Category Archives: 3D Printing

3D Printed RF Components

Most RF system designers view air simply as a medium for electromagnetic energy propagation from the source to the receiver. This is usually the case, allowing them to focus the bulk of their design effort on interconnections and integrated circuits that define the physical system.

However, that is only a simplistic view, as other properties of air are also important. For instance, air can keep electronics cool with convection, and it has dielectric properties that some RF components find critical.

Heinrich Hertz first demonstrated wireless signals in 1888. He energized a spark gap of 1 millimeter using high voltage, creating a wideband pulse. A dipole antenna transmitted this pulse. The antenna had two collinear metal rods with capacitive metal plates. At standard atmospheric conditions, air has a dielectric strength of about 30-70 volts/mil or 3-7 kV/mm. Discharged through air across the gap, the high voltage spark caused brief standing waves of oscillating current in the antenna, which then radiated this energy as a brief pulse of radio waves.

With the growth and maturing of wireless, RF tuners often had variable capacitors. These consisted of multiple parallel plates with air gaps that decided the capacitance value of the tuning assembly. By rotating a shaft, it was possible to adjust the position of the moving plates with reference to the static ones, thereby changing the capacitance between them from near zero to several hundred picofarads.

Vacuum has the ideal unit dielectric constant, while air is very close, with a value of 1.00058986. In comparison, the dielectric constant of PTFE is 2.0, and for FR4 it is about 4.4.

Another important property of vacuum, is its dielectric loss, dissipation factor, or loss tangent is zero, and so it is for air as well. Moreover, air characteristics are stable well into the terahertz frequency range, but it is not so for other dielectrics.

However, both vacuum and air have a common weakness. Neither has any structural strength. Therefore, they require a supporting form to hold them. Engineers find this a challenge as there must be an adequate amount of air within the structural medium of the dielectric.

The solution to this problem lies in using AM or additive manufacturing, also known as 3D printing, along with foam, and a family of photopolymer materials. Roger’s Corp typically supplies specialty RF materials, such as the Radix family of 3D printable, high-resolution materials. Radix is a photo-curable, highly viscous resin. It is a high filler concentration that offers good mechanical and electrical properties even at high frequencies.

3DFortify, of Boston, makes a particular type of Flux Core 3D printer. This is the only printer in the market that can effectively print using the Radix resin. The two companies are now partnered to produce 3D-printed RF components.

The printer layers the material with a thickness of less than 100 µm and cures it with a UV digital light processing projector in one flash for every layer. They provide both metalized and non-metalized versions. With the 3D-printing approach, the manufacturer can vary the structural strength of the material as necessary. They can give thick and strong structures at places subject to physical pressure or connections. 

3D Printing and Electricity from Waste Heat

There are several techniques existing for recovering energy from waste heat. The typical approach is to use waste heat to generate electricity. Now 3-D printing methods are taking the lead to make devices that will convert waste heat into electricity.

UNIST is located in the largest industrial city of Ulsan in Korea. Engineers there have conducted breakthrough research. They have developed a new thermoelectric technology for producing power-generating tubes. The best part of their research is they can print the tubes using 3-D printing methods.

Most automobile and industrial exhaust gases generally go to waste. But they are usually hot. By generating electricity from these hot exhaust gases, it is possible to enhance the efficiency of fossil energy production techniques. For this, the most suitable method is to use thermoelectric or TE methods. However, this is not an easy task, as typical thermoelectric products that the traditional processes produce are neither cost-effective nor do they fulfill efficiency requirements. According to the researchers, exhaust pipes fall into this category.

Engineers addressed this inefficiency issue by creating a special type of exhaust pipe. They built it out of lead and tellurium and used 3-D printing techniques for creating it. According to the researchers, they created the ink for the 3-D printer by mixing metal particles with a glycerol solvent. This provided them with the necessary viscoelasticity necessary for the ink and gave the ink the necessary characteristics of elasticity and viscosity.

The tube printed with this ink offers a high thermoelectric performance between temperatures of 400 and 800 °C. Most exhaust gases from vehicles exhibit this range of temperatures.

The research was a joint venture between the Department of Mechanical Engineering, UNIST, and the Department of Materials Science and Engineering, UNIST.

With their computational and experimental findings, the researchers have demonstrated the efficacy of their 3-D printed TE tubes they made from PbTe for power generation from waste heat. Their design has proven to be a system-adaptive and high-performance thermoelectric generator.

