CA1203562A - Ultrasonic oscillator device for surgical operations - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An ultrasonic oscillation device adapted for use in surgical operations includes, for the purpose of producing ultrasonic vibrations of an amplitude and power capable of exhibiting a satisfactory tissue shattering capacity in a wide field of living tissues, an ultrasonic oscillation section having a power amplifier circuit for adjusting the amplitude of its output without any differ-ence in phase between the output and a feedback signal, and a starting impulse reducing circuit for reducing the impulse due to a transient current upon the starting of oscillation. Also, an ultrasonic transducer includes an electrostriction type transducer and a horn, and the horn forming a scalpel portion is provided with a suction opening adapted for irrigating an affected part operated on and its surrounding, floating shattered cellular pieces and sucking and removing the floated cellular pieces.

Description

:3L2~5~i2 1 The present invention relates to an ultrasonic oscillation device, and more particularly to an ultrasonic oscillation device adapted for use in surgical operations.
While, a scalpel, one of surgical instruments, is used for the purpose of incising a tissue of a living body, an electric scalpel or laser scalpel is a surgical instrument which has the function of simultaneouslv cauterizing a cellular tissue and cauterizing blood vessels such as capillary vessels and thereby simultaneous-ly effecting the incision and hemostasis and which issuitable for use in the field of operations in which both the incision and hemostasis are effected, However, since these surgical instruments simultaneously ~ffect the in-cision of a tissue and the cutting of blood vessels or nerves, in the case of an operation on such an affected part as a lever or brain tissue where a large number of blood vessels or nerves gather or in the case of an oper-ation on any other affected part to be operated on where it is desirable to leave the blood vessels or nerves as such, it is rather difficult to use an electric scalpel or laser scalpel and thus a recourse is had to a stainless steel knife, steel knife, mosquito or the like which has heretofore been in use.
As regards the conventional surgical instruments utilizing the tissue cutting or shattering capacity of 1 ultrasonic vibrations, the ultrasonic surgical instru-ments which have been put in practical applications in-clude those which chip bones or joints in the fields of plastic surgery and general surgery, surgical instruments for operating on cataract in the field of ophthalmology and dental instruments for removing the tartar on teeth, However, these surgical instruments u~ilizing ultrasonic vibrations are not deslgned to display ultrasonic vibra-tions of an amplitude and power only sufficient to ex-tensively shatter tissues and they are each used as anexclusive surgical instrument for an extremely limited surgical field.
On the other hand, Japanese Patent Laid-Open Publication No. 54-152383 (1979) discloses an ultrasonic surgical instrument having a magnetostriction type trans-ducer composed of a laminate of nickel alloys having different mechanical characteristics and intended for application to a wide range of body tissues.
However, in the case of a magnetostriction type transducer using ferrite, for example, the transducer is strong to axial compression but weak to axial elonga~
tion and therefore the amplitude cannot be increased.
Also, in the case of a nickel type magnetostriction trans-ducer the transducer lacks in shock resistance so that the 2S transducer tends to be damaged if a large load is applied to the forward end of the horn and also the mechanical Q
inevitably becomes low as comparared with the electro-striction type transducer, thus increasing the electric ~Z~356~

1 loss, correspondingly increasing the heat generation of the transducer and giving rise to the possibility of damaging the transducer unless the thus generated heat is removed by cooling means such as water.
Also, a known ultrasonic oscillation device employing an electrostriction type transducer is dis-advantageous in that any attempt to increase the amplitude of the horn forward end causes a difference between the phase of an output power waveform for the vibration of the ultrasonic transducer and the phase of a feedback voltage waveform, thus making it impossi~le to increase the amplitude.
It is an object of the present invention to pro-vide an ultrasonic oscillation device capable of producing ultrasonic vibrations of such amplitude and power sufficient to exhibit a satisfactory tissue shattering capacity in the field of wide range of living tissues.
An electrostriction type ultrasonic oscillation device according to the invention has a circuit construc-tion such that an ultrasonic oscillation section forexciting a ultrasonic transducer includes a starting im-pulse reducing circuit which serves as a circuit for pre-venting the generation of a transient impulse current during the starting period and also a power amplifier circuit has a circuit construction adapted to make its output voltage voltage waveform and feedback voltage wave-form equal in phase. Thus, the device is ad~antageous in that the device is not susceptible to any load applied to ~203~æ

