JP4719525B2 - Ultrasonic probe - Google Patents

Description

  The present invention relates to an ultrasound probe that is applied to capture an ultrasound image as a diagnostic image related to a subject.

  An ultrasound probe that sends and receives ultrasound to and from the subject converts the drive signal to ultrasound and sends it to the subject, and also receives reflected echoes generated from the subject to receive signals. A transducer for conversion is arranged. As this vibrator, a vibrator in which ultrasonic transmission / reception sensitivity is changed in accordance with the magnitude of an applied bias and an electrode connected to the vibration element are formed.

  In such an ultrasonic probe, when applying a bias to the vibrating element via the electrode, the beam profile of the ultrasonic beam transmitted and received by the ultrasonic probe is controlled by controlling the magnitude of the bias. Improvement is made to narrow the beam width (see, for example, Patent Document 1).

JP 2004-274756 A

  By the way, in the conventional method such as Patent Document 1, when a bias is applied to the vibration element and a temporary transient phenomenon occurs in the bias power source (for example, power supply interruption), an overvoltage exceeding the rating is applied to the vibration element. May be applied. In that case, for example, an avalanche phenomenon or an abnormal state of a short circuit may occur in the vibration element, and an overcurrent may flow. When an overcurrent flows through the vibration element, the temperature of the electrode of the vibration element rises, and as a result, a failure such as disconnection due to evaporation of the electrode conductor may occur.

  An object of the present invention is to realize an ultrasonic probe that is more suitable for protecting a vibration element from a transient phenomenon occurring in a bias power source.

  In order to solve the above-described problems, the ultrasonic probe of the present invention is configured by arranging transducers that mutually convert ultrasonic waves and electrical signals, and the transducer has an ultrasonic transmission / reception sensitivity with a magnitude of an applied bias. A protective element is provided between the electrode and the bias power supply. The protective element has a vibration element that changes in response to the vibration element and an electrode connected to the vibration element, and prevents overvoltage exceeding the rated voltage of the vibration element. And

  According to this, when an overvoltage occurs due to a transient phenomenon of the bias power source, the overvoltage is suppressed before being applied to the vibration element. Therefore, since it is possible to prevent an overcurrent from flowing through the vibration element, it is possible to prevent a failure caused by the overcurrent. Thus, the vibration element can be protected from the transient phenomenon occurring in the bias power source.

In this case, the protection means has a resistance connected in series between the electrode and the bias power source, and the resistance has a resistance value larger than the electric resistance of the vibration element when an overvoltage is applied to the vibration element. Can be set. Thereby, the overvoltage resulting from the transient phenomenon generated in the bias power source is suppressed before being applied to the vibration element. Accordingly, it is possible to prevent an overcurrent from flowing through the vibration element. Further, the protection means includes a switch connected in series between the electrode and the bias power supply, and the switch has a current flowing between the electrode and the bias power supply. As the value increases, the impedance can be increased. Thereby, an overcurrent caused by a transient phenomenon generated in the bias power source is detected and reduced before flowing into the vibration element.

  Further, the protection means has a voltage limit circuit disposed between the electrode and the bias power source, and the voltage limit circuit can hold the magnitude of the bias applied to the vibration element below a set voltage. . As a result, the voltage applied to the vibration element can be shunted and clipped below the set voltage after being detected before being applied to the vibration element.

  Further, the ultrasonic probe of the present invention includes a plurality of transducers that mutually convert ultrasonic waves and electrical signals, and the transducer includes a plurality of ultrasonic transmission / reception sensitivities that change according to the magnitude of the applied bias. And a plurality of electrodes divided in the minor axis direction orthogonal to the arrangement direction, and the divided electrodes are divided into groups each consisting of one or adjacent divided portions, and between each set and the bias power source Furthermore, it is assumed that protective means for preventing overvoltage exceeding the rated voltage of the vibration element is provided, and the protective means can be configured by setting the allowable voltage to be smaller in units from the center to the end in the minor axis direction.

  According to this, each vibration element of the set located in the central part in the short axis direction can be made into a strong electric field, and can be made into a weak electric field in units as it goes to the end in the short axis direction. Therefore, the ultrasonic energy corresponding to the central portion is relatively high, and the ultrasonic energy is relatively low in units of pairs toward the end. Thereby, each vibration element can be protected from overcurrent while forming the shape of the short axis direction of the ultrasonic beam transmitted and received in each group more sharply.

