ES2524733B2 - Wireless sensor to detect pressure - Google Patents

Abstract

Wireless sensor for detecting pressure. # The present invention relates to a wireless sensor for detecting pressure comprising a closed ring of magneto-elastic amorphous micro thread. # It also refers to a device for detecting the pressure exerted by a fluid flowing through a conduit or a tube of rigid or flexible walls that includes this sensor and the method with which to detect the pressure in the conduit or tube.

Description

Wireless sensor to detect pressure.

Technical Sector

The present invention is part of the sensor manufacturing sector to relieve the pressure of a fluid, as well as pressure variations, by using magnetoelastic magnetic materials. In a specific application, it refers to the manufacture of implantable and wireless biomedical sensors that allow obtaining information on blood pressure.

State of the art

The determination of the pressure exerted by a liquid on the walls of the

element that contains it may be of interest in numerous situations. The

Tubes and pipe systems are the fast and economical transportation of

liquid and gaseous products. Generally, these pipes are buried

in order to protect them from environmental effects and for safety reasons. The burial of the pipe does not prevent damage caused by possible phenomena

geological as avalanches and landslides. Any movement

of the earth that surrounds the conduction, or any increase in unforeseen pressure, transmits in it forces, which can cause damage in some

abnormal cases or tensions. Hence the need for a system of

diagnosis capable of monitoring the safety parameters related to the

pipe and surrounding areas. For these detections they have been used

different types of sensors such as piezoelectric (G.P. Carroll.

Noninvasive measurement of dynamic pressure inside pipes using piezoelectrie

strip; J. Acoust. Soco Am. 89, 1943 (1991 »or fiber optic (Method and apparatus

for the non-invasive measurement of pressure inside pipes using a fiber optie

interferometer sensor: US 5218197) or indirect measurements of relative pressure changes (A. M. Sadeghioon, et al. SmartPipes: Smart Wireless Sensor Networks for Leak Detection in Water Pipelines J. Sens. Aclualor Netw. 2014, 3.64-78).

Especially interesting is the determination of vascular tension, that is,

the tension of the blood vessel wall, which results from the pressure of the circulating blood and the muscular and elastic tone of the vessel walls.

As an example, a particular case is the determination of blood pressure and of special interest is the postoperative follow-up of vascular reconstructions, such as those that may occur in the case of abdominal aortic aneurysm (AAA). The aorta is the main artery that carries oxygen-laden blood from the heart to all other parts of the body. AAA occurs when a weakened section of the aorta cannot withstand the blood flow pressure and is defined as the increase in the diameter of the aorta in

more than 50% of its original size. Its rupture is the biggest clinical consequence. With the early practice of surgical resection and replacement techniques

prosthetic breakage is avoided. The treatment of choice of AAA is the replacement of the aneurysm segment with an aortoaortic or bifurcated prosthetic graft,

depending on the affectation of the territory ¡liaco for atherosclerotic disease

aneurysm or obliterans.

Aneurysmal exclusion, that is, aneurysm isolation, is achieved by implantation of a stent and is known as repair.

endovascular aneurysm (EVAR). The stent is a synthetic prosthesis

in the form of a reinforced tube with a metal structure; It aims at thrombosis of the excluded sac, reduction of aneurysmal diameter and,

finally, the elimination of the risk of rupture when blood flow passes through the

inside the stent to the rest of the organism. However, the

Specific complications require an indefinite follow-up of the

patient and are a frequent cause of reinterventions. It is precisely the reinterventions, the majority of endovascular nature with low mortality, the

that limit the extensive application of EVAR.

Therefore, conventional surgery requires long-term clinical and instrumental follow-up, since conventional prostheses are not

free of complications, such as infection, thrombosis, pseudoaneurysms,

aortoenteric fistula, stomosis and anastomosis. The EVAR, by its character

novel, the fatigue of the materials involved in the construction of the

stents and fixation less active than the surgical suture, makes

a closer and more intense clinical and instrumental follow-up is advisable. The

contrast computed tomography (CT angiography) (Link J, Brossman J Grabener M. Spiral CT angiography of interval carotid artery stenosis. Am J Neuroradiol1996; 17:89) is the technique of choice for preoperative study and for the detection of most complications, particularly of the

stenosis. The limitations of this technique are the radiation and contrast used, which have been related to the worsening of renal function to a greater extent than the intervention itself.

