World’s Smallest, Lowest Power, Highest Sensitivity Magnetic Sensor Debuts At Sensors Expo

Coto Technology’s RedRock TMR RR121 Series magnetic sensor fulfills a design engineer’s dream: the perfect trifecta of the lowest power, highest sensitivity, and smallest packaged magnetic sensor on the market. The RedRock RR121 seamlessly combines a full-bridge tunneling magnetoresistive sensor array with a CMOS latch to provide a simple voltage output trigger for a microprocessor or other CMOS circuitry. The voltage output, normally high, goes low when a sufficiently strong magnetic field of the right polarity is brought within range of the sensor, thus providing the trigger.


This magnetic sensor offers omnipolar, unipolar, and bipolar polarity responses depending on the needs of the application (i.e., it can respond to either magnetic polarity, a particular polarity oriented correctly to the sensor, or it can activate and latch itself under the presence of one polarity and only release once exposed to the other, respectively). Further, it offers clock frequencies ranging from less than 1 Hz to 300 kHz and average current consumption as low as 185 nA. Its magnetic sensitivity can be tuned to as low as 5 Gauss or as high as 100 Gauss. It’s offered in a tiny industry-standard SOT-23 package, but is also available in an even smaller LGA-4 package that measures a mere 1.4 mm x 1.4 mm x 0.45 mm – a critical factor when circuit board real estate is truly at a premium. Taken together, the RR121 Series offers an incredibly small package, ultra-low average current consumption, and maximum sensitivity. All of these features provide unprecedented flexibility for design engineers, giving them complete freedom to build their ideal systems.

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Ideal applications span medical, industrial, consumer, automotive, security, and energy industries where very low average current consumption and high sensitivity, combined with a small package size, are necessary.  Medical applications include portable and battery-powered devices such as ingestibles and implantables that are hermetically sealed and, therefore, need a way to be triggered without compromising their protective encasement. Many of these devices (such as capsule endoscopes) need to be able to be stored in standby mode on a doctor’s shelf for up to 18 months before being used; Battery power conservation is critical to ensure there is a sufficient charge left in the device when it comes time to activate it.


The small size of these devices and their hermetic seals (which enable them to survive the gastrointestinal tract) necessitate a tiny, contactless means for “waking up” the microprocessor from the outside (e.g. presenting a small permanent magnet near where the sensor is installed inside the device). Insulin management via continuous feed insulin pumps is another critical medical application. These battery-powered pumps are worn on the belts of diabetic patients who have implanted micro-syringes continuously measuring blood sugar levels and administering insulin doses as needed. The insulin reservoirs need to be replaced when they are empty and the pump needs to both recognize when the reservoir is empty, and when it is not present in order to avoid complications. The RR121 magnetic sensor can provide a seamless means of detecting the replacement of the insulin reservoir by responding to the presence of a small magnetic shunt on it.


Hearing aids also use magnetic sensors as a means of mode switching, whether it’s for turning the device on or off, performing diagnostic checks, or re-tuning the hearing aid’s response when a telephone speaker is brought near the ear. Hearing aid usage is expected only to increase as baby boomers continue to age; meanwhile the device size continues to decrease as users transition from “behind-the-ear” to “in-ear” designs that cater to those who need help hearing but do not want the associated stigma of a visible device. Those same consumers also want maximum battery life. The decrease in size, emphasis on prolonged battery life, and need for a long air gap activation distance are all answered by the RR121’s ultra-miniature LGA-4 package, low average current consumption, and high sensitivity, respectively.


The RR121 magnetic sensor is also ideal in many other applications. A number of consumer appliances we take for granted today, such as dishwashers, washing machines, coffeemakers, and refrigerators, require a means of accurate liquid level measurement. The RR121 can replace historically-used large reed switches to provide a more accurate measure of the liquid level, saving energy, water usage, and costs for consumers while improving sustainability for the environment. It can also be used to measure flow of both liquids and gases in these same applications to ensure that the devices are operating accurately.


That flow measurement can also be utilized in residential and commercial water meters to provide accurate reporting of usage while the unipolar response can act as an additional inherent resistance to tampering. As with utility meters, the RR121 can replace reed switches used in the rotational counting common to gas and electric meters as well as providing a fail-safe activation method for the wireless circuit that facilitates remote measurement as advanced metering systems replace aging infrastructure in the US and overseas.


The RR121 also provides a smaller, more robust solution for residential and commercial security systems as its small size and high sensitivity allow it to be embedded into door jams and window sills to monitor their opening and closing and prevent unauthorized entry. They can even be integrated with ambient light sensors as part of automated window blinds that adjust to reduce solar heating, saving homes and businesses on HVAC energy costs.


Yet another application for the RR121 magnetic sensor includes position sensing of other rotating mechanisms, such as the drill heads used in down-hole exploration in the oil & gas industry. Position sensing in linear positioners, as well as linear and rotary encoders, is also another critical space. The RR121’s tiny size and sensitivity facilitate higher resolution position sensing, increasing accuracy in automated systems in factories, thereby improving tolerances and reducing costs for end customers.

Coto Technology will be showcasing the RR121 and its other TMR magnetic sensors and switches, as well as its Coto Classic reed relays and molded reed switches and its CotoMOS MOSFET relays, at Booth #934 at Sensors Expo in San Jose, CA June 27-29th. For more information, please visit and/or contact us at [email protected] and visit us at the show!



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