Category Archives: Sensors

Microwave Motion Sensor

For detection of motion and direction of motion, the most common sensor was the Passive Infrared sensor or PIR. The presence of a human radiates infrared rays, and the sensor detects this along with variations in infrared rays to sense motion. Now, Infineon offers a fully integrated microwave motion sensor that includes antennas in the package along with built-in detectors for motion and its direction. The BGT60LTR11AIP, from Infineon, does not need an external microcontroller, as it has a built-in state machine to enable its operation. When operating in the autonomous mode, the sensor can detect the presence of a human being at a distance of 7 m at low power consumption.

To use the BGT60LTR11AIP, one does not need any know-how in Radio Frequencies, radar signal processing, or antenna design. Therefore, this sensor brings radar technology to all. Moreover, the small-sized radar unit has special features that provide a compelling cost-effective, and smart replacement for the traditional PIR sensors, providing low power operation for battery-powered applications.

The BGT60LTR11AIP microwave motion detector system makes the traditional motion-sensing applications smarter. For instance, the motion detector is useful in applications like screen-based systems (tablets, notebooks, TVs), automated door openers, security systems including IP cameras, smart lighting systems, smart appliances like kitchen appliances and vacuum cleaners, smart building appliances like proximity sensors, occupancy sensors, and contact-less switches, and smart home devices like smart speakers, smoke detectors, and thermostats.

Infineon has designed the BGT60LTR11AIP sensor as a low-power Doppler radar sensor working in the 60 GHz ISM-band. The tiny 3.3 x 6.7 x 0.56 mm package has a transmitter and a receiver antenna built into the package. It also has the built-in direction of motion detector along with a built-in motion detector. It can operate in multiple modes of operation, including a completely autonomous mode. The user can adjust performance parameters like detection sensitivity, frequency of operation, and hold time. The PCB design of the sensor uses FR-4 material.

In the autonomous mode, the BGT60LTR11AIP can detect up to a range of 7 m while consuming less than 2 mW of power. For this mode of operation, the BGT60LTR11AIP uses minimum external circuitry like crystal, LDO, along with some passive resistors and capacitors, and a shield.

The user can extend the flexibility of the BGT60LTR11AIP by adding an M0 MCU. This improves the detection range up to 10 m in SPI mode. The addition of an MCU offers advanced capabilities through configuration and signal processing via the SPI mode.

The user can incorporate the BGT60LTR11AIP sensor into systems to wake them up when required and put them to sleep or in auto-lock condition when it detects no motion for a specified time period. It has the capability to trigger additional functionality when it detects motion or senses a change in the direction of motion.

The BGT60LTR11AIP can thus add smart power-saving for many devices. Also, as microwaves can operate through non-metallic materials, the sensor can be placed out of sight in the end product. Therefore, the BGT60LTR11AIP sensor enables smooth integration of radar technologies in systems of daily use.

Ultra-Low Pressure Sensors with High Accuracy

Board-mounted ultra-low pressure sensors are in great demand. Especially as they provide extremely high accuracy, as necessary for diverse designs like medical ventilators. Variable air volume control systems also need them for the conservation of building energy. These pressure sensors are useful for addressing problems that engineers face with limited space and reliability. Board-mounted ultra-low pressure sensors with high accuracy are available to measure differential, gauge, and absolute pressure.

Board-mountable pressure sensors are popular as it is possible to mount them on printed circuit boards, allowing direct integration into an electronic assembly. Being compact, their low footprint addresses space constraints. In addition, their microstructure is highly sensitive to the differential, gage, and absolute pressure changes. This enables the electronics to acquire accurate, ultra-low pressure readings.

Several medical applications require ultra-low pressure readings with high accuracy. Some of these medical applications include medical chemistry, sleep apnea machines, anesthesia machines, ventilators, and hemodialysis machines. For instance, the hemodialysis machine depends on such pressure sensors for regulating the pressure in their mixing tanks. This is necessary as blood reaches the artificial kidney, and then it needs regulation to and from the patient.

