Acoustic wave devices

[0001] The present invention relates to devices for acoustic waves, and in particular, but not exclusively for devices of the type Surface Acoustic Wave (SAW). SAW devices have been known for almost two decades, where their main application is signal processing in telecommunications, and recently also as distance sensors in the automotive industry. Their main advantages in use are a) acting as transducers in physical and chemical measurements b) introduction of complex function processing signals on small piezoelectric substrates on a completely passive path, and c) communication with remote electronic systems using electromagnetic waves [0002] The present invention focuses in one aspect on the use of SAW devices implantable (inside the body) or used outside (outside physiological monitoring and not necessarily in direct contact with it).

[0003] The purpose of physiological monitoring is to obtain a system that would allow continuous, direct, long-term and accurate monitoring of various variables under safe and clinically acceptable conditions. Many different tests were carried out to achieve such effects, but unfortunately in practice these tests did not bring the expected results due to such problems as the large size of the device, the need for power supply (limitation due to battery life), lack of accuracy, risk of infection and degradation of performance such devices.

[0004] In routine health care, it is often required to measure certain parameters that indicate the patient's state of health. For some measurements, there is an infinitely small risk and there is practically no problem in making such measurements. For many other measurements, there is a risk associated with this, and then the clinical technician uses risk evaluation and experience to determine if such measurements are made or not. The measurement of signals that are located inside the body usually involves balancing the measurement values ​​with respect to the risks associated with the invasive procedure.

[0005] For example, blood pressure measurement can be performed in a number of ways, which are listed here in order of increasing risk:

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1. A representative system blood pressure can be measured indirectly via an externally pumped cuff or forearm.

2. A representative systemic blood pressure measurement can be more accurately measured by venous artery penetration and catheter insertion.

3. The measurement of left ventricular pressure involves inserting the catheter into the venous artery and directing it so that the tip is in the left ventricle.

[0006] With long-term monitoring of patients, the repeated use of invasive measurements increases the risk and ultimately may lead to the doctor's conclusion that the entire procedure is too dangerous for the patient.

[0007] Implantable sensors are an alternative to existing problems with measuring blood pressure by the techniques described above, for example. When the implant is inserted, it can provide the desired information for a long time without unnecessary risk throughout its life.

[0008] Communication with the implant can be via inductive coupling or via radio frequency from a transmitter / receiver located outside the patient's body.

[0009] US-A-6206835 describes the use of SAW devices whose characteristic impedance is changed by different types of condenser pressure transducers that charge SAW. Another application is disclosed in US-A-5702431, in which the implemented and battery-driven circuit is charged by inductive coupling. US-A-6539253 describes the use of SAW filters in implants: their high stability and high Q factor in the SAW device is considered to be predominant in the design of electronics.

[0010] When surface acoustic wave type devices are preferred for foreseeable applications, large acoustic wave devices can alternatively be used to obtain more electricity.

[0011] With respect to one aspect of the present invention, there is provided a method of monitoring pressure in the human or animal body, where an acoustic wave device that is implanted or attached to the body is an acoustic wave device and a large wave device acoustic (bulk acoustic wave device), contains connected transducers separated from each other by a surface composed of a piezoelectric substrate, which seals the chamber to form the transducer body, and which substrate is exposed to monitored pressure, where the antenna is connected to one of the transducers, where the radio frequency signal is supplied from the outside of the apparatus to the antenna and is transmitted over or through the surface of the substrate as an acoustic wave to others transducers, and then it is reflected to one of the transducers and transmitted from the antenna to the receiver, and where a comparison of the supplied and received signal provides information about the pressure measurement.

[0012] With respect to the second aspect of the invention, an acoustic wave device that is one of the surface acoustic wave devices and bulk acoustic wave devices created to monitor pressure in the human or animal body by implanting or attaching to the body contains a transducer that defines the chamber and piezoelectric substrate that seals the chamber to form the transducer body, and which substrate is exposed to monitored pressure, and comprises connected transducers separated from each other by the surface of the substrate and an antenna connected to one of the connected transducers.

[0013] The pressure measurement can be made by determining the delay or change in the resonant frequency of the acoustic wave.

[0014] Several acoustic wave devices may also be used such that each of them operates at a different frequency.

[0015] SAW devices are particularly suitable for such applications because of their sensitivity to physical and chemical variables, very small size, original stability and zero in situ energy demand. This causes a significant change in the quality and amount of information that becomes available to the clinician with little risk to the patient. SAW devices can also be used as a communication link to and from an implanted system or device.

[0016] Thus, the present invention relates, for example, to a medical implant-type device used as a sensor that can be attached to the outside of the body excluding physical contact. The signal received from the sensor contains information about the patient's medical condition, which can then be used for diagnostic purposes and / or for automatic control of the device or therapy used.

[0017] The invention relates to the use of the SAW device as both a sensor element for required measurements as well as as a communication element for distance adaptation of measurements.

[0018] The use of the present invention for use as a SAW device for measuring pressure will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a schematic isometric view of one SAW device; Fig. 2 shows the section of line II-II for Fig. 1.

[0019] One of the most demanding and critical goals in physiological monitoring is to assess the condition of the heart and the main circulatory system. Currently, the only type of information that a cardiac or cardiovascular surgeon can receive is that of an indirect nature or is the result of a non-invasive measurement, i.e. as a result risky in terms of data, which exposes the surgeon to inaccurate information, and thus the use of not necessarily good therapy. The minimally invasive transducers for monitoring local cardiac or venous pressure according to the present invention allow a significant step forward. The transducer can be implanted in the ventricles of the heart or anywhere in the circulatory system to monitor local pressure to obtain absolute or differential pressure through the described system.

[0020] Two of the possible approaches include:

1. Use of a delay line: pressure refers to the time it takes the SAW to transport on the surface of the device

2. Use as a resonator: pressure changes the natural frequency of the device.

Use as a delay line

[0021] The monitoring system consists of an implantable transducer 2 formed of the SAW device (Fig. 1) and antenna 4.

[0022] The SAW 2 device is sensitive to pressure changes by forming it on an etched substrate sealed on a reference chamber that is vacuum or filled with gas under pressure. Referring to Fig. 1, the SAW device transducer has a generally rectilinear structure 6 of piezoelectric material. Two sets of metal connected fingers (IDTs) 8, 10 are arranged at a distance from each other on the main upper surface 12 of element 6. As shown, antenna 4 is connected to one of IDT 8, while the antenna is not connected to IDT 10. Another, lower surface 14 of transducer 6 is etched to form chamber 16, which is a closed sealing surface 18. Chamber 16 can be emptied or filled with gas under pressure at the right pressure. This structure causes the upper surface of the transducer 12 to carry idts 8, 10 to respond to external pressure.

[0023] The pressure difference between the reference chamber 16 and the measurement site against which the upper surface 12 of the device is exposed will lead to separation between SAW IDTs 8, 10 on surface 12 at both ends of the transducer

2. This change in separation will change the delay of the surface acoustic wave that is generated outside the patient, in which the transducer 2 is implanted, and which is detected by the antenna 4 by transmitting along the surface of the transducer 12 from IDT 8 to IDT 10, and then reflected back to IDT 8 and antennas 4.

[0024] The acoustic wave created by IDT 8 by radio frequency (RF) stimulation of the pulse received on antenna 4 of device 2 from a non-external source will pass through device 2 and will be reflected through device 2, where IDT 8 will change RF energy again, which will be transmitted through antenna 4 to an external receiver. The time between stimulation and RF pulse transmission is used to measure pressure.

[0025] An alternative solution is to have two antennas, where the second antenna is a 4 'antenna as shown in Fig. 1, and is connected to the second IDT 10 of the transducer 2.

The stimulating RF pulse received by one of the 4 or 4 'antennas is then processed into

A surface acoustic wave that will pass through the transducer 2 until it reaches the second

IDT 10, where it will be converted back to RF and will be transmitted through one of the 4 or 4 'antennas. Again, the time between stimulation and RF pulse transmission is used to measure pressure.

Use as a resonator:

[0026] With devices as described above, with one or two IDTs and one or two antennas, the pressure difference between the reference chamber and the place where the measurement takes place differentiates the separation of the IDT fingers of structures 8, 10, and thus also the natural surface frequency an acoustic wave that will be generated by receiving an RF pulse. The pressure difference will change the distance between the fingers connected in the SAW and as a result change the outgoing frequency of the device 2. Other physical parameters such as temperature, liquid viscosity and even flow may change the frequency and therefore you need to be careful that the sensor is specific for pressure changes in order to eliminate the undesirable effects caused by changing other parameters on the output signal of device 2.

[0027] Changing the outgoing frequency facilitates the detection of information transmitted to an external receiver. In traditional systems such as RF ID equipped with sensor devices, the main problem to overcome is the difference between transducer results and reflections that occur naturally at the border of two different tissues. As the SAW device changes the outgoing frequency, you can easily distinguish information from natural reflections.

[0028] The external system consists of an external antenna placed orthogonally, which leads to stimulation of the implemented device and collects the sent signal. With both approaches, the delay line and resonator, the whole system can be obtained so that it is insensitive to other factors by using SAW devices - one sensitive to the desired measurement parameters and the other which is not sensitive by designing and using references to block the undesirable effect parameters such as temperature and distance changes.

[0029] The present invention may, for example, find application in long-term monitoring of pressure dependence on left ventricular volume which provides critical information on cardiac function. Patients with an implanted cardiac support device or with a transplanted heart can be monitored continuously during the postoperative period and at specific times later throughout their life. Implanting biocompatible, hermetically sealed SAW sensors during surgery provides a simple and acceptable addition to the operating procedure and can provide information that can be used in the early diagnosis of subsequent heart problems without the risk of invasive interference with this organ.

[0030] Cardiological monitoring is only one application of the device shown. Another of its applications is the use of closed loop control in cardiac assistive devices, where immediate pressure measurement is generated by a combination of natural heart activity and an assisting device and can be used to control the settings of the assisting device to control good blood circulation in the patient.

[0031] The use described above relates to the use of the SAW device for monitoring a single cardiological parameter - pressure. It is believed, however, that the above device may be implanted anywhere in the patient's body to monitor, for example, intracranial pressure, pressure at sites of function and function of the digestive system, or bladder pressure. The long-term accuracy of these devices leads to better knowledge about the patient, which makes it easier to care for his health.

[0032] In other applications, SAW can be obtained to obtain particularly sensitive parameters with respect to temperature, stress and neurosis, or to determine the concentration of certain chemical ions, e.g. oxygen, to determine the pH value, determine the concentration of compounds, e.g. dioxide carbon, and when a special coating is used, to analyze specific compounds such as protein or in particular glucose. A very large number of transducers can be used, and each of them uses a transducer requiring no energy to communicate with the external element, as described in the pressure measurements above.

[0033] The devices described in this invention can also be used externally, and not necessarily in the form of implants, as long as the desired chemical or physical parameter can be measured in this way. What's more, SAW devices can be used to both control and monitor functions in conjunction with other implanted systems, such as pacemakers or cardiac assistive devices.

[0034] The devices described above are surface acoustic wave devices. However, it is also believed that bulk acoustic wave devices can be used as an alternative to physiological monitoring in which the acoustic wave passes through the body of the device rather than along its surface.

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