Dielectric and AC conductivity studies of novel porous armalcolite nanocomposite‐based humidity sensor

Armalcolite, a current motivated rare earth ceramic usually available in the moon, had been used for the first time, as dielectric‐type humidity sensors. The armalcolite nanocomposite was prepared using multistep solid‐state sintering under high pressure and a high‐sensitive dielectric sensor was developed for humidity controlling applications. Different concerning phases developed by the proper sintering were analyzed precisely by X‐ray diffraction (XRD) as well as scanning electron microscopy (SEM). At 100 Hz frequency, the obtained dielectric constant was 24 times greater at 95% relative humidity (RH) as compared to 33% RH. The armalcolite‐based sensor showed lower hysteresis (<3.5%), good stability, and faster response (~18 seconds) and recovery (~35 seconds) times compared to conventional humidity sensors. The sensing mechanism of the nanocomposite was categorically determined by the analyzed characteristics parameters such as dielectric constants, normalized loss tangent, and alternating current conductivity properties. This study also confirmed that the whole conduction mechanism was accomplished by electrons or ions and dipoles in the entire RH range. Therefore, the present armalcolite‐based porous nanocomposite would be a potential sensing material for novel humidity sensors.     

Humidity Sensor Based on PEO/PEDOT:PSS Blends for Breath Monitoring

The discrimination of humidity in exhaled breath is of utmost importance to turn breath analysis into an efficient noninvasive tool for early diagnosis or treatment monitoring of several diseases. Herein, by assembling different ratios of the conductive poly(3,4-ethylenedioxythiophene): polystyrene sulfonate with the polymer matrix polyethylene oxide (PEO), humidity chemiresistor-based sensors are designed and investigated. The testing results display a broad relative humidity detection range (6–92%), repeatability, reproducibility, and good reversibility. Meanwhile, the sensors possess good reliability for distinct temperatures and in the presence of typical volatile organic compounds found in human exhaled air. The hygroscopic idiosyncrasy of PEO is attributed to be the main responsible for the high sensibility toward humidity. In a proof-of-principle for detection of respiration humidity, the outcome shows the ability of the chemiresistors to detect the humidity variation in a real case of breath exposure up to 2 s intervals. The 30 d trial of stability readings shows a standard deviation of only 2.6%. These sensing devices appear as a new array component able to distinguish moisture from biomarkers of diagnosed diseases in breath analysis.     

Durable,Sensitive, and Wide‐Range Wearable Pressure Sensors Based on Wavy‐Structured Flexible Conductive Composite Film

Flexible pressure sensors have potential applications in human motion monitoring and electronic skins. To satisfy the practical applications, pressure sensors with a high sensitivity, a low detection limit, a broad response range, and an excellent stability are highly needed. Here, a piezoresistive pressure sensor based on wavy‐structured single‐walled carbon nanotube/graphite flake/thermoplastic polyurethane (SWCNT/GF/TPU) composite film is fabricated by a prestretching process. Due to the random wavy structure, high conductivity, and good flexibility, the prepared sensor displays a low detection limit of 2 Pa, a wide sensing range of 0–60 kPa, and a high sensitivity of 5.49 kPa^?1 for 0–50 Pa. Furthermore, the sensor shows a remarkable repeatability of over 1.1 × 10⁴, 9.0 × 10³, and 2.0 × 10³ pressure loading/unloading cycles at 50 Pa, 500 Pa, and 30 kPa, respectively, and a fast responsibility of 100–150 ms of loading response time and 400–600 ms of relaxation time. Therefore, the pressure sensor is successfully adopted to monitor both the large‐scale human activities (e.g., walk and jump) and the small‐scale signals (e.g., wrist pulse). Furthermore, a sensor array is assembled to map the weight and shape of an object, indicating its various potential applications including human–machine interactions, human health monitoring, and other wearable electronics.     

