Lecture 13 (EM21) -- Metamaterials

[@steved9670]

The best introductory lecture on metamaterials I've seen. Great job

[@empossible1577]

Thank you! You maybe interested in checking out the official course website. There have been a few revisions and improvements to the notes. The website also has links to the videos and other resources. emlab.utep.edu/ee5390em21.htm Enjoy!

[@igorkrotov1565]

This kecture opened a whole new world for me. Thanks a lot

[@coolbud356]

Amazing lecture!! I became so addicted to your lecture that I simply watched for whole day from begining upto here. Definitely would go remaining. Thank you so much..

[@empossible1577]

Thank you!

[@NuwarMisconi]

Great video...I like the fact that you provide information about the different research papers. Definitely handy when searching for resources about the subject. (trusting your choice :) ). Pity that the video stopped without getting the idea behind the near field interaction.

[@leeorshimhoni8949]

excellent. professional and explicit. the speaker is logical, immaculate thinker.

[@empossible1577]

Thank you!!

[@rajatsharma6256]

The speaker is a prof. Respect for him. Doing great work, helping students and researchers worldwide.

[@ignatiolu863]

Thank you for the lecture! Could there be a list about gain materials (semiconductors & doped glasses, crystals) that have their complex refractive index sign inverted to positive?

[@empossible1577]

I am not entirely sure what to point you to other than the literature. One good website is: www.ioffe.ru/SVA/NSM/nk/

[@ANANTHASANKAR_UA]

Excellent in depth video ❤

[@empossible1577]

Thank you!

[@zakireee01]

A very good way of understanding the Metamaterials. Many many thanks

[@empossible1577]

Thank you!

[@gulzarali7566]

many thanks. great lecture which clear so many point, at the moment i am working on double negative prism and trying to demonstrate negative refraction but unfortunately, i am unable to observe any backward refraction. any suggestion

[@sama1s2d3]

Interesting stuff- thanks!!

[@mohammadazadifar969]

Amazing lecture, thanks for sharing the knowledge! One question: why in the Lorentz derivation from oscillation of an atom (slide 10), we only consider the electric field?

[@empossible1577]

There are only electric charges, not magnetic charges. Electric and magnetic fields interact with those charges differently so they produce resonances at different frequencies due to different mechanisms. Here I am analyzing only a resonance produced by the interaction with the electric field. This analysis will ultimately lead up to a permittivity. A similar analysis can be done that ultimately leads up to a permeability. Both happen at the same time and so materials possess both a permittivity and a permeability. Both leads to the same equation of resonances, but the constants defining the resonances will be different. Also, real materials will have multiple and sometimes overlapping resonances. The field of science that deals with this most directly is spectroscopy. Hope this helps!

[@mohammadazadifar969]

very helpful, thanks!@@empossible1577

[@syedusama7393]

Thanks bro Is there any video of yours how to design and analyze MTM unit cell in cst for gain enhancement of patch antenna?

[@Vlado93CG]

I am extremely grateful for all the content you produce, it helped me a lot during my research! I have a question regarding the zero-thickness angle-insensitive optical filters you mentioned here. If the thickness is essentially zero, is there a way to modulate the wavelength of the transmitted light, because that's normally the purpose of these filters - transmission modulation by thickness variation? Are you aware of any papers/research groups I could check to learn more about this concept? Thank you!

[@empossible1577]

Thank you for the compliment! First, let me point you to the official course website. From here, you can download the notes, get links to the latest version of the videos, and get access to other learning resources. empossible.net/academics/emp6303/ You will find this lecture now in Topic 5, Lecture 5b. As for the design, you design them the same way would you would a typical multilayer film. For example, let's say you have a Bragg grating with two alternating layers, each a quarter wavelength thick. Those thickness define the reflection band of the Bragg grating. However, if you make one layer positive quarter wavelength and the other negative quarter wavelength, you get the same reflection band, but the overall thickness is zero and angle insensitive. Does this make sense?

[@Vlado93CG]

@@empossible1577 thank you!

[@abdulazizdessalew4678]

Great introductory lecture !!! I hope You will do successive lectures on this area too. Thank You.

[@empossible1577]

Thank you!! Yes, I am hard at work on this. For now, check out the official course website that contains links to the videos, the latest version of the notes, and other resources. The notes contain a lot of revisions, additions, and other improvements that are not in the videos. emlab.utep.edu/ee5390em21.htm

[@nanimedicherla]

great lecture on MTMs

[@empossible1577]

Thank you!

