冷凝管自动弯管机切割部分设计(外文翻译)

Two-layered piezoelectric bender device for micro-power generatorAbstract：In this study, we investigated the possibility of use of bender type piezoelectric devices. To match the external vibration frequency with the device resonant frequency, the various devices with different resonant frequency were chosen. The two-layered device consists of different thick layers, in which each layer shows different resonant frequency. The highest power was obtained under optimization of the capacitive nature of piezoelectric device which is connected to small storage capacitor and its impedance matching by selection of suitable resistive load. Under an external vibration acceleration of 0.1G at 120 Hz, the device exhibited a peak-to-peak voltage of 2.0V and a power of 0.5mW in resonance mode.Keywords：Piezoelectric ceramics Bender device Micro-power harvesting1.IntroductionWearable and ubiquitous micro systems will be greatly growing and their related devices should be self-powered in order to avoid the replacement of finite power sources, for example,by scavenging energy from the environment. With ever reducing power requirements of electronic circuits, power scavenging approaches are in reality. One approach is to drive an electromechanical converter from ambient motion or vibration.Vibration-driven generators based on electromagnetic,electrostatic and piezoelectric technologies have been demonstrated. Although some of the generators have already been fabricated and evaluated, their performances are behind the requirements of self-powered system. Among various generator types proposed so far, piezoelectric generator possesses considerable potential in micro system. In the system, piezoelectric device exhibits high voltage and power at a specific frequency where its resonant frequency accounts for vibrational natural frequency for achieving high efficiency in transforming from external mechanical vibration energy into electric energy.To enhance mechanical-to-electric energy conversion, several considerations were proposed in piezoelectric device,which are searching high conversion material (high d×g (figure of merit)),matching resonant frequency of piezoelectric device with natural frequency of environmental vibration source, finding novel power conditioning and its power management technique. Among such considerations, matching the resonance frequency of piezoelectric device with that of external vibration source is the most realistic method in scavenging system based on piezoelectricity. That is,one can acquire high conversion power by designing piezoelectric device in a way that it activates in resonance mode in response to external vibration. However, the difficulty of employing such mode lies on the fact that environmental vibration is not in static state but in variable state. To overcomesuch a difficulty, the supplements of piezoelectric system can be considered. One is to adopt multiple piezoelectric devices in which their resonant frequencies are somewhat different. Therefore, resonance mode covers a frequency range which matches variable vibration frequency source. The other is to make the frequency of device to modulate in a response to variation of external vibration source. This is possible by changing payload, like mass, and external resistor magnitude.The objective of this article is to propose a bender structure device easily in response to variable external vibration condition.The two-layered device consists of different thick layers, in which each layer shows different resonant frequency. The voltage and piezoelectric properties of the device were examined. The effect of layer thickness on resonant frequency of piezo-bender device and its power were also investigated.2. Experimental procedurePiezoelectric ceramics for this study were 0.2Pb (Mg1/3Nb2/3) O3–0.8Pb (Zr0.475Ti0.525)O3 (PMNZT). The piezoelectric d31 coefficient and other physical properties of the ceramic materials were measured in a circular plate (diameter 18mm, thickness 1mm) by a resonance method, as listed in Table 1. The piezoelectric coefficients d31, d33 and kp of the ceramic material used in the device were measured in a circular plate (diameter 18mm, thickness 1mm)by the resonancemethod, using an impedance analyzer(HP 4194, Hewlett-Packard Co). The d31 coefficient of the material was .210 pC/N.Ceramic green tapes were prepared using a conventional tape casting method. Then, Ag.Pd electrodes were coated on their surfaces,and actuator samples were fabricated by stacking the coated tapes. Removal of organic materials existing in the ceramic tapes were, then, carried out by annealing at 500 .C for 24 h, followed by sintering at 1150 .C for 2 h. The samples were, then, poled under an electric field of 3kV/mm at 120 .C for 30 min. It has been confirmed that the piezoelectric ceramic PMNZT were completely sintered at 1150 .C.The structure geometry consisting of four layers was designed.The characteristics of benderwere examined as a function of thickness(t) of each piezoelectric layer over thickness of total layers.The schematic diagram of the actuator geometry was illustrated in Fig. 1(a)–(d). Samples were prepared with various thickness t1 =247μm, t2 =204μm, t3 =149μm and t4 =100μm. They were denoted as I, II, III, IV and V, respectively. The component, thickness,length, width and height of total layers of samples were shown in Table 2.The device conversion performance was measured by a testing set-up shown in Fig. 2. The electromagnetic shaker (B&K 4810)was used to supply reliable mechanical vibrations to the device. The device consisting of piezoelectric element and copper sheet was tightly fixed to acrylic plate support connected to the shaker by a screw pin. The shaker was controlled by a function waveform generator(Agilent 33220 A) incorporated with a power amplifier (NF 200B). An accelerator was attached to rod of the shaker. An oscilloscope (Tektronix TDS4014A) was used to monitor the voltage signal from the piezoelectric device. The energy conversion test was performed by placing the piezoelectric power generation device on the top part of vibrating load of electromagnetic shaker. The payload was 1.0 g.To determine their resonance frequencies, a hammer test was performed by giving a pulse force to the piezoelectric devices. Then,vibration voltage from the devices was measured as a function of lapse time. The voltage was converted