CN100365840C - Planar Composite Ultrasonic Transducer - Google Patents

Abstract

Ultrasonic transducer with planar composite structure: PZT piezoelectric material is used to transmit ultrasonic waves, and PVDF is used to receive echo signals. A PZT piezoelectric transducer is provided on the second matching layer material, and then the first matching layer material is provided, and a PVDF piezoelectric transducer is provided on the first matching layer material, or a PVDF piezoelectric transducer is directly used As the first matching layer material; the backing material is epoxy material plus tungsten powder: the present invention uses two piezoelectric materials to give full play to the advantages of the two materials in transmitting and receiving. The transmitting and receiving parts are separated to avoid interference between transmitting and receiving. The matching layer of PZT can be replaced by PVDF layer, which can make the design simpler.

Description

Planar Composite Ultrasonic Transducer

1. Technical field

The invention relates to a novel structure of an ultrasonic transducer, in particular to a planar composite ultrasonic transducer made of two kinds of piezoelectric materials.

2. Background technology

With the development of ultrasound medicine, ultrasound imaging is attracting more and more interest. Compared with X-rays, the biggest advantage of ultrasound is that it is non-destructive to the human body. One of the keys to ultrasound imaging is the ultrasound transducer. Usually, the transducer used for imaging is a single structure using a piezoelectric material, which is used for both transmitting and receiving ultrasound. Although the transducer with this structure is simple to manufacture, the overall performance of the transducer is not very good due to the limitation of the characteristics of the piezoelectric material. The transducers made at present generally use two kinds of materials, one is PZT (Lead-Zirconate-Titanate, lead zirconate titanate) material, PZT has a high electromechanical coupling coefficient, and the ultrasonic transducer made with it has a lower input power loss, is a good emitting piezoelectric material. However, since the acoustic impedance of the PZT material is generally large, the matching with the coupling liquid (usually water) is not very good, and there are many coda waves that reverberate during reception, which is not conducive to the extraction and analysis of the signal. Another is to use PVDF (Polyvinylidene difluoride, polyvinylidene fluoride) material, PVDF is a polymer piezoelectric polymer material, this material has small elastic stiffness, large mechanical damping, and the acoustic impedance is close to the acoustic characteristic impedance of human tissue. It is easy to obtain better matching, and at the same time, its low permittivity is also easy to match with the electrical output circuit, and there are few coda waves when receiving, so it is a good receiving piezoelectric material, but the disadvantage of PVDF material is that the transmitting sensitivity is very low. Low.

Some basic concepts for characterizing ultrasound transducer performance:

Working frequency: refers to the vicinity of the mechanical resonance frequency of the transducer.

Electromechanical Coupling Coefficient: The ratio of the stored mechanical energy to the total energy obtained from the power source.

Receive Sensitivity: The ratio of output voltage to input stress.

Input power loss: The input power loss of the transducer is the ratio of the power obtained by the water load to the maximum output power of the power supply.

Bandwidth: The difference in frequency at which the maximum power falls by half.

The transducer made of a piezoelectric material has some disadvantages: the acoustic impedance of the PZT piezoelectric material is greatly different from that of water (human body), the tail of the echo signal is long, and the bandwidth is small. PVDF piezoelectric material has a high piezoelectric voltage constant, which is 20 times higher than that of PZT piezoelectric receiving ceramics; light weight, its density is only a quarter of that of PZT, soft and not brittle, high mechanical strength; wide frequency response, And the vibration mode is simple; the acoustic impedance is close to that of water (human body), and the disadvantage is that the piezoelectric strain constant is small.

For the design of ultrasonic transducers, there are now some improvements:

In order to improve the performance of the ultrasonic transducer, the existing solutions mainly improve the matching layer and backing of the ultrasonic transducer, but due to the limitation of the material, the overall performance of the transducer is not very superior. Another way is to use new materials. In the past, piezoelectric ceramics with a uniform structure have been used, but there have been worrying and slow developments. At the same time, a heterogeneous material with excellent piezoelectric properties has appeared. The basic principle is to connect piezoelectric ceramics with organic polymers to obtain piezoelectric composite materials. Although piezoelectric composite materials can improve the performance of ultrasonic transducers, it is still in its infancy and many problems have not been well resolved. Conventional B-ultrasound probes use PZT for both emission and echo signal acquisition.

