JP2015173841A - Device with element having capacitance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of detecting more accurately than before change of the capacitance of an element in a device such as an electromechanical conversion device using change of the capacitance.SOLUTION: A device such as an electromechanical conversion device comprises: an element 109 having a cell 106; first application means 111 for applying a DC voltage between electrodes; and second application means 112 for applying a detection signal to detect the capacitance of the element to one of the electrodes. A signal conversion unit 114 converts a current signal output from the other electrode into a voltage signal. A band rejection filter unit 113, disposed between the other electrode and the signal conversion unit, has a cutoff frequency in a frequency region outside the main band of the current signal generated at the other electrode by the vibration of a vibration film due to reception of an acoustic wave.

Description

  The present invention relates to an apparatus having an element having an electrostatic capacity, such as an electromechanical transducer using an electrostatic capacitance change, an apparatus or method for detecting the electrostatic capacity of an element, and the like.

  In order to generate and detect acoustic waves, a capacitive electromechanical transducer (CMUT) manufactured using MEMS technology has been proposed. The basic structure of CMUT includes a cell including a first electrode disposed on a substrate, a vibration film disposed immediately above the first electrode, and a second electrode disposed on the vibration film, An element is configured by electrically connecting the first electrode and the second electrode of each cell. In order to generate an acoustic wave using the CMUT, a time-varying voltage signal (for example, a pulse voltage) is applied between the first electrode and the second electrode. Thereby, an electrostatic attraction is generated between the first electrode and the second electrode, and an acoustic wave is generated by vibrating the vibration film by the electrostatic attraction. In order to detect an acoustic wave using CMUT, a DC voltage is applied between the first electrode and the second electrode. When the vibrating membrane is vibrated by an acoustic wave in this state, the capacitance between the first electrode and the second electrode changes, so that a current signal is generated at the second electrode. An acoustic wave is detected by detecting this current signal. In this specification, the acoustic wave includes what are called sound waves, ultrasonic waves, and photoacoustic waves. For example, it includes photoacoustic waves generated inside the subject by irradiating the subject with light (electromagnetic waves) such as visible light and infrared rays.

  In order to improve and maintain the image quality of ultrasonic images using CMUT, the performance of all elements of CMUT, that is, the generation efficiency of acoustic waves and the detection sensitivity of acoustic waves, are always kept constant at designed values. It is desirable. One of the main factors that determine the performance of the CMUT is the capacitance between the first electrode and the second electrode (hereinafter referred to as the capacitance of the CMUT). By detecting the capacitance of the CMUT, it can be determined whether the performance of the CMUT has changed from a desired state. The electromechanical transducer described in the fourth embodiment of Patent Document 1 has a function of applying an AC voltage signal to one of the first electrode and the second electrode of the CMUT, and the other electrode. And a function of detecting a current signal generated in Since the current signal has an amplitude corresponding to the capacitance of the CMUT, the capacitance of the CMUT can be detected from the current signal.

JP 2011-004280 A

  In the above field, in order to maintain the performance of a device such as a CMUT with higher accuracy, it is desired to detect a change in capacitance of the device such as a CMUT with higher accuracy than before. An object of the present invention is to detect a change in capacitance of a device such as a CMUT with higher accuracy than before.

  In view of the above problems, the apparatus of the present invention has the following components. That is, an element including a first electrode and a vibrating membrane including a second electrode formed with a gap from the first electrode, and having a cell that receives at least an acoustic wave. First application means for applying a DC voltage between the first electrode and the second electrode. A second applying means for applying a detection signal for detecting a capacitance of the element to one of the first electrode and the second electrode; A signal conversion unit that converts a current signal output from the other electrode of the first electrode and the second electrode into a voltage signal. A band that is provided between the other electrode and the signal conversion unit and has a cutoff frequency in a frequency region outside the main band of a current signal generated by the other electrode due to vibration of the vibration film due to reception of the acoustic wave Blocking filter part.

  Further, in view of the above problems, a book for detecting the capacitance of an element having a cell including a first electrode and a vibration film including a second electrode formed with a gap from the first electrode. The device of the invention has the following components. That is, application means for applying a detection signal for detecting the capacitance of the element to one of the first electrode and the second electrode. A signal converter that converts a current signal output from the other electrode of the first electrode and the second electrode by vibration of the vibrating membrane into a voltage signal. Band blocking provided between the other electrode and the signal conversion unit and having a cutoff frequency in a frequency region outside a main band of a current signal generated at the other electrode due to vibration of the vibrating membrane due to an external action Filter part. Frequency control means for changing the frequency of the detection signal in the vicinity of the cutoff frequency. Storage means for storing information relating to the output signal from the signal conversion unit corresponding to the frequency of the detection signal. Capacitance detection means for acquiring a frequency of the detection signal that maximizes the output signal based on information stored in the storage means, and detecting a capacitance of the element based on information including the frequency.