  According to the present invention, it is possible to realize an ultrasonic probe that is more suitable for protecting a vibration element from a transient phenomenon occurring in a bias power source.

(First embodiment)
A first embodiment of an ultrasonic probe to which the present invention is applied will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of the ultrasonic probe of the present embodiment.

  As shown in FIG. 1, the ultrasonic probe is composed of transducers that mutually convert ultrasonic waves and electrical signals, and the transducer has ultrasonic transmission / reception sensitivity corresponding to the magnitude of the applied bias. A plurality of changing vibration elements 10-1 and 10-2, an upper electrode 12a-1 and a lower electrode 12b-1 as electrodes connected to the vibration element 10-1, and an electrode connected to the vibration element 10-2 And an upper electrode 12a-2 and a lower electrode 12b-2.

  Here, in the ultrasonic probe of the present embodiment, the protection circuit 14-1 serving as a protection unit that prevents overvoltage exceeding the rated voltage of the vibration element 10-1 is provided between the vibration element 10-1 and the bias unit 16. It is arranged. Similarly, a protection circuit 14-2 is disposed between the vibration element 10-2 and the bias unit 16. The vibration element may be referred to as a cell, and the number thereof may be increased as necessary.

  The ultrasonic probe will be described in more detail. The ultrasonic probe is connected to an ultrasonic diagnostic apparatus. As shown in FIG. 1, the ultrasonic diagnostic apparatus includes a transmission unit 18 that supplies a drive signal to the ultrasonic probe, a reception unit 20 that processes a reception signal output from the ultrasonic probe, and an ultrasonic wave. Bias means 16 having a bias power source (DC power source) for applying a bias to the probe is disposed. The transmission unit 18 and the reception unit 20 exchange signals with the ultrasonic probe via the transmission / reception separating unit 22. For example, a signal line and a signal return line are AC-coupled between the transmission / reception separating means 22 and, for example, the vibration element 10-1.

  The vibration element 10-1 applied to the ultrasonic probe is an ultrasonic transducer in which the electromechanical coupling coefficient changes according to the magnitude of the applied bias. For example, FIG. 1 shows an example in which cMUT (Capative Micromachined Ultrasonic Transducer: IEEE Trans. Ultrason. Ferroelect. Freq. Contr. Vol 45 pp. 678-690 May 1998) is applied as the vibration element 10-1.

  The cMUT has a so-called capacitor structure in which a drum-shaped hollow film is sandwiched between a top electrode 12a-1 and a bottom electrode 12b-1 on a semiconductor substrate. When a bias is applied to the cMUT from the bias means 16, an electric field is generated between the upper electrode 12a-1 and the lower electrode 12b-1, and the film is in a tension state. When a driving signal is supplied from the transmission unit 18 to the cMUT in this state, an ultrasonic wave is transmitted to the subject due to the vibration of the film. Further, when the reflected echo generated from the subject is input to the cMUT, the capacity of the internal space changes, so that a received signal can be obtained by taking out the change in capacity as an electrical signal. Further, since the degree of tension of the film changes according to the magnitude of the bias applied to the cMUT, the intensity of the ultrasonic wave can be weighted by controlling the magnitude of the bias. In addition, although cMUT was demonstrated on behalf of the element, you may apply the element formed including an electrostrictive material.

  In the vibration element 10-1, the upper electrode 12a-1 is formed at the top, and the lower electrode 12b-1 is formed at the bottom. The upper electrode 12a-1 is connected to the positive bias side of the bias means 16 via a terminal 24a. The lower electrode 12b-1 is connected to the negative bias side of the bias means 16 via a terminal 24b. A protection circuit 14-1 is disposed between the vibrating element 10-1 and the bias means 16. To supplement the arrangement position, the protection circuit 14-1 is provided closer to the bias means 16 than the connection position where the transmission means 18 or the reception means 20 and the transmission / reception separating means 22 are connected to the vibration element 10-1. Specific examples of the protection circuit 14-1 will be described in Examples 1 to 5 below. The vibration element 10-1 has been described as a representative, but the same applies to the other vibration elements 10-2.