When used in ventilators, the ultra-low pressure sensors aid in monitoring the breathing of the patient, while detecting if there is a sudden deterioration due to a clogged filter. Anesthesia machines use high-accuracy pressure sensors to measure the pressure of oxygen and air and ensure it never exceeds the safe level, both to and from the patient.

Ultra-low pressure sensors in sleep apnea machines monitor the pressure of air delivery to the patient. It is also possible to monitor blood pressure and hospital room air pressure. Anesthesia equipment and ventilators also use these board-mounted, high-accuracy, low-pressure pressure sensors.

Chemistry analyzers in medical chemistry also use these high-accuracy pressure sensors. For instance, they help with pipettes in drawing the proper amount of fluids, detecting displacement of vials, checking if the air is not being drawn in, and recognizing the presence of obstructions. Additionally, they are useful in applications like automated laboratory testing equipment, molecular testing, and flow cytometry.

Energy conservation in buildings also requires high-accuracy, ultra-low pressure sensors for monitoring the pressure in filters and optimizing it when they are replaced. They are also helpful in determining if the filter is missing or clogged. These high-accuracy sensors are sensitive enough to determine the change in room pressure if a window is opened. They can automate the change necessary in airflow to accommodate adjustments in window positions.

Variable air volume or VAV systems can integrate these sensors to ensure a balanced airflow throughout the building. Flow calibrators, gas flow instrumentation, barometry, chromatography, and pneumatic controls also use them among many others.

Selecting a suitable board-mounted sensor requires making design choices involving the environmental temperature, operating pressure range, and media type, among others. However, there are other considerations also when selecting a board-mounted, high-accuracy, ultra-low pressure sensor. These include pressure range and burst pressures, accuracy, total error band, stability, energy efficiency, and moisture sensitivity levels.

Radar Sensors for Smart Homes Enable Energy Efficiency

With the increase in the application of smart homes, the number of connected devices is also growing. Although this is making the lives of users more convenient, it is also resulting in an increase in energy consumption. This is due to the devices being either permanently active or in standby mode, ready for use at all times, even when there is no one home. Now Infineon is offering their radar sensor, the XENSIV, to make smart homes become more energy-efficient.

By an estimate, at present, there are more than 200 million smart homes around the world. This number is forecast to exceed 500 million by the end of a few years in the future.

The use of digital devices with increasingly ingenious functionalities helps to make houses smarter. However, there is a flip side to this—the increase in energy consumption—despite most modern devices showing a trend of steadily decreasing standby power consumption. This is because most smart devices need power even when they are in standby mode, to be capable of reacting instantaneously to user input. On many occasions, it is not at all necessary for a device to run in standby mode, consuming energy, primarily when there is no one present.

The radar sensor from Infineon aims to solve this issue while meeting the requirements of both digitization and energy efficiency. Capable of operating in almost all smart home systems, radar sensors are highly sensitive devices. They can detect the presence of a person and whether a device needs to be ready. This action is similar to that of the screensaver that kicks-in in on the monitor of a personal computer, when there is no activity from the mouse or keyboard after a certain time but reactivates the monitor as soon as the mouse or keyboard detects a new input. The truly smart and energy-saving device from Infineon, operating at 60 GHz, performs a reliable detection of the absence or presence of a human.

Devices like smart speakers, thermostats, and digital assistants consume very little power when in their normal standby mode. However, their energy consumption can reduce still further if they are forced into a deep sleep mode, especially when no one is around. Doing this can save a few more watts of power.

Other devices like a TV, laptop, sound system, or the air-conditioner can consume several 100 Watts when they are on. Switching them off when no one is likely to use them soon, such as when no one is present at home, can therefore save a lot of energy.

