The 10 Year Development History of Silicon Audio
In our very first newsletter, we reviewed the history of Silicon Audio’s inception with micromachined-electromechanical systems (MEMS) and our audio beginning with the initial shift into Seismic. For this post, we’ll be breaking down the prototypes that led to the model you are familiar with today.
The first sensor functioned more as a crude version of a seismometer. It was a concept validation that a non-MEMS, interferometer built at a macro scale could be created and was built out of 3-D printed materials. Although the prototype was bare boned, it performed with high fidelity optical readout, detecting 20 femtometers (fm) of displacement – that's 1/10,000th the size of a hydrogen atom!
Fast forward and now and we have the optics all combined into one cell. The proof mass lives in the silver component while the optics and lasers live in the black component thus successfully creating a singular optical cell in a compact design.
We took this optical sensor and successfully created a 3-axis model system. The sensor below was the first to be demoed out into the world. As our success continued, we built out a model that worked with Fairfield Nodal (now Fairfield Geotechnologies) for 3-axis seafloor nodes and partnered with oil and gas companies to develop a customized product. This was the first-time components started to look reminiscent of the current sensing element we use today.
After the steady success of the analog sensors, a need for a digital system became increasingly necessary to facilitate quick plug seamless setups, and to take full advantage of the sensor’s extreme dynamic range. The latter requires double digitizing using two 24-bit analog-digital converters (ADCs). This was the motivation behind the creation of the digitizer. Our digitizer works in combination with the geo computer to create a fully digital system that can capture a high dynamic range while attaining the data with a time reference and the ability to store this data in an accessible format.
Today, we have a breadth of products that range from 3-axis to 1-axis to digital systems that can be modulated to fit your analog sensor. Don’t hesitate to reach out to us for more information about customized products based upon your research needs!
Developing a Sensor for Europa
In our previous newsletters, we’ve touched on the field deployments in Gulkana and Greenland for the Seismometer to Investigate Ice and Ocean Structure (SIIOS). These functioned as a dress rehearsal for future missions to Europa, the icy moon of Jupiter. On the other side of this research is the development of the actual instrument that will be sent for deployment. In this post, we will delve into the journey of sensor development, from testing mechanics and robustness, to overcoming obstacles and the quest for planetary protection.
As the design of the instrument progressed there were a battery of tests to mature the design through the NASA Technology Readiness Levels (TRL). Vibrational and shock tests were conducted to check the robustness of the sensor against conditions encountered during the mission including launch and landing. The vibrational test simulated the vibrations from a launch vehicle, i.e. a big rocket, and was performed on each axis of the sensor for 1 minute. The shock test ensures the sensor can survive an unexpected rough landing.
Before sending the sensor off to a third-party lab for a TRL-6 qualification, some tests were done in-house for troubleshooting. In the video below, the sensor is placed on a shaker with parameters modeled from the General Environmental Verification Standards (GEVS) from NASA (GSFC-STD-7000A). During initial tests, springs supporting the proof mass in the sensor were fractured due to metal fatigue. The cyclic loading applied to the spring arms due to the lateral motion of the proof mass induced stress higher than the fatigue strength of the spring material. To prevent this, metal stops were installed around the proof mass and precisely adjusted to limit the lateral motion of the proof mass, which successfully fixed this issue. As an interesting side note, we found there is a noticeable change in the sound of the vibration test when there is a failure that we were able to use as a diagnostic method.
Two thermal tests were also conducted as a part of the TRL-6 qualification. A Thermal-vacuum test (TVAC) was performed to test the sensors survivability under the environmental conditions in space. The sensor was subjected to thermal cycling with temperatures ranging from -55°C to 75°C for about a week and a half in vacuum (10-5 Torr or 0.00000001316 atmospheric pressure). Dry heat microbial reduction (DHMR) was carried out to ensure the sensors survive the rigorous planetary protection protocols put in place to make sure missions don’t send Earth’s microbes to other bodies. In other words, instruments sent out into the solar system are subjected to long exposure to a high temperature in order to rid the devices from any unwanted microbes. Think of it as the barbequing of microbial reduction. The sensor was baked at 130°C for 43 hours. The sensor that was sent for this testing is still running and used in our lab to this day.
Silicon Audio is getting ready to go through this whole process again with a new larger, higher performance instrument developed for deployment onto an asteroid. Stick around for future updates on this ongoing project once we hit significant milestones!
Sensors in Boreholes
A Study of Geothermal Monitoring
Ever since the inception of our newsletters, Silicon Audio has taken you on a journey through our past, sharing the captivating old projects we've worked on. However, today, we're breaking the pattern to shine a spotlight on a current ongoing project, providing an exclusive glimpse into Silicon Audio’s present activities.
Lawrence Berkeley National Laboratory, working in collaboration with the Department of Energy, has many research projects that encompass geothermal monitoring. Silicon Audio’s sensors are utilized in multiple studies. One study took place at the Cascadia borehole and three of our sensors were grouted in a vertical array. The idea was to test the efficacy of a small array in comparison to colocated geophones and nearby broadband sensors as a comprehensive seismic monitoring tool. For over the past four years, our sensors have functioned without incident at the site due to our high sensitivity, low noise floor, and a passband from hundreds of seconds to 1.5 kHz.