  Further, in view of the above problems, a book for detecting the capacitance of an element having a cell including a first electrode and a vibration film including a second electrode formed with a gap from the first electrode. The method of the invention has the following steps. That is, a step of applying a detection signal for detecting the capacitance of the element to one of the first electrode and the second electrode. A current signal generated at the other electrode of the first electrode and the second electrode due to vibration of the vibration film is a current signal generated at the other electrode due to vibration of the vibration film due to external action. A process of processing by a band rejection filter unit having a cutoff frequency in a frequency region outside the main band. Converting the current signal processed by the band rejection filter unit into a voltage signal; Changing the frequency of the detection signal in the vicinity of the cutoff frequency; Storing information related to the voltage signal corresponding to the frequency of the detection signal. Obtaining a frequency of the detection signal that maximizes the voltage signal based on the stored information, and detecting a capacitance of the element based on the information including the frequency.

  According to the present invention, it is possible to detect a change in capacitance of an element of a device such as a CMUT with higher accuracy than in the past.

The figure which shows the basic structural example of the apparatuses of this invention, such as an electromechanical converter. The figure which shows the 1st Example of this invention. The figure which shows the 2nd Example of this invention. The figure which shows the 4th Example of this invention. The figure of the frequency characteristic of the voltage signal amplitude of the signal conversion part at the time of electrostatic capacitance detection. The figure of the frequency characteristic of the current voltage conversion coefficient from a 2nd electrode to a signal conversion part. The figure of the frequency characteristic of the voltage signal amplitude of the signal conversion part in the 1st example of the present invention. The figure of the frequency characteristic of the current-voltage conversion coefficient from the 2nd electrode in the 1st Example of this invention to the signal conversion part. The figure which shows the 5th Example of this invention.

In the present invention, the band signal having a cutoff frequency in the frequency region outside the main band of the current signal generated at the electrode due to the vibration of the vibration film due to the external action is generated at the element electrode due to the vibration of the vibration film. Process by the filter unit. Here, the main band includes frequency components representing the main characteristics of external action waves such as acoustic waves detected by this device, among the frequency components of current signals generated by vibrations of the diaphragm caused by external actions. Refers to the frequency range. For example, in an ultrasonic diagnostic imaging apparatus that detects an ultrasonic pulse that is transmitted from a single rectangular wave to a subject and reflected by the subject, the frequency is 0 to a frequency that is the reciprocal of the time width of the transmitted ultrasound. Until now, the main frequency components of the ultrasonic wave exist in the region defined by the above, and this frequency range corresponds to the main band. Further, the frequency region outside the main band may be either a frequency region higher or lower than the main band. As an example of the place where the band rejection filter unit is arranged, the band rejection filter unit is inserted between the electrode of the element and the signal conversion unit, so that the detection signal input from the electrode is detected to detect the capacitance. On the other hand, the frequency characteristic of the output signal from the signal converter has a peak at a frequency corresponding to the capacitance. Thereby, a change in the capacitance of the element can be detected with higher accuracy than in the past. This amount of change in capacitance can be used for various controls such as correction of the voltage signal converted by the signal converter.

Hereinafter, embodiments and examples of the present invention will be described.
With reference to FIG. 1, an embodiment according to a basic configuration example of the electromechanical transducer of the present invention will be described. A first electrode 102 is disposed on a substrate 101, a membrane 103 is disposed through a gap (cavity) so as to face the first electrode 102, and a second electrode 105 is formed thereon. The vibrating membrane including the membrane 103 and the second electrode 105 is supported by a supporting portion 104 disposed on the substrate 101 so as to be able to vibrate. Thus, the membrane 103 can vibrate with the second electrode 105. A structure including the above elements is referred to as a cell 106. In addition, one or more cells 106 are arranged, the first electrodes 102 of each cell are electrically connected by a wiring 107, and the second electrodes 105 are electrically connected by a wiring 108. Called element 109.

