Patent Publication Number: US-2011074244-A1

Title: Ultrasonic probe

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ultrasonic probe used in an ultrasonic diagnostic apparatus, an electronic endoscope, and the like. 
     2. Description Related to the Prior Art 
     A medical diagnosis using an ultrasonic image is widely carried out. To produce the ultrasonic image, an ultrasonic probe, which has a lot of ultrasonic transducers arranged at a distal end, is used. Each ultrasonic transducer is constituted of a backing material, a piezoelectric layer, electrodes for sandwiching the piezoelectric layer, an acoustic impedance matching layer, and an acoustic lens. The ultrasonic transducers apply ultrasonic waves to a human body to be imaged, and receive echoes from the body. By electrically processing the echoes received by the ultrasonic transducers, the ultrasonic image is obtained. 
     Also, an ultrasonic tomographic image can be obtained by applying the ultrasonic waves with scanning. A scanning method for taking the ultrasonic tomographic image includes a mechanical scanning method in which the ultrasonic transducers are mechanically rotated, swung, or slid, and an electronic scanning method in which the plurality of ultrasonic transducers are arranged into an array (hereinafter called ultrasonic transducer array) and which ultrasonic transducers to drive are selectively switched with an electronic switch or the like. 
     It is desired to improve transmission and reception sensitivity of the ultrasonic transducers to get the higher definition ultrasonic image. To increase the transmission sensitivity, it is first conceivable to increase a voltage applied to the ultrasonic transducers to enhance transmission power of the ultrasonic waves. However, in consideration of an adverse effect on the human body, a mechanical index (MI) and a thermal index (TI) define sound pressure and an amount of energy of the ultrasonic waves that are allowable to be applied to the human body. Thus, the transmission power of the ultrasonic waves cannot be increased indiscriminately. 
     Also, increase in the application voltage to the ultrasonic transducers causes upsizing of voltage application circuits (pulsers) and high power consumption. In a case where the ultrasonic probe contains the pulsers, the upsizing of the pulsers causes increase in size of the ultrasonic probe and impairs operatability, which is one of the most important factors of the ultrasonic probe. In addition, if the ultrasonic probe with the pulsers is of a wireless type, increase in the application voltage shortens battery life and results in inconvenience in use. 
     To increase the transmission power of the ultrasonic waves with restraining the application voltage to the ultrasonic transducers, it is proposed to use a multilayer piezoelectric element in the ultrasonic transducer. The multilayer piezoelectric element, however, has a problem of the reception sensitivity, because the reception sensitivity of the multilayer piezoelectric element to the echo at a certain sound pressure level is one-Nth (“N” denotes the number of layers of the multilayer piezoelectric element) of that of a single-layer piezoelectric element. 
     Therefore, the ultrasonic probe is proposed in which the multilayer piezoelectric elements are used for transmitting the ultrasonic waves, and the single-layer piezoelectric elements are used for receiving the echoes. For example, in Japanese Patent Laid-Open Publication No. 2000-217196, the multilayer piezoelectric element for transmitting the ultrasonic waves is disposed on an echo receiving surface of the single-layer piezoelectric element. U.S. Pat. No. 6,640,634 describes a two-dimensional arrangement of the multilayer piezoelectric elements for transmitting the ultrasonic waves and the single-layer piezoelectric elements for receiving the echoes. 
     However, in the Japanese Patent Laid-Open Publication No. 2000-217196, since the multilayer piezoelectric element is disposed on the single-layer piezoelectric element, the whole of the two elements substantially has the same structure as that of the single multilayer piezoelectric element. The reception sensitivity of the multilayer piezoelectric element is one-Nth of that of the single-layer piezoelectric element, as described above, and hence the reception sensitivity is not improved. The U.S. Pat. No. 6,640,634 does not obviously describe how to arrange the multilayer and single-layer piezoelectric elements for transmission and reception and by which unit the piezoelectric elements are driven. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an ultrasonic probe that has improved transmission and reception sensitivity without degrading ultrasonic image quality. 
     To achieve the above and other objects, an ultrasonic probe according to the present invention includes a plurality of multilayer piezoelectric elements for transmitting an ultrasonic wave, a plurality of single-layer piezoelectric elements for receiving an echo of the ultrasonic wave, and a K number of transmitting and receiving channels. The multilayer piezoelectric elements and the single-layer piezoelectric elements are alternately arranged to form a piezoelectric element line. The transmitting and receiving channels virtually partition the piezoelectric element line, and each of the transmitting and receiving channels includes at least one multilayer piezoelectric element and at least one single-layer piezoelectric element. 
     It is preferable that the ultrasonic probe further include a transmission circuit for actuating the multilayer piezoelectric element and generating the ultrasonic wave from the multilayer piezoelectric element, and a reception circuit for actuating the single-layer piezoelectric element and receiving the echo through the single-layer piezoelectric element. 
     The ultrasonic probe may further include a first conductor connected to an electrode of each of the multilayer piezoelectric elements, and a second conductor connected to an electrode of each of the single-layer piezoelectric elements. The first conductor extends on a first side face of each of the multilayer piezoelectric elements in a direction orthogonal to the piezoelectric element line. The second conductor extends on a second side face of each of the single-layer piezoelectric elements in a direction orthogonal to the piezoelectric element line. The second side face is opposite to the first side face. 
     The ultrasonic probe may further include an amplifier for amplifying a signal from each of the single-layer piezoelectric elements. The single-layer piezoelectric element is directly connected to the amplifier without passing through a capacitance transmission line. 
     According to the present invention, the multilayer piezoelectric element and the single-layer piezoelectric element are alternately arranged to form the piezoelectric element line. The multilayer piezoelectric element transmits the ultrasonic wave, and the single-layer piezoelectric element receives the echo. At least two piezoelectric elements adjoining to each other compose the transmitting and receiving channel. The present invention makes it possible to improve transmission sensitivity of the ultrasonic wave and reception sensitivity of the echo without degrading ultrasonic image quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For more complete understanding of the present invention, and the advantage thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an ultrasonic diagnostic apparatus; 
         FIG. 2  is a perspective view of an ultrasonic transducer array; 
         FIG. 3  is a side view of a transmitting ultrasonic transducer; 
         FIG. 4  is a side view of a receiving ultrasonic transducer; 
         FIG. 5  is a block diagram of the ultrasonic diagnostic apparatus; and 
         FIG. 6  is a perspective view of an ultrasonic transducer array according to a second embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , an ultrasonic diagnostic apparatus  2  is constituted of a portable ultrasonic observing device  10  and an extracorporeal ultrasonic probe  11 . The portable ultrasonic observing device  10  has a main body  12  and a cover  13 . On a top surface of the main body  12 , there is disposed an operation unit having a number of buttons and a trackball to input various operation commands to the portable ultrasonic observing device  10 . Inside the cover  13 , a monitor  15  is provided to display not only an ultrasonic image but also various operation screens. 
     The cover  13  is hinged on the main body  12 , and is rotatable between an illustrated open position in which the operation unit  14  and the monitor  15  are exposed, and a closed position (not illustrated) in which the top surface of the main body  12  is faced to an inner surface of the cover  13  to cover the operation unit  14  and the monitor  15  with each other for protection. A grip (not illustrated) is attached to a side face of the main body  12  to make the portable ultrasonic observing device  10  convenient to carry about in a state of closing the main body  12  and the cover  13 . In the other opposite side face of the main body  12 , there is provided a probe connection portion  17  to which the ultrasonic probe  11  is detachably connected. 
     The ultrasonic probe  11  is constituted of a scan head  18 , which a doctor holds and presses against a human body part to be imaged, a connector  19  connected to the probe connection portion  17 , and a cable  20  for connecting the scan head  18  to the connector  19 . An ultrasonic transducer array  21  is contained at a distal end of the scan head  18 . 
     The ultrasonic transducer array  21 , as shown in  FIG. 2 , has such structure that a backing material  26 , a plurality of transmitting ultrasonic transducers  27   a  and a plurality of receiving ultrasonic transducers  27   b , acoustic impedance matching layers  28   a  and  28   b , and an acoustic lens  29  are stacked in this order on a mount support  25  made of a glass-epoxy resin plate or the like. 
     The backing material  26  is made of an epoxy resin, a silicone resin, or the like, and absorbs ultrasonic waves that are emitted from the transmitting ultrasonic transducers  27   a  in a direction of the mount support  25 . The backing material  26  is in a gentle dome shape, and has a convex cross-section in an azimuth (AZ) direction, which is orthogonal to an elevation (EL) direction. 
