Monthly Archives: July 2022

What is a Thermal Switch?

Future spacecraft carrying humans require thermal management systems with high turn-down capabilities. In widely varying thermal environments, thermal switches can dissipate a wide range of heat loads. Thermal switches are electromechanical on/off switches, and they are thermally actuated. In contrast with thermal fuses, thermal switches are reusable. They are well suited for protection against common temporary thermal situations, that the user can correct.

A temperature differential activates a thermal switch. When activated, the state of the switch changes over from either normally open to closed or normally closed to open. The movement of the contacts can generate a faint audible noise, as they interrupt the power to an electrical circuit. 

Applications of thermal switches include preventing damage from over-heating of electrical circuits. However, these switches may also be useful as temperature control devices, such as in water heaters. The switches are helpful in preventing overheating in various consumer, industrial, and commercial products. In practice, they control the power to circuitry in electric motors, power supplies, lighting fixtures, transformers, ballasts, and battery packs. When controlling temperature, these switches are useful in electronic cooling fans, heat pumps, low voltage relays, or gas furnaces operated by a solenoid valve.

Several types of thermal switches are available. These include bi-metallic disc or snap action, mercury switches, thermal reed switches, rod and tube switches, vapor-tension switches, and gas-activated switches.

The snap action or bi-metallic disc switches operate based on the phenomenon of thermal expansion. The switch has two dissimilar metals that expand at different rates. As the temperature reaches the threshold, the snap action of the discs forces the switch to activate.

In mercury switches, the contacts are sealed within a glass envelope containing a small amount of mercury. At temperatures above 40 ℃, mercury is always in a liquid state. As mercury is also a good conductor, it can make or break the contacts based on the angle of inclination. Typically mounted on a metal coil, the switch activates with thermal expansion that causes the coil to tilt.

Thermal reed switches have a pair of contacts on ferrous metal reeds inside a hermetically sealed glass tube. As the metal reeds are ferrous, a magnetic field can activate them. The switch can have either normally open or normally closed contacts, kept in that state by a ferromagnetic material surrounding the glass tube. As temperature rises and reaches the curie point of the ferromagnetic material, it loses its magnetic strength, and this alters the state of the contacts.

Rod and tube thermal switches are made of an outer tube surrounding an internal rod, both made of metals with dissimilar coefficients of thermal expansion. When the temperature rises, the rod expands faster than the tube can, and induces a plunger-style contact. Rod and tube thermal switches have rapid response times and can operate at high temperatures.

Vapor tension or gas-activated thermal switches use a sensing bulb with a gas or vapor inside. As temperature rises, the thermal expansion of the vapor or gas leads to a proportional pressure increase on a piston assembly or a diaphragm, actuating an electrical switching system.

Batteries without Mass

Electric vehicles use various types of batteries to operate. But all of them have one thing in common—the weight of the batteries. Depending on the size of the vehicle, the battery weight is a significant part of the total weight of the vehicle. As a vehicle must carry its batteries along with it, it is unable to fully utilize its total capacity. Engineers and scientists are researching various ways of reducing the battery weight while enhancing its energy density.

Some scientists are thinking in more innovative ways. For instance, scientists in Sweden claim to have developed a structural battery. The advantage of such a battery is it is purportedly stored without mass, as its weight is actually a part of the load-bearing structure. With an energy density of 24 Wh/kg, the design of the battery allows solar-powered vehicles to integrate it easily.

At the Chalmers University of Technology in Sweden, scientists claim to have developed a structural battery. The construction primarily uses carbon fiber, and apart from the structure of the battery, the carbon fiber also acts as a load-bearing material, conductor, and electrode.

Structural batteries use materials with properties of electrochemical energy storage. The primary aim of such devices is to reduce the weight of an object, as the manufacturer can embed the battery to be a part of the structure of the object, such as a drone or an electric vehicle.

According to the scientists, they had started research and developing their massless batteries in 2007. Their main challenge had been to build devices that had good mechanical and electrical properties. They settled on carbon fibers for their battery, as it has the required strength and stiffness to allow integration into structures of electric vehicles. In addition, carbon fibers also exhibit good storage properties.