The wiring 107 is connected in series by the switching means 110 to the DC voltage applying means 111 as the first applying means, or the DC voltage applying means 111 and the second applying means 112 of the detection signal for detecting the capacitance. Connected to one of the connected circuits. Here, as the second applying means 112, a voltage signal generating source such as a sine wave, a rectangular wave or a pulse wave whose frequency can be set to a desired value is used. The wiring 108 is connected to the band rejection filter unit 113, and the band rejection filter unit 113 is connected to the signal conversion unit 114. The signal conversion unit 114 has a function of converting the current I into the voltage V, and the conversion ratio is K _o = V / I. As the band rejection filter unit 113, a circuit including a coil 115 and a capacitor 116, which is the simplest configuration example, is used here.

A method for detecting the capacitance between the first electrode 102 and the second electrode 105 of the element 109 using the above configuration will be described below. First, the wiring 107 and the second application unit 112 are connected using the switching unit 110, and a capacitance detection signal (here, a sine wave voltage signal) is applied to the first electrode 102. At this time, the relationship between the amplitude V _{o of the} voltage signal obtained by the signal converter 114 and the amplitude V _i of the sine wave voltage signal of the angular frequency ω applied to the first electrode 102 is expressed by the following equation (1). It is expressed in
V _o = V _i · | L · ω ² −1 / C | / √ ((L · ω ² − (1 / C + 1 / C _m )) ² + (R · ω) ² )
... Formula (1)
Here, the inductance of the coil 115 is L, the capacitance of the capacitor 116 is C, the capacitance of the element 109 is C _m , and the wiring resistance between the second electrode 105 and the band rejection filter unit 113 is R. V _o is a function of the angular frequency ω as shown in the graph of FIG. 5, and has a sharp peak at ω _p .

When the wiring resistance R is sufficiently small and approximated to be 0, ω _p is expressed as the following equation (2).
ω _p = √ (1 / (L · (C · C _m / (C + C _m )))) Equation (2)
This indicates that ω _p changes in accordance with the capacitance C _m of the element 109. That is, the capacitance C _m of the element 109 can be detected by measuring the angular frequency ω _{p at} which the amplitude V _o of the voltage signal in the signal converter 114 is maximum. Further, the angular frequency ω _p is constant irrespective of the conversion magnification of the means for measuring the amplitude V _i of the capacitance detection signal and the amplitude V _o of the voltage signal in the signal converter 114. Therefore, by measuring ω _p , the capacitance C _m of the element 109 can be detected without being affected by these fluctuations.

On the other hand, a method for detecting an acoustic wave from the outside using the above configuration will be described below. The switching unit 110 is used to connect the wiring 107 and the DC voltage application unit 111, and the DC voltage _Vd is applied to the first electrode 102 which is one of the electrodes. In this state, it is assumed that the acoustic wave P is incident on the vibration film including the element 109. Since the second electrode 105 vibrates together with the membrane 103 of the vibrating membrane by the acoustic wave P, the capacitance of the element 109 changes, and a current signal corresponding to the acoustic wave P is generated from the second electrode 105 which is the other electrode. Occur. The amplitude I of the current signal is converted into the amplitude V of the voltage signal by the signal conversion unit 114 by the current-voltage conversion coefficient K as in the following equation (3).
K = V / I = K _o · | (L · ω ² −1 / C) | / √ ((L · ω ² −1 / C) ² + (R · ω) ² )
... Formula (3)

K is a function of the angular frequency ω as shown in the graph of FIG. 6, and is 0 at the cutoff frequency ω _s expressed by the following equation (4), and in an outer region that is more than a certain angular frequency away from ω _s . _Has a band rejection characteristic of a substantially constant value _Ko .
ω _s = 1 / √ (L · C) (4)

Therefore, in order to convert the acoustic wave P into the voltage signal amplitude V without losing the angular frequency component representing the main feature, the parameters (here, L and C) of the band rejection filter unit 113 are set as follows. Just design. Among the angular frequency characteristics of the current signal I corresponding to the acoustic wave When the P, the component representing the main characteristics of the acoustic wave P is present in the region of _{ω 1 ~ω 2 (ω 1 <} ω 2), ω s <ω The values of L and C are designed so that either ₁ or ω _s > ω ₂ holds. More preferably, ω ₁ ~ω ₂ of angular frequency K is a constant percentage of the mean value of K in the region omega _d is, ω _{d <ω 1} or ω _d> ω ₂ of to meet either Design the values of L and C. The fixed ratio may be set as appropriate according to the accuracy of detecting the size of the component representing the main feature of the acoustic wave P. For example, if the detection is performed with an accuracy of 5%, the fixed ratio is 95. % May be set.

