《毕业设计的英文翻译.docx》由会员分享，可在线阅读，更多相关《毕业设计的英文翻译.docx（16页珍藏版）》请在taowenge.com淘文阁网|工程机械CAD图纸|机械工程制图|CAD装配图下载|SolidWorks_CaTia_CAD_UG_PROE_设计图分享下载上搜索。
1、毕业设计的英文翻译 DEVELOPMENT OF POLYMER-BASED SENSORS FOR INTEGRATION INTO A WIRELESS DATA ACQUISITION SYSTEM SUITABLE FOR MONITORING ENVIRONMENTAL AND PHYSIOLOGICAL PROCESSES Biomolecular Engineering Volume 23, Issue 5, October 2022, Pages 253-257 ABSTRACT In this work, the pressure sensing properties of
2、polyethylene (PE) and polyvinylidene fluoride (PVDF) polymer films were evaluated by integrating them with a wireless data acquisition system. Each device was connected to an integrated interface circuit, which includes a capacitance to frequency converter (C/F) and an internal voltage regulator to
3、suppress supply voltage fluctuations on the transponder side. The system was tested under hydrostatic pressures ranging from 0 to 17kPa. Results show PE to be the more sensitive to pressure changes, indicating that it is useful for the accurate measurement of pressure over a small range. On the othe
4、r hand PVDF devices could be used for measurement over a wider range and should be considered due to the low hysteresis and good repeatability displayed during testing. It is thought that this arrangement could form the basis of a cost-effective wireless monitoring system for the evaluation of envir
5、onmental or physiological processes. Key words: pressure; thick film; polymers; sensor; wireless 1. Introduction In many professions and industries, the ability to make measurements in difficult to reach or dangerous environments without risking the health of an individual is now a necessity. A way
6、of wirelessly transmitting data from the sensor,which is at the point of interest, to a remote receiver is required. Using this approach, sensors can be implanted in a difficult to reach or harsh environment and left there for a period of time. Sensors designed to measure any number of parameters in
7、cluding pressure, conductivity and pH could be used (Barrie, 1992, Astaras, 2022and Flick and Orglmeister, 2000). Data transfer is typically achieved using radio frequencies to send information to a receiver, which is remote from the area of interest. Apart from industrial and environmental applicat
8、ions, these acquisition systems could revolutionise the healthcare system in a number of areas. They could find applications in the treatment of patients which have experienced extreme traumas by monitoring critical parameters such as intra-cranial pressure (Flick and Orglmeister, 2000). However, in
9、 a more routine setting they could also be used to make long term measurements of biological fluid pressure for clinical studies in several areas, such as cardiology, pulmonology and gastroenterology (Yang et al., 2022). In the future, it may even be possible to monitor patients while they reside in
10、 their home or continue to work (Budinger, 2022). With these applications in mind, a wireless data acquisition system, including a capacitance to frequency converter (C/F) and an internal voltage regulator to provide a stable operation has been developed. The circuitry was developed to minimise powe
11、r consumption, as power will not be randomly available in the test environment. The system was developed specifically for the measurement of pressure. Two capacitive structures were formed using polyethylene (PE) and polyvinylidene fluoride (PVDF) for the sensing layer. These materials were chosen f
12、or their biocompatible and mechanical properties. Capacitive structures are preferred as they lead to lower power consumption and higher sensitivity than their piezoelectric counterparts (Puers, 1993). PVDF is a low-density semi-crystalline material, consisting of long repeating chains of CF2CH2mole
13、cules. The crystalline region consists of a number of polymorphs, of which the - and -phase are most common. The -phase is piezoelectric and has many advantages including its mechanical strength, wide dynamic range, flexibility and ease of fabrication (Payne and Chen, 1990). Poled PVDF films have be
14、en employed in the development of devices, which can be used in a wide range of applications, for example, providing robots with tactile sensors and the measurement of explosive forces (Payne et al., 1990 and Bauer, 1999). In a medical context, poled PVDF films have been popular in the development o
15、f plantar pressure-measurement systems, where their flexibility and the ease with which electrode patterns can be attached has been a particular advantage (Lee and Sung, 1999). Micromachined devices using PVDF as a flexible element in the system have also been developed for use in an endoscopic gras
16、per because of its high force sensitivity, large dynamic range and good linearity (Dargahi et al., 1998). Polyethylene is a cost effective and versatile semi-crystalline polymer consisting of repeating CH2CH2units. The most common forms are low-density polyethylene (LDPE) and high-density polyethyle
