A flexible polymer ultrasound probe

Abstract

The present invention belongs to the field of flexible electronics, and specifically is a flexible polymer ultrasonic probe. The flexible polymer ultrasonic probe of the present invention is a multi-layer structure, which includes a shielding layer, a backing layer, an upper electrode, a piezoelectric layer, a lower electrode, a matching layer, and a coupling layer from top to bottom; all functional layers are made of polymers and their composite materials, have very good flexibility, and can withstand complex deformations such as bending and twisting. The flexible polymer ultrasonic probe can emit ultrasonic waves under the excitation of electrical signals as an ultrasonic transmitting unit, and can also collect ultrasonic signals as an ultrasonic receiving unit. The flexible polymer ultrasonic probe can be made into a patch for industrial flaw detection of irregular surface objects and long-term health monitoring of the human body. For example, based on the ultrasonic Doppler principle, long-term continuous monitoring of blood flow velocity in human blood vessels can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of flexible electronics, and in particular relates to a flexible polymer ultrasonic probe. Background Art

[0002] Medical ultrasound testing is a medical diagnostic technology based on ultrasound. It has the advantages of being non-invasive, high-precision, high-sensitivity and strong penetrating power. It has been widely used. Ultrasound technology can detect the size, shape and physical characteristics of solid organs. In recent years, it has also made great progress in the fields of cardiac ultrasound, obstetrics and gynecology ultrasound, intracavitary ultrasound and ultrasound angiography. In addition, ultrasound technology can also be used to monitor the structure, function and hemodynamic status of arterial blood vessels. In industrial flaw detection, ultrasound testing has the advantages of high sensitivity and non-destructiveness, and has broad application prospects.

[0003] For example, taking blood flow as an example, the changes in blood flow in time and space reflect the condition of a person's blood vessels. The blood flow in the blood vessels is usually not uniform. Due to the periodic beating of the heart to pump blood, the blood flow in the arteries presents periodic pulsating changes. Due to the viscosity of the liquid, the liquid flowing in the pipe will be stratified. The blood layer in contact with the blood vessel wall is close to static. The closer to the center of the blood vessel, the faster the flow rate. The blood flow velocity near the blood vessel wall is inconsistent with the blood flow velocity in the center of the blood vessel. Turbulence will also occur in some blood vessels with fast blood flow. The distribution of blood flow velocity can indicate a variety of vascular diseases such as thrombosis, arterial stenosis, sclerosis, occlusion, etc. Ultrasonic Doppler technology can detect the distribution of blood flow velocity in blood vessels, and long-term continuous monitoring of blood flow velocity is of great significance for the diagnosis and prevention of some vascular diseases. For example, the occurrence of ischemic stroke is partly due to carotid artery stenosis. The formed blood clots block the carotid artery or transfer to the brain to cause embolism. Timely detection of abnormalities is very important for the prevention of such diseases. Continuous monitoring is also important for preventing patients from recurring diseases after surgery. In addition, after surgeries such as vascular reconstruction or stent implantation, there are certain risks at the surgical site of the patient, which requires continuous monitoring and evaluation. Patients can only receive evaluations for a limited time in the hospital and lack effective long-term monitoring methods after discharge.

[0004] However, current ultrasound probes are rigid and large in size, requiring high hand-held stability from the operator, and will compress the skin, which can cause great discomfort to patients who have undergone surgery. Rigid probes are usually unable to make close contact with soft and irregular surfaces such as the skin. The gas gaps at these interfaces will cause large acoustic energy reflections and waveform distortion, so it is necessary to use ultrasonic coupling agents to achieve good coupling effects. However, the current commercial coupling agents will lose water after being exposed to air for 48 hours, resulting in failure of continuous monitoring. In addition, the existing flexible ultrasound patches are all prepared based on rigid piezoelectric ceramics, and the local flexibility is not ideal. Moreover, since ceramics are brittle materials, it is difficult to make high-frequency flexible probes. Therefore, it is urgent to develop an ultrasound probe with good flexibility and light weight to minimize damage to patients while achieving long-term stable monitoring, thereby meeting the application requirements of flexibility, lightness, and comfort. Polymer materials usually have the advantages of flexibility, light weight, and simple processing. If functional polymers are used to replace rigid materials such as piezoelectric ceramics, it will be possible to construct a new type of ultrasound probe with excellent flexibility and light weight. Through literature and patent searches, there are currently no reports on flexible polymer ultrasound probes that can monitor blood flow velocity. Summary of the invention

[0005] The object of the present invention is to provide a flexible polymer ultrasound probe with good flexibility and comfortable fit.

