Fundamentals and Practices of Sensing Technologies by Dr. Keiji Taniguchi, Hon. Professor of Engineering University of Fukui, Fukui, Japan Xi’ an University of Technology, Xi’ an, China Dr. Masahiro Ueda, Honorary Professor, Faculty of Education and Regional Studies University of Fukui, Fukui, Japan Dr. Ningfeng Zeng, an Engineer of Sysmex Corporation (A Global Medical Instrument Corporation), Kobe, Japan Dr. Kazuhiko Ishikawa, Assistant Professor Faculty of Education and Regional Studies, University of Fukui, Fukui, Japan
[Editor’s Note: This paper is presented as Part VII of a series from the new book “Fundamentals and Practices of Sensing Technologies”; subsequent chapters will be featured in upcoming issues of this Journal.] Chapter 3 (Section II):Some Practical Examples of Recent Ceramic Sensors
3.5 Acoustic Transducers 3.5.1 Structure of Acoustic Transducer (1)-(4) Fig. 3.16 shows the structure of an acoustic transducer using piezoelectric ceramic element. This transducer can radiate acoustic wave in a medium of space by means of the electrical signal. Therefore, the piezoelectric ceramic transducer is used as a radiator of the acoustic wave. This transducer can, also convert some of acoustic wave propagated in a medium of space into the electrical signal. Therefore, the piezoelectric ceramic transducer is used as the acoustic sensor. The backside of this element is filled with an acoustic absorbing material to absorb acoustic energy propagated to the backside.
A capacitive deviation of the piezoelectric ceramic element due to temperature changes can be compensated by means of the capacitor implemented in a metal case shown in this figure.
3.5.2 Equivalent Circuit for Acoustic Transducer (5) Figure 3.17 shows the equivalent circuits for the piezoelectric ceramic element and a parallel resonant circuit for a receiver using this transducer.
Figures 3.17 (a) and (b) are the piezoelectric ceramic element and its equivalent circuit, respectively. Figure 3.17 (c) is a simplified equivalent
circuit in the frequency range of Figure 3.17 (d) is a parallel equivalent circuit of Fig. (c), where Figure 3.17 (e) is a parallel resonant circuit of a receiver used for suppressing reverberations. The resonance angular frequency where The overall characteristic
for two parallel capacitors ( 3.5.3. Principle of Distance Measurement (1)-(4) Figure 3.18 shows a block diagram for transmitting and receiving circuits using the transducer. This system consists of two sets of these circuits. Firstly a timing generator is triggered by a start signal from the CPU, and a rectangular pulse is generated. This pulse is amplified by a transmitting signal amplifier and is then sent to an acoustic transducer which transforms from the electric power to the acoustic power. Secondary, this acoustic signal is radiated into a medium of space, and reflected and scattered waves from the medium are propagated toward the transducer of the original position as echo signals. Finally, the received signal on the transducer is amplified and reformed into the pulse waveform.
Figure 3.19 shows a transmitted signal and a
received (echo) signal. The round-trip time of
the transmitting signal
where These details are described in section1.3 in chapter 1.
3.5.4 Important Characteristics for Automobile Sensing Systems (1)-(4) Important characteristics as a back acoustic sensor used for automobile sensing systems are as follows: (1) The acoustic signal from the back wall must be detected, and that from the stopper must not detected as shown in Fig. 3.20(a). (2) The horizontal directivity must have a wide radiation pattern, and the vertical directivity must have a sharp radiation pattern as shown in Figs.3.20 (a) and (b).
3.5.5 Application Examples of Transducers (1)-(4) Figure3.21 shows an example of four back acoustic sensors used for an automobile. A large number of sensing systems can precisely measure the position of objects.
3.6 Piezoelectric Vibrating Gyro Sensor(1)-(4) 3.6.1 Outlines of Sensor A gyro sensor is used for measuring an angular velocity of an object. This sensor converts the angular velocity into an electrical signal. 3.6.2 Vibrating Gyro Sensor Elements As shown in Fig. 3.21(a), a square
bar vibrates caused by a vibrating PZT along the direction of The voltage Wires for supporting square bar are
positioned to the nodes of vibration of square bars as shown in
Fig. 3.21 (b). The relationships among the angular velocity
where
(c)Relationships among vibration, rotation, and Corioli’s force
3.6.3 Relationships between Input and Output Characteristics of Sensor The
output
where Figure
3.23 shows an experimental result between the angular velocity
3.6.4 Signal Processing Circuit for Sensor Figure 3.24
shows a signal processing circuit for the gyro sensor. The output
voltage
3.6.5 Application Examples of Gyro Sensor We show here two application examples of the gyro sensor. (1) Figure 3.25(a) shows the gyro sensor used for a correction of azimuth in a global positioning system (GPS) implemented for the automobile navigation. (2) Figure 3.25(b) shows the two gyro sensors used for two- dimensional corrections of the center of an image obtained from a video camera supported by unstable human hands.
【References】 (1)Akira Murata : Wonderful stones, Nikkei Inc. (1994) (2) Wonderful Ceramics (New materials and new technologies in 20th Century), Supervised by Yutaka Takagi, Teturo Tanaka, Edited by Murata Manufacturing Co. Ltd, MARUZEN Co. Ltd(1990) (3) Satoru Fujishima: Piezo-ceramics, Shokabo Publishing Co. Ltd (1993) (4) Technical data for sensing devices (2007), Presented by Murata Manufacturing Co. Ltd. (5) Metamorphosis,pp.8-9,No11(2005.12), Edited by Murata Manufacturing Co. Ltd.
【Problems and solutions】
3.1 Find the
output voltage
【Solution】Let’s show again the circuit in Fig. 3.17.
In
Fig.3.26,
In this equation, (1) If (2) The
frequency satisfying a condition of
3.2 Find the
output voltage
【Solution】 The following equations can be obtained in the circuit shown in Fig.3.27.
(1) An output voltage is then expressed as: (2) The
frequency satisfying a condition of
3.3 Show a circuit diagram for measuring ranges (round- trip times).
【Solution】 We show a circuit configuration and a truth table of a R-S flip flop used in the circuit in Figs. 3.28 (a) and (b). We also show the operating waveforms of the R-S flip flop, an and- circuit, and a clock pulse generator in Fig.3.28(c).
3.4 Find the
output
voltage 【Solution】 This circuit is well known as a source follower or a common drain circuit.
The following equations are obtained from the equivalent circuit in figure 3.20 (b).
The output voltage
where 3.5 In the circuit shown in Fig.3.21, (1)
Find an output voltage (2) Find
【Solution】 (1) We obtain the following equations using Fig.3.21.
The output voltage
(2) Inserting as follows:
The required condition is as
follows, for which the output voltage
受信パルス
[Chapter 4 will be presented in the upcoming May-June 2010 issue of this Journal.]
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