along the fiber axis. This configuration has the advantages ofsimplicity, low cost, and insensitivity to environmental changes,and thus has excellent potential for applications in optical-fibercommunication systems or fiber sensors. By adopting the splicingmethods to achieve a broadband fiber mirror, the reflectivity andrepeatability must be further improved in order to achieve therequired specifications. The experimental results demonstrate thatthe laser-output power changes only slightly when the reflectivityof the FBG varies from 60% to 99%. In the future, the tuning rangewill be increased by improving the fiber-etching techniques anddeveloping better fiber holders.

REFERENCES

1. N.J.C. Libatique et al., A broadly tunable wavelength-selectable DFBsource using a fiber Sagnac loop filter, Photonic Tech Letters 13(2001), 1283–1285.

2. S. Sakano et al., Tunable DFB laser with a striped thin film heater,Photonic Tech Letters 4 (1992), 321–323.

3. P. Honzatko et al., Modulational-Instability �-resonator fiber laser,Optical Letters 26 (2001), 810–812.

4. S. Yamashita and K. Hotate, Distributed pressure sensor with a mode-locked fiber-ring laser, Optical Letters 26 (2001), 590–592.

5. D.B. Mortimore, Fiber loop reflectors, Journal of Lightwave Technol-ogy 6 (1988), 1217–1224.

6. G. Meltz et al., Formation of Bragg gratings in optical fibers by atransverse holographic method, Optical Letters 14 (1989), 823–825.

7. I.D. Miller et al., A Nd�3-doped CW fiber laser using all-fiber reflec-tors, Appl Optics 26 (1987), 2197–2201.

8. M. Takahara, T. Yokoo, and H. Gomi, Splice effects of Er-doped fiberamplifiers, Singapore ICCS/’94, 1994.

9. J.P. Meunier and S.I. Hosain, An accurate splice-loss analysis forsingle-mode graded-index fibers with mismatched parameters, Journalof Lightwave Technology 10 (1992), 1521–1526.

10. M.P. Singh, J.O. Reese, T.M. Wei, and D.G. Storch, Low-loss fusionsplicing of erbium-doped optical fibers for high-performance fiber ampli-fiers, IEEE Trans Compon Hybrids Manufac Technol 13 (1990), 811–813.

© 2005 Wiley Periodicals, Inc.

OPTICALLY ACTIVATED NOVEL FORCESENSOR CALIBRATED AS WEIGHINGBALANCE

Atul Kulkarni, R. N. Karekar,2 and R. C. Aiyer1

1 Thin Film Lab2 RCMF Transducer LabDepartment of PhysicsUniversity of PunePune–411 007, India

Received 29 October 2004

ABSTRACT: This paper presents the use of plastic optical fibers(POFs) as a weighing balance. A force sensor with a critically adjustedpair of deforming plates and weighing 1 g to 3 kg is constructed, havingan accuracy of 1% over the range of �0.5% linearity with regard toresponse and a recovery time of 250 msec with no observable hystere-sis. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45:300–303, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20802

Key words: plastic optical fiber; force sensor; deforming plate; micro-bending; balance

1. INTRODUCTION

The technique of weight measurement is highly evolved, as it is theprinciple means of determining the quantity of goods sold. Weighingis also an important part of many industrial processes, which requirea combination of batching, handling, and storage of materials. Elec-tronic weighing systems have become the most commonly usedinstruments in plants and processes, and the balances used in normalmarkets are mostly based on the piezo-resistive principle [1].

Plastic optical fibers (POFs) have attracted a considerable amountof attention for a number of reasons, such as their insensitivity toelectromagnetic fields, lightweight and minimal intrusiveness, ease oftermination and coupling, and their relatively high resistance to frac-ture, for use in various applications. The cost of POFs is low and theiruse as sensors requires only basic solid-state devices such as light-emitting diodes and photodiodes. The inherent fracture toughness andflexibility of POFs makes them much simple to handle in fieldapplications [2–4]. The use of fiber Bragg grating (FBG) sensors forstrain and bending measurements (for structural-health monitoring)has attracted significant attention in recent years [5–7]. However, thecost of implementing an FBG sensing system frequently limits itsapplications. A force sensor in which the sensing element is a vibrat-ing metallic glass strip under tension has been reported [8]. The forceapplied at one end of the specially designed frame is converted intohaving a proportional change in tension along the strip. An intensity-based POF sensing system for performing strain and bending mea-surements in loaded structures was reported in [4].

