S1600525 has been coated in Fort Collins with 480nm of pure tantala. I used the emasured loss angles (after deposition, before annealing) to estimate the shear and bulk loss angles.

Model

First, my COMSOL simulation shows that even if I don’t include the drum-like modes, I still have a significant scatter of shear/bulk energy ratio. The top panel shows indeed the ratio shear/bulk for all the modes I can measure, and the variation is quite large. So, contrary to my expectation, there is some room for fitting here. The bottom panel just shows the usual dilution factors.

Results

One loss angle - constant

One loss angle - linear in frequency

Bulk and shear - constant

Bulk and shear - linear in frequency

To quantify which of the fit below is the most significant, I did a Bayesian analysis (thanks Rory for the help!).

In brief, I compute the Bayes factors for each of the models considered below. As always in any Bayesian analysis, I had to assume some prior distribution for the fit parameters. I used uniform distributions, between 0 and 20e-4 for the loss angles, and between -100e-6 and 100e-6 for the slope. I checked that the intervals I choose for the priors have only a small influence on the results.

The model that has the highest probability is the one that considers different bulk and shear frequency depent loss angles. The others have the following relative probabilities

One loss angle constant:                       1/13e+13
One loss angle linear in frequency:      1/5.5
Bulk/shear angles constant:                  1/48784
Bulk/shear angles linear in frequency: 1/1

So the constant loss angle models are excluded with large significance. The single frequency dependent loss angle is less probable that the bulk/shear frequency dependent model, but only by a factor of 5.5. According to the literature, this is considered a substantial evidence in favor of frequency dependent bulk/shear loss angles.

Silicon wafer from WRS materials, diameter 3", thickness 356-406 microns.

2016-12-09

• 1:00pm, retaining ring and pins installed back, optical system realigned to horizontal reference
• 1:08pm, in chamber, balanced. Since silicon reflection is higher than silica, installed a ND0.3 to avoid QPD saturation
• 1:10pm, roughing pump on
• 1:23pm, turbo pump on
• Excitations

  • Quiet time before excitation: 1165359305
    Excitation (broad band) at 1165359337 (60 s)
    Quiet time after excitation: 1165359399

2016-12-12

• Excitation:
  • Quiet time before excitation: 1165611248
    Broadband excitation
    Quiet time after excitation: 1165611382
  • Quiet time before excitation: 1165611540
    100-1000 Hz excitation
    Quiet time after excitation: 1165611619
• 2:05pm, pumps stopped