[0006] The flexible polymer ultrasonic probe provided by the present invention is composed of a multi-layer structure, which includes, from top to bottom: a shielding layer, a backing layer, an upper electrode, a piezoelectric layer, a lower electrode, a matching layer, and a coupling layer; the flexible polymer ultrasonic probe can emit ultrasonic waves under the excitation of an electrical signal as an ultrasonic transmitting unit, and can also collect ultrasonic signals as an ultrasonic receiving unit; wherein:

[0007] The shielding layer is used to shield the electromagnetic waves existing in the space and reduce the interference of the electromagnetic waves on the ultrasonic probe signal;

[0008] The backing layer is used to absorb the ultrasonic waves radiated backwards by the piezoelectric material crystals in the piezoelectric layer, reduce the residual vibration of the piezoelectric element, improve the energy utilization rate, and increase the bandwidth of the probe;

[0009] The upper electrode is located between the backing layer and the piezoelectric layer;

[0010] The piezoelectric layer can convert electrical energy into acoustic energy and emit ultrasonic waves when a certain voltage is applied on both sides of the piezoelectric layer; at the same time, when it receives the vibration caused by ultrasonic waves, it can convert the acoustic energy into electrical energy and output an electrical signal;

[0011] The lower electrode is located between the piezoelectric layer and the matching layer;

[0012] The matching layer is used to match the acoustic impedance of the human body and the piezoelectric material, wherein the thickness of the matching layer is one quarter of the wavelength of the ultrasonic wave in the matching layer, and the acoustic impedance of the matching layer is approximately the geometric mean of the acoustic impedance of the piezoelectric material and the acoustic impedance of the human body;

[0013] The coupling layer is used to closely fit human skin and has the characteristics of being soft and comfortable. The acoustic impedance of the coupling layer is close to that of the human body.

[0014] All functional layers are composed of polymers and their composite materials, which have very good flexibility and can be bent at any angle along any axis; specifically;

[0015] The shielding layer includes, but is not limited to, copper-plated polyimide composite film, copper-plated polyethylene terephthalate composite film, silver nanowire (AgNW) / polymer composite film and other materials;

[0016] The backing layer, whose material includes but is not limited to flexible polymer materials such as polyurethane (PU), polydimethylsiloxane (PDMS), polyimide (PI), etc.; the backing layer can improve the time resolution of the flexible polymer ultrasound probe;

[0017] The piezoelectric layer, the material of which includes but is not limited to flexible piezoelectric polymers such as polyvinylidene fluoride (PVDF) and its copolymer (PVDF-TrFE);

[0018] The matching layer, whose material includes but is not limited to polyethylene (PE), polyurethane (PU), polydimethylsiloxane (PDMS) and other flexible polymer materials, can be filled with nano-scale ZnO, Al2O3 powder or other nano-scale powder to adjust the acoustic impedance;

[0019] The coupling layer is composed of a solid coupling agent Ecoflex; or composed of two polyurethane films and a hydrogel with a coupling function, wherein the two polyurethane films are bonded together on all sides, and a coupling agent or a hydrogel with a coupling function is sandwiched in the middle;

[0020] The upper and lower electrodes are obtained by plating copper or gold on the upper and lower surfaces of the PVDF film or by screen printing silver paste.

[0021] The flexible polymer ultrasonic probe provided by the present invention weighs only about 2 grams and does not exceed 2.5 grams, and has a thickness of only about 1.5 millimeters and does not exceed 2 millimeters.