In some cases, CT angiography can be replaced by conventional radiography

and vascular echo-Doppler (Radermacher J, Chavan A, Bleck J, Vitzthum A, Stoess B, Gebel MJ, Galanski M, Koch KM, Haller H. Use of Doppler ultrasonography to predict the outcome of therapy for renal-artery stenosis. N Engl J Med. 2001 Feb 8; 344 (6): 410-7). The radiograph allows you to evaluate the integrity of the stent metal structure, the plications (that is, the

folding, shortening or decreasing the tamat "the blood vessel

through the formation of folds), disconnections and migration of the prosthesis. Echo-Doppler determines the aortic diameter, prosthetic permeability and the presence of leaks, with a sensitivity of 95% and a specificity of 97%. However, there are limitations related to the person who practices the examination and also to its practicability in obese patients. Magnetic resonance imaging (MRI) with contrast has the same properties as CT angiography, but eliminates the risk of nephrotoxicity

and ionizing radiation; in the follow-up of certain stents has

presented good results in the detection of leaks.

The possibility of quantifying blood pressure in the prosthesis as well as the pressure

in the aneurysm sac, non-invasively, after the operation

endovascular, provides great advantages since an increase in tension in

the area of the artery or prosthesis near the "bypass" between both elements

It has a clear relationship with the presence of anastomosis and / or stenosis.

For the measurement of physical parameters in living organisms, passive resonator circuits have been used that allow the design of wireless sensors without

Need to use batteries. For example, they have been designed for the continuous measurement of intraocular pressure (S. Lizón-Martinez, R. Giannet! I, J. L. Rodrlguez-Marrero and B. Tellini, "Design of System for Continuous Intraocular Pressure Monitoring," IEEE Transaction or (Instrnmentation and Measurement, vol. 54, no. 4, (2005)), transcranial (MR Shah, RP Phillips and RA Normann, "A Study of Printed Spiral Coils for Neuroprosthetic Transcranial Telemetry Applications," IEEE Transactions on Biomedical Engineering, vo1.45, no. 7, (1998)), in the aneurysm sac (l. A. Sanches et al. "Chronic

intraaneurysmal pressure measurement: An experimental method ter evaluating the effectiveness of endovascular aortic aneurysm exclusion, n J. Vascular Surgery, vol. 26, issue 2, pp 222-230, (1997)). A limitation of these devices is their size and their biocompatibility (MA Fonseca, M. G. Allen,

J. Kroh and J. White, "Flexible wireless passive pressure sensors for biomedical applications, Solid-State Sensors, Actuators, and Microsystems Workshop Hilton Head Island, South Carolina, June 4-8, 2006). Another option is the use of MEMS (Microelectromechanical Systems), which detect pressure using a piezoresistive material, as in US8529474 in which

an implantable system for monitoring tension is described as an indicator of biological conditions, such as spinal fusion, glucose levels,

heart rate; or US20100024561 in which a

implantable sensor in the wall of the arteries, which can be inserted between the layers of the wall or secured to the vessel by bands of materials

Biocompatible with several possible provisions.

Detailed description of the invention

Wireless sensor to detect pressure.

The present invention relates to a wireless sensor for detecting pressure

in a duct or in a tube where a fluid flows. Duct or tube

It can be simple or have one or more bifurcations along its length. 5 In addition, the walls of the duct or tube can be flexible or rigid,

provided they are not metallic. In a preferred embodiment, the wireless sensor of the invention serves to detect blood pressure or pressure in a stent.

The sensor comprises a closed micro-wire ring with a magnetoelastic size sensitive to pressure variations, variations detectable by electromagnetic waves.