​Results

% Freq        Q                Q (C.I. 95%)        Q (C.I. 95%)
2043.9        6.5333e+03        6.5061e+03        6.5607e+03
2307.9        1.6958e+04        1.6895e+04        1.7022e+04
3671.0        2.7458e+04        2.7324e+04        2.7595e+04
4909.0        4.1605e+04        4.1322e+04        4.1892e+04
5268.1        2.5236e+04        2.5186e+04        2.5286e+04
6079.0        2.6835e+04        2.6311e+04        2.7382e+04
7317.4        5.1946e+04        5.1799e+04        5.2095e+04
7391.0        1.3702e+04        1.3441e+04        1.3973e+04
8586.6        5.3491e+04        5.2271e+04        5.4769e+04
8719.9        5.4501e+04        5.3904e+04        5.5111e+04
9600.4        6.6514e+04        6.6390e+04        6.6639e+04
9622.1        3.0667e+04        3.0505e+04        3.0830e+04
10507.0        8.1040e+04        8.0965e+04        8.1115e+04
11053.9        6.0651e+04        5.9853e+04        6.1471e+04
11397.5        5.2873e+04        5.2242e+04        5.3520e+04
11950.0        3.2045e+04        3.1514e+04        3.2593e+04
12083.0        8.8181e+04        8.7571e+04        8.8800e+04
12330.6        4.9761e+04        4.8997e+04        5.0549e+04
13799.0        4.8752e+04        4.7609e+04        4.9951e+04
14911.9        8.7301e+04        8.6550e+04        8.8066e+04
15849.6        3.7500e+04        3.6882e+04        3.8139e+04
17381.4        7.5930e+04        7.4582e+04        7.7328e+04
17585.0        9.7947e+04        9.6811e+04        9.9110e+04
17597.0        2.8465e+04        2.7318e+04        2.9712e+04
18310.4        9.0019e+04        8.9175e+04        9.0879e+04
18542.1        6.8287e+04        6.7506e+04        6.9088e+04
18547.5        1.4131e+05        1.4017e+05        1.4248e+05
18774.9        1.0588e+05        1.0490e+05        1.0687e+05
19066.6        8.0216e+04        7.8924e+04        8.1551e+04
20253.5        9.6914e+04        9.4540e+04        9.9411e+04
20463.0        1.0020e+05        9.9323e+04        1.0109e+05
21188.2        1.1931e+05        1.1851e+05        1.2012e+05
21828.5        1.4420e+05        1.4290e+05        1.4552e+05
21837.5        1.5768e+05        1.5639e+05        1.5899e+05
22976.0        5.6472e+04        5.6229e+04        5.6717e+04
23356.5        1.2871e+05        1.2729e+05        1.3017e+05
23398.5        1.4698e+05        1.4422e+05        1.4984e+05
23455.0        1.1209e+05        1.0950e+05        1.1479e+05
23457.7        1.0716e+05        1.0509e+05        1.0932e+05
23496.0        1.4477e+05        1.4295e+05        1.4665e+05
23703.5        1.5954e+05        1.5695e+05        1.6222e+05
23993.0        1.3344e+05        1.3183e+05        1.3510e+05
24758.2        1.4752e+05        1.4655e+05        1.4850e+05
24952.6        1.3025e+05        1.2972e+05        1.3077e+05
25139.0        3.3941e+04        3.3575e+04        3.4316e+04
25298.5        1.0825e+05        1.0603e+05        1.1056e+05
25387.1        1.3101e+05        1.3055e+05        1.3148e+05
25391.7        1.2021e+05        1.2011e+05        1.2032e+05
26752.9        1.0624e+05        1.0595e+05        1.0653e+05
26762.0        1.8838e+05        1.8490e+05        1.9200e+05
26838.0        6.9555e+04        6.7066e+04        7.2237e+04
27147.7        1.0675e+05        1.0571e+05        1.0780e+05
27698.0        8.3204e+04        8.1975e+04        8.4471e+04
28101.4        1.7792e+05        1.7748e+05        1.7836e+05
28109.4        8.9486e+04        8.8527e+04        9.0466e+04
28480.6        1.1985e+05        1.1934e+05        1.2037e+05
28972.0        4.5087e+04        4.3490e+04        4.6806e+04
28979.3        1.3823e+05        1.3750e+05        1.3897e+05
29044.6        1.7261e+05        1.7177e+05        1.7347e+05
29166.4        1.7820e+05        1.7785e+05        1.7855e+05
29222.0        1.8986e+05        1.8640e+05        1.9345e+05
29451.0        3.4557e+04        3.3927e+04        3.5211e+04
30284.4        1.9755e+05        1.9701e+05        1.9810e+05
30691.3        9.7139e+04        9.6728e+04        9.7553e+04
31228.6        1.2060e+05        1.2028e+05        1.2092e+05
32159.5        2.0041e+05        1.9800e+05        2.0288e+05
32226.8        7.3880e+04        7.3119e+04        7.4658e+04
32366.0        2.0220e+05        2.0185e+05        2.0255e+05

I made a COMSOL simulation of our wafer (75 mm with flats, 1 mm thick) with a 1 micron thick coating (Tantala), and computed the dilution factor (E_coating / E_total). The result is shown in the plot below:

The dilution factor is slighly mode dependent, around a value of 5.7e-3.

The Q we measured on the latest two annealed wafers are in the range of 5e6 - 10e6 for the good modes, meaning that the total loss angle (subtrate, surface and edge combined) is 1e-7 - 2e-7.

Assuming an undoped tantala coating with loss angle of 4e-4 (http://authors.library.caltech.edu/55765/2/1501.06371.pdf), the disk loss angle after coating will be 2.2e-6, a factor 5 to 10 higher than our uncoated and annealed wafers.

So we can use the wafers as they are for our measurements.

I finished populating the new four QPD boards, and fixed the first one I populated weeks ago. I tested all five new boards: the output of the transimpendance respond correctly to the ambient light; the output of the whitening also respond correctly and has increased high frequency noise; the differential driver stages are all functional and balanced.

In summary, we have six QPD circuits ready: serial 02 is installed into the box and it has been used for the previous tests. Serial number 01, 03, 04, 05, 06 are not yet into a box, but fully functional. Boxes are ready.