[0022] The flexible polymer ultrasonic probe provided by the present invention has the following preparation process: electrode leads are made on the upper and lower surfaces of a polarized PVDF film with electrodes printed on the surface; a coupling layer with coupling effect is prepared; the coupling layer and the matching layer, the matching layer and the piezoelectric layer, the piezoelectric layer and the backing layer, and the backing layer and the shielding layer are sequentially bonded with glue, and during the process, it is necessary to press and discharge the air between the layers; the shielding layer is connected with the lead of the lower electrode, and the two are grounded together.

[0023] The flexible polymer ultrasonic probe provided by the present invention can be used for industrial flaw detection of objects with irregular surfaces, blood flow velocity monitoring and ultrasonic imaging, including but not limited to. In blood flow velocity monitoring, the flexible polymer ultrasonic probe is based on the ultrasonic Doppler principle. Different blood flow velocities will cause ultrasonic echo signals to produce different frequency offsets, thereby achieving quantitative monitoring of the distribution of blood flow velocity in human blood vessels.

[0024] The flexible polymer ultrasound probe provided by the present invention can be combined with wireless signal transmission technology, and biological glue is coated on the joint between the flexible polymer ultrasound probe and the skin to further prepare a flexible polymer ultrasound patch.

[0025] The flexible polymer ultrasound probe provided by the present invention has good flexibility and can fit the skin for long-term wearing without causing obvious discomfort, thus minimizing the harm to the patient. The flexible polymer ultrasound patch prepared based on the flexible polymer ultrasound probe can realize long-term continuous monitoring of blood flow velocity, which is of great significance for the diagnosis and prevention of certain cardiovascular diseases. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the layer-by-layer structure of the flexible polymer ultrasound probe.

[0027] Figure 2 This is the time-frequency analysis diagram of the water flow rate in the water pipe measured by the flexible polymer ultrasonic probe.

[0028] Figure 3 This is a time-frequency analysis diagram of carotid artery blood flow velocity measured by a flexible polymer ultrasound probe during human exercise. DETAILED DESCRIPTION

[0029] Example 1

[0030] (1) Electrode leads: Use conductive silver paste as an adhesive to bond nickel-plated copper wires to the upper and lower surfaces of the polarized PVDF film with silver electrodes printed on the surface. Let it stand for a while until the conductive silver paste solidifies to complete the electrode leads.

[0031] (2) Preparation of coupling layer: Mix the two components of Ecoflex-0030 in a ratio of 1:1 and stir evenly, evacuate to remove bubbles, drop the mixture on a spin film machine, and spin coat at 1000 rpm to obtain an Ecoflex film coupling layer with a thickness of about 100 um;

[0032] (3) Interlayer connection: Add M540 glue on the coupling layer (Ecoflex film), press the 50um thick matching layer (PU) lightly on the Ecoflex film, expel the air, and then stick the piezoelectric layer (PVDF) with leads on the matching layer (PU), press to expel the air between the layers, so that the glue is evenly dispersed in the gap between the two layers, and let it stand for a while until the glue solidifies; use the same method to connect the piezoelectric layer (PVDF) and the backing layer (PI), and the backing layer (PI film) and the shielding layer (nanosilver wire / polymer composite film) in sequence;

[0033] (4) Shielding layer grounding: Connect the shielding layer to the lead of the lower electrode and ground them together;

[0034] (5) The prepared flexible polymer ultrasonic probe can be used to measure the flow rate of liquid in a water pipe, see Figure 2 , showing the liquid flow velocity distribution in the water pipe.

[0035] Example 2

[0036] (1) Electrode leads: Use conductive silver paste as an adhesive to bond copper-plated polyimide wiring to the upper and lower surfaces of the polarized PVDF film with silver electrodes printed on the surface. Let it stand for a while until the conductive silver paste solidifies to complete the electrode leads.