[@coltennabers634]

Amazing!

[@empossible1577]

Thank you!!

[@Soryatuz]

Hello, Greetings from Brazil o/ Ur vídeo helped me soo much, i'm looking forward to see ur entery series of lectures =) Tyvm for this.

[@empossible1577]

Thank you!!

[@MuhammadGulzari]

Very interesting!

[@rajatsharma6256]

An interesting and relevant topic for a future video could be optical anapole that is not a part of conventional course.

[@empossible1577]

I agree. Great idea!

[@wojciechdojlido8235]

That's great! Its a pity, that I haven't discover that channel sooner!

[@empossible1577]

ha ha. Thank you!! Check out the official course websites. These have links to the videos, other resources, as well as the latest version of the notes, which have seen many corrections, revisions, additions, and other improvements. empossible.net/academics/

[@한두혁]

great lecture. What textbook do you recommend sir?

[@empossible1577]

When I first developed this course, I did not like any book as an introduction to metamaterials. I used my course website as the book: empossible.net/academics/emp6303/ I have not searched in a while, but I suspect there are some good metamaterial books available now. I just don't know which ones to tell you. If you are interested in computational electromagnetics of things like metamaterials, parameter retrieval, photonic crystals, diffraction gratings, etc., I recently wrote a book. Here is a link to see more about it: empossible.net/fdfdbook/

[@abinayashree8199]

Very good lecture sir.

[@versatile_gentlemen]

Hi, thanks for sharing this nice lecture on metamaterials. Could you please refer a book that explains about how to optimize or calculate the metamaterials effective properties, permittivity and permibility?

[@empossible1577]

That is a very difficult question. I do not know of a book that covers everything you will need. Instead, consider taking the following steps: 1. Learn to simulate a metamaterial in order to calculate its effective properties. 2. Benchmark your parameter retrieval tool using multiple results from the literature. 3. Learn to do parameters sweeps in your simulation tool. Study how the various features of the metamaterial affect its effective properties. 4. Use #3 to study various metamaterials in the literature. 5. Learn optimization. Optimize a single variable at a time to...say...make the dielectric constant equal to 10. Now optimize two things to do the same. Now optimize multiple things to make er = 10 and ur equal something else. By the time you get through this, you will be an expert in design of metamaterials!

[@duruengiz3261]

Thank you for this video and all of the lectures you have made about fss's and meta surfaces. They are really clear and understandable. I have two questions . If a material transparent, does it have to be always visible frequency? Or does it mean it is absorbing a specific kind of em wave? And are mm's absorbing because they are actually making the evanescent waves grow? Is it right to make this reasoning?

[@empossible1577]

When I read "transparent" I think that means transmission at any frequency whether we can see that frequency or not with our eyes. I suspect the dictionary definition of "transparent" requires it to be a visible wavelength of light. The first interpretation is probably the better one when reading the literature. There are many mechanisms for a metamaterial to exhibit loss. Having large evanescent fields is not directly one of them. Evanescent waves are sort of just temporary places for electromagnetic energy. That energy will eventually radiate away as a propagating wave. Loss is typically ohmic loss in the metals. Metamaterials are resonant so the loss is amplified and a big problem actually. There is also dielectric loss, but that is small compared to the ohmic loss in the metals. If the metamaterial is close to something else, large evanescent fields can play a role in loss because they can provide a leakage path for energy.

[@duruengiz3261]

@@empossible1577 thank you very much sir.

[@hongbinbin24]

Thank you. It is very useful.

[@TechnicallyExplained]

why do metamaterials have negative permitivity and negative permeability? why do they behave differently to light or incident wave?

[@empossible1577]

To fully understand metamaterials, I recommend first studying ordinary materials. Work to understand different resonances that materials have. You will find that permittivity can be negative even in ordinary materials, particularly around resonances or in metals. I cover this topic in Lecture 2 of this same course. Next, study metamaterials and see how current resonance in the metallic structures is emulating the atomic scale resonances in ordinary materials. At this point, it will be less mysterious how permittivity and permeability can be negative. It is just a consequence of the phenomenon arising due to resonance. When one or the other is negative, the materials acts like a conductor (magnetic conductor for negative permeability). When both are negative, you have a left-handed metamaterial with a negative refractive index! Crazy things happen then.