The radar-based smart device continuously checks to sense if there is anyone present or is moving about. If it detects there is no one present, it can switch other devices to a deep-sleep mode or switch them off entirely, thereby helping to save energy. The radar module consumes only about 0.1 W, and this is significantly lower than the energy demands of many other devices, even when they are in their standby mode.

How to Effectively Mount Accelerometers

An appropriate coupling between the accelerometer and the system it is monitoring is essential for accurate measurements. Engineers use different methods for mounting MEMS accelerometers, and this affects their frequency response.

The resonance of the mounting fixture plays an important role, as it can introduce an error in the measurement. Accelerometers using MEMS sensors typically use a printed circuit board or PCB for mounting the sensor, and there may also be other mechanical interfaces between the PCB and the surface of the object it is monitoring. This creates a mechanical system that can have multiple resonances within the frequency range of interest.

For instance, the resonant frequency of the mounting structure may be close to the frequency of the acceleration signal. This will cause the sensor to receive an amplified signal in place of the original acceleration.

Again, if the mechanical coupling causes damping, the sensor will likely receive an attenuated signal.

That means, unless applying proper mounting techniques, it is not possible to take full advantage of the accelerometer’s bandwidth. This is especially so when the measuring acceleration signals are above 1 kHz. Engineers apply three types of accelerometer-mounting techniques such as stud, adhesive, and magnetic mountings.

Stud mounting requires drilling a hole in the object and fixing the sensor to the device under test with a nut and a bolt or a screw. This method of mounting provides an immobile mechanical connection. But it is capable of effectively transferring vibrations of high frequencies from the object to the sensor.

Proper stud mounting requires the coupling surfaces to be as clean and flat as possible. Using a thin film of some type of coupling fluid like oil or grease between the coupling surfaces aids in improving the coupling. The fluid fills small voids between the surfaces, thereby improving transmissivity. It also helps to use a torque wrench to tighten the stud to the manufacturer’s specifications.

Where it is not possible to drill a hole in the device, engineers use an adhesive to couple the sensor to the object it has to monitor. Depending on the nature of the object, engineers use glue, epoxy, or even wax for the coupling. They select the adhesive depending on whether the mounting is temporary or permanent. In case the surface of the object is not smooth, engineers sometimes use an adhesive mounting pad or mounting base. While adhesives fix the mounting pad to the test surface, a stud mounting fixes the sensor to the mounting base.

Engineers have an alternative method of fixing accelerometers, that is, by using magnetics. However, this method is only suitable for ferromagnetic surfaces. If the surface is non-magnetic metal or very rough, engineers often weld a ferromagnetic pad to it to act as a magnetic base.

As the stud mounting method offers a relatively firm connection as compared to the adhesive and magnetic methods, it is suitable for higher frequency signals for measuring acceleration. The adhesive and magnetic methods of mounting accelerometers are suitable for applications where the acceleration signals are below a few kilohertz.

Human-Machine Interaction in Automobiles

In automobiles, there is a need to realize sensing of force, proximity, ambient light dimming, and gesture control with digital optoelectronics components. Optoelectronics sensor devices enable HMI or Human-Machine Interaction. This requires sensing user inputs and lighting conditions, allowing drivers to keep their eyes on the road. It is possible to connect most optical sensors nowadays to the central controller via the I2C interface.

By setting the internal settings of ASICs or Application Specific Integrated Circuits, it is possible to adjust and fine-tune sensitivity, driving currents, measurement speed, and other parameters to the specifications of the application. This allows force measurement on a given surface for detection or inputs, proximity, and gesture control on the central console, and contrast regulation for adjusting the screen backlight.

Force sensing is necessary to detect an input or control function requiring a force or pressure, adequately strong, to trigger a function. Force sensing in automobiles can also detect false forces, such as from an accidental brush over a touch screen or button. Proper sensing of force allows expanding on input possibilities, like coupling it with menu selections. Low-profile, AEC-Q101-qualified proximity sensors with high sensitivity can have programmable driver current, adjustable in 10 mA steps, flowing through the internal infrared emitter.