1 the forward end of a horn and the mechanical Q can be increased thereby reducing the electric loss, decreasing the heat generation of a ultrasonic transducex and exhibit-ing a satisfactory durability without using any cooling means, and the device is best suited for such applications as an ultrasonic scalpel which is particularly required to have reliabily thus making it possible to cut and re-move by shattering any tissue to be cut off in any affected part to be operated on, i.e., an affected part to be operated on where blood vessels or nerves gather, without hurting the blood vessels or nerves.
The present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
Fig. 1 is a basic block diagram of an ultrasonic oscillation device according to the invention~
Fig. 2 is a detailed block diagram of the basic block diagram shown in Fig. 1, Fig. 3 is a circuit diagram of a known power amplifier circuit, Fig. 4 is a circuit diagram of a power amplifier circuit according to the invention, Fig. S is a waveform diagram of the known power amplifier circuit, Fig. 6 is a waveform diagram of the power am plifier circuit according to the invention, Fig. 7 is a circuit diagram of a known starting 1 circuit, Fig. 8 is a circuit diagram of a starting im-pulse reducing circuit according to the present invention, Fig. 9 i5 a waveform diagram of the known start-ing circuit, Fig. 10 is a waveform diagram of the starting impulse reducing circuit according to the invention, Fig. 11 is an overall view of a handpiece section according to the invention, Fig. 12 shows an external view and vibration characteristic of an ultrasonic transducer according to the invention, and Fig. 13 is an external view of another example of the ultrasonic transducer according to the invention, Now describing an embodiment in which an ultra-sonic oscillation device of this invention is applied to an ultrasonic scalpel, an ultrasonic oscillation section basically includes a power supply unit 1, an amplifier unit 2, a matching unit 3, a feed back unit 4 and an ultrasonic transducer 5 for converting electric vibra-tory energy to mechanical vibratory energy which are shown in Fig. 1.
Describing the details of these basic circuits in greater detail with reference to Fig. 2, in accordance with the invention the amplifier unit 2 improves on the conventional circuit construction as will be described later. The power supply unit l includes a rush curreni reducing circuit 7, a rectifier circuit 8 and a smoothing ~2~35~Z

1 circuit 9. The power is supplied in the form of A.C. 100 V fxom a commercial ~.C. power source 6 or a suitable voltage and it is coupled to the rush current reducing circuit 7. Since, when the power source is connected to the oscillator circuit of this ultrasonic scalpel, there is the possibility of an excessive current flowing upon the connection damaging the recti~ier element in the rectifier circuit 8 which is ~n A.C.-D.C. converter circuit for converting an A.C. power supply to a D,C.
power supply, the rush current reducing circuit 7 is pro-vided for the purpose of reducing the possibility and the protection and stabilization of the power supply circuit are intended by means of the rush current reducing circuit 7. Also, if the ripple factor of the ripple in the D,C, waveform produced by the rectifier circuit ~ large, a mechanical vibration system formed by the ultrasonic transducer 5 and a horn 10 is made unstable and therefore the smoothing circuit 9 is provided for the purpose of reducing the ripple factor. By virtue of this smoothing circuit 9, extremely stable ultrasonic vibrations are pro-duced at the forward end of the horn 10 or the scalpel forward end.
The amplifier unit 2 includes a power amplifier circuit 11, a starting impulse reducing circuit 12, a spike wave suppression circuit 13 and an amplitude ad~ust-ing circuit 14. Of these circuts, the power ampli~ier circuit 11 and the starting impulse reducing circuit 12.
differ from the conventional circuits.

