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Indian Journal of Physics

, Volume 92, Issue 7, pp 883–891 | Cite as

Investigations on colour dependent photo induced microactuation effect of FSMA and proposing suitable mechanisms to control the effect

  • A Bagchi
  • S Sarkar
  • P K Mukhopadhyay
Original Paper
  • 245 Downloads

Abstract

Three different coloured focused laser beams were used to study the photo induced microactuation effect found in some ferromagnetic shape memory alloys. Besides trying to uncover the basic causes of this unique and as yet unexplained effect, these studies are to help find other conditions to further characterize the effect for practical use. In this study some mechanisms have been proposed to control the amplitude of actuation of the sample. Control of the actuation of the FSMA sample both linearly with the help of a continuously variable neutral density filter as well periodically with the help of a linear polarizer was achieved. Statistical analysis of the experimental data was also done by applying ANOVA studies on the data to conclusively provide evidence in support of the relationship between the actuation of the sample and the various controlling factors. This study is expected to pave the way to implement this property of the sample in fabricating and operating useful micro-mechanical systems in the near future.

Keywords

Ferromagnetic shape memory alloys Laser Polarization Microactuation Analysis of variance 

PACS Nos.

42.55.Px 42.62.Cf 68.35.bd 78.20.Ek 

1 Introduction

In the year 2012 it was first reported that a Ferromagnetic Shape memory Alloy (FSMA) sample was showing photo induced micro actuation (PIMA) effect when subjected to a focused red laser beam [1]. When a tiny spot of a focused laser beam (of power about 20 mW) was incident on the sample it immediately moved away, only to return to the original position as soon as the light was switched off. A lot of effort has been given to fully understand the cause of this phenomenon. But till now the cause of this effect is not understood. This PIMA effect is unique and does not have any parallel with any hitherto known phenomenon. In order to understand this effect, a systematic study is now undertaken. The first effort was to try to see if any other material would show this effect. Experiments were tried with pieces of paper, aluminium foil, thin sheets of iron, copper, various plastics etc. but it was never observed in any of them. It seems that somehow only some FSMA materials are endowed with this property.

However, even with little understanding of the basic Physics behind this, it is still possible to utilize this effect for practical use. For proper harnessing the effect for use, the PIMA effect must be fully characterized. Towards this, the present study was devoted. FSMA materials have immense potential to be used as microactuators due to their ability to generate mechanical work under the influence of thermal or magnetic stimuli [2, 3, 4, 5, 6, 7]. With the discovery of the PIMA effect a new method to extend the control on the actuation mechanism of the microactuator systems can be proposed. In the first report of the PIMA effect only a red coloured laser of wavelength 660 nm and power of 20–80 mW was studied [1]. In order to understand this effect in detail, systematic investigations were carried out using three different coloured diode lasers viz. red, blue and green. In this communication the findings on one such alloy system are reported. With this study on the microactuation effect an effective, new and unique controlling mechanism for the fabrication and operation of various microactuator systems is proposed.

2 Experimental details

The FSMA material used was a Co34Ni35Al31 metglass ribbon with a dimension of 20 mm × 2.5 mm × 10 µm. When the first observation of the PIMA effect was made, the laser beam was directed onto the sample through a microscope system [1]. This reduced the actual power of the laser beam to about 30% of its original value. Additionally the nature of the laser beam was affected by the internal optics of the microscope system. As a result the full extent of the microactuation effect could not be studied at that time. In order to apply the PIMA effect to control various microactuator systems in real life the phenomenon has to be studied where the laser beam directly interacts with the sample. Only then implementation of this effect can be proposed to effectively control a microactuator system. Further, the PIMA operation should be operable even without an elaborate microscope. So the observations were carried out in the following manner.

The sample was mounted on an electrically non-conducting x–y translation stage as shown in Fig. 1(a) and (b). One end of the sample was attached to the stage while the other end was kept free to allow for the actuation. The sample was placed in such a way that it directly faced the incoming laser beam. This mounted sample was then placed under the lens of a SHODENSHA® High Resolution 2-Megapixel USB Microscope. An external white light source was used to illuminate the sample. The microscope was then connected to a PC system which contained the software for its operation. Using the software the microscope was focused onto the tip of the free end of the sample. The laser was placed in front of the sample with enough room in between to place other optical components like continuously variable neutral density filter, linear polarizer, optical chopper etc. All optical components were mounted on an optical breadboard. The experimental setup is shown in Fig. 2.
Fig. 1

(a) Mounted sample front view (b) Mounted sample side view

Fig. 2

Experimental setup

To observe the effect of colour of laser beam on the actuation phenomenon three different diode lasers were used. All of them had a nominal power of 100 mW. The λ values were 655 nm for the red, 450 nm for the blue and 532 nm for the green laser. It was found that all of them had no definite polarization in the output beams. So, an external linear polarizer was used to study the effect of polarization. The first set of experiment that was done was to measure the actuation of the sample when the laser beam was directly focused onto the sample without using any optical component. The diode laser was rotated from 0° to 360° at an interval of 10° and the actuation of the sample was noted down using the software provided with the microscope. This experiment was repeated using all the three coloured lasers. During this experiment the power of all the lasers were reduced to and kept constant at 95 mW. This ensured that all incident powers were exactly the same. Next the power dependence of the actuation behavior was studied. So a continuously variable neutral density filter was used in the path of the laser beam to vary the output power of the laser up to its maximum value at an interval of 5 mW. To investigate the effect of polarization of the laser lights, observations were carried out in the presence of a linear polarizer. The polarizer was kept in the path of the laser beam and rotated from 0° to 360° at an interval of 10°. During these observations the output power of all the three lasers were also kept at a constant 95 mW. In the studies that were made in 2012 efforts were made to measure the response time of the deformation of the sample using an optical chopper [1]. The same observations were also conducted this time for all three colors. In this time the effects of the optical chopper on the actuation were studied in much more detail. Not only the vibration amplitude of the sample at different chopping frequencies was measured, the total deformation showed by the sample at different chopping frequencies in response to the colour of the laser light was also measured. The entire experimental setup was kept in a controlled environment and the experiments were carried out at an ambient temperature of 25 °C and at a constant relative humidity of 45%.

3 Results and discussions

3.1 Experimental results

The optical experiments showed that when the laser beam was focused onto the sample, the sample deformed and moved away from the direction of the incident light ray. This deformation of the sample was instantaneous (in a few milliseconds) and was found for all the lasers used in the experiment. The sample held its new deformed position as long as the laser beam was kept on. As soon as the light source was cut off, the sample reverted to its original quiescent shape. This reversal in the shape of the sample was also found to be fast. It was reported earlier the PIMA effect of the FSMA sample was found to be fatigue resistant [1]. Figure 3(a), (b) and (c) show the PIMA effect in action against the blue, green and red lasers respectively. Panel (i) of each of the three figures shows the sample at its rest position i.e. when it was not excited by any laser beam. The actuated or deformed sample in response to the incident laser beam is shown in panel (ii) of the three figures. The panel (iii) of the figures shows the sample when it returned to its initial resting position after the lasers were switched off. These figures were captured in real time using the USB microscope and its associated software.
Fig. 3

(a) PIMA effect of FSMA sample in presence of blue, (b) green and (c) red lasers

The amplitude of the actuation phenomenon found in the sample with respect to all the three unpolarized lasers is graphically shown in Fig. 4. Here the 0° was assumed randomly at the starting time and the laser was rotated at a fixed angle from it each time. The result shows that the actuation does not follow any predefined pattern and is not dependent on the angle of rotation of the unpolarized lasers. The variations are more than that are expected from random noise, so it indicates the partially polarized nature of the as received lasers. It is noteworthy and evident from the data that even here colour of light does play an important role in the amplitude of actuation of the sample. The sample showed maximum actuation for the blue laser whereas it showed minimum amplitude for the red coloured laser. This is very surprising, for there is no known analog wherein this photonic energy can do a macroscopic work, generally this is manifested in quantum phenomenon like in photoelectric effect. PIMA may be the first such macroscopic evidence for the effect in larger objects. From Fig. 4, it can be seen that the amplitude of actuation of the sample can be varied by simply using different coloured lasers. However, it is quite evident that the amplitude of actuation of the sample cannot be fully controlled in this way. To effectively control the operation of any microactuator system, amplitude of actuation of the sample needs to be reliable and repeatable.
Fig. 4

Microactuation of sample against unpolarized lasers

Another important parameter is the power of the incident laser. This was shown before to have a linear dependence on displacement of the sample [1], but it was done only for a red laser beam. Here the power dependence of the PIMA effect was measured for all the three lasers, taken at 0° as stated before. The data obtained are plotted in Fig. 5. The data show the linear relationship between powers of all laser colours and the displacements, up to the maximum power incident on the sample. The slopes of the blue, green and red lines are 1.97, 1.79 and 1.60 respectively, implying that the blue is more effective (about 25%) in achieving PIMA effect, and this fact is consistent with the observation made in Fig. 4. Therefore, the effect of colour of laser plays an important role on the actuation phenomenon. Hence it can be implemented as a control mechanism for the actuation property to be used in fabrication and operation of various microactuator systems by controlling the output power of the focused laser beam. In this regard it can be noted that the controlling mechanism will be much more effective if the polarization of the lasers can also be simultaneously controlled.
Fig. 5

Power dependence of PIMA effect on colour of laser beam

To test the effect of polarization of incident beam, studies were carried out for the three coloured beams for linear polarization. The results are shown in Fig. 6. The graph depicts the periodic variation of the amplitude with gradual change in polarizing angle from 0° to 360°. Here the polarizer was rotated and angles were measured by the scale attached to it, but the laser was kept steady. It can be seen here that the maximum amplitude of the actuation of the sample had drastically reduced when the linear polarizer was used as against unpolarized light. This is due to removal of components in other directions by the polarizer. From Fig. 6 it can be seen that much more controlled actuation can be achieved with the help of the linear polarizer. The effect of laser colour on the amplitude of actuation of the FSMA sample is also evident from the data obtained, with blue still giving more displacement than green which gave more than red. Most importantly, it shows that all the colours have exactly the same periodicity, and showed a dip at 90° and 270°, while the peaks were at 0° and 180°. This is the same as was reported earlier [1] and is as intriguing as the colour dependence of the PIMA effect.
Fig. 6

Effect of polarization on actuation

Figure 7(a) depicts the effect of an optical chopper on the vibration amplitude of the sample [1] when subjected to stimulation from the three lasers respectively. It is very clear from the data that colour of laser had no effect on the vibration amplitude of the sample. The vibration amplitude was solely dependent on the frequency of rotation of the optical chopper. At a frequency of 0 Hz or when there was no chopper present, the sample did not vibrate at all and remained in its deformed state as long as the laser was kept on. As the frequency of the optical chopper was kept on increasing, the amplitude of the sample was seen to decrease until it completely stopped near 50 Hz and beyond. This vibration of the sample was a result of the constant on–off like operation of the optical chopper. There is a time required for the sample to physically respond fully to the incident beam, and if the on/off happens before that, the sample cannot deform properly during that time. The total actuation of the sample in this state is depicted here in Fig. 7(b). As the frequency of the chopper was gradually increased the total deformation that the sample was able to achieve gradually decreased. Beyond 20 Hz, actuation was very small. Thus from Fig. 7(a) and (b) it can be inferred that for a constant laser power though the amplitude of actuation of the sample was dependent on the colour of laser used, the response time required by the sample to deform and come back to its original position is solely dependent on the property of the sample used. Knowledge of this property of the sample will be useful when making an actual microactuator system.
Fig. 7

(a) Vibration amplitude (b) Total actuation

3.2 Statistical analysis of experimental data

From the experimental data shown above it is seen that the microactuation property of the selected FSMA sample is dependent on various factors. To implement this property of the sample to actually make a microactuator system, analysis of the results of the experiments needs to be done in detail. Then only it can be found which controlling mechanism can be better used to operate any proposed microactuator system. Thus basic “Design of Experiments” (DOE) analysis [8] was performed on the experimental data to find out the relations between response i.e. actuation of the sample with respect to various controlling factors. “Analysis of variance” i.e. ANOVA studies [8, 9, 10] was chosen to be implemented on the experimental data. Minitab ® software [9, 10] was chosen for this purpose.

First, One-way ANOVA was performed on the unpolarized laser data. This is because the only difference between the three lasers used was their colours as all of them had the same output power and no other optical component was used to control the amplitude of actuation of the sample. So the output response that was shown by the sample was only dependent on one controlling factor i.e. the colour of the laser used. In the Minitab software the data for the unpolarized lasers were submitted. While performing One-way ANOVA displacement or actuation of the sample was selected as the response against laser colour as the factor. The standard confidence level of 95% was selected which means the significance level or alpha (α) value was set to 0.05. This indicates that there is a 5% risk of concluding that response is not dependent on the factor even if it depends on it. The results are shown below in Table 1.
Table 1

One-way ANOVA results (displacement versus laser colour)

Source

DF

SS

MS

F

P

Laser colour

2

31,462.3

15,731.1

306.55

0.000

Error

108

5542.1

51.3

  

