JP2001286447A - Resonance based pressure transducer system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resonance based transducer system to be implanted inside an organism for measuring the pressure in vivo. SOLUTION: The resonant transducer system comprises a resonance sensor 2 with a mechanical resonator 16 whose resonance frequency depends on the pressure, and an ultrasonic energy source 4. The sensor 2 and the ultrasonic energy source 4 are mechanically connected, both of which are mounted at the distal part of a common elongated member 6. The system for measuring the pressure includes an AC power source, the resonance based pressure transducer system, and a control device for controlling the power supply mode of the AC power source and analyzing resonant signals released from the resonant pressure transducer system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring physiological pressure, and more particularly, to an apparatus and a system using resonance as a medium for transmitting information.

[0002]

BACKGROUND OF THE INVENTION The need to measure and record physiological pressure in coronary vessels has triggered the development of microscopic devices that allow access to very small coronary vessels. Typically, a very small size sensor is attached, for example, to a guide wire that is inserted into the femoral artery and guided to the desired measurement point, for example, a coronary vessel. There are several problems associated with integrating guidewires and pressure sensors suitable for measurements of the type described above. The first major problem is to make the sensor sufficiently small. Also, the number of electrical connections and leads must be minimized in order to obtain a guidewire that is easily guided to the desired location through the coronary vessels and is sufficiently flexible. One method of removing electrical leads and connections is to respond to external stimuli, for example in the form of ultrasonic energy, by emitting a resonant frequency that can be correlated to the pressures that are likely to be in the environment in which the sensor is located. That is, a resonance sensor is used. Such a device is disclosed in pending U.S. patent application Ser.
No. 9 / 219,798.

Another case is disclosed in US Pat. No. 5,619,997 (Kaplan). The patent relates to a passive sensor system that includes an implantable sensor that uses ultrasonic energy to respond to ultrasonic waves by emitting resonances that vary according to changes in selected physical variables that can be detected. I do.

[0004]

A disadvantage of these systems is that they require an external ultrasonic energy source located outside the body near the measurement location. This makes the system bulky and makes it difficult to accurately locate the resonant sensor in the body, which can result in suboptimal signal quality.

Accordingly, it is an object of the present invention to provide a system which overcomes the above-mentioned disadvantages.

[0006]

This object is achieved by a resonant pressure transducer system as described in claim 1. This allows the resonance sensor to operate with an ultrasonic energy source, e.g.
It is located close to, or preferably on, an ultrasonic energy source capable of producing vibrations in the frequency range of 00 MHz. The system is preferably provided on a wire that facilitates insertion into the patient, for example a guide wire.

In a further aspect of the invention, an AC power supply, a resonant pressure transducer system, and the A
And a controller for controlling a power supply mode of the C power supply and analyzing a resonance signal emitted from the resonance type pressure transducer system. Such a system is defined in claim 15. The invention will now be described in detail with reference to the drawings.

[0008]

DETAILED DESCRIPTION OF THE INVENTION As used herein, the expressions "mechanically coupled" or "mechanically coupled" allow the transmission of vibrations from one element to another, particularly within the ultrasonic range. Should be considered as encompassing any connection between the two elements that make it.

FIG. 1 illustrates the concept of the invention, namely the installation of a resonant sensor 2 which responds to ultrasonic energy by resonating at a selected frequency and causes a resonant frequency shift when the sensor experiences a pressure differential. Is schematically shown. The inventive concept also includes an ultrasonic energy source 4 located in close proximity to the sensor. The amount of energy stored by the resonator is very small. Therefore, a very small distance between the energy source and the resonator is essential to allow a reasonable detection level. As the distance between the two increases, it becomes more difficult to detect resonance. In the illustrated embodiment, the sensor and the energy source are preferably guide wires that are on the order of 1.5 meters in length to allow easy insertion into the patient's body and manipulation of the measurement site. Core wire 6 extending inside
Attached to the far end of the The guide wire comprises a base tube 9 and a coil 11 providing flexibility and sensor assemblies 2, 4 attached to the core wire 6 at the distal end. The sensor assembly comprises a protective tube segment 1 having an opening 13 such that the surrounding medium contacts the resonant sensor 2.
2 is desirable. At the distal end of the protective tube segment 12, a second coil 15 is mounted. The ultrasonic energy source 4 is, for example, 10 KHz
It is electrically operated by a high frequency AC voltage source of 1 to 100 V at 100 MHz. This electrical energy is supplied via leads 8,10. If necessary, the core wire 6 may be used as a lead wire to reduce the number of lead wires to one.

The ultrasonic energy source 4 preferably comprises a plate 4 of a piezoelectric material, for example lead zirconate titanate (PZT), which is adhered to the flat surface of the guide wire. Board 4
Comprises electrodes 21,22 attached to at least two faces of the plate and connected to leads 8,10.
When an AC voltage is applied between these electrodes, the applied A
Mechanical vibration occurs on the plate 4 in synchronization with the C frequency. This vibration propagates to the resonance sensor 2 via the guide wire.