The scientists claim their batteries may also be applicable to the roof of light city vehicles such as rickshaws. The roof of these vehicles may have solar cells.

The batteries have a structural battery electrolyte matrix material, housing a negative electrode made of carbon fiber, and a positive electrode supported with aluminum film. A glass fiber separator keeps the two electrodes apart.

Apart from reinforcing the material, the carbon fiber also helps to conduct electrons while acting as a host for Lithium. In the same way, the positive electrode foil, apart from providing electrical functionality, also provides mechanical support.

The structural battery electrolyte favors the transport of Lithium ions while transferring mechanical load between the fibers of the device, its particles, and plies. The scientists demonstrated a battery with an elastic modulus of 25 Gpascals and a tensile strength that exceeded 300 Mpascals. While the elastic modulus demonstrates the resistance of the material to elastic deformation, the tensile strength demonstrates the maximum load that the material can support without damage.

With an energy density of 24 Wh/kg, the battery has about twenty percent capacity relative to presently available lithium batteries. However, as the battery reduces the weight of the vehicle significantly, the electric vehicle requires much less energy. Additionally, the lower energy density results in increased safety for the vehicle and its passengers.

Advancements in Hybrid Thermal Management

Over the past few decades, the fastest-growing electronic industries have been power and energy. These include fuel cell and battery technologies, and power inversion, conversion, and rectification.

With form factors getting smaller, power electronic systems are becoming increasingly complex, while, at the same time, performing at higher power ranges. That makes heat generated within the system the greatest limiting factor to its functioning. To dissipate the amount of power the system generates, it is necessary for the designer to optimize and enlarge air cooling systems to remove the heat effectively. In some cases, size is the limiting factor for systems using forced convection. Where the weight or size of the air-cooled solution becomes impractical, engineers prefer to use liquid cooling as an alternative method.

However, it is not easy to switch quickly from an air-cooled system to a liquid one. Designers must consider several factors and possibilities for improving thermal management for handling higher heat loads. Although the market is trending towards full liquid cooling as the industry standard for cooling power electronic systems in the future, engineers can also consider various hybrid solutions. That helps to apply the benefits of hybrid systems as the system evolves or upgrades.

Engineers use liquid cooling systems, making them complementary to existing air-cooled solutions. That allows them to expand it gradually to replace the air-cooled system. They do this with a focus on the electronic systems that benefit from liquid cooling. For this, they employ fluid couplings, dependable pump systems, and compact heat exchangers. The system transfers heat from airflow to liquid flow that transports it elsewhere to manage it. If this is not possible, engineers have the option of fully replacing the air-cooled system with a liquid-cooled one, thereby enabling higher power outputs while optimizing the thermal performance.

Engineers must consider numerous key determining factors for improving the performance of any power electronic devices and facilities while switching to liquid cooling. They must consider the thermal performance requirements in addition to the size and weight requirements. They must also look into further optimizing the present air cooling system and whether it will still remain a viable thermal option. Furthermore, they must also look into any limitations on the availability of the liquid cooling system. As cost is always a huge factor in any project, the engineer must also look into the return on efficiency and performance when investing in liquid cooling. Also, they must look into the downtime necessary for the conversion and the easiest way of implementing the changeover.

Both forced, and natural thermal management has limitations. The total surface area necessary to dissipate heat limits natural thermal management systems, necessitating heavy and large, but impractical solutions.

On the other hand, pressure drop limits solutions using forced convection. Heat sinks require large surface areas in viable volumes. This creates high amounts of air resistance. But this also hinders the amount of airflow, thereby limiting the heat transfer from a fan. This, in turn, requires larger or more fans, and this increases the amount of noise in the system.

Two-Phase Thermal Switches

Spacecrafts frequently make use of a wide range of variable conductance devices for thermal management. These devices, also known as thermal switches, help to maintain the temperature of heat sources that operate under varying thermal environments and thermal loads within a spacecraft. Many such applications are already operating in Lunar and Mars landers and rovers, and in satellites. Being highly reliable, scientists may be using thermal switches in the future for human spacecraft transiting through space.

Two-phase thermal switches are low-mass, and they meet the above requirements very well. The temperature of the heat source passively triggers the switching mechanism. The operation of thermal switches is similar to the functioning of a heat pipe with flexible walls.

A two-phase thermal switch consists of a hermetic enclosure housing sealed metallic bellows. The bellows have one of its ends fixed to the enclosure, which, in turn, is in contact with the heat source. Within the bellows, there is a wick structure along with a small amount of saturated working fluid.

The heat from the source enters the enclosure and the bellows, heating the working fluid. The heat vaporizes the fluid, increasing the saturated vapor pressure inside the bellows. The increasing pressure causes the bellows to expand until it makes contact with the other end of the enclosure, which is in contact with a heat sink.

The temperature of the saturated vapor that causes the pressure at which the bellows makes contact with the heat sink end of the enclosure, is the setpoint temperature of the two-phase thermal switch. The design of the two-phase thermal switch determines its setpoint temperature. One of the components deciding the set point temperature is the gas pressure within the enclosure, as it opposes the expansion of the bellows. Users can remotely adjust the set point temperature of a two-phase thermal switch by changing this counter pressure. The switch maintains the heat source at its set-point temperature as the heat sink conducts heat away from the enclosure.

As the name suggests, a two-phase thermal switch operates in two phases. The first phase is similar to a conventional thermal switch. The device switches from a low conductance state to a high conductance state and back as the heat source supplies heat or removes it.

The second phase of the switch comes into effect during its high conductance state. In this condition, the device also operates as a variable conductance device for maintaining the heat source at its set-point temperature. The design of the device allows it to maintain the temperature of the heat source at the set point while the heat sink temperature varies wildly. The variable conductance is a result of the dynamic motion of the bellows as it oscillates and periodically connects with the heat sink.

Two-phase thermal switches are capable of dissipating a wide range of heat loads during widely ranging thermal environments. Their low mass, simple design, low cost, and higher on to off conductance ratios are positive factors in spacecraft applications. At high temperatures of the heat source, the bellows may not disconnect from the sink, essentially acting as a heat pipe.

Selecting Industrial Enclosures

Industrial environments can be harsh, possessing the potential for causing expensive damage to equipment accompanying any investments in technology. Therefore, it is important to select the right industrial enclosures to protect, cool, and power systems for applications. Several key questions can come up when considering industrial enclosures and their selection.

Modern businesses prefer modular enclosures, as they provide flexibility, allowing evolution with the changing demands of business lifecycles. Compared to traditional unibody enclosures, modular enclosures may provide up to 30% more mounting space. Additionally, modular enclosures are typically lighter than welded units but capable of holding an equivalent weight of the material.

Modular enclosures may have additional advantages over their traditional counterparts. For instance, most modular enclosures offer greater surface area, thereby increasing the capacity for adding more accessories. The additional accessories may include fold-up keyboard shelves, LED lighting, and busbar power.

With doors capable of opening from either the right or the left side, modular enclosures offer swapping of lock systems without requiring tools. Reversible doors offer easy addition of IoT-enabled access controls or biometric controls. One can also send alerts by email and/or phone if the door is open, thereby improving remote security monitoring.

As it is possible to allow the frame to hold components also, the design does not limit itself to mounting the panel alone. Therefore, the user can fully utilize the interior of the enclosure. In other words, users can shrink the footprint of the enclosure, while still maintaining the operational capabilities.

When selecting the material for an industrial enclosure, it is preferable to look for carbon steel or stainless steel. Painted carbon steel is most suitable for indoor enclosures and is the most cost-effective among all metallic enclosures. It is easy to get a paint finish that is scratch resistant. Carbon steel with a painted surface has limited resistance to acids, alkalis, and solvents.

However, for the greatest protection from corrosion, rust, high-pressure washes, chemicals, and various harsh weather conditions, stainless steel enclosures offer the best solutions. Industries dealing with food and beverages, pharmaceutical, mining, wastewater, and oil and gas, use stainless steel enclosures extensively. Of the two main types of stainless steel available for enclosures, type 316 and 304, type 316 offers the highest resistance to corrosion, both for indoor and outdoor use.