For testing purposed, I also built another ADC interface board: it's complete with the exception of the connector that goes to the ADC.

The SkyHook has been put in place and bolted down to the floor.

1. created a single interface to move the picomotors in front of QPD1 ... QPD4
   • the command qpdcenter will open an interactive python shell to control the picomotors
2. two scripts for automatic excitations are saved in /opt/rtcds/userapps/CyMAC/src/auto_excite*.py
   • they must run on the cymac. But they can be started from the control station using the commands autoexcite0 and autoexcite14
   • before starting the commands, set the parameters in the file. The two commands edit_autoexcite0 and edit_autoexcite14 will open the correct files
   • a log file of the excitation times will be saved
   • the scripts will check if there is an excitation going
3. the two commands noise0 and noise14 can be used to start awggui to inject the correct noise
4. updated the autocentering scripts, so that only one instance can run at a time.
   • launch them with the commands autocenter0 and autocenter14

• assembled the four in-vacuum periscopes (no mirrors yet)
• soldered kapton wires to the four ESD board; the vacuum side HV connectors are installed
• installed the picomotor into the traslation stage, and soldered the two picomotor wires to a twisted kapton pair. Note: the white wire is connected to the kapton wire which is twisted on the other side.

Today I wrote some auxiliary functions that will be useful for the measurement system:

• noise.py: set of functions to generate band-limited noise (using inverse FFT) and multiple band noise. Using the awg python interface I can also start and stop the noise injection. Some examples of the result:
  
   
• readdata.py: read data online, compute a spectrum, and additionally a function that find peaks in a whitened spectrum. All peaks above a minimum SNR are returned: the central frequency is computed by an average of the bin SNR:
  
   
• diskmodel.py: reads a list of mode frequencies from txt files. In each file, the first row is the disk diameter in mm, the second is the disk thickness in mm, all other rows are the modes are computed by COMSOL. I also produced a whole bunch of such files, with diameters within 75 +- 0.1 mm and thickness within 1 +- 0.1 mm

I did two set of measurements with the new coated samples from Montreal. I reshuffled the position in the two measurements. In both cases, the measurement being performed in bay 4 was bad, in the sense that it was very hard to see excited modes. Since the two measurements were carried out with two different disks, it's clear it is a problem with that setup.

SOLVED: there was a connection problem for the DAC output signal controlling the switch

REALLY SOLVED: it was not a cabling issue. The power supply for the switching box had the current limiter on: when all four switches are closed, the box drain about 270mA, which is more than the limit of 250mA. Therefore the power supply voltage dropped and only three switches were actually closed. I switched the power supply to 500mA range and maxed the current limit. Now all four switches are working properly

We initially received 20 disks (75 mm diameter, 1 mm thickness) from Mark Optics. Here's their status as of today

• MO-01 was annelaed and measured at LMA. It was then taken back to Mark Optics by Julie Houser at the time of her visit
• MO-02 was initially used to test the "dirty" measurement apparatus, then it was installed into the new chamber and measured on Saturday August 20th
  Then this disk was used as a guinea pig for the laser edge polishing, and it's now in a pretty bad shape
• MO-03 was installed into the new chamber and measured a couple of times on Sunday and Monday. Then we laser polished the edges, with good results, although there are small damages on the surface. It has been installed back into the chamber and a couple of rind-down measurement carried out on Monday and Tuesday.
• MO-04 is still untouched

All the other disks have been sent back to Mark Optics to grind out flats. 

[EricQ, Gabriele]

The real time system seems to be working properly, except for the excitations: we can't activate any excitation using awggui or diaggui

Eric rebuilt the workstation from scratch installing Debian 8.5. All CDS software seem to be working. We setup a ssh-key for ssh'ing into cymac3 and configured the automatic mount of the remote /opt/rtcds.

I checked that the QPD electronics works as expected, and that I can acquire the signals using the ADCs. A new model (x3cr1) is up and running. It acquires the four quadrants, convert them from counts to volts, and compensate for the analog whitening filter. The four quadrant signals are X3:CR1-Q1_OUT, X3:CR1-Q2_OUT, X3:CR1-Q3_OUT, X3:CR1-Q4_OUT.

A matrix is used to compute the X and Y signals, defined as X = (Q1+Q4-Q2-Q3) and Y = (Q2+Q4-Q1-Q3). The SUM signal is also computed as SUM = (Q1+Q2+Q3+Q4).