Flexible strain sensors with high sensitivity and large working range prepared from biaxially stretched carbon nanotubes/polyolefin elastomer nanocomposites

Flexible strain sensors are a new generation of flexible and stretchable electronic devices that attracted increasing attention due to their practical applications in many fields. However, maintaining a wide detectable strain range while improving the sensitivity of flexible strain sensors remains challenging. In this study, flexible strain sensors with a large working range based on biaxially stretched carbon nanotubes (CNTs)/polyolefin elastomer (POE) nanocomposites were fabricated. Biaxial stretching was demonstrated to enhance the uniform dispersion and orientation of CNTs, thereby improving the performance of sensors. The optimal stretching ratios (SRs) of nanocomposites were investigated and the data revealed an increment in the sensitivity of sensors with SRs, while the working range first increased after biaxial stretching and decreased at higher SRs. Compared to the 9 wt% CNT/POE-1.0 sensor with a gauge factor (GF) value of 2.37 and a detectable range of 0.5%–230%, the CNT/POE-2.0 sensor exhibited an enhanced sensitivity (GF = 3935.12) coupled with a wider detectable range (0.5%–710%) and better stability. Besides, CNT/POE-2.0 sensor also achieved the monitoring of head movements, mouth opening, facial expression, and physiological signals, showing a potential for use in wearable electronic products.     

Low-Cost,Highly Sensitive,and Flexible Piezoresistive Pressure Sensor Characterized by Low-Temperature Interfacial Polymerization of Polypyrrole on Latex Sponge

Piezoresistive pressure sensors based on sponge are widely concerned because of their wide strain range, convenient signal acquisition, and good compressibility, yet it is still a challenge to acquire sponge-based pressure sensors with low cost and excellent sensing performance. Herein, low-priced FeCl₃^.6H₂O and pyrrole (Py) are dispersed in deionized water to form FeCl₃^.6H₂O/Py solution. Commercial latex sponge is impregnated into this solution to prepare conductive polypyrrole/latex (PPy/latex) sponge through low-temperature interfacial polymerization. The surface of latex sponge is covered by the micro-wrinkled PPy, which endows the PPy/latex sponge with a certain electrical conductivity. The specific porous structure and high elasticity of the latex sponge are the basic conditions for PPy/latex sponge excellent piezoresistive behaviors. PPy/latex sponge based piezoresistive pressure sensor shows high sensitivity (0.084 kPa⁻¹ at below 3.12 kPa), wider sensing range (0–85.0%) and long durability over 3800 s (1800 cycles). At the same time, the ability of the PPy/latex sponge based piezoresistive pressure sensor to monitor human movement has been successfully evaluated in some application scenarios, such as bending fingers, grabbing objects, tiptoe rising, and crouching.     

Microwave-assisted synthesis of Co-doped SnO2/rGO for indoor humidity monitoring

The evaluation of indoor humidity is challenging compared to other environmental parameters such as light intensity, temperature, sound and so forth. The proper selection of sensing materials and structural tuning will lead to high-performance humidity sensors. Herein, the SnO₂/rGO and SnO₂/rGO doped with Co nanocomposite were produced by microwave route. The obtained nanocomposite was characterized by XRD, SEM, EDAX, DTA, TGA, FTIR, Raman, and HRTEM. The successful incorporation of Co onto the rGO/SnO₂ is affirmed by the XRD and supported with matching SEM and TEM outcomes where nanoscale particles exist. FTIR reveals the existence of the CC stretching band at ～1570 cm^?1 indicating graphene network sustaining upon reduction. Micro-pores presence is claimed by the adsorption-desorption isotherm curve. The humidity sensing behavior of both structures was evaluated in a wide range of humidity (11–97% RH). The obtained results confirmed that best working frequency for highest humidity change is 50 Hz. Furthermore, upon doping the SnO₂/rGO composite with Co, sensitivity, the response time and recovery time has improved reaching 52 s and 100 s respectively.     

High-yield,in-situ fabrication and integration of horizontal carbon nanotube arrays at the wafer scale for robust ammonia sensors

This paper reports the successful experimental demonstration of the localized growth of horizontal, dense carbon nanotube (CNT) arrays in situ and at the wafer scale. The selectivity and directionality of the CNT catalytic growth process along with the adequate design and fabrication of the catalyst support enables the direct integration of nanotubes arrays into heterogeneous devices. This novel CNT integration method is developed to manufacture conductance based gas sensors for ammonia detection and is demonstrated to produce a yield above 90% at the wafer scale. Owing to its flexibility, the integration process can be useful for a wide range of applications and complies with industrial requirements in terms of manufacturability and yield, requirements for the acceptance of CNTs as alternate materials. A state-of-the-art CNT array resistivity of 1.75 × 10⁻⁵ Ω m has been found from the CNT characterization. When exposed to low NH₃ concentrations, the CNT sensors show good repeatability, long-term stability, and high design robustness and tackle the reproducibility challenge for CNT devices. Individual device calibration is not needed. The ammonia adsorption isotherm on the sensor is well fitted by Freundlich equation. The extrapolated detection limit is about 1 ppm. The dependence of the sensitivity with temperature indicates that ammonia sensing is likely to involve an endothermic process. Finally, relative humidity cross sensitivity has been found to have no adverse effect on the ammonia response enabling NH₃ monitoring in ambient conditions.     