As described above, the wire 6 composed of the guide wire core wire 6 is connected to the resonance sensor 2 and the PZT plate 4.
May be a long member for accommodating the above. For example, wire 6
May consist of a thin wire that functions as an antenna for wireless communication between the PZT plate 4 and an external electronic device.

In FIG. 2, for simplicity, another embodiment without leads and protective tubes is shown.
In the figure, the resonance sensor 2 is mounted on the top of the piezoelectric oscillator 4. In this way, intimate contact occurs between the ultrasonic energy source and the resonant structure, which results in a very efficient energy transfer.

Another variant is also conceivable, in which the sensor 2 and the energy source 4 are interconnected end to end, as shown in FIG. A preferred embodiment is shown in FIG. 2 and FIG. 4 schematically illustrates, but in some detail, a preferred structure of the sensor and energy source assembly. As shown in the figure, a piezoelectric element (that is, quartz) 4 is provided, and the resonance sensor 2 is mounted on the surface of the piezoelectric element 4 in close contact with the piezoelectric element 4. This resonance sensor is mounted by an undamped mechanical coupling. That is,
The energy generated by this piezoelectric element is not significantly absorbed in the connection area. Several attachment methods are possible, such as bonding, gluing or soldering in a general sense.

The resonance sensor includes a housing 14 having bottom and side walls and having a box-like structure. The opening of the housing 14 is closed by the thin film 18. Inside the housing is a resonant beam structure 16 that can take a variety of different shapes, such as a thin film shape that can be redesigned. One end of the beam structure 16 is attached to the housing wall, and the other end is
Attached to a suspension element 20 attached to the membrane 18. The beam structure 16 has a unique resonance frequency, the value of which varies according to the strain of the material constituting the beam structure. In response to a pressure change in the environment surrounding the sensor 2, which causes a change in the pressure difference between the two sides of the membrane 18, the membrane 18 will bow inward or outward, which also deflects the beam structure 16. You. This is because the beam structure 16 is attached to the membrane 18 via the suspension element 20. A suitable sensor of this type is disclosed in commonly assigned US patent application Ser. No. 09 / 219,79.
No. 4 and claimed.

A chamber or cavity 23 for receiving the beam structure 16
Is desirably evacuated in order to minimize the viscous damping of the resonance vibration of the resonance sensor 2. The quality factor Q of the resonance, defined as the ratio between the reaction energy of the vibration and the dissipated energy, must be as high as possible to produce sufficient measurement accuracy. The optimized design and structure of the resonant sensor 2 using silicon micromachining techniques typically results in a quality factor Q of 10 or more, preferably 50 or more, and most preferably 100 or more.

In the preferred embodiment, the ultrasonic energy source 4 is a device made of PZT, which is generally amorphous or polycrystalline. This ultrasonic energy source is used for both "excitation" and "listening". That is, it sends out energy that causes the resonator to resonate,
It also receives energy at the resonant frequency from the resonant beam structure in the sensor via a "box" structure and produces a detected output signal. This requires that the crystal operate at a frequency that matches the resonant frequency of the resonator.

There are several possible modes of operation of the device according to the invention (in this regard, the unpublished International Patent Application P.
CT / SE99 / 02467 is incorporated by reference). 5a and 5b show typical waveforms for excitation and detection, respectively. The excitation waveform is a sine wave burst. In an acoustic / mechanical system, the desired excitation frequency is 1 MHz and the burst consists of 10 to 1000 periods, depending on the quality factor Q of the resonator. Higher quality factors Q result in larger vibration amplitudes, so more periods are more desirable. FIG.
Indicates the formation of such vibrations. When the external power supply causing the excitation is cut off, energy is released from the resonator and attenuates at a rate determined by the quality factor Q. The frequency f _{0 of the} free vibration is equal to the resonance frequency of the resonator. FIG.
Followed by a relaxation cycle until the next burst. This relaxation period is desirably longer than the duration of the burst.

Thus, the first desirable mode is P
The ZT unit is excited by a short pulse of the applied voltage. Such an excitation includes a very broad spectrum of excitation frequencies (ideally, short pulses having a duration not exceeding a period corresponding to the resonance frequency of the resonance sensor 2). For this reason,
There is always energy available for the pulse, which causes the resonator to oscillate at its resonant frequency.

There is a non-excitation period between the pulses. During this period, the resonant sensor produces vibrations that attenuate at its resonant frequency. The PZT unit is affected by resonance energy from the resonance sensor, and a voltage is generated in the PZT unit. The change in voltage response caused by the vibrating quartz when exposed to the pressure difference, compared to the response at the nominal pressure, is measured and converted to a pressure value. The actual nominal resonant frequency of the resonant sensor under standard conditions (eg, 25 ° C. and 1 bar pressure) is determined during manufacture.