17、ne (HDPE), where the density is related to the degree of chain branching. It is a material which is useful in pressure-sensing applications and has been popular for use in the development of flexible electronics (Harsanyi, 1995 and Domenech et al., 2022). PE is particularly popular in the fabricatio
18、n of polymer/carbon-black composites for pressure measurement (Zheng et al., 1999 and Xu et al., 2022). Furthermore, polyethylene terephtalate (PET) has been identified as an electret material with possible dynamic pressure sensing applications (Paajanen et al., 2000). In this work, both PE and PVDF
19、 films were formed into a sandwich capacitor, which was then subjected to changing hydrostatic pressures. The films deformed under pressure and the resulting change in capacitance was transmitted wirelessly through the liquid to an external receiver, which converts the signal to a corresponding volt
20、age. 2. Experimental procedure The sensing layers were in the form of films with thickness of approximately 100 m. The PVDF film has a dominant -phase and was purchased from Precision Acoustics Ltd. The LDPE film was supplied from Goodfellow Cambridge Ltd. The Youngs modulus of each material is an i
21、ndication of how likely the material is to deform under applied pressure and is quoted to be 8.3 GPa and 0.10.3 GPa for PVDF and PE, respectively. To form the capacitors, DuPont 4929 silver paste was deposited using a DEK RS 1202 automatic screen-printer to form electrodes measuring 15 mm 10 mm. The
22、 sensor structure is shown in Fig. 1. This approach was used as difficulties in depositing other electrode materials on PVDF have been recorded (Payne and Chen, 1990). After deposition, the electrodes were dried in air and cured at 100 C for 30 min. The electrical properties of each device were meas
23、ured, from 1 Hz to 1 MHz, using a Solatron S1 1260 Impedance Gain/Phase Analyser. Fig. 1.Structure of the PVDF and PE capacitor. To evaluate the performance of each material under pressure, capacitors were individually connected to the interface and transmitter circuit. The sensor was protected usin
24、g a thin, flexible waterproof membrane. The circuit was contained in a weatherproof housing. This was a rigid structure of dimensions 54 59 mm2 and was necessary to protect the electronics from the liquid environment. To connect the sensor to the interface an opening was drilled into the housing and
25、 the connections were made waterproof. The change in capacitance with increasing depth in a liquid environment was then recorded.The pressure in this case ranged from 0 to 17 kPa. The change in capacitance was converted to a frequency, which was wirelessly transmitted to an external receiver. The tr
26、ansmitter and receiver are battery powered. A comparison of the power requirements, this circuit (marked with an asterisk) is compared to other sensor sensor sensor （1）where f out is the output frequency, C x is the sensor capacitance, R1 and R2 are the timer frequency set-up resistors. A frequency
27、shift-keying (FSK) transmitter of 160 kbps has been selected to send the signal coming from the CMOS oscillator. At the receiver side, the received tones are converted to voltage levels using phase locked loop (PLL) unit. This IC is a micro-power device since it typically draws 20 A. The relationshi
28、p between the frequency (f) and the voltage (V) has been measured to be f=V13.1kHz/V （2） The value of 13.1 kHz/V was found by measuring the slope of the change in frequency with voltage for the voltage-controlled oscillator as shown in Fig. 3. It should be noted that while the PLL unit reduces power
29、 supply, it creates a non-linear output signal. Therefore the sensor response will appear to be non-linear. Fig. 3. Measured F/V characteristics of the VCO.Finally, a Lloyd Instruments LR50k was used to evaluate the sensitivity of the PVDF material over a wider pressure range. The LR50k is commonly
30、used to place materials under tension or compression. In this work, it was used in compression mode, increasing the load on the capacitor over time. The change in sensor output was measured using a HP 4192 A LF Impedance Analyser at a frequency of 100 kHz. The capacitor was repeatedly tested in the
31、range 0560 kPa. 3. Results and discussion When parallel plate capacitors, such as those formed in this study, are placed under pressure, the thickness of the sensing layer changes, resulting in an alteration of the distance, d, between the electrodes or plates. When the pressure is applied uniformly
32、, there is a correspondingly uniform change in d, which leads to a change in the overall capacitance, according to Eq. (3) (3) where, C is the capacitance, r, is the relative permittivity of the dielectric, o, is the permittivity of free space and A is the area of the capacitor plates. The capacitan
