PHOTOACOUSTIC SPECTROSCOPY DETECTOR AND SYSTEM

• US 20090229345A1
• Filed: 02/22/2006
• Published: 09/17/2009
• Est. Priority Date: 03/04/2005
• Status: Abandoned Application

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Van Kesteren, Hans Willem
• Application Number:
  US11/817,042
• Publication Number:
  US 20090229345A1
• Time in Patent Office: Days
• US Class Current: 73/24.20
• CPC Class Codes: G01N 2021/1704 in gases
• CPC Class Codes: G01N 2021/1708 with piezotransducers
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• CPC Class Codes: G01N 29/2425 optoacoustic fluid cells therefor
• CPC Class Codes: H04R 17/02 Microphones
• CPC Class Codes: H04R 23/008 using optical signals for detecting or generating sound

Abstract

An acoustic detector (10), for detecting acoustic signals generated in a photoacoustic spectroscopy system (1) through absorption of light by a fluid, comprising a sensing unit (11), said sensing unit (11) exhibiting structural resonance at or near a frequency of the acoustic signals. The sensing unit (11) forms at least part of a cavity resonator, which is arranged to enable a formation of standing pressure waves inside said cavity resonator at a cavity resonance frequency substantially coinciding with a structural resonance frequency of the sensing unit (11). The present invention is based on the realisation that an enhanced sensitivity of an acoustic detector in a PAS-system can be obtained by forming the acoustic detector as a cavity resonator with dimensions chosen so that the cavity resonance of the detector cooperates with the structural resonance of the sensing unit comprised in the detector, thereby achieving optimal amplification of the acoustic signals generated in the PAS-system.

Claims

1. An acoustic detector (10), for detecting acoustic signals generated in a photoacoustic spectroscopy system (1) through absorption of light by a fluid, comprising a sensing unit (11), said sensing unit (11) exhibiting structural resonance at or near a frequency of the acoustic signals,

characterized in that the sensing unit (11) forms at least part of a cavity resonator, which is arranged to enable a formation of standing pressure waves inside said cavity resonator at a cavity resonance frequency substantially coinciding with a structural resonance frequency of the sensing unit (11).

2. A detector (10) according to claim 1, wherein the sensing unit (11) comprises a piezo-electric material, such as quartz.

3. A detector (10) according to claim 1, wherein the sensing unit (11) comprises a tube (12;

21;

31), having inner dimensions adapted to enable cavity resonance in a cavity formed by the detector (10) at a frequency substantially coinciding with a structural resonance frequency of said tube (12).

4. A detector (10) according to claim 3, wherein said structural resonance frequency is a breathing mode eigenfrequency for said tube (12).

5. A detector (10) according to claim 3, wherein said tube (21) comprises at least one slit (22a, 22b) in an envelope of the tube (21), said slit (22a, 22b substantially extending in an axial direction.

6. A detector (10) according to claim 3, wherein said tube (31) is divided in the axial direction into at least two segments (33a, 33b), held together by connecting means (32a, 32b) and said connecting means comprise bridges (32a, 32b) formed between the segments (33a, 33b).

7. A detector (10) according to claim 1, wherein the sensing unit (11) is a tuning fork (50;

60) with two prongs (52a, 52b;

62a, 62b) attached to a base (53;

61).

8. A detector (10) according to claim 7, wherein the prongs (62a, 62b) of said tuning fork (60) are configured to form cavity (63) between said prongs (62a, 62b), said cavity (63) having dimensions which are adapted to enable cavity resonance of the detector (10) at a frequency substantially coinciding with a structural resonance frequency of said tuning fork (60).

9. A detector (10) according to claim 7, further comprising a cavity-forming member (54), said member being arranged to enable the formation of a cavity (51), bounded by the cavity-forming member (54) and the prongs (52a, 52b) and base (53) of said tuning fork (50), said cavity (51) having dimensions which are adapted to enable cavity resonance of the detector (10) at a frequency substantially coinciding with a structural resonance frequency of said tuning fork (50).

10. A detector (10) according to claim 1, wherein the sensing unit (11) is formed as an open-ended box (70), having dimensions which are adapted to enable cavity resonance of the detector (10) at a frequency substantially coinciding with a structural resonance frequency of said open-ended box (70).

11. A detector (10) according to claim 10, wherein two sides (71a, 71b) of said open-ended box are made of a piezoelectric material, said sides (71a, 71b) facing each other and being held together by two passive elements (72a, 72b) facing each other.

12. A detector (10) according to claim 11, wherein said passive elements (72a, 72b) of said open-ended box (70) are configured to form an essentially tube-shaped cavity (75) between said them.

13. A detector (10) according to claim 1, further comprising signal enhancing means (82a, 82b), said signal enhancing means (82a, 82b) being arranged to co-operate with said sensing unit (11) to form a cavity resonator having dimensions which are adapted to enable cavity resonance of the detector (10) at a frequency substantially coinciding with a structural resonance frequency of said sensing unit (11).

14. A photoacoustic spectroscopy system (1), comprising a light source (4), an acoustic detector (10) according to claim 1 and an output device (34) configured to display information from the detector (10) to a user.