a fragrance, moisturizes skin, or
`heals skin tissue. Tl1e ratio of wax to liquid (liquids such as
`natural oil, essential oil and water) may determine the
`consistency of the biocompatible oil—based transmission
`medium. The biocompatible oil—based transmission medium
`may be applied between an ultrasonic monitor and a user’s
`skin with an applicator device, as a disposable transmission
`medium component, or as part of the ultrasonic monitor.
`Oil—based transmission media are discussed in more detail
`below.
`
`the monitor of the present
`In one embodiment,
`[0060]
`invention is implemented on a printed circuit board (PCB).
`By implementing the circuitry 011 a PCB, the monitor system
`has a very small footprint with a much lower power require-
`ment. The transducers are mounted directly to the PCB.
`
`[0061] The PCB can implement an ultrasound signal
`refiection layer. In one embodiment, a portion of the outer
`layer of the PCB is removed to create an air gap portion.
`Transducer elements are placed over the air gap portion.
`When driven, the transmitting crystal generates an ultra-
`sound signal that travels towards the PCB in addition to the
`desired direction towards a target. The portion of the origi-
`nally transmitted ultrasound signal traveling towards the
`PCB is reflected by the thin air gap away from the PCB and
`towards the intended target.
`
`In another embodiment, the PCB can be entirely
`[0062]
`encapsulated in plastic, an adhesive, an encapsulant, a gel, or
`a combination ofthese. This provides for keeping the system
`of the ultrasonic monitor protected from debris such as dirt,
`dust and water. These advantages are discussed in more
`detail below.
`
`[0063] The ultrasonic monitor may be implemented with a
`display. FIG. 2A illustrates a wrist worn ultrasonic monitor
`system 200 in one embodiment. System 200 includes an
`ultrasonic monitor module 210, a strap 220, a display device
`230 and a transmission medium 240. Ultrasonic monitor
`module 210 detects blood flow through the radial artery at
`the subject’s wrist. Heart rate data is then provided directly
`to display module 230. In one embodiment, connecting
`wires are molded into strap 220 between the ultrasonic
`monitor module 210 and display device 230.
`
`[0064] The ultrasonic monitor can also be implemented
`with a remote display. The ultrasonic monitor system 250 of
`FIG. 2B includes monitor module 260, first strap 270
`attached to monitor module 260, remote display module 280
`and second strap 290 at'ached to remote display module 280.
`Ultrasonic monitor module 260 detects the blood llow
`through the radial artery in the wrist. Heart rate data is then
`provided to remote display module 280. Monitor 260 can
`wirelessly transmit in onnation to a remote display 280
`using a wireless transmitter. The remote display 260
`includes a receiver to receive the transmission from monitor
`260. The remote display 280 may also be a monitor screen
`or other device. The ultrasonic monitor module 280 may be
`attached to another part of the body (such as the chest over
`the subject’s heart) with a biocompatible adhesive or a
`transmission medium.
`
`[0065] Detennining what ultrasound signal frequency to
`use may depend on the particular object being monitored.
`The wrist olfers a convenient location for positioning the
`monitoring device. The relatively shallow focal depth of the
`radial artery in the wrist suggests using a high frequency
`carrier signal.
`
`[0066] The size of the transducer elements also alfects the
`ultrasound signal
`frequency. Thinner electromechanical
`resonators emit at higher frequencies. Transducer elements
`driven by high frequency signals tend to vibrate more
`rapidly and consume more power than those operating at
`lower frequencies. This is primarily due to internal loss. The
`ultrasonic monitor amplifier and demodulation circuits will
`also consume more power processing the higher frequen-
`cies.
`
`[0067] A block diagram of one embodiment of an ultra-
`sonic monitor system 300 is illustrated in FIG. 3. Ultrasonic
`monitor system 300 includes a microcontroller 310, a trans-
`mitting transducer element 320 connected to microcontroller
`310, a receiving transducer element 330, a radio frequency
`(RF) amplifier 340 connected to receiving transducer 330, a
`mixer 350 comiected to RF amplifier 340 and n1icrocontrol-
`ler 310, an audio amplifier 360 connected to mixer 350, and
`band pass (BP) filter 370 connected to audio frequency
`amplifier 360 and microcontroller 310. Ultrasonic monitor
`system 300 may optionally include a local display 380
`connected to microcontroller 310, a wireless transmitter 390
`connected to microcontroller 310, a wireless receiver 392
`receiving a wireless signal from wireless transmitter 390,
`and a remote display 394 connected to receiver 392.
`
`In one embodiment, an ultrasonic monitor can be
`[0068]
`implemented with a system similar to that represented by
`block diagram 300, but with a driver circuit and high pass
`and low pass filters. In this case, the microcontroller drives
`driver circuitry with a carrier signal. The driver circuitry
`drives transmitting transducer to transmit an ultrasonic sig-
`
`21 of 30
`
`
`
`US 2006/0264756 A1
`
`Nov. 23, 2006
`
`nal at a carrier frequency. The ultrasonic signal is refiected
`and received by receiving transducer. The received signal
`includes a frequency shift from the signal transmitted by
`transducer. The received ultrasonic signal is amplified by RP
`amplifier circuitry. The amplified ultrasonic signal is then
`processed by a mixer, which demodulates the received
`signal and generates a signal with an audio range frequency.
`The resulting signal is then amplified by an audio frequency
`amplifier circuit. The amplified audio signal is then filtered
`by a high pass filter circuit and a low pass filter circuit. The
`filtered signal is then received by the microcontroller. The
`microcontroller processes the filtered signal and provides an
`output signal to a wireless transmitter. The Wireless trans-
`mitter transmits the signal through a wireless means to a
`receiver. A display then receives the signal from the receiver
`and displays information derived from the signal.
`
`[0069] Method 400 of FIG. 4 illustrates the operation of
`one embodiment of an ultrasonic monitor such as that
`represented in FIG. 3. An ultrasound signal is transmitted at
`step 410. With respect to system 300, microcontroller 310
`drives a transmitting transducer element 320 with a carrier
`signal fC. As a result, the transmitting transducer generates
`an ultrasound signal. In one embodiment, the carrier signal
`may be Within a range of 30 KHZ to 30 MHZ. In another
`embodiment, the carrier signal may be within a range of l
`MHZ to 10 MHZ. In yet another embodiment, the carrier
`signal is about 5 MHZ.
`
`[0070] Arefleeted ultrasonic signal is received at step 420.
`The reflected ultrasonic signal is generated by the refiection
`of the ultrasonic signal of step 410 fror11 a blood vessel.
`When the ultrasonic monitor is worn on a wrist, the radial
`artery refiects the signal. The received ultrasonic signal will
`contain an ultrasonic carrier frequency that has experienced
`a Doppler shift from the signal transmitted by transmitting
`transducer 320. The received signal is then amplified at step
`430. In one embodiment, the amplifier 340 of system 300 is
`implemented as a radio frequency amplifier. The received
`ultrasonic signal is amplified by a factor that allows it to be
`processed for demodulation. Once the ultrasonic signal is
`amplified at step 430, it is processed by mixer 350 at step
`440. The mixer uses the carrier signal fc to demodulate the
`reflected ultrasonic signal in order to extract the Doppler
`signal. Accordingly, mixer 350 is driven by carrier signal fc.
`and the reflected ultrasound signal. The output signal pro-
`vided by mixer 350 is then amplified at step 450 by amplifier
`360. As the output of the mixer will have a f
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