into voltage amplitude with frequency via fast Fourier transform (FFT) method.To simulate the natural environment source, acceleration was set to be 0.1 G,0.2G and 1.0G (G= 9.8 m/s2). The rod of shaker was vibrated in a sinusoidal form ina frequency range of 70–150 Hz.When the vibration was in action, the voltage was produced in the piezoelectric device. Then, the voltage was rectified in a full-bridge circuit consisting of four germanium diodes. The power output acquired fromthe device was determined by detecting voltage drop obtained from the resistor connecting to the device and bridge circuit.The resistive load was in a range of 100–1M . The power output was calculated as follows:power =[Upeak-peak/2*2½]²/R,where Upeak–peak is load voltage of the rectified AC peak-to-peak and R is load resistance.Then, the output voltage was regulated with an active voltage regulator. The electrical circuit is shown in Fig. 3. The output of each piezoelectric device was rectified using full-wave bridge rectifiers. This unipolar output was then filtered and stored with 0.01–10 F storage capacitors. (This capacitor is chosen to match the effective capacitance of the piezoelectric device.) A low power MAX 667 low voltage regulator was used to supply constant output voltage, 3.3V in this case. The pure power generated from the piezo-device was 0.5mW, and 0.2mW of a regulated power was supplied.3. Results and discussionPiezoelectric type power generation device is dependent upon the vibration amplitude and frequency. In its practical application,high power should be produced in wide range of frequency. However,bender type piezoelectric device exhibited significant power drop down in a small deviation of frequency. One way to maintain considerable power generation, even though change in external frequency occurs, is to design geometry structure to possess everal resonant frequencies of which half bandwidth overlaps.To do so, we designed and fabricated the multilayer bender device of which layer has different thickness, showing several resonant frequencies, as shown in Fig. 1.The schematic illustration showing bending action of two layered piezoelectric device, and its mechanical lumped model and simplified equivalent circuit are presented in Fig. 4. For comparison, the single layer device was also shown. The interesting characteristics of the two-layered piezoelectric device are that the two layers are serial-connected in mechanical the dumped model, while they are parallel-connected in electrical equivalent model. Therefore, in the dumped model the piezoelectric layers are coupled each other with additional boundary condition when compared with single layer device. In single layer device, two boundary conditions, one end is clamped and the other end is free vibrating, should be maintained. As described in study for the piezoelectric mutimorph, internal stress should be null in the interface of the piezoelectric layer in order to maintain the equilibrium of mechanical and electrical potential at interface of two layers as shown in Fig. 4(a). Then, in the dumped model the terms of piezoelectric layer 1 and 2 should be separately considered as shown in Fig. 4(b). In a similar manner, as shown in the equivalent model of Fig. 4(c), equivalent circuit of piezoelectric layers is separately established. The equivalent circuit model for the device can be thought of as two piezoelectric elements that are assembled back to back, similar to the multilayer piezoelectric transformer and other cases. This model is only valid up in range of resonance. These devices are connected together by an ideal device representing the mechanical coupling between the two layers.To estimate the simplified resonant frequency, the equation of single piezoelectric layer was used. The resonant frequency of cantilever device was calculated by Eq. (2).∫n=Vn²/2π[0.236ωpeEo（l-lm/2）³/0.236mωpl7+△ml³（l-lm/2）³]½.With Eo=2Eptp³/3+Eptctp²+Eptc²tp/2+tc³Esh/12，m=2ρptp-ρct c，△m=ρmlmωmhm,where l is the total length of the cantilever, lm the length of the proof mass,m the effective mass of the bender structure without proof mass, ωp the width of the bender. Pp, Pc, tp, tc, Ep and Ec are the densities, the thicknesses,and the Y oung’s modulus of the piezoelectric material and the base metal (copper in this study), respectively.The designed fundamental bending resonant frequencies 90 Hz,100 Hz, 110Hz and 120Hz were attained by varying the thickness of the bender. Based on the Eq. (2), the thickness were calculated to be 160μm, 180μm, 220μm and 250μm, respectively, to achieve the designated first bending resonance frequencies 90 Hz, 100 Hz,110Hz and 120 Hz.Fig. 5 is the plots of voltage response vs. time for piezoelectric device sample I, II, III and IV upon a pulse type hammer test. The voltage amplitude vanishes with time lapse. The sample I showed the typical decay of vibration voltage as a functionof time. Meanwhile,in sample II, III and IV the vibration voltages have abnormaldecay patterns. They became decay at the initial time, and then sudden increases of the voltage were observed at a certain time. These changes in vibration voltage in samples were evaluated by expressing relation of vibration voltage to frequency. The plots of vibration amplitude vs. frequency were calculated by interpreting fast Fourier transform from the data in Fig. 5.The results were shown in Fig. 6.Sample I exhibited one peak of voltage amplitude in a range of frequency,being located at 120 Hz. Sample II, III and IV showed more than two peaks of amplitude in frequency range measurement,indicating that resonant frequencies are fr = 110 Hz and 120Hz for sample II, fr = 100 Hz and 120Hz for sample III, and fr =88Hz and 120Hz for sample IV, respectively. The measurements were in a similar trend to the calculations listed in Table 3. This can results fromthe concept,we designed, that different thickness of eachlayer shows different resonant frequency. Since the thickness of layer 1 and 2 is same in sample I, one main resonance frequency can be shown. The other samples have different layer thickness, and consequently each layer showed the first bending resonance frequency.In addition, for sample II, III and IV the existence of minor extra peaks may be originated from different bending behaviors due to the rigidness of materials and the fixture aswell as the unavoidable parasitic damping of two layers at vibration.。