A Seismometer in the Sea

You’ve read about our sensors in space analog environments, placed near volcanoes, or buried deep in boreholes. Today we’re diving into a project that would send our sensors deep under the sea. Silicon Audio has teamed up with Subsea Data Systems on their development of Sensor Monitoring and Reliable Telecommunication (SMART) Cables by equipping each repeater with one of our seismometers. This technology will revolutionize our ability to detect early warnings of tsunamis and earthquakes, global monitoring of the climate, as well as improve ways to monitor fiber cables for increased critical information resiliency. Check out Subsea Data Systems’ website to learn more about SMART Cables and their mission. 

The Silicon Audio team traveled to the Albuquerque Seismological Laboratory to test sensors in one of the quiet vaults at the facility. For the initial testing of our prototype, we developed a sensor with an integrated digitizer for this SMART system by taking our digital system and combining it as the single package shown below.  

For this project we wanted a low noise omnitilt sensor since there will be no way of controlling the orientation of the sensors while deploying these cables to the seafloor. Using insights gained from working on our NASA projects, we adjusted the optics to create a lower noise omnitilt sensor that will work with any tilt up to 180 degrees.   

We hope to deploy these sensors in the future, and until then, we will be undergoing a series of tests to validate the design of this sensor package. As we venture deeper into uncharted waters, we invite you to stay tuned for more updates on the future of seismic exploration.  

From Analog to Digital

The Creation of the Digitizer and TerraHub

In the early years of Silicon Audio Seismic, the team worked on a project with the Department of Energy (DOE) developing infrasound sensors. In creating the experimental design, it became glaringly difficult to connect all the analog sensors in an array. Gears shifted to creating a digital system and as a result, the inception of the digitizer began. 

The motivation was simple: create an analog-to-digital converter (ADC) by sampling the output voltage of the sensor. A larger goal was to create a digital system that was not only low power but also tailored to the sensor. The result was to divide the system into two components.  Near the sensor are the ADCs, clock, and control electronics.  A digital link connects this to a remote Linux server called the TerraHub.  The modular design of the digital system couples the digitizer to a sensor for a complete system calibration and offers an easy upgrade of Si-Audio analog-only seismometers to more-capable digital systems.  Due to our analog sensor’s high dynamic range (DR), i.e., approx. 180 dB, a typical digitizer with a 24-bit ADC, offering approx. 138-dB DR, would not be able to record the full DR of our sensor.   The solution – send each analog signal into two digitizers, one to capture the faintest of signals and the other to simultaneously capture very large signals faithfully. This “double digitizing” strategy is essential for capturing all the dynamic range that the seismometer has to offer. The digital seismometer we created has six on-board high-resolution ADCs. 

The process to create the digital system can be broken into two phases. During Phase I, the initial focus was getting the digitizer that lives close to the sensor to store digitized data in an industry standard format. An integrated micro-SD card can be found on the digitizer circuit board for data storage. A second challenge was incorporating the Global Positioning System (GPS) to use as a time base reference. The digitizer code is written on bare metal and uses a Real-Time Operating System (RTOS). This is a multitasking code base to coordinate data sampling, storage, and communication on a small low-power processor. This concludes the end of Phase I: capturing the data, synchronizing with GPS (time reference), and storing the data on an accessible format.  

Phase II revolved around the development of the TerraHub (we toyed around with different names for this system, and this is the only name that has stuck). The TerraHub uses custom spun distribution of the Linux operating system. This allows the operating system to build the code necessary for the custom-built low-power TerraHub and avoids the installation of unnecessary Linux applications to conserve space and processing power. As new features are added, new builds of Linux will be created to accommodate it. The TerraHub distributes time information to the digitizer. There is a single line maintained to the digitizer as a pulse-per-second (PPS) reference, which allows the digitizer to maintain a time reference to keep the clock going if there is a loss of the GPS server. Applications on the TerraHub are often multithreaded while on the digitizer, RTOS is used to achieve the appearance of multiprocessing. Below is a list of some features of the TerraHub: 

  • Running ring server for sample data distribution (not necessarily hardware but goes through the network SeedLink server) 
  • Dual USB ports for both storage and accessories like a Wi-Fi access point 
  • SD card for data storage 
  • Solar charge controller 
  • Network access via ethernet 
  • State-of-health (SOH) monitoring 

Follow along for more updates of the digitizer and TerraHub as they come!  

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!

El Misti Volcano

The Exploration of El Misti Sensor

Silicon Audio has sensors all over the world.

We’re even shooting for our sensors to be all over the solar system, but we’ll touch more on that on a later day. Today, we are going to explore a sensor whose story dates back to 1985 in the city of Arequipa, Peru.

In 1985, El Misti erupted and caused disastrous effects that rippled through the nation. Scientists in the area began aggressively monitoring and studying this volcano to properly prepare for the next eruption. 

Fast forward to 2019 and Silicon Audio was contacted by the government of Peru about using our sensors to expand the volcano monitoring network.

In 2022, we were invited to a conference in Arequipa, Peru to demonstrate our sensors and their functionalities. 

The Volcano Monitoring Conference

During this visit, we hiked up to El Misti to visit one of the sites that was built to house our seismometers. The sensor was placed in a steel frame box near a GNSS pier and a gas meter pointed up at the volcano to detect trace gases. These three components combined work together to collect data that is monitored at the observatory back in Arequipa. 

Peru is one of many places around the globe where our sensors reside. Tune into the next newsletter to follow along for more of Silicon Audio’s adventures! 

Welcome to the Silicon Audio Newsletter!

Silicon Audio is starting a newsletter to keep customers up to date on the latest engineering challenges we face as well as getting further insight into the brains of the company. To kick things off, let’s explore a commonly received question: Why the name Silicon “Audio” Seismic? 

Silicon Audio began operations in 2009 making high-SNR MEMS microphones for consumer electronics while using a compact embodiment of the optical interferometer used in Silicon Audio’s seismic sensor today. By 2012, Silicon Audio had partnered with a market-leading smartphone OEM and MEMS microphone chip maker.  In a 2013 pilot manufacture, the best-in-class SNR was successfully created  The microphone, however, had an Achille’s heel. Operating in open-loop, the intrinsic dynamic range was limited to 100 dB, and the product was difficult to manufacture. 

While working on the microphone, The Department of Energy asked Silicon Audio if the low-noise optical read-out technology could be used to measure seismic signals to listen for nuclear explosions anywhere in the world. Around the same time, the oil and gas industry asked if the sensor could be used for seafloor seismic exploration and beat the low-frequency performance of common geophones. This led to an evolution of products to address hi-fi seismic. Silicon Audio’s engineers borrowed tried-and-true design features of the workhorse geophone and added low-noise optical readout. The moving element of the seismometer was now equipped with a strong, linear coil-magnet actuator.  When combined with interferometric detection and low noise electronics, a closed-loop, force-balanced sensor was born.  

Fast forward and Silicon Audio has built high-fidelity seismometers for dam monitoring, volcano monitoring, and deep bore-hole deployments over 1 km beneath the surface. A recent project has been building space-ready sensors to survive shuttle launch and land on the moon. As the genesis seismic application was oil and gas, the product was designed from the very beginning for high shock tolerance and rough handling.  The sky’s the limit with what these sensors can do and Silicon Audio is glad to have you on this journey.


Group photo of the Silicon Audio team

Cheers from the Silicon Audio team!