Nondestructive Measurement of Sugar Content in Apples by Millimeter-Wave Reflectometry
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Nondestructive Measurement of Sugar Content in Apples by Millimeter-Wave Reflectometry Makoto Oda · Atsushi Mase · Kiichiro Uchino
Received: 28 June 2011 / Accepted: 1 December 2011 / Published online: 29 December 2011 © Springer Science+Business Media, LLC 2011
Abstract A millimeter-wave reflectometer has been developed for the nondestructive measurement of the sugar content in apples. The intensity of the reflected wave from fruit was confirmed to depend on the sugar content and temperature by performing reflectometry with a vector network analyzer of aqueous sucrose solutions. Moreover, the developed reflectometer was applied to the sugar content measurement of apples. We obtained a strong, almost linear relationship between the intensity of the reflected wave and the sugar content in apples. Keywords Millimeter wave reflectometry · Sugar content · Nondestructive 1 Introduction Improving the quality of fruit and branding have become important in the promotion of agricultural regions. Information about the sugar content in fruit is one of the most important factors for assessing quality. Currently, the sugar content is measured by using a destructive juice extraction method,
M. Oda (B) Miyazaki Prefecture Industrial Technology Center, 16500-2 Higashikaminaka, Sadowara-cho, Miyazaki-shi, Miyazaki 880-0303, Japan e-mail: [email protected] A. Mase Art, Science and Technology Center for Cooperative Research, Kyushu University, 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816-8580, Japan K. Uchino Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816-8580, Japan
J Infrared Milli Terahz Waves (2012) 33:228–236
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such as Brix refractometry. However, the application of this method to all the harvested fruit (i.e., every apple) is unfeasible, because it is a destructive inspection technique; the destructive inspection technique would render the inspected fruit unsellable. Consequently, the development of nondestructive inspection devices has been required. Recently, several nondestructive methods to measure the sugar content in fruit using near-infrared light have been reported [1–3]. In the near-infrared region, the accuracy of the measurement is degraded by low transmissivity, especially for fruits with a thick peel, as well as any background light. In contrast, there are a few examples using radio waves as a light source for the nondestructive sugar content measurement [4, 5]. Compared to near-infrared and visible radiation, the penetration characteristics for radio wave is high, although the spatial resolution is not as high due to the longer wavelength. Since millimeter waves (MMWs) are located between radio waves and near-infrared light in wavelength, they provide both good penetration and spatial resolution. Also, MMW systems can be made more compact than microwave systems. Two types of measurement systems have been developed for electromagnetic wave diagnostics: an active system and a passive system. In the active system, the object is irradiat
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