Monthly Archives: September 2022

What are Floating Sensors?

Floating sensors support applications for environmental monitoring and agriculture. Designed by researchers from the University of Washington, floating sensors typically spread just like seeds of the dandelion plant do, when a drone drops them from a height. The sensors are battery-free devices, hovering over 100 meters. The sensors have electronics on board, including a capacitor for storing overnight charge, sensors, and a microcontroller for running the system. The entire structure resides in a flexible body.

The evolution of dandelions allows them to disperse their seeds further than a kilometer in the air. Although for valuable wireless sensors, it is not a good idea to drop them from great heights. However, the researchers did just that by creating a tiny device that can carry the sensor, with the wind blowing it at it tumbles towards the ground.

Just like the dandelion seeds do, the sensors too, float in the breeze. As the device is about 30 times heavier than a dandelion seed weighing one milligram is, it can travel only up to a distance of about 100 meters on a windy day. The researchers had to mimic the shape of the dandelion seeds as it was necessary to ensure that the device landed with its solar panels facing skywards.

The structure of dandelion seeds has a central point where little bristles stick out. These tend to slow down their fall. The researchers took a 2-D projection of the seed and used it to create the base design for the structure of their floating sensors. When they added more weight, the bristles started to bend inwards. The researchers then added a ring structure to make the bristles stiffer, and take up more area, allowing it to slow down the fall. The team tested more than 75 designs with various sizes and patterns using laser micro-machining.

The sensor can share data related to pressure, temperature, humidity, and light up to a distance of 60 meters. The researchers have added a capacitor to the design of their floating sensors, allowing it to store some charge for the night. As an experiment, the researchers used a drone to drop sensors from a height of 20 meters, sending the sensors sideways to about 100 meters towards a parking area.

According to the researchers, from an engineering point of view, imitating dandelion seeds allows for achieving some amazing capabilities. Although dandelion plants cannot move, they can disperse their seeds up to a kilometer away, provided the right conditions exist. The team has been trying for a similar achievement by automating the deployment of wireless sensors to create a network. Conventional methods of studying climate changes or monitoring the environment over really large geographic areas can be very expensive and time-consuming. Dandelion seeds and their dispersion methods provided the team with the necessary inspiration to create sensors that can disperse in the wind, and automate this process.

The team had to look at nature again to get good coverage over the area of interest. They mimicked the random process followed by plants to disperse their seeds. The researchers designed a large array of different structures to make them float for different periods.

Monitoring Battery Health

The prolific use of battery-powered instruments for regular use in the consumer and industrial fields requires monitoring battery health for proper functioning. Usually, a battery health monitoring system uses a microcontroller and a software user interface. This arrangement monitors all the batteries in a battery bank 24×7 and identifies weak batteries before they actually fail. This helps to improve the overall performance of the system. Stationary applications such as data centers commonly use such battery health monitoring systems.

In vehicles too, it is necessary to have precise and reliable information about the state of health and state of charge of the battery. Battery health is sensitive to temperature, and conventional trucks and buses with diesel engines also frequently fail during winter and autumn. Now, vehicle fleets use solutions for monitoring battery health and the fleet manager does this in a centralized manner.

Analog Devices Inc. presents a solution for monitoring the state of health of primary batteries. The LTC3337 from Analog Devices provides information such as battery cell impedance, voltage, discharge, and temperature. The data from LTC3337 is not only accurate, but the readings are in real-time.

For monitoring the state of health of the battery in real-time, the user must place the LTC3337 in series with the battery terminals. Analog Devices ensure that the series voltage drop is negligibly small when the IC is in series with the battery. Analog Devices has integrated an infinite coulomb counter with a dynamic range to tally all the accumulated battery discharges. LTC3337 stores this information in an internal register which the user can access through an I2C interface. The user can program a discharge alarm with a threshold based on this state of charge. As soon as the state of charge crosses this threshold, the IC generates an interrupt at its IRQ pin. The accuracy of the coulomb counter is constant down to a no-load condition on the battery.

Analog Devices has designed the LTC3337 to be compatible with a wide range of primary batteries with varying voltages. For this, the user can select the peak input current limit of the LTC3337 from 5 mA to 100 mA.

The user can calculate the coulombs from either the BAT IN or BAT OUT pin of the LTC3337—the AVCC pin connection decides this. Some applications require using supercapacitors at the output of the IC. Analog Devices has provided a BAL pin for connecting a stack for supercapacitors for the purpose.

Analog Devices offers LTC3337 as an LFCSP or Lead Frame Chip Scale Package with 12 leads. There is an exposed pad for improving its thermal performance.

The LTC3337 can withstand a voltage range of 5.5 VDC to 8.0 VDC at its input. Its quiescent current is as low as 100 nA. The user can preset the peak input current limits depending on the type of the primary battery. The presents are 5, 10, 15, 20, 25, 50, 75, and 100 mA levels.

LTC3337 is meant for monitoring the state of health of batteries in low-power systems powered by primary batteries. It is very helpful for batteries providing backup and supplies in keep-alive scenarios.

Optical Microphone Watches Sound

A research team from Carnegie Mellon University has claimed to have developed an optical microphone or camera system that can monitor sound vibrations very precisely. The precision is so high that the camera can capture separate audio of individual guitars playing simultaneously. That allows the camera to reconstruct the music faithfully and accurately from a single instrument even when it is playing in an orchestra or band.

Even using the most directed and high-powered microphones it is not possible to totally eliminate neighboring sounds, effects of acoustics, and ambient noise when capturing audio. The research team has used a novel approach. They used two cameras along with a laser beam. This allows them to sense the high-speed but low-amplitude vibrations from the surface of the instrument. The team uses these vibrations for reconstructing sound. The unique arrangement allows them to isolate the audio and capture it without a microphone and with no interference.

The team claims to have invented a new way of seeing sound. The camera system is innovative, represents a new device for imaging, and makes it possible to see things that are not visible ordinarily to the naked eye. The team has successfully completed several demonstrations for showcasing the effectiveness of sensing vibrations and reconstructing sound faithfully and with quality.

During their demonstrations, the team was able to successfully capture isolated audio from separate guitars that were playing together, and the audio of individual speakers that were playing assorted music at the same time. For instance, they analyzed vibrations from a tuning fork. They also captured the vibrations on a bag of burritos placed near a speaker thereby capturing the sound from the speaker.

The team significantly improves the work done earlier for capturing sound by computer vision. Where earlier researchers used high-speed cameras for producing a high-quality recording, the present researchers used ordinary cameras costing only a fraction. The dual-camera is necessary for capturing vibrations from moving objects, such as the movements of the instrument when the musician is playing it, while at the same time, sensing individual sounds from many other points.

The team claims they have improved the optical microphone to make it more usable and practical. They claim to have improved the quality while reducing the expenses.

According to the team, the system operates with two types of shutters—a global shutter and a rolling shutter. An algorithm analyzes the difference in speckle patterns between the two streams of video. It converts the differences into vibrations for the reconstruction of the sound.

A speckle pattern is a result that coherent light or laser generates after its reflection off a rough surface. By aiming a laser beam at the vibrating surface, the team created the speckle pattern. This speckle pattern changes with the changes on the surface as it vibrates. The rolling shutter rapidly scans the speckle pattern from top to bottom and produces the image by stacking rows of pixels one on top of the other. At the same time, a global shutter captures the entire speckle pattern in a single instance.

How Piezoelectric Accelerometers Work

Vibration and shock testing typically require piezoelectric accelerometers. This is because these devices are ideal for measuring high-frequency acceleration signals generated by pyrotechnic shocks, equipment and machinery vibrations, impulse or impact forces, pneumatic or hydraulic perturbations, and so on.

Piezoelectric accelerometers rely on the piezoelectric effect. Generally speaking, when subject to mechanical stress, most piezoelectric materials produce electricity. A similar effect also happens conversely, as applying an electric field to a piezoelectric material can deform it mechanically to a small extent. Details of this phenomenon are quite interesting.

When no mechanical stress is present, the location of the negative and positive charges are such as to balance each other, making the molecules electrically neutral.

The application of a mechanical force deforms the structure and displaces the balance of the positive and negative charges. This leads the molecules to create many small dipoles in the material. The result is the appearance of some fixed charges on the surface of the piezoelectric material. The amount of electrical charges present is proportional to the force applied.

Piezoelectric substances belong to a class of dielectric materials. Being insulating in nature, they are very poor conductors of electricity. However, depositing two metal electrodes on the opposite surfaces of a piezoelectric material makes it possible to produce electricity from the electric field that the piezoelectric effect produces.

However, the electric current that the piezoelectric effect produces from a static force can last only a short period. Such a current flow continues only until free electrons cancel the electric field from the piezoelectric effect.

Removing the external force causes the material to return to its original shape. However, this process now causes a piezoelectric effect in the reverse direction, causing a current flow in the opposite direction.

Most piezoelectric accelerometers constitute a piezoelectric element that mechanically connects a known quantity of mass (proof mass) to the accelerometer body. As the mechanism accelerates due to external forces, the proof mass tends to lag behind due to its inertia. This deforms the piezoelectric element, thereby producing a charge output. The input acceleration produces a proportional amount of charge.

