SI21242A

SI21242A - Optical fiber pressure sensor

Info

Publication number: SI21242A
Application number: SI200200150A
Authority: SI
Inventors: Edvard Cibula; Denis ĐONLAGIĆ
Original assignee: Feri Maribor
Priority date: 2002-06-13
Filing date: 2002-06-13
Publication date: 2003-12-31

Abstract

The optical fiber sensor solves the problem of implementing a pressure sensor, which is no wider than the standard optical fiber, this is 125 micrometer. The key element of the sensor is an elastic diaphragm, which is located inside the cavity at the end of the optical fiber. The measurement of the flexion of the diaphragm or pressure is based on the phenomena of interference of light between the diaphragm and the end of the optical fiber. The procedure of manufacture includes the etching of the end of the optical fiber and implementation of the diaphragm. A short section of a multimode optical fiber with a core having been etched by immersion into HF acid, is welded to the end of the monomode optical fiber. The thus provided end of the optical fiber is immersed into a solution of material, suitable for the manufacture of the diaphragm, dissolved in a suitable solvent. After withdrawal of the fiber from the solution a part of the solution in the shape of a droplet sticks to the fiber where as a result of evaporation it gradually becomes thinner. This way a thin diaphragm is created inside the recess at the end of the optical fiber.

Description

OPTIČNI VLAKENSKI SENZOR TLAKAOPTICAL FIBER PRESSURE SENSOR

Predmet izuma je senzor tlaka in postopek za izdelavo senzorja tlaka, ki se nahaja na koncu optičnega vlakna in ima premer, ki je manjši ali enak premeru optičnega vlakna. Konstrukcija senzorja omogoča realizacijo visoko občutljivega senzorja, primernega za merjenje nižjih tlakov.The object of the invention is a pressure sensor and a method for manufacturing a pressure sensor located at the end of an optical fiber having a diameter smaller than or equal to the diameter of the optical fiber. The construction of the sensor enables the realization of a highly sensitive sensor suitable for measuring lower pressures.

Tehnični problem, ki ga rešuje izum je realizacija občutljivega senzorja tlaka majhnega premera, primernega za vrsto aplikacij, pri katerih se zahtevajo majhne dimenzije senzorja in/ali električna pasivnost. Poleg tega omogoča uporabo biokompatibilnih materialov, kar je odločilnega pomena za področje medicine. Izum obenem rešuje problem visoke cene izdelave te vrste senzorjev in sicer zaradi enostavnega postopka izdelave in možnosti uporabe cenenih materialov.A technical problem solved by the invention is the realization of a sensitive small diameter pressure sensor suitable for a variety of applications requiring small sensor dimensions and / or electrical passivity. In addition, it enables the use of biocompatible materials, which is crucial in the medical field. At the same time, the invention solves the problem of the high cost of manufacturing this type of sensor, due to the simple manufacturing process and the ability to use cheap materials.

Znanih je nekaj izvedb optičnih vlakenskih merilnikov tlaka. Rešitev po patentu WO 02/23148 uporablja ohišje iz silicija, v katero sta pritrjena konec dovodnega optičnega vlakna in tanka silicijeva membrana. Gladko odrezan konec optičnega vlakna in membrana predstavljata dve reflektivni površini, ki tvorita t i. Fabry-Perot interferometer. Tukaj prihaja do razdelitve optičnega vala na dva dela, ki medsebojno interferirata. Njuna interferenčna vsota je odvisna od razdalje med koncem vlakna in membrano, kar je v osnovi merilo tlaka. Druge znane rešitve so po patentih EP 1 089 062, US 5657405, US 5381229 US 4991590 in WO 99/45352, ki se razlikujejo predvsem po izvedbi ohišja za membrano in optično vlakno. Vsem navedenim rešitvam je skupna značilnost omenjeno ohišje, ki pa je povsod večjega premera od optičnega vlakna. Edina znana rešitev, kjer je celoten senzor enak premeru optičnega vlakna je po patentu EP 0 997 721, le da je postopek izdelave zapleten in zahteva uporabo posebnih orodij in materialov.Some embodiments of optical fiber pressure gauges are known. The solution according to patent WO 02/23148 uses a housing made of silicon, to which is attached the end of the inlet optical fiber and a thin silicon membrane. The smoothly cut end of the optical fiber and the membrane represent two reflective surfaces that form t i. Fabry-Perot interferometer. This is where the optical wave is divided into two parts that interfere with each other. Their interference sum depends on the distance between the end of the fiber and the membrane, which is basically a measure of pressure. Other known solutions are those of EP 1 089 062, U.S. Pat. All of the above solutions are a common feature of the said housing, which is everywhere larger than the optical fiber. The only known solution where the entire sensor is the same as the diameter of the optical fiber is EP 0 997 721, except that the manufacturing process is complicated and requires the use of special tools and materials.