Silicon Audio is currently gearing up to dispatch additional sensors to Lawrence-Berkeley. Among them, two will be going to the Newberry Enhanced Geothermal System (EGS) site, while seven will be heading to other new TBD projects. Designed to withstand demanding downhole environments, these specialized sensors are coated with epoxy and grease to enhance their waterproof capabilities. Each sensor cable is equipped with a Kevlar lift, allowing you to pick the sensor up from its wire that’s permanently attached. The sensor housing is crafted from waterproof stainless steel, ensuring durability in challenging conditions.
The first image depicted above highlights a challenge encountered during the testing phase: the height of the sensors. As a work around, the sensors were placed in cinderblocks filled with sand to maintain stability and orientation. The other pictures illustrate the Silicon Audio team preparing these sensors for shipment. Stay tuned for new updates regarding these geothermal experiments.
The Greenland Deployment
An Exploration of an Analog for Icy Ocean Worlds
In our previous newsletters, we explored the icy depths of Interior Alaska to learn about the successes and learning opportunities of the Gulkana glacier deployment. We travel once again to another polar region to continue the research of the Seismometer to Investigate Ice and Ocean Structure (SIIOS) funded by NASA. After troubleshooting the experimental design used during the Gulkana mission, the SIIOS team treks to Greenland - where the workspace is vaster, and the ice layer is thicker - to further investigate the potential to rapidly deploy a seismic station on the Europa lander.
Getting to the actual location of deployment in Greenland was no easy task. The SIIOS team was comprised of scientists from all over the country who traveled through many layovers before arriving at the Thule airbase (now named Pituffik airbase). This was the closest accessible base before traveling via helicopter to get to the analog field site. The team was staggered in their arrival over the span of two days due to inclement weather, one of the major challenges of this experiment. After 6 helicopter loads, all the necessary equipment finally arrived at the field site and work could finally begin.
The overall experimental design consisted of the lander in the center and 4 independent stations positioned 1 km out from all cardinal directions. The purpose of this was to compare data from the sensors of the lander versus a small baseline array - i.e., can a single sensor perform as well as an array? A deep hole was dug at the independent stations to mitigate ice from melting and moving the sensors. In addition, the lander was also placed in a deep hole underneath a windshield to replicate the absence of wind on Europa. Many sensors were placed inside the windshield creating a data mine for any future research. Similar to the Gulkana deployment, active and passive source experiments were performed on the Greenland ice sheet.
The picture below illustrates the field site right before the team returned to Thule airbase. The orange boxes are the data acquisition systems comprising of batteries and digitizers powered by solar panels. Data was to be collected throughout the summer but only 2 weeks were captured as the snow piled on top of the equipment burying the solar panels and leaving the batteries to die. Despite this, our sensors performed comparably to traditional equipment. The following year, another experiment in Greenland was planned after the discovery of a crater nearby in satellite imagery, however, COVID-19 delayed this project.
The Gulkana Deployment: Part 2
This write-up is a continuation of the last newsletter where we used our sensors to measure seismic activity at the Gulkana glacier. The Silicon Audio team ventured out to the interiors of Alaska as an analog for Europa; there, we tested the viability of the experimental design of the proposed Europa lander. Although the team of scientists faced a few challenges, the mission was an overall success.
Our sensors were put to the test in low temperatures and functioned well. The ability to withstand the low temperatures of Europa is a necessary attribute for the sensors that will be placed on the lander. During the experiment, the glacier would slowly move causing the sensors to move along with it. This normally would be a problem, but due to the high tilt tolerance of our sensors it was able to overcome these conditions.
Of course, we know we can use seismic to measure the thickness of the ice, but the main purpose of this project was to determine if a seismic station could be rapidly deployed in icy conditions. The team discovered that the small table that was used needed to be stiffer in construction so the vibrations coming from the table were minimized. This caused an inability to differentiate the vibrations coming from the table versus the passive seismic. Changing the experimental design was a key lesson learned as well as the minimum amount of gear that was needed for future experiments.
The next steps of this project were to improve the lander design and continue testing in icy conditions such as Greenland. Stay tuned for the next newsletter where we dive deeper into the Greenland deployment.
The Gulkana Deployment
A Study of Earth's Artic Domains
In the fall of 2017, Silicon Audio embarked on a journey to the icy terrains of the Gulkana Glacier in the interior of Alaska. This project was sponsored by NASA’s Planetary Science and Technology Through Analog Research (PSTAR) program. The mission: use seismology to determine the thickness of the ice on Gulkana as a stand-in for Europa’s icy crust.
Europa is highly remarked in the solar system for its potential for extraterrestrial life, boasting necessary elements for the creation of life. So why Gulkana? For starters, its topography poses as an excellent candidate to replicate Europa with its icy layer atop bedrock. But most importantly, it’s on planet Earth and accessible to scientists to trial the lander before its final launch to Europa.
Partnering with the University of Alaska, the team loaded up all the equipment into a sling and had a helicopter transport everything to the location. The team, however, did not get the same treatment and drove as far as they could before hiking the rest of the way to the site.
We had 16 of our 3-axis sensors deployed during this test. The sensors were laid out on top and below a small table that represented the test lander. Passive seismic was measured including the noises of the water trickling, ice cracking and other natural events while active seismic was created with a hammer. These were the basic parameters of the experiment and the logistics that went behind the test lander.
Want to know more? Check out the article written about this expedition on Anchorage Daily News!