Piezoelectric accelerometers vary in their mechanical designs. Fundamentally, there are three designs, working in the compression mode, shear mode, and flexural mode. The sensor performance depends on the mechanical configuration. It impacts the sensitivity, bandwidth, temperature response of the sensor, and the susceptibility of the sensor to the base strain.

Just as in a MEMS accelerometer, Newton’s second law of motion is also the basis of the piezoelectric accelerometer. This allows modeling the piezoelectric element and the proof mass as a mass-damper-spring arrangement. A second-order differential equation of motion best describes the mass displacement. The mechanical system has a resonance behavior that specifies the upper-frequency limit of the accelerometer.

The amplifier following the sensor defines the lower frequency limit of the piezoelectric accelerometer. Such accelerometers are not capable of true DC response, and hence incapable of performing true static measurements. With a proper design, a piezoelectric accelerometer can respond to frequencies lower than 1 Hz, but cannot produce an output at 0 Hz or true DC.

What are Tactile Switches?

Tactile switches are electromechanical switches that make or break an electrical circuit with the help of manual actuation. In the 1980s, tactile switches were screen-printed or membrane switches that keypads and keyboards used extensively. Later versions offered switches with metal domes for improved feedback, enhanced longevity, and robust actuation. Today, a wide range of commercial and consumer applications use tactile switches extensively.

The presence of the metal dome in tactile switches provides a perceptible click sound, also known as a haptic bump, with the application of pressure. This is an indication that the switch has operated successfully. As tactile switches are momentary action devices, removal of the applied pressure releases the switch immediately, causing the current flow to be cut off.

Although most tactile switches are available as normally open devices, there are normally closed versions also in the market. In the latter model, the application of pressure causes the current flow to turn off and the release of pressure allows the current flow to resume.

Mixing up the names and functions of tactile and pushbutton switches is quite common, as their operation is somewhat similar. However, pushbutton switches have the traditional switch contact mechanism inside, whereas tactile switches use the membrane switch type contacts.

Their construction makes most pushbutton switches operate in momentary action. On the other hand, all tactile switches are momentary, much smaller than pushbutton switches, and generally offer lower voltage and current ratings. Compared to pushbutton switches, the haptic or audible feedback of tactile switches is another key differentiator from pushbutton switches. While it is possible to have pushbutton switches in PCB or panel mounting styles, the design of tactile switches allows only direct PCB mounting.

Comparing the construction of tactile switches with those of other mechanical switches shows a key area of difference, leading to the tactile switches being simple and robust. This difference is in the limited number of internal components that allows a tactile switch to achieve its intended function. In fact, a typical tactile switch has only four parts.

A molded resin base holds the terminals and contacts for connecting the switch to the printed circuit board.

A metallic contact dome with an arched shape fits into the base. It reverses its shape with the application of pressure and returns to its arched shape with the removal of pressure. This flexing process causes the audible sound or haptic click. At the same time, the dome also connects two fixed contacts in the base for the completion of the circuit. On removal of the force, the contact dome springs back to its original shape, thereby disconnecting the contacts. As the material for both the contacts and the dome are metal, they determine the haptic feel and the sound the switch makes.

A plunger directly above the metallic contact dome is the component the user presses to flex the dome and activate the switch. The plunger is either flat or a raised part.

The top cover, above the plunger, protects the switch’s internal mechanism from dust and water ingress. Depending on the intended function, the top cover can be metallic or other material. It also protects the switch from static discharge.

Proximity Sensor Technology

Proximity sensor technologies vary with operating standards, strengths, and determining detection, proximity, or distance. There are four major options for compact proximity sensors useful in fixed embedded systems. It is necessary to understand the basic principles of operation of these four types for determining which to select.

Most proximity sensors offer an accurate means of detecting the presence of an object and its distance, without requiring physical contact. Typically, the sensor sends out an electromagnetic field, a beam of light, or ultrasonic sound waves that pass through or reflect off an object, before returning to the sensor. Compared with conventional limit switches, proximity sensors have the significant benefit of being more durable and, hence, last longer than their mechanical counterparts.

Reviewing the performance of a proximity sensor technology for a specific application requires considering the cost, size, range, latency, refresh rate, and material effect.


Ultrasonic proximity sensors emit a chirp or pulse of sound with a frequency beyond the usual hearing range of the human ear. The length of time the chirp takes to bounce off an object and return determines not only the presence of the object but also its distance from the sensor. The proximity sensor holds a transmitter and a receiver in a single package, with the device using the principles of echolocation to function.


Photoelectric sensors are a practical option for detecting the presence or absence of an object. Typically, infrared-based, their applications include garage door sensing, counting occupancy in stores, and a wide range of industrial requirements.

Implementing photoelectric sensors can be through-beam or retro-reflective methods. The through-beam method places the emitter on one side of the object, with the detector on the opposite side. As long as the beam remains unbroken, there is no object present. An interruption of the beam indicates the presence of the object.

The retro-reflective method requires the emitter and the detector to be on the same side of the object. It also requires the presence of a reflector on the other side of the object. As long as the beam of light returns unimpeded, there is no object detected. The breaking of the beam indicates the presence of an object. Unfortunately, it is not possible to measure distances.

Laser Rangefinders

Although expensive, these are highly accurate, and work on the same principle as that of ultrasonic sensors, but using a laser beam rather than a sound wave.

Lasers require lots of power to operate, making laser rangefinders non-suitable for portable applications or battery operations. Being high-power devices, they can be unsafe for ocular health. Although their field of view can be fairly narrow, lasers do not work well with glass or water. 


Inductive proximity sensors work only with metallic objects, as they use a magnetic field to detect them. They perform better with ferrous materials, typically steel and iron. A cost-effective solution over a huge range, the limited use of inductive proximity sensors to detect objects reduces their usefulness. Moreover, inductive proximity sensors can be susceptible to a wide range of external interference sources.

What is Tactile Sensing Technology?

Scientists have been exploring the field of soft robotics for use in healthcare systems. They aim to emulate the sense of touch. However, they have not had much success with tactile-sensing technology while fine-tuning dexterity.

In an experimental study, published in the Journal of the Royal Society Interface, scientists made a comparison of the performance of an artificial fingertip with that of neural recordings made from the human sense of touch. The study also describes an artificial biometric tactile sensor, the TacTip, which the scientists had created. According to the study, TacTip offers artificial analogs of the dynamics of the human skin and the nerves that pass information from skin receptors to the central nervous system. In simple words, TacTip is an artificial fingertip that mimics nerve signals on human fingertips.

The researchers created the artificial sense of touch. They used papillae mesh that they 3-D printed and placed on the underside of the compliant skin. This construction is similar to the dermal-epidermal interface on real skin and is backed by a mesh of dermal papillae and biometric intermediate ridges, along with inner pins that are tipped with markers.

They constructed the papillae on advanced 3-D printers. The printers mixed soft and hard materials, thereby emulating textures and effects found in real human fingertips. They actually reconstructed the complex internal structure of the human skin and the way it provides for the sense of touch in human hands.

The scientists described the effort as an exciting development in soft robotics. They claim that 3-D printing tactile skin would lead to more dexterous robots. They also claim that their efforts could significantly improve the performance of prosthetic hands by imbibing them with an in-built sense of touch.

The scientists produced artificial nerve signals from the 3-D printed tactile fingertips. These signals look very similar to the recordings from actual, tactile neurons. According to scientists, human fingers have several nerve endings known as mechanoreceptors that transmit signals through human tactile nerves. The mechanoreceptors can signal the shape and pressure of contact. Earlier, others had mapped electrical signals from these nerves. By comparing the output from their 3-D printed artificial fingertip, the scientists found a startlingly close match to the earlier neural data.

A cut-through section of the 3-D printed tactile skin shows a white plastic that forms the rigid mount for the flexible black rubber skin. Scientists made both parts on advanced 3-D printers. The inside of the skin has dermal papillae, just as the real human skin also has.

In comparing the artificial nerve recordings from the 3-D printed fingertip with the 40-year-old real recordings, the scientists were pleasantly surprised. The complex recordings had many dips and hills over ridges and edges, and the artificial tactile data also showed the same pattern.

However, the researchers feel that the artificial skin still needs more refinement, especially in the sensitivity area pertaining to fine detail. As such, the artificial skin is much thicker than the real skin is. Scientists are now exploring different means of printing 3-D skins that mimic the scale of human skin.

Comparing Polyimide Flex Heaters and Silicone Rubber Heaters

Commercial, industrial, military, and aerospace applications use flexible heaters to deliver particular amounts of heat to specific places. The heaters serve multiple purposes, starting from warming food in cafeterias, drying the condensation on aerospace control panels, to controlling temperatures in medical equipment.

These tiny heaters are unique in the sense they are flexible. It is possible to bend them without compromising their heating operations. As flex heaters are very thin, they can squeeze into inter-component space without dislodging. However, the types of materials that make up these heaters impose certain limitations. These are temperature limitations, and the limitation on how much they can bend. Understanding these limitations is necessary for creating designs suitable for the application.

