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| The OW detector consists of a sapphire disc (0.3mm thick and 13mm in diameter), the rear side of which is glued to the annular ringmade of the piezoelectric material. Sapphire is amaterial characterized by high transmission in the visible range as well as by a large thermal expansion coefficient. The concept of the OWdetection is as follows. About 0.25 cm3 fluid (or semi-fluid) sample (here watermelon homogenate) that contains the chromophore of interest isdepositedona surface of a sapphiredisc.Goodthermal contact between homogenate and the surface of the disc is required. The emission wavelength of a periodically modulated beam of radiation (often laser) is chosen such as to correspond to thewavelength at which the chromophore of interest shows appreciable absorption. The modulated radiation beam enters the rear side of thesapphire disc at a normal incidence. It penetrates through a thin disc and eventually reaches the homogenate on a top surface of the sapphire disc. The transmission of the disc should be high so that as much as possible of the incident laser power reaches the homogenate. As a result of selective excitation, heat will be generated in a homogenate leading to an increase of its temperature. Due to good thermal contact between the homogenate and a disc, the temperature of disc follows these temperature oscillations causing it to expand and contract periodically. The annular ring made frompiezoelectric lead zirconiumtitanate (PbZrxTi1−xO3) responds to these changes by generating an alternate voltage at the same modulation frequency. This voltage, termed the OWsignal, has the amplitude andphase (relative to the incident radiation).Bothcanbe readily detected using the two phase lock-in amplifier. Thermal and optical properties of the test sample and of disc, themodulation frequency, the intensity of the incident radiation, the diameter of the excitation beam, the intrinsic responsivity, and the thermalmass of piezoelectricmaterial all affect the amplitude and phase of the OW signal in a rather complex manner. The OWsignal is mainly due to the heat producedwithin the layer of homogenate, the thickness of which is approximately equal to one thermal diffusion length (see below). |
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Ìú¸Ëľ³æ (Ö°Òµ×÷¼Ò)
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- ¹ó±ö: 1.257
- ½ð±Ò: 5347.3
- Ìû×Ó: 3712
- ÔÚÏß: 1225.5Сʱ
- ³æºÅ: 1150928
tianenlee(½ð±Ò+10, ·ÒëEPI+1): 2011-03-15 15:25:07
|
The OW detector consists of a sapphire disc (0.3mm thick and 13mm in diameter), the rear side of which is glued to the annular ringmade of the piezoelectric material. Sapphire is a material characterized by high transmission in the visible range as well as by a large thermal expansion coefficient. ¸Ãµ¥³Ì̽²âÆ÷ÓÉÒ»¸öÀ¶±¦Ê¯µúƬ£¨ºñ¶ÈΪ0.3ºÁÃ×£¬Ö±¾¶Îª13ºÁÃ×£©×é³É£¬Æä±³ÃæÕ³ÔÚÒ»¸öѹµç²ÄÁÏ»·ÉÏ¡£À¶±¦Ê¯ÊÇÒ»ÖÖÒÔÔڿɼû¹â·¶Î§Äڸߴ«Êä¡¢ÈÈÅòÕÍϵÊý´óÎªÌØµãµÄ²ÄÁÏ¡£ The concept of the OW detection is as follows. About 0.25 cm3 fluid (or semi-fluid) sample (here watermelon homogenate) that contains the chromophore of interest is deposited on a surface of a sapphire disc.Good thermal contact between homogenate and the surface of the disc is required. ¸Ãµ¥³Ì̽²âÆ÷µÄ¸ÅÄîÊÇÕâÑùµÄ£ºÔ¼0.25Á¢·½ÀåÃ×Á÷Ì壨»ò°ëÒºÌ壩ÑùÆ·£¨ÕâÀïÊÇÖ¸Î÷¹ÏÔȽ¬£©£¬ÆäÖÐËù¹Ø×¢µÄÉúÉ«Íű»¾Û¼¯ÔÚÀ¶±¦Ê¯µúƬµÄ±íÃæ¡£²¢ÔÚÔȽ¬ºÍµúƬµÄ±íÃæÖ®¼äÐèÒªÓÐÁ¼ºÃµÄÈȽӴ¥¡£ |
2Â¥2011-03-15 15:11:10
Mally89
Ìú¸Ëľ³æ (Ö°Òµ×÷¼Ò)
- ·ÒëEPI: 79
- Ó¦Öú: 7 (Ó×¶ùÔ°)
- ¹ó±ö: 1.257
- ½ð±Ò: 5347.3
- Ìû×Ó: 3712
- ÔÚÏß: 1225.5Сʱ
- ³æºÅ: 1150928
|
The emission wavelength of a periodically modulated beam of radiation (often laser) is chosen such as to correspond to the wavelength at which the chromophore of interest shows appreciable absorption. The modulated radiation beam enters the rear side of the sapphire disc at a normal incidence. Ò»¸ö·ÅÉäÎͨ³£ÊǼ¤¹â£©¶¨ÆÚµ÷ÖÆ¹âÊø·¢É䲨³¤µÄ£¨ÕýÈ·£©Ñ¡Ôñ£¬ÀýÈçÓëËù¹Ø×¢µÄÉúÉ«ÍŵÄÏà¶ÔÓ¦µÄ²¨³¤£¬»áÓÐÃ÷ÏÔµÄÎüÊÕ£¨ÏÖÏ󣩡£¾¹ýµ÷ÖÆµÄ·øÉäÊøÒÔÕý³£µÄ·¢ÉäÂÊÉäÈëµ½Õâ¸öÀ¶±¦Ê¯µúƬµÄ±³Ãæ¡£ It penetrates through a thin disc and eventually reaches the homogenate on a top surface of the sapphire disc. The transmission of the disc should be high so that as much as possible of the incident laser power reaches the homogenate. As a result of selective excitation, heat will be generated in a homogenate leading to an increase of its temperature. Ëü´©Í¸±¡±¡µÄµúƬ£¬²¢×îÖÕ´ïµ½ÔÚÀ¶±¦Ê¯µúƬ±íÃæÉϵÄÔȽ¬¡£µúƬµÄ´«ÊäËٶȺܿì´Ó¶øÊ¹¾¡¿ÉÄÜ¶àµØÈëÉ伤¹â¹¦ÂÊÉäÈëÔȽ¬¡£ÕâÖÖÑ¡ÔñÐÔ¼¤·¢µÄ½á¹û¾ÍÊÇÔÚÔȽ¬ÖвúÉúµÄÈÈÁ¿»á¾¡¿ì´ïµ½ËüËùÐèÒªµÄµ½´ïµÄζȡ£ |
3Â¥2011-03-15 15:25:44














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