The magnetic wire to be used must be a magnetostrictive amorphous magnetic wire with a borosilicate glass cover; FexCoa_ composition

,., Ni, Si, BwMt (where a + z + w + t ~ 100, 70,; axy,; 7S, O,; x + y,; S, 0,; z + w,; 2S, 0, ; 1,; 3, M ~ Nb, Mo); with a low but negative magnetostriction constant whose values are between -1 ppm and -O.OS ppm; with low anisotropla field, between 100 and 2000 Nm; and with a diameter of the metal core 20 of value between 30 and 100 microns. In this way, the length of

penetration of a GHz electromagnetic wave is not negligible against

to the radius of the micro thread, so the reflectivity coefficients of said wave

can be modified according to the impedance of the wire which, being magnetic,

It is conditioned by its magnetic permeability.

Said magnetic permeability, due to the low magnetic anisotropy of the

micro thread is easily modifiable by the application of a magnetic field and, due to its magnetostrictive character, by the application of mechanical tension.

The presence of a closed ring of magnetic thread, subjected

constantly at a low frequency magnetization and demagnetization cycle,

•

It allows the modulation of a high frequency wave. This modulation is

It will be affected by mechanical stress. The negative magnetostriction of this type of wire favors the response of the ring to the electromagnetic wave because

radial tensions translate into increased susceptibility according to

the circular direction favoring the dispersion of the wave. To optimize the

detection, the radius (r) of the ring must be less than the wavelength (Al of the electromagnetic radiation, fulfilling the ratio r / A = 1/20.

In the present invention, low frequency means between 10 and 100

millihertz, and high frequency means between 1 and 20 GHz.

Likewise, when the magnetic micro-wire ring of the invention is mentioned, mention will be made at all times of a closed magnetic micro-wire ring.

Another aspect of the invention relates to a system for wireless detection of the voltage variations to which the closed micro-magnetic ring is subjected and which depend on the pressure variations that

experience This system consists of two parts. A first electrical circuit powered by a low frequency sinusoidal signal that feeds a winding that generates a magnetic field lower than the anisotrop field of the micro wire used. Said circuit allows the magnetization and periodic dewatering of the micro-wire ring placed in the conduit or the tube through which a fluid flows and whose tension is to be evaluated. A second circuit is used

to emit and receive, by means of both transmitting and receiving antennas, a high frequency signal so that the frequency coincides with the frequency of

resonance of the chosen thread, being between 1 and 2 GHz the

Resonance frequency of the chosen thread.

For the specific case of blood pressure detection, the electromagnetic wave dispersion coefficients, due to magnetic susceptibility,

They are modified simultaneously by:

-

the alternating magnetic field generated by the electrical circuit, that is, the first circuit of the detection device, and involves the periodic magnetization of the micro wire, with a frequency of between 10 and 100 millihertz,

-

the process of periodic mechanical relaxation and relaxation generated by the pumping

5 of the blood flow, with a periodic frequency signal between 0.5 and 2 Hz.

That is, the signal reflected by the thread will present a modulation of the frequency of the low frequency field generated by the first circuit to which another periodic signal of frequency between 0.5 and 2 Hz is superimposed

10 from the pumping of blood flow.

On the other hand, another aspect of the invention includes the necessary means for

process the signal by Fourier transform to detect the

modifications in the pressure in the tube or conduit in which the closed ring of magnetoelastic amorphous micro thread has been integrated or introduced and to detect problems of narrowing of the tube or conduit.

The invention also relates to an arterial stent that includes a ring

of magnetoelastic amorphous micro thread introduced into the wall of the own

20 prostheses concentrically in light of it.

Another aspect of the invention relates to a method for detecting the pressure in a conduit or a tube through which a fluid flows comprising: including in the conduit or tube a closed ring of amorphous magnetic micro thread

25 magnetostrictive with borosilicate glass cover; FexCoa composition

, _yNiySi, BwMt (where a + z + w + t = 100, 70,; ax-y575, 0,; x + y,; 5, 0,; z + w,; 25, 0,; t,; 3 , M = Nb, Mo); with a magnetostriction constant between -1 ppm and -0.05 ppm; with anisotropy field between 100 and 2000 Nm; and with a diameter of the metal core of value between 30 and 100 microns;

30 -apply, simultaneously, a magnetic frequency field between 10 and 100mHz and a high frequency electromagnetic wave, between 1 and 20 GHz, by means of a transmitting antenna (11);

-

process the signal received by the receiving antenna (12) by Fourier transform.

