Ultrasonic Transducer Research Articles

Joint segmentation and image reconstruction with error prediction in photoacoustic imaging using deep learning

Deep learning has been used to improve photoacoustic (PA) image reconstruction. One major challenge is that errors cannot be quantified to validate predictions when ground truth is unknown. Validation is key to quantitative applications, especially using limited-bandwidth ultrasonic linear detector arrays. Here, we propose a hybrid Bayesian convolutional neural network (Hybrid-BCNN) to jointly predict PA image and segmentation with error (uncertainty) predictions. Each output pixel represents a probability distribution where error can be quantified. The Hybrid-BCNN was trained with simulated PA data and applied to both simulations and experiments. Due to the sparsity of PA images, segmentation focuses Hybrid-BCNN on minimizing the loss function in regions with PA signals for better predictions. The results show that accurate PA segmentations and images are obtained, and error predictions are highly statistically correlated to actual errors. To leverage error predictions, confidence processing created PA images above a specific confidence level.

Coupling Low-Frequency Ultrasound to a Crossflow Microfiltration Pilot: Effect of Ultrasonic Pulse Application on Sono-Microfiltration of Jackfruit Juice.

To reduce membrane fouling during the processing of highly pulpy fruit juices into clarified beverages, a crossflow Sono-Microfiltration (SMF) system was employed, strategically equipped with an ultrasonic probe for the direct application of low-frequency ultrasound (LFUS) to the juice just before the entrance to the ceramic membrane. Operating conditions were standardized, and the application of LFUS pulses in both corrective and preventive modes was investigated. The effect of SMF on the physicochemical properties and the total soluble phenol (TSP) content of the clarified juice was also evaluated. The distance of ultrasonic energy irradiation guided the selection of the LFUS probe. Amplitude conditions and ultrasonic pulses were more effective in the preventive mode and did not cause membrane damage, reducing the operation time of jackfruit juice by up to 50% and increasing permeability by up to 81%. The SMF did not alter the physicochemical parameters of the clarified juice, and the measured LFUS energy ranges did not affect the TSP concentration during the process. This study is the first to apply LFUS directly to the feed stream in a pilot-scale crossflow microfiltration system to reduce the fouling of ceramic membranes and maintain bioactive compounds in jackfruit juice.

Development and performance investigation of a novel ultrasonic-assisted non-contact membrane distillation process to prevent membrane fouling

A novel non-contact membrane distillation (NCMD) process is proposed that prevents membrane fouling by preventing direct physical contact between the feed and membrane. The feed channel of the NCMD module is equipped with an ultrasonic transducer that provides high-frequency mechanical oscillations to the feed film, which forms a fine mist of droplets and water column. Experiments are conducted to determine the feed height required to maximize the evaporation rate, and the effects of feed temperature, flow rate, and ultrasonic power on the permeation flux. The results reveal that the highest permeation flux occurs at a feed height of 20 mm, and an increase in the feed height and flow rate decreases the ultrasonic cavitation effect, while a higher feed temperature and ultrasonic power significantly increases the permeation flux. At the feed temperature of 60 °C, feed flow rate of 1.0 L/min, and ultrasonic current of 600 mA, the permeation flux is 6.3 kg/m2h, which is 8.4 times greater than that of the NCMD process without ultrasonic treatment. The corresponding specific energy consumptions with and without the ultrasonication are 647 and 6028 kWh/m3, respectively. Moreover, the long-term experimental results indicate that the proposed system is unaffected by high feed concentrations.

Enhanced buoyancy and propulsion in 3D printed swimming micro-robots based on a hydrophobic nano-fibrillated cellulose aerogel and porous lead-free piezoelectric ceramics

