JP4961362B2 - Measuring method of electric potential between both electrodes of electret capacitor - Google Patents

Description

  The present invention relates to a method for measuring an electric potential between both electrodes of an electret capacitor, and more particularly to a method for nondestructively measuring an electric potential between both electrodes in an assembled state of an electret capacitor.

  FIG. 1 is a cross-sectional view for explaining an example of the structure of an electret condenser microphone (mechanical microphone formed by a diaphragm, a spacer, and a back electrode). FIG. 1 (a) shows the structure of the electret condenser microphone. Sectional drawing shown, (b) is a sectional view of an electronic component connected to the electret condenser microphone.

  As shown in FIG. 1A, in the electret condenser microphone, a front plate 101a is integrally formed on the front surface of a metal case 101, a sound hole 107 is formed on the front plate 101a, and the periphery of the inner surface of the front plate 101a. The diaphragm plate 102 made of metal is in contact with and electrically connected to the part, and the diaphragm 103 is attached to the surface of the diaphragm ring 102 opposite to the front plate. Metal is deposited on one surface of the film, and the deposited film is attached in contact with the diaphragm ring 102.

  The vibrating membrane 103 is closely opposed to the back electrode 105 via the spacer 104, and the back electrode 105 is held on the front surface of the cylindrical back electrode holder 106. An impedance conversion IC element 109 is arranged in a back chamber 110 configured inside the back electrode holder 106, an input terminal 109a of the IC element is connected to the back electrode, and an output terminal 109b protrudes from the back of the case. The wiring is connected to the wiring of the wiring board 108 that closes the back of the case. The rear terminal portion of the case is bent on the back surface of the wiring board 108, and the internal portions are pressed against the front plate 101a to be fixed as a whole.

  An electret material such as FEP is fused to the back electrode 105, and the electret material is converted into an electret, whereby a potential Vg is generated between the back electrode and the vibrating membrane. Reference numeral 120 is a connection part, reference numeral 120a is a spring contact, reference numeral 120b is a connection part housing, and reference numeral 121 is a rubber bush.

  When a sound signal is input to the microphone of FIG. 1A, the capacitance and loss of the capacitor formed by the diaphragm, the spacer, and the back pole change, and are input to the impedance conversion IC element 109 as a voltage signal. The electric signal subjected to impedance conversion is output via the output terminal 109b. The signal output from the impedance conversion IC 109 is output to the wiring pattern through the through hole 111. Here, since the microphone sensitivity is proportional to the potential Vg between the back electrode 105 and the vibrating membrane 103, the measurement technique of the potential Vg between both electrodes becomes a technique necessary for supplying stable Vg, and therefore is precise and varies. It is an important technology for manufacturing electret microphones with low sensitivity.

  As a conventional method of measuring Vg, as shown in Patent Document 1, instead of measuring Vg, it is common to measure the surface potential of the back electrode 105. When creating a microphone, the surface potential of the back electrode is measured. By controlling, a microphone having a desired sensitivity was created.

  In recent years, an electret condenser microphone formed by processing a silicon substrate using MEMS (micro electro mechanical system) technology has also appeared (for example, see Patent Document 2).

  FIG. 2 is a diagram showing a cross-sectional structure of a microphone on which an acoustic transducer formed by processing a silicon substrate is mounted.

  In FIG. 2, an acoustic transducer 300 and an impedance conversion IC 200 are mounted on a wiring board 404. Reference numeral 400 is a case, and reference numeral 402 is a case side plate.

  The impedance conversion IC 200 includes a signal output terminal 204a and a signal input terminal 204b, and the terminals 204a and 204b are connected to a wiring pattern on the wiring board 404 by, for example, solder 202.

  The acoustic transducer 300 includes a silicon substrate 300, a first electrode (for example, made of silicon) 302 provided with holes (sound holes) 304, and a second electrode (for example, made of a silicon oxide film) 307. The first electrode 302 and the second electrode 307 are provided to face each other with a predetermined air gap 306 therebetween. Reference numeral 308 is a spacer (for example, made of metal) that forms an air gap, and reference numeral 309 is a bonding wire.

  The wiring board 404 is provided with through holes 312a and 312b. A ground wiring pattern 314 a and a signal wiring pattern 314 b are formed on the back surface of the wiring substrate 404.