Finally, the X and Y signals are normalized with the sum to produce X3:CR1-X_NORM_OUT and X3:CR2-Y_NORM_OUT.

A filter bank (ESD) is connected to the DAC channel #0 to produce the excitation that will be sent to the high voltage amplifier. I checked that the DAC is working properly (adding offsets). The input to the ESD filter bank is in volts.

The normalized X and Y signals, the sum of all four quadrants and the output of the ESD driver filter bank are saved to frames. The model runs at 65kHz.

The plot below shows the best loss angle we expect foer our samples, based on Steve Penn's model of surface and volume losses (Phys. Lett. A 352, 3). That paper contains data only for Suprasil 2 and Suprasil 312, so it might be a bit wrong for our Corning 7980. The two experimental data sets are for samples that have been laser polished.

Installed two new 2TB disks into the cymac3. Also, the main disk has a 1TB partition with the operating system, so I created a new 1TB partition. I created a logic volume that spans the three partitions, for a total of about 5TB. This partition is mounted in /mnt/data and linked to the /frames folder. Frames are written to this new logic volume.

2017-12-06

Four fused silica substrates from University Wafers, 76.2mm diameter / 0.5 mm thickness installed in chamber

• 7:50am in chamber
• 7:54am roughing pump on
• 8:03am turbo pump on

I suspended the roughing pump with four springs. The reduction of the 58 Hz peak is similar to what I got when the pump was sitting on a box. So most of the coupling is due to acousting noise.

The JDSU HeNe laser 1103P that I was using is dead. I swapped it with a JDSU 1125P borrowed from the 40m.

Since I had recurrent problems with the picomotors used for QPD3, I swapped them with another Newport motorized mirror that was previously used in the Crackle1 experiment. This is the same model used for the other three QPD centering. Everything looks to be working fine now.

I also realigned all optical levers and swapped out an iris with a smaller one, to avoid beam clipping. All beam paths look clear now.

2017-07-26

• I ran a sweep of the gap between the ESD and the sample, first from .5 mm to 1 mm. That sweep suggested that there is a significant jump in force across almost all of the modes at 1 mm. To confirm this I double checked the geometry and it appears that COMSOL is building everything as expected when changing the spacing parameter. Then I ran a finer sweep in .02 mm increments for the spacing between .9 and 1.1 mm. Once again it appears there is a large jump as the gap approaches 1 mm, but the behavior does not seem to be symmetric about that point, the force appears to diminish linearly as the gap increases beyond 1 mm. I will run a sweep of the ESD arm spacing along with the vertical gap to confirm that the jump occurs when the gap between the ESD and the sample is equivalent to the spacings between the ESD arms.

Here's a trend of the QPD signals when the IGM was turned on:

Turning it off does not bring the disk back.

Elogs for the new Coatin RIng-down MEasurement lab had to start somewhere, so here is a couple of pictures of the optical table with shorter legs and of one of the two vacuum chambers that have been moved in.

We discovered a couple of days ago that the table was sitting on three legs only and the fourth one was dangling. I managed to adjust the height of the fourth leg using the large screw on the leg support. Now the table is properly supported by all four legs.

We set up the model x3tst to acquire at 65kHz four signals coming from the PSL lab:

• X3:TST-BEAT_OUT_DQ: beat note
• X3:TST-ACC_X_OUT_DQ: accelerometer X
• X3:TST-ACC_Y_OUT_DQ: accelerometer Y
• X3:TST-ACC_Z_OUT_DQ: accelerometer Z

This morning I installed temporarily a second QPD to monitor the input beam. The goal was to understand where the vibrations at frequencies below 2kHz couple from. As shown in the photo, the second QPD was close to the first one.

The signals in the two QPDs were quite different, and the coherence between them wasn't great. So I concluded that the main coupling path is not through input beam of QPD vibration, but more likely real motion of the disk.

I removed the additional QPD and restored the setup to its nominal configuration. The readout infrastructure is still in the model.

In brief, it doesn't work. The magnets and coils are strong enough to push up the ring with a sample inside, but the friction with the three alignment pins is too large and random, so when the current to the coils is increased slowly, the ring doesn't move up smoothly (see first attached video). On the other hand, if the current is switched on abruptly, the ring shoot to the top and stays there. However, if a disk is placed on the support, it is ejected out (see second video). When the current is cut (smoothly or abruptly) the ring doesn't alway comes back to the bottom, but sometimes it stays stuck inclinded.