The invention also relates to a method for detecting narrowings in

a conduit or tube through which a fluid flows comprising:

-

include in the duct or tube, concentrically in the light of said duct

or tube, a closed ring of magnetostrictive amorphous magnetic micro wire with borosilicate glass cover; of composition FexCoa.x-yNiySizBwMt (where

a + z + w + t = 100, $ 70 a-x-y $ 75, $ 0 X + and $ 5.0 $ z + ws. 25, $ 1 $ 3, M = Nb, Mo); with a magnetostriction constant between -1 ppm and -0.05 ppm; with anisotropy field between 100 and 2000 Alm; and with a diameter of the metal core of value between 30 and 100 microns;

-

apply, simultaneously, a magnetic field of frequency included

between 10 and 100 mHz using Helmholtz coils, and a wave

High frequency electromagnetic, in the range of 1-20 GHz, by means of a

transmitter antenna (11);

-

process the signal received by a receiving antenna (12) by Fourier transform.

-

identify decreases in the intensity of the first frequency of the

Fourier transform with respect to the intensity of [at the first frequency of the Fourier transform in the same tube or conduit when it does not show alterations.

Description of the figures

Figure 1 shows a schematic of the hydraulic circuit with the following

elements: micro thread-sensed artery (1), fluid flow (2), seal for

hydraulic resistance (3), pressure gauge (4), valves for hydraulic resistance

(5), ventricular assist device (6)

Figure 2 shows a scheme of the electromagnetic circuit with the

following elements: function generator (7), amplifier (8), ammeter (9), Helmholtz coils (10) transmitting antenna (11) and receiving antenna (12),

stent or sensorized artery with micro-wire ring (1), vector analyzer (13).

Figure 3 shows the curve associated with the modulation of the GHz wave by the presence of a magnetic micro-wire ring in the absence of pulsatile flow

(a) and the same curve modified by a pulsatile flow of 40 beats per minute (b).

Figure 4 shows the evolution of the signal associated with the presence of pulsatile flow with the pressure difference in the vicinity of the micro-wire ring

stent magnetic; it shows a succession of attenuation registers for different pressures of the circuit (a) together with the values of

the amplitudes of the register as a function of the pressure (b).

Figure 5 shows the evolution of the signal associated with the presence of pulsatile flow with the pressure difference in the vicinity of the micro-wire ring

magnetic for artery; it shows a succession of records of

attenuation for different circuit pressures (a) together with the values of the amplitudes of the register as a function of the pressure (b).

Figure 6 shows the evolution of the signal associated with a difference of

pressure of 70 mmHg (a) with the presence of pre-ring stenosis (b) and postanillo (e).

Figure 7 shows a graft with a closed micro-wire ring positioned

in one of the bifurcations of the graft (a) and at the tip of the anastomosis (b).

Figure 8 shows, for the micro thread located in the graft, the cases of

graft stenosis (a), anastomosis (b) and distal stenosis (e), as well as the corresponding graphs for a pressure of 155 mmHg (a, bye, respectively), together with the graph associated with O mmHg (e) and the graph associated with 155 mmHg without stenosis (d).

Figure 9 shows, for the micro thread located at the tip of the anastomosis, the cases of graft stenosis (a), anastomosis (b) and

distal stenosis (e), as well as the corresponding graphs for a pressure of 155 mmHg (a, b and e, respectively) together with the graph associated with O mmHg (e) and the graph associated with 155 mmHg without stenosis (d).

Embodiment of the invention

The present invention is further illustrated by the following examples, which are not intended to be limiting in scope.

In order to show the embodiment of the invention, the

blood flow pressure detection because it is a special case in which

we must also take into account the pumping of the flow produced by the heart.

Example 1. Hydraulic circuit to simulate blood flow.

In order to simulate the pumping of the blood flow located in an artery, a hydraulic circuit was designed (figure 1) consisting of a circuit with pulsatile flow connected to a ventricular assistance system (Abiomed / AB5000), in which a seal of water (3) and two resistors (5) in parallel to

allow control over fluid pressure. To ensure that the fluid flowing through the circuit had a viscosity similar to that of blood at 37 ° C,

0.33% agar agar solution was performed.

The described hydraulic circuit allows to have a fluid flow (2) with a

pumping frequency of 0.666 Hz, which is a signal with a period of 1.5 s that would correspond to a pumping of 40 beats per minute.

To be able to record at every moment the pressure of the fluid that crosses the

Two systems were connected non-invasively connected distally and proximally to the sensor, that is, to the micro-wire ring (1). This arrangement allows to calculate the fluid pressure index as a quotient between the two

values.

Example 2. Monitoring of tension variations in arteries. As a sensor element, a closed micro-wire ring (1) was placed on a

Bovine renal artery sample. The micro thread ring (1), due to its character

magnetoelastic, allows to monitor non-invasively the variations of mechanical tension due to the variations in pressure that occur in the artery.

A closed 6 mm diameter micro-wire ring with a borosilicate glass and metal core cover composition of

Fe2 ,,, Co72,75ShoB15, magnetostriction constant, A, -0.1 ppm and anisotropy field of 400 Nm; the metal core diameter was 50 microns and the total diameter 80 microns, in this case, adjusted the diameter of the ring to that of

the 6 mm artery.

The ring-artery assembly was included in the hydraulic circuit described more

above (figure 1). Said set was simultaneously subjected to a field

Low frequency magnetic (10mHz) generated by Helmholtz coils

(10) and to a high frequency electromagnetic wave (1.29GHz) coming

of a transmitting antenna (11) (figure 2). Mechanical tension variations

on the sensor element, they suppose a modulation of the emitted wave

detectable by a second antenna, which is a receiver (12). Both

antennas are connected to a vector analyzer (13) so that

we will obtain a variation of power due to the different pressures.

The device described in figures 1 and 2 allows monitoring

Wireless pressure variations in the ring-artery system. The presence of the magnetic micro-wire ring (1) subjected to an alternating field of 10 mHz implies a modulation of the GHz signal received in the receiving antenna (12). The increase in fluid pressure as it passes through the circuit implies

superposition of another signal with the frequency of pumping the blood flow.

The amplitude of the superimposed signal (As) is proportional to the overpressure.

Example 3. Monitoring of tension variations in prostheses. Examples 1 and 2 were repeated using a tetlon stent

(Polytetrafluoroethylene, or PTFE, 6 mm) in which a ring had been included

micro thread closure as described in example 2.

Example 4, Correlation between the pressure in the artery or the stent and the electromagnetic signal.

The previous examples allowed the pressure in the artery or stent to be correlated with the attenuation signal generated by the electromagnetic circuit.

In the case of the stent, for a fluid pressure of 50mmHg,

generated a signal variation of 2.25-10-3 dB, for a pressure of

142mmHg was 3.97'10-3 dB for and for 170mmHg a variation of 7'10-3 dB. Therefore, a direct relationship between the fluid pressure and the attenuation signal generated by the electromagnetic circuit was obtained (Figure 4). In the case of the artery, for a fluid pressure of 100mmHg a signal variation of 0.025dB was generated, for a pressure of 140mmHg it was 0.030 dB and for 200mmHg a variation of 0.064 dB (Figure 5).

Example 5. Detection of stenosis. The variation in the amplitude of the signal received by the receiving antenna (12) when producing stenosis in different locations and of different degrees was also studied. This grade is quantified from the pressure index considered.

as the relationship between the pressures detected in the distal zone -post-ring

(c) in Figure 6-and proximal-pre-ring (b) in Figure 6-with respect to fluid flow. The amplitude of the superimposed signal (As) on the curve of

Attenuation obtained for stent measures varies with the degree of

severity of stenosis Variations in the baseline associated with both the severity of the stenosis and its location were also observed.

