JPS5817360A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To enable the switching of frequency of an ultrasonic beam in a wide range by selectively connecting a plurality of frequency varying elements to a vibrator formed with a high molecular piezo-electric film. CONSTITUTION:A sound absorbing material is laminated on a vibrator 10 formed with a high molecular piezo-electric film to make the frequency of the vibrator 10 a side band. A frequency setting circuits 20-1-20-n in which turning coils as frequency varying element and damping resistances are combined in parallel are selected as desired with a selection switch 22 and connected in parallel to the vibrator 10. The frequency of an ultrasonic beam transmitted ore received with the vibrator 10 is determined by the capacity of the vibrator 10 and the inductance of a frequency selection circulation circuit selected with the selector switch 22. Thus, an ultrasonic beams can be obtained in a desired frequency according to part to be inspected by the operation of the selector switch 22.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved ultrasonic probe, particularly an ultrasonic probe that adjusts the frequency of an ultrasonic beam.

An ultrasonic probe is pressed against the subject, and an ultrasonic beam is emitted into the subject from a transducer installed on the probe surface of the probe, which is obtained from the difference in acoustic impedance within the subject. Ultrasonic diagnostic apparatuses are generally used in which the reflected echoes are received by the transducer and a tomographic image along a desired tomographic plane is displayed on a display device provided separately from the probe. In an ultrasonic diagnostic apparatus using such a pulse echo method, it is necessary to use an ultrasonic beam of an appropriate frequency depending on the region to be examined of the subject. Generally, the frequency used for ultrasonic diagnosis is about 1 to 15 MHz.

In other words, when using a high frequency, it is possible to distinguish minute changes in tissue, but on the other hand, the attenuation of ultrasound waves in the body increases, making it impossible to reach deep tissue, and when using a low frequency, The opposite is true, so depending on the area to be examined, for example, 2.25 M for diagnosis of mammary glands, abdomen, etc.
Hz or 5 MHz, 1 for diagnosis of eyeballs, etc.
5 MHz ultrasonic beams are used separately.

Conventionally, in this type of ultrasound diagnosis, the ultrasound probes used could only transmit and receive ultrasound beams of a single frequency, so it was necessary to prepare multiple ultrasound probes depending on the area to be examined. Unfortunately, it was inconvenient. For this reason, it has been desired to develop an ultrasonic probe that is capable of transmitting and receiving ultrasonic beams of different frequencies as necessary. However, since piezoelectric materials such as ceramic horn have been used for vibrators used in conventional probes, it has not been possible to obtain a sufficient frequency band. In other words, the acoustic impedance of a vibrator made of a piezoelectric material such as ceramic is 30 x 10' kg/m2s, which is much larger than the acoustic impedance in a living body of 1.5 x 10' kg/m2s, so it is difficult to obtain The frequency band that can be used becomes extremely narrow.

FIG. 1 is an explanatory diagram of such a conventional probe. 10
is a vibrator formed using a piezoelectric material such as ceramic, and an acoustic matching layer 12 that transmits an ultrasonic beam is laminated on the front surface of the vibrator.

As mentioned above, since the acoustic impedance of the vibrator 10 is 20 times larger than that in the living body, the single frequency bandwidth is narrow and it cannot be used as a probe using the Hals echo method. Therefore, usually 10 vibrators
A sound wave absorbing material 14 is laminated on the back surface of the vibrator 10 to damp vibrations of the vibrator 10. However, in this way, the sound wave absorbing material 1
4, the acoustic impedance of the absorber 14 is 6 x lo' kg/m2s, that is, the oscillator 10
The frequency band of the vibrator 10 is not sufficiently improved. Therefore.

In order to change the frequency of the ultrasonic beam transmitted and received from the probe configured in this way, a tuning coil 16 and a damping resistor 18 as frequency variable elements are connected in parallel to the transducer 10, and the inductance Even if the value was changed, almost no change in the frequency of the ultrasound beam could be obtained because the acoustic impedance of the transducer 10 was too large by [2] compared to that in the living body.