Po izumu je problem rešen s postavitvijo senzorja na konec optičnega vlakna in sicer znotraj samega vlakna. Izum bo opisan na izvedbenem primeru in slikah, ki prikazujejo:According to the invention, the problem is solved by placing the sensor at the end of the optical fiber inside the fiber itself. The invention will be described in the embodiment and in the drawings showing:

sl. 1 standardno enorodovno optično vlakno s privarjenim segmentom mnogorodovnega optičnega vlakna sl. 2 zjedkan konec optičnega vlakna sl. 3 Posamezne faze izdelave membrane znotraj optičnega vlaknaFIG. 1 shows a standard single-layer optical fiber with a welded segment of a multiple-layer optical fiber; 2 shows the etched end of the optical fiber; 3 Individual phases of membrane fabrication within an optical fiber

Priprava konca optičnega vlakna:Fiber optic end preparation:

Na enorodovno optično vlakno 1 (v nadaljevanju EOV), po katerem se prenaša svetloba od svetlobnega vira do senzorja in nazaj do detektorja je privarjeno mnogorodovno optično vlakno 2 (v nadaljevanju MOV) in odrezano na dolžini 10Ομηη od spoja 3. Varjenje je izvedeno z uporabo standardnega varilnika za optična vlakna in odrezano z rezalnikom za optična vlakna. Obe uporabljeni optični vlakni imata zunanji premer 125μιτι 4. Premer jedra EOV je 9pm 5. MOV ima stopnični lomni lik s premerom jedra okoli 60pm 6 in je izdelano s standardno tehnologijo za izdelavo optičnih vlaken, kjer je jedro dopirano z GeO₂. Masni delež GeO₂vjedru je okoli 40%.Single-mode optical fiber 1 (hereinafter referred to as EOV), after which light is transmitted from the light source to the sensor and back to the detector, is welded multi-fiber optical fiber 2 (hereinafter MOV) and cut to length 10Ομηη from junction 3. Welding is performed using standard optical fiber welder and cut with fiber optic cutter. The two optical fibers used have an external diameter of 125μιτι 4. The diameter of the EOV core is 9pm 5. The MOV has a stepwise fracture character with a core diameter of about 60pm 6 and is manufactured using standard fiber optic technology where the core is doped with GeO ₂ . The weight of GeO ₂ is about 40%.

Jedkanje konca optičnega vlakna:Optical fiber end etching:

Tako pripravljen konec optičnega vlakna je potopljen v 40%-no HF kislino, kjer pride do raztapljanja oz. jedkanja MOV. Ker je jedro optičnega vlakna dopirano z GeO₂, se le-to raztaplja bistveno hitreje kot obloga. Izmerjena hitrost jedkanja jedra z 40% masnim deležem GeO₂ MOV znaša okoli 7pm na minuto, obloge, ki jo sestavlja čisti SiO₂ pa 0,5μηη. Jedkanje poteka vse do spoja obeh optičnih vlaken, kjer pride do porasta reflektivnosti na meji vlakno-zrak z 0,01% na ca. 2%. Tolikšna reflektivnost je nujna za delovanje senzorja na osnovi interference svetlobe. Pomembno je, da se jedkanje prekine trenutku, ko je dosežen spoj obeh vlaken, sicer pride do poškodbe površine EOV na spoju in s tem do naglega padca reflektivnosti. V ta namen se med procesom jedkanja meri moč odbite svetlobe in ko ta doseže maksimum, se jedkanje prekine. Neposredno po jedkanju se konec vlakna potopi v alkohol, da se odstranijo ostanki HF kisline. Zjedkan konec vlakna z vdolbino 7 na čelni strani je prikazan na sliki 2.The optical fiber end thus prepared is immersed in 40% HF acid, where it dissolves. etching MOV. Because the fiber optic core is doped with GeO ₂ , it dissolves significantly faster than the coating. The measured etching rate of the core with 40% by weight of GeO ₂ MOV is about 7pm per minute and the coating consisting of pure SiO ₂ is 0.5μηη. The etching proceeds to the junction of the two optical fibers, where there is an increase in reflectivity at the fiber-air interface from 0.01% to ca. 2%. Such reflectivity is essential for the operation of the sensor based on light interference. It is important that the etching be interrupted at the moment when the joint of the two fibers is reached, otherwise the surface of the EOV at the joint is damaged and thus a sudden drop in reflectivity occurs. To this end, the power of reflected light is measured during the etching process and when it reaches its maximum, the etching is interrupted. Immediately after etching, the fiber end is immersed in alcohol to remove residual HF acid. The etched end of the fiber with recess 7 in the front is shown in Figure 2.

