TMR empowers sensors in health wearables, building automation

In the rapidly evolving field of consumer health, building automation and personal electronics, the demand for advanced, reliable, and efficient sensing solutions is ever-increasing. Here, tunneling magnetoresistance (TMR) technology has emerged as a game-changer, offering remarkable improvements across various applications.

This article focuses on the design challenges of wearable consumer health devices and other adjacent applications and how sensors with TMR technology meet these challenges with power efficiency, size, sensitivity, robustness, precision, and predictable performance over temperature.

Power efficiency and extended operation time

In wearable consumer health devices, such as continuous glucose monitors (CGMs) and hearing aids, uninterrupted monitoring is crucial for managing health conditions effectively. Interruptions chiefly occur when the device battery has lost its charge and must be recharged. To ensure uninterrupted operation of these devices, battery life must be conserved as much as possible.

CGMs and other wearable sensors are typically hermetically sealed. To ensure optimal battery life upon receipt by customers or patients, it is important to keep the CGM sensor turned off while in storage or during transportation.

In CGMs (Figure 1, left), a sensor with TMR technology can be used to activate the device when triggered by a magnet upon unboxing. The extremely low power consumption of a sensor with TMR technology—as low as a few tens of nano-amperes, compared to Hall-effect devices consuming >1 mA—virtually consumes no power while the device is in a non-active state, thus maintaining battery life while in storage.

Figure 1 Continuous glucose monitor is shown on left and hearing aid on right. Source: Allegro MicroSystems

In wireless rechargeable hearing device earbuds (Figure 1, right), a sensor with TMR technology can optimize battery life by detecting when the device is in use or when it’s placed in its charging case to activate charging. A separate switch using TMR technology can be used to detect when the lid of the charging case has been opened or closed.

These same advantages of TMR technology apply to personal electronic devices such as wireless earbuds and battery-operated building security systems like motion sensors and smoke detectors, where the detection of the presence of a magnet can be used to activate, charge, or troubleshoot the device.

Small size and high sensitivity

Another design challenge for wearable consumer health devices is their relatively small size. Design space is at a premium in compact devices such as CGMs and hearing aids.

Sensors with TMR technology meet this challenge with their small form factor and their high sensitivity. Their form factor can be as small as 1.45 mm × 1.45 mm × 0.44 mm in an LGA-4 package, and sensitivity can be as high as B_OP = 0.9 mT and B_RP = 0.5 mT (Figure 2). This high sensitivity translates into reduced magnet size and cost. By reducing the size and cost of the magnets, sensors with TMR technology enable manufacturers to design smaller, lower cost, and more efficient devices without compromising on accuracy or performance.

Figure 2 This TMR sensor comes in a 1.45 mm × 1.45 mm × 0.44 mm LGA package. Source: Allegro MicroSystems

Sensors with TMR technology detect magnetic fields in the x and y directions. This enables smaller, low-profile designs as magnets no longer need to be placed 90 degrees above the sensor. Instead, they can be positioned adjacent to the sensor, resulting in a slimmer design.

The small size and high sensitivity of sensors with TMR technology also plays a pivotal role in gaming controllers and cameras. In gaming controllers, sensors with TMR technology enable precise distance measurements, improving user control and enhancing the gaming experience.

Similarly in cameras, sensors with TMR technology can contribute to superior image stabilization by accurately detecting and compensating for minute movements.

Robustness, precision, and predictable performance over temperature

Consumer health devices must deliver consistent and predictable performance with dependable data for better charging and device activations despite being exposed to environmental and electrical variations such as temperature fluctuation. For example, hearing aids must maintain accuracy over varying temperatures to ensure that charging is activated when it should be and not falsely activated.

Sensors with TMR technology maintain precision and predictable linear performance over a wide temperature range, making them easier to predict and calibrate and ensuring correct device activation and charging of consumer health devices (Figure 3).

Figure 3 B_OP and B_RP are shown versus temperature for CT813x magnetic sensors. Source: Allegro MicroSystems

This same precision and predictable performance over temperature extend to building security systems and smart locks, where sensors with TMR technology provide reliable detection of open and close states regardless of temperature, thus enhancing reliability.

TMR in next-generation sensing applications

Battery life, small design space, reliability, accuracy, and immunity to external variations—these design challenges in wearable consumer health devices and other adjacent applications are met by sensors with TMR technology with their extreme power efficiency, small size, high sensitivity, robustness, precision, and predictable performance over temperature.

TMR technology ensures that devices remain space-efficient and power-optimized while delivering exceptional performance. In consumer electronics, the seamless integration of sensors with TMR technology enhances user experiences by providing more reliable device activation or charging initiation. In security and building automation, sensors with TMR technology contribute to accurate, more reliable systems that offer enhanced safety and efficiency.

Ultimately, the adoption of TMR technology in various applications highlights its potential to drive the next wave of innovation in sensing solutions. By meeting the demands for efficiency, reliability, and cost-effectiveness, TMR technology is poised to play a pivotal role in shaping the future of consumer health, building automation, and consumer electronics.

Motaz Khader is senior director for global business development at Allegro MicroSystems.

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