毕业论文外文文献翻译测控技术与仪器聚合物传感器集成到无线数据采集系统中以适合监测环境和生理的发展过程.docx

1、毕业论文外文文献翻译测控技术与仪器聚合物传感器集成到无线数据采集系统中以适合监测环境和生理的发展过程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 2006, Pages 253-257 ABSTRACTIn this wo

2、rk, the pressure sensing properties of 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

3、) and an internal voltage regulator to 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 p

4、ressure over a small range. On the other 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 monito

5、ring system for the evaluation of environmental or physiological processes.Key words: pressure; thick film; polymers; sensor; wireless1. IntroductionIn many professions and industries, the ability to make measurements in difficult to reach or dangerous environments without risking the health of an i

6、ndividual is now a necessity. A way 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 t

7、o measure any number of parameters including pressure, conductivity and pH could be used (Barrie, 1992, Astaras, 2002and 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 i

8、ndustrial and environmental applications, 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

9、 and Orglmeister, 2000 B.B. Flick and R. Orglmeister, A portable microsystem-based telemetric pressure and temperature measurement unit, IEEE T. Bio-Med. Eng. 47 (2000), pp. 1216. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (15)Flick and Orglmeister, 2000). However, in a more

10、 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., 2003). In the future, it may even be possible to monitor patients while they reside in their

11、home or continue to work (Budinger, 2003).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 power consum

12、ption, 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 for their

13、 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 CF2CH2 molecules. T

14、he 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 been emplo

15、yed 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 of plantar

16、 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 grasper becau

17、se 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 CH2CH2 units. The most common forms are low-density polyethylene (LDPE) and high-density polyethylene (HDPE)

18、, 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., 2005). PE is particularly popular in the fabrication of poly

19、mer/carbon-black composites for pressure measurement (Zheng et al., 1999 and Xu et al., 2005). 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 films wer

20、e 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 voltage.2. Exp

21、erimental procedureThe sensing layers were in the form of films with thickness of approximately 100m. 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 indication of

22、how likely the material is to deform under applied pressure and is quoted to be 8.3GPa and 0.10.3GPa 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 15mm10mm. The sensor structure i

23、s 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 100C for 30min. The electrical properties of each device were measured, from 1Hz to 1MH

24、z, 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 using a thin, flexible water

25、proof membrane. The circuit was contained in a weatherproof housing. This was a rigid structure of dimensions 5459mm2 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 the connections were made

26、 waterproof.The change in capacitance with increasing depth in a liquid environment was then recorded. The pressure in this case ranged from 0 to 17kPa. The change in capacitance was converted to a frequency, which was wirelessly transmitted to an external receiver. The transmitter and receiver are

27、battery powered. A comparison of the power requirements, this circuit (marked with an asterisk) is compared to other standard interface circuits is shown in Table 1. A block diagram of the transmitter and receiver system can be seen in Fig. 2.Table 1. Power consumption for sensor interface circuitsI

28、nterface Current consumption Supply voltage (V) (minimum) Universal capacitive readout IC MS33102.96.0mA5AC bridge210mANoneAnderson loop13mA3C-F-V (using F-V converter) LM 290758mA3C-F-V (using F-V converter) TC94001.56mA10C-F-V (using PLL)*500A2.3Fig. 2.Block diagram of the interface, transmitter a

29、nd receiver system used to make measurements under hydrostatic pressure.The main element of the sensor interface circuit is an integrated capacitance to frequency converter, which is used to link the sensor to the telemetry subsystem. An external voltage regulator is used to improve the stability of

30、 the output frequency and RF transmission. A CMOS dual timer (TLC 556) was selected to implement the C/F conversion in astable mode. The output frequency is given in Eq. (1). （1）where fout is the output frequency, Cx is the sensor capacitance, R1 and R2 are the timer frequency set-up resistors. A fr

31、equency shift-keying (FSK) transmitter of 160kbps 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 20A. The relat

32、ionship between the frequency (f) and the voltage (V) has been measured to bef=V13.1kHz/V （2）The value of 13.1kHz/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 supply, it creates a non-linear output signal. Therefore the sensor response will appear to be non-linear. Fig. 3. Measured F/V characteristics