3. Contents of the invention

The object of the invention is to: propose a novel composite structure ultrasonic transducer, use two kinds of piezoelectric materials-piezoelectric ceramics PZT and piezoelectric film PVDF in the same transducer, PZT is used for emission, PVDF is used for Receiving: Two kinds of piezoelectric materials are used to improve the performance of the transducer, and the advantages of PZT material and PVDF material in transmitting and receiving are used, so that the ultrasonic transducer not only has a small input power loss, but also has a relatively short return Wave.

Technical scheme of the present invention: adopt multi-layer structure (Fig. 1) in the design of ultrasonic transducer, adopt PZT piezoelectric material to transmit ultrasonic wave, and adopt PVDF to receive echo signal: specific structure is: first on the backing The second matching layer material is provided, and the PZT piezoelectric transducer is arranged on the second matching layer material, and then the first matching layer material is arranged, and the PVDF piezoelectric transducer is arranged on the first matching layer material.

The choice of the backing material is epoxy material plus tungsten powder: thickness size range: 1.00-4.00

The choice of second matching layer material is epoxy material: Thickness size range: 0.50-1.00

The choice of the first matching layer material is glass or rubber material or directly use PVDF piezoelectric transducer as the first matching layer material: thickness size range: 0.20-0.40

The size range of PZT piezoelectric transducer thickness is: 0.80-2.00

The size range of the thickness of the PVDF piezoelectric transducer is: 0.05-0.30, and the unit of size is mm.

When transmitting, the PZT piezoelectric material is used to transmit ultrasonic waves, and the PVDF layer is used as a matching layer to improve the transmission efficiency of the transducer. At the same time, a layer of backing material is added to the back end of the PZT to increase the bandwidth of the transducer. When receiving, PVDF piezoelectric material is used to receive, and the transmitting part and receiving part are separated.

Compared with the prior art, the present invention has the advantages that two kinds of piezoelectric materials are used, and the advantages of the two kinds of materials in transmitting and receiving are brought into full play. The transmitting and receiving parts are separated to avoid interference between transmitting and receiving. The matching layer of PZT can be replaced by PVDF layer, which can make the design simpler. In terms of performance, the emission efficiency is much higher than that of a single-layer PVDF ultrasonic transducer, and the tailing of the received echo signal is smaller than that of a single-layer PZT ultrasonic transducer, so the bandwidth of the transducer has been greatly improved.

The structure of the present invention is characterized in that two kinds of piezoelectric materials—piezoelectric ceramics PZT and piezoelectric thin film PVDF are used in the same transducer, PZT is used for emission, and PVDF is used for reception. That is, two piezoelectric materials are used to improve the performance of the transducer, so that the ultrasonic transducer not only has a small input power loss, but also has a relatively short echo. The invention can be used to design a medical ultrasonic transducer, can greatly improve the performance of the transducer, improve the reliability of medical diagnosis, and can obtain higher economic benefits. Moreover, it can receive high-order harmonics, realize harmonic imaging, and open up a new way for ultrasonic imaging.

4. Description of drawings

Fig. 1 is the structure of composite structure ultrasonic transducer of the present invention

Fig. 2 is the KLM electromechanical coupling equivalent circuit of composite structure ultrasonic transducer when the present invention is launched

Fig. 3 is the KLM electromechanical coupling equivalent circuit of composite structure ultrasonic transducer when the present invention receives

Fig. 4 is a block diagram of the experimental system of the present invention

Fig. 5 is the echo waveform of three kinds of transducers in the experiment of the present invention

(a) PZT transducer (b) composite transducer (c) PVDF transducer

5. Specific implementation

The KLM electromechanical coupling equivalent circuit shown in Figure 2 is used to analyze the transmitting part, and the relationship between the parameters of the transducer and the input response of the transducer is obtained.