The 3-D printed power-generating PbTe TE tubes are made of p-type material and n-type material, with insulating material separating them. The TE tube has a series of p-type PbTe tubes followed by an insulating tube, and an n-type tube repeating many times. One complete power-generating TE tube may have ten pairs of p-type and n-type PbTe tubes in series.

According to the lead researcher, this 3-D printed power-generating PbTe TE tube technology can efficiently convert waste heat escaping through factory chimneys into electricity. In fact, factory chimneys are the most common type of source of waste heat. The shape of the tube makes it very effective for collecting heat as compared to the conventional rectangular shape of present TE generators.

Using 3-D printing technology for producing thermoelectric materials overcomes the limitations that engineers typically face while using commercial materials. According to the researchers, other fields can also use the viscoelastic characteristics that 3-D printed materials offer. The publication Advanced Energy Material features this novel and innovative research in thermoelectric materials.

3-D Printed Skin Improves Dexterity

The healthcare industry has always had a longstanding relationship with soft robotics. Soft robots are increasingly making their presence felt by assisting physicians in surgical procedures and turning major surgeries into minimally invasive procedures. With more physicians using soft robots that can feel and respond to stimuli, they can be substantially more precise, thereby posing a vastly lower risk of damaging sensitive organs and soft tissues with the wrong amounts of pressure.

Soft robots are more responsive to various stimuli, making them substantially more delicate and refined grippers for machines. They allow researchers to pick up delicate specimens deep underwater, or make complicated repairs outside the ISS. It is essential to have robots with dexterous and easy-to-control extremities. Their pressure-sensitive grippers can detect if they are holding a soft squid or a tiny metal part. They can adjust their grip accordingly, thereby preventing dangerous and time-consuming mistakes.

However, while emulating the sense of touch, researchers have had limited success with tactile-sensing technology, especially when fine-tuning dexterity. This is now changing with researchers from the University of Bristol creating the bionic sense of touch. Researchers from the Department of Engineering Maths are using 3-D printed papillae mesh on the under-surface of a compliant skin.

Scientists, in an empirical study, have made substantial comparisons of the performance of a bionic fingertip against neural recordings made of the sense of human touch. Not only have they published their findings in a Journal of the Royal Society Interface, they have also described the creation of an artificial biometric tactile sensor, which they call the TechTip. Their creation can behave dynamically just like human skin does, and provide sensory responses. In simple words, the artificial fingertip mimics human nerve signals.

The robotic hand has a 3-D printed tactile fingertip on its finger. A black flexible 3-D printed skin covers the white rigid back of the fingertip. The construction is similar to the dermal-epidermal interface of the skin and is backed by a mesh consisting of dermal papillae and intermediate biometric ridges. The dermal papillae comprise markers tipping the inner pins.

Scientists constructed the papillae on advanced 3-D printers with the capability of mixing hard and soft materials to emulate effects and textures similar to human biology.

The scientists claim their work uncovers the complex internal structure of the human skin and recreates the human sense of touch. For them, this represents an exciting development in the field of soft robotics. They have been able to 3-D print an artificial tactile skin that can lead to robots that are more dexterous. They can also significantly improve the performance of prosthetic hands, providing them with an in-built sense of touch.

According to scientists at the University of Bristol, a 3-D printed tactile fingertip can produce signals from its artificial nerves. These signals are similar to the recordings from real tactile neurons. They claim human tactile nerves transfer signals from numerous mechanoreceptors or nerve endings. These indicate the shape and pressure of contact. In their work, the scientists claim to have tested their 3-D printed artificial fingertip, and they found the same ridged profiles and a startlingly close match to the recorded neural data.

Driving Motors and Servos with the ZeroPi

If you are looking for a development board for the 3-D printer you are designing, ZeroPi may be the best fit. Suitable for use with the Arduino and the Raspberry Pi (RBPi) single board computers, ZeroPi offers an integrated solution allowing makers to build projects easier and faster.

This miniature board for the Arduino and RBPi is a next generation development kit ideal for maker projects that involve any type of robotic motion control including CNC milling and 3-D printers. According to technical specifications, the ZeroPi runs on an Atmel 32-bit, ARM Cortex M0+ processor the SAMD21J18 operating at 48 MHz. This MCU is fully compatible with the RBPi, the Arduino Zero, and so many more hardware resources that drive robots.

Capabilities of the ZeroPi include driving and controlling 11 micro servos and 8 DC motors simultaneously. Alternatively, you can use ZeroPi to control four stepper motors. The four-channel SLOT module is compatible with the regular DC motor and stepper motor drivers such as the TB6612 DC motor driver and the A4988 or DRV8825 Stepper motor drivers.