Highly sensitive flexible strain sensor based on carbon nanotube/styrene butadiene styrene@ thermoplastic polyurethane fiber with a double percolated structure

The combination of a high sensitivity and a wide strain detection range in conductive polymer composites-based flexible strain sensors is still challenging to achieve. Herein, a double-percolation structural fiber strain sensor based on carbon nanotubes (CNT)/styrene butadiene styrene (SBS)@thermoplastic polyurethane (TPU) composite was fabricated by a simple melt mixing and fused filament fabrication strategy, in which the CNT/SBS and TPU were the conductive and insulating phases, respectively. Compared with the sensor without the double percolated structure, the CNT/SBS@TPU sensor achieved a lower percolation threshold (from 2.0 to 0.5 wt%, a reduction of 75%), and better electrical and sensing performance. It is shown that the strain detection range of the CNT/SBS@TPU sensor increases with increasing CNT loading. An opposite trend was observed for the sensitivity. The 1%-CNT/SBS@TPU sensor exhibited a high conductivity (1.08 × 10⁻³ S/m), high sensitivity (gauge factor of 2.65 × 10⁶ at 92% strain), wide strain detection range (0.2%–92% strain), high degree of linearity (R² = 0.954 at 0–10% strain), broad monitoring frequencies (0.05–0.5 Hz), and excellent stability (2000 cycles). Moreover, the CNT/SBS@TPU sensor was shown to successfully monitor a range of human physiological activities and to be capable of tactile perception and weight distribution sensing.     

A comparative study of Pb selective sensors based on derivatized tetrapyrazole and calix[4]arene receptors

Two neutral ionophores, 2,12-dimethyl-7,17-diphenyltetrapyrazole (I) and 5,11-dibromo-25,27-dipropoxycalix[4]arene (II) have been explored for preparing PVC based membrane sensors selective to Pb²⁺. The addition of sodium tetraphenylborate and various plasticizers viz. DOS, TEHP, DBP, DOP and TBP has been found to substantially improve the performance (working concentration range, slope and response time) of the sensors. The best performance was obtained with the sensor having a membrane of composition (w/w) of (I) (1%):PVC (33%):TBP (65%):NaTPB (1%). The sensor exhibits Nernstian response in the concentration range 2.5 × 10⁻⁶ to 5.0 × 10⁻² M Pb²⁺, performs satisfactorily over wide pH range (1.6-6.0) with a fast response time (∼10 s). The sensor was found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetone, methanol or ethanol and could be used over a period of 5 months. Potentiometric selectivity coefficients as determined by match potential method (MPM) indicate excellent selectivity for Pb²⁺ ions. The sensors could be used successfully in the estimation of lead in Eveready battery waste and also as an indicator electrode in potentiometric titration.     

High performance H2 sensor based on rGO-wrapped SnO2–Pd porous hollow spheres

Hydrogen (H₂) sensors based on metal oxide semiconductors (MOS) are promising for many applications such as a rocket propellant, industrial gas and the safety of storage. However, poor selectivity at low analyte concentrations, and independent response on high humidity limit the practical applications. Herein, we designed rGO-wrapped SnO₂–Pd porous hollow spheres composite (SnO₂–Pd@rGO) for high performance H₂ sensor. The porous hollow structure was from the carbon sphere template. The rGO wrapping was via self-assembly of GO on SnO₂-based spheres with subsequent thermal reduction in H₂ ambient. This sensor exhibited excellently selective H₂ sensing performances at 390 °C, linear response over a broad concentration range (0.1–1000 ppm) with recovery time of only 3 s, a high response of ～8 to 0.1 ppm H₂ in a minute, and acceptable stability under high humidity conditions (e. g. 80%). The calculated detection limit of 16.5 ppb opened up the possibility of trace H₂ monitoring. Furthermore, this sensor demonstrated certain response to H₂ at the minimum concentration of 50 ppm at 130 °C. These performances mainly benefited from the special hollow porous structure with abundant heterojunctions, the catalysis of the doped-PdO_x, the relative hydrophobic surface from rGO, and the deoxygenation after H₂ reduction.     