1 The power amplifier circuit 11 is OL the low loss circuit type whlch allows continuous oscillations without any coollng. Thus, while it has been the practice to connect a resistor 54 to the base of an amplifying transistor 55 as shown in Fig. 3, in the power amplifier circuit 11 of the invention, as shown in Fig.
4, a parallel circuit of adiode 56 and a capacitor 57 is connected to the base of an ampli~ying transistor 55 so that the diode 56 and the capacitor 57 facilitate the flow of a bias current even if a feedback voltage is low, and also a capacitor 59 is added in parallel with a resis-tor 58 between the amplifying transistor 55 and the fol-lowing transistor 64 thus connecting the capacitor 59 of a predetermined capacity so as to greatly change the output voltage between the collector and emitter of the transistor 64 and thereby to prevent any deviation of the phase of a feedback signal from the feedback unit 4 when the output is adjusted, that is, when the amplitude of the ultrasonic transducer 5 is adjusted.
As a result, while, with the prior art of Fig. 3, the phase relation between an amplifier circuit output voltage waveform 63 and a feedback voltage waveform 62 becomes as shown in Fig. 5, in accordance with the in-vention the phase difference between an output voltage waveform 63 and a feedback voltage waveform 62 of the power amplifier circuit 11 is corrected as will be seen from their phase relation shown in Fig 6.
Generally, where a high power is generated by ~3~æ

1 the ultrasonic oscillation circuit, during the starting of oscillation the power amplifying element and the ultra-sonic transducer 5 are frequently subjected to electric impulses with the resulting deterioration of the per-formance or damage thereto and also there are many caseswhere the starting is made difficult when the mechanical vibration system including the ultrasonic transducer 5 and the horn 10 is under load conditions, in accordance with the invention, with a view to overcoming these deficiencies, the starting inpulse reducing circuit 12 is pro~ided so that the po~er amplifier circuit 11 and the ultrasonic transducer 5 are protected and stabilized and the horn 10 forming the ultrasonic scalpel portion is enabled to start very easily under load conditions. In other words, while it has heretofore been composed of a transistor 46 and a Zener diode 47 of the starting circuit as shown ïn Fig 7, in the starting inpulse reducing circuit 12 of the in-vention, as shown in Fig. 8, a resistox 49 is connected in series between a switch 48 and the base of a transistor 50, and a resistor 51 and a capacitor 52 are connected in parallel between the base of the transistor 50 and a connection 53. Thus, when the operator closes the start-ing switch 48 to start oscillation, the starting circuit prevents any transient circuit from flowing simultaneously with the rise of the voltage. Consequently, while a current waveform 60 from the conventional circuit of Fig, 7 rises as shown in Fig. 9, the rise of a current wave-foxm 61 from the starting inpulse reducing circuit 12 of ~3Sf~:~

1 the invention becomes flat as shown in Fig. 10.
Moreover, while the power amplifier circuit 11 generates a spike wave which is superposed on the output voltage waveform of the power amplifier circuit 11 or the rectangular wa~e of an ultrasonic frequency, this spike wave frequently becomes two or more times the rectangular wave tending to cause deterioration of the characteristics of the amplifying element and the ultrasonic transducer 5 or damages thereto and the spike wave suppression circuit 13 is provided to follow the power amplifier circuit 11 thereby suppressing the spike wave and protecting and stabilizing the amplifying element in the power amplifier circuit 11 and the ultrasonic transducer 5, Also, the amplitude adjusting circuit 14 is provided so that the vibration amplitude of the forward end of the horn 10 or the scalpel forward end can be varied continuously and the degree of shattering can be easily adjusted in accordance with the affected part to be operated on.
The ultrasonic scalpel oscillator matching unit 3 includes a matching circuit 15, an amplitude level setting circuit 16, a feedback signal detecting circuit 17, a power detector 18 for detecting the power drawn by the ultrasonic transducer 5, and an amplitude detector 19 for displaying the amplitude of the horn 10. The matching circuit 15 is such that an electric power is supplied with a reduced loss to the ultrasonic transducer 5 without any decrease in the vibration amplitude of the scalpel forward :~. end even if the load on the forward end of the horn 10 or ~Z