According to the team that developed ZeroPi, the board works perfectly for a 3-D printer, acting as its mainboard. Additionally, with the ZeroPi and a web interface, it is possible to control the 3-D printer remotely. The team claims to have successfully ported the Repetier and Marlin firmware to ZeroPi. They have tested the combination on Delta and I3 open source 3-D printers, with success. The combination directly controls the printer without requiring any additional expansion boards. Compared to the Mega2560, ZeroPi is all open-source, cheaper and four times faster. In addition, it is only half the size of the Mega 2560. All board schematics, Repetier and Marlin firmware, and the user manual for the ZeroPi is available on GitHub.

Apart from 3-D printers, you can also use the ZeroPi for driving laser cutters and CNC mills. In fact, it is perfectly possible to use the ZeroPi for developing an all-in-one mainboard suitable for all three. This open-source mainboard can serve the creativity and innovation of an entire community, advancing their ambitions. That makes the ZeroPi useful to several people and projects.

Some key features of the ZeroPi are operating voltage of 3.3 V, 2 UARTs, 35 general-purpose IO pins, 4 analog input pins, 12-bit ADC channels, 1 analog output pin, 10-bit DAC. Other features include external interrupts on any pin except pin 4, 7-mADC current per IO pin, Flash memory of 256 KB, SRAM of 32 KB. The ZeroPi board has dimensions of 73 x 61 mm.

You can program the ZeroPi from the Arduino IDE using example codes available for specific functions such as temperature monitoring and encoder readout. By connecting the ZeroPi to the GPIO connector of the RBPi, it is possible to add further functionality such as controlling the ZeroPi via Bluetooth, wireless control, and tablet. By installing a web interface, it is possible to control the motors and servos remotely. The interface can use Java Script as well.

3D Printer based on the Raspberry Pi

3D printers are becoming so very popular now and you can get them in many different sizes and configurations to suit your purpose. AON, a company providing 3D printer services in Montreal has built a prototype of a high-end dual extrusion 3D printer. A notable feature about this printer is the huge build volume of 129,600 cubic centimeters, which users can heat up to 70°C. However, most importantly, the device has an SBC that runs it – a Raspberry Pi or RBPi running the open source Linux Operating System and a 3D printer host software named OctoPrint.

AON was frustrated with the limitations of dual-extrusion printers available. They had to contend with limited build volumes, high failure rates and warped and cracked products. AON decided to address the above problems by building their own 3D printer. The result was an RBPi based high-end, 3D printer with a huge build area – 18x18x12 inches or 45x45x64 cm.

Estimated at an eventual retail price of US$4,000, the AON 3D printer (still a Kickstarter project) may not exactly be an impulse buy, since consumer 3D printers are available from $300 onwards. However, the discount price for this fascinating printer finds favor in a write-up in the website.

The AON 3D printer makes use of FDM, or Fused Deposition Modeling. This is a thermoplastic extrusion technology and most other 3D printer manufacturers such as the MakerBot Replicators use it. However, the difference is AON offers dual extruder heads that operate independently.

Users printing a complex object can speed up the printing by using both extruders simultaneously. Alternatively, printing of two identical designs is possible using the same or different colors or filament materials. To prevent waste of plastic oozing from a temporarily inactive extruder, the user can park the extruder off to one side.

To heat the chamber up to 70°C, the AON 3D printer uses its 1800W heaters. AON claims this helps to reduce cracking and warping with use of high-end materials such as Polycarbonate, Nylon or ABS. The printer allows printing with PLA or other special high-temperature materials and eliminates heat creep with special devices. These include high-end E3D Volcano hot ends reinforced with a heat-resistant thermocouple and cooled with water. Another robust feature is the high-end XY gantry that can travel at 500mm/s on the XY axis.

The printer, with a size of 80x90x125cm, integrates an Azteeg X3 Pro controller board. This features SD8825 SureStepr motor drivers and the Wi-Fi enabled RBPi. According to AON, the price includes the preloaded OctaPrint and a license for a copy of the Simplify3D printer software.

As the RBPi is Wi-Fi enabled, users do not need to tether a laptop. They can use any web browser to link to OctaPrint, which runs on the RBPi or any other embedded Linux board, supporting a huge variety of 3D printers. All usual print control features are available with the web interface, and this includes uploading and previewing the gcode files. Users can also configure custom controls. Remote visual monitoring via a webcam is possible, including remote temperature monitoring.