[0037] (2) Preparation of coupling layer: 3% (w / w) high molecular weight chitosan, 12% (w / w) acrylamide, and 0.5% (w / w) α-ketoglutaric acid were dissolved in deionized water; the mixture was centrifuged at 9000 rpm to remove bubbles and poured into a transparent glass mold. The solution was cured under ultraviolet light (365 nm, 12 W power) for 60 min to obtain a hydrogel after curing; the obtained hydrogel was cut into the required size and shape, the hydrogel was lightly pressed on the PU film to expel bubbles, and another PU film was attached to the hydrogel, lightly pressed to expel bubbles and bond the two PU films together, and the edges of the films were sintered and sealed using a laser;

[0038] (3) Interlayer connection: Add M540 glue to the coupling layer, press the 50um thick matching layer (PU) lightly on the coupling layer, expel the air, and then stick the leaded piezoelectric layer (PVDF) on top of the 50um thick PU film in the coupling layer, press to expel the air between the layers, so that the glue is evenly dispersed in the gap between the two layers, and let it stand for a while until the glue solidifies; use the same method to connect the piezoelectric layer (PVDF) and the backing layer (PI), and the backing layer (PI) and the shielding layer (copper-plated polyethylene terephthalate composite film) in sequence;

[0039] (4) Shielding layer grounding: Connect the shielding layer to the lead of the lower electrode and ground them together;

[0040] (5) The prepared flexible polymer ultrasound probe can be used to monitor human blood flow velocity, see Figure 3 , the distribution of carotid artery blood flow velocity changes over time when people exercise, and it can be observed that the heart rate of the subjects is faster during exercise.

Claims

1. A flexible polymer ultrasonic probe, characterized in that: It is a multi-layer structure, which includes, from top to bottom: shielding layer, backing layer, upper electrode, piezoelectric layer, lower electrode, matching layer, coupling layer; it transmits ultrasonic waves under the stimulation of electrical signals, acting as an ultrasonic transmitting unit, and can collect ultrasonic signals, acting as an ultrasonic receiving unit; wherein: The shielding layer is used to shield the electromagnetic waves existing in the space and reduce the interference of the electromagnetic waves on the ultrasonic probe signal; The backing layer is used to absorb the ultrasonic waves radiated backwards by the piezoelectric material crystals in the piezoelectric layer, reduce the residual vibration of the piezoelectric element, improve the energy utilization rate, and at the same time increase the bandwidth of the ultrasonic probe; The upper electrode is located between the backing layer and the piezoelectric layer and has good bending resistance; The piezoelectric layer converts electrical energy into acoustic energy when a certain voltage is applied on both sides of the piezoelectric layer, emitting ultrasonic waves; at the same time, when it receives the vibration caused by the ultrasonic wave, it converts the acoustic energy into electrical energy and outputs an electrical signal; The lower electrode is located between the piezoelectric layer and the matching layer and has good bending resistance; The matching layer is used to match the acoustic impedance of the human body and the piezoelectric material; the thickness of the matching layer is one quarter of the wavelength of the ultrasonic wave in the matching layer, and the acoustic impedance of the matching layer is the geometric mean of the acoustic impedance of the piezoelectric material and the acoustic impedance of the human body; The coupling layer is used to fit closely to human skin and has the characteristics of being soft and comfortable. The acoustic impedance of the coupling layer is close to that of the human body. The shielding layer material is selected from copper-plated polyimide composite film, copper-plated polyethylene terephthalate composite film, and nano silver wire / polymer composite film material; The backing layer material is selected from polyurethane, polydimethylsiloxane, and polyimide; The piezoelectric layer material is selected from polyvinylidene fluoride and its copolymers; The matching layer material is selected from polyethylene, polyurethane, and polydimethylsiloxane, and is filled with nano-scale ZnO and Al2O3 powder to adjust the acoustic impedance; The coupling layer is composed of a solid coupling agent Ecoflex; or composed of two polyurethane films and a hydrogel with a coupling function, wherein the two polyurethane films are bonded together on all sides, and a coupling agent or a hydrogel with a coupling function is sandwiched in the middle; The flexible polymer ultrasound probe weighs no more than 2.5 grams and has a thickness of no more than 2 mm.

2. The flexible polymer ultrasonic probe according to claim 1, characterized in that: Combined with wireless signal transmission technology, biological glue is coated on the joint between the flexible polymer ultrasound probe and the skin to form a flexible polymer ultrasound patch.

3. Application of the flexible polymer ultrasonic probe as claimed in claim 1 in industrial flaw detection of irregular surface objects, blood flow rate monitoring or ultrasonic imaging.

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