[@TechnicallyExplained]

@@empossible1577 thanks for the reply sir... can you tell me why do they metamaterials act as frequency selective surfaces? thanks in advance..

[@empossible1577]

@@TechnicallyExplained While metamaterials can filter frequencies like a frequency selective surface (FSS), I would not think of metamaterials as an FSS. Metamaterials are more analogous to bulk materials. Flat, essentially planar, structures are the metasurfaces, frequency selective surfaces, diffractive surfaces, etc. Most metamaterials are resonant. This inherently leads to filtering because resonance itself is a frequency selective process. Even at frequencies where the metamaterial is not resonant, you can tailor metamaterial lattices to resonate across multiple units cells, more of a macroscopic resonance. For example, a metamaterial slab will produce a sort of Fabry-Perot resonance that can filter frequencies.

[@adnanyousaf5755]

excellent tutorial sir :)

[@empossible1577]

Thank you! This section of the notes is one of my oldest now. I hope to revise and modernize it soon.

[@adnanyousaf5755]

​@@empossible1577 Dear Sir, how can i extract/ find the relative permittivity and impedance using CST studio or mathematically using S11 etc , kindly help. Regards.

[@empossible1577]

@@adnanyousaf5755 I do not use CST so I cannot tell you how to do it in that tool. If you have S11, it seems like you should be able to work the Fresnel equations backwards to extract the effective impedance. I have ever analyzed artificial impedance planes, but this is my guess. I suspect there should be a lot of literature on this topic.

[@adnanyousaf5755]

@@empossible1577 grateful sir

[@NoOne-cf2ji]

Do have any lectures on acoustic meta materials for low frequency absorption ?

[@empossible1577]

Sorry no.

[@nikzax7147]

hello.Can you tell me please how did you get these dimensions at 13:09 ? Which are the equations or the theory behind these calculations? thanks in advance

[@empossible1577]

I do not have a specific memory about creating this slide, but it is safe to assume it all came from the publication referenced on the slide. If not, please let me know!

[@educativeedge4622]

Can u tell about book which u following?

[@empossible1577]

No book. This is all taken from my own experience or various journal articles I have read.

[@younesszaarour284]

please a question how can i calculate the parametre of the a cssr or csrr (extern ray, the gap or the width) for each frequency ? and how can i do it if have two resonance frequency ? thanks

[@empossible1577]

I first recommend searching the literature. These structures have been pretty extensively studied. If you want to do all of this yourself, I recommend studying parameter retrieval and homogenization. There is a lecture about that on this channel. Calculate the effective parameters for some known structures from the literature to be sure your tools are working correctly. Once you have these, do a bunch of parameter sweeps that connect your structural parameters to the effective parameters.

[@younesszaarour284]

@@empossible1577 i just understand yes i will do it by my self thanks so much :D

[@mohaasad2690]

hello hello.Can you tell me please how did you get damping force (collision frequency) in drude model ? Which are the equations or the theory calculations? thanks in advance

[@empossible1577]

I think the best way to obtain these values is to retrieve the effective permittivity and back calculate the parameter from that. There is another lecture in this series on homogenization and parameter retrieval. Let me also point you to the course website that has links to these videos, plus the latest version of the notes. There have been quite a few revisions and improvements since these were recorded. emlab.utep.edu/ee5390em21.htm

[@AmritZoad]

Hi. I checked the EM21 course website . Seems very interesting. I am specifically interested in metamaterials and the related theory. Can you tell me which other videos are related to this one. :) Also, I would like to know if you recommend any books regarding metamaterials. Thanks! You are doing god's work!! :)

[@empossible1577]

Pretty much the entire course is related to metamaterials although the connection may not be obvious to you at first. Lecture 2 -- Lorentz and Drude Models This lecture covers why materials have a dielectric or magnetic response and covers general properties of materials. Metamaterials are mimmicking nature and have a good background in this will give you insight about how metamaterials work. Lecture 3 -- Metamaterials are usually anisotropic and even bi-anisotropic. I also cover topics hear needed for using transformation optics to design metamaterial devices. Lecture 5 -- Coupled-mode theory is a framework that you can use to understand just about any electromagnetic device. This ties into metamaterials and periodic structures in order to engineer the coupling. Lecture 7 -- This is a key lecture to understanding anything periodic, like metamaterials, photonic crystals, frequency selective surfaces, metasurfaces, gratings, etc. Lecture 9-12 -- While not traditional metamaterials, this are very related topics and good to understand. For example, at a high enough frequency, metamaterials diffract. The lecture on subwavelength gratings are metamaterials and explains how to engineer the anisotropy. Lectures 12-15 -- These are the core metamaterial lectures that covers all engineered materials including mixtures, metamaterials, and photonic crystals. It has has a discussion about how to retrieve the effective parameters of metamaterials. Lecture 16-18 -- These lectures cover techniques for designing metamaterial devices. The spatially variant lattice stuff is a somewhat new topic that we are finding to be very powerful and enabling. We have done amazing things with it! BTW, below is a link to the course website. Many of the notes have been revised, improved, added-to, etc. since the videos were recorded. Be sure to look at the electronic notes as well. emlab.utep.edu/ee5390em21.htm

[@ericpham6192]

We could engineer molecular electron spin so that it contrast inversely with temperature by increase internal gravity to balance absorbed heat so that it could survive extreme temperature and could be use to build extreme small CPU that can compute high speed without increasing resistance like super conductor and utilize the shadow emf to help the self sustaining motion of survival in extreme temperature according to law of conservation of matter and energy. This could help reverse agimg process in material and human. The path of electron could be in infinity sign could keep energy and mass in balance in and out

[@cssaziado]

Really interesting! Thank you for this lecture! You really put me a lot of interest on this! What are the lights wavelength used? should be meters or centimeters? In visible you can you apply those materials? Thank you Fernando, from Porto University, Portugal

[@empossible1577]

Probably the most common optical wavelength is 1.55 micrometers because that is common in telecommunications. Longer wavelengths are used in infrared imaging. Shorter wavelengths (visible wavelengths) are used for cameras, microscopes, etc. The concept of metamaterials is applicable to any frequency. The struggle may be achieving the size and the material properties needed. For example, metals do not act like metals at x-ray frequencies so I am not sure how we would make things like split-ring resonators at x-ray frequencies. On the other side of the spectrum, imagine the size of a metamaterial unit cell operating at 1 Hz. The concepts work electromagnetically, but when it comes to actually making the structures we sometimes struggle. Microwave frequencies is a very convenient scale to make things because the elements are roughly the size of a coin. That is why you see so much metamaterial work at microwave frequencies.

[@cssaziado]

@@empossible1577 , Nice I got it! Thank you! So to be able to make a Harry potter invisibility cloak, I would need a 500nm/10 resonator rings and capacitor to be able to produce a n

[@empossible1577]

@@cssaziado That is about right. The other problems you will face is making it broadband enough to cover the entire visible spectrum and then also combating the loss. Metals are very lossy at optical frequencies.

[@cssaziado]

@@empossible1577 ,Thank you very much, again, for your answers. I would love to know what your group is studying atm, do you have any link to articles or stuff? I became really interested in these materials and proprieties. I am a masters student, so I am thinking about a thesis.

[@empossible1577]

@@cssaziado Here is a link to our research website. emlab.utep.edu/ I have a PhD student about to defend his PhD and I will be posting his PhD defense likely today (assuming I get it from him). That will give you the latest and greatest. Subscribe to CEM Lectures and I think it will notify you of new uploads.

[@navyagayathri449]

Sir if we are getting error as port 1 supports additional propagation mode in hfss software What should we do sir

[@empossible1577]

For metamaterials, it is typically the zero order mode.

[@fernandolamas8381]

Is a LHM like a BWO?

[@bhavnaghai3292]

more lectures on metamaterials? Or any courses available?

[@empossible1577]

For more lectures on metamaterials, check out the other lectures in the EM21 series. This entire course is on that subject and they are archived here: emlab.utep.edu/ee5390em21.htm The the lectures in this series essentially lead up to this metamaterials lecture. The following lecture is on band gap materials that many still consider in the family of metamaterials. I have a similar course on finite-difference time-domain here: emlab.utep.edu/ee5390fdtd.htm And a follow-on course to this titled "Computational Electromagnetics" here: emlab.utep.edu/ee5390cem.htm Maybe more will happen over time. We'll see. Enjoy!