Thus, if we compare both types of curves based on the location of the

5 stenosis (Figure 6), we clearly observe that post-ring stenosis (e) produces a wave of greater frequency and amplitude with respect to the baseline (device in 70mmHg) (a); and preanillo stenosis (b) also produces

significant changes with respect to the control curve (a). In both stenosis, an increase in the curl of the curve can be seen and can be related to the

10 appearance of the turbulent flow typical of stenosis (figure 6).

Graft stenosis and distal stenosis have also been detected for the case in

which the micro thread ring is located in the graft (figures 8a and 8c,

respectively) and in the case of the micro thread ring located at the tip

15 of the anastomosis (Figures 9a and 9c, respectively).

Example 6. Detection of stenosis in anastomosis. The detection of stenosis in the anastomosis was also performed for cases

in which the micro thread ring is located at the tip of the anastomosis (figure 20 9b) and in which the micro thread ring is located in the graft (figure 8b),

observing variations in the amplitude of the signal with respect to the graph

associated with O mmHg (e) and the graph associated with 155 mmHg without stenosis (d).

Claims (10)

1. Wireless sensor for detecting pressure in a tube or conduit through which a fluid flows comprising a closed ring of magneto-elastic amorphous micro-wire of FexCoa_x_yNiySizBwMt composition (where a + z + w + t = 100, 70, ;; axy, ;; 75, 0, ;; x + y, ;; 5, 0, ;; z + w, ;; 25, 0, ;; t, ;; 3 and M = Nb, Mo) ; with borosilicate glass cover; with magnetostriction constant between -1 ppm and 0.05 ppm; with anisotropy field between 100 and 2000 Nm; often resonance between 1 and 2 GHz; and with a metal core diameter comprised between 30 and 100 microns. 2. Wireless sensor according to claim 1 wherein the composition of the Magnetoelastic amorphous microbe is Fe2.25Co72.75SilOB15. 3. Wireless sensor according to any of claims 1-2 wherein the metal core diameter of the amorphous micro-wire closed ring magnetoelastic is 50 microns and the total diameter of the closed ring of Magnetoelastic amorphous microhil0 is 80 microns. 4. Wireless sensor according to any of claims 1-3 wherein the Closed ring of magnetoelastic amorphous micro thread has a diameter of 6 mm. 5. System for detecting pressure in a tube or conduit through which a fluid flows comprising:

-

a sensor as defined in claims 1-4; -An electrical circuit powered by a sinusoidal signal of frequency between 10 and 100 millihertz that feeds a winding that generates a field

magnetic equal to less than 99 Nm; -a circuit that includes a transmitting antenna (11) and a receiving antenna (12) with which it emits and receives a signal between 1 and 20 GHz whose frequency coincides with the resonance frequency of the sensor micro thread defined in claims 1-4:

-

means to process the GHz signal.

6. System for detecting pressure according to claim 5 wherein the wavelength (A) of the electromagnetic radiation and the radius of the closed micro-wire ring (r) meet the ratio r / A = 1/20.

7. Method to detect the pressure in a conduit or tube through which a

fluid comprising:

-include in the duct or tube, concentrically in the light of said duct

5

or tube, a sensor as defined in claims 1-4;

-apply, simultaneously, a magnetic field of frequency included

between 10 and 100 mHz using Helmholtz coils, and a wave

High frequency electromagnetic, in the range of 1-20 GHz, by means of a

transmitter antenna (11);

10

-process the signal received by a receiving antenna (12) by

Fourier transform.

8. Method for detecting narrowings in a conduit or tube through which it flows

a fluid comprising:

fifteen

-include in the duct or tube, concentrically in the light of said duct

or tube, a sensor as defined in claims 1-4;

-apply, simultaneously, a magnetic field of frequency included

between 10 and 100 mHz using Helmholtz coils, and a wave

High frequency electromagnetic, in the range of 1-20 GHz, by means of a

twenty

transmitter antenna (11);

-process the signal received by a receiving antenna (12) by

Fourier transform.

-identify decreases in the intensity of the first frequency of the

Fourier transform with respect to its intensity in the tube or conduit without

2S

alterations

9. Arterial stent that includes a wireless sensor defined according to the

claims 1-4 introduced into the wall of said prosthesis in a manner

Concentric in light of the stent.

30