l the scalpel forward end is increased and this matching circuit 15 maintains the power of the ultrasonic vibrations against variations in the load of the affected part to be operated on. Moreover, in accordance with the invention it is important to optimize the driving amplitude for ensuring stable operation of the ultrasonic transducer 5 and the amplitude level setting circuit 16 is provided to reduce the loss and stabilize the ultrasonic transducer 5. The feedback signal detecting circuit 17 is one for detecting the resonant frequency and amplitude of the mechanical vibration system which vary in accordance with the load condition on the forward end of the horn 10 and the temperature and its signals are fed back to the pre-ceding ampliying stage or the power amplifier circuit 11 thereby enabling a constant amplitude control and an auto-matic requency follow-up.
The ultrasonic scalpel oscillator feedback unit 4 includes a feedback signal Q adjusting circuit 20 and a feedback signal filter circuit 21. Its purpose is such tha-t the resonance frequency and amplitude of the mech-anical vibration system detected by the feedback signal detecting circuit 17 are fed back to the power amplifier circuit 11 through the feedhack signal Q adjusting circuit 20 and the feedback signal filter circuit 21, While the Q of the feedback circuit must be increased at the start of oscillation so as to ensure a sharp start of ultrasonic oscillation, the Q of the feedback circuit should prefer-ably be low to maintain stable vibrations against -- 10 .--1 variations in the load of the horn 10 after the ultra-sonic oscillation has come to a steady state and the fee~ back signal Q adjusting circuit 20 is designed to serve the purpose of automatically adjusting the Q of the feedback circuit and thereby stabilizing the transient state and steady state of the vibrations. On the other hand, the mechanical vibration system including the ultra-sonic transducer S and the horn 1~ frequently includes several spurious frequencies in addition to the main re-sonant frequency and such spurious frequencies oftenbecome a factor which makes the ultrasonic scalpel un-stable. In accordance with the invention, the feedback signal filter circuit 21 is used for the purpose of suppressing the spurious frequencies and thereby stabiliz-ing the ultrasonic scalpel.
Then, the handpiece portion of the ultrasonic scalpel according to the invention differs from the con-ventional one and this will be described flrst in detail with reference to Figs. 11 and 12, Fig. 11 is an overall view of the handpiece portion of the ultrasonic scalpel. The handpiece portion includes mainLy a cable 22 connected to the matching unit 3 of the ultrasonic oscillation section, a connector 23, a handle 24, a protective pipe 25, the horn 10 forming the ultrasonic scalpel, an irrigation pipe 26 for supply-ing a physiological salt solution or the like to an affect-ed part to be operated on, a suction pipe 27 for sucking the liquid substance or the like from the part under going 1 an operation. A connecting pipe 28 is a pipe for mech-anically connecting the handle 24 and the protective pipe 25 with screws or the like. The handle 24, the connect-ing pipe 28 and the protective pipe 25 should preferably S be made of a metal which is light and also resisting to corrosion, e.g., aluminum or Duralumin or a synthetic resin which is high ln strength, e.g., phenolic resin or ABS r~sin in order to reduce the weight of the handpiece on the whole and ensure easy and convenient handling by the operator. While the horn 10 forming the ultrasonic scalpel portion is made of a material which satisfactorily transmits high frequency mechanical vibrations and has a resistance to breaking, e.g., Duralumin or titanium alloy, a suction opening 29 is formed inside the horn 10 so as to suck and remove the blood bleeding at the part under-going an operation, a cleaning physiological salt solu-tion, the cell pieces shattered by the horn 10, etc., and the suction opening 29 is connected to the suction pipe 27 through a pipe joint 30 connected to the outer side of the protective pipe 25 by a suitable method. A suction nipple 31 is connected to the other end of the suction pipe 27 by a suitable method such as soldering or argon welding. Although not shown, the suction nipple 31 is connected to a fle~ible tube made of a material and having a shape to withs~and the suction negative pressure of suction means, e.g., vinyl chloride or silicone resin and connected to the suction means, e.g., a vacuum pump through a trap consisting of a glass bottle or the like which is 3~

1 not shown.
The irrigation plpe 26 is provided for the pur-pose of supplying an irrigation solution such as phy-siological salt solution to the part undergoing an opera-S tion and it is desirable that the pipe 26 has an open endnear the forward end of the horn 10 and it is arranged to be near to the horn 10 without contacting it. Since the horn 10 is set in ultrasonic vibrations, there is the possibility of the irrigation pipe 26 being damaged if it is brought into contact with the horn 10 and there is the possibility of the irrigation pipe 26 becoming a hindrance in the case of microsurgery such as the brain surgery if it is excessively apart from the horn 10. The irrigation pipe 26 is fastened or connected to the pipe joint 30 by a suitable method so as to prevent the irrigation pipe 26 from coming into contact with the horn 10 or separating excessively from the horn 10. An irrigation nipple 32 is connected to the other end of the irrigation pipe 26 by a suitable method such as soldering or argon welding.
Although not shown, connected to the irri~ation nipple 32 is a flexible tube which is medically safe and which is made from vinyl chloride, silicone resin or the li~e for supplying an irrigation liquid such as physiological salt solution contained in an irrigation liquid container and having a shape to withstand severe handling by a roller type pump such as a peristalsis pump, A pipe fastener 33 is a fastener for fastening the suction pipe 27 and the irrigation pipe 26 to the ~ 03S~2 1 handle 24. The material for the suction pipe 27~ the irrigation pipe 26, the suction nipple 31, the irrigation nipple 32, the pipe joint 30 and the pipe fastener 33 should preferably be stainless steel or the like having corrosion resistance and elution resistance properties, Further, the internal construction, vibration characteristic, etc., of the handpiece portion of the ultrasonic scalpe; according to the invention will be described in detail with reference to Fig. 12, The previously mentioned ultrasonic transducer 5 is of the so-called BLT (bolted Langevin type transducer) type transducer construction in which a back plate 35 and a front plate 36, each made of a high tension metal material such as Duralumin or high strength aluminum alloy, are disposed before and back or to the left and right in Fig. 12 of an electrostriction type transducer 34 and the back plate 35, the electrostriction type transducer 34 and the front plate 36 are tightly connected and fasten-ed with each other by bolts made of a high tension metal material and not shown. The front plate 35 and the horn 10 forming the ultrasonic scalpel are firmly coupled to-gether with a plain screw 37 made of a high tension metal material. The electrostriction type transducer 34 should preferably be made of PZT (lead zirconate titanate) and its natural frequency is in the range 1 MHz to 100 ~Hz, preerably on the order of 10 MHz to 20 MHz, With the back plate 35 and the front plate 36 which are attached to the ends of the electrostriction type transducer 34, ~;~03~

1 their diameters and lengths are det~rmined in such a manner that the frequency of the ultrasonic transducer 5 including the back plate 35, the electrostriction type transducer ~4, the front plate 36 and the horn 10 ranges from 20 kHz to 40 k~, preferably from 23 kHz to 38 kHz.
While the shape of the horn 10 is an important factor which determines the amplitude of a forward end 38 of the horn 10, generally the amplitude of the forward end 38 of the horn 10 is inversely proportional to the ratio of the cross-sectional area of a base 39 of the horn 10 to the cross-sectional area of the forward end 38 of the horn 10. The amplitude of the forward end 38 of the horn 10 used for the ultrasonic scalpel of the invention is desir-ably in the range 50 ~m to 250 ~m, preferably 100 ~m to 150 ~m. Also, the material of the horn 10 is desirably a high tension metal material, preferably titanium alloy.
The ultrasonic transducer 5 employing the ele-ctrostriction type transducer 34 made of PZT and forming the ultrasonic scalpel of the invention .s ad~antageous in that it is less susceptible to the load applied to the forward end 38 of the horn 10 compared with other trans-ducers such as a magnetostriction transducer using ferrite and nickel type magnetostriction transducer, that the electric loss is reduced due to the increased mechanical Q, that the hëat generation of the transducer is reduced and that satisfactory durability is displayed without using any cooling means, and the ultrasonic transducer 5 is best suited for applications such as an ultrasonic ~2~3~

1 scalpel which must have reliability above all, Next, the vibration characteristic of the ultra-sonic transducer 5 of the invention employing the ele-ctrostriction type transducer will be described in refer-ence to Fig. 12. The graph shown in the upper part of Fig. 12 shows the axial amplitude patterns of the various parts of the ultrasonic transducer 5, that is, the am~
plitude is zero at the axial central portion of the ele_ ctrostriction type transducer 34, the amplitude is zero at a point 40 of the horn 10 where it starts to constrict and the pattern between the electrostriction transducer 34 and the constriction starting point 40 of the horn 10 takes the form of an arc in which the peak is near a plain screw 37. Also, the pattern between a left end 41 of the back plate 35 and the electrostriction type transducer 34 tahes the form of a half arc in which the maximum ampli-tude is attained at the left end 41 of the back plate 35, Between the constriction starting point 40 of the horn 10 and the forward end 38 of the horn 10 the pattern takes the form of a half arc in which the maximum amplitude is attained at the forward end 38 of the horn 10. Since the magnitude of the amplitude at the forward end 38 of the horn 10, one of the efficiencies of the ultrasonic scal-pel, is approximately inversely proportional to the ratio of the cross-sectional area of the base 39 of the horn 10 to the cross-sectional are~ of the forward end 38 of the horn 10 as mentioned previously, these cross-sectional areas may be varied to provide horn shapes of different ~2~

amplitudes in accordance with the parts to be treated with the present ul-trasonic scalpel, the severity of operations, etc.
Another embodiment of the ultrasonic transducer or the ultrasonic scalpel according to the invention will be described with reference to Figures 13 and 11.
Since the vibrator of the ultrasonic transducer or the ultrasonic scalpel according to the invention employs an electro-striction type transducer as mentioned previously, the electric loss of the transducer is reduced with the resulting reduction in the heat generated at the transducer portion and it is also apparent that preferably the durability of the transducer can be improved by far if the heat genera-ted in the vibrator portion is eliminated. Thus, by providing a suction opening 42 extending over the entire axial length of the ultrasonic transducer 5 as shown in Figure 13 so that the irrigation liquid, e.g., physio-logical salt solution supplied to the affected part operated on is sucked by the suction opening 42 via an irrigation pipe 26 set in the same manner as the irrigation pipe 26 shown in Figure 11, it is possible -to cool a hollow electrostriction type transducer 43.
While the hermetic sealing of a plain screw 44 and the suction opening 42 of the hollow electrostriction type transducer 43 is not shown, they may be sealed hermetically by a suitable sealing method such as O-ring or Teflon* sealing tapes. Also, while, in Figure 13, the suction opening 42 is provided to extend over the whole length of the *Trade Mark - ]7 -~Z~ 6~
1 ultrasonic transducer 5 the outlet port of the suction opening may be provided in a direction normal to the axis of the ultrasonic transducer 5 provided it is located on a back plate 45.
As described so far in detail, the ultrasonic oscillation device according to the invention can exhibit a satisfac-tory function as an ultrasonic scalpel for surgical operation purposes.

Claims (8)

CLAIMS:

1. An ultrasonic oscillation device comprising power supply means for rectifying an A.C. signal from a power source to a D.C. signal, amplifier means for amplifying the D.C. signal from said power supply means, said amplifier means includ-ing a power amplifier circuit for adjusting an amplitude of an output thereof without any difference in phase be-tween said output and a signal fed back thereto, and a starting impulse reducing circuit for reducing an ele-ctric impulse during a start of oscillation, matching means for matching an output signal from said amplifier means, feedback means for feeding certain signals from said matching means back to said power amplifier circuit in said amplifier means, and an ultrasonic transducer having an electro-striction type transducer connected to said matching means.

2. An ultrasonic oscillation device as set forth in claim 1, wherein said starting impulse reducing circuit includes a resistor connected in series between an oscil-lation starting switch and a base of a transistor, and another resistor and a capacitor connected in parallel between the base of said transistor and a connection.

3. An ultrasonic oscillation device as set forth in claim 1, wherein said power amplifier circuit includes a parallel circuit of a diode and a capacitor connected in series with a base of an amplifying transistor, and a parallel circuit of a resistor and another capacitor connected between an emitter of said transistor and a base of a following transistor.

4. An ultrasonic oscillation device as set forth in claim 1, wherein said ultrasonic transducer includes a horn at a forward end thereof wherein a suction opening is formed within said horn, and wherein an irrigation pipe is arranged at a position near said horn.

5. An ultrasonic oscillation device as set forth in claim 4, wherein said ultrasonic transducer includes a hollow electrostriction type transducer, and wherein said suction opening extends through said horn up to a given point of a back plate.

6. An ultrasonic oscillation device as set forth in claim 4, wherein a physiological salt solution or the like is supplied through said irrigation pipe to an affected part to be operated on, and wherein a tissue of said operated part contacting a forward end of said horn is hsttered with ultrasonic vibrations produced in said horn whereby said physiological salt solution or the like and cellular pieces, etc., floated by said ultrasonic vibrations are sucked and removed through said suction opening.

7. An ultrasonic oscillation device as set forth in claim 6, wherein a material of said horn is titanium alloy.

8. An ultrasonic oscillation device as set forth in claim 6, wherein each of a handle, a connecting pipe and a protective pipe is made of aluminum alloy.