Selecting modular enclosures with frame options that accommodate multiple door options offers more flexibility. For instance, it is easy to configure several small partial doors when considering a solution for custom motor control centers.

Consider foamed-in-place gaskets for modular enclosures, as it is possible to pour the gasket in a continuous manner around the perimeter of the doors and sidewall, thereby ensuring no gaps exist. Not only does this provide a better seal and memory retention, it also increases protection from corrosive materials and atmospheric conditions.

It is also possible to use an external skin with modular enclosures. This feature allows removing the sidewall, doors, and other parts, thereby offering greater access to internal components. It also allows more accurate modifications and cutouts on the enclosure. Stainless steel panels with an L-fold around the perimeter offer greater stiffness.

MEMS Technology for CO2 Sensing

Most technologies for detecting CO2 are based on photo-detection, where smoke particles reflect light that photo-sensors can detect. However, MEMS technology now offers a more sensitive technology for detecting CO2. Using their knowledge in sensors and MEMS technology, Infineon has now introduced a disruptive gas sensor for sensing CO2 gas.

Coming in a minuscule form factor, the XENSIV PAS CO2 from Infineon is a real CO2 sensor. Infineon has based it on the principle of photoacoustic spectroscopy or PAS. Infineon uses a MEMS microphone, which they have optimized for low-frequency operation. The sensor has a cavity that can detect pressure changes generated by CO2. An integrated microcontroller in the sensor then delivers the CO2 concentration in the form of a direct ppm readout. As the absorption chamber of the sensor is acoustically isolated from external noise, the sensor guarantees highly accurate readings of CO2.

XENSIV PAS CO2 has impressive features. Its operating range extends from 0 ppm to 10,000 ppm, with a linear response giving an accuracy of 30 ppm +3% of reading between 400 ppm and 5,000 ppm. The operating temperature range of the sensor is 0-50 °C at a relative humidity (non-condensing) of 0-85%.

The sensor requires two supply voltages, 12VDC for the emitter and 3.3VDC for its other components, and its average power consumption is typically 30 mW when operating at 1 measurement per minute. With a package dimension of 13.8 x 14 x 7.5 mm, the sensor offers three interface standards—I2C, UART, and PWM.

XENSIV PAS CO2 has several potential applications. On account of its high accuracy, SMD capabilities, and compact size, the sensor is ideally suitable for indoor air quality monitoring with numerous potential applications. For instance, the sensor is highly suitable for home appliances for air conditioners and air purifiers. It is also suitable for smart home IoT devices like smart lighting, indoor air quality monitors, personal assistants, baby monitors, speakers, and thermostats. Apart from use in in-cabin air quality monitoring in aircraft, the sensor is eminently suitable for city management and CO2 emission control in advertising billboards, bus stations, and outdoor lighting.

While measuring the CO2 concentration, the sensor operates in one of two modes—active state and inactive state. In the active state, the integrated CPU is in an operating state and performs tasks like running a measurement sequence or serving an interrupt. However, when the sensor has no specific task to perform, the CPU enters an inactive state. The device may enter an inactive state from an active state at the end of a measuring sequence.

During an inactive state, the CPU controlling the device can enter a sleep mode to optimize the consumption of power. Several events can wake up the CPU from its inactive state—a falling edge on the PWM pin, reception of a message on the serial communication interface, or the internal generation of a measurement request when the device is in continuous measurement mode.

It is possible to program the sensor module via its serial communication interface to operate in one of three modes—idle mode, Continuous mode, and Single-Shot mode.

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.

What is HD Audio?

With the advent of wireless headphones, there has been a steadily increasing demand for HD or High Definition audio. People of all ages like the HD sound experience, especially those with age-related hearing degradation. These trends are driving the HD audio support development at all stages of the delivery chain.

High definition audio or high-resolution audio has no strict technical definition. Industry experts use the term to describe audio systems supporting higher data rates than older equipment could handle. Initially, industry experts first used the term to describe digital systems that could handle higher data rates as compared to the Compact Disc format. Now, it applies to wireless headphones that can deliver better audio quality.