Flexible heaters are typically made from two types of materials—Polyimide and silicone rubber. The thickness of the materials used defines the amount the heater can safely bend without damage. Polyimide flex heaters with etched foil heating elements can be as thin as 0.0007 inches. This thickness allows Polyimide flex heaters to bend around multiple curves within the application.

In contrast, silicone rubber flexible heaters, with etched foil elements, can only go down to a thickness of 0.03 inches. Those with wire-wound elements can at best be 0.056 inches thin. Therefore, although the heater with etched foil elements can have a bend limitation of 1.5 inches, those with the wire-wound elements can bend still less.

Therefore, applications with curved and bent surfaces prefer using Polyimide flex heaters, and those with flat surfaces can do with either Polyimide or silicone rubber.

The range of temperatures offered by a flexible heater depends on the elements and the types of materials it uses. The application defines the temperature desired from the flex heater, depending on the ability of the system to remove the heat and disperse it away from the heater. The heat transfer is important to prevent the heater from overheating and malfunctioning.

Silicone heaters have an operating range of -70 °F (-56.66 °C) to +400 °F (204.44 °C). This makes them ideal for medium to higher temperature applications. However, they tend to fail if the environment cools below the minimum temperature.

On the other hand, Polyimide flex heaters can operate between -320 °F (-195.55 °C) and +392 °F (+200 °C). This makes Polyimide flex heaters suitable for applications working in very low temperatures, such as in spacecraft and satellites. They can help keep electronics functioning in such low temperatures.

Apart from the outer silicone rubber or the Polyimide covering, there are other structures also that add to the overall thickness. These are the solder tabs, wire connections, and other electronics that must connect to the heater.

Both silicone and Polyimide flex heaters with etched foil elements can have a maximum size of 10 X 70 inches. Their size cannot be larger as the heat produced will not be uniform. On the other hand, wire-wound elements can be as big as 36 X 144 inches. However, the wire-wound elements are strictly for silicone heaters, and suitable for large applications.

MEMS Pressure Sensors in Industrial Applications

A wide range of industrial applications requires the usage of pressure sensors. Continuous improvements in these sensors are necessary for new applications, including their use in more common applications like measuring fluid and steam pressure.

Recent power sensor technologies have made available devices with reduced size, better economics, more integration capabilities, and wider operating supply voltages, enabling OEMs to deploy sensors for applications like the Internet of Things. Additionally, with these sensors, it is possible to create products that are not only more sustainable but also feature additional embedded innovative features and less power consumption.

Along with a focus on applications, these sensors demonstrate a variety of methods and techniques for detecting pressure in industrial settings. Most notable among these are the MEMS or micro-electric-mechanical sensor technology.

Pressure is the force on a surface with a given surface area. Commonly, units for pressure measurement include the Bar, Pascal, and PSI or pounds per square inch. The sensor for a specific application typically defines the units it uses. For instance, it is customary to use bars or millibars to indicate pressure value in water-level applications. The automobile industry uses PSI to indicate pressure, such as in tires.

While measuring vertical distance or altitude, barometric air pressure is a common indicator. The reference here is the air pressure at sea level, which is equivalent to 1013.25 Mb or millibar. As the altitude changes, so do the air pressure.

In industrial applications, pressure sensors are generally of three types. These are the gauge pressure, absolute pressure, and differential pressure sensors.

A gauge pressure sensor uses the atmospheric or ambient pressure as its reference. This is typically 1013.25 Mb or 14.7 PSI at sea level. If the measurement is above ambient, it represents positive pressure, while a measurement below ambient is negative pressure. These sensors are useful in applications that require pressure measurement over longer periods, with little or no calibration.

Absolute pressure sensors use vacuum as the reference, with the absolute pressure of a full vacuum being zero PSI. Most absolute pressure sensors detect pressure below the atmospheric pressure. Altimeters are absolute pressure sensors using gauge pressure sensors.

Differential pressure sensors use a second pressure as a reference. This second pressure may be higher or lower than the pressure under measurement, or the atmospheric pressure. Differential pressure sensors are useful for measuring flow rates.

Industrial applications for pressure sensors have now evolved to the level where most sensors are smaller, smarter, and more conscious of energy consumption.

The various types of pressure sensors in use in the industrial environment, and the progress of MEMS technology, has enabled the semiconductor industry to make pressure sensors economical in high volumes.

With embedded compensation, low power consumption, and small size, these MEMS pressure sensors come in robust packaging. This allows wider use of MEMS sensors in industrial environments than was possible before. Most modern industrial systems now use a mixture of sensor technologies that not only run more efficiently but also waste much less energy. MEMS technology is the one leading in sensor applications in most industrial settings.