Such sensors are popular in force sensing applications. Such applications typically require fine-tuning of sensor performance depending on the given mechanical setup. Implementation of this function requires placing the sensor underneath a surface where the application of force is likely. The high sensitivity of the sensor within a region of 3-10 mm allows the detection of small changes in the displacement of the surface.

Center displays in vehicles use AEC-Q101-qualified proximity sensors. This allows for both gesture and proximity control. Rather than use an internal emitter, the proximity sensor has three current drivers, each with a designated pin. These can directly drive external infrared emitters without needing additional circuitry. This results in a highly flexible solution, where it is possible to choose a specific external infrared emitter to use and their placement with reference to the sensor.

For detecting gestures, it is typical to use narrow-angle emitters. This allows properly defining the area wherein it is necessary to detect motion. For wide areas, it is customary to use wide-angle emitters, such that the sensor solution can cover a wide area. This allows the sensor to cover a wide area, and allows detection of user input, regardless of the direction of the user’s hand entering the sensor’s field of view.

Furthermore, it is possible to have individual ADCs on each channel to allow differentiation of the direction of detection. For instance, this allows detecting user inputs from the passenger side, without distracting the driver.

While proximity sensors gather information about happenings in front of the display, ambient light sensors help with the dimming of the display. The main challenge in such applications is the increasing use of dark cover material used in the interiors of vehicles. At times, these cover materials allow the passing of less than 1% of visible light. Therefore, it is necessary to use a sensor with high sensitivity.

Smart Sensors from Sensirion

Sensirion is offering three smart sensors that make it easy for electronic system designers to incorporate them into their applications. These are the AMT4x Smart Gadget, the SCD30 Sensor Module, and the STC31 Thermal Conductivity Sensor for CO2.

As a simple circuit board for a reference design, the AMT4x Smart Gadget from Sensirion is a demonstration kit for the SHT4x temperature and humidity sensors. The gadget displays information for temperature and humidity on an LCD screen. The built-in BLE or Bluetooth Low Energy module allows communication with smartphones and other Bluetooth-enabled devices.

The kit for the Smart Gadget includes an SHT40 sensor for temperature and humidity, a liquid crystal display, a push button, a Bluetooth MCU module, batteries, and other supports. Sensirion also provides detailed resources for the hardware design and information for an app download.

The Smart Gadget offers designers a simple reference design along with a circuit board. They can use it for measuring temperature and humidity while displaying it on an LCD, The MyAmbiance app for iOS and Android phones enables remote access and export capabilities along with data logging.

To sense CO2, Sensirion is offering their SCD30 Sensor Module. SCD30 uses the NDIR sensor technology for sensing CO2. It also has an integrated humidity and temperature sensor. The sensor measures the humidity and temperature in the ambient atmosphere while monitoring and compensating for external heat sources, without using any additional components. The height of the sensor module is low, and this allows easy integration in systems for various applications. The SCD30 achieves high accuracy and superior stability with its dual-channel capability.

The SCD30 sensor, with its NDIR CO2 sensor technology, and integrated humidity and temperature sensor, offers outstanding stability owing to the compensation from long-term drifts provided by its dual-channel capability. The sensor has a small form factor of 35 x 23 x 7 mm. Its measurement range covers 400 to 10,000 ppm, with an accuracy of ±30 ppm +3%. Apart from measuring the absolute concentration of carbon dioxide, the sensor can also measure temperature and relative humidity.

Applications of the SCD30 sensor include IoT devices, Smart Homes, Air purifiers, Air conditioners, HVAC equipment, and demand-controlled ventilation systems.

Sensirion also offers the STC31, a thermal conductivity sensor for the detection and measurement of Carbon dioxide. The gas concentration sensor is chip-sized, offers 16-bit resolution for high range, and is accurate for high volume production CO2 measurement.

