JPS59136638A - Optoacoustic analyzer - Google Patents

Abstract

PURPOSE:To enable measurement of a phenomenon having a short time constant, such as the process of the heat emission from a sample, by measuring the optoacoustic effect utilizing a high optical modulating frequency at good S/N ratio. CONSTITUTION:A measuring method for the grain size distribution of suspended particles in a suspension is exampled as below. A suspension of Zr powder having a central grain size of 5mum is fed into a measuring cell having 11mm. inside diameter and 50mm. length through a sample inlet 1 thereof and Ar laser light of an output 1W is made incident to the same through an optical window 3. An oscillator is used to oscillate the laser light which is moudlated to pulse light by an acoustooptic modulator. The optoacoustic signal generated in the cell is detected with a cylindrical piezo-electric element 4 and is inputted from a signal taking out terminal 5 to a lock-inamplifier by means of a conductor. The intensity and phase of the optoacoustic signal are measured by the lock-in amplifier. The light modulating frequency characteristic (solid line) of the intensity of the optoacoustic signal and the light modulating frequency characteristic (broken line) of S/N ratio are thus obtd. The measurement in this case necessitates simply the use of the optical modulating frequency of a peak P4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a photoacoustic analyzer, and particularly to a photoacoustic analyzer suitable for measurements using high optical modulation frequencies.

[Prior art]

The photoacoustic tube signal has the tendency to attenuate as the optical modulation frequency increases (
Ho? Conventional photoacoustic analyzers use optical modulation frequencies as low as possible because of the
It has the disadvantage of being easily susceptible to mechanical vibration noise. In addition, because conventional photoacoustic analyzers use a low optical modulation frequency,
It was difficult to measure fast transient phenomena such as the heat release process of the sample.

[Purpose of the invention]

An object of the present invention is to provide a photoacoustic analyzer that generates a photoacoustic signal that has high-frequency optical modulation frequency characteristics and is strong enough for measurement.

[Summary of the invention]

The optical modulation frequency characteristics of the photoacoustic signal include an electrical resonance peak of the detector, a structural resonance peak of the cell, a resonance peak of the photoacoustic wave, and the like. These peaks are usually around 10kHz
It often appears in the optical modulation frequency region above z. In this region, for optical modulation frequencies other than resonance and resonance peaks, 7
Therefore, the photoacoustic signal is small and is rarely detected. However, at the peak, the photoacoustic signal is enhanced by more than 102 times and becomes strong enough for detection.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be fully explained with reference to FIGS. 1 to 4. This example is an example in which the present invention was fully applied to a method for measuring the size distribution of suspended particles in a suspension. FIG. 1 shows a measuring cell with an inner diameter of 111 mm and a length of 50 mm used for measurement. A suspension of zirconium powder having a center particle size was injected into a sample population of 1 x 5 μm in a measurement cell, and argon laser light with an optical output of IW was totally incident on it through the optical window 3. The argon laser beam uses all 488 nm oscillation lines and is modulated into pulsed light by an acousto-optic modulator. A photoacoustic signal generated within the cell is detected by a cylindrical rlEl current collector 4 and inputted to a lock-in amplifier via a signal output terminal 5 via a conductive wire. A lock-in amplifier measures the intensity and phase of photoacoustics (M number).

FIG. 2 shows the optical modulation same wavenumber characteristic (solid line) of the photoacoustic signal intensity and the optical modulation frequency characteristic (broken gl) of S/N measured with this analysis cell. In FIG. 2, the peak 1 at 10 kHz and the peak P2 at 20 kHz are the structural resonance of the cell, and the peaks at 40 kHz and 80 kHz are resonance peaks due to the electrical resonance of the piezoelectric element. These peaks were measured and identified using a force oscillator and an impedance meter for the cell, and it was found that the peak P, l-, which appeared at 150 kHz was the peak associated with the cavity resonance of the photoacoustic wave. be. From the optical modulation frequency characteristics of the photoacoustic signal strength and S/N, it can be seen that the optical modulation frequency of peak P4 can be used to measure the high frequency optical modulation frequency characteristics.

In the optical modulation frequency region below 400Hz, the photoacoustic signal strength is strong, but it is easily affected by external vibration noise, and S/
N is not good.

Below, 400Ffz, 60kHz, 80kHz
An example of particle size distribution measurement using f is shown. Particle size distribution of the zirconium suspension used as a sample) is shown in Figure 3. On the other hand, as a result of measuring the entire phase spectrum of the photoacoustic signal,
As shown in the figure. The phase spectra in Figure 4 are 8-80, respectively.
Compatible with kHz, 9-60kHz, 10-400Hz. In the 400Hz spectrum 9, when the sample releases heat 1
Since 1JI is sufficiently fast compared to the time width of the optical pulse, it does not reflect the particle size distribution shown in FIG. Unfortunately, in spectrum 10 of 60kHz, the signal level is low and good measurement results cannot be obtained. On the other hand, 8
In spectrum 8 of (lkl(z), the particle size distribution shown in FIG. 3 was well reflected, and 8/N was also 10 or more, which was a good measurement result 2.

According to this example, by utilizing the 8 flkHz electrical resonance of the piezoelectric element, it is possible to measure the particle size distribution of suspended particles with a center of 5 μm, and the S/N ratio is also as good as 10. You can get great results.

〔Effect of the invention〕

According to the present invention, the photoacoustic effect using a high optical modulation frequency can be measured with a good S/N ratio, making it possible to measure phenomena with short time constants such as the heat release process of a sample.

[Brief explanation of the drawing]

FIG. 1 (d) is a perspective view of a photoacoustic analysis cell according to an embodiment of the photoacoustic analysis cell of the present invention, and FIG. , Fig. 3 Particle size distribution of the zirconium suspension in Fig. 1 Fig. 2 (7, 1, Fig. 4 is an explanatory diagram of the phase spectrum of the photoacoustic signal of the second meat. 1... sample population, 2... ...Sample exit, 3...Optical window, 4...Piezoelectric element (ceramics), Signal output line, 6...Photoacoustic signal, 7...S/N 0 Hole 1 Figure 2 Figure 0-1 1 ro to.

Claims (1)

[Claims] 1. In a photoacoustic analyzer consisting of a light source, a light modulator, a measurement amplifier, a recording needle, etc., it is used for light modulation frequencies near the resonance frequency such as the natural frequency of the detector or the electrical resonance frequency. A photoacoustic analyzer featuring: