{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,13]],"date-time":"2026-05-13T21:15:58Z","timestamp":1778706958962,"version":"3.51.4"},"reference-count":34,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2014,2,3]],"date-time":"2014-02-03T00:00:00Z","timestamp":1391385600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Among palm oil millers, the ripeness of oil palm Fresh Fruit Bunch (FFB) is determined through visual inspection. To increase the productivity of the millers, many researchers have proposed with a new detection method to replace the conventional one. The sensitivity of such a sensor plays a crucial role in determining the effectiveness of the method. In our preliminary study a novel oil palm fruit sensor to detect the maturity of oil palm fruit bunches is proposed. The design of the proposed air coil sensor based on an inductive sensor is further investigated to improve its sensitivity. This paper investigates the results pertaining to the effects of the air coil structure of an oil palm fruit sensor, taking consideration of the used copper wire diameter ranging from 0.10 mm to 0.18 mm with 60 turns. The flat-type shape of air coil was used on twenty samples of fruitlets from two categories, namely ripe and unripe. Samples are tested with frequencies ranging from 20 Hz to 120 MHz. The sensitivity of the sensor between air to fruitlet samples increases as the coil diameter increases. As for the sensitivity differences between ripe and unripe samples, the 5 mm air coil length with the 0.12 mm coil diameter provides the highest percentage difference between samples and it is amongst the highest deviation value between samples. The result from this study is important to improve the sensitivity of the inductive oil palm fruit sensor mainly with regards to the design of the air coil structure. The efficiency of the sensor to determine the maturity of the oil palm FFB and the ripening process of the fruitlet could further be enhanced.<\/jats:p>","DOI":"10.3390\/s140202431","type":"journal-article","created":{"date-parts":[[2014,2,3]],"date-time":"2014-02-03T11:17:25Z","timestamp":1391426245000},"page":"2431-2448","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Improvement in Sensitivity of an Inductive Oil Palm  Fruit Sensor"],"prefix":"10.3390","volume":"14","author":[{"given":"Norhisam","family":"Misron","sequence":"first","affiliation":[{"name":"Faculty of Engineering, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia"},{"name":"Institute of Advanced Technology (ITMA), Universiti Putra Malaysia, 43400 Serdang,  Selangor, Malaysia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Noor","family":"Harun","sequence":"additional","affiliation":[{"name":"Faculty of Engineering, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yeoh","family":"Lee","sequence":"additional","affiliation":[{"name":"Faculty of Engineering, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Roslina","family":"Sidek","sequence":"additional","affiliation":[{"name":"Faculty of Engineering, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ishak","family":"Aris","sequence":"additional","affiliation":[{"name":"Faculty of Engineering, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hiroyuki","family":"Wakiwaka","sequence":"additional","affiliation":[{"name":"Faculty of Engineering, Shinshu University, Wakasato 4-17-1, Nagano, 380-8553, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kunihisa","family":"Tashiro","sequence":"additional","affiliation":[{"name":"Faculty of Engineering, Shinshu University, Wakasato 4-17-1, Nagano, 380-8553, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2014,2,3]]},"reference":[{"key":"ref_1","unstructured":"(2003). Oil Palm Fruit Grading Manual, Malaysian Palm Oil Board (MPOB). [2nd ed.]."},{"key":"ref_2","unstructured":"Siregar, I.M. (1976, January 14\u201317). Assessment of Ripeness and Crop Control in Oil Palm. Kuala Lumpur, Malaysia."},{"key":"ref_3","first-page":"570","article-title":"Prediction model for estimating optimum harvesting time of oil palm fresh fruit bunches","volume":"9","author":"Razali","year":"2011","journal-title":"J. Food Agric. Environ."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"654","DOI":"10.1016\/j.foodchem.2008.07.052","article-title":"Extraction and physicochemical properties of low free fatty acid crude palm oil","volume":"113","author":"Tan","year":"2009","journal-title":"Food Chem."},{"key":"ref_5","first-page":"355","article-title":"Palm fruit chemistry and nutrition","volume":"12","author":"Kalyana","year":"2003","journal-title":"Asia Pacific J. Clin. Nutr."},{"key":"ref_6","first-page":"72","article-title":"Potential application of colour and hyperspectral images for estimation of weight and ripeness of oil palm (Elaeis guineensis Jacq. Var. tenera)","volume":"18","author":"Junkwon","year":"2009","journal-title":"Agric. Inf. Res."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"223","DOI":"10.1205\/096030801753252298","article-title":"Stepwise discriminate analysis for colour grading of oil palm using machine vision system","volume":"79","author":"Abdullah","year":"2001","journal-title":"Food Bioprod. Proc."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"55","DOI":"10.1016\/j.compag.2011.12.010","article-title":"Classification of oil palm fresh fruit bunches based on their maturity using portable four-band sensor system","volume":"82","author":"Osama","year":"2012","journal-title":"Comput. Electron. Agric."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"213","DOI":"10.1111\/j.1745-4549.2002.tb00481.x","article-title":"Colour vision system for ripeness inspection of oil palm","volume":"26","author":"Abdullah","year":"2002","journal-title":"Elaeis guineensis. J. Food Proc. Preserv."},{"key":"ref_10","first-page":"56","article-title":"Development of imaging application for oil palm fruit maturity prediction","volume":"4","author":"Ismail","year":"2009","journal-title":"Eng. E-Trans."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Jamil, N., Mohamed, A., and Abdullah, S. (2009, January 4\u20137). Automated Grading of Palm Oil Fresh Fruit Bunches (FFB) Using Neuro-Fuzzy Technique. Malacca, Malaysia.","DOI":"10.1109\/SoCPaR.2009.57"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"14179","DOI":"10.3390\/s121014179","article-title":"Intelligent colour vision system for ripeness classification of oil palm fresh fruit bunch","volume":"12","author":"Fadilah","year":"2012","journal-title":"Sensors"},{"key":"ref_13","unstructured":"Shariff, R., Adnan, A., Mispan, R., Mansor, S., Halim, R., and Goyal, R. Correlation Between Oil Content and DN Values. Available online: http:\/\/www.gisdevelopment.net\/application\/agriculture\/yield\/agriy0001pf.htm."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"838","DOI":"10.2202\/1556-3758.1090","article-title":"Digital image processing of palm oil fruits","volume":"2","author":"Choong","year":"2006","journal-title":"Int. J. Food Eng."},{"key":"ref_15","first-page":"72","article-title":"Hyperspectral imaging for nondestructive determination of internal qualities for oil palm (Elaeis guineensis Jacq. Var. tenera)","volume":"18","author":"Junkwon","year":"2009","journal-title":"Agric. Inf. Res."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"217","DOI":"10.3923\/jps.2006.217.227","article-title":"Relationship between oil content and fruit surface colour in oil palm (Elaeis guineensis Jacq.)","volume":"1","author":"Balasundram","year":"2006","journal-title":"J. Plant Sci."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"838","DOI":"10.1002\/ejlt.201000020","article-title":"Imaging technique for quantification of oil palm fruit ripeness and oil content","volume":"112","author":"Tan","year":"2010","journal-title":"Eur. J. Lipid Sci. Technol."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"534","DOI":"10.1016\/j.jfoodeng.2012.07.008","article-title":"Oil palm bunch ripeness classification using fluorescence technique","volume":"113","author":"Hazir","year":"2012","journal-title":"J. Food Eng."},{"key":"ref_19","unstructured":"Alfatni, M.S.M., Shariff, A.R.M., Shafri, H.Z.M., Saaed, O.M.B., Eshanta, O.M., and Abuzaed, M. (2007, January 2\u20135). Automated Oil Palm Fruit Bunch Grading System Using Density of Colour (RGB). Riyadh Saudi Arabia."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"1444","DOI":"10.3923\/jas.2008.1444.1452","article-title":"Oil palm fruit bunch grading using red, green and blue digital number","volume":"8","author":"Alfatni","year":"2008","journal-title":"J. Appl. Sci."},{"key":"ref_21","first-page":"38","article-title":"Optical properties for mechanical harvesting of oil palm FFB","volume":"12","author":"Ismail","year":"2000","journal-title":"J. Oil Palm Res."},{"key":"ref_22","first-page":"18","article-title":"Photogrammetric grading of oil palm fresh fruit bunches","volume":"9","author":"Jaffar","year":"2009","journal-title":"Int. J. Mech. Mechatron. Eng."},{"key":"ref_23","unstructured":"Ismail, W.I.W., and Razali, M.H.H. (2012, January 11\u201315). The Optical Properties to Model Oil Palm Fresh Fruit Bunches Maturity Index. Orlando, FL, USA."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"7","DOI":"10.2478\/v10048-010-0002-x","article-title":"Application of microwave moisture sensor for determination of oil palm fruit ripeness","volume":"10","author":"Yeow","year":"2010","journal-title":"Meas. Sci. Rev."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1281","DOI":"10.1109\/JSEN.2005.859249","article-title":"Complex permittivity and moisture measurements of oil palm fruits using an open-ended coaxial sensor","volume":"5","author":"Abbas","year":"2005","journal-title":"IEEE Sensors J."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Khalid, K., Ghretli, M.M., Abbas, Z., and Grozescu, I.V. (2006, January 12\u201314). Development of Planar Microwave Moisture Sensors for Hevea Rubber Latex and Oil Palm Fruits. Putra Jaya Malaysia.","DOI":"10.1109\/RFM.2006.331027"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"1191","DOI":"10.1088\/0957-0233\/9\/8\/008","article-title":"Development of conductor-backed coplanar waveguide moisture sensor for oil palm fruit","volume":"9","author":"Khalid","year":"1998","journal-title":"Meas. Sci. Technol."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"63","DOI":"10.1023\/B:SSTA.0000034543.03885.49","article-title":"The analysis of multi-layre conductor-backed coplanar waveguide for moisture sensor application","volume":"5","author":"Khalid","year":"2004","journal-title":"Subsurf. Sens. Technol. Appl."},{"key":"ref_29","first-page":"101","article-title":"Monitoring development and ripeness of oil palm fruit (Elaeis guineensis) by MRI and bulk NMR","volume":"12","author":"Sharifudin","year":"2010","journal-title":"Int. J. Agric. Biolog."},{"key":"ref_30","first-page":"1055","article-title":"Determination of palm oil residue in palm kernel and palm oil methyl ester using near infrared spectroscopy","volume":"volume","author":"Bonnie","year":"2011","journal-title":"J. Oil Palm Res."},{"key":"ref_31","unstructured":"Zakaria, Z. (1998). Dielectric Properties of Oil Palm Mesocarp at Various Stages of Maturity. [M.Sc. Dissertation, Universiti Putra Malaysia]."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"2254","DOI":"10.3390\/s130202254","article-title":"Investigations on a novel inductive concept frequency technique for the grading of oil palm fresh fruit bunches","volume":"13","author":"Harun","year":"2013","journal-title":"Sensors"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"470","DOI":"10.1016\/j.sna.2008.05.033","article-title":"Consideration of theoretical equation for output voltage of linear displacement sensor using meander coil and pattern guide","volume":"147","author":"Norhisam","year":"2008","journal-title":"Sens. Actuat. A Phys."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"10522","DOI":"10.3390\/s111110522","article-title":"Effect of inductive coil shape on sensing performance of linear displacement sensor using thin inductive coil and pattern guide","volume":"11","author":"Norhisam","year":"2011","journal-title":"Sensors"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/14\/2\/2431\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T21:07:55Z","timestamp":1760216875000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/14\/2\/2431"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2014,2,3]]},"references-count":34,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2014,2]]}},"alternative-id":["s140202431"],"URL":"https:\/\/doi.org\/10.3390\/s140202431","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2014,2,3]]}}}