Sensirion has based the sensor on an innovative principle of thermal conductivity measurement, which results in long-term stability and superb repeatability. With a digital I2C interface, the STC31 sensor can directly interface with a microprocessor. Working from a voltage ranging from 2.7 to 5 VDC, and a 5 mA maximum current rating, the STC31 sensor operates ideally from batteries while delivering top performance at minimal power budgets.

The STC31 is RoHS and REACH compliant, and its measurement range covers 20 to +85 °C. At a measurement rate of 1 reading per minute, the sensor consumes only 15 µW of power. With a track record of above 15 years, the STC31 sensor is an industry-proven technology.

Sensors for Structural Health Monitoring

Public bridges and roads require their structural health to be monitored, and engineers use sensors for continuous measurement. To power these embedded sensors, they exploit several sources of ambient energy. This can include vibrational energy obtained from vehicular traffic, which can generate adequate power for sensor nodes that engineers have built into the infrastructure. Off-the-shelf devices make it easier for engineers to design structural monitoring devices. Many manufacturers now provide such sensors.

Drivers are rather well-acquainted with potholes on the bridges and roads on which they frequently travel. However, apart from the surface damage, there are more insidious structural damages that may be less obvious. One of them is stress corrosion cracks in structural components that may lead to a bridge collapse.

Therefore, engineers are rightly concerned about existing infrastructure developing similar defects. The rise in vehicular traffic over bridges and roads, often going beyond the original design specifications, together with rapid aging from the stress, can lead to their continual wear and tear and deterioration. Engineers use Structural Health Monitoring or SHM based on continuous monitoring of infrastructure. This is critical for identifying structures at risk.

Monitoring the system through wireless means is more practical, as this avoids the expenses of using wired system monitoring. Wireless monitoring also leads to the simpler placement of sensors within the existing infrastructure. Powering the wireless sensors with energy harvesting techniques further enables avoiding the cost and maintenance concerns related to using batteries and their periodic replacement.

Engineers use various ambient sources for powering the nodes of SHM wireless sensors. This includes vibrational, thermal, and solar sources. Ultimately, the optimum choice depends less on the technical requirements but rather on the logistics, cost, and maintenance requirements related to the target structure. For instance, noise barriers may be necessary for roads in urban areas with heavy traffic. These noise barriers may double as solar panels for energy harvesting.

Some situations may offer alternative sources of energy for powering sensors. These could be thermoelectric generators or TECs, which generate power based on the temperature differential across them. Such differentials often exist between the subgrade layers and the pavement surface of a road. Although using TECs in new constructions may be quite effective, retrofitting in existing roads may involve prohibitive costs.

Engineers often use a heavier tip mass to augment the mechanical loading of a piezoelectric device. Such loading helps to reduce the natural frequency of the device, bringing it closer to the predominant frequencies from the ambient vibrational energy source, enabling maximization of power generation.

In some cases, the ambient vibrational energy source may have frequencies well below the tunable range of the piezoelectric devices available. Engineers then turn to alternative low-frequency vibrational energy transducers like electromagnetic generators. The low-frequency vibrations cause a spring-mounted magnetic core to move through a coil, thereby converting the energy of vibrations to a current following Faraday’s law of induction.

Ambient-powered wireless sensors also require power conditioning and management. Power management circuits monitor the energy harvested, regulate the voltage applied to the load, and use the excess energy to charge external energy storage devices like a rechargeable battery or a supercapacitor.

 Important Sensors

Engineers use two important types of sensors—superstar sensors and workhorse sensors. The superstar sensors usually provide information in high-profile applications such as advanced driver assistance systems, and engineers update them regularly for improving their performance. On the other hand, the workhorse sensors are more reliable, providing consistent information on more common applications. These workhorse sensors are simple to use, and meet the necessary performance specifications at reasonable price tags.