The microbend effect of fiber has also been used in the mea-surement of many physical variables, such as displacement, pres-sure, and so forth, but no direct reference to balance has beenreported to date [9, 10].

The present study reports the use of the microbend principle foran inexpensive POF force sensor used as single-pan balance. Theunit is found to be sensitive to force applied in the form of weightdue to the proper geometry used. It has been calibrated as asingle-pan weighing balance. This instrument is presently designedfor use as a general-purpose weighing machine for weighing up to3 Kg with a resolution of 1 g; this can be modified to higherresolution with critical changes in geometry and electronic-signalprocessing. The unit’s principle of operation and details of thestructure design and calibration are outlined in the followingsections.

2. CONSTRUCTION

The single-pan balance (Fig. 1) mainly consists of POF, an optical

Figure 1 Single-pan balance construction

300 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 45, No. 4, May 20 2005

transmitter-receiver pan with its related structure, and a pair offiber-deforming plates.

2.1 Balance StructureTo reduce the weight of the weighing balance, the body of thebalance-stand structure is made of aluminum. Proper bearing isused in the vertical direction in order to achieve minimum frictionbetween the shaft and the body of the structure. As the weighingpan, rod, and top deforming plate (all made of stainless steel) arecoupled together with fixed (screwed) joints, the weight of theobject to be weighed is the only force on the POF. The POF isclamped and compressed between a pair of corrugated deformingplates. The force on the top deformer plate causes compressionmicrobending in the POF, while the bottom deformer plate is fixedon the aluminum stand. A 10-mm-diameter stainless-steel rod isconnected between the weighing pan and deformer top plate via alinear ball bearing of 20-mm length. The POF becomes clampedand compressed between the top and bottom segments of thedeforming plates, and is finally clamped at two ends, through theoptical transmitter and receiver to the aluminum base stand.

2.2 Pair of Deforming PlatesThe deforming plate’s geometry is the most critical part of thissystem. Three different combinations of deforming plates aretested in this study. The square deforming plates are made fromstainless steel with different pitch values of 2, 5, and 10 mm. Thelength and thickness (including tooth length) of the toothed de-forming plates are 30 and 3 mm, respectively. The width of thedeforming plates is maintained such that it will cover the POF. Thebasic shape of the deforming plate is shown in Figure 2.

2.3 Plastic Optical FiberThe POF consists of a polymethylmethacrylate (PMMA) coreapproximately 980-�m thick with 20-�m-thick cladding made ofa fluoride-containing carbon polymer. The refractive indices of thecore and cladding are 1.492 and 1.417, respectively. With its PVCprotective sheath, the POF has a total diameter of 2.2 mm. Thelength of the optical fiber is 150 mm. Care was taken while cuttingthe POF. To maximize the bend sensitivity of the POF, wetpolishing of the fiber end with 600-grain sandpaper is done for apre-defined time. The POF is clamped between the transmitter andreceiver modules by the deforming plates.

2.4 Optical Transmitter-ReceiverSiemens plastic fiber components (PFC) emitters and detectors areused. These low-cost components permit the use of plastic fibers,even in the most cost-sensitive applications. An SFH 450 emitterdiode (infrared) is used as a transmitter and has a peak emissionwavelength of 950 nm. A phototransistor SFH 350 with respon-sivity of 0.3 �A/�W is used as a receiver. The advantage of theSiemens PFC’s is the housing aperture into which a standard POFis introduced without having to remove the cladding. This has theadditional benefit of automatically centering the fiber on the chip.

The transmitter and receiver are connected to the POF ends andclamped to the aluminum structure.

3. TESTING EXPERIMENTATION

A standard �5-V supply was used to power the transmitter andreceiver. The receiver-output voltage for testing was measured onan HP multimeter (HP-34401A) and a Tektronix storage oscillo-scope (THS 73A) was used to measure response time of the forcesensor.

The single-pan balance was tested for all its specifications. Wechecked the calibration and linearity by using standard calibratedweights. For repeatability of the reading, it was checked at thelowest and highest linear ranges (1 g to 3 Kg), at least 10 times.Hysteresis was checked by incrementally increasing the force byadding weights one at a time, noting the reading after each additionand removing the weights in reverse order, then noting the readingafter each removal. The readings were compared for the same load.The fiber’s reproducibility was tested using about 15 pieces andthat of the deforming-plate pairs by using two plates for each of the

Figure 2 Deforming-plate pair

Figure 3 Variation of receiver intensity in terms of voltage with respectto weight for three deforming plates with 2-, 5-, and 10-mm pitch

Figure 4 Repeatability result for the 2-mm pitch deforming plate witherror bar of 0.1%

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 45, No. 4, May 20 2005 301

three types. The results of this experiment are given in section 4and discussed in section 5.

4. RESULTS

In order to evaluate the functionality of the POF force sensor as asingle-pan weighing balance, the modulation of the POF lightintensity was systematically compared with standard calibratedweights. Figure 3 shows the variation of receiver intensity in termsof voltage with respect to the weight of three deforming plats. It isclear from the figure that the POF force sensor exhibits a linearresponse within �0.5% of a full range.

The repeatability of the POF sensor under loading was found tobe very encouraging and the results of six sets for three differentdeforming plates are summarised in Figures 4–6. The repeatabilityis found up to 1% of a full span.

Hysteresis is one of the important parameters used for measur-ing the devices. Figure 7 shows the hysteresis for the deformingplate (10-mm pitch) while loading and unloading of the weights. Itis clearly seen from the figure that there is no sign of hysteresis.

The response time of the force sensor for three deformingplates is shown in Figure 8. Rise and fall times of up to 250 msecwere obtained.

5. DISCUSSION

This research has investigated the use of a novel POF sensor formeasuring force in terms of weights applied on a POF through apair of deforming plates. The deforming plates squeeze the POFunder measured perturbation and thereby induce microbending.This causes coupling between the guided and continuing claddingmodes, which results in an irreversible leak of the optical powerfrom the POF. It was observed that the optical power in the fibercore attenuated in proportion to the applied force. The deformingplate’s geometry is the most critical part of this system. From theresults, it was seen that increasing the corrugation pitch of thedeforming plates enhanced microbend sensitivity. The more severethe mechanical perturbation or bending, the more light is coupledto the radiation modes and hence is lost, resulting in lower trans-mitted intensity. Thus, the important characteristics of a microbendsensor are that it uses multimode POF, it is a light-intensity sensor,and the light intensity decreases with mechanical bending. Thesensor offers a number of advantages, including ease of fabrica-tion, high microbend sensitivity, linearity, and a high signal-to-

Figure 5 Repeatability result for the 5-mm pitch deforming plate witherror bar of 0.2%

Figure 6 Repeatability result for the 10-mm pitch deforming plate witherror bar of 1%

Figure 7 Hysteresis result for the 10-mm pitch deforming plate forloading and unloading weights

Figure 8 Oscilloscope trace of the response time for 2-, 5-, and 10-mmpitch deforming plates on 200-mV and 1-sec time scale

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noise ratio. The sensor was found to offer excellent signal linear-ity. Repeatability tests confirmed that the signal was well behavedand highly reproducible. The findings of the analysis performed toevaluate the accuracy of the sensor measurement has shown thatPOFs are capable of force measurement to within a standarddeviation of 0.5%.

The results of a series of repeated loading and unloading offorce (weights) are also encouraging. Here, no significant hyster-esis was observed and the response of the sensor was well be-haved. The results also show that the sensor linearity was main-tained throughout the measurements.

6. CONCLUSION

This investigation has demonstrated the potential of this inexpen-sive plastic optical fiber (POF) system for measuring force(weights). The proper design of the deformer plates can enhancethe microbend sensitivity. Accordingly, the application-improvedbalance structure can be designed while keeping the basic principlethe same.

By integrating POFs into the design of weighing machines, anew application of fiber optics has been explored.

REFERENCES

1. U. Erdem, Force and weight measurement, J Phys E Sci Instrum 15(1982), 857–872.

2. P. Fuhr, Introduction to fiber-optic sensing Pt 1, Sensorsmag Lett, SanJose State Univ., (2002).

3. E. Udd, Fiber-optic sensors for scientists and engineers, Wiley, NewYork, 1993.

4. K.S.C. Kuang, An evaluation of a novel plastic optical fiber sensor foraxial strain and bend measurements, Meas Sci Technol 13 (2002),1523–1534.

