Detecting device for detecting photoacoustic elastic waves
A detecting device 100 detects an elastic wave propagating through the air. The detecting device 100 includes: a first electrode 12 that is a plate having a cantilever structure with a fixed end FX and a free end FR and that vibrates by being bent by the elastic wave; and a second electrode 32 that is a plate, that is opposed to the first electrode, and that has a predetermined distance from the first electrode. The detecting device 100 detects the elastic wave on the basis of a change in capacitance between the first electrode and the second electrode 32 . An end of the second electrode 32 in a direction from the fixed end FX to the free end FR is closer to the fixed end than the free end.
1. A detecting device, comprising:
a light source configured to irradiate a target with light; and
a detector configured to detect a photoacoustic elastic wave propagating through air, the photo-acoustic elastic wave being generated by the target irradiated with light from the light source;
the detector comprising:
a first electrode that is a plate including a cantilever structure with a fixed end and a free end and that is configured to vibrate by being bent by the photoacoustic elastic wave; and
a second electrode that is a plate, that is opposed to the first electrode, and that has a predetermined distance from the first electrode, wherein
the detector is configured to detect the photoacoustic elastic wave on a basis of a change in capacitance between the first electrode and the second electrode,
an end of the second electrode in a direction from the fixed end to the free end is closer to the fixed end than the free end.
2. The detecting device according to claim 1 , further comprising:
a first electrode layer;
an insulation layer that includes insulator material and that is in contact with the first electrode layer; and
a second electrode layer that is in contact with the insulation layer on the opposite side of the first electrode layer, wherein
the first electrode layer comprises the first electrode and a first support configured to support the first electrode,
the second electrode layer comprises the second electrode and a second support configured to support the second electrode,
the fixed end of the first electrode is coupled to the first support,
a portion of an end of the first electrode except for the fixed end is spaced apart from the first support,
the insulation layer includes a first penetrating hole configured to open at a portion opposed to the first electrode, and
the second electrode layer includes a second penetrating hole configured to open at a portion that is opposed to the first electrode and that is closer to the free end than the second electrode in the direction from the fixed end to the free end.
3. The detecting device according to claim 1 , wherein
the second electrode comprises a plurality of penetrating holes.
4. The detecting device according to claim 1 , wherein the light is either of a pulsed light or a laser light.
5. The detecting device according to claim 1 , wherein oscillation cycle of a pulsed light or a laser light is set to correspond to a resonance frequency of the first electrode.
6. The detecting device according to claim 1 , comprising:
a body that includes an inner space being in contact with the detector and an opening being communicated with the inner space.
7. The detecting device according to claim 6 , wherein
the body has a vent through which the light generated by the light source passes.
8. The detecting device according to claim 7 , wherein
the vent is located at the same side as the detector with respect to the inner space.
9. The detecting device according to claim 7 , wherein
the inner space includes a base and a pipe configured to communicate the base with the opening; and
at least part of the pipe extends along a straight line connecting the vent to the opening.
10. The detecting device according to claim 7 , wherein further comprising an irradiation controller configured to control a position irradiated with the generated light to each of a plurality of positions being different from one another.
11. The detecting device according to claim 6 , wherein
the body includes a diaphragm that is vibratably provided on a wall of the inner space, and
the detecting device further comprises:
a second detector that has a frequency band of a detectable photoacoustic elastic wave wider than that for the detector serving as a first detector, configured to detect an photoacoustic elastic wave propagating through air, and that is in contact with the inner space; and
a vibration controller configured to control vibration of the diaphragm on the basis of a result of the detecting by the second detector.
12. The detecting device according to claim 6 , wherein
the body includes a shape such that a resonance frequency of Helmholtz resonance in the inner space matches with a resonance frequency of the first electrode.
13. The detecting device according to claim 6 , wherein the light source is configured to generate light beams comprising respective different wavelengths, and
wherein the detecting device is configured to detect a plurality of photoacoustic elastic waves respectively generated by irradiations with the light beams and detects an photoacoustic elastic wave generated by the target on the basis of a result of the detecting.
14. A detecting device, comprising:
a light source configured to irradiate a target with light;
a plurality of detectors configured to detect a photoacoustic elastic wave propagating through air, the photoacoustic elastic wave being generated by the target irradiated with light from the light source;
the detectors each comprising:
a first electrode that is a plate including a cantilever structure with a fixed end and a free end and that vibrates by being bent by the photoacoustic elastic wave; and
a second electrode that is a plate, that is opposed to the first electrode, and that has a predetermined distance from the first electrode, wherein
each detector is configured to detect the photoacoustic elastic wave on a basis of a change in capacitance between the first electrode and the second electrode, an end of the second electrode in a direction from the fixed end to the free end being closer to the fixed end than the free end; and
processor circuitry configured to estimate a position of a wave source of the photoacoustic elastic wave on the basis of a time period from a time point at which the light is generated to a time point at which each of the plurality of detectors is configured to detect the elastic wave.
15. The detecting device according to claim 14 , further comprising an irradiation controller configured to control a position irradiated with the generated light to each of a plurality of positions being different from one another.
16. The detecting device according to claim 14 , wherein the light source is configured to generate light beams having respective different wavelengths, and
wherein the detecting device is configured to detect a plurality of photoacoustic elastic waves respectively generated by irradiations with the light beams and is configured to detect an photoacoustic elastic wave generated by the target on the basis of a result of the detecting.