Omega resonator - Page 1
Forum section: electronics / rf-microwave

author: branadic
author_rank: Super Contributor
timestamp: October 01, 2024, 11:35:59 am
content: Hello,I'm placing my request again over here, hoping that the right people see it and can help me.After building first NV-based setups with microdiamonds to demonstrate Quenching we went forward and build our first ODMR/Zeeman splitting setup using a discrete build Omega resonantor based on some SMA posts that were soldered together with 1 pF Mica capacitor and a magnet wire loop in between. After some tweaking of the lenght of the magnet wire we achived a nice 2.87 GHz resonance frequency.I now wanted to go a step further using planar Omega resonators. There are quite a few publications out there addressing this topic, which would be a good starting point for simulation, replication and adjusting to individual needs, such as:Antenna for microwave manipulation of NV colour centresAs my pocket is not that deep I tried simulating the geometry from the aforementioned paper using Sonnet Lite. I think I have setup everything properly. Unfortunately, the simulation is far of from what I expected (see images below). Is anyone into RF simulation and can help?Is there any other free tool for such tasks?The Sonnet Lite file can be found here:https://www.eevblog.com/forum/metrology/is-anyone-into-quantum-technologies-and-quantum-metrology/?action=dlattach;attach=2383977-branadic-

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 01, 2024, 06:22:04 pm
content: What are the boundary conditions?Is there a ground via, or is that tail meant to be a 1/4 wave "grounding" stub? But then, how is it the same length as the width of the loop?If the bounds are shielding, I'm impressed anything is absorbed at all; you've only got copper inside a box, of course it's going to reflect.Networks for physical influence tend to be limited by mechanical constraints, and thus require far more drive power than physically necessary -- the rest is taken up by the matching network and termination resistor needed to couple it to a practical (usually 50Ω) amp.Perhaps you also don't measure anything because you don't have a simulated NV diamond in the near field. I have no idea how strong the coupling will be. Sounds weak like NMR stuff, but who knows.Tim

author: branadic
author_rank: Super Contributor
timestamp: October 01, 2024, 07:10:15 pm
content: I tried replicating what is given in the paper, so only the resonator is simulated. The ground plane as per manuscript is defined as "And the copper film on the lower layer of the dielectric substrate is the reference ground of the microstrip antenna, the size of which is 14.2 × 0.5 mm2."As for the boundary conditions I've found the following:"The Sonnet EM analysis is performed inside a six-sided metal box as shown below. This box contains any number of dielectric layers which are parallel to the bottom of the box. Metal polygons may be placed on levels between any or all of the dielectric layers, and vias may be used to connect the metal polygons on one level to another.The four sidewalls of the box are lossless metal, which provide several benefits for accurate and efficient high frequency EM analysis:- The box walls provide a perfect ground reference for the ports. Good ground reference is very important when you need S-parameter data with dynamic ranges that might exceed 50 or 60 dB, and Sonnet’s sidewall ground references make it possible for us to provide S-parameter dynamic range that routinely exceeds 100 dB.- Because of the underlying EM analysis technique, the box walls and the uniform grid allow us to use fast-Fourier transforms (FFTs) to compute all circuit cross-coupling. FFTs are fast, numerically robust, and map very efficiently to computer processing.- There are many circuits that are placed inside of housings, and the box walls give us a natural way to consider enclosure effects on circuit behavior."There is a 50 ohm port on the very left feeding the geometry, at least that is what I think.-branadic-

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 01, 2024, 08:59:13 pm
content: Yeah OK, so hard terminating field lines at the boundary. Then...Is that realistic to your physical model? Is your test in a box of the same size? Is it metal, solid and contiguous?Or would it be more realistic to expand the dimensions, and add (in whatever way Sonnet permits; perhaps not very effectively, by the sound of it) damping materials to simulate the radiation resistance of a test article in free space?And, do you have any way to express the NV element? A high(ish?)-Q resonant tank coupled to a port (loop or antenna) above the omega resonator, perhaps?Tim

author: szoftveres
author_rank: Regular Contributor
timestamp: October 01, 2024, 09:54:43 pm
content: What is the significance of "Omega resonators"?What does it do that other planar resonators (stub, hairpin, etc .) don't?

author: branadic
author_rank: Super Contributor
timestamp: October 01, 2024, 10:04:48 pm
content: I think I found the culprit, it's the complete ground plane on the bottom layer.I replicated another microwave antenna with an overall groundplaneBroadband, large-area microwave antenna for optically-detected magnetic resonance of nitrogen-vacancy centers in diamondand the simulation results fit.I now need to figure out a way how to reduce the groundplane to the 14.2 × 0.5 mm² mentioned in the manuscript for the omega resonator.QuoteIt's the need to excite the diamond with the magnetic nearfield portion of the microwave.-branadic-

author: branadic
author_rank: Super Contributor
timestamp: October 02, 2024, 02:16:21 pm
content: I played with different things like changing the covers of the box to free space and adding, as suggested by someone else, a 50 mm layer of air underneath the board and changed the top air layer also to 50 mm. While that changed at least something in the resonant frequency, it's still far apart from the mentioned 2.87 GHz.I also tried a microwave planar ring antenna design descibed inBroadband, large-area microwave antenna for optically detectedmagnetic resonance of nitrogen-vacancy centers in diamond, which worked out just fine in Sonnet and showed resonant frequency where expected.So that leaves the impression that either I'm still doing something stupidly wrong in Sonnet or that the numbers given for the geometry are just wrong. Hence why I'm asking, is there anyone out there who could simulate theAntenna for microwave manipulation of NV colour centresin HFSS, CST, ADS or whatever you are familiar with?-branadic-

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: October 03, 2024, 04:04:08 pm
content: Try to use "linear sweep" with fine frequency step before (or instead of) "adaptive sweep". My experience is that Sonnet's default "adaptive sweep" doesn't work most of time for narrow band resonances. For example, a narrow-band patch antenna in Sonnet often shows bogus S11 with no resonance dip at all. But after adding "linear sweep" with 0.025 GHz step resonance is back. I think that adaptive sweep adds two more frequency simulations near all "suspicious" points and performs some calculations very similar to drawing a circle through three points on a 2d plane of Smith chart. This approach may fail to detect reflection coefficient "curls" through the center of Smith chart.