Example 1
FIG. 2 is a diagram illustrating a first example of a protection circuit applied to the ultrasonic probe of the present embodiment. FIG. 2A is a diagram illustrating a configuration and a connection form of the protection circuit 14-1. FIG. 2B is a characteristic diagram showing the relationship between the output bias V _dc of the bias means 16 and the applied bias V _cell of the vibration element 10-1. FIG. 2C is a characteristic diagram showing the relationship between the output bias V _dc of the bias means 16 and the current I _cell flowing through the vibration element 10-1.

As shown in FIG. 2A, the protection circuit 14-1 includes a resistor R _s (resistor 26 in the figure) connected in series between the upper electrode 12a-1 and the bias unit 16. The resistance value of the resistor R _s is greater than the electrical resistance of the vibrating element 10-1 is set smaller than the electric resistance of the vibrating element 10-1, and when an overvoltage is applied when the normal bias is applied Has been. The normal bias is a bias that is equal to or lower than the rated voltage of the vibration element 10-1. The overvoltage is a bias that exceeds the rated voltage of the vibration element 10-1.

Here, as illustrated in FIG. 2A, the vibration element 10-1 is represented by an equivalent circuit having a capacitor C _cell and a resistor R _cell connected in parallel to the capacitor C _cell . Here, V _dc indicates the output bias of the bias power source of the bias means 16. V _cell represents a bias applied to the vibration element 10-1. I _cell shows the current through resistor _{R cell} of the vibrating element 10-1.

First, when a normal bias is applied to the vibration element 10-1, the applied bias V _cell is expressed by the following equation (1). On the other hand, when an overvoltage is applied to the vibration element 10-1, the applied bias V _cell is expressed by Equation 2. Note that, when an overvoltage is applied to the vibration element 10-1, an overcurrent exceeding the rated current flows to the vibration element 10-1, and the resistance of the vibration element 10-1 at that time is defined as R _cell ′.

(Formula 1)
V _cell = V _dc · R _cell / (R _s + R _cell )
(Equation 2)
V _cell = V _dc · R _cell '/ (R _s + R _cell ')

In equation 1 and equation 2, the resistance value of the resistor R _s is a condition shown in Equation 3. Therefore, Formula 1 and Formula 2 are expressed as Formula 4. As can be seen from Equation 3 and Equation 4, the multiplication term for the output bias V _dc on the right side of Equation 4 is smaller than “1”. Therefore, when the output bias V _dc of the bias means 16 exceeds the rated voltage of the vibrating element 10-1, a voltage drop of the applied bias V _cell occurs as shown in FIG. 2B. Further, the steep slope of the DC load line of the current I _cell is alleviated as shown in FIG. 2C. As a result, the time until the failure of the vibration element 10-1 can be extended.

(Formula 3)
R _cell >> R _s >> R _cell '
(Formula 4)
V _cell ≒ V _dc · R _cell '/ R _s

  According to the present embodiment, an overvoltage caused by a transient phenomenon generated in the bias power supply is suppressed by the protection circuit 14-1 before being applied to the vibration element 10-1. Therefore, since it is possible to prevent an overcurrent from flowing through the vibration element 10-1, a failure caused by the overcurrent can be prevented. As a result, for example, the device life of the ultrasonic probe can be extended, and stable operation of the device can be ensured. Further, the protection circuit 14-1 of the present embodiment can be realized relatively inexpensively and easily.

Add described resistance value of the resistor R _s. The resistance value of the resistance R _cell of the vibration element 10-1 may vary due to a wafer manufacturing process or the like. Therefore, as a first method of controlling the resistance value of the resistor R _s, the variation in the resistance values statistically not breakdown value as to absorb all the resistance value of the resistor R _s can be adjusted uniformly. However, as a result of being sometimes set higher than the value of the resistance R _s during normal operation, the voltage drop may increase and unnecessary power loss may occur.

As a second method of controlling the resistance value of the resistor R _s, the resistance value of the resistor R _s can be controlled individually and specifically. For example, a probe that conducts electrical contact is brought into contact with each electrode of the vibration element 10-1, and the resistance R _cell is measured. Then, based on the measurement value, by laser irradiation by the laser machining apparatus and a laser processing method with the resistor _{R s} (for example, Japanese 2001-47270 JP), trimming the resistance value of the resistor _{R s.} Thereby, since the resistance value is adjusted in units of each resistance R _s , generation of unnecessary power loss can be suppressed. Further, instead of the laser trimming method, a plurality of resistance patterns can be obtained by applying a technique (for example, Japanese Patent Application Laid-Open No. 2004-273679) for applying a metal paste and refining a metal wiring layer as in a semiconductor device manufacturing method. in it it is also possible to adjust the connection status of the configuration the resistor R _s.