33、ce was found to be 40 pF and 140 pF for the PE and PVDF sensors, respectively. The relative permittivity was measured to be 3.45 for PE and 9.27 for PVDF at a frequency of 1 MHz. The capacitance of both materials showed a high stability over a wide range of frequencies, as shown in Fig. 4, making th
34、em well suited for integration into the wireless data acquisition system. Previous work on thick film capacitors using a PZT and PVDF dielectric layer have shown that device sensitivity is affected by operating frequency (Arshak et al., 2000). The differences are attributed to changes in dissipation
35、 factor. The PE sensor showed a stable response, however there is some variation the capacitance of the PVDF sensor at higher frequencies. Therefore, operating frequency could be used to optimize the sensor response. Fig. 4.Variation of capacitance with frequency for PE and PVDF devices. Fig. 5 show
36、s the response of the PE and PVDF sensors to pressure in the range 017 kPa. It was observed that PE shows a higher sensitivity to pressure changes than the PVDF film. The change in voltage is related to the capacitance change, which is a direct result of deformation of the dielectric layer under pre
37、ssure. For the PE sensor,the voltage changes by 20 mV over the entire range. For the PVDF sensor the change is 5 mV. The relationship between capacitance and voltage is shown in Eqs. (1) and (2). Therefore, it can be seen from the results that PE sensors show the highest sensitivity, and are well su
38、ited to pressure measurement over the range tested. On the other hand PVDF devices may be more useful for measurements over larger ranges. For example, shock sensors based on PVDF are used to measure impact pressures up to 12 GPa (Bauer, 1999). Fig. 5.Change in voltage with pressure in the range 017
39、 kPa for the PE and PVDF sensors. In order to investigate the behaviour of the PVDF over a large pressure range, it was tested using an LR50k and the results are shown in Fig. 6. It can be seen that the material showed a high sensitivity, particularly for pressures up to 100 kPa. It is thought that
40、the dissimilarity in Youngs modulus can explain their different behaviour under pressure. PVDF is a tougher, more resilient material that PE and so it requires higher pressures, to achieve a measurable change in capacitance. Alternatively, PE will deform more easily, resulting in larger changes in c
41、apacitance over a reduced pressure range. Fig. 6.Relative change in capacitance for PVDF sensors,tested using a Lloyd Instruments LR50k. The maximum difference between loading and unloading cycles was measured and expressed as a percentage of the full-scale deviation in order to calculate the hyster
42、esis. Values ranging from 6 to 30% have previously been calculated for polymer thick film devices (Arshak et al., 1995 and Arshak et al., 2000). In this work, the hysteresis was calculated to be 5% and 6% for the PE and PVDF sensors, respectively, as shown in Fig. 7. This corresponds well with the v
43、alues quoted above. Fig. 7.Hysteresis of (a) the PE sensor and (b) the PVDF sensor as measured for one loading and unloading cycle.Each device was also subjected to repeated cycling, in order to establish its repeatability (the maximum difference between output readings as determined by two calibrat
44、ing cycles). Five cycles are shown for PE in Fig. 8(a) and PVDF in Fig. 8 (b). The repeatability was calculated to be 10% and 6% for PE and PVDF, respectively. This can be attributed to movement of the polymer chains while they are under pressure (Arshak et al., 1995). The more rigid nature of the P
45、VDF can explain the lower percentage repeatability, as it does not suffer the same degree of slippage. Fig. 8.Repeatability of (a) the PE sensor and (b) the PVDF sensor as measured for five loading cycles.From the results shown above, it can be seen that both PE and PVDF have shown a good sensitivit
46、y to pressure. The measured levels of hysteresis and repeatability are similar to that previously measured for polymer devices (Arshak et al., 1995 and Arshak et al., 2000). PVDF is best suited to the measurement of pressure in the range 0100 kPa. PE could also be used over this range, but it is exp
47、ected that because of its lower Youngs modulus, the sensor would experience a high level of hysteresis and slippage of the polymer chains during its operation. However, for medical purposes, it is not likely, that measurements over a pressure of 40 kPa will be required. In this respect, PE is more s
48、uited for the measurement of physiological processes. 4. Conclusion In this work, the pressure sensing properties of sandwich capacitors based on PE and PVDF were evaluated using a specially constructed data acquisition system. It was seen that each material displayed a high sensitivity to pressure changes in the range 017 kPa. It was found that the PE sensors were the most sensitive, but each device displayed low hysteresis and repeatability. It can be concluded that PE is the most sensitive to pres