The present invention was made in view of the above-mentioned conventional problems, and its purpose is to provide an ultrasonic probe that can switch the frequency of an ultrasonic beam over a wide range as necessary.

In order to achieve the above object, the present invention includes a transducer formed using a polymer piezoelectric film and transmitting and receiving an ultrasonic beam to a subject, a plurality of variable frequency elements connected to this transducer, A changeover switch that selectively connects a variable element to the vibrator and switches the frequency of the ultrasonic beam transmitted and received by the vibrator.0 Next, a preferred embodiment of the present invention will be described. explain.

FIG. 2 is an electrical circuit diagram of the ultrasonic probe of the present invention. Here, 10 is a vibrator, which is formed using a polymer piezoelectric film.

Polymer piezoelectric film refers to piezoelectric materials obtained by polarizing polyvinylidene fluoride, polyvinyl fluoride, copolymers containing these as main components, and mixtures of these and ferroelectric ceramic powders. Meaning 0 Polymer piezoelectric films generally have an acoustic impedance close to that in vivo. For example, when PVDF (polyvinylidene fluoride) is used as a polymer piezoelectric film, its acoustic impedance is 4 x 10'.
kg/m2s, that is, about 2.7 times the acoustic impedance in the living body, and a probe with broadband characteristics can be easily realized without using an acoustic absorbing material. Further, by laminating an acoustic absorbing material on the vibrator 10 formed using the above polymer piezoelectric film, the frequency band of the vibrator 100 can be made even wider. 20-1.20-2. ...
. . . are frequency setting circuits formed by combining a tuning coil and a damping resistor in parallel as frequency variable elements, and each of the circuits 20-1, 20-2.・・・
The tuning coils 10 and 10 each have different inductances and are connected in parallel. Note that it is convenient to use a relay switch as the changeover switch 22 because it can be easily operated.

The embodiment of the present invention consists of the above configuration, and its operation will be explained below.

Referring to FIG. 3, A is the vibrator 10 of the present invention, that is, the PV
DF shows the frequency characteristics of the polymer piezoelectric film, and B shows the frequency characteristics of the ceramic piezoelectric material. As is clear from the figure, the transducer 10 of the present invention exhibits extremely good broadband frequency characteristics, and therefore the frequency of the ultrasonic beam transmitted and received from the transducer 10 is switched by the capacitance of the transducer IO. Any frequency setting circuit 20-1, 20-2, . selected by the switch 22 and connected in parallel to this vibrator 10.
It is uniquely determined by the inductance of... That is, if the electric capacity of the transducer 10 is C, and the tuning coil inductance of the selected frequency setting circuit is L, then the frequency f of the ultrasonic beam transmitted and received from the transducer 10 is '=2. It is given in r07. Here, each frequency setting circuit 20-1, 20-2. ...
The tuning coils have different values, so by switching the changeover switch 22, it is possible to easily obtain an ultrasonic beam of any frequency depending on the region to be examined.

In the above embodiment, a probe was described in which the electric capacitance C of the transducer 10 is constant and the inductance of the tuning coil connected by the changeover switch 22 is changed to set the frequency of the ultrasonic beam.

However, the present invention is not limited to this, and it is also possible to have a structure in which the electric capacity of the vibrator JO is also changed to set the frequency of the ultrasonic beam.

FIGS. 4 and 5 are explanatory diagrams of such a probe. This embodiment is characterized by the electrode structure of the vibrator 10,
One electrode 24 is laminated over the entire surface of the vibrator 10, and the other electrode 26 includes a first electrode 26a laminated at the center of the other surface of the vibrator 10, and a vibrator along the first electrode 26a. 10, and a second electrode 26b laminated on the outer periphery of the other surface of 10. The second electrode 26b is turned on and off by the switch and the switch.