(Example 2)
FIG. 3 is a diagram illustrating a second example of the protection circuit applied to the ultrasonic probe of the present embodiment. FIG. 3A is a diagram illustrating a configuration and a connection form of the protection circuit 14-1. FIG. 3B is a characteristic diagram showing a relationship between the resistance R _sw of the switch element SW and the current I _cell flowing through the vibration element 10-1. FIG. 3C is a characteristic diagram showing the relationship between the output bias V _dc of the bias means 16 and the current I _cell flowing through the vibration element 10-1.

As shown in FIG. 3A, the protection circuit 14-1 includes a switch element SW (switch element 30 in the figure) connected in series between the upper electrode 12a-1 and the bias means 16. The switch element SW here is a positive temperature coefficient thermistor including barium titanate (BaTiO ₃ ) and tungsten nitride silicide (WSiN) containing Si. The thermistor has a characteristic of changing the resistance value based on the temperature caused by the magnitude of the current flowing through itself. For example, in the positive temperature coefficient thermistor of this embodiment, heat is generated due to an increase in the current flowing through the positive temperature coefficient thermistor, so that the resistance value increases by 10 ⁶ to 10 ⁷ times, for example.

The vibration element 10-1 flows a current of about several pA to several hundred pA during normal operation. During normal operation, the switch element SW is in a closed state, and its resistance R _sw is a substantially constant low value. On the other hand, when an overvoltage is applied to the vibration element 10-1, an abnormal state such as an avalanche phenomenon or a short circuit occurs, and a current of about several μA to several hundred mA starts to flow. In the abnormal state, the switch element SW is opened, and the current I _cell is cut off as shown in FIGS. 2B and 2C. Thereby, the overcurrent which flows into the vibration element 10-1 is suppressed.

  In addition, after the switch element SW is in the open state, in order to perform heat management, the heat storage design may be performed so that the open state of the switch element SW is continued until the bias power source of the bias unit 16 is reset. Or you may design heat dissipation so that it may close gradually according to the elapsed time after switch element SW will be in an open state. Moreover, although the example which applied the positive temperature coefficient thermistor as switch element SW was demonstrated, it is not restricted to this, In short, what is necessary is just to apply the element from which an impedance changes according to the magnitude | size of the electric current which flows through self.

  According to the present embodiment, an overcurrent caused by a transient phenomenon generated in the bias power source is detected by the protection circuit 14-1 before flowing into the vibration element 10-1, and is reliably reduced. Therefore, it is possible to prevent an overcurrent from flowing through the vibration element 10-1.

(Example 3)
FIG. 4 is a diagram showing a third example of the protection circuit applied to the ultrasonic probe of the present embodiment. FIG. 4A is a diagram illustrating a configuration and a connection form of the protection circuit 14-1. FIG. 4B is a characteristic diagram showing the relationship between the output bias V _dc of the bias means 16 and the current I _cell flowing through the vibration element 10-1. In the present embodiment, a voltage limit circuit is disposed as a protection circuit 14-1 between the vibration element 10-1 and the bias means 16.

As shown in FIG. 4A, the protection circuit 14-1 is connected in series between the upper electrode 12a-1 and the bias means 16 and the resistor 40 connected in series, and between the vibration element 10-1 and the bias means 16. It is composed of a constant voltage source 42 and the like. Resistor 40, the resistance value is the same as the resistance R _s of the first embodiment. The constant voltage source 42 is, for example, a Zener diode, and a constant voltage value Vz is set according to the maximum voltage rating of the vibration element 10-1. In short, the protection circuit 14-1 keeps the magnitude of the bias applied to the vibration element 10-1 below the constant voltage value Vz.

Such a protection circuit 14-1 does not operate when the output bias V _dc of the bias means 16 is less than or equal to the maximum voltage rating of the vibration element 10-1. When the output bias V _dc reaches the maximum voltage rating of the vibration element 10-1, the protection circuit 14-1 operates as a voltage limiter circuit that holds the output voltage at the constant voltage value Vz. For example, when a Zener diode is used as the constant voltage source 42, the tunnel effect is exhibited when the output bias V _dc reaches the constant voltage value Vz. With respect to the Zener diode here, the donor compounding ratio of the Zener diode is controlled so as to have a predetermined constant voltage value Vz. It is also possible to control the resistance R _s for the current control to be supplied to the Zener diode to a predetermined constant voltage value Vz such trimming.