Total

110

37,004.4

   

S = 7.164; R-sq = 85.02%; R-sq(adj) = 84.75%

The risk or P value (0.000) obtained here is less than the ‘α’ value (0.05). This proves that the laser colour has statistically significant effect on the level of actuation of the sample, but this analysis does not determine which data falls under which group. To convincingly prove that the actuation obtained in the sample is significantly different for each laser colour used, Tukey Grouping Information Method was implemented on the data analysis [9, 10, 11]. From the result shown below in Table 2 it is found that the actuation obtained in the sample by using three different coloured lasers is significantly different. This signifies that on an average the different coloured laser beams though having the same output power produced different levels of actuation in the sample. This can also be proved by looking at the boxplot as shown in Fig. 8. The effect of the factor i.e. laser colour in this case on the response i.e. displacement or actuation of the sample can be displayed by using the boxplot of the data. The graph shows that actuation of the sample increases when the laser colour was changed from red to green to blue.
Table 2

Grouping analysis using Tukey method

Laser colour

N

Mean

Grouping

Blue

37

178.584

A

  

Green

37

167.692

 

B

 

Red

37

138.692

  

C

Means that do not share a letter are significantly different

Tukey 95% simultaneous confidence intervals

All pairwise comparisons among levels of laser colour

Individual confidence level = 98.07%

Fig. 8

Boxplot of displacement

ANOVA makes certain assumptions before analysing any data. If those assumptions can be validated it can definitely be proved that the conclusions that were drawn from the ANOVA results are true.

ANOVA requires that the residuals be normally distributed. The straight line fit in the log-linear plot in Fig. 9 signifies that the residuals are normally distributed. So the normality assumption of the ANOVA analysis is validated.
Fig. 9

Normplot of residuals for displacement

ANOVA also assumes that the residuals are randomly distributed and have constant variance. The residuals vs fits plot shown in Fig. 10 validates this assumption as it can be seen that there are no recognizable pattern in the graph with the points randomly falling on both sides of zero.
Fig. 10

Residuals versus fits for displacement

The third assumption that ANOVA makes is independence i.e. the residuals are independent from one another. Here also the random nature of the graph shown in Fig. 11 signifies that the residuals are independent of each other especially of time related effects. Thus the order of data collection does not play any part in determining the response.
Fig. 11

Residuals versus order for displacement

Hence it has been proved by statistical analysis of the experimental data that different levels of PIMA effect can be achieved by just varying the colour of the laser beam. Now analysis of the effects of various optical components on the microactuation phenomenon can be done. This will help to propose an effective control mechanism for use in future microactuator systems. Two-way ANOVA analysis [8, 9, 10] have been used on the next data sets as the PIMA effect found was in response to two controlling factors viz. the colour of the laser beam as well as the optical component used. When applying the Two-way ANOVA study on the power dependence of the PIMA effect the colour of the laser beam and the output power of the laser were selected as the two factors which controlled the response that is the actuation or displacement of the sample. The results of the analysis is shown here in Table 3.
Table 3

Two-way ANOVA results (displacement versus colour, power)

Source

DF

SS

MS

F

P

Colour

2

2822

1410.95

42.61

0.000

Power

19

159,644

8402.33

253.74

0.000

Error

38

1258

33.11

  

Total

59

163,725

   

S = 5.754; R-sq = 99.23%; R-sq(adj) = 98.81%

The result clearly shows that P value is less than the ‘α’ value for both the controlling factors i.e. colour and power of laser respectively. Hence it can be inferred that the actuation achieved by the sample is dependent on both the controlling factors. Figure 12 shows the relation of the actuation or displacement of the sample with the two controlling factors. Hence it is proved that the PIMA effect depends on both the laser colour as well as the output power of the laser. So by controlling these two factors together significant variations in the actuation amplitude of the sample can be achieved and hence it proves to be an effective control mechanism to be deployed in future microactuator systems. The assumptions made by ANOVA were validated by following the earlier guidelines.
Fig. 12

Main effects plot for displacement

The next mechanism that was proposed for operating any microactuator systems was by controlling the polarization of the laser beams. Hence Two-way ANOVA study was applied to the linear polarizer data assuming the colour of the laser and the polarization angles as the two controlling factors. The results are depicted in Table 4. Here also analysing the P value of the ANOVA calculations it can be said without any doubt that the actuation phenomenon of the sample is very much dependent on both the controlling factors i.e. colour of laser as well as polarization angle of the incident beam. Figure 13 shows the relationship between the response i.e. actuation of the sample and the two controlling factors. Hence another mechanism to effectively control and apply the PIMA effect to any microactuator design has been successfully proposed. The assumptions made by ANOVA are again validated as earlier.
Table 4