  By having the above configuration, the following effects can be obtained. The frequency characteristic of the synthesis circuit in which the element of the device such as the CMUT and the band element filter unit are connected in series has a sharp peak having a peak at a frequency corresponding to the capacitance of the element of the device. Since the frequency of this peak changes greatly with respect to the change in the capacitance of the element of the apparatus, it is possible to detect the change in the capacitance of the element of the apparatus with higher accuracy than before. Furthermore, when the apparatus is controlled based on the detected change in capacitance of the element of the apparatus, the performance of the element of the apparatus can be kept constant with higher accuracy.

Example 1
A description will be given of a first embodiment relating to a configuration in which means for searching for the peak frequency is embodied. A transimpedance circuit 217 using an operational amplifier can be used as the signal converter 114 in the electromechanical transducer of this embodiment. An example will be described below with reference to FIG. The transimpedance circuit 217 includes an operational amplifier 218, a feedback resistor 219 (R _f ), and a compensation capacitor 220 (C _f ). The operational amplifier 218 used in this example is an LM6622H (manufactured by National Semiconductor), which is a relatively high-speed operational amplifier with a gain-bandwidth product of 160 MHz. The parameters of the other elements shown in FIG. 2 are as follows.
C _m = 20 [pF], L = 1 [μH], C = 100 [pF], R = 10 [Ω], R _f = R _g = 10 [kΩ], C _f = 5 [pF], C _g = 0.1 [μF], R _d = 120 [Ω], R _o = 50 [Ω], R _y = 50 [Ω]

When the relationship between the amplitude V _{o of the} voltage signal obtained from the signal conversion unit and the frequency f when the capacitance C _m of the element 109 is detected by the method described in the above embodiment, the frequency characteristics as shown in FIG. A curve is obtained. A circuit simulator PSPICE (Cadence Design Systems) was used for the calculation. Here, the relationship between the frequency f and the angular frequency ω used in the present embodiment is expressed as f = ω / (2π) using the circumference ratio π. This curve has peaks at two locations with respect to the frequency, and the peak on the high frequency side corresponds to the capacitance C _m of the element 109.

The frequency (hereinafter referred to as the peak frequency) f _{p at} which the peak portion takes a maximum value changes by about ± 0.6 MHz when the capacitance C _m of the element 109 changes from 20 pF to ± 1 pF. Further, when the relationship between the current-voltage conversion coefficient K and the frequency f when the acoustic wave is received by the method described in the embodiment, a frequency characteristic curve as shown in FIG. 8 is obtained. In the present embodiment, it is assumed that the frequency component representing the main characteristics of the acoustic wave P is in the region of 0.3 MHz to 3 MHz. Therefore, it is necessary to prevent K from being reduced more than a certain ratio in this frequency region band. is there. In this embodiment, the band rejection filter unit 113 is designed so that K does not fluctuate by 3% or more up to 3 MHz, and the acoustic wave from the outside is detected without damaging the frequency component representing the main feature of the acoustic wave P. be able to. By having such a configuration, it is possible to obtain the same effect as in the above embodiment.

(Example 2)
A second embodiment according to another configuration in which means for searching for the peak frequency is embodied will be described. Referring to FIG. 3, the electromechanical transducer of the present embodiment, a configuration example for realizing a function of measuring the peak frequency f _p corresponding to the capacitance C _m of the element below.

The electromechanical transducer according to this embodiment includes a voltage waveform generator 312 that generates a sine wave voltage signal having a desired frequency f as a detection signal applying unit for detecting capacitance. In addition, the electromechanical conversion device of this embodiment includes a capacitance detector 323 connected to both the voltage waveform generator 312 and the signal conversion unit 114. The capacitance detector 323 has a function of outputting a control signal for generating a sine wave voltage signal having a frequency f to the voltage waveform generator 312. That is, it has a function of a frequency control means for changing the frequency of the detection signal in the vicinity of the cutoff frequency. The capacitance detector 323 has a function of measuring the amplitude V _o of the voltage signal generated by the signal conversion unit 114 and storing the value in the storage device 324 in association with the frequency f of the sine wave voltage signal. And the capacitance detector 323, from the data of the combination of a plurality of V _o and f stored in the storage unit 324 has a function of determining the frequency f _p which takes the maximum value of the peak portion.