  An electret condenser microphone manufactured by using the MEMS technology as shown in FIG. 2 is described in Patent Document 2, for example.

Japanese Patent Laid-Open No. 6-313782 (page 5, FIG. 1) Japanese Patent Laid-Open No. 2005-183437

  However, in the conventional surface potential measurement method described in Patent Document 1, measurement with a microphone assembled is impossible.

  Furthermore, in an electret condenser microphone mounted with an acoustic transducer (acoustic-electric conversion element) created by a semiconductor manufacturing process as shown in FIG. 2, for example, when an electret material is used for the second electrode, the second When measuring the surface potential applied to an electrode (for example, a silicon oxide film), the first electrode made of silicon becomes an obstacle, making it difficult to measure the surface potential non-destructively and accurately. Even when the first electrode is an electret material, this time, the second electrode becomes an obstacle, and therefore it is difficult to measure the surface potential accurately in a non-destructive manner.

  The present invention has been made on the basis of the above circumstances, and the object thereof is to measure the potential between the two electrodes of the electret capacitor in a state where the electret capacitor is assembled and non-destructively. There is.

  A method for measuring an electric potential between both electrodes of an electret capacitor according to the present invention includes a diaphragm and a fixed pole disposed opposite to the diaphragm, and one of the diaphragm and the fixed pole is electretized. A method for measuring an electric potential between both electrodes of an electret capacitor that is an electret material, wherein a bias voltage is swept and applied between the diaphragm and the fixed electrode, while an electrostatic potential between the diaphragm and the fixed electrode is measured. A first step of measuring capacitance and loss, and a second step of identifying a potential between the diaphragm and the fixed pole based on a relationship between the measured capacitance and loss and the bias voltage value Steps.

  When a bias voltage is applied to both poles of the electret capacitor in an assembled state and the voltage value is linearly changed, the capacitance and loss between both poles change accordingly. Here, since one pole of the electret capacitor is made of an electret material (a material having permanent electric polarization), a potential Vg is generated between the two poles. This is different from when one pole is not electretized. Since the behavior of the variation in capacitance and loss is closely related to the potential Vg generated by electretization, it is based on the relationship between the measured capacitance and loss and the bias voltage value applied at that time. Thus, it is possible to identify the potential between both poles (that is, between the diaphragm and the fixed pole). Further, based on capacitance and loss, more accurate measurement than potential identification by either one is possible.

  Moreover, in one aspect of the method for measuring the potential between both electrodes of the electret capacitor of the present invention, in the first step, the frequency when measuring the capacitance is set to 1/8 or more and 1/4 or less of the resonance frequency. .

  By setting the measurement frequency of capacitance and loss to 1/8 or more and 1/4 or less of the resonance frequency, that is, a low frequency, each peak value at the measurement frequency tends to appear remarkably, so accurate potential measurement is possible. is there. Therefore, the potential between both electrodes of the electret capacitor can be accurately measured in a non-destructive manner.

  In another aspect of the method for measuring a potential between both electrodes of the electret capacitor according to the present invention, in the first step, the oscillator voltage level is set to 0.05 V or more when measuring the capacitance. To do.

  When the oscillator voltage is too small, it is greatly affected by noise. According to the above configuration, the potential can be measured without being affected by noise by setting the oscillator voltage level when measuring the capacitance and loss to be 0.05 V or more. Therefore, the potential between both electrodes of the electret capacitor can be accurately measured in a non-destructive manner.

  Further, in another aspect of the method for measuring a potential between both electrodes of the electret capacitor of the present invention, when measuring the capacitance in the first step, the electret capacitor is in a vacuum state or a reduced pressure of 13.332 Pa or less. Measure in state.

  Comparing the potential measurement in the vacuum state or the reduced pressure state with the potential measurement in the atmospheric pressure, for example, when the measurement frequency is 20 kHz or 50 kHz, the potential measurement in the vacuum state or the reduced pressure state has a peak value of capacitance and loss. Remarkably easy to come out. Therefore, by measuring the electret capacitor in a vacuum state or a reduced pressure state of 13.332 Pa or less, the potential between both electrodes of the electret capacitor can be accurately measured in a non-destructive manner.

  According to the potential measurement of the present invention, the potential between the two electrodes of the electret capacitor in a state assembled with the microphone can be measured nondestructively.