Two-way ANOVA results (displacement versus colour, angle of rotation)

Source

DF

SS

MS

F

P

Colour

2

752.7

376.34

14.86

0.000

Angle of rotation

36

50,927.5

1414.65

55.87

0.000

Error

72

1823.1

25.32

  

Total

110

53,503.3

   

S = 5.032; R-sq = 96.59%; R-sq(adj) = 94.79%

Fig. 13

Main effects plot for displacement

Finally the effect of the optical chopper on the actuation of the sample was studied. Here colour of the laser beam and frequency of the optical chopper are the two controlling factors. In this study two different responses were taken into consideration viz. total actuation as well as the vibration of the sample. The results of the Two-way ANOVA analysis of the data are shown in Tables 5 and 6 respectively. Looking at the actuation data of the sample in presence of the optical chopper it can be inferred that both laser colour and frequency of chopper can be considered as an effective control mechanism for the PIMA effect as again the P value is well within the significance level or α value. On the other hand, on further analysis of the vibration data it can be seen that control of the actuation mechanism of the sample cannot be definitely achieved as the vibration patterns of the sample cannot be differentiated by controlling the colour of the laser beam. This is evident from the fact that here the P value is larger than the specified α value of 0.05. Further it can be said that as the sample is vibrating in presence of the optical chopper it will not be suitable to apply this control mechanism to any microactuator system. The actuator will not be able to perform to its maximum potential as it will be vibrating and it is very difficult to control this vibration. If any special purpose microactuator is designed where the actuator is supposed to vibrate then only this design option can be considered. Otherwise it is not feasible to consider this control mechanism for further study.
Table 5

Two-way ANOVA of chopper actuation (displacement versus colours, frequency)

Source

DF

SS

MS

F

P

Colour

2

2460.0

1229.98

141.45

0.000

Frequency

22

42,296.7

1922.58

221.10

0.000

Error

44

382.6

8.70

  

Total

68

45,139.2

   

S = 2.949; R-sq = 99.15%; R-sq(adj) = 98.69%

Table 6

Two-way ANOVA of chopper vibration (vibration versus colour, frequency)

Source

DF

SS

MS

F

P

Colour

2

2.01

1.004

2.83

0.070

Frequency

22

8755.00

397.955

1121.10

0.000

Error

44

15.62

0.355

  

Total

68

8772.63

   

S = 0.5958; R-sq = 99.82%; R-sq(adj) = 99.72%

4 Conclusions

In this communication a report and analysis of the detailed study made on the photo induced microactuation effect of an FSMA sample when excited by a focused laser beam was made. It was found that laser colour plays an important role in the actuation properties of the sample. Efforts were made to control the amplitude of actuation of the sample by using various optical components. Thus the relation of the actuation amplitude with various controlling factors like colour, output power and polarization of the laser beam was established. The response time of the actuation phenomenon for the different coloured lasers was also studied. From the studies that were conducted and also from the statistical analysis of the experimental data, two controlling mechanisms for the microactuation property of the sample can be proposed. One control mechanism which is dependent on the power of the laser is linear in nature. Another one which is dependent on the polarization of the incident laser beam is periodic in nature. These control mechanisms can be implemented to successfully fabricate and operate various microactuator systems in the near future. Hence a remotely controlled micro-mechanical system can be conceived by implementing this property of the FSMA samples. Though the cause of this unique phenomenon is still not clear, these studies should provide a bigger data base in order to track the root of it. Structural, magnetic, thermal and mechanical properties of the system are being further and systematically studied to explain the reasons behind this photo induced microactuation effect. Once those studies are successful it will be possible to explain this property of the sample and other suitable alloy systems can be produced for use in microactuator systems.

Notes

Acknowledgements

One of the authors, AB, would like to thank the Council of Scientific and Industrial Research, Govt. of India, for the grant of a senior research fellowship. He is also thankful to The Director, S. N. Bose Centre to allow him to work in this institute.

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Copyright information

© Indian Association for the Cultivation of Science 2018

Authors and Affiliations

  1. 1.LCMPS. N. Bose National Centre for Basic SciencesKolkataIndia
  2. 2.Department of Mechanical EngineeringJadavpur UniversityKolkataIndia

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