[@letslearn3277]

Sir can you please tell how to plot permittivity in hfss 19 version without using matlab code

[@empossible1577]

This is covered in a later lecture. Take a look at the video for Lecture 5d here: empossible.net/academics/emp6303/

[@letslearn3277]

Sir,can you please tell me if we can use copper as a metamaterial

[@empossible1577]

Copper itself will not be a metamaterial, but you can certainly build the metallic structures from copper that will be the metamaterial.

[@letslearn3277]

@@empossible1577 thankyou sir

[@zeyupan7282]

Our prof totally 'borrowed' your slide!

[@empossible1577]

Ha ha. No worries. I am happy as long as the course materials are helping people like you!

[@nikoletazacharaki8828]

hello,I want to ask something that I am looking for it a month..how did you get these dimensions for srr?for example why is a=3.333mm and not 4 or 5? Is there any equation? thanks in advance

[@empossible1577]

Happy to answer. The parameter 'a' is the lattice spacing that is largely, but not completely, responsible for the frequency of operation. In this case, a = 3.3 mm makes the metamaterial resonate at 15 GHz. If we chose to scale the unit cell so that a = 6.6 mm, it would work the exact same way at 7.5 GHz. For the most part, the values of the parameters are chosen by running some sort of optimization. Sometimes you can derive an equivalent circuit model and then determine the values of the dimensions using closed form equations. Hope this helps!

[@nikoletazacharaki8828]

thanks a lot. I dont know how can optimize the parameter. Should I put a random value for a and then optimize it with simulator?To be clear I try to design a multiband microstrip antenna based on metamaterial and I have 9 SRRs as substrate.I want a resonant frequency at 2.5 and 2 or three more frequencies. I take these results but I am not sure that I use the right dimensions for SRRs. Thanks again for youw answer

[@empossible1577]

A big mistake that everybody makes it jumping straight into the big problem. The best thing you can do is learn how to break your problem down into smaller steps. Do not try to immediate simulate an antenna with metamaterials. There is too much going on. Take a step back. First, I suggest just studying metamaterials. Learn how to calculate their effective properties, permittivity and permeability. Then simulate some simple patch antennas with known properties. Duplicate those results. After doing all this, you will be in a position to begin designing your fancy antenna. I would simulate a patch antenna and just add a homogeneous slab of material with effective properties of your metamaterial. This will run faster and allow you to study your antenna without having to consider the actual design of your metamaterials. Next, move on to learning optimization and then design the metamaterials to give you the effective properties you need. Only as a last final step will you actually simulate the antenna with the metamaterial structures. I think you will also learn more by approaching your research this way.

[@nikoletazacharaki8828]

You are right but sometimes it is not on my hand to do these steps properly.Thank you

[@empossible1577]

Do you best to break down your topic into small steps. Ideally, the steps can be checked for correctness. For example, duplicate similar results in the literature.

[@missmarvellous2247]

Can u plz tell fundamentals of MTM LH

[@empossible1577]

Let me point you to the official course website: empossible.net/academics/emp6303/ The lecture on metamaterials is in Lecture 5b. If you want more of a background, see previous lectures in this course. It is all there for LH MTMs.

[@missmarvellous2247]

@@empossible1577 thank u

[@yvonneshenlong]

Is this video a completed version? It doesn't contains hyperbolic metamaterials.

[@empossible1577]

The video is complete, but the notes have seen considerable revisions, content additions, and reorganization. The electronic notes now include hyperbolic metamaterials, but I have not yet rerecorded the videos. You can get the latest electronic notes along with other resources from the course website: emlab.utep.edu/ee5390em21.htm Hope this helps!

[@yvonneshenlong]

Thank you a lot!

[@nag4741]

sir, you placed some .p files in MATLAB files for FDTD.how can i open them using matlab? i am using matlab2013a version

[@empossible1577]

You can't "open" p files in MATLAB. You can only run them. Just drag them to your working directory and run them like there were a MATLAB program. I use p-code for my classes when I want the students to use the program, but not see the code. For example, in FDTD there are some codes to check the values assigned to certain parameters. In order to do this check, I have to calculate the correct values. I don't want the students to see that code or it would make the assignment useless. If you want to create pcode, write an m-file script and then type at the command prompt ">>pcode filename"

[@nag4741]

CEM Lectures sir, i want to design an implantable antenna using FDTD method in MATLAB..will you please tell me the designing steps and brief introduction on how to analyse body simulation.please send to my email [e-mail]

[@empossible1577]

I am not sure I can do all of that in one e-mail. I can tell you that you will need a 3D FDTD model. My recommendation is to find a good paper in the literature that has done something similar. Work to duplicate their results. Having done that, you will learn a lot and also have an answer that you know is correct and can work toward. You will be in a much better position to solve the problem of of new antenna. Two other things I can provide. First, check out a program called Blender. It is free and open source and there are a lot of models available for free, including human heads or any other body part you may be interested in. Second, I have some links to sites that provide the electromagnetic properties of virtually any fluid or tissue there is in the human body. Get them here: emlab.utep.edu/resources.htm They are at the very top under "Useful Links" Hope this helps!

