Flexible Printed Circuit Board Technology Research Articles

Theoretical and Experimental Investigation of a Wireless Passive Pressure Sensor Based on Flexible Printed Circuit Board Technology

Theoretical and Experimental Investigation of a Wireless Passive Pressure Sensor Based on Flexible Printed Circuit Board Technology

Miniature water flow energy harvester based on savonius-type microturbine: an experimental study

In this experimental study, a miniature turbine-based water flow energy harvester designed for the purpose of providing power to wireless sensors within water pipes is reported. The device comprises a Savonius-type turbine and a radial flux permanent magnet electromagnetic generator. The two are magnetically coupled so that, while the turbine is submerged in the water flow, the generator operates in air. The device is cylindrical with a diameter of 0.8 cm and a length of 7.2 cm and, when inserted through a hole in a pipe wall so that only the turbine protrudes into the flow, it presents a cross-sectional area to the flow of only 1.25 cm2. Manufacturing was achieved through a blend of conventional machining methods, laser cutting, rapid prototyping, and the utilization of flexible printed circuit board technology for the generator stator. To ensure low friction and minimize cut in speed, ceramic ball bearings were employed. The prototype can function effectively at water velocities as low as 0.5 m s−1, generating electrical power within the range of 125 µW–5.1 mW when subjected to flow speeds between 0.5 and 2 m s−1. A maximum overall efficiency of 2.2% is achieved, when the water speed is 0.8 m s−1. Performance curves derived from experimental testing of the turbine for a range of rotor designs, obtained on a water flow rig, are presented and discussed.

Development of a flexible embedded neurostimulator for animal robots

The neural stimulator is a core component of animal robots. While the control effect of animal robots is influenced by various factors, the performance of the neural stimulator plays a decisive role in regulating animal robots. In order to optimize animal robots, embedded neural stimulators had been developed using flexible printed circuit board technology. This innovation not only enabled the stimulator to generate parameter-adjustable biphasic current pulses through control signals, but also optimized its carrying mode, material, and size, overcoming the disadvantages of traditional backpack or head-inserted stimulators, which have poor concealment and are prone to infection. Static, in vitro, and in vivo performance tests of the stimulator demonstrated that it not only had precise pulse waveform output capability, but also was lightweight and small in size. It had excellent in vivo performance in both laboratory and outdoor environments. Our study has high practical significance for the application of animal robots.

Wireless-controlled cubic neural stimulator for free-moving animals.

An electrical stimulator transmitting information into selected neural circuits is a promising approach for neural prostheses or animal robots. However, traditional stimulators are based on rigid printed circuit board (PCB) technology; technological limitations hindered the development of stimulators, especially for experiments involving free-moving subjects. Here we described a small (1.6 × 1.8 × 1.6 cm), lightweight (4 g, including a 100 mA h lithium battery) and multi-channel (eight unipolar or four bipolar biphasic channels) cubic wireless electrical stimulator exploiting flexible PCB technology. In comparison with the traditional stimulator, an appliance of both flexible PCB and cube structure makes it smaller and lighter, and enhances its stability. Stimulation sequences can be constructed with 100 selectable current levels, 40 selectable frequency levels and 20 selectable pulse-width-ratio levels. Moreover, the distance of wireless communication can reach approximately 150 m. Both in vitro and in vivo results have demonstrated functionality of the stimulator. The feasibility of remote pigeon's navigation using the proposed stimulator was successfully verified.

A capacitive sensor for differentiation between virus-infected and uninfected cells

Traditional biosensors are costly, cumbersome, and take a long time to report results, which limit their use in resource-constrained areas. Due to its high integration, customized architecture, and ease of mass processing, biosensors have been widely used in biomedical applications in recent years. In this paper, a biosensor is implemented using flexible printed circuit board technology for monitoring and identifying the effect of Baculovirus infection on one of its host cells (Sf9 cells) through many electrical features such as capacitance, impedance, permittivity, and conductivity. Furthermore, the effect of viral infection with different particle concentrations at different times was characterized. The results proved that the virus has a rapid effect on the cell by losing its electrical properties, which were clear from the decrease in electrical properties (e.g., capacitance, impedance, permittivity, and conductivity). Moreover, we introduced an equivalent model to represent the normal cells and infected cells based on the experimental results obtained for capacitance values. The proposed model simulation results are matched with the results obtained experimentally, which leads to the use of the model for predicting baculovirus infection.

