# Improving MEMS Sensor Accuracy with a Co-located Reference Structure > This patent describes a tiny sensor (MEMS) that measures motion, especially up-and-down (z-axis), by including a special stable reference part electrically connected to the moving part, which helps cancel out environmental noise and makes measurements much more accurate. - **Patent:** US 8939029 - **Original title:** MEMS sensor with movable Z-axis sensing element - **Owner:** Analog Devices - **Granted:** 2015 - **Status:** Active - **Times cited:** 4 - **Field:** consumer_electronics, semiconductors, telecommunications, automotive, aerospace ## What it does The patent details a Micro-Electro-Mechanical System (MEMS) sensor designed for improved accuracy. It features a main MEMS structure with a movable mass, which is the part that actually senses motion, built on a substrate (Claim 1). Crucially, it includes a separate reference structure that is electrically connected, or 'coupled,' to this movable mass (Claim 1). This reference structure is positioned radially inward, meaning the main MEMS structure surrounds it (Claim 1, Claim 2). By applying an electrical potential and measuring changes in capacitance between the sensing element (movable mass + reference structure) and electrodes on the substrate (Claim 16), the sensor can detect z-axis motion. The reference structure's purpose is to provide a stable baseline, helping the sensor ignore environmental changes like temperature fluctuations that might otherwise throw off its measurements, thus increasing accuracy (Abstract). For example, in a smartphone's accelerometer, this design would help ensure that a measurement of the phone dropping is accurate, even if the phone's internal temperature has changed. ## What it does NOT cover - Does not cover MEMS sensors that lack a dedicated reference structure electrically connected to the main movable sensing part. - Does not cover MEMS sensors where the main movable sensing part is not positioned radially outward from the reference structure. - Does not cover MEMS sensors where a surface of the reference structure is not largely on the same plane as a surface of the main movable sensing part. - Does not cover MEMS sensors without a z-plane reference electrode positioned beneath the reference structure, coplanar with the z-plane MEMS electrode. ## The clever bit The innovation lies in integrating a separate, electrically coupled reference structure directly with the movable sensing mass, and arranging the main MEMS structure radially outward from it. This specific arrangement allows the reference to effectively cancel out common-mode environmental noise, significantly boosting measurement accuracy without needing complex external compensation. ## Real-world examples 1. Smartphone accelerometers for screen rotation and step counting 2. Wearable fitness trackers for activity monitoring 3. Automotive airbag deployment sensors 4. Industrial control systems requiring precise vibration monitoring 5. Drone flight stabilization systems ## Why it matters Accurate z-axis motion sensing is vital for many modern devices, from stabilizing drone flight to precisely tracking activity in wearables. This patent's approach to using an integrated reference structure helps ensure that these tiny sensors provide reliable data, even in changing conditions. This reliability is crucial for the performance and safety of products that depend on precise motion detection. ## Frequently asked questions ### What does Improving MEMS Sensor Accuracy with a Co-located Reference Structure cover? This patent describes a tiny sensor (MEMS) that measures motion, especially up-and-down (z-axis), by including a special stable reference part electrically connected to the moving part, which helps cancel out environmental noise and makes measurements much more accurate. ### Who owns patent US 8939029? Analog Devices owns this patent, granted in 2015. ### When does this patent expire? This patent is expected to expire on April 2, 2032, when the invention enters the public domain. ### What is patent US 8939029 cited by? This patent has been cited by 4 later patents that build on its ideas. ### What problem does this patent solve? Accurate z-axis motion sensing is vital for many modern devices, from stabilizing drone flight to precisely tracking activity in wearables. This patent's approach to using an integrated reference structure helps ensure that these tiny sensors provide reliable data, even in changing conditions. This reliability is crucial for the performance and safety of products that depend on precise motion detection. ### What does this patent NOT cover? Does not cover MEMS sensors that lack a dedicated reference structure electrically connected to the main movable sensing part. **Full plain-English explainer:** https://patentbrief.org/patent/us/8939029/mems-sensor-with-movable-z-axis-sensing-element-8939029 **Original patent:** https://patents.google.com/patent/US8939029 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How a MEMS Sensor Uses a Reference to Improve Z-Axis Accuracy](https://patentbrief.org/patent/us/8146425/mems-sensor-with-movable-z-axis-sensing-element) — This patent describes a tiny sensor that measures up-and-down motion more accurately by including a special surrounding structure that helps cancel out environmental interference. - [How Tiny Sensors Stay Steady When Their Mounts Shake](https://patentbrief.org/patent/us/10655963/anchoring-structure-for-a-sensor-insensitive-to-anchor-movement) — This patent describes a microelectromechanical system (MEMS) sensor design that uses special springs and a stable internal mass to keep its measuring parts steady, even when the sensor's attachment points are vibrating or moving. - [How a Tiny Sensor Uses an Extra Weight to Detect Motion](https://patentbrief.org/patent/us/20110120221/mems-sensor-method-of-manufacturing-thereof-and-electronic-apparatus) — This patent describes a miniature sensor that detects movement or force by measuring changes in electrical signals between tiny plates, featuring a clever extra weight to make it more sensitive. - [How to Combine Pressure and Motion Sensors on One Tiny Chip](https://patentbrief.org/patent/us/8487387/mems-sensor-device-with-multi-stimulus-sensing) — This patent describes a method for building a single microchip that contains both a pressure sensor and a motion sensor, making devices smaller and more efficient. - [Combining Sealed and Exposed Sensors on One Microchip](https://patentbrief.org/patent/us/8387464/laterally-integrated-mems-sensor-device-with-multi-stimulus-sensing) — This patent describes a microchip design that integrates multiple tiny sensors on the same side, where one sensor is exposed to the outside world through a backside hole while others remain protected by a sealed cap.