5. S. Lebid, How to reliably measure composite-embedded fiber Bragggrating sensors influenced by transverse and point-wise deformations?Meas Sci Technol 15 (2004), 1441–1447.

6. B.G. Grossmann, Fiber-optic sensor array for multi-dimensional strainmeasurement, Smart Mater Struct 7 (1998), 159–165.

7. X.Y. Dong, H.Y. Meng, Z.G. Liu, and G.Y. Jkai, Bend measurementwith chirp fiber Bragg grating, Smart Mater Struct 10 (2001), 1111–1113.

8. S. Ramakrishnan, An optically activated resonant force sensor cali-brated as a weighing balance, Meas Sci Technol 2 (1991), 549–552.

9. D. Donlagic, Fiber-optic sensors: An introduction and overview, Uni-versity of Maribor, 2000.

10. R.J. Bartlett, Plastic optical fiber sensors and devices, Trans InstMeasurement Control 22 (2000), 431–457.

© 2005 Wiley Periodicals, Inc.

A NOVEL COMPACT INTEREMBEDDEDAMC STRUCTURE FOR INTEGRATEDCIRCUITS AND ANTENNA ARRAYS

Dunbao Yan, Chao Wang, Qiang Gao, and Naichang YuanSchool of Electronic Science and EngineeringNational University of Defense TechnologyChangsha, HuNan Province 410073, P. R. China

Received 28 October 2004

ABSTRACT: A novel compact interembedded artificial magnetic con-ductor (IE-AMC) structure is introduced in this paper. For a desiredbandgap frequency, the cell size of this novel IE-AMC structure is only30% to 40% of the conventional Sienvenpiper structure with the same

substrate used. The IE-AMC structure is very suitable to microwave in-tegrated circuits and antenna-arrays applications, especially in wireless-communication bands (GSM, PCS, and ISM). © 2005 Wiley Periodicals,Inc. Microwave Opt Technol Lett 45: 303–305, 2005; Published onlinein Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20803

Key words: artificial magnetic conductor (AMC); electromagneticband-gap (EBG); inter-embedded (IE); surface wave; mutual coupling

1. INTRODUCTION

Artificial magnetic conductor (AMC) structures have been widelystudied recently because of its two valuable properties, suppressingsurface waves and reflecting the plane waves in-phase. A mush-roomlike AMC structure introduced firstly by Sievenpiper [1, 2] iscalled the Sievenpiper structure in this paper. Its unit cell iscomposed of a patch and a via connecting the patch and groundplane, which is shown in Figure 1(a). It is a resonant electromag-netic band-gap (EBG) structure instead of a Bragg scattering one,because it does not derive its surface-wave suppressing propertyfrom Bragg scattering between the waves and its periodic unit cell.Because of its two unique properties, this AMC structure has beenwidely used in electromagnetic and antenna research [3–9]. How-ever, in low-frequency bands, that is, wireless communicationbands (GSM, PCS, and ISM), it is difficult to utilize the AMCstructure due to its large cell size. Three-layer AMC structures [2]have been proposed and used for GSM and Bluetooth applications[10, 11]. Nevertheless, three-layer structures are difficult to fabri-cate and their cost is high. Moreover, it is difficult to integrate athree-layer structure with microwave integrated circuits and anten-nas, which are two-layer structures. Some methods for reducingthe cell size of two-layer AMC structure were presented [12];however, none of them can decrease the size by more than 30%.

In this paper, an interembedded technique is used. Every cellextends four meandered branches, which are embedded in neighbor-ing four cells, and the structure becomes interembedded, as shown inFigure 1(b). With this novel technique, a decrease about 30% to 40%in cell size can be achieved compared with Sievenpiper structure,which uses the same substrate as the IE-AMC structure.

2. STRUCTURE DESIGN

For the Sievenpiper structure, the proximity of the neighboringmetal patch provides the capacitance C, and the long conductingpath linking them together provides the inductance L; hence, the

Figure 1 Geometry of Sievenpiper AMC structure and IE-AMC struc-ture (simulated cells are outlined in dashed lines): (a) Sievenpiper struc-ture; (b) IE-AMC structure

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