PL214327B1 - Photoacoustic chamber - Google Patents

Description

(21) Filing Number: 386945 (51) Int.Cl.

G01N 21/17 (2006.01) G01N 29/00 (2006.01)

Patent Office of the Republic of Poland (22) Application date: 29.12.2008 (54)

Photoacoustic chamber

(73) The right holder of the patent: WARSAW UNIVERSITY OF TECHNOLOGY, (43) Application was announced: Warsaw, PL 05.07.2010 BUP 14/10 (72) Inventor (s): TOMASZ STARECKI, Zalesie Górne, PL (45) The grant of the patent was announced: 31.07.2013 WUP 07/13 (74) Representative: item. stalemate. Krystyna Lewińska

PL 214 327 B1

Description of the invention

The subject of the invention is a photo-acoustic chamber, which is an element of photo-acoustic devices intended especially for determining the physical and chemical properties of gases or liquids.

Many different types of photoacoustic measurement chambers are known. One of the frequently used solutions of the photoacoustic measuring chamber is the Helmholtz resonator, which consists of two cavities connected by a channel. An important feature of such a chamber is that the resonance used in it does not arise on the basis of the standing wave phenomenon, but is related to the cyclic pumping of gas or liquid through the channel connecting the cavities. From the patent application P.380367, a design of a windowless photoacoustic chamber is known, in which the amplification of the photoacoustic signal takes place in a Helmholtz resonator consisting of a cavity with the tested substance, a microphone cavity and a channel connecting them. On the opposite sides of the cavity with the test substance there are through-going channels coaxially located. A properly collimated light beam used to excite a photoacoustic signal in a cavity with the test substance passes through one of the passage channels, the cavity with the test substance and the other passage, without encountering any windows or other elements absorbing or reflecting the light beam. Consequently, no parasitic photoacoustic signals arise due to light absorption by the windows or other elements of the chamber. A significant disadvantage of the known solution, however, is that the acoustic disturbances occurring outside the chamber relatively easily penetrate its interior through the passage channels, disturbing the photoacoustic signal produced and measured therein, and consequently limiting the measurement sensitivity of such a non-windowless photoacoustic Helmholtz chamber.

The essence of the invention is that acoustic filters are attached to the passage channels of the cavity with the tested substance, consisting of buffer cavities connected to the passage channels with volumes much larger than the volume of the cavity with the tested substance, and external channels located coaxially with the passage channels, connecting the buffer cavities with the tested substance. surroundings. The length of the external channels is selected so that at the frequency on which the light beam used to induce the photoacoustic effect is modulated, it corresponds to 1/4 of the acoustic wave length generated in the substance to be tested, preferably gas or liquid, filling the chamber.

With the length of the external channels selected in this way, the acoustic impedance of these channels, seen from the outside of the chamber, is very high. Thus, the penetration of external acoustic disturbances into the chamber interior is significantly reduced.

The advantages of the photoacoustic chamber according to the invention are the absence of parasitic photoacoustic signals from the absorption of light through the windows, walls or other elements of the chamber and, at the same time, a strong suppression of the penetration of external acoustic disturbances into the chamber.

The subject of the invention is presented in the embodiment in the drawing which shows the photo-acoustic chamber.

In the embodiment shown in the drawing, the outer channels 1 are arranged coaxially with the through-channels 2. A suitably collimated and modulated light beam 3 passes successively through the outer channel 1, the buffer cavity 4, the through channel 2, the cavity with the test substance 5, and then through the second channel passage 2, buffer cavity 4 and outer channel 1. Thus, the light beam 3 passes through the entire chamber and the test substance therein, preferably liquid or gas, without encountering any obstacles, in particular windows or other light transmitting or reflecting elements and thus without causing parasitic photoacoustic effects, and passing through the cavity 5 with the substance to be tested, the light beam 3 causes excitation of a photoacoustic signal, the amplitude of which is then measured by means of a microphone 6 placed in the microphone cavity 7. The length of the external channels 1 is chosen such that it corresponds to 1/4 of the wavelength of the excited acoustic wave j in the substance filling the chamber at the frequency with which the beam 3 of the light used to excite the photoacoustic effect is modulated.

PL 214 327 B1

Claims (1)

Patent claim A photoacoustic chamber in the form of a Helmholtz resonator, for amplifying the photoacoustic signal, containing cavities connected with a channel filled with the tested substance, while one cavity has in opposite walls opposite to each other coaxial through-channels, characterized in that the cavities with the tested substance (5) are connected to the through-channels (2) acoustic filters are included, consisting of buffer cavities (4) attached to the through channels (2) with volumes much larger than the volume of the recess (5) with the test substance and external channels (1) located coaxially with the through channels (2), connecting the cavities buffer (4) with the environment, and the length of the external channels (1) is selected so that at the frequency at which the beam (3) of the light used to induce the photoacoustic effect is modulated, it corresponds to 1/4 of the acoustic wavelength generated in the tested substance preferably a gas or liquid filling the chamber.