Title of Invention

A NON-DESTRUCTIVE MOISTURE SENSOR

Abstract

A non-destructive moisture sensor is provided which comprises a microwave generator, a microwave detector and a microstrip resonator connected between the said microwave generator and the microwave detector. The output from the microstrip resonator is connected to a microprocessor through an interfacing circuit consisting an amplifier to obtain an output corresponding to the normalised percentage of moisture in the material to be tested. A display is provided for displaying the output from the processor.

Full Text

This invention relates to a non-destructive moisture sensor for deteraining the moisture in biological materials or synthetic materiais Determination of moisture in various types of biomaterials such as papers, leaves of tea. tobacco etc. and other natural or synthetic naterials like rubber, polymer etc, have become very important in characterizing such materials before use in various applications, Absorbed moisture often becomes detrimental to the end properties of the product made from them and make them unsuitable for the application they are made. For example excessive moisture content in paper is undesirable because it may lead to fungal infections. On the other hand if the moisture content is too low, the paper become brittle. The critical moisture content in other materials like tea leaves, tobacco leaves are also important. Thus moisture is an important factor in maintaining quality, both in preventing spoilage and as controlling intrinsic property such as taste and smell of oertain products. Similarly, insulation is severely affected by the moisture content in the atmosphere, especially in humid places where the relative humidity is greater than 80% in all seasons through out the year. Determination of moisture content in material used for insuiation is very important. Out of the various methods of moisture determination. the gravimetry is taken as the standard one, wherein the moisture content is estimated by heating at about 100°C for twenty-four hours and estimating the difference in weight due to the moisture content. This method is specified by American Society of Agricultural Engineers (ASAE) Standards. But the loss of weight is not always exclusively due to moisture alone. Any other volatile matter such as solvent or hydrooarbon oils, which will volatilize at a temperature equal to or less than the heating temperature will cause an error in the estimation of moisture content. Radio frequency CRF) methods of measurement are known for the determination of moisture content. Two types of RF measurements are in use. One of the methods measures the complex impedance of a parallel plate capacitor with the material whose moisture to be determined being kept between the plates. The measurement is carried out in two frequencies to minimize the effect of shape and weight of the material. The impedance of the parallel plate capacitor is a function of the complex dielectric constant e -e-t + jeo of the material kept in-between, in which is the real part and 2 is the immaginary part of the dielectric constant. The capacitance C is a function of dielectric constsnt of the material. The value of C will increase as the moisture content in the material increases. Similarly differences in sre reflected in tangent of loss angle of the tjapaeitor. The value of C is calibrated in terms of percent of moisture present in the material. This method is also used for measuring moisture content in biomaterials. (Moisture determination in single grain kernels and nuts by RF impedance meaeurementB" by S.O.Nelson, C.V,K.Kandala, R.C.Lawrence in IEEE Transactions on Instrumentation and Measurement, 41. 1992, pg.no.1027-1031 and US patent no.4259632). Uince these sensors use RF field, they are sensitive to the ionic conductivity of the material and therefor there is a possibility of inherent errors. Another method, which is widely used for determining moisture content in materials is based on infra-red absorption in materials. Mainly two types cf instruments are used based on this principle. One is the "Moisture Balance . As the name suggests, it is a balance to weigh the moist sample. It has a built in IR lamp, which dries the sample, till it is completely dried. This dry sample is again weighed to get the final dry weight. The difference between the two weights gives the moisture content in the material. It has the same problem as indicated in the standard gravimetric drying method. It is a destructive and time-consuming technique. Moreover its response time is not fixed, as the time required for drying different materials are different. ^ Another raost commonly used instrument is an on-line near infrared analyser. The material in a sheet form is irradiated with two different IR wavelengths. one having a wavelength A nois with high absorption and the other having a wavelength A ref with very little absorption in a moist material. The transmission is measured at these two wavelengths P\ mois and A ref and the moisture in the material is computed from these measured signals, which give percentage of moisture present in the material. (US patent no.4345150). Though this method has low response time and can be used for on-line measurements, it suffers from the disadvantage that the measurements using IR radiation are affected by environmental conditions like dust and humidity. Also it is necessary to oool the detector during measurements. Microwave can be used as a powerful tool detection of moisture in bio/synthetic materialB like papers, leaves, rubber etc. Various moisture meters are known using microwave. Some of these make use of cranked hollow wave-guide as disclosed in US patent no.3628135. The mutually opposed channel-section wave¬guide portions are adapted to provide a slot between them to receive in the form of a sheet. If the moisture content in the oaterial is more, the absorption of microwave power in the sheet will be more and hence transmittd power will be less. The transmitted power is calibrated in terms of percentage noisture content present in the material. Some other type of moisture meter uses a microwave cavity. The instrument provides a cavity resonator made up of a pair of metai box sections with a gap interposed in-between, which allows the material in the form of a sheet to pass through. The percentage moisture content of the material is measured by detecting the variable reasonant voltage and weight of the material as disclosed in US patent no,4298774. Another type of microwave moisture indicator and control device uses transmitter and receiver horn antennas mounted on the same side of the material whose moisture content is to be measured. A portion of the transmitted modulated wave signal is reflected by the material, which is received by the receiver horn. The microwave detector in the base of the receiver horn detects the reflected microwave signal and produces a sine wave output. the amplitude of which is inversely proportional to the amount of moisture present in the material (US patent no.4399403). Still another method of determining moisture content in materials uses parabolic reflectors instead of horn antennas. The material whose moisture content is to be measured is kept between two such reflectors. The amount of microwave power absorbed by the material is governed by moisture to a major extent. The microwave detector produces an output signal which provides the amount of moisture present in the material. (U.S. no.4156843) . 6 All these methods suffer from one major disadvantage that they sre bulky. Moreover the minimum size of the material for measuring the moisture content should be at least more than the antenna aperture. cross-section of wave-guide or cavity slot to avoid error. One mora method used for measuring the moisture content in materials having moisture content in excess of 50% uses the dielectric wave-guide. The wave-guide is either embedded into a wail of a process pipe or it may pass through the pipe. A microwave frequency is chosen for the microwave signal to travel mainly inside the guide and reflect preferably at least ten times from the interface between wave-guide and the material. The output signal strength measured is proportional to the moisture content in the material (US patent no.4755743). The limitations of this method is that the moisture content of more than 50!K only can be measured and the geometry of the sensor assembly is fixed. Yet another varient of microwave moisture sensor uses stripline arrangement in which the sensor is inserted in the bulk of a penetrable material. The amount of microwave radiation absorbed in the bulk material is dependent on its moisture content. The detector detects the change in the signal received which is calibrated in terms of moisture content in the material. (US patent no.4991915>. The limitation of this method is that, it is useful only for penetrable bulk material and the size of the sensor cannot be small. "ioKie miniaturised microwave noistur© sensors use wicrostripline. A Bicrostripline is connected to receive microwave signal at one end and a detector is connected at its other end. A flowing sa»pie such as cereal contacts only the surface. The connected detector neasures the power level after absorption by the flowing sanples, which is calibrated in terns of moisture content in the sanple. (US patent no,4104564) . However just use of microstripiine alone cannot have full advantage unless proper microstripline circuit configuration is envisaged, To achieve better sensitivity and accuracy microstripline resonator have been used as a. probe to estiiiate moisture in bio/synthetio materials. The material to be tested can be loaded easily on the microstrip resonator without connecting or d isconnecting the microstrip resonator from the remaining system. Thus the method imposes no restriction regarding the shape and size of the aiaterial to be tested. When material is overlaid on microstrip resonator the resonating frequency sheet and it cannot be used to neasure moisture content of less than tJ0% . The strip line aioisture neters cannot be used for moisture ceasurements in the materials which are not bulk or penetrabie. The microstripline moisture meter known in the art is suitable for only flowing ob.iects like cereals. Since the system is not using resonant measurements, the sensitivity and accuracy of the system will be low, To improve the sensitivity and accuracy and to achieve miniaturization, the invention proposes a non destructive moisture sensor with a microstrip line resonator. The f and Qr. measurements with the moisture sensor according to the invention provides good sensitivity and accuracy. • in order to bring down the cost and overcoioe the difficu 1 ty in calibrating the moisture sensor according to the invention uses a microstrip resonator sensor element as a moisture probe at a single frequency to estimate the moisture in bio/synthetic materials in the form sheets. Th material to be tested is loaded easily, without disconnecting the nicrostrip resonator from the main system. Horever the sensor imposes no restriction on shape and size of the sample. The microstrip resonator sensor element 13 fabricated on a dielectric substrate such as alumina. First the substrate is thoroughly cleaned and then it is metallized on both sides by a conducting metal. A nicrostrip resonator pattern is delineated using photolithography and chemical etching. The generated pattern is characterised for transmitted power at s single frequency, The bio/synthetic material whose moisture content is to bo measured is overlaid on the nicrostrip resonator. The bio/synthetic material nay be in direct contact with the microstrip resonator or there nay be a small constant gap between the resonator and th© overlaid material. If the moisture content is more, power absorbed in the material is more and hence less power is transmitted. The transmitted power is measured at a predetermined single frequency. This transmitted power is further given to the electronic circuitry, the output of which is calibrated in terns of percentage of moisture content in the material. Thus this technique overcomes aii the disadvantages of the Boistur© sensors known in the prior art. Since the neasureeents are done using microwave, all the inherent errors of the other measurement techniques using IR, RF etc are eliminated. There is no limitation on the size and shape of the sample in contrast to the microwave devices like slotted wave-guides/cavities or antennas. Horeover moisture measurements using slotted cavity requires a costly saw-tooth generator and a voltage controlled oscillator which are not needed for the moisture sensor according to the invention. This sensor can be used for neasurenent of moisture in the whole range of interest, in contrast to the microwave dielectric sensor, which measures moisture content only above 50%. The test materials may be in direct contact with the microstrip resonator or there can be a small constant gap between the microstrip resonator and the test material. Since resonant circuit is used for moisture measurements, the sensitivity and accuracy is bound to be more compared to the moisture sensor using only microstrip line. Thus the invention provides a non-destructive moisture sensor comprising a microwave generator, a microwave detector and a microstrip resonator connected between the said microwave generator and the microwave detector, the output from the nicrostrip resonator being connected to a Kicroprocessor through an interfacing circuit consisting an amplifier to obtain an output corresponding to the normalised percentage of moisture in the material to be tested and a display for displaying the said output from the processor. / The minrastrip resonator can be preferably a ring resonator or a straight line resonator. The invention will now be described with reference to the accompanying drawings. Fig. 1 shows a schematic configuration of the non¬destructive moisture sensor according to the invention. Pig. 2 shows the microstrip resonator with a ring resonator. Fig. 3 shows the microstrip resonator with a straight line resonator. The non-destructive moisture sensor according to the invention comprises a microwave generator (11), a microwave detector (12) and a microstrip resonator (13) connected between the said microwave generator and the detector (12). The transmitted power of the microstrip resonator (13) at s selected frequency is sensed by the detector (12) whose output is given to an electronic circuit (14) consisting of an amplifier unit. This direct reading is used as a reference for minimizing the errors. The bio/synthettic material is kept as an overlay on the said microstrip resonator (13), The microstrip resonator is either insulated or has a constant gap between the reeonator and the sample. As a result of overlay, the air dielectric (e = 1), is replaced by a wet bio/synthetic material. Since the complex dielectric constant e is high compared to that of dry bio/synthetic material, the amount of power absorbed is substantially governed by wioisture content. The amount of power transmitted is measured at a predetermined single frequency. The detected power output is given to a micro-processor (15) through an interphasing electronic circuit consisting of an amplifier which converts output power appropriately into the percent normalized moisture content and give it to a display (16). The data can also be stored if desired. A typical microstrip resonator may be of any shape such as ring or straight line. It comprises of a plane layer WE CLAIM: 1 . A non-destructive moisture sensor conprising a microwave generator (11), a microwave detector (12) and a microstrip resonator (13) connected between the said microwave generator (11) and the microwave detector , the output from the nicrostrip resonator (13) being connected to a microprocessor (lb.) through an interfacing circuit (14> consisting an amplifier to obtain an output corresponding to the normalised percentage of moisture in the material to be tested and a display 2. The non-destructive moisture sensor, as c1aimed in claim 1, wherein the microstrip resonator (13 ) comprises a dielectric substrate 3. The non-destructive moisture sensor, ae claimed in claim 2, wherein the microstrip resonator is a ring resonator, 4. The non-destructive moisture sensor, as claimed in claim 2. wherein the microstrip resonator (13) is a straight line resonator. 5. A non-destructive moisture sensor, substantially as hereinabove described and illustrated with reference to the accompanying drawings.

Documents:

1051-mas-1999 abstract.pdf

1051-mas-1999 claims-duplicate.pdf

1051-mas-1999 claims.pdf

1051-mas-1999 correspondence-others.pdf

1051-mas-1999 correspondence-po.pdf

1051-mas-1999 description (complete)-duplicate.pdf

1051-mas-1999 description (complete).pdf

1051-mas-1999 drawings-duplicate.pdf

1051-mas-1999 drawings.pdf

1051-mas-1999 form-1.pdf

1051-mas-1999 form-19.pdf

1051-mas-1999 form-26.pdf

1051-mas-1999 form-3.pdf

1051-mas-1999 form-8.pdf