  According to the present embodiment, the voltage applied to the vibration element 10-1 is reliably shunted to the constant voltage value Vz or less after being detected by the protection circuit 14-1 before being applied to the vibration element 10-1. Clipped. Therefore, since it is possible to prevent an overcurrent from flowing through the vibration element 10-1, a failure caused by the overcurrent can be prevented.

  Note that a constant voltage source including a transistor may be used instead of the Zener diode. Further, instead of the resistor 40, a switch element SW that is a positive temperature coefficient thermistor of the second embodiment may be applied.

Example 4
FIG. 5 is a diagram showing a fourth example of the protection circuit applied to the ultrasonic probe of the present embodiment. FIG. 5A is a diagram illustrating a configuration and a connection form of the protection circuit 14-1. FIG. 5B is a characteristic diagram showing the relationship between the output bias V _dc of the bias means 16 and the current I _cell flowing through the vibration element 10-1. This embodiment is another example in which a voltage limit circuit is disposed as a protection circuit 14-1 between the vibration element 10-1 and the bias means 16.

As shown in FIG. 5A, the protection circuit 14-1 has an FET 50 connected in series between the upper electrode 12a-1 and the bias means 16, and a source resistor 52 connected to the output terminal side of the FET 50. Configured as a constant current source. This constant current source is a circuit that produces a specific current regardless of the output bias V _dc . For example, in the constant current source of this embodiment, the constant current value _Id is set according to the maximum current rating of the vibration element 10-1. More specifically, to generate the gate-source voltage of FET50 a current I _cell flowing through the source resistor 52, the output current is operated as a current limiter circuit becomes a constant current value I _d. If the output current is less than the constant current value I _d, the constant current source is not activated. Here specific method of controlling the constant current value I _d in is realized by adjusting the like trimming source resistance 52 to the desired current value.

According to the present embodiment, the current flowing through the vibration element 10-1 is reliably shunted and clipped to a constant current value _Id or less after being detected by the protection circuit 14-1 before flowing through the vibration element 10-1. The Therefore, since it is possible to prevent an overcurrent from flowing through the vibration element 10-1, a failure caused by the overcurrent can be prevented.

(Example 5)
FIG. 6 is a diagram showing a fifth example of the protection circuit applied to the ultrasonic probe of the present embodiment. FIG. 6A is a diagram illustrating a configuration and a connection form of the protection circuit 14-1. FIG. 6B is a characteristic diagram illustrating a relationship between the resistance R _sw of the switch element SW and the current I _cell flowing through the vibration element 10-1. FIG. 6C is a characteristic diagram showing the relationship between the output bias V _dc of the bias unit 16 and the current I _cell flowing through the vibration element 10-1.

As shown in FIG. 6A, the protection circuit 14-1 is roughly divided into an overvoltage detection means 60 and a switch element control means 62. As for the overvoltage detection means 60, a resistor 64 and a resistor 66 connected in series are connected in parallel to the vibration element 10-1 and the bias means 16. The switch element control means 62 includes a switch element 68 connected in series between the upper electrode 12a-1 and the bias means 16, and a switch element control FET 70 for controlling the opening and closing of the switch element 68. The gate of the switching element control FET 70 is connected to the common connection point of the resistor 64 and the resistor 66 of the overvoltage detection means 60, the source is connected to the lower electrode 12b-1, and the drain is set to the set voltage _Vcc via the resistor 72. It is connected. The switch element 68 is controlled by the drain potential.

The protection circuit 14-1 of this embodiment controls the switch element by switching the drain voltage of the switch element control FET 70 from the set voltage value _Vcc to 0V based on the voltage value of the resistance voltage division of the resistor 64 and the resistor 66. This is different from the second embodiment in which the switch element is controlled based on the current flowing through itself. For example, in the normal state where the output bias V _dc of the bias unit 16 is equal to or lower than the rated voltage of the vibration element 10-1, the switch element 68 is closed. When the output bias V _dc reaches the rated voltage of the vibration element 10-1, the voltage value of the resistance divided voltage of the resistor 64 and the resistor 66 activates the switch element control FET 70. The switching element control FET outputs an opening command to the switching element 68.