  Therefore, it is possible to accurately obtain the electrification amount of the electret material in a state where the microphone is assembled, and thereby it is possible to optimize the conditions for producing the electret and to optimize the manufacturing process conditions.

  Therefore, it is possible to manufacture a highly sensitive electret condenser microphone that is precise and has little variation.

  Next, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 3 is a diagram showing a basic configuration for carrying out the measurement method according to the first embodiment of the present invention. In this embodiment, the measurement under atmospheric pressure is assumed.

  As shown in the figure, a sweep bias voltage generator 500 is connected to both poles of an electret capacitor 300 composed of a first electrode (fixed pole) 302 and a second electrode (vibration membrane) 306 that has been electretized. The bias voltage Vb is swept applied, and at the same time, the capacitance and loss between the two electrodes are measured by the capacitance loss measuring device 600.

  The electret capacitor 300 is an electret material that includes a diaphragm and a fixed pole that is disposed to face the diaphragm, and either the diaphragm or the fixed pole is electretized.

  FIG. 4 is a diagram illustrating an example of capacitance (C) -bias voltage (DC bias) characteristics obtained by capacitance measurement according to the first embodiment of the present invention. This characteristic is a capacitance-bias voltage characteristic when the vibrating membrane 306 is electretized. In FIG. 4, the measurement frequencies are 10 kHz, 20 kHz, 50 kHz, 80 kHz, 100 kHz, 150 kHz, and 200 kHz. Moreover, in FIG. 4, the resonant frequency of the electret capacitor 300 is, for example, 80 kHz. From FIG. 4, it can be understood that the maximum value (peak) of the electrostatic capacitance is likely to be noticeable when the measurement frequency is low, such as 10 kHz or 20 kHz. This is because in the case of a high frequency, the resonance frequency of the electret capacitor 300 approaches and the waveform of this characteristic is disturbed. Thus, it is preferable that the frequency when measuring the electrostatic capacitance be approximately 1/8 or more and 1/4 or less of the resonance frequency of the electret capacitor 300.

  Next, FIG. 5 is a diagram illustrating an example of loss (D) -bias voltage (DC bias) characteristics obtained by loss measurement in the first embodiment of the present invention. This characteristic is a loss-bias voltage characteristic when the vibrating membrane 306 is electretized. In FIG. 5, the measurement frequencies are 10 kHz, 20 kHz, 50 kHz, 80 kHz, 100 kHz, 150 kHz, and 200 kHz. Moreover, in FIG. 5, the resonance frequency of the electret capacitor 300 is 80 kHz. From FIG. 5, it can be understood that the maximum value (peak) of the loss tends to be noticeable when the measurement frequency is low, such as 10 kHz or 20 kHz. This is because in the case of a high frequency, the resonance frequency of the electret capacitor 300 approaches and the waveform of this characteristic is disturbed. Thus, it is preferable that the frequency for measuring the loss is about 1/8 to 1/4 of the resonance frequency of the electret capacitor 300.

  The electrostatic capacity C and loss D of the electret capacitor 300 include the electrostatic capacity Cs and loss Ds when the capacitor 300 is an electric field capacitor, as shown in FIG. 6A, and as shown in FIG. 6B. In addition, there are a capacitance Cp and a loss Dp when the capacitor 300 is an electric field capacitor. The present invention can be applied to both.

  In the above description, the method of identifying the potential between two electrodes based on the capacitance C and the loss D has been described. However, | Z | (impedance), | Y | (admittance), θ (phase), R (resistance), The potential between the two electrodes may be identified based on X (reactance), G (conductance), B (susceptance), L (inductance), and the like.

  For example, L, | Z |, Y of Y, and the like are proportional to the reciprocal of the electrostatic capacitance, and thus become peak peaks. Further, R, X, G, B, | Y |, Z of Z, and the like have the same characteristics as the capacitance.

(Second Embodiment)
FIG. 7 is a diagram showing a basic configuration for carrying out the measurement method according to the second embodiment of the present invention. In this embodiment, measurement under vacuum (or reduced pressure) and measurement under atmospheric pressure are assumed.

