(A) ;ULTRASONIC PENETRATING DEVICE

摘要

1530997 Analysis by optical methods MONSANTO CO 10 Nov 1975 [11 Nov 1974 26 Sept 1975] 46349/75 Heading G2J [Also in Division G1] The presence and/or quantity of a first material is detected and/or determined by observing the change in optical transmission of a waveguide whose critically reflective surface bears a reagent specifically reactive to said first material. Many examples are given (i) An optical fibre was coated in polyvinyl alcohol containing sodium picrate. Exposure to CN- (e.g. aqueous NaCN or gaseous HCN) changed the transmittance of the waveguide. Adsorbed water in the coating affected the results but could be compensated for by monitoring water adsorbtion in white light and correcting for it in measurements taken in green light (the green being complementary to the coloured (red-brown) product of reaction of picrate with CN-). Alternatively the waveguide was thoroughly dried before each measurement. (ii) NH 3 detected by reaction with coating containing Fe 2 (SO 4 ) 3 # violet Fe 2 (SO 4 ) 3 À(NH 4 ) 2 SO 4 . (iii) Antigen on fine polystyrene (latex spheres adhered to a waveguide coated with specific antibody. The adhered spheres affected the light transmitting properties of the waveguide (iv) CO 2 detected by a coating containing sodium carbonate/bicarbonate bulks and methyl red (v) SO 3 detected by a coating containing BaCl 2 (vi) Phosgene detected by a coating pdimethyl amino benzaldehyde with dimethyl aniline or p-nitrobenzylpyridine and N-benzylaniline. (vii) Tolylene diisocyanate detected by a coating containing p-dimethylaminobenzaldehyde and acetic acid (viii) SO 2 detected by a coating containing p-phenylenediamine and formaldehyde, or iodine and starch, or potassium tetrachlormercurate with pararosaniline and formaldehyde. A suitable optical arrangement is shown in Fig. 2. Light from lamp 1 is condensed by arrangement 2 and passed through a selectable filter 3. After reflection from a 45 degrees mirror an annular aperture 4 transmits a cylinder of rays which is condensed by optics 5 to a hollow cone of rays which is conducted into the waveguide via a hemisphere and central aperture 6. A detector 8 controls an operational amplifier 9 which drives a digital voltmeter 10. Arrangement 7 supports the waveguide with minimal surface contact. The critical reflective surface of the waveguide may be that between the reactive coating and the case, in which case the sensitivity is low due to only the evanescent waves being affected. Alternatively, if the refractive index of the coating exceeds or equals that of the cone, the coating/air boundary is the critical surface and sensitivity is high.