For instance, sensors have been readily available for detecting particulate matter in a dusty environment. However, in recent times, governments have tightened their regulations and have changed the definition of the acceptable levels of particulate matter. Advancement in technology has led to the development of small commodity dust sensors capable of being incorporated into mobile devices. This makes it easier for air monitors, air conditioners, and air purifiers to detect airborne dust particles in all types of environments.

Sharp Microelectronics offers a compact optical dust sensor, the GP2Y1010AU0F. It consists of an infrared light-emitting diode and a phototransistor placed in a diagonal position within the device. The phototransistor picks up infrared light reflected by dust particles. As the system is based on optical sensing, the device is thin and compact with dimensions of 46 x30 x 17.6 mm. The sensor from Sharp Microelectronics is sensitive enough to detect very fine particles such as those in cigarette smoke.

Honeywell offers their LLE Series of sensors for sensing liquid levels. Their technology uses a phototransistor trigger. The sensor can detect the presence or absence of liquid and presents the output in digital format. The sensor uses an LED and a phototransistor that Honeywell has placed inside a plastic dome at the head of the device. In the absence of liquid, light from the LED reaches the phototransistor after total internal reflections from the dome. As liquid fills up, it covers the dome, changing the refractive index at the liquid-dome boundary. This prevents light from the LED from reflecting back to the phototransistor, instantaneously switching the output and indicating the presence of liquid.

Omron offers their digital differential pressure-type mass-flow sensor, the D6F-PH. The sensor has an I2C output and uses a mass-flow MEMS chip, a proprietary of Omron. The company has redesigned the internal flow path such that it produces a high-velocity low flow for an impedance sensor to produce differential pressure. Users can buy these sensors in three models—for measuring a specific pressure range while being calibrated for several types of gases.

Measurement Specialties offers their compression load cell, the FC22. This is a low-cost, high-performance, medium compression force sensor. The sensor offers normalized zero and span, and thermal compensation for changes in span and zero as the temperature changes. The sensor is based on the Microfused technology of Measurement Specialties. It uses several micromachined piezoresistive strain gauges made of silicon fuzed with high-temperature glass to a stainless-steel substrate. While competitive designs suffer from lead-die fatigue, the FC22 sensor does not and can measure the direct force with unlimited life cycle expectancy, while offering superior resolution, and high over-range capabilities.

SensorTile Wireless Industrial Node

For testing advanced industrial IoT applications, ST Microelectronics offers a wireless industrial node, which they call the STWIN SensorTile. This development kit from ST amplifies prototyping of applications like predictive maintenance and condition monitoring.

The STWIN SensorTile kit has a core system board, using a microcontroller operating at ultra-low power. The microcontroller can analyze vibrations from motion-sensing data across 9 degrees of freedom. The vibrational data may cover a wide range of frequencies. The spectra can cover very high-frequency audio including ultrasound. It is also capable of monitoring local temperature and environmental conditions at high precision.

The user can also tie up the core system board with a wide range of embedded sensors of industrial-grade type. To aid in speeding up design cycles for providing end-to-end solutions, ST compliments the development kit with a rich set of optimized firmware libraries and software packages.

An on-board module on the kit provides BLE wireless connectivity. Users can connect a special plugin expansion board to get Wi-Fi connectivity. Those who require wired connectivity for their projects can use the onboard RS485 transceiver. ST has a host of daughter boards using the STM32 family. This includes the LTE Cell pack. Users can connect these compatible, small form factor, and low-cost daughter boards to the development kit through an on-board STMod+ connector.

Along with the core system board, the wireless industrial node kit also has a protective plastic case, a Li-Po battery rated for 480 mAh, a programming cable, and a STLINK-V3MINI programmer cum debugger for STM32.

Users can employ a comprehensive range of sensors available with the core system board. ST has specifically designed these sensors to enable and support industry 4.0 applications. The microcontroller has various serial interfaces for communicating with these sensors. The interfaces include SPI for communicating with motion sensors with high data rates, and I2C for communicating with environmental sensors and magnetometers. The microcontroller can directly communicate with analog and digital microphones.