MoS2-Polyaniline Based Flexible Electrochemical Biosensor: Toward pH Monitoring in Human Sweat

Wearable pH sensors for sweat analysis have garnered significant scientific attention for the detection of early signs of many physiological diseases. In this study, a MoS₂-polyaniline (PANI) modified screen-printed carbon electrode (SPCE) is fabricated and used as a sweat biosensor. The exfoliated MoS₂ nanosheets are drop casted over an SPCE and are functionalized by a conducting polymer, polyaniline (PANI) via the electropolymerization technique. The as-fabricated biosensor exhibits high super-Nernstian sensitivity of −70.4 ± 1.7 mV pH⁻¹ in the linear range of pH 4 to 8 of 0.1 m standard phosphate buffer solution (PBS), with outstanding reproducibility. The sensor exhibits excellent selectivity against the common sweat ions including Na⁺, Cl⁻, K⁺, and NH₄⁺ with tremendous long-term stability over 180 min from pH 4 to 6. The enhanced active surface area and better electrical conductivity as a consequence of the synergistic effect between MoS₂ and PANI are correlated with the boosted performance of the as-produced biosensor. The feasibility of the sensor is further examined using an artificial sweat specimen and the successful detection confirms the potential of the biosensor for a real-time noninvasive, skin attachable, and flexible wearable pH sensor.     

Flexible and high-sensitivity piezoresistive sensor based on MXene composite with wrinkle structure

Due to the portability, good flexibility and excellent sensing performance, flexible piezoresistive sensors have received great attention in the field of transient electronic skin, intelligent robots and human-machine interaction. However, achieving both high sensitivity and wide sensing range by low-cost and large-scale method still remains a key challenge for developing high performance piezoresistive sensors. Here, a flexible and highly sensitive piezoresistive sensor was designed and realized by combining the 2D MXene material with wrinkle structure. The MXene composite based sensor with wrinkle structure was fabricated by spraying the active material onto the surface of a pre-stretched polyacrylate tape, which is facile, efficient and low-cost. The MXene composite based sensor demonstrates high sensitivity (148.26 kPa⁻¹), wide pressure range (up to 16 kPa), short response time (120 ms) and excellent durability (>13000 cycles). Moreover, benefiting from the extraordinary sensing performance and flexibility, the sensor can detect human physiological signals, monitor intelligent robot postures and map spatial pressure distributions, thus exhibiting great potential in physiological analysis systems, humanoid robotics and biomedical prostheses.     

A High–Performance Flexible Piezoresistive Pressure Sensor Features an Integrated Design of Conductive Fabric Electrode and Polyurethane Sponge

Due to its porous structure and good elasticity, conductive polyurethane (PU) sponge is used as the main substrate of the flexible piezoresistive pressure sensor. The effective combination of conductive PU sponge and electrode material is the foundation for the pressure sensor, but it needs to be bonded by expensive conductive silver paste or copper paste. In addition, the common electrode materials weaken the flexibility of the PU sponge pressure sensors because of their rigidity. Herein, PU sponge and polyester (PET) fabric are first bonded to produce (PET-PU) composite, which is then impregnated with graphene oxide (GO). The obtained reduced graphene oxide(rGO)@PET fabric and rGO@PU are used as electrode and piezoresistive material, respectively. Then rGO@(PET-PU) composite is assembled into a pressure sensor only by using wire connections in the rGO@PET fabric. Benefiting from excellent piezoresistive behavior, rGO@(PET-TPU) pressure sensor displays high sensitivity (0.255 kPa⁻¹ at below 2.6 kPa), wide detection limit (≈0–85.0%), and long durability (over 1800 cycles). Besides, the pressure sensor demonstrates good performance in monitoring human activities, including finger bending, clicking keyboard, breathing, elbow bending, and walking posture, thus providing a promising material for human activity monitoring.     

Development of flexible sensors using knit fabrics with conductive polyaniline coating and graphite electrodes

The aim of this study was to develop flexible sensors with cotton and polyester knit fabrics as substrates coated with polyaniline (PAni) doped with hydrochloric acid or phosphoric acid. The deposition of PAni onto the knit, polymerization synthesis, and doping of the aniline monomer were performed via an in situ reaction. Graphite dispersion was used to obtain the electrodes of the sensors, which were prepared differently for each substrate. The main evaluation of the sensors was carried out in a humidity chamber under nitrogen (N₂) with the application of drying and wetting cycles. Significant differences were observed in the responses of the sensory devices to humidity, according to the dopant and substrate types. In all tests, the sensor response to variations in the ambient conditions was very good, with a rapid response to changes in the relative humidity, a good sensitivity (up to 34%), and a high reversibility (ca. 70–100%). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44785.     

Fabricating patterned polyelectrolyte brushes by dynamic microprojection lithography for selective electroless metal deposition

The emerging need for flexible and wearable electronics has been pushing the edge of the traditional electroless deposition (ELD) technique. With the rapid development of polymer-assisted ELD (PAELD), its time-consuming and possess-complicated procedures have hindered the application of the technique. Here, for purpose of addressing the challenge, the work demonstrates a highly efficient and versatile method, based on the procedure consisting of the customized polyelectrolyte brushes patterns fabrication with the assistance of mask-free dynamic microprojection lithography and sequential selective ELD (DML-ELD), for the fabrication of arbitrary electrode on the silicon dioxide/silicon (SiO₂/Si) substrate. The resistivity of the patterned copper electrode maintained around 0.062 Ω∙mm at room temperature, indicating the high reproducibility and stability of the method. Furthermore, an interdigital copper electrode fabricated with the DML-ELD method was coated with a poly(vinyl alcohol) sensing layer, forming a sandwich structure for the ambient humidity detection. The sensitivity of the lab-made humidity sensor achieves 0.82 pF/%RH (<80%RH) and 19.3 pF/%RH (>80%RH). The work has demonstrated the broad prospect of the proposed DML-ELD method in the rapid and customized manufacturing of microcircuit fabrication for electronic devices.     

Microwave-assisted synthesis of ZnO doped CeO2 nanoparticles as potential scaffold for highly sensitive nitroaniline chemical sensor

Herein, we report the successful fabrication of highly sensitive, reproducible and reliable nitroaniline chemical sensor based on ZnO doped CeO₂ nanoparticles. The ZnO doped CeO₂ nanoparticles were synthesized through a simple, facile and rapid microwave-assisted method and characterized by several techniques. The detailed characterizations confirmed that the synthesized nanoparticles were monodisperse and grown in high density and possessing good crystallinity. Further, the synthesized ZnO doped CeO₂ nanoparticles were used as efficient electron mediators for the fabrication of high sensitive nitroaniline chemical sensors. The fabricated nitroaniline chemical sensor exhibited very high sensitivity of 550.42 μA mM⁻¹ cm⁻² and experimental detection limit of 0.25 mM. To the best of our knowledge, this is the first report in which CeO₂–ZnO nanoparticles were used as efficient electron mediators for the fabrication of nitroaniline chemical sensors. Thus, presented work demonstrates that ZnO doped CeO₂ nanoparticles are potential material to fabricate highly efficient and reliable chemical sensors.     

A supersensitive wearable sensor constructed with PDMS porous foam and multi-integrated conductive pathways structure

In recent years, wearable multifunctional strain sensors have attracted attention for their promising applications in wearable electronics and portable devices. To achieve a high-performance wearable strain sensor with a wide sensing range and high gauge factor (GF), wisely choosing appropriate conductive materials and a rational structural design is essential. Herein, we develop a supersensitive sensor that contains one-dimensional conductive material CNT and two-dimensional material MXene built on a PDMS porous foam that is made based on a sugar template. The one-dimensional carbon nanotube (CNT) functionalizes as a conductive scale layer through solvent swelling and evaporation on the surface of the PDMS skeleton. The two-dimensional MXene is applied on top of the CNT layer to form final conductive pathways. The PDMS/CNT@MXene (PCM) sensor has a wide sensing range (150%), high sensitivity (GF = 26438), rapid response speed (response/recovery time of 60/71 ms), and exceptional durability (>1000 cycles) owing to its unique porous structure with scale layers and graded fracture of conductive pathways. Moreover, the PCM sensor is capable of monitoring subtle and significant human activities and is used for wireless sensing and medical diagnostics, even for solvent identification. The superior performance of the PCM sensor provides vast application potential in human movement, health monitoring, and warning devices.     