Design and Characterization of a Flexible Relative Pressure Sensor With Embedded Micro Pressure Channel Fabricated by Flexible Printed Circuit Board Technology

This paper presents a relative pressure sensor fabricated by a standard industrial flexible printed circuit board (FPCB) technology. The passive wireless sensor consists of a variable sensing capacitor and a planar coil inductor. When the external pressure is applied to the sensing capacitor, it changes the air gap and shifts the LC resonance frequency which is detected by an antenna wirelessly. The sensing cavity of the variable capacitor is extended to the opening at the end of an embedded pressure channel in the FPCB strip to enable relative pressure measurement. Measurement results showed that the proposed sensor with such an open sensing cavity had much higher frequency sensitivity (up to 0.4 %/mmHg) compared with the sensor with a sealed cavity (< 0.01 %/mmHg in this work and ≤ 0.08 in literature). With the enhanced sensitivity, the measured pressure resolution could reach 0.2 mmHg. The potential application of the proposed sensor includes gauge pressure measurement with respect to local atmospheric pressure, such as intracranial pressure (ICP) monitoring, without complicated re-calibration procedures. The flat FPCB structure facilitates applications with limited space for sensor installation, such as in the subdural implantation procedures. Furthermore, the proposed technology enables future development of flexible microfluidic devices.

Detection of foodborne pathogens using novel vertical capacitive sensors

Food poisoning, infection of open wounds, and sepsis are the serious clinical consequences that pathogens can cause. Rapid identification of these pathogens allows prompt monitoring of infections, which improves clinical outcomes. An integrated platform is proposed to manipulate and identify the microorganisms (e.g., foodborne pathogens) in this work. An electrokinetic-based Actuator and capacitive-based sensor are the two primary components of the proposed platform. Dielectrophoresis-based microelectrode is proposed to manipulate the microorganisms. A novel vertical array of capacitive sensors is suggested To identify the levitated microorganisms. The mass of microorganisms can be extracted according to the applied dielectrophoretic force respecting the gravitational force. The whole platform is simulated using 2D numerical simulation, COMSOL Multiphysics, to evaluate design efficiency. Furthermore, the proposed platform is developed and experimentally evaluated using the most common food bacterium type (Escherichia coli (E. coli)). The practical prototype is implemented using cheap technology (rigid and flexible printed circuit board technology). Experiments demonstrated that the proposed biochip could identify E. coli without the need of complex and expensive tools and with a simple manufacturing method.

Intraoperative Cerebral Measurements Using Implantable Cortical Multimodality Probe.

In this study, a multimodality probe that simultaneously measures electroencephalograms, cerebral hemodynamics, and brain surface temperature was developed. This probe has six channels, and each channel has a platinum electrode for cortical electroencephalogram measurements, light emitting diodes, and photodiodes for hemodynamic measurements using near-infrared spectroscopy (NIRS), and a thermistor for measuring the cerebral surface temperature (BrT). A probe with a width of 8.0 mm and maximum total thickness of 0.7 mm was fabricated using flexible printed circuit board technology for chronic intracranial placement. Brain activity using the prototype probe at the resected site was measured and its function performance was evaluated. Characteristic epileptogenic abnormal electroencephalograms accompanied by polarity reversal between channels occurred at 16 min and 38 s. It was concluded that the brain cells consumed oxygen during the occurrence of abnormal electroencephalograms. At this time, no noticeable change in HbT values could be confirmed.

Multi-range sensors for the measurement of liquid film thickness distributions based on electrical conductance

The paper presents an approach toward an enhancement of the measuring range of high-speed sensors for the measurement of liquid film thickness distributions based on electrical conductance. This type of sensors consists of electrodes mounted flush to the wall. The sampling of the current generated between a pair of neighboring electrode is used as a measure of the film thickness. Such sensors have a limited measuring range, which is proportional to the lateral distance between the electrodes. The range is therefore coupled to the spatial resolution. The proposed new design allows an extension of the film thickness range by combining electrode matrices of different resolution in one and the same sensor. In this way, a high spatial resolution is reached with a small thickness range, whereas a film thickness that exceeds the range of the high resolution measurement can still be acquired even though on the costs of a lower spatial resolution. A simultaneous signal acquisition with a sampling frequency of 3.2kHz combines three measuring ranges for the characterization of a two-dimensional film thickness distribution: (1) thickness range 0–600µm, lateral resolution 2×2mm2, (2) thickness range 400–1300µm, lateral resolution 4×4mm2, and (3) thickness range 1000–3500µm, lateral resolution 12×12mm2. The functionality of this concept sensor is demonstrated by tests in a horizontal wavy stratified air–water flow at ambient conditions. Using flexible printed circuit board technology to manufacture the sensor makes it possible to place the sensor at the inner surface of a circular pipe.