     Each of the transmitting and receiving ultrasonic transducers  27   a  and  27   b  takes the shape of a block that is long in the EL direction. The transmitting and receiving ultrasonic transducers  27   a  and  27   b  are alternately arranged at regular intervals in the AZ direction. A filling material  30  is charged into gaps between the transmitting and receiving ultrasonic transducers  27   a  and  27   b  and around the transmitting and receiving ultrasonic transducers  27   a  and  27   b.    
     The acoustic impedance matching layers  28   a  and  28   b  alleviate the difference in impedance between the ultrasonic transducer  27   a  or  27   b  and a human body. The acoustic lens  29  is made of the silicone resin or the like, and concentrates the ultrasonic waves emitted from the transmitting ultrasonic transducers  27   a  onto an internal body part to be imaged. The acoustic lens  29  may be omitted, and a protective layer may be provided instead of the acoustic lens  29 . 
     A pair of a transmitting ultrasonic transducer  27   a  and a receiving ultrasonic transducer  27   b  adjoining to each other composes a single transmitting and receiving channel  80  (surrounded by alternate long and short dashed lines in  FIG. 2 ). The ultrasonic transducer array  21  has the plurality of transmitting and receiving channels  80  arranged in the AZ direction. 
     As shown in  FIG. 3 , the transmitting ultrasonic transducer  27   a  being a multilayer piezoelectric element is constituted of two internal electrodes  35   a  and  35   b , a top electrode  36 , a bottom electrode  37 , three piezoelectric layers  38   a  to  38   c , insulator layers  39   a  and  39   b , and two conductor layers  40   a  and  40   b . The piezoelectric layer  38   a  is sandwiched between the top electrode  36  and the internal electrode  35   a . The piezoelectric layer  38   b  is sandwiched between the internal electrodes  35   a  and  35   b , and the piezoelectric layer  38   c  is sandwiched between the internal electrode  35   b  and the bottom electrode  37 . The insulator layer  39   a  is so formed as to expose a part of the internal electrode  35   a , that is, an end face of the internal electrode  35   a  contacting the conductor layer  40   a . In a like manner, the insulator layer  39   b  is so formed as to expose a part of the internal electrode  35   b , that is, an end face of the internal electrode  35   b  contacting the conductor layer  40   b . The conductor layer  40   a  electrically connects the internal electrode  35   a  to the bottom electrode  37  beyond the insulator layer  39   b , and the conductor layer  40   b  electrically connects the internal electrode  35   b  to the top electrode  36  beyond the insulator layer  39   a.    
     As shown in  FIG. 4 , the receiving ultrasonic transducer  27   b  is a single-layer piezoelectric element that has a single piezoelectric layer  45  sandwiched between a top electrode  46  and a bottom electrode  47 . The top electrode  46  is disposed on the side of the acoustic impedance matching layer  28   a , and the bottom electrode  47  is disposed on the side of the backing layer  26 . 
     The piezoelectric layers  38   a  to  38   c  of the transmitting ultrasonic transducer  27   a  are polarized in directions illustrated by arrows, so that the piezoelectric layers next to each other are polarized in the directions opposite to each other. The piezoelectric layer  45  of the receiving ultrasonic transducer  27   b  is polarized in a direction from the bottom electrode  47  to the top electrode  46 . The piezoelectric layers of the transmitting and receiving ultrasonic transducers  27   a  and  27   b  are made of the same material of PZT (lead zirconate titanate)-based piezoelectric ceramic. 
     In the transmitting ultrasonic transducer  27   a , the top electrode  36  and the internal electrode  35   b , which are connected by the conductor layer  40   b , are grounded. The bottom electrode  37  and the internal electrode  35   a , which are connected by the conductor layer  40   a , are connected to a first conductor pattern  31   a  formed on a single side face of the backing material  26 , as shown in  FIG. 2 . In the receiving ultrasonic transducer  27   b , the top electrode  46  is grounded. The bottom electrode  47  of the receiving ultrasonic transducer  27   b  is connected to a second conductor pattern  31   b.    
     Each of the first and second conductor patterns  31   a  and  31   b  downward extends on the backing material  26 . The first conductor patterns  31   a  are connected to transmission circuit boards  32   a  attached to the single side face of the mount support  25 , with bonding wires  33 , and the second conductor patterns  31   b  are connected to reception circuit boards  32   b  in a like manner. The transmission circuit boards  32   a  and the reception circuit boards  32   b  are flexible printed circuit boards made of a polyimide or the like. The two transmitting ultrasonic transducers  27   a  are connected to the single transmission circuit board  32   a , and the two receiving ultrasonic transducers  27   b  are connected to the single reception circuit board  32   b . Otherwise, the three or more transmitting ultrasonic transducers  27   a  may be connected to the single transmission circuit board  32   a , and the three or more receiving ultrasonic transducers  27   b  may be connected to the single reception circuit board  32   b.    
     In manufacture of the ultrasonic transducer array  21 , a green sheet method is used, for example. In this case, layers of the internal electrodes  35   a  and  35   b  are printed on only parts of piezoelectric ceramic green sheets corresponding to the transmitting ultrasonic transducers  27   a , while no electrode layer is printed on parts corresponding to the receiving ultrasonic transducers  27   b . Then, the printed green sheets are stacked. A stack of the green sheets manufactured as above is baked and glued on the backing material  26 , and is cut into the transmitting ultrasonic transducers  27   a  and the receiving ultrasonic transducers  27   b  by dicing. Then, the insulator layers  39   a  and  39   b  and the conductor layers  40   a  and  40   b  are formed on a single side face of each of the transmitting ultrasonic transducers  27   a . After that, charge of the filling material  30 , attachment of the acoustic impedance matching layers  28   a  and  28   b  and the acoustic lens  29 , bonding between the transmitting ultrasonic transducers  27   a  and the transmission circuit boards  32   a  and between the receiving ultrasonic transducers  27   b  and the reception circuit boards  32   b , and the like are carried out to complete the ultrasonic transducer array  21 . 
     As shown in  FIG. 5 , pulsers  50  are connected to the transmitting ultrasonic transducers  27   a  on a one-by-one basis. The pulsers  50  are controlled by a scan controller  52  under the control of a CPU  51 . Each pulser  50  sends exciting pulses to the corresponding transmitting ultrasonic transducer  27   a  to generate the ultrasonic waves. The scan controller  52  selects which pulsers to drive from among the plurality of pulsers  50 , and successively switches the selection at established time intervals. To be more specific, for example, from among a hundred and twenty-eight transmitting and receiving channels, the adjoining forty-eight channels are regarded as a single block, and the pulsers  50  of the transmitting ultrasonic transducers  27   a  belonging to this block are driven with an arbitrary time delay. Whenever transmission and reception of the single block is completed, the scan controller  52  shifts the selection of the channels to be driven by one or some channels to configure a new block, and drives the pulsers  50  of the transmitting ultrasonic transducers  27   a  belonging to the new block. Thus, each of the transmitting and receiving channels is successively driven from block to block with overlapping. 
     To each receiving ultrasonic transducer  27   b , a receiver  54  is connected through an amplifier  53 . The receiver  54  is connected to an analog-to-digital converter (A/D)  55 . The amplifier  53  is of a voltage feedback type or a charge storage type. The amplifier  53  amplifies a detection signal outputted as a voltage from the receiving ultrasonic transducer  27   b  in response to reception of the echoes. The receiver  54  receives the detection signal amplified by the amplifier  53 . The A/D  55  digitizes the detection signal from the receiver  54 . The receivers  54 , the A/Ds  55 , the amplifiers  53 , and the pulsers  50  of the three channels are illustrated in  FIG. 5 , but are actually provided for every channel. 
     The pulsers  50  are implemented on the transmission circuit boards  32   a . The amplifiers  53 , the receivers  54 , and the A/Ds  55  are implemented on the reception circuit boards  32   b . Since the receiving ultrasonic transducer  27   b  is connected to the reception circuit board  32   b  via the conductor pattern  31   b  and the bonding wire  33 , as described above, the receiving ultrasonic transducer  27   b  is directly connected to the amplifier  33  without passing through a capacitance transmission line such as a coaxial cable. 
     The A/Ds  55  are connected to a parallel-to-serial converter (P/S)  56 . The P/S  56  converts parallel data of the detection signals outputted from the A/Ds  55  into serial data. This serial data is inputted to a serial-to-parallel converter (S/P)  60  of the portable ultrasonic observing device  10  through the cable  20 , the connector  19 , and the probe connection portion  17 . 
     The S/P  60  converts the serial data sent from the ultrasonic probe  11  back into the parallel data. A beamformer (BF)  61  performs a phase matching operation on the parallel detection signals. A log compression and detection circuit (LOG)  62  performs a log compression operation on the detection signals outputted from the BF  61  to detect amplitude. The detection signals outputted from the LOG  62  are temporarily stored on a memory (not illustrated). 
     A digital scan converter (DSC)  63  converts the detection signals into a television signal under the control of a CPU  64 . The television signal produced by the DSC  63  is subjected to a digital-to-analog conversion by a not-illustrated digital-to-analog converter, and is displayed as the ultrasonic image on the monitor  15 . 
     The CPU  64  controls the operation of each part of the portable ultrasonic observing device  10 . The CPU  64  actuates each part based on an operation input signal from the operation unit  14 . The CPU  64  also controls a power supply to the ultrasonic probe  11 . 
     The operation of the ultrasonic diagnostic apparatus  2  having above structure will be described. First, the connector  19  of the ultrasonic probe  11  is inserted and fixed into the probe connection portion  17  of the portable ultrasonic observing device  10 , to connect the ultrasonic probe  11  to the portable ultrasonic observing device  10 . Then, the portable ultrasonic observing device  10  is turned on with operation from the operation unit  14 . The doctor observes the ultrasonic image displayed on the monitor  15  of the portable ultrasonic observing device  10  and carries out diagnosis, while pressing the scan head  18  of the ultrasonic probe  11  against the human body part to be imaged. 
     In the ultrasonic probe  11 , the exciting pulses are sent from the forty-eight pulsers  50  of the single block selected by the scan controller  52  to the transmitting ultrasonic transducers  27   a  of the corresponding channels, and the ultrasonic waves are applied to the human body part to be imaged. The scan controller  52  successively switches driving of the pulsers  50  on a block basis, whenever the ultrasonic waves are transmitted and received. Thus, the human body part is scanned with an ultrasonic beam. 
     The ultrasonic waves emitted from the transmitting ultrasonic transducer  27   a  of one channel are reflected by the human body part, and the detection signal corresponding to the echoes is outputted from the receiving ultrasonic transducer  27   b  of the same channel. The detection signal from the receiving ultrasonic transducer  27   b  is amplified by the amplifier  53 , and is received by the receiver  54 , and is digitized by the A/D  55 . The digital detection signals from the A/Ds  55  are converted into the serial data by the P/S  56 , and the serial data is sent to the portable ultrasonic observing device  10 . 
     In the portable ultrasonic observing device  10 , the S/P  60  converts the serial data back into the parallel detection signals. Then, the detection signals are subjected to the phase matching operation by the BF  61 , and the log compression operation by the LOG  62  to detect the amplitude, and then are temporarily stored on the memory. 
     The detection signals after the log compression and the amplitude detection are converted into the television signals by the DSC  63 . The television signal produced by the DSC  63  is displayed on the monitor  15  as the ultrasonic image after the digital-to-analog conversion. 
     As described above, the transmitting ultrasonic transducers  27   a  being the multilayer piezoelectric elements and the receiving ultrasonic transducers  27   b  being the single-layer piezoelectric elements are alternately arranged in the AZ direction, so as to form a piezoelectric element line. The adjoining two ultrasonic transducers  27   a  and  27   b  compose the single transmitting and receiving channel, which transmits the ultrasonic waves and receives the echoes, so that it is possible to increase transmission sensitivity of the ultrasonic waves and reception sensitivity of the echoes without degrading ultrasonic image quality. 
     In a conventional ultrasonic probe, the two or three adjoining ultrasonic transducers compose the single channel. Taking a case where the single channel has the two ultrasonic transducers as an example, both of the two ultrasonic transducers are actuated to emit the ultrasonic waves, and signals received by both of the two ultrasonic transducers are added up to obtain the single detection signal. In the present invention, on the contrary, out of the two ultrasonic transducers composing the single channel, one of the ultrasonic transducers is used for transmitting the ultrasonic waves, and the other one is used for receiving the echoes. Therefore, it is possible to obtain the ultrasonic image that has equal azimuth resolution and image quality to those of conventional one. 