A method for detecting the capacitance of the element 109 will be described below. First, the capacitance detector 323 outputs a control signal for generating a sine wave voltage signal having a predetermined frequency f ₁ to the voltage waveform generator 312, and a voltage signal generated by the signal conversion unit 114. _Is measured. Next, the capacitance detector 323 stores the measured value of the amplitude V _o1 of the voltage signal in the storage device 324 in association with the value of the frequency f ₁ . Similarly, the capacitance detector 323 generates a sine wave voltage signal of frequency f ₂ = f ₁ + Δf from the voltage waveform generator 312 and measures the amplitude V _{o2 of the} voltage signal generated by the signal conversion unit 114. And stored in the storage device 324.

Thereafter, the same operation is repeated until f reaches a predetermined frequency f _n , and the combination of the values of f and V _o is stored in the storage device 324. The value of _{f 1} and _{f n} in the vicinity of the peak frequency _{f p} is the peak frequency _{f p} corresponding to the possible values of the capacitance _{C m} of the element 109 is determined to be in the range of _f 1 ~f _n It is desirable that Finally, the peak frequency f _p is determined from the combination of the values of f and V _o . The means for determining the peak frequency f _p, is considered the following means. A method may be used in which the frequency f _k corresponding to the maximum value V _k of V _{o1 to} V _oN is set to the peak frequency f _p . Alternatively, by fitting an appropriate function to the combination of the values of f and V _o, a method may be used for the f that function takes the maximum value and the peak frequency f _p. This example can obtain the same effect as that of the above embodiment by having such a configuration.

(Example 3)
A description will be given of a third embodiment relating to a configuration in which a correction means for a vibration detection signal depending on the vibration of the vibration film is embodied. Desirable in electromechanical transducer of the present embodiment, by utilizing the value of the capacitance C _m of the detected elements, acoustic wave conversion efficiency of the element (the ratio between the size of the acoustic wave intensity and the vibration detection signal) Means for maintaining this value will be described below.

The electromechanical transducer according to the present embodiment includes a correction unit that corrects acoustic wave conversion efficiency. In the description of this embodiment, since the result of detecting the capacitance of the element 109, and it is found that the value has changed from C _m to C _{m +} [Delta] C. The correction unit has a function of outputting a control signal to the DC voltage applying unit 111 so that a desired DC voltage _Vb is applied to the first electrode 102 in accordance with the change amount ΔC of the capacitance of the element 109. . That is, it has a function of instruction means for instructing the first application means to apply the target value of the DC voltage determined based on the change amount of the capacitance of the element to one of the electrodes. The acoustic wave conversion efficiency of the element 109 is proportional to the amount of electricity Q accumulated between the electrodes of the element 109, and Q is expressed as Q = V _b · C _m . Accordingly, when the capacitance of the element 109 changes by ΔC, the target value of the DC voltage V _b may be determined as V _b = V _b0 · C _m / (C _m + ΔC). However, _Vb0 represents the DC voltage applied before the capacitance of the element 109 changes.

Alternatively, as another example of the acoustic wave conversion efficiency correction unit, a circuit unit having a function of multiplying the amplitude V _o of the voltage signal in the signal conversion unit 114 by a desired correction coefficient α may be used. The correction coefficient α may be determined as α = C _m / (C _m + ΔC) from the above equation of the electric quantity Q. This example can obtain the same effect as that of the above embodiment by having such a configuration.

Example 4
[Embodiment 4] Embodiment 4 according to a configuration embodying a device having a plurality of elements will be described. With reference to FIG. 4, the structural example using several elements in the electromechanical transducer of a present Example is demonstrated. The electromechanical conversion device of this embodiment includes a plurality of elements 109, a band rejection filter unit 113, and a signal conversion unit 114 for one DC voltage application unit 111. The first electrodes 102 of the element 109 are electrically connected to each other, and all the first electrodes are similarly connected to either the DC voltage application means 111 or the electrostatic detection signal application means 112. . On the other hand, the second electrode 105 of the element 109 is connected to different band rejection filter units 113.