  In the measurement according to FIG. 7, as in the measurement according to FIG. 1, the sweep bias is applied to both poles of the electret capacitor 300 configured by the first electrode (fixed pole) 302 and the second electrode (vibration membrane) 306 that has been electretized. The bias voltage Vb is swept and applied by connecting the voltage generator 500, and at the same time, the capacitance and loss between the two electrodes are measured by the capacitance loss measuring device 600. However, in FIG. 7, the electret capacitor 300 is disposed in the vacuum chamber and can perform in-vacuum measurement.

  FIG. 8 is a diagram illustrating an example of a capacitance (C) -bias voltage (DC bias) characteristic obtained by capacitance measurement according to the second embodiment of the present invention. This characteristic is a capacitance-bias voltage characteristic when the vibrating membrane 306 is electretized. FIG. 8 shows characteristics when the measurement frequency is 20 kHz under atmospheric pressure and characteristics when the measurement frequency is 20 kHz under vacuum. Moreover, in FIG. 8, the resonant frequency of the electret capacitor 300 is 80 kHz. From FIG. 8, it can be understood that in this case, the maximum value (peak) of the electrostatic capacitance is more likely to appear significantly under vacuum than under atmospheric pressure.

  FIG. 9 is a diagram illustrating an example of capacitance (C) -bias voltage (DC bias) characteristics obtained by capacitance measurement according to the second embodiment of the present invention. This characteristic is a capacitance-bias voltage characteristic when the vibrating membrane 306 is electretized. FIG. 9 shows characteristics when the measurement frequency is 50 kHz under atmospheric pressure and characteristics when the measurement frequency is 50 kHz under vacuum. In FIG. 9, the resonance frequency of the electret capacitor 300 is 80 kHz. From FIG. 9, it can be understood that in this case, the maximum value (peak) of the electrostatic capacitance is more likely to be generated under vacuum than under atmospheric pressure.

  FIG. 10 is a diagram illustrating an example of capacitance (C) -bias voltage (DC bias) characteristics obtained by capacitance measurement according to the second embodiment of the present invention. This characteristic is a capacitance-bias voltage characteristic when the vibrating membrane 306 is electretized. FIG. 10 shows characteristics when the measurement frequency is 80 kHz under atmospheric pressure and characteristics when the measurement frequency is 80 kHz under vacuum. In FIG. 10, the resonance frequency of the electret capacitor 300 is 80 kHz. From FIG. 10, it can be understood that the maximum value (peak) of the electrostatic capacitance is more prominent in the vacuum than in the atmospheric pressure, but the waveform largely fluctuates in the vicinity of the bias voltage of −20V, for example. This is because the vibration film 306 resonates when the measurement frequency is 80 kHz.

  As shown in FIGS. 8 to 10, when the measurement frequency is outside ± 10% of the resonance frequency, for example, a desired capacitance-bias voltage characteristic is obtained under vacuum, and the above relationship is, for example, ± If it is within 10%, the desired capacitance-bias voltage characteristics may not be obtained under vacuum. However, not only in the case of the resonance of the vibration film 306 shown in FIG. 10, the resonance frequency (140 to 150 kHz) of the fixed pole 302 formed of the fixed film, or the fixed pole 302 formed of the vibration film 306 and the fixed film. Even in the vicinity of the resonance frequency after each secondary mode, a desired capacitance-bias voltage characteristic may not be obtained under vacuum.

  FIG. 11 is a diagram showing an example of loss (D) -bias voltage (DC bias) characteristics obtained by loss measurement in the second embodiment of the present invention. This characteristic is a loss-bias voltage characteristic when the vibrating membrane 306 is electretized. FIG. 11 shows characteristics when the measurement frequency is 20 kHz under atmospheric pressure and characteristics when the measurement frequency is 20 kHz under vacuum. Moreover, in FIG. 11, the resonant frequency of the electret capacitor 300 is 80 kHz. From FIG. 11, it can be understood that in this case, the maximum value (peak) of the loss is more likely to occur under vacuum than under atmospheric pressure.

  FIG. 12 is a diagram showing an example of loss (D) -bias voltage (DC bias) characteristics obtained by loss measurement in the second embodiment of the present invention. This characteristic is a loss-bias voltage characteristic when the vibrating membrane 306 is electretized. FIG. 12 shows characteristics when the measurement frequency is 50 kHz under atmospheric pressure and characteristics when the measurement frequency is 50 kHz under vacuum. In FIG. 12, the resonance frequency of the electret capacitor 300 is 80 kHz. From FIG. 12, it can be understood that in this case, the maximum value (peak) of the loss is more likely to occur under vacuum than under atmospheric pressure.