Izdelava membrane:Membrane production:

Pripravi se raztopina iz ustreznega materiala, kot so razni polimeri in poliuretani s primernimi mehanskimi lastnostmi za izdelavo membrane. Izbira materiala je odvisna od želene aplikacije, tako da membrana izpolnjuje zahteve glede natezne trdnosti, temperaturne obstojnosti ter za področje medicine pogoj biokompatibilnosti. Pomembna lastnost materiala za izdelavo membrane je med drugim dober oprijem na steklo oz. optično vlakno. Za primer izdelave membrane iz elastičnega poliuretana P-1190A se pripravi 5%-na raztopina tega poliuretana v topilu dimetil formamid (DMF) - 8. Zjedkan konec optičnega vlakna se nato vertikalno potopi v raztopino - 9. Po dvigu optičnega vlakna iz raztopine se del raztopine v obliki kapljice oprime vlakna - 10. Ker je na spodnji oz. zunanji strani kapljice parni tlak DMF manjši od tistega na zgornji strani t.j. znotraj vdolbine v optičnem vlaknu, DMF tukaj hitreje izhlapeva. Zaradi tega pride do tanjšanja spodnje strani kapljice, dokler se na zunanjem robu vdolbine vlakna ne ustvari tanka membrana - 11. Končna debelina membrane (in s tem njene mehanske lastnosti) je odvisna od hitrosti izhlapevanja topila. V ta namen je potrebno kontrolirati tako koncentracijo hlapov DMF kot temperaturo v okolici membrane.Prepare a solution of suitable material, such as various polymers and polyurethanes, with suitable mechanical properties for the manufacture of the membrane. The choice of material depends on the application desired, so that the membrane meets the requirements of tensile strength, temperature resistance and biocompatibility condition for the field of medicine. An important feature of the membrane fabrication material, among other things, is its good adhesion to the glass and / or glass. optical fiber. For the manufacture of a membrane of elastic polyurethane P-1190A, prepare a 5% solution of this polyurethane in solvent dimethyl formamide (DMF) - 8. The etched end of the optical fiber is then immersed vertically in the solution - 9. After lifting the optical fiber from the solution, part solutions in the form of a drop of fiber grip - 10. Because it is at the bottom or. on the outside of the droplet the DMF vapor pressure is less than that on the upper side i.e. inside the well in the optical fiber, the DMF evaporates here faster. This causes thinning of the underside of the droplet until a thin membrane is formed at the outer edge of the fiber well - 11. The final thickness of the membrane (and thus its mechanical properties) depends on the rate of evaporation of the solvent. For this purpose it is necessary to control both the DMF vapor concentration and the temperature around the membrane.

Claims

Optical fiber pressure gauge, characterized in that it consists of a single inlet fiber (1) extending into a short cylindrical element (2) with an inside diameter between 10 and 200pm (6), an outer diameter between 80 and 300pm (4). ) and a length of 10 and 300gm (3) and a polymeric membrane attached to the end of the cylindrical element (11).

A method for manufacturing an optical pressure gauge according to claim 1, characterized in that a short segment of the multipart optical fiber (2) is welded to a single-optical fiber (1) followed by etching in HF acid.

A method for manufacturing an optical pressure gauge according to claim 1, characterized in that the center of the multipart optical fiber is etched in HF acid to the junction of the single and multipart optical fiber.

A method for manufacturing an optical pressure gauge according to claim 1, characterized in that a solution (8) of the membrane material in a suitable solvent is used in which the etched end of the optical fiber is immersed and oriented vertically downwards (9); that after extraction of the fiber, a portion of the droplet solution adheres to the end of the fiber (10), where, due to the faster evaporation of the solvent on the lower (outer) side of the droplet, its thinning occurs by creating a thin membrane inside the recess at the end of the optical fiber ( 11).

5. Multiple-fiber optical fiber, characterized in that it has a step or gradient fracture pattern, a core diameter of between 10 and 200pm, an outer diameter of between 80 and 300pm and a length of 10 and 300pm.