Capacitive Fringing Field Moisture Sensors Implemented in Flexible Printed Circuit Board Technology

Capacitive fringing field sensors are often used in applications where moisture is detected, since the dielectric constant of liquid water is approximately 80 times greater than the dielectric constant of air. Most of these sensors, however, are realized using rigid substrates. Some applications would benefit from using a flexible capacitive fringing field sensor that could be conformally mounted on a nonplanar surface. Flexible printed circuit board technology is a mature commercially available process for manufacturing flexible electronics. This same technology can also be used to realize flexible fringing field moisture sensors where the patterned Cu foil is used for the electrodes and the soldermask coating electrically insulates the electrodes from being electrically shorted by moisture in the detection environment. Sensors were designed and characterized through flat and bending tests in air and in water. The tests demonstrated that bending a sensor over a radius of curvature as small as 13.7 mm had no measurable impact on sensor performance in air or in water. The sensors achieved a 3:1 increase in capacitance when immersed in water compared with in air.

Performance of a thermally deformable mirror for correction of low-order aberrations in laser beams

The thermally deformable mirror is a device aiming at correcting beam-wavefront distortions for applications where classical mechanical methods are precluded by noise considerations, as in advanced gravitational wave interferometric detectors. This moderately low-cost technology can be easily implemented and controlled thanks to the good reproducibility of the actuation. By using a flexible printed circuit board technology, we demonstrate experimentally that a device of 61 actuators in thermal contact with the back surface of a high-reflective mirror is able to correct the low-order aberrations of a laser beam at 1064 nm and could be used to optimize the mode matching into Fabry-Perot cavities.

Impedance measurement technique for high-sensitivity cell detection in microstructures with non-uniform conductivity distribution

Particle detection in microstructures is a key procedure required by modern lab-on-a-chip devices. Unfortunately, state of the art approaches to impedance measuring as applied to cell detection do not perform well in regions characterized by non-homogeneous physical parameters due, for example, to the presence of air-liquid interfaces or when the particle-electrode distance is relatively high. This paper presents a robust impedance measurement technique and a circuit for detecting cells flowing in microstructures such as microchannels and microwells. Our solution makes use of an innovative three-electrode measurement scheme with asymmetric polarization in order to increase cell detection ability in microstructures featuring large electrode distances of up to 100 μm as well as to limit signal loss due to cell position relative to the electrodes. Compared to standard techniques, numerical simulations show that, with the proposed approach, the cell detection sensitivity is increased by more than 40%. In addition, we propose a custom circuit based on division instead of difference between signals, as in standard differential circuits, so as to reduce the baseline signal drift induced by non-homogeneous conductivity. A simplified analytical model shows an increase in the signal-to-noise-ratio comprised in the range 3.9-5.9. Experimental results, carried out using an open-microwell device made with flexible printed circuit board technology, are in agreement with simulations, suggesting a six-fold increase of the signal-to-noise ratio compared to the differential measurement technique. We were thus able to successfully monitor the process of isolating K562 leukemia cells inside open-microwells determining all single-cell events with no false positive detection.

Design Techniques for Thermal Management in Switch Mode Converters

Thermal management plays a pivotal role in achieving high power densities in converters. Improvement on thermal performance of critical components in printed-circuit board (PCB) assembled switch mode converters is achieved by using design techniques that extend across electromagnetic, geometrical, and thermal-integration technologies. For better use of the already available PCB material, three-dimensional component layout and flexible PCB technology are utilized to gain advantages. A theory to evaluate the thermal-management effectiveness of switch mode converters is introduced based on two new figures of merit, namely thermal-management loss density and thermal-design rating. These two figures of merit quantify the effective use of thermal-management material as well as the thermal performance of a converter design. The figure-of-merit criteria allow flexibility so that it can be adjusted to an appropriate design objective. Design objectives include achieving higher power densities or achieving good reliability. The thermal-management-effectiveness theory is applied here to thermally optimize a Flyback converter that has been geometrically integrated. The design technique to adjust the thermal-management effectiveness of integrated switch mode converters to achieve a set objective, by means of the introduced figures of merit, forms the core of the publication, validated by experimental measurements

The micro-hole-and-strip plate gas detector: experimental results

We report the performance characteristics of a new microstructure, the Micro-Hole-and-Strip Plate (MHSP), operated initially as an X-ray proportional counter. The MHSP is a combination of the features of a microstrip plate (MSP) and a gas electron multiplier (GEM) in a single microstructure. Like the GEM, the MHSP is fabricated using flexible printed circuit board technology. The MHSP provides two independent charge-amplification stages: a first stage consisting of slotted holes, operated as a GEM, and a second stage, the MSP anodes, that also function as the final charge-collection electrodes. Two obvious benefits accrue from this design: for a given total gain, the MSP anode-to-cathode voltage can be maintained well below the breakdown threshold, and the charge-amplification stages are optically isolated, in anticipation of future applications as a photosensor. Full electron transmission and total gains up to 1000 were achieved, with slotted-hole gains as high as 14. The best energy resolution achieved thus far for 5.9-keV X-rays is 23%. Measurements of gains, electron transmission, and energy resolution, as functions of biasing voltages, are reported.