On the positive side, we probably don't need such a complicated system:

1. in all the pump down I've done so far (ten or more), the disk never moved
2. the ring is very useful, even when used manually, to find the initial centering of the disk: if we machine three small aluminum wedges that can be put under the ring to keep it raised (or three set screws), it can be used to place down the sample in a roughly centered position, that has always been good enough to get the beam almost back into the QPD.

Links to the two videos:
Video1 Video2

Disk excited at 12:01pm. Exited the room at 12:03pm.

Opened the chamber at about 2:30pm, got the disk out for edge polishing, installed it back at 3:30pm, pumping down at 3:40pm.

Stopped the roughing pump at 4:44:00pm (+60 seconds clean data, GPS 1155944657). Switched on the HV amplifier, excitation at 4:47:30pm. Recentered QPD, clean data from 4:48:30pm (GPS 1155944927)

After a first look at the data, it seems that something went wrong. I restearted the roughing pump and will pump overnight.  I found the QPD miscentered, so I centered it again.

Excited again at about 5:46:35pm. Clean data from 1155948460

Cleaned the chamber in the washing machine at 40m and started 48 baking at 120 C

Yesterday we received the prototype of the disk suspension and retain system. Everything looks good. I checked that the disk fits in the holder, and all dimensions are good. The coil holders are out for winding, so I couldn't test the movimentation yet.

Following the model from R. Nawrodt et al. Investigation of mechanical losses of thin silicon flexures at low temperatures, CQG 30 (2013) 115008, I predicted the thermo-elastic losses in the Si sample. The model matches quite well the measurements:

Here are some details on the model, eq. 1 and 2 of the cited paper:

where:

• alpha  = thermal expansion coefficient 2.6e-6/K
• Y = Young's modulus 150 GPa
• T = temperature 300 K
• C_P = specific heat 705 J/kg/K
• rho = density 2329 kg/m^3
• t_f = sample thickness 400 um
• k = thermal conductivity 130 W/m/K

The model is for a cantilever, but it fits well enough for our disk too.

My previous test showed that the timing drift was somehow related to the output of the signal generator being connected to the DAC.

Some more findings follow. When the CyMAC is powered down, the timing sent to the DAC is highly distorted. It stays the same even when I power the CyMAC up again, and it gets better only after the IOP process is started. My guess is this has something to do with the DAC board initialization. In the following: first trace is the timing signal with CyMAC off; second with the CyMAC powering on, but IOP not yet started; third when the IOP process is running.

A small residual distortion around the transitions is visible. This is not present on the original signal, or even if the ADC only is connected to the timing.

To try to debug the problem, I set up a second signal generator (not locked to the first one) and used it to provide the DAC timing. In this way ADC and DAC get their timing from two different signal generators.

I still see the same small distortion on the DAC timing. More important, I noticed that the signals generated by the DAC (here a 1kHz sinusoid) are very noisy: there is a very large glitch at every clock transition. Is this a sign that tha DAC is malfunctioning? I don't recall seeing anything like that in any other case. In both screeshots, the purple trace is the DAC output (1 kHz sinusoid) and in the second screenshot the blue trace is the DAC timing. It's clear that there is a glitch every time the clock signal transitions.

I swapped the DAC with another one, but I see the same behavior in the output signal. Here's a spectrum of the DAC output, with and without output.

I find sometimes that the probe configuration can give these distorted signals. For the Tektronix probes, its best to use a 500 MHz probe instead of the BNC clip leads. The probe also should be compensated by attaching to the gold fingers square wave generator on the scope front and adjusting the capacitor in the probe with a little screwdriver until the square wave becomes perfect.

This afternoon I installed the picomotor and the translation stage that will be used to move the retaining rings up and down. No partciular problem: I only had to add some small aluminum foil shims between the ear of some rings and the square plate, to make the rings as horizontal as possible.

I tested the motion: with 300000 steps it's possible to move the rings all the way from the parked (down) position, to the up position. I also checked that when the rings are up, I can place four substarates and they fall properly into the alignment groove. Since the maximum speed of the picomotor is 2000 steps/s, it takes 150 seconds to move up and down the ring. 

Finally, positive steps means that the rings are moving up, negative that they're moving down.

I raeligned the optical levers to the position I obtained by centering the samples with the rings. I haven't tested the repeatability yet.

The ring motion up and down was not very smooth, again due to friction on the centering pins.