     Conventionally, the both of the two ultrasonic transducers composing the single channel carry out transmission and reception. In the present invention, on the contrary, one of the two ultrasonic transducers carries out the transmission, and the other one carries out the reception. According to the present invention, the size of an ultrasonic wave transmitting surface (top surface) is reduced by approximately half and transmission power is also reduced, as compared with those of the conventional one. Thus, it is necessary to increase the number of layers of the multilayer piezoelectric element, as compensation for reduction in the transmission power. 
     The number N of layers of the multilayer piezoelectric element satisfies the following expression (1): 
         N=V 1/( Vn·S )  (1)
 
     Wherein, V 1  represents an application voltage in the case of using the single-layer piezoelectric element for transmission of the ultrasonic waves, Vn represents an application voltage in the case of using the multilayer piezoelectric element for transmission of the ultrasonic waves, and S represents a size rate of the ultrasonic wave transmitting surface. The transmission power obtained by the application of the voltage Vn to the multilayer piezoelectric element having an N number of layers is equal to the transmission power obtained by the application of the voltage V 1  to the single-layer piezoelectric element. 
     When the single transmitting and receiving channel is constituted of one multilayer piezoelectric element and one single-layer piezoelectric element, “S” stands at 0.5. If V 1 =±100 (V) and V 2 =±20 (V), for example, the number “N” of layers becomes 10, according to the expression (1). As is apparent from above, the number “N” of layers of the multilayer piezoelectric element is appropriately changeable in accordance with the number of the multilayer piezoelectric elements included in the single transmitting and receiving channel and performance of the used pulser (a voltage applied from the pulser to the multilayer piezoelectric element), though the multilayer piezoelectric element of the above embodiment, i.e. the transmitting ultrasonic transducer  27   a  has three layers just as an example. 
     In a case where the single transmitting and receiving channel is constituted of the multilayer piezoelectric element and the single-layer piezoelectric element, capacitance of the single-layer piezoelectric element for reception is reduced as compared with that of the conventional ultrasonic probe, and hence the detection signal outputted in response to the reception of the echoes has a relatively lower voltage level. To compensate for reduction in the voltage level, in the above embodiment, the receiving ultrasonic transducer  27   b  is directly connected to the amplifier without passing through a capacitance transmission line. This allows minimization of reduction in the voltage level. 
     Therefore, it is possible to improve the transmission sensitivity of the ultrasonic waves and the reception sensitivity of the echoes without adverse effect on the ultrasonic image quality, even if the single transmitting and receiving channel is constituted of the multilayer piezoelectric element and the single-layer piezoelectric element. Improvement in the transmission and reception sensitivity makes it possible to more accurately capture harmonics for use in harmonic imaging, which becomes a focus of attention in recent years. For example, the multilayer piezoelectric element may be used for transmitting and receiving a fundamental, and the single-layer piezoelectric element may be used for receiving the harmonics. This structure contributes to improvement in image quality in the harmonic imaging. 
     In the above embodiment, the first and second conductor patterns  31   a  and  31   b  are disposed on the single side face of the backing material, and the transmission and reception circuit boards  32   a  and  32   b  are disposed on the single side face of the mount support  25 . However, in an ultrasonic transducer array  70 , as shown in  FIG. 6 , a transmission circuit board and the first conductor patterns may be disposed on the single side face of the backing material  26  and the single side face of the mount support  25  that are orthogonal to the EL direction, while a reception circuit board and the second conductor patterns may be disposed on the other side faces thereof. 
     In  FIG. 6 , the ultrasonic transducer array  70  has similar structure to that of the ultrasonic transducer array  21  of  FIG. 2 , but is different therefrom in the way that the first and second conductor patterns  31   a  and  31   b  are separately formed on the opposite two side faces of the backing material  26 , and a transmission circuit board  71   a  and a reception circuit board  71   b  are separately disposed on the opposite two side faces of the mount support  25 . Each of the circuit boards  71   a  and  71   b  is composed of a single flexible printed circuit board that is long in the AZ direction. Use of the single long circuit board  71   a  or  71   b  eliminates the need for preparing and attaching the plurality of circuit boards as in the case of the ultrasonic transducer array  21  of  FIG. 2 , and hence contributes reduction in component cost and the number of manufacturing processes. Also, since the transmission circuit board  71   a  and the reception circuit board  71   b  are separately disposed on the opposite two side faces, noise occurring in one of the circuit boards  71   a  and  71   b  cannot propagate to the other. This allows stabilization of operation of the circuit boards  71   a  and  71   b.    