  A method for detecting the capacitance of each element 109 will be described below. The switching means 110 is used to connect the first electrode 102 of the element 109 and the applying means 112 to apply a capacitance detection signal to the first electrode 102. Accordingly, a voltage signal corresponding to the capacitance of the corresponding element 109 is output from each signal conversion unit 114. Therefore, for example, the electrostatic capacity of each element 109 can be detected at the same time using the same method as in the second embodiment. This example can obtain the same effect as that of the above embodiment by having such a configuration.

(Example 5)
The devices described in the above embodiments or examples can be applied to a subject information acquisition device such as an ultrasonic diagnostic device using acoustic waves. An object that reflects the difference in object information or acoustic impedance that reflects the optical characteristic value of the object such as the optical absorption coefficient using the electrical signal that is received and output by the electromechanical transducer from the acoustic wave from the object Information etc. can be acquired.

  FIG. 9A shows an object information acquisition apparatus using the photoacoustic effect. Pulse light generated from the light source 2010 is applied to the subject 2014 via an optical member 2012 such as a lens, a mirror, or an optical fiber. The light absorber 2016 inside the subject 2014 absorbs the energy of the pulsed light and generates a photoacoustic wave 2018 that is an acoustic wave. The electromechanical transducer 2020 in the probe 2022 receives the photoacoustic wave 2018, converts it to an electrical signal, and outputs it to the signal processor 2024. The signal processing unit 2024 performs signal processing such as A / D conversion and amplification on the input electrical signal and outputs the signal to the data processing unit 2026. The data processing unit 2026 acquires object information (characteristic information reflecting the optical characteristic value of the object such as a light absorption coefficient) as image data using the input signal. Here, the signal processing unit 2024 and the data processing unit 2026 are collectively referred to as a processing unit. The display unit 2028 displays an image based on the image data input from the data processing unit 2026.

  FIG. 9B shows a subject information acquisition apparatus such as an ultrasonic echo diagnostic apparatus using acoustic wave reflection. The acoustic wave transmitted from the electromechanical transducer 2120 in the probe 2122 to the subject 2114 is reflected by the reflector 2116. The electromechanical transducer 2120 receives the reflected acoustic wave 2118 (reflected wave), converts it into an electrical signal, and outputs it to the signal processing unit 2124. The signal processing unit 2124 performs signal processing such as A / D conversion and amplification on the input electrical signal, and outputs the signal to the data processing unit 2126. The data processing unit 2126 acquires object information (characteristic information reflecting a difference in acoustic impedance) as image data using the input signal. Here, the signal processing unit 2124 and the data processing unit 2126 are also referred to as a processing unit. The display unit 2128 displays an image based on the image data input from the data processing unit 2126.

  Note that the probe may be mechanically scanned, or may be a probe (handheld type) that a user such as a doctor or engineer moves with respect to the subject. In the case of an apparatus using a reflected wave as shown in FIG. 9B, a probe that transmits an acoustic wave may be provided separately from a probe that receives the acoustic wave. Furthermore, the apparatus has both the functions of the apparatus of FIG. 9A and FIG. 9B, and the object information reflecting the optical characteristic value of the object and the object information reflecting the difference in acoustic impedance Both of them may be acquired. In this case, the electromechanical transducer 2020 in FIG. 9A may not only receive photoacoustic waves but also transmit acoustic waves and receive reflected waves.

  102 ... first electrode, 105 ... second electrode, 106 ... cell, 109 ... element, 110 ... switching means, 111 ... DC voltage applying means (first application) Means), 112 ... Capacitance detection signal application means (second application means), 113 ... Band rejection filter unit, 114 ... Signal conversion unit, 323 ... Capacitance detector (Capacity detection means), 324... Storage device (storage means)

Claims (15)