So, after centering the rings using the pins and securing the rings to the translation stage, I removed all pins.

Now the motion up and down is very smooth.

I still have to fine tune the amount of steps that are needed to go up and down.

However, initial tests don't show a good repeatability of the positioning. My main suspect is that the vibration caused by the picomotor cause the disks to slip on the silicon lens. Indeed, when the disks are sitting on the rings, one can clearly hear them "rattle".

2017-08-09

• I compared the triangular geometry to the original geometry and the excitation was only improved in 7 of the of 20 modes. In four of those modes the improvement factors ranged from almost 2 to over 3 while the other modes where only improved by about 25%. The other 13 modes were diminished drastically, 9 of them where less than half as excited. Given more time it may have been interesting to try and optimize the geometry of a triangular drive, but that would easily take the better part of a week. 

For a long time I had problems with the GPS time in frames being different from the real one.

This morning I rebooted the cymac3 and swapped the function generator with a new one.

I tested the GPS time in frames by switching on teh ESD noise at a given GPS time and checking the frames. The times are aligned.

I'll have to wait and see if this remains stable over time (in the past i saw an acculation of few seconds per day)

EDIT: I checked the two SR DS345 one against the other. Indeed, when bpth set to generate 65536 Hz, there is a continuos drift in the relative phase, accounting for one cycle over about 3.9 seconds. This would sum up to one second over ~256000 seconds, or about 3.5 days. It seems more or less comparable with the amount of GPS time mis-syncronization I saw. I'll have to wait a few days to see if the new clock is stable.

Things seems to be worse now. This morning I injected noise at GPS 1165078533 (real time, as obtained from the python command line, and consistent with what displayed in the MEDM screen) and found the injection in the data at GPS 1165078555, so 22 seconds later...

UPDATE:

Now the time difference is about 30 seconds. It seems that the real time model is about 29 seconds advanced with respect to the GPS time one gets from a python script command running on the cymac3

The GPS time I get from python is the same I get from a shell script on the workstation or on the cymac3. I checked that it is also consistent with the GPS time on cymac2.

I moved the picomotors at precise times and looked at the data in the frames. Indeed the data has the wrong time stamp.

I swapped the SR signal generator with an Agilent 33210A. Shut down and restarted the cymac3. Now the command line GPS and the IOP model GPS are aligned within one second. Let's see if it stays this way.

Update at 5pm, GPS times are still in sync.

Unfortunately, this morning the model time is again wrong...

I put back the Stanford Reserch signal generator. On a scope, the timing signal looks good. There is a small ripple and some noise in the flat parts. I found that when I unplug the DAC timing cable, the ripple and the noise goes away. 

I'm leaving the DAC timing unplugged for the night, and I'm using a script to track the difference between the machine time and the front-end time.

For the last ~day the difference between the frontend GPS time and the machine GPS time remained constant between -1 and -2 seconds

I reconnected the DAC timing cable at

PST: 2016-12-08 09:23:06.934999 PST
UTC: 2016-12-08 17:23:06.934999 UTC
GPS: 1165253003

After that, the timing started to drift at a rate of about 1 second every 2300 seconds (4.35e-4). So the conclusion is that the culprit for the timing issue is on the DAC connection side.

I looked into a couple of turbo pump switch on periods, and in both cases when the pump speed hits 58 Hz, a resonance is excited. I'm not sure what's resonating.

Today I let the roughing pump reduce the pressure to a level lower than usual, and this seems to mitigate the effect. The disk wasn't shaking as much as it did in previous pump-downs.

I changed the set point of the test chamber turbo pump to 666 Hz. This was done by setting the "standby rotation speed" to 80% and enabling the standby condition.

The turbo pump of the CR0 chamber runs at 833 Hz. It causes vibrations that pollute the measurements in the CR1-4 chamber. In particular CR1 is extremely sensitive and the line is highly up-converted. It's not clean why CR1 is more sensitive than CR2-3-4.

2017-08-16

• I created a model with two ESD's, essentially a combination of my previous two attempts with one ESD on the edge and one closer to the center of the disk. This test was quite successful compared to previous trials, the improvement seems to be on an average of a factor of 10. No modes are weakened by this design. I am going to run a sweep adjusting the central ESD and see what placement is best.
• Attached is an overlay of the force profile and all of the modes. Note that this image is very large, and is useful as a digital reference or very large print only.