3D-Printed Flexible Piezoresistive Sensors for Stretching and Out-of-Plane Forces

Conductive polymer composites (CPCs) of carbon nanotubes (CNTs) and graphite nanosheet (GNP)-filled thermoplastic polyurethane (TPU) are 3D-printed into flexible piezoresistive sensors via fused filament fabrication. The sensor, with a customized lever-cross structure, allows detection of stretching and out-of-plane forces of different magnitudes and frequencies. The out-of-plane force direction is obtained by combing the relative electrical resistance change in the cross section of the sensor with a force analysis. The 75-CNT/25-GNP sensor (CNT-to-GNP mass ratio of 75%-to-25%) demonstrates excellent sensing performance at a total nanoparticle loading of 3 wt%. The linearity of the 75-CNT/25-GNP sensor is 0.98, while those of the 100-CNT and 50-CNT/50-GNP sensors are 0.93 and 0.86, respectively. The gauge factor of the 75-CNT/25-GNP sensor is 52% higher than that of the 100-CNT sensor, and its sensing strain range is 79% above that of the 50-CNT/50-GNP sensor. Excellent sensing stability is demonstrated for the 75-CNT/25-GNP sensor after 1500 stretching (out-of-plane force) cycles. The synergistic effect of CNTs and GNPs on sensing performance of piezoresistive sensors is clearly shown in this study.     

Durable and highly sensitive flexible sensors for wearable electronic devices with PDMS-MXene/TPU composite films

MXenes, as two-dimensional (2D) transition metal carbides, carbonitrides, and nitrides, have very excellent electrical properties and surface activity and are increasingly used in supercapacitors, batteries, electromagnetic interference shielding, and composite materials. Still, the poor stability of MXene when exposed to aqueous oxygen and the poor ability to interact with the polymer matrix have become important factors limiting its’ practical applications. To enhance stability, highly conductive and stretchable Ti₃C₂MXene/TPU sensing elements were prepared by a simple spraying process using thermoplastic polyurethane (TPU) as a substrate, and the sensing elements were encapsulated by polydimethylsiloxane (PDMS) to obtain MXene-TPU/PDMS constructed flexible strain sensors with excellent performance. This strain sensor features low detection limits (less than 0.005%, 0.5 μm), a wide sensing range (0–90%), a short response time (120.1 ms), and excellent durability (>3000 cycles). This strain sensor can be applied to a range of applications such as health detection, motion signals, detection of robot movements, and wearable electronic devices.     

Effect of the graphitization level of the free carbon on the temperature sensitivity of silicon carbonitride-based pressure sensors

Polymer-derived ceramics (PDCs) have recently attracted an increasing attention because of their applications for wireless passive pressure sensors in the harsh environment. However, due to the effect of temperature on the frequency of PDC-based wireless passive pressure sensors, it is not beneficial to accurate measurement of pressure. In this paper, a dense polymer-derived silicon carbonitride (SiCN) ceramic was prepared by precursor infiltration and pyrolysis (PIP) technique to reduce the temperature sensitivity of PDC–SiCN-based pressure sensor. The open porosity and density of SiCN ceramics varied from 13.34% and 1.89 g/cm³ without PIP process to 3.24% and 2.09 g/cm³ after three PIP cycles, respectively. Raman spectroscopy revealed that the level of graphitization of free carbon in dense SiCN ceramics is higher than that in porous SiCN ceramics, which would lead to an increase in the conductivity of dense SiCN ceramics. After three PIP cycles, the conductivity increased by almost two orders of magnitude from 3.01E − 10 to 1.28E − 08 S/cm. In addition, SiCN ceramic discs after PIP cycles and without PIP were applied to wireless passive pressure sensor based on resonator, which were tested at high temperature, respectively. Results confirmed that the temperature sensitivity of PDC–SiCN-based pressure sensor decreased from 220.5 to 50.8 kHz/°C by PIP process.