The KLM electromechanical coupling equivalent circuit in Figure 3 is used to analyze the receiving part, and the relationship between the parameters of the transducer and the output response of the transducer is obtained.

Adopt the present invention to design and manufacture the ultrasonic transducer of composite structure, the material parameters used are shown in Table 1. The specific plan is as follows:

PZT is used to make the transmitting transducer, and the method of adding matching and backing is used to improve the transmitting performance of the ultrasonic transducer;

Use PVDF to make the receiving part, use suitable matching materials to match with PZT, and pay attention to the insulation of the transmitting part and the receiving part.

For comparison, we used the same PZT or PVDF single material to make a single-structure ultrasonic transducer.

The transducer was tested by the following method, as shown in Figure 4. In the experiment, the manufactured ultrasonic transducer was excited by a single pulse signal generator (peak-to-peak value 300V, pulse width 15ns). The pulse emitted by the transmitting transducer is received by the receiving transducer through the reflector, and sent to the digital waveform oscilloscope (Hp54502A) after passing through a broadband amplifier (AU-4A-015-BNC, 60dB, bandwidth 1-500MHz), and finally It is collected into the computer through the IEEE488 bus interface card.

The results of the test are shown in Figure 5. Figure 5 shows the echo waveforms of the three transducers, (a) is the PZT transducer (b) is the composite transducer (c) is the PVDF transducer, it can be seen from the results that it is similar to the PZT transducer Compared with the transducer, the tail of the transducer of the composite structure is shorter, and the amplitude is larger than that of PVDF. Therefore, the echo of the transducer of the composite structure has a larger amplitude and a wider bandwidth.

When utilizing the present invention to prepare ultrasonic B-ultrasound probes, conventional processing methods are adopted for PZT piezoelectric transducers and PVDF piezoelectric transducers, such as cutting into multiple structures to make array transducers for making B-ultrasound probes . The method for preparing other transducers by using the present invention is also similar to the manufacturing methods of various existing transducers.

Table 1 Physical parameters for composite structure transducer materials

Z/[Kg.(m²s)^-1] c/[m.s^-1] d/mm ε_r^s K_T Matching layer 1PVDF matching layer 2PZT backing 2.56×10⁶3.9×10⁶11.46×10⁶33.7×10⁶39.5×10⁶   21302200288043502189 0.2450.100.561.002.00 /10.0/830/ /0.17/0.49/

The definitions of the above units are: Z means acoustic impedance, unit: kg/( ^m2s ); c means sound velocity, unit: m/s; d means thickness, unit: mm; ε _r ^s means dielectric constant; K _T means Electromechanical Coupling Coefficient. The choice of backing material is epoxy material plus tungsten powder: density is 1.8045×10 ⁴ kg/m ³ , thickness range: 1.00-4.00mm, generally 2.00-3.00mm.

Claims (1)

1. the ultrasonic transducer of plane-type compound structure, it is characterized in that adopting the PZT piezoelectric to launch ultrasonic wave, adopt PVDF to receive echo-signal, ultrasonic transducer adopts sandwich construction: be provided with the second matching layer material on backing earlier, on the second matching layer material, be provided with the PZT PZT (piezoelectric transducer), on the PZT PZT (piezoelectric transducer), be provided with the first matching layer material, on the first matching layer material, be provided with the PVDF PZT (piezoelectric transducer); The material of described backing is that epoxy material adds tungsten powder: gauge scope: 1.00-4.00; The selection of the second matching layer material is an epoxy material: gauge scope: 0.50-1.00, the selection of the first matching layer material is glass or elastomeric material: gauge scope: 0.20-0.40, the size range of PZT PZT (piezoelectric transducer) thickness is: 0.80-2.00, the size range of PVDF PZT (piezoelectric transducer) thickness is: 0.05-0.30, the unit of size are millimeter.

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