An element including a first electrode and a vibrating membrane including a second electrode formed with a gap from the first electrode, and having at least a cell for receiving an acoustic wave;
First application means for applying a DC voltage between the first electrode and the second electrode;
Second application means for applying a detection signal for detecting the capacitance of the element to one of the first electrode and the second electrode;
A signal converter for converting a current signal output from the other electrode of the first electrode and the second electrode into a voltage signal;
A band that is provided between the other electrode and the signal conversion unit and has a cutoff frequency in a frequency region outside the main band of a current signal generated by the other electrode due to vibration of the vibration film due to reception of the acoustic wave A blocking filter section;
A device characterized by comprising: Frequency control means for changing the frequency of the detection signal in the vicinity of the cutoff frequency; storage means for storing information relating to the output signal from the signal conversion unit corresponding to the frequency of the detection signal;
Capacitance detection means for acquiring the frequency of the detection signal that maximizes the output signal based on information stored in the storage means, and detecting the capacitance of the element based on information including the frequency;
The apparatus of claim 1, comprising: Based on the amount of change in the capacitance of the element detected by the capacitance detection means, the vibration is generated in the other electrode by the vibration of the vibration film due to the reception of the acoustic wave, and is converted by the signal converter. The apparatus according to claim 2, further comprising correction means for correcting the voltage signal. 2. The apparatus according to claim 1, further comprising instruction means for instructing the first applying means to apply a target value of the DC voltage determined based on a change amount of capacitance of the element to the one electrode. 2. The apparatus according to 2. When detecting the current signal generated at the other electrode due to the vibration of the vibration film due to reception of the acoustic wave, the one electrode and the first applying means are connected, and the capacitance of the element 5. The apparatus according to claim 1, further comprising a switching unit that switches connection so as to connect the one electrode and the second application unit when detecting a change amount of the first electrode. 6. Equipment. 6. The apparatus according to claim 1, comprising a plurality of the elements, the signal conversion unit, and the band rejection filter unit. An apparatus for detecting the capacitance of an element having a cell comprising: a first electrode; and a vibration film including a second electrode formed with a gap from the first electrode,
Applying means for applying a detection signal for detecting a capacitance of the element to one of the first electrode and the second electrode;
A signal converter that converts a current signal output from the other electrode of the first electrode and the second electrode by vibration of the vibrating membrane into a voltage signal;
Band blocking provided between the other electrode and the signal conversion unit and having a cutoff frequency in a frequency region outside a main band of a current signal generated at the other electrode due to vibration of the vibrating membrane due to an external action A filter section;
Frequency control means for changing the frequency of the detection signal in the vicinity of the cutoff frequency;
Storage means for storing information relating to the output signal from the signal conversion unit corresponding to the frequency of the detection signal;
Capacitance detection means for acquiring the frequency of the detection signal that maximizes the output signal based on information stored in the storage means, and detecting the capacitance of the element based on information including the frequency;
A device characterized by comprising: The device according to claim 1, wherein the band rejection filter unit includes a coil and a capacitor. The apparatus according to claim 1, wherein the signal conversion unit includes a transimpedance circuit including an operational amplifier. An apparatus according to any one of claims 1 to 9, and a processing unit,
The device receives acoustic waves and converts them into electrical signals,
The object information acquisition apparatus, wherein the processing unit acquires information of an object using the electrical signal. A light source,
The object information acquiring apparatus according to claim 10, wherein the apparatus receives a photoacoustic wave generated when the object is irradiated with light from the light source and converts the photoacoustic wave into an electric signal. A method for detecting the capacitance of an element having a cell comprising: a first electrode; and a vibrating membrane including a second electrode formed with a gap from the first electrode,
Applying a detection signal for detecting a capacitance of the element to one of the first electrode and the second electrode;
A current signal generated at the other electrode of the first electrode and the second electrode due to vibration of the vibration film is a current signal generated at the other electrode due to vibration of the vibration film due to external action. Processing by a band rejection filter unit having a cutoff frequency in a frequency region outside the main band;
Converting the current signal processed by the band rejection filter unit into a voltage signal;
Changing the frequency of the detection signal in the vicinity of the cutoff frequency;
Storing information relating to the voltage signal corresponding to the frequency of the detection signal;
Obtaining a frequency of the detection signal that maximizes the voltage signal based on the stored information, and detecting a capacitance of the element based on information including the frequency;
A method characterized by comprising: Based on the amount of change in the capacitance of the element detected in the step of detecting the capacitance, the vibration is generated in the other electrode by the vibration of the vibration film due to an external action, and is processed by the band rejection filter unit. 13. The method according to claim 12, further comprising the step of correcting the converted voltage signal in the step of converting the current signal into a voltage signal. When detecting the current signal generated at the other electrode due to the vibration of the vibrating membrane due to an external action, the target value of the DC voltage determined based on the amount of change in the capacitance of the element is the first value. The method according to claim 12, further comprising the step of instructing application between the first electrode and the second electrode. When detecting the current signal generated at the other electrode due to vibration of the vibrating membrane due to an external action, a DC voltage is applied between the first electrode and the second electrode, 13. The method according to claim 12, further comprising a step of switching connection so that a detection signal for detecting the capacitance of the element is applied to the one electrode when detecting a change in capacitance. 15. The method according to any one of 14.