High Β-phase Content Research Articles

Hierarchically structured hollow PVDF nanofibers for flexible piezoelectric sensor

The emergence of flexible sensors addresses the limitations of traditional detection equipment, such as large size, high cost, and inconvenient portability. These sensors have significantly advanced the development of wearable electronic devices for applications in electronic skin, energy harvesting, and energy storage. To enhance the sensitivity of flexible sensors, we developed a hierarchical polyvinylidene fluoride (PVDF) nanofiber-based piezoelectric sensor. By utilizing coaxial electrospinning, we fabricated nanofibers with hollow interiors and porous outer walls. Additionally, microstructures were constructed on the fiber membrane surface by modifying the collector’s shape. The resulting microstructured hollow PVDF nanofiber membrane exhibited high β-phase content (91.31 %), excellent flexibility (maximum strain 56.9 %), and high porosity (88.94 %). The sensor demonstrated a sensitivity of 2.7 V/N (1.08 V/kPa) and a maximum output voltage of 10.1 V, approximately three times higher than that of solid PVDF nanofibers without microstructures. Even after 14,400 cycles of impact, the sensor maintained stable output. The sensor was successfully applied to human activity monitoring and gesture recognition, showcasing its ability to monitor various human activities, respond rapidly (60.4 ms), and synchronously control a mechanical palm to perform different gestures. This work highlights the potential of hierarchically structured hollow PVDF nanofibers in advancing the performance and application scope of flexible piezoelectric sensors.

Improving energy harvesting through femtosecond laser surface modification of PVDF/ZnS composite nanofibrous nanogenerators for electronic applications

Surface modification in ceramic/polymer composites holds paramount importance for electronic devices applications. Laser is a versatile and flexible device for modifying the surface characteristics of various materials. Here, we propose a novel approach to enhance the energy harvesting efficiency of polyvinylidene fluoride (PVDF) and zinc sulfide (ZnS) composite nanofibrous membranes through femtosecond laser surface modification. The electrospinning technique is used to produce nanofibers with a high β-phase content in a single step. The PVDF membrane was further enriched with ZnS nanoparticles to enhance the β-phase content. The membranes were systematically investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Electron Energy Loss spectroscopy (EELS), and Fourier-transform infrared spectroscopy (FTIR) to characterize their morphological and chemical properties. Femtosecond laser was employed to induce controlled surface modifications, resulting in hierarchical microstructures and surface functionalization. The results showed patterned tracks on the fiber surface while preserving its inherent nature. To validate its utility as an energy harvesting device, the membrane's capability was assessed by measuring the open circuit voltage. The results revealing average output voltages for nanogenerators treated with laser fluences of 0.5 J/cm2, 0.7 J/cm2, and 0.9 J/cm2 are 15.6 V, 25 V, and 17 V, respectively. The maximum output voltage is observed for a laser fluence of 0.7 J/cm2, attributed to the deeper structure created, increasing the surface area of contact and deformation in the structure. This work offers promising avenues for enhancing energy harvesting efficiency and expanding the scope of electronic devices such as sensors and actuators.

Crystallization of the β-Form of Polypropylene from the Melt with Reduced Entanglement of Macromolecules.

The influence of decreasing the entanglement density of macromolecules on the crystallization of the β-form of polypropylene was investigated. Polypropylene with seven times less entanglement was obtained from a solution in xylene, and its properties were compared with those of fully entangled polypropylene. To obtain a high β-phase content, the polymer was nucleated using calcium pimelate. In non-isothermal crystallization studies, accelerated growth of β-crystals was found, increasing the crystallization temperature. Also, the isothermal crystallization was fastest in the nucleated, partially disentangled polypropylene. Increased growth rate of spherulites and enhanced nucleation activity in the presence of more mobile macromolecules were responsible for the high rate of melt conversion to crystals in the disentangled polypropylene. It was also observed that the equilibrium melting temperature of β-crystals is lower after disentangling macromolecules. Better conditions for crystal building after reduction of entanglements resulted in enhanced crystallization according to regime II.

A novel centrifugal electrospinning design for preparing of high alignment β-phase PVDF nanofibers for high-performance piezoelectric nanogenerators

The effects of polyvinylidene fluoride (PVDF) wt. % and electric fields on the production of PVDF fibers using a novel centrifugal electrospinning design were investigated. High-quality, bead-free fibers with diameter of (0.55 ± 0.04) μm were successfully produced. Fibers with exceptionally high β-phase content of 96.1 % and piezoelectric coefficient, d33 of (−157 ± 5) pC N−1 were obtained using PVDF amount and electric field of 14.0 wt % and 400 V cm−1, respectively. Under 3.0 N repetitive vertical forces, the fabricated piezoelectric nanogenerator (PENG) exhibited impressive open-circuit voltage, short-circuit current and power density of (32.6 ± 0.7) V, (3.26 ± 0.07) μA and (15.4 ± 0.6) μW cm⁻2, respectively. The production of high and well aligned β-phase in the fibers indicated by good d33 values are the likely reasons for the excellent performance of the PENG. Ultimately, potential of the fabricated PENG as a self-power supply for low-energy electronic devices was demonstrated.

Enhanced magnetoelectric and energy storage performance of strain-modified PVDF-Ba0.7Ca0.3TiO3-Co0.6Zn0.4Fe2O4 nanocomposites

The experimental development of thin films that exhibit higher room-temperature low-field magnetoelectric (ME) sensing without compromising reliable electrical energy storage capabilities is rare. Here, an improved ferroelectric polarization, ME coupling and energy storage performance of polymer-based nanocomposites, which find applications in portable high-power dielectric capacitors, are studied. Multiferroic nanofiller-based three-phase flexible nanocomposites, polyvinylidene fluoride (PVDF)-(Ba0.7Ca0.3)TiO3-(Co0.6Zn0.4)Fe2O4, were fabricated using compression molding to enhance polarization which is pivotal for applications. PVDF with a high β-phase content (92.4 %), switchable ferroelectric behavior and higher breakdown strength (510 kV/mm) was obtained under optimized process conditions (500 MPa at 165 °C). The fabrication assisted alteration of intermolecular chain distance results in a tensile strain (1.42 %) of β-crystallites corresponding to an internal stress of ~21 MPa. The progressive increase of nanofiller content has led to enhanced polarization (11 μC/cm2), soft ferromagnetic properties, and enhanced ME coupling of 59 mV/cm-Oe due to switchable magnetostriction (λ11 = −18 ppm and dλ11/d = −22 × 10−9 Oe−1) at lower saturation field of 1.2 kOe. The ME sensitivity was found to be more than two-folds enhanced compared to solution-cast films making them prospective self-biased flexible devices for wearable electronics. Simultaneously, enhanced change of magnetization (19.6 %) under electric field was obtained. Detailed energy storage characteristics confirm that the nanofiller inclusion up to 7.12 vol% effectively improved the recoverable energy storage density (21.2 J/cm3) with an efficiency of 67 %. The experimental and simulation results corroborate a significantly improved breakdown strength of 617 kV/mm with reliable performance. Thus, careful processing provides viable polymer dielectrics with beneficial storage characteristics.

Enhanced output performance piezoelectric nanogenerators based on highly polarized PVDF/TBAHP tree-like nanofiber membranes for energy harvesting

As a piezo-polymer, the most contribution of polar phases (β-, γ-phases) to the piezoelectricity of polyvinylidene fluoride (PVDF) has been researched. Herein, a new type PVDF/tetrabutylammonium hexafluorophosphate (TBAHP) tree-like nanofiber membrane (TLNM) with high polar phase content and numerous fine branch fibers was successfully developed via electrospinning. PVDF-TLNMs exhibited mass branch fibers whose diameters of less than 50 nm. The β-phase content of 88.94 % disclosed piezoelectric polarization ability in the presence of TBAHP and tree-like structure. The best output current and voltage of flexible PVDF-TLNMs based piezoelectric nanogenerators (PENGs) could reach 2.04 μA and 4.08 V at 0.07 mol L−1 TBAHP, which increased the current of pure PVDF by approximately six times and a 217 % improvement to voltage output. Likewise, the peak power density of 0.07 mol L−1 PVDF-TLNM was 13 times above that of pure PVDF-NM. The significant reduction of internal resistance occurred after the addition of TBAHP. Such significant enhancements for electrical output depended on the high β-phase content, originated through TBAHP induced self-alignment of electric dipoles in PVDF polymer and high extent of mechanical drawing. The new kind of PVDF-TLNMs-base PENGs can provide a large scope for the ideas of smart wearable devices.

Flexible Film Bulk Acoustic Wave Filter Based on Poly(vinylidene fluoride-trifluorethylene).

Poly(vinylidene fluoride-trifluorethylene) (P(VDF-TrFE)) has promising potential applications in radio-frequency filters due to their excellent piezoelectric properties, flexibility, and stability. In this paper, a flexible film bulk acoustic wave filter is investigated based on P(VDF-TrFE) as piezoelectric film. A new method based on three-step annealing is developed to efficiently remove the porosity inside the P(VDF-TrFE) films so as to improve its properties. The obtained film achieved high β-phase content beyond 80% and a high piezoelectric coefficient of 27.75 pm/V. Based on the low porosity β-phase films, a flexible wide-band RF filter is designed, which consists of a bulk acoustic wave resonator and lumped inductor-capacitor elements as a hybrid configuration. The resonator sets the filter's center frequency, while the lumped LC-based matching network extends the bandwidth and enhances out-of-band rejection. The testing results of the proposed wide-band filter show its good performance, with 12.5% fractional bandwidth and an insertion loss of 3.1 dB. To verify the possibility of folding and stacking the flexible bulk acoustic wave devices for high-density multi-filter integration in MIMO communication, bending tests of the filter are also conducted with the bending strain range up to 5500 με. The testing results show no noticeable performance degradation after four bending cycles. This work demonstrates the potential of β-phase P(VDF-TrFE) bulk acoustic wave filters to expand the scope of future flexible radio-frequency filter applications.

PVDF composite fibers for wireless fall-alert detection

As the demand for healthcare devices continues to rise, novel technologies centered on personalized motion monitoring systems are being developed, wherein wearable sensors play a pivotal role. In the present investigation, an innovative wireless apparatus for detecting falls is introduced, which encompasses a specifically engineered pressure sensor composed of polyvinylidene fluoride (PVDF) composite fibers. Our design consists of high β-phase content of electrospun composites including 0.1 wt% of zinc oxide/reduced graphene oxide (ZnO/rGO) hybrid (mass ratio 90/10) which shows enhanced electrical voltage of 11.36 ± 0.72 V compared to pristine PVDF fiber. This piezoelectric pressure sensor is integrated with a wireless embedded system capable of transmitting an “SOS” message to a mobile phone upon the user’s fall experience. Such wearable fall alert detection systems with improved characteristics could benefit the elderly and patients requiring continuous monitoring for possible falls.

Molecular Mechanism of the Piezoelectric Response in the β-Phase PVDF Crystals Interpreted by Periodic Boundary Conditions DFT Calculations.

A theoretical approach based on Periodic Boundary Conditions (PBC) and a Linear Combination of Atomic Orbitals (LCAO) in the framework of the density functional theory (DFT) is used to investigate the molecular mechanism that rules the piezoelectric behavior of poly(vinylidene fluoride) (PVDF) polymer in the crystalline β-phase. We present several computational tests highlighting the peculiar electrostatic potential energy landscape the polymer chains feel when they change their orientation by a rigid rotation in the lattice cell. We demonstrate that a rotation of the permanent dipole through chain rotation has a rather low energy cost and leads to a lattice relaxation. This justifies the macroscopic strain observed when the material is subjected to an electric field. Moreover, we investigate the effect on the molecular geometry of the expansion of the lattice parameters in the (a, b) plane, proving that the rotation of the dipole can take place spontaneously under mechanical deformation. By band deconvolution of the IR and Raman spectra of a PVDF film with a high content of β-phase, we provide the experimental phonon wavenumbers and relative band intensities, which we compare against the predictions from DFT calculations. This analysis shows the reliability of the LCAO approach, as implemented in the CRYSTAL software, for calculating the vibrational spectra. Finally, we investigate how the IR/Raman spectra evolve as a function of inter-chain distance, moving towards the isolated chain limit and to the limit of a single crystal slab. The results show the relevance of the inter-molecular interactions on the vibrational dynamics and on the electro-optical features ruling the intensity pattern of the vibrational spectra.

Phase-Engineering of Layered Nickel Hydroxide for Synthesizing High-Quality NiOx Nanocrystals for Efficient Inverted Flexible Perovskite Solar Cells.

Nickel oxide (NiOx) nanocrystals have been widely used in inverted (p-i-n) flexible perovskite solar cells (fPSCs) due to their remarkable advantages of low cost and outstanding stability. However, anion and cation impurities such as NO3- widely exist in the NiOx nanocrystals obtained from calcinated nickel hydroxide (Ni(OH)2). The impurities impair the photovoltaic performance of fPSCs. In this work, we report a facile but effective way to reduce the impurities within the NiOx nanocrystals by regulating the Ni(OH)2 crystal phase. We add different alkalis, such as organic ammonium hydroxide and alkali metal hydroxides, to nickel nitrate solutions to precipitate layered Ni(OH)2 with different crystalline phase compositions (α and β mixtures). Especially, Ni(OH)2 with a high β-phase content (such as from KOH) has a narrower crystal plane spacing, resulting in fewer residual impurity ions. Thus, the NiOx nanocrystals, by calcinating the Ni(OH)x with excess β phase from KOH, show improved performance in inverted fPSCs. A champion power conversion efficiency (PCE) of 20.42% has been achieved, which is among the state-of-art inverted fPSCs based on the NiOx hole transport material. Moreover, the reduced impurities are beneficial for enhancing the fPSCs' stability. This work provides an essential but facile strategy for developing high-performance inverted fPSCs.

Investigation of electrospun piezoelectric P(VDF-TrFE) nanofiber-based nanogenerators for energy harvesting

A piezoelectric nanogenerator (PENG) from thin poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) polymer fiber films synthesized by the electrospinning method demonstrated the enhanced output. The β-phase content in thin films that is essential for piezo responses in polymers was analyzed using Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) imaging. The results showed an extremely high 92,8% of β-phase content in P(VDF-TrFE) thin films. The fabricated PENG device using P(VDF-TrFE) film demonstrated an outstanding peak-to-peak open-circuit voltage (Voc) of ∼25 V and short-circuit current (Isc) of 0.3 μA under 3 N applied force. The device could produce a maximum power density of ∼125 nW cm −2 under a 6 N load. The maximum voltage of ∼100 V was achieved with the compressive force of 20 N. Moreover, the ability to charge 0.1 μF capacity to ∼6.5 V within 180 sec was demonstrated under an external load of 6 N at 5 Hz. It can be concluded that the improved piezoelectric performance of PENG was achieved due to high β-phase content and the optimized synthesis route. The obtained electrical performance of PENG demonstrated its potential for powering low-power electronic devices by scavenging mechanical energy.

Enhanced dielectric and energy storage properties of P(VDF-HFP) through elevating β -phase formation under unipolar nanosecond electric pulses

Structural manipulation of electroactive β-phase of poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] is of great importance in high-energy-density polymer devices. In this Letter, an efficient way to improve dielectric and energy storage properties of P(VDF-HFP) films by inducing a high β-phase content and lowering the crystallite size through repetitive unipolar nanosecond electric pulses (nsEP) is proposed. It is found that the percentage of the β-phase in P(VDF-HFP) can be significantly enhanced to ∼84% under a low unipolar nsEP of 5 V/mm vs only 35% in pristine P(VDF-HFP). Meanwhile, the orientation of the amorphous chains is also achieved, which improves the dielectric constant, electric breakdown, and energy storage properties of P(VDF-HFP). Specifically, the P(VDF-HFP) film processed under nsEP of 5 V/mm exhibits a high breakdown field of 541 MV/m, and discharged energy density of 14 J/cm3, which is 28.8% and 127% higher than those of the pristine polymer, respectively. This work provides a facile approach to optimize the crystalline morphology of P(VDF-HFP) polymers for dielectric energy storage applications.

Phase separation of a PVDF–HFP film on an ice substrate to achieve self-polarisation alignment

Flexible self-polarised poly(vinylidene fluoride) (PVDF) piezoelectric films that have a high electroactive phase content and can be easily prepared are applied in force–electricity conversion, particularly as self-power supplies for small devices and the detection of body signals. Filler addition, phase separation and polarisation by a substrate are the most used methods to fabricate self-polarised PVDF films. However, the alignment of films is hard to realise using these self-polarising techniques, thus making it difficult to increase piezoelectric generation. In this study, phase separation on an ice substrate was used to prepare a self-polarised poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) film. Strong polarisation via hydrogen bonding between PVDF–HFP and a flat ice substrate contributes toward a high β-phase content of 86.5% and good film alignment. Moreover, the low preparation temperature provided by ice has considerable impact on self-polarisation, with excellent alignment observed because of the reduced disturbance by solvent flow and the Brownian motion of the PVDF–HFP solution at low temperature having less impact on self-polarisation via hydrogen bonding. The phase separation on ice of the PVDF–HFP film was confirmed to be an efficient self-polarisation method to considerably improve its β-phase content, alignment and piezoelectric generation performance.

In-situ electrostatic field regulating the recrystallization behavior of P(VDF-TrFE) films with high β-phase content and enhanced piezoelectric properties towards flexible wireless biosensing device applications

Fabrication of flexible piezoelectric polymers is essential for the development of wearable biosensors. Nevertheless, the piezoelectric coefficient of polymers is usually an order of magnitude lower than the inorganic piezoelectric materials, which limits the miniature of the devices. Herein, a simple and cost-effective technique is proposed by applying an electrostatic field to in-situ regulate the recrystallization behavior of the poly(vinylidene fluoride-trifluorethylene) (P(VDF-TrFE)) film during the thermal annealing and recrystallization stage. Significantly enhanced properties are obtained, including a large piezoelectric coefficient (d33~30.7 pC/N) and a high voltage sensitivity of 167.12 mV/kPa. The outstanding performance is mainly attributed to the applied electrostatic field maintained during the film growth stage, which promotes the generation of nucleation sites for the polar β lamellae crystals. A wireless sensor system is further established with the obtained P(VDF-TrFE) film, demonstrating great potential applications in movement monitoring. The proposed facile approach could potentially be applied to the large-scale production of polymer films with excellent piezoelectric properties for flexible wireless biosensing device applications.

Piezoelectric Property of Electrospun PVDF Nanofibers as Linking Tips of Artificial-Hair-Cell Structures in Cochlea.

The death of hair cells and damage of natural tip links is one of the main causes of hearing-loss disability, and the development of an advanced artificial hearing aid holds the key to assisting those suffering from hearing loss. This study demonstrates the potential of using electrospun polyvinylidene fluoride (PVDF) fibers to serve as the artificial tip links, for long-term hearing-aid-device development based on their piezoelectric properties. We have shown that the electrospun PVDF-fiber web, consisting of fibers ranging from 30–220 nm in diameter with high β-phase content, possesses the high piezoresponse of 170 mV. Analyses based on combined characterization methods including SEM, TEM, XRD, FTIR, Raman, DSC, XPS, PFM and piezoelectricity have confirmed that an optimized value of 15 wt.% PVDF could act as an effective candidate for a tip-link connector in a vibration-frequency prototype. Based on this easily reproducible electrospinning technique and the multifunctionalities of the resulting PVDF fibers, this fundamental study may shed light on the bio-inspired design of artificial, self-powered, high performance, hair-cell-like sensors in cochlea to tackle the hearing loss issue.

Fabrication of β-Phase-Enriched PVDF Sheets for Self-Powered Piezoelectric Sensing.

The fabrication of self-powered pressure sensors based on piezoelectric materials requires flexible piezoelectric generators produced with a continuous, large-scale, and environmentally friendly approach. In this study, continuous poly(vinylidene fluoride) (PVDF) sheets with a higher β-phase content were facilely fabricated by the melt-extrusion-calendering technique and a PVDF-based piezoelectric generator (PEG) was further assembled. Such a PEG exhibits a remarkable piezoelectric output performance. Moreover, it possesses prominent stability even after working for a long time, exhibiting potential applications for real-time monitoring of various human movements (i.e., hopping, running, and walking) and gait. This work not only provides the possibility of continuous and environmentally friendly fabrication of PVDF sheets with remarkable piezoelectric properties but also paves a new promising pathway for powering portable microelectronic applications without any external power supply.

Fabrication of Poly(Vinylidene Fluoride)/Graphene Nano-Composite Micro-Parts with Increased β-Phase and Enhanced Toughness via Micro-Injection Molding.