  FIG. 13 is a diagram illustrating an example of loss (D) -bias voltage (DC bias) characteristics obtained by loss measurement in the second embodiment of the present invention. This characteristic is a loss-bias voltage characteristic when the vibrating membrane 306 is electretized. FIG. 13 shows characteristics when the measurement frequency is 80 kHz under atmospheric pressure and characteristics when the measurement frequency is 80 kHz under vacuum. In FIG. 13, the resonance frequency of the electret capacitor 300 is 80 kHz. From FIG. 13, it can be understood that although the maximum value (peak) of the loss is more prominent under vacuum than under atmospheric pressure, for example, the waveform fluctuates greatly in the vicinity of the bias voltage of −20V. This is because the vibration film 306 resonates when the measurement frequency is 80 kHz.

  As shown in FIGS. 11 to 13, when the measurement frequency is outside the resonance frequency, for example, ± 10%, a desired loss-bias voltage characteristic is obtained under vacuum, and the above relationship is, for example, ± 10%. If it is within the range, a desired loss-bias voltage characteristic may not be obtained under vacuum. However, not only in the case of the resonance of the vibration film 306 shown in FIG. 13, the resonance frequency (140 to 150 kHz) of the fixed pole 302 formed of the fixed film, and the fixed pole 302 formed of the vibration film 306 and the fixed film. Even in the vicinity of the resonance frequency after each secondary mode, a desired loss-bias voltage characteristic may not be obtained under vacuum.

  By the way, in the measurement of capacitance, the oscillator voltage is also changed and measured. FIG. 14 is a diagram illustrating an example of capacitance (C) -bias voltage (DC bias) characteristics obtained by measuring capacitance according to the second embodiment of the present invention. Here, the oscillator voltage refers to an AC component of a voltage applied to both electrodes, that is, the fixed electrode 302 and the vibrating membrane 306 at the time of measurement.

  The measurement in FIG. 14 was performed under atmospheric pressure, and the measurement was performed with the oscillator voltage set at 10 mV and 50 mV. From FIG. 14, it can be understood that noise is strongly influenced when measured at 10 mV, and that noise is hardly affected when measured at 50 mV.

  Further, also in the loss measurement, the measurement is performed by changing the oscillator voltage as shown in FIG. FIG. 15 is a diagram illustrating an example of a loss (D) -bias voltage (DC bias) characteristic obtained by measuring the loss in the second embodiment of the present invention.

  The measurement in FIG. 15 was performed under atmospheric pressure, and the measurement was performed with the oscillator voltage set at 10 mV and 50 mV. From FIG. 15, it can be understood that noise is strongly influenced when measured at 10 mV, and that noise is hardly affected when measured at 50 mV.

  Thus, in order to more accurately measure capacitance and loss, it is desirable that the oscillator voltage be 0.05 V or higher.

  In the capacitance measurement in FIG. 14 and the loss measurement in FIG. 15, it has been explained that if the oscillator voltage is too low at atmospheric pressure, it is easily affected by noise. I can say that.

  In the present embodiment, measurement may be performed in a reduced pressure state (for example, a state of 13.332 Pa (= 0.1 Torr) or less) instead of a vacuum state.

  The first and second embodiments have been described assuming the case of an electret condenser microphone using an acoustic transducer (for example, FIG. 2) created by a semiconductor process. Although the present embodiment can be applied to a mechanical electret condenser microphone (for example, FIG. 1), it is desirable to apply the present embodiment to an electret condenser microphone using an acoustic transducer produced by a semiconductor process.

  As described above, according to the present invention, the potential between the two electrodes of the electret capacitor in the state assembled with the microphone can be measured nondestructively.

  Therefore, it is possible to accurately obtain the electrification amount of the electret material in a state where the microphone is assembled, and thereby it is possible to optimize the conditions for producing the electret and to optimize the manufacturing process conditions.

  Therefore, it is possible to manufacture a highly sensitive electret condenser microphone that is precise and has little variation.