     The conductor patterns and the circuit boards may be embedded in the backing material and the mount support. In this case, a water-cooling mechanism may be provided for the purpose of cooling components, especially absorbing heat due to a drive of the amplifiers implemented on the circuit boards. To be more specific, a conduit through which a liquid coolant such as water flows is installed inside the mount support and/or the backing material. Then, a refrigerator and a circulating pump are connected to the conduit, so that the circulating pump circulates the coolant in the conduit, while the refrigerator cools the coolant that has absorbed the heat of the amplifiers. 
     The above instances describe about disposition of the circuit boards on the side faces of the mount support and embedment thereof, but the disposition and the embedment may be combined. For example, the one of the circuit boards may be disposed on the side face of the mount support, and the other one may be embedded inside the mount support. 
     In the above embodiment, the ultrasonic probe is connected to the portable ultrasonic observing device with the cable, but the present invention is applicable to the ultrasonic probe that transmits/receives data to/from the portable ultrasonic observing device by radio. In this case, a wireless transmitting section is provided behind the P/S  56  of  FIG. 5 , and a wireless receiving section is provided before the S/P  60  in order to communicate the detection signal by radio. Also, the ultrasonic probe has a battery to supply electric power from the battery to each part of the ultrasonic probe. 
     According to the present invention, since the multilayer piezoelectric element is used for transmission of the ultrasonic waves, even if the transmitting ultrasonic transducer is driven with a relatively low voltage, high transmission sensitivity is obtained. Thus, long battery life is obtained in a battery-driven type wireless ultrasonic probe, as described above. Also, low voltage driving allows reduction in size of circuits including the pulsers, and hence contributes size reduction of the ultrasonic probe. 
     A multiplexer may be interpolated between the ultrasonic transducer array, and the pulsers and the receivers to selectively switch the ultrasonic transducers to be driven. Output terminals of the multiplexer are connected to all of the one hundred twenty-eight channels, and input terminals of the multiplexer are connected to forty-eight channels. With successively switching the multiplexer, each ultrasonic transducer is driven with the arbitrary delay. In this case, the forty-eight pulsers and the forty-eight receivers are enough to be prepared because the number of the pulses and the receivers corresponds to the number of channels driven at a time, and thus it is possible to further reduce the size of the ultrasonic probe. Also, scan control becomes easier, because all the scan controller has to do is to transmit a switch signal to the multiplexer. 
     In the above embodiment, the piezoelectric layers of the multilayer piezoelectric element and the single-layer piezoelectric element are made of the same material of the piezoelectric ceramic, but may be made of different materials. The single transmitting and receiving channel is constituted of the single transmitting ultrasonic transducer and the single receiving ultrasonic transducer, but may be constituted of three or more ultrasonic transducers including, for example, two transmitting ultrasonic transducers and one receiving ultrasonic transducer, or one transmitting ultrasonic transducer and two receiving ultrasonic transducers. Even in this case, the transmitting ultrasonic transducers being the multilayer piezoelectric elements and the receiving ultrasonic transducers being the single-layer piezoelectric elements are still alternately arranged in the AZ direction. 
     In the above embodiment, the so-called convex electronic scanning type extracorporeal ultrasonic probe is described, but the present invention is applicable to a linear electronic scanning type or a radial electronic scanning type of ultrasonic probe. The ultrasonic transducers are arranged in one dimension, but may be arranged in two dimensions. The present invention may be applied to an intracorporeal ultrasonic probe inserted into a forceps channel of an electronic endoscope, or an ultrasonic endoscope integrated with the electronic endoscope. 
     Although the present invention has been fully described by the way of the preferred embodiment thereof with reference to the accompanying drawings, various changes and modifications will be apparent to those having skill in this field. Therefore, unless otherwise these changes and modifications depart from the scope of the present invention, they should be construed as included therein.