  According to the present embodiment, an overvoltage caused by a transient phenomenon generated in the bias power source is reliably detected by the protection circuit 14-1 before being applied to the vibration element 10-1, and then reliably shunted below the set voltage. Clipped. Therefore, since it is possible to prevent an overcurrent from flowing through the vibration element 10-1, a failure caused by the overcurrent can be prevented.

  Further, the overvoltage detection means 60 can be realized by adjusting the ratio of the resistor 64 and the resistor 66 by trimming or the like so that a desired voltage value is obtained. Further, a thermistor can be applied instead of the resistor 64 and the resistor 66. In that case, the temperature or current can be compensated by controlling the resistance value by the temperature or self-current of the thermistor.

  In addition, although the example of the voltage division by two resistances 64 and 66 was shown about the overvoltage detection means 60, you may make it operate | move as a constant current source by replacing one of two resistances with FET. Further, as the switch element control means 62, a comparator such as a comparator may be applied instead of the switch element control FET.

  As described above, the protection circuit 14-1 described in the first to fifth embodiments can be integrally formed as a part of the transducer of the ultrasonic probe by a semiconductor processing process. For example, in addition to resistors, donor zener diodes and transistors, ceramics such as tungsten nitride silicide (WSiN), MEMS micro relay switches or electrostatic micro relay switches can be used for integral molding, and multi chip modules. ). In short, the protection circuit 14-1 can be mounted on the ultrasonic probe. However, for example, in order to mount on an existing ultrasonic probe, it may be configured to be externally attached to the ultrasonic probe.

(Comparative example)
FIG. 7 is a view showing a form for comparison with the ultrasonic probe of the present embodiment. As shown in FIG. 7, when a transient transient occurs in the bias power supply of the bias unit 16 (for example, power supply cutoff) when the output bias V _dc is applied to the vibration element 10-1, an overvoltage exceeding the rating. Is applied to the vibration element 10-1, an overcurrent exceeding the rating may flow through the vibration element 10-1. Here, when an insulator is disposed between the upper electrode 12a-1 and the lower electrode 12b-1, the voltage at which the insulator breaks is, for example, 8 MV / cm. Further, when the thickness of the insulator is 200 nm, the voltage at which the avalanche phenomenon occurs is 160 V, for example. Furthermore, when an insulator is not provided between the upper electrode 12a-1 and the lower electrode 12b-1, a short circuit or the like occurs, and as a result, the equivalent impedance of the vibration element 10-1 is reduced. As a result, the vibration element 10-1 Overcurrent begins to flow. When such an overcurrent flows, the temperature of the electrode of the vibration element 10-1 rises, and there is a possibility that a failure such as a disconnection due to conductor evaporation of the upper electrode 12a-1 or the lower electrode 12b-1 may occur. .

(Second Embodiment)
A second embodiment of an ultrasonic probe to which the present invention is applied will be described with reference to the drawings. FIG. 8 is a diagram showing the configuration of the ultrasonic probe of the present embodiment. This embodiment is different from the first embodiment in which a protection circuit is provided for each vibration element in that a protection circuit is provided for each set of vibration elements.

  As shown in FIG. 8, the ultrasonic probe is configured by arranging transducers that mutually convert ultrasonic waves and electrical signals into a strip shape, and the transducer has ultrasonic transmission / reception sensitivity with a magnitude of applied bias. And a plurality of electrodes that are divided in a short axis direction orthogonal to the strip axis and connected to the vibration elements.

  The plurality of electrodes are divided into sets S1 to SM each including one or adjacent divided portions, and a plurality of protection circuits 80-1 to 80-M are disposed between each set and the bias unit 16. For example, a protection circuit 80-1 is provided between the set S1 and the bias means 16. In short, the present embodiment protects each vibration element in units of cells in that each vibration element is protected in units of blocks. Note that M corresponds to the number of sets in the minor axis direction.

  Such protection circuits 80-1 to 80-M are configured with different characteristics at the center and the end in the minor axis direction. For example, in the protection circuits 80-1 to 80-M, the allowable voltage is set to be smaller for each set from the center to the end in the minor axis direction. More specifically, the protection circuit corresponding to the group located at the center in the minor axis direction has a relatively high allowable voltage (for example, 160 V). In the protection circuit corresponding to the pair located at the end in the minor axis direction, the allowable voltage is set to a relatively low value (for example, 140 V).

  According to the present embodiment, the group located at the central portion in the short axis direction can be a strong electric field, and the electric field can be weakened on a group basis toward the end in the short axis direction. Therefore, the ultrasonic energy corresponding to the central portion is relatively high, and the ultrasonic energy is relatively low in units of pairs toward the end. Thereby, each vibration element can be protected from overcurrent while forming the shape of the short axis direction of the ultrasonic beam transmitted and received in each group more sharply.

  Further, although the case where a plurality of vibration elements are divided in the short axis direction has been described, as shown in FIG. 9, protection circuits 90-1 to 90 -N can be provided for each vibrator. Here, N is a number corresponding to the number of transducers arranged.

Further, the resistance value R _cell of each vibration element belonging to the set S1 may vary in resistance value due to a wafer manufacturing process or the like. Therefore, when an overvoltage is applied to the set S1, vibration elements that cause a failure such as disconnection are statistically varied. Therefore, the parameters to be controlled may be adjusted according to such statistical distribution.

  Further, even when a plurality of the protection circuits 80-1 to 80-M are simultaneously operated, the current of the individual elements may be concentrated and exceed the allowable value in units of sets or vibrators. Accordingly, by combining the installation of protection circuits in units of individual cells, blocks, and vibrators, each vibration element can be protected more safely from a transient phenomenon that occurs in the bias power supply.

  Also in the case of the Fresnel ring type beam focus, the protection circuits 80-1 to 80-M can be configured with different allowable voltage values at the center and the end of the ring focus beam. Also, as shown in FIG. 9, when the protection circuits 90-1 to 90N are arranged in units of transducers, the allowable voltage of the protection circuits 90-1 to 90-N is directed from the beam center to the end. Accordingly, the allowable voltage value may be set gradually smaller for each vibrator.

It is a figure which shows the structure of the ultrasonic probe of 1st embodiment to which this invention is applied. It is a figure which shows the 1st Example of the protection circuit of FIG. It is a figure which shows the 2nd Example of the protection circuit of FIG. It is a figure which shows the 2nd Example of the protection circuit of FIG. FIG. 6 is a diagram illustrating a fourth embodiment of the protection circuit in FIG. 1. FIG. 10 is a diagram showing a fifth embodiment of the protection circuit in FIG. 1. It is the figure which showed the form for comparing with the ultrasonic probe of 1st embodiment to which this invention is applied. It is a figure which shows the structure of the ultrasonic probe of 2nd embodiment to which this invention is applied. It is a figure which shows the other example of the ultrasonic probe of 2nd embodiment to which this invention is applied.

Explanation of symbols

10-1 Vibration element 12a-1 Upper electrode 12b-1 Lower electrode 14 Protection circuit 16 Biasing means 18 Transmitting means 20 Receiving means 22 Transmission / reception separating means

Claims (5)

The transducer is configured by arranging transducers that mutually convert ultrasonic waves and electrical signals. The transducer includes a vibration element whose ultrasonic transmission / reception sensitivity changes according to the magnitude of an applied bias, and an electrode connected to the vibration element. And
The ultrasonic probe according to claim 1, wherein protective means for preventing an overvoltage exceeding a rated voltage of the vibration element is disposed between the electrode and a bias power source. The protection means has a resistance connected in series between the electrode and the bias power source, and the resistance has a resistance value higher than an electric resistance of the vibration element when an overvoltage is applied to the vibration element. The ultrasonic probe according to claim 1, wherein is set to be large. The protection means includes a switch connected in series between the electrode and the bias power source, and the switch has an impedance that increases as a current flowing between the electrode and the bias power source increases. The ultrasonic probe according to claim 1. The protection means includes a voltage limit circuit disposed between the electrode and the bias power source, and the voltage limit circuit holds the magnitude of the bias applied to the vibration element below a set voltage. The ultrasonic probe according to claim 1, wherein: The transducers are arranged to mutually convert ultrasonic waves and electrical signals, and the transducers are orthogonal to the arrangement direction with a plurality of vibration elements whose ultrasonic transmission / reception sensitivity changes according to the magnitude of the applied bias. A plurality of electrodes divided in the minor axis direction,
The divided electrodes are divided into groups each composed of one or adjacent divided portions, and protective means for preventing overvoltage exceeding the rated voltage of the vibration element is disposed between each set and the bias power source. The ultrasonic probe is characterized in that the protective means is configured such that an allowable voltage is set to be smaller in units from the center to the end in the minor axis direction.

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