  INDUSTRIAL APPLICABILITY The present invention has an effect of enabling non-destructive measurement of the potential between the two electrodes of the electret capacitor in a state assembled in a microphone, and is therefore useful as a method for measuring the potential between both electrodes of the electret capacitor. .

It is sectional drawing for demonstrating an example of the structure of an electret condenser microphone (mechanical microphone formed with a diaphragm, a spacer, and a back pole), (a) is sectional drawing which shows the structure of an electret condenser microphone, (B) is sectional drawing of the electronic component connected to an electret condenser microphone The figure which shows the cross-section of the microphone carrying the acoustic transducer formed by processing a silicon substrate The figure which shows the basic composition for enforcing the measuring method in the 1st Embodiment of this invention. The figure which shows an example of the electrostatic capacitance-bias voltage characteristic obtained by the measurement in the 1st Embodiment of this invention The figure which shows an example of the loss-bias voltage characteristic obtained by the measurement in the 1st Embodiment of this invention The figure for demonstrating an example of the electrostatic capacitance and loss of the electret capacitor | condenser in the 1st Embodiment of this invention The figure which shows the basic composition for enforcing the measuring method in the 2nd Embodiment of this invention. The figure which shows an example of the electrostatic capacitance-bias voltage characteristic obtained by the measurement in the 2nd Embodiment of this invention The figure which shows an example of the electrostatic capacitance-bias voltage characteristic obtained by the measurement in the 2nd Embodiment of this invention The figure which shows an example of the electrostatic capacitance-bias voltage characteristic obtained by the measurement in the 2nd Embodiment of this invention The figure which shows an example of the loss-bias voltage characteristic obtained by the measurement in the 2nd Embodiment of this invention The figure which shows an example of the loss-bias voltage characteristic obtained by the measurement in the 2nd Embodiment of this invention The figure which shows an example of the loss-bias voltage characteristic obtained by the measurement in the 2nd Embodiment of this invention The figure which shows an example of the electrostatic capacitance-bias voltage characteristic obtained by the measurement in the 2nd Embodiment of this invention The figure which shows an example of the loss-bias voltage characteristic obtained by the measurement in the 2nd Embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Case 101a Front plate 102 Diaphragm ring 103 Vibration membrane 104 Spacer 105 Back pole 106 Back pole holding body 107 Sound hole 108 Wiring board 109 Impedance conversion IC
109a Impedance conversion IC input terminal 109b Impedance conversion IC output terminal 110 Back chamber 111 Through hole 120 Connection component 120a Spring contact 120b Connection component casing 121 Rubber bush 130 Mounting target component 130a Connection component input terminal 200 IC for impedance conversion
202 Solder 204a Impedance conversion IC input terminal 204b Impedance conversion IC output terminal 300 Electret capacitor (assembled state)
302 First electrode 304 Hole (sound hole)
306 Air gap 307 Second electrode 308 Joining material also serving as spacer 309 Boding wire 310 Silicon substrate 312a, 312b Through hole 314a Ground wiring pattern 314b Signal wiring pattern 400 Case 402 Case side plate 404 Wiring board 500 Sweep voltage application device 600 Static Capacitance loss measuring instrument

Claims (4)

A method for measuring an electric potential between both electrodes of an electret capacitor, which is an electret material having an oscillating plate and a fixed pole disposed opposite to the oscillating plate, and one of the oscillating plate and the fixed pole being electretized Because
A first step of measuring a capacitance and a loss between the diaphragm and the fixed pole while sweeping and applying a bias voltage between the diaphragm and the fixed pole;
A second step of identifying a potential between the diaphragm and the fixed pole based on a relationship between the measured capacitance and loss and the bias voltage value;
A method for measuring the electric potential between both electrodes of an electret capacitor. A method for measuring a potential between both electrodes of the electret capacitor according to claim 1,
In the first step, the frequency at which the capacitance and loss are measured is set to 1/8 or more and 1/4 or less of the resonance frequency. A method for measuring a potential between both electrodes of the electret capacitor according to claim 1,
In the first step, when measuring the capacitance and loss, the level of the oscillator voltage is set to be 0.05 V or more. A method for measuring a potential between both electrodes of the electret capacitor according to claim 1,
In the first step, when the capacitance and loss are measured, the electret capacitor is measured in a vacuum state or a reduced pressure state of 13.332 Pa or less.

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