[@nag4741]

CEM Lectures thank you sir

[@waldemargregorkaiser4080]

thank you very much for this answer but this is not a meta material it is an antenna

[@empossible1577]

Waldemar Gregor Kaiser You are right! Most metamaterials are arrays of small antennas that receive and re-radiate waves. The interference between the re-radiated waves and the applied wave gives an overall macroscopic response that is analogous to what happens at the atomic scale. Thus, a metamaterial is born because the effective properties can be controlled through the physical dimensions of the elements.

[@jwp98765]

@@empossible1577 Wow. I know nothing about it, just popped into the comments section to see what the hell it's about and... cool. Tiny antennas receive, then emit waves - are the re-radiated waves identical matches to, or different than the origin waves? - creating an interference pattern that can be controlled? Ok. Time to watch your video, lol. Count me a little bit fascinated.

[@empossible1577]

@@jwp98765 The secondary waves are at the same frequency as the applied wave so they are able to interfere with it. Otherwise, they are much smaller amplitude and out of phase. I suggest also listening to Lecture 2 which describes why materials exhibit a dielectric response. This will give you more insight about how metamaterials work because you will hear the same story about secondary waves. Also, I should point you to the official course website. Many of the notes have seen corrections, revisions, improvements, new content, etc., but I have not yet rerecorded the videos. emlab.utep.edu/ee5390em21.htm

[@waldemargregorkaiser4080]

where is your meta material on a photograph and the whole experiment

[@empossible1577]

Waldemar Gregor Kaiser Most of the time when a metamaterial is shown, only a single unit cell is shown. it is implied that it really needs to be in an array. A photograph of the world's first left-handed metamaterial is provided around slide 20. A photograph of the world's first electromagnetic cloak is shown on Slide 28. A photograph of some anisotropic metamaterials are shown on Slide 37. Each of these photographs is cited and you can refer to the publications to read the results of the experiments for each.

[@hodamoner1103]

Can I have the PPT, please?

[@empossible1577]

Below is the link to the course website where you can download the latest versions of the notes and videos as well as other learning resources. empossible.net/academics/21cem/

[@hodamoner1103]

@@empossible1577 thank you

[@empossible1577]

@@hodamoner1103 You are very welcome!

[@meghjitmajumder3468]

Great video but it seems like an incomplete one.

[@empossible1577]

It definitely is. It is hard to squeeze everything into a single lecture. Also, have you watched the videos that come before and after? All periodic structures share a lot of math and theory and this is covered in other lectures. Also, let me point you to the official course website. This has the latest version of the notes which have seem some revisions and improvements since the videos were recorded. empossible.net/academics/emp6303/

[@meghjitmajumder3468]

@@empossible1577 Thanks..those resources are quite good.

[@waldemargregorkaiser4080]

show me the reality man

[@empossible1577]

Waldemar Gregor Kaiser Metamaterials are very real! This is not fake or even stuck in theory. Metamaterials are being reduced to practice and doing wonderful things for humanity. Tell me what you think is not real and I am sure that I can point you to a real device based on it.

[@waldemargregorkaiser4080]

this is not cute to me

[@empossible1577]

Waldemar Gregor Kaiser LOL. There is a lot of hype or excitement about metamaterials. You may enjoy a book written by Ben Munk that is quite critical of the field of metamaterials: www.amazon.com/Metamaterials-Alternatives-Munk-Ben-Benedikt/dp/B0088OXX4U/ref=sr_1_6?ie=UTF8&qid=1428444895&sr=8-6&keywords=ben+munk I think this conversation is great. Tell me where your troubles or skepticism begins.

A mandatory commercial with an offensive loud announcer,, fuck you channel.

[@avicohen3035]

In Israel ,your freedom of speech is restricted. My device has been compromised and my comments are being segregated/erased/edited.