Here, the capacitance of the vibrator 10 sandwiched between the first electrode 26a and the electrode 24 is C1, the capacitance of the vibrator 10 sandwiched between the second electrode 26b and the electrode 24 is 02,
If the inductance of the tuning coil of the frequency setting circuit connected in parallel with this transducer 10 is L, then the frequency of the ultrasonic beam transmitted and received by the transducer lO when the switch path is turned off is f1='-1. The frequency of the ultrasonic beam transmitted and received by the transducer 10 when the switch 28 is turned on is f2 = '2 *V'T
□1°.

In this embodiment, it is possible not only to simply switch the frequency of the ultrasonic beam, but also to switch the pattern of the ultrasonic beam at the same time.

Generally, an ultrasonic beam emitted from a small-diameter transducer has a small beam diameter at short distances and a large beam diameter at long distances. In addition, the ultrasonic beam emitted from a large-diameter transducer has a large beam diameter at short distances, but
As the distance increases, the beam diameter becomes smaller compared to the diameter of the ultrasonic beam emitted from the small-diameter transducer. Further, the higher the frequency, the greater the attenuation of the ultrasonic beam in the subject to be radiated, that is, in the living body. Therefore, depending on whether the switch path is turned on or off, ultrasonic beams with different nodules can be emitted as shown in FIG. First, when the switch path is turned off, the aperture of the transducer 10 that emits the ultrasonic beam becomes substantially smaller, and an ultrasonic beam as small as one aperture is emitted. Since the frequency of this ultrasonic beam is higher than when the switch path is turned on, when the switch path is turned off, as shown by the X in the figure, short distances can be diagnosed using a thin beam with a high frequency. . Furthermore, when the switch 28 is turned on, the aperture of the transducer 100 that emits the ultrasonic beam becomes larger, and the frequency of the ultrasonic beam also becomes lower. In this example, one of the electrodes of the transducer is divided into two parts, but the electrode of the transducer can be divided into three or more parts. It is possible. Still connecting the vibrator 10 to the electrode 26
It is also possible to divide both.

Although this example shows a probe in which a variable frequency element is connected in parallel to a transducer and the frequency of the ultrasound beam is switched using parallel resonance, the probe is not limited to this, and may also use series resonance. It is also possible to adopt a structure in which the frequency of the ultrasonic beam is switched by changing the frequency of the ultrasonic beam.

As described above, according to the present invention, the transducer is formed using a polymer piezoelectric film, and the acoustic impedance of the transducer is made close to that in the living body, thereby increasing the frequency of the ultrasonic beam transmitted and received from the transducer. It is possible to provide an ultrasonic probe that can perform switching over a wide range as necessary.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the structure of the ultrasonic transducer, Fig. 2 is an electric circuit diagram showing an embodiment of the ultrasonic transducer of the present invention, Fig. 3 is a characteristic diagram of the transducer, and Fig. 4 is the book. FIG. 5 is an explanatory diagram showing another embodiment of the invention, FIG. 5 is an explanatory diagram of its electrode structure, and FIG. 6 is an explanatory diagram showing its ultrasonic beam pattern. The same members in each figure are given the same reference numerals, 10 is a vibrator, 2 is
0-1.20-2. . . . is a frequency setting circuit consisting of a frequency variable element, 22 is a changeover switch, 24, 2
6 is an electrode. 1st figure, 2nd figure, 3rd figure, wave number

Claims (1)

[Claims] (1) A transducer formed using a polymeric piezoelectric film and transmitting and receiving an ultrasound beam to the subject, a plurality of frequency variable elements connected to this transducer, and any frequency variable element selectively An ultrasonic probe comprising: a changeover switch connected to a transducer to switch the frequency of an ultrasonic beam transmitted and received by the transducer. (2. In the ultrasonic probe described in claim (1), the electrode of the vibrator is divided into a plurality of parts, and the area of the substantial vibrating surface of the vibrator that transmits and receives ultrasonic waves can be freely adjusted. Features of ultrasonic probe.