This paper provides the first demonstration of additively manufactured swimming micro-robots which combine a hydrophobic nanofibrillated cellulose aerogel, to provide long-term buoyancy, with a low acoustic impedance porous piezoelectric ceramic for improved propulsion. The hydrophobic nanocellulose aerogel is shown to exhibit a high and stable contact angle that was maintained for extended periods of time, which facilitates long-term and stable buoyancy of the micro-robot. To quantify the benefits of introducing porosity into the active piezoelectric element, a new analysis model was developed to inform material design and maximize the acoustic propulsion force. Detailed characterisation and modelling of the swimming robots demonstrated that a swimming robot based on a lead-free porous Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramic exhibited a higher acoustic radiation propulsion force and a faster swimming speed compared to a robot fabricated using a dense ceramic element. These benefits were associated with the lower elastic modulus, density and acoustic impedance of the porous piezoelectric material. The lower dielectric constant, reduced device capacitance, and lower resonant frequency of the porous piezoelectric element also significantly reduced the driving current and power requirements of the robot. This work therefore provides new insights on the impact of hydrophobic and acoustically matched piezoelectric materials on the performance of swimming micro-robots, and successfully demonstrates the use of porosity to improve acoustic impedance matching of resonant piezoelectric devices, such as micro-robots and ultrasonic transducers.

Assessment of aging degradation in rubber using quasi-static components of ultrasonic longitudinal waves

Abstract Aging degradation is the main form of failure of rubber in service, leading to a decline in its physical and mechanical properties. This paper presents an efficient method for assessing the aging degradation of rubber using the quasi-static component (QSC) of ultrasonic longitudinal waves induced by acoustic radiation. The experiments quantitatively observe the response of the QSC pulse to different levels of ageing degradation. A pulse-echo ultrasonic transducer is employed to simultaneously capture the primary longitudinal wave (PLW) and QSC echoes, enabling the determination of the acoustic nonlinearity parameter of QSC with a single transducer excitation. The results suggest that, in comparison to traditional linear ultrasonic techniques based on attenuation coefficient and wave velocity measurements, the relative acoustic nonlinear parameter of QSC proves to be more sensitive to aging degradation in rubber. Particularly, the amplitude of the QSC pulse undergoes a significant change with increasing aging degradation, even when the PLW tone burst is completely attenuated. These findings confirm the effectiveness of QSC as a method for evaluating aging degradation in highly attenuative materials.

Revealing regional variations in scleral shear modulus in a rabbit eye model using multi-directional ultrasound optical coherence elastography

The mechanical properties of the sclera play a critical role in supporting the ocular structure and maintaining its shape. However, non-invasive measurements to quantify scleral biomechanics remain challenging. Recently introduced multi-directional optical coherence elastography (OCE) combined with an air-coupled ultrasound transducer for excitation of elastic surface waves was used to estimate phase speed and shear modulus in ex vivo rabbit globes (n = 7). The scleral phase speed (12.1 ± 3.2 m/s) was directional-dependent and higher than for corneal tissue (5.9 ± 1.4 m/s). In the tested locations, the sclera proved to be more anisotropic than the cornea by a factor of 11 in the maximum of modified planar anisotropy coefficient. The scleral shear moduli, estimated using a modified Rayleigh-Lamb wave model, showed significantly higher values in the circumferential direction (65.4 ± 31.9 kPa) than in meridional (22.5 ± 7.2 kPa); and in the anterior zone (27.3 ± 9.3 kPa) than in the posterior zone (17.8 ± 7.4 kPa). The multi-directional scanning approach allowed both quantification and radial mapping of estimated parameters within a single measurement. The results indicate that multi-directional OCE provides a valuable non-invasive assessment of scleral tissue properties that may be useful in the development of improved ocular models, the evaluation of potential myopia treatment strategies, and disease characterization and monitoring.

Measurement Method of Stress in High-Voltage Cable Accessories Based on Ultrasonic Longitudinal Wave Attenuation.

High-voltage cables are the main arteries of urban power supply. Cable accessories are connecting components between different sections of cables or between cables and other electrical equipment. The stress in the cold shrink tube of cable accessories is a key parameter to ensure the stable operation of the power system. This paper attempts to explore a method for measuring the stress in the cold shrink tube of high-voltage cable accessories based on ultrasonic longitudinal wave attenuation. Firstly, a pulse ultrasonic longitudinal wave testing system based on FPGA is designed, where the ultrasonic sensor operates in a single-transmit, single-receive mode with a frequency of 3 MHz, a repetition frequency of 50 Hz, and a data acquisition and transmission frequency of 40 MHz. Then, through experiments and theoretical calculations, the transmission and attenuation characteristics of ