STUDY ON AOTF-BASED NEAR-INFRARED SPECTROSCOPY ANALYSIS SYSTEM OF FARM PRODUCE QUALITY

Transcription

1 STUDY ON AOTF-BASED NEAR-INFRARED SPECTROSCOPY ANALYSIS SYSTEM OF FARM PRODUCE QUALITY Xiaochao Zhang *, Xiaoan Hu, Yinqiao Zhang, Hui Wang, Hui Zhang 1 Institute of Mechatronics Technoogy and Appication, Chinese Academy of Agricutura Mechanization Sciences, Beijing, P. R. China * Corresponding author, Address: Box25, No.1 Beishatan, Dewai St, Beijing, , China, Te: , Fax: , Emai: zxc@caams.org.cn Abstract: Keywords: The technoogy of near-infrared spectroscopy anaysis is one of the important ways to test agricutura products inside quaity quantitativey. The nearinfrared spectra anaysis system which used the technoogy of sound and ight tunabe fiter (AOTF) can be appied to on-ine measurement. The system constructed by AOTF, anaysis optimization waveength together with genetic agorithm, execute data fitering with waveet anaysis technoogy, process data of signa with second differentia and Mahaanobis-distance, estabish Partia Least-Squares mode, tested the wheat and powdered mik. Refects the deveopment of the near-infrared spectra anaysis system can be appied to the quaity of agricutura products preferaby. Near-infrared, AOTF, Mik Powder, Quaity Anayses, Waveet Anaysis, Support Vector Machine 1. INTRODUCTION Information coection, processing and monitoring technoogy are the key probem of digita agricuture. Near-infrared spectra anaysis method is a better way to measure food and mik power quaity rapidy (Hao, 2003; Geadi, 1985). Acousto-optic tunabe fiter (AOTF) (Pozhar V E et a, 2002) is a new technoogy appeared in the eary 1990s. Using birefringent crysta, by changing the radio frequency to change the waveength, AOTF made homochromatic ray.

2 2068 Xiaochao Zhang, Xiaoan Hu, Yinqiao Zhang, Hui Wang, Hui Zhang The device has no mobie components, with a high scanning speed and better stabiity (R. TSENKOVA, 2000), so, it is suitabe for on-ine anaysis particuary, is one of the deveopment directions of near-infrared on-ine measurement technoogy (Xu Kexin, 2002). This is a more mature technoogy in west countries but at the initia stage in china. Since this method can be widey used in quaity measurement and contro during the process of agricutura production, it wi bring new vitaity for agricutura equipment industry, and promote the deveopment of quaity of agricutura products on-ine anaysis rapidy with the character of ow-cost, non-contact and rea-time (Guyon I, 2002). 2. HARDWARE DESIGN OF AOTF SPECTROMETRY SYSTEM 2.1 Structure of the system The system is composed of seven departments: rotating sampe poo and contro unit, high stabiity ight source, AOTF optica system, temperature contro unit of detector, detection signa acquisition system, DDS frequency seection contro system and computer signa processing system, which is shown in Fig. 1. Fig.1: AOTF based spectroscopy anaysis system Use the revoving sampe poo to test sampes adequatey; current-feedbackbased ight source contro system provide 50 to 150 watts of ight; AOTF spectrometry system uses diffuse refectance measurement method; temperature contro unit provide stabe environment with an error of ± 0.2 degree for detectors; the computer issue 20 MHz ~ 70MHz inspirit signa through the DDS

3 Study on AOTF-based Near-infrared Spectroscopy Anaysis System of Farm Produce Quaity 2069 frequency seective circuit; and 16 bit A/D converter coect the corresponding spectrum signas to the computer in rea-time. 2.2 Principe of AOTF Sound-ight tunabe fiter is an eectro-optica moduator device. Its main principe is to use the Prague dissemination of sound wave to the ight insinuated into medium when the sound wave spreading in anisotropic medium. Sound-ight tunabe fiter was composed of singe crysta birefringence (common materia is TeO 2 ), piezoeectric transducers that gued to one side of the singe crysta, and high-frequency signa source that used on the piezoeectric transducer. When certain frequency radio signas were imported, AOTF wi diffract muticoor ight, and choose homochromy ight with the waveength of. The homochromy ight waveength and radio frequency f has corresponding reations. Choose the second refraction crysta teurium dioxide designed AOTF, which has the characters as foows: Waveength: 800nm 1700nm; Aperture: 4mm; Frequency: 2070MHz; Spectra resoution: 9nm at 1700nm Diffraction efficiency: 2nm at 800nm; 40% at 800nm; 20% at 1700nm; Drive power: 1W. The examination showed that the centre-correation coefficient between the radio driver frequency and the number of diffraction ight waves center. 2.3 Design of DDS radio frequency driver According to the frequency range of 20 MHz ~ 70MHz that AOTF RF driver needed, DDS (Direct Digita Synthesizer) cip AD9854 was seected. The chip has a 300 MHz interna cock, 4 to 20 times interna programmabe frequency mutipier, which generated an externa input cock frequency range of 15 ~ 75 MHz. In addition, the cip has a 100 MHz parae interface bus, and an inside orthogona dua-channe DAC output, working with a variety of programming fashion, and can produce compex signas such as inear and noninear FM signas and so on. The working process is as foows: (1) Transate digita waveform stored in severa forms to Anaog waveform by D/A. (2) Change the frequency of the output signa by changing the step of Addressing. The step is the incrementa phase of digita waveform. The accumuator vaue is search address; accumuate according to the phase

4 2070 Xiaochao Zhang, Xiaoan Hu, Yinqiao Zhang, Hui Wang, Hui Zhang accumuator. (3) Output ow-sound anaog waveform by ow-pass or band-pass fiter. The core department of DDS System is phase accumuator, which is composed of an adder and a phase-based register. Suppose the bit width of the adder is 2 N, the high P-bit accumuator is to search Sin function tabe, and the frequency of cock is f c, then the output frequency is: fc fout N 2 Fig.2: circuits of DDS 2.4 Design of RF ow pass fiter The requisition of designing an eiptic function ow pass fiter is: the decay from 0 to 70 MHz shoud ess than 1 db and greater than 50 decibes if the frequency bigger than 75 MHz, termina match resistance is 50 ohm. The design steps are as foows: (1) Eiptic function obtained shoud have an order of seven. (2) Search for components vaue from the normaization tabe according to the vaue of A P, A S, C, S and n. (3) Cacuate components vaue with integrated caibration formua and design circuit.

5 Study on AOTF-based Near-infrared Spectroscopy Anaysis System of Farm Produce Quaity 2071 The transfer function is as foows: Fig.3: design of fiter (1) 3. SOFTWARE DESIGN OF AOTF SPECTROMETRY SYSTEM To avoid the effect of equipment measuring noise, temperature drifting, ight fuctuations and density variety, the foowing technoogy were adopt: (1) Mutipicative scatter correction, standard norma variety, de-trending agorithm and vector normaize. (2) One-eve and two-eve window difference technoogy. (3) Digita signa processing technoogy based on waveet anaysis and orthogona signa correction fiter. (4) Best waveength automaticay search technoogy based on genetic agorithm. (5) Principa component based mahaanobis-distance together with spectrum error forecast technoogy. (6) Buid mode whit the technoogy of support vector machine. 3.1 Signa processing technoogy Sove the noise interference probems whit the combination of waveet anaysis and orthogona signa correction. The technoogy can fuy retain effective information when signa fitering processing, and extract objectives reated signa. With the characteristics of muti-resoution of waveet anaysis, fiter a ayers of signa. Utimate of orthogona signa correcting: before estabish correction quantitative modes; remove the spectrum signa that has nothing to do with concentration matrix with the method of orthogona mathematica method, and then conduct mutipe corrections, so as to simpify the mode and improve the abiity forecast abiity.

6 2072 Xiaochao Zhang, Xiaoan Hu, Yinqiao Zhang, Hui Wang, Hui Zhang Utimate of waveet fiter: in waveet transform, the signa is divided into the custer overay of a series waveet functions, decompose the signa to be anayzed to different scaes with the method of muti-scae anaysis, and achieve the purpose of signa processing through the hierarchica signa processing and remodeing. Waveet packet anaysis further decomposed not ony ow frequency but aso high frequency part of coefficient; so that it enhanced the time-frequency differentiate. The formua of fast discrete waveet packet is: k d j1,2 n d j, nh2k k (2) d j1,2 n1 d j, n g2k The formua of discrete waveet packet reconstruction is: k d h d g j1,2 n k2 j1,2 n d j, n 1 With the method of compusory noise canceation, set zero to some highfrequency and ow frequency coefficient of waveet packet, and reconstruct the muti-signa. 3.2 Mode construction technoogy Construct mode with the method of Support Vector Regression. The use of characteristics of minimum rise, get more stabe and precise caibration mode. Suppose the sampe set is: n y x y x x R, 1, 1,,,, y R (3) And regression function was expressed as the foowing inear equations: f ( x) w, x b (4) The best regression function is the minimum vaue to the foowing function: Where C is set penaties vaues, and are upper and ower imits of the sack variabe. Use the foowing insensitive oss function: And the optimize function:

7 Study on AOTF-based Near-infrared Spectroscopy Anaysis System of Farm Produce Quaity 2073 Under the construction of: Cacuate the formua: 1 * 2, arg min *, * * T i i j j x i x j i1 j 1 * * i i y i i i i1 * We get the coefficient i and i of Lagrange equation, and then regression coefficient and constant as foows: i1 1 b 2 w i i xi w, r x x s i1 3.3 Practica technoogies for products Practica technoogies adopted in this thesis incude: Designed Low-power and high-precision portabe ight source, designed core components of temperature contro process; dynamic adjust technoogy of doube-caibration of standard ight and background; competed signa and mode standardization; Rotating dynamic correction technoogy and density ight automaticay tracking measurement method. (5) 4. APPLICATIONS IN FARM PRODUCE CHARACTER DETECTION Examination was done to test the quaity of grain and mik powder with deveoped apparatus. Take dairy products as an exampe, choose 50 sampes

8 2074 Xiaochao Zhang, Xiaoan Hu, Yinqiao Zhang, Hui Wang, Hui Zhang of mik powder, and set the measure range of waveength of nm, points of waveength is 400, estabish mode caibration for pretreatment spectra data of water, ash, acidity and protein respectivey. We found that mik ingredients in different waveength absorption strength were very different, for exampe, water had a strong absorption peak in the waveength of 960 nm and 1440nm (Fig. 4). Fig.4: absorption peak of water The best main components are determined by the square of forecast error of correction aggregate and the predictive residua error sum of squares. Considering the origina baseine drift of the absorption spectrum, a first derivative and second derivative processing technoogy were adopted. Fig. 5, Fig. 6 and Fig.7 are separatey the mode correation of water, ash and protein. Fig.5: mode correation of water

9 Study on AOTF-based Near-infrared Spectroscopy Anaysis System of Farm Produce Quaity 2075 Fig.6: mode correation of ash Fig.7: mode correation of protein Obigate 20% sampes as forecast ones, four regression modes was forecasted separatey. Predicted resuts of protein were shown in tabe 1 and measurement repeatabiity test resuts in tabe 2. Tabe.1: anaysis data of protein type Mode or not? number R SEC Revise aggregate YES Forecast aggregate NO Tabe.2: errors and repetition of each component Component Water (%) Ash (%) Acidity (T) Protein (%) Error Repetition

10 2076 Xiaochao Zhang, Xiaoan Hu, Yinqiao Zhang, Hui Wang, Hui Zhang 5. CONCLUSIONS The examination shown that it was feasibe to detect the component of mik powder with the AOTF based principe of near-infrared spectroscopy system. But there were sti disparity in errors and repetition with nationa standard. In order to ensure the accuracy and stabiity, we wi continue to study the foowing aspects: (1) Improve the capabiity of AOTF apartments, (2) Improve the stabiity of the frequency signa drive, and, (3) Enhance the stabiity and sensitivity of detectors. The diffuse refection we used in the spectrum system can detect grain iquid and powder agricutura products directy. The system is especiay suitabe for the rapid anaysis of arge number of repetitive sampes, which can detect a the eements in 40 seconds, and the method is simpe and repeatabe. REFERENCES B Shokopf,K Sung, CJ C Burges,et a.comparing support vector machine with Gaussian kernes to radia basis function cassifiers. IEEE Trans. Signa Processing,1997,45: Guyon I, Weston J, Barnhi S, et a. Gene seection for cancer cassfication using support vector machines. Machine Learning,2002, 46(1): Hao Li,Tong Liu,Changyun Wen. A-fiber acousto-optica tunabe fiter with oop structure. Optica Engineering.2003,42(12):26-31 Johan A.Westerhuis,Sijmen de Jong,Age K.Smide.Direct orthogona sigha correction. Chemom.Inte.Lab.Syst.,2001,56: O. Svensson,T. Kourti,J. F.MacGregor.An investigation of orthogona signa correction agorithms and their characterics. J. chemometrics,2002,16: P Geadi,D MacDouga,H Martens. Linearization and scatter-correction for near-infrared refectance spectra of meat. Appied Spectrotroscopy,1985,39(03), Pozhar V E, Pustovoit V I. Long-pathoptica spectra AOTF-based gas anayzer[j]. SPIE, 2002, 4574: R J Barnes, M S Dhanoa,S J Lister.Standard norma variate transformation and de-trending of near-infrared diffuse refectance spectra. Appied Spectroscopy,1989,43(05): R. TSENKOVA, Y. OZAKI, et a. Near Infrared Specerosoopy for Biomonhoring: Cow Mik Composition Measurement in a Spectra Region from 1100 to 2400 Namometers[J].J. Anim, Sci., 2000, 78: Xu kexin, Ni Yong. The optica characteristics of the acousto-optic tunabe fiter with the equivaent point[j]. Chinese Journa of Lasers, 2002, B11(2):