Based on poly(vinylidene fluoride)/graphene (PVDF/GP) nano-composite powder, with high β-phase content (>90%), prepared on our self-designed pan-mill mechanochemical reactor, the micro-injection molding of PVDF/GP composite was successfully realized and micro-parts with good replication and dimensional stability were achieved. The filling behaviors and the structure evolution of the composite during the extremely narrow channel of the micro-injection molding were systematically studied. In contrast to conventional injection molding, the extremely high injection speed and small cavity of micro-injection molding produced a high shear force and cooling rate, leading to the obvious “skin-core” structure of the micro-parts and the orientation of both PVDF and GP in the shear layer, thus, endowing the micro-parts with a higher melting point and crystallinity and also inducing the transformation of more α-phase PVDF to β-phase. At the injection speed of 500 mm/s, the β-phase PVDF in the micro-part was 78%, almost two times of that in the macro-part, which was beneficial to improve the dielectric properties. The micro-part had the higher tensile strength (57.6 MPa) and elongation at break (53.6%) than those of the macro-part, due to its increased crystallinity and β-phase content.

Catalysis of the Thermal Decomposition of Transition Metal Nitrate Hydrates by Poly(vinylidene difluoride).

Poly(vinylidene difluoride) (PVDF) doped with transition metal nitrate hydrates are cast into thin films giving a high β-phase content. Analysis of the thermal behavior of the doped PVDF shows that the decomposition of the metal (II) nitrate hydrates to metal (II) oxides is catalyzed by the PVDF, as evidenced by reduction in the decomposition temperature by as much as 170 °C compared to the pure metal salts. In contrast, there is little to no apparent catalysis for the decomposition of the metal (III) nitrate hydrates. The FTIR spectra of the gas phase decomposition products show H2O and NO2 are the major components for both PVDF-doped material and the pure metal nitrate hydrates. A mechanism for the role of PVDF is proposed that uses the internal electric field of the ferroelectric phase to orient the nitrate ions and polarize the N–O bonds.

Piezoelectricity of PVDF composite film doped with dopamine coated nano-TiO2

In this work, dopamine (DA) coated nano-TiO2 (DA@TiO2) modified polyvinylidene fluoride (PVDF) piezoelectric composite films (DA@TiO2/PVDF) with a high β-phase content are successfully fabricated by solvothermal method. The β-phase content of the DA2.0@TiO2/PVDF reaches 84.33%. Furthermore, DA2.0@TiO2/PVDF has the highest crystallinity (Xc) and melting enthalpy (ΔH). Due to synergistic effect between DA and TiO2, the piezoelectric coefficients (d33) and remnant polarization (Pr) of DA2.0@TiO2/PVDF composite films increase by up to 163% and 278% than that of the pure PVDF film, respectively. This work provides a new method to present promise in broadening nanometer preparation technology and improving performance of piezoelectric composites, and contributes to the study on new curved panel energy harvesters for aeroelastic vibration.

High-Performance Poly(vinylidene difluoride)/Dopamine Core/Shell Piezoelectric Nanofiber and Its Application for Biomedical Sensors.

Fabrication of soft piezoelectric nanomaterials is essential for the development of wearable and implantable biomedical devices. However, a big challenge in this soft functional material development is to achieve a high piezoelectric property with long-term stability in a biological environment. Here, a one-step strategy for fabricating core/shell poly(vinylidene difluoride) (PVDF)/dopamine (DA) nanofibers (NFs) with a very high β-phase content and self-aligned polarization is reported. The self-assembled core/shell structure is believed essential for the formation and alignment of β-phase PVDF, where strong intermolecular interaction between the NH2 groups on DA and the CF2 groups on PVDF is responsible for aligning the PVDF chains and promoting β-phase nucleation. The as-received PVDF/DA NFs exhibit significantly enhanced piezoelectric performance and excellent stability and biocompatibility. An all-fiber-based soft sensor is fabricated and tested on human skin and in vivo in mice. The devices show a high sensitivity and accuracy for detecting weak physiological mechanical stimulation from diaphragm motions and blood pulsation. This sensing capability offers great diagnostic potential for the early assessment and prevention of cardiovascular diseases and respiratory disorders.