Although the industry has improved the recording and distribution of audio with increased data rates and these are available to mobile listeners, wireless headphones were left behind mainly due to Bluetooth limitations. With newer Bluetooth codecs, it is now possible for wireless headphones too to deliver HD quality audio. Therefore, the trend is to improve the audio hardware, especially the drivers.

Digital audio formats are mainly defined by two terms — sample rate and bit depth. When converting from the analog sound, the digital audio samples the signal amplitude and saves each sample as a binary number. The sample rate represents the number of times the system samples the analog signal every second. The binary number size that represents the amplitude is the bit depth.

To accurately capture the information in a sine wave, it is necessary to sample it at least two times per cycle. Therefore, for music, the sample rate must be at least two times the highest frequency in the music. Therefore, if the maximum audio frequency to be reproduced is 20 kHz, the sampling frequency must be at least 40 kHz. Additionally, the ADC will require a very sharp 20 kHz low-pass filter to remove all frequencies above 20 kHz. However, in practice, nothing is perfect. Therefore, experts set the actual sample rate to 44.1 kHz, as this produces a better hearing experience.

The size of the byte that describes the audio sample, or its bit depth, determines the accuracy of each sample when digitized. Each additional bit in the binary word describes the amplitude with twice the original number of values. Alternately, this reduces errors by a factor of two. In the digital music system, this reduces the distortion and quantization noise, allowing each added bit of depth to reduce the noise floor by 6 dB.

Typically, digital systems work on multiples of 8 bits. Therefore, digital audio also uses multiples of 8 bits for its word size. With 8 bits as the word size, the noise floor is only 48 dB below the loudest music and is not very practical. Compact discs use a bit depth of 16, providing a signal-to-noise ratio of 96 dB, which is more reasonable.

At present, it is possible to deliver HD audio to the listener, as it is possible to upgrade all the stages in the delivery chain. Bluetooth codecs have been upgraded, mobile phone capability is better, and music streaming services have improved.

What is a DIP Switch?

DIP or Dual-In-line-Package switches have been popular since the 1970s. OEMs and end-users use them widely to change the functionality of electronic devices at the point of use. For instance, DIP switches allow users to set region codes for equipment to make them work in different areas, to change to a specific radio channel, which garage door the opener will engage, or to select the type of memory a PC motherboard has.

The DIP switch comprises a set of switches within a single unit, typically mounted on a PCB. Each switch is very basic in construction and functionality. The user must set each switch manually, and therefore, the user can simply determine the status by viewing the switch bank during system startup. This is in direct contrast to a membrane keypad connected to a microcontroller, which must be powered up and polled to know the status. Therefore, DIP switches have the simplicity and provide input to basic system firmware, and need not be powered up to know their current status.

Users can select the number of operations on their DIP switch depending on the configuration of the electronic application. This is possible as DIP switches are available in a variety of sizes, configurations, power ratings, and styles.

Just like any other switch, users can select from the number of poles and throws the DIP switch must-have. For instance, they can use the SPST switch or single pole single throw switch, as it has a two-terminal option, with the pole either engaging with the throw to enable continuity or disengaging with the throw to enable electrical isolation.

Likewise, there are SPDT switches or single pole double throw switches, where the user may push the single pole to engage with any one of the throws, and push it the other way to engage with the other throw. It is possible to direct any signal on the pole to either one of the throws at any time.

Other switches are available as a combination of the above SPST and SPDT arrangements. For instance, there may be mechanically linked double poles engaging with double throws, making the switch DPDT or double pole double throw type.

Typically, the number of switches in a package is dependent on the application, with 1 to 16 positions being a common number. For instance, a common DIP switch package may have eight positions, allowing it to be set to 256 different ways. This is equivalent to the 256 binary values that an eight-bit byte may express.

Mechanically, DIP switches are available in various types, depending on the way they operate, whether they have slide actuators, rotary actuators, piano actuators, and so on.

DIP switches with slide actuators usually have two positions, either closed or open, acting as an SPST switch. However, there can be DIP switches with slide actuators and three positions. Frequently, in such switches, the middle position acts as the neutral. As the actuator moves to either side, it makes contact with the position on that side.

DIP switches are low-cost, flexible, and provide a simplicity rarely found.