Alternatively, continuous sinusoidal excitation can be used. If the sine wave is swept continuously within the frequency range that includes the resonance frequency of the resonance sensor 2, the resonance will appear as a steep peak in the mechanical load on the PZT plate 4. This will affect the electrical impedance of the PZT plate 4 which is telemetered by the connecting leads 8,10.

The complete system of pressure measurement shown schematically in FIGS. 5a and 5b includes an AC power supply that can supply an output voltage in a controlled manner. This control is performed by a suitable controller such as a computer programmed for a number of excitation modes. Thus, the excitation mode can be selected at hand to suit a particular measurement.

The actual procedure is performed as follows. The piezoelectric device is energized with an AC voltage of an appropriate frequency in the range of 10 KHz to 100 MHz. When the piezoelectric device generates an ultrasonic wave that strikes a resonant sensor in the sensor box structure, the box structure begins to vibrate at its resonant frequency. When the membrane in the sensor structure experiences a different pressure than the surroundings, the membrane is curved, thereby causing the resonant sensor to distort, which changes the resonant frequency. When the excitation voltage is interrupted, the piezoelectric device is exposed to a damped resonant output from the resonant sensor, thereby producing a piezo voltage at the same frequency as the vibrating resonant sensor.

The piezoelectric element is, for example, 1 atm ± 500 mmH
It must be possible to detect the entire dynamic frequency range generated by the resonant beam structure of the sensor due to the pressure change of g.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a system according to the present invention.

FIG. 2 is a diagram showing a second embodiment of the system according to the present invention.

FIG. 3 is a diagram showing a third embodiment of the system according to the present invention.

FIG. 4 illustrates a preferred embodiment of a sensor / energy source assembly according to the present invention.

5A is a graph showing a typical waveform for excitation, and FIG. 5B is a graph showing a typical waveform for detection.

FIG. 6 is a schematic diagram illustrating a system encompassing the present invention.

[Explanation of symbols]

2: resonance sensor, 4: ultrasonic energy source, 6: core wire, 8, 10: lead wire, 9: base tube,
11: coil, 12: protective tube segment,
13: opening, 14: housing, 15: second coil,
16: resonance beam structure, 18: membrane, 20: suspension element,
21, 22: electrode, 23: cavity

Claims (15)

[Claims] 1. A resonant pressure transducer system implantable in vivo for in vivo measurement of pressure, comprising: a resonant sensor 2 having a mechanical resonator 16 whose resonant frequency is pressure dependent; An energy source (4), wherein the sensor (2) is mechanically coupled to the ultrasonic energy source (4), wherein the sensor and the ultrasonic energy source are remote from a common elongated member (6). A pressure transducer system provided at the end. 2. The ultrasonic energy source 4 according to claim 2, wherein:
The pressure transducer according to claim 1, which is mounted on
system. 3. The common elongated member is a wire 6.
A pressure transducer system according to claim 1 or 2. 4. The ultrasonic energy source 4 is connected to the wire 6
4. The pressure transducer system of claim 3, wherein the pressure transducer system is mounted on a pressure transducer. 5. The sensor 2 and the ultrasonic energy source 4.
2. The pressure transducer system of claim 1, wherein the pressure transducers are mounted on wires 6 and mounted adjacent to each other. 6. The ultrasonic energy source 4 has a frequency of 10 KHz.
The pressure transducer system according to any one of claims 1 to 5, wherein the pressure transducer system is a piezoelectric element capable of generating a vibration having a frequency in a range of １００100 MHz. 7. The pressure transducer system according to claim 6, further comprising an electrical connection (10) for enabling a voltage to be applied to said piezoelectric element. 8. The beam sensor according to claim 1, wherein said resonance sensor includes a membrane.
A pressure transducer system according to any of the preceding claims, wherein 6 is attached to the membrane 18 by a suspension element 20 and the beam is housed in an evacuated chamber 23. 9. The pressure transducer system according to claim 1, wherein a resonance frequency of the resonance sensor 2 has a quality factor (Q) of 10 or more. 10. The method according to claim 1, wherein the excitation of the ultrasonic energy source comprises pulses having a duration not exceeding a period corresponding to a resonance frequency of the resonance sensor. Pressure transducer system. 11. The pressure according to claim 1, wherein the excitation of the ultrasonic energy source comprises a sine wave swept in a frequency range including a resonance frequency of the resonance sensor. Transducer system. 12. The pressure transducer system according to claim 1, wherein the resonance sensor includes a housing having a box-like structure and having a bottom and a side wall. 13. The method according to claim 1, wherein the opening of the housing is closed by a thin film, thereby forming a vacuum cavity in which the mechanical resonator is provided. A pressure transducer system as described. 14. The pressure transducer according to claim 1, wherein the beam has an inherent resonance frequency, the size of which can be changed according to the strain of the material from which the beam is made. ·system. 15. An AC power supply capable of supplying AC power in a frequency range of 10 KHz to 100 MHz, a resonance type pressure transducer system according to claim 1, and controlling the AC power supply mode. A control device for analyzing a resonance signal emitted from the resonance type pressure transducer system.