When interfacing with analog microphones, a low-noise opamp amplifies the signal. An internal 12-bit ADC is available in the microcontroller for sampling the output from the opamp. A digital filter manages the signal output from digital microphones. The microcontroller has a Sigma-Delta modulator interface for signals from digital microphones.

The core system has several sensors on the board. These include a digital MEMS microphone of industrial grade, a wideband MEMS analog microphone, an ultra-low-power 3-axis magnetometer, a high-performance ultra-low-power MEMS motion sensor, an ultra-wide-bandwidth MEMS vibrometer up to 5 kHz, a 3D accelerometer and 3D gyro IMU with a core for machine-learning, a high-output current rail-to-rail dual opamp, a digital low-voltage local temperature sensor, a digital absolute pressure sensor, relative humidity and temperature sensor.

The ultra-low-power microcontroller in the STWIN core system board is a part of the STM32L4+ series of MCUs. The series is based on the ARM Cortex-M4 core, which is of the high-performance 32-bit RISC type. The processors operate up to 120 MHz, and the board has 2 MB Flash memory, along with 640 Kb SRAM. The board has several connectivity options of both wired and wireless types.

Smart Batteries with Sensors

Quick-charging batteries are in vogue now. Consumers are demanding more compact, quick-charging, lightweight, and high-energy-density batteries for all types of electronic devices including high-efficiency vehicles. Whatever be the working conditions, even during a catastrophe, batteries must be safe. Of late, the Lithium-ion battery technology has gained traction among designers and engineers as it satisfies several demands of consumers, while at the same time being cost-efficient. However, with designers pushing the limits of Li-ion battery technology capabilities, several of these requirements are now conflicting with one another.

While charging and discharging a Li-ion battery, many changes take place in it, like in the mechanics of its internal components, in its electrochemistry, and its internal temperature. The dynamics of these changes also affect the pressure in its interface within the housing of the battery. Over time, these changes affect the performance of the battery, and in extreme cases, can lead to reactions that are potentially dangerous.

Battery designers are now moving towards smart batteries with built-in sensors. They are using piezoresistive force and pressure sensors for analyzing the effects charging and discharging have on the batteries in the long run. They are also embedding these sensors within the battery housing to help alert users to potential battery failures. Designers are using thin, flexible, piezoresistive sensors for capturing relative changes in pressure and force.

Piezoresistive sensors are made of semi-conductive material sandwiched between two thin, flexible polyester films. These are passive elements acting as force-sensitive resistors within an electrical circuit. With no force or pressure applied, the sensors show a high resistance, which drops when the sensor has a load. With respect to conductance, the response to a force is a linear one as long as the force is within the range of the sensor’s capabilities. Designers arrange a network of sensors in the form of a matrix.

When two surfaces press on the matrix sensor, it sends analog signals to the electronics, which converts it into a digital signal. The software displays this signal in real-time to offer the activity occurring across the sensing area. The user can thereby track the force, locate the region undergoing peak pressure, and identify the exact moment of pressure changes.

The matrix sensors offer several advantages. These include about 2000-16000 sensing nodes, element spacing as low as 0.64 mm, capable of measuring pressure up to 25,000 psi, temperature up to 200 °C, and scanning speeds up to 20 kHz.

Designers also use single-point piezoresistive force sensors for measuring force within a single sensing area. They integrate such sensors with the battery as they are thin and flexible, and they can also function as a feedback system for an operational amplifier circuit in the form of a voltage divider. Depending on the circuit design, the user can adjust the force range of the sensor by changing its drive voltage and the resistance of the feedback. This allows the user complete control over measuring parameters like maximum force range, and the measurement resolution within the range. As piezoresistive force sensors are passive devices with linear response, they do not require complicated electronics and work with minimum filtering.