A method for the fabrication of flexible electrical circuits on polyaramid substrates is presented based on laser-induced carbonization followed by copper electroplating. Locally carbonized flexible sheets of polyaramid (Nomex), by laser radiation, create rough and highly porous microstructures that show a higher degree of graphitization than thermally carbonized Nomex sheets. The found recipe for laser-induced carbonization creates conductivities of up to ∼45 S cm–1, thereby exceeding that observed for thermally pyrolyzed materials (∼38 S cm–1) and laser carbon derived from Kapton using the same laser wavelength (∼35 S cm–1). The electrical conductivity of the carbonized tracks was further improved by electroplating with copper. To demonstrate the electrical performance, fabricated circuits were tested and improvement of the sheet resistance was determined. Copper films exhibit antimicrobial activity and were used to fabricate customized flexible antibacterial coatings. The integration of laser carbonization and electroplating technologies in a polyaramid substrate points to the development of customized circuit designs for smart textiles operating in high-temperature environments.

A control circuit for inductive levitation micro-actuators was developed in this research, the circuit’s performance and its electrical parameters are discussed. The developed control circuit was fabricated on a four-layer printed circuit board (PCB) board with a size of 60 × 60 × 25 mm. It consisted of a generator based on high-speed Flip-Flop components and a current amplifier build on a H-bridge configuration. The circuit was able to generate an AC current with a squared waveform in a frequency range from 8 to 43 MHz and with a peak-to-peak amplitude of up to 420 mA. To demonstrate the efficiency of developed circuit and its compatibility with a micro-actuation system, an inductive levitation micro-actuator was fabricated by using 3D micro-coil technology. The device was composed of two solenoidal coil designs, a levitation and a stabilization coil, with outer diameters of 2 and 3.8 mm, respectively. A 25 μm diameter gold wire was used to fabricate the coils, with the levitation coil having 20 turns and the stabilization coil having 12 turns, similar to the micro-structure presented previously by our group. Using the developed control circuit, the micro-actuator was successfully excited and it demonstrated the actuation of aluminum disc-shaped micro-objects with diameters of 2.8 and 3.2 mm and, for the first time, an aluminum square-shaped object with a side length of 2.8 mm at a frequency of 10 MHz. To characterize the actuation, the levitation height and the current amplitude were measured. In particular, we demonstrated that the square-shaped micro-object could be lifted up to a height of 84 μm with a current of 160 mA. The characterization was supported by a simulation using a 3D model based on the quasi-finite element model (FEM) approach.

Electrodeposition is a highly versatile and well explored technology. However, it also depends strongly on the experience level of the operator. This experience includes the pretreatment of the sample, and the composition of the electrolyte settings of the plating parameters. Accurate control over the electroplating current is needed especially for the formation of small structures, where pulsed electrodeposition has proven to reduce many unwanted effects. To bring precision into the formation of optimal recipes, a highly flexible current source based on a microcontroller was developed. It allows a large variety of pulse waveforms, as well as maintaining a feedback loop that controls the current and monitors the output voltage, allowing for both galvanostatic (current driven) and potentiostatic (voltage driven) electrodeposition. The system has been implemented with multiple channels, permitting the simultaneous electrodeposition of multiple substrates in parallel. Being based on a microcomputer, the system can be programmed using predefined recipes individually for each channel, or even adapt the recipes during plating. All measurement values are continuously recorded for the purpose of documentation and diagnosis. The current source is based on a high power operational amplifier in a modified Howland current source configuration. This paper describes the functionality of the electrodeposition system, with a focus on the stability of the source current under different electrodeposition current densities and frequencies. The performance and high capability of the system is demonstrated by performing and analyzing two nontrivial plating applications.

Abstract. Improvements to the signal-to-noise ratio of magnetic resonance detection lead to a strong reduction in measurement time, yet as a sole optimization goal for resonator design, it would be an oversimplification of the problem at hand. Multiple constraints, for example for field homogeneity and sample shape, suggest the use of numerical optimization to obtain resonator designs that deliver the intended improvement. Here we consider the 2D Lenz lens to be a sufficiently broadband flux transforming interposer between the sample and a radiofrequency (RF) circuit and to be a flexible and easily manufacturable device family with which to mediate different design requirements. We report on a method to apply topology optimization to determine the optimal layout of a Lenz lens and demonstrate realizations for both low- (45 MHz) and high-frequency (500 MHz) nuclear magnetic resonance.

Abstract. Improvements to the signal-to-noise ratio of magnetic resonance detection leads to a strong reduction in measurement time, yet as a sole optimization goal for resonator design it would be an oversimplification of the problem at hand. Multiple constraints, for example for field homogeneity, and sample shape, suggests the use of numerical optimization to obtain resonator designs that delivers the intended improvement. Here we consider the 2D Lenz lens as a sufficiently broad-band flux transforming interposer between the sample and an RF circuit, as a flexible and an easily manufacturable device family with which to mediate different design requirements. We report on a method to apply topology optimization to determine the optimal layout of a Lenz lens, and demonstrate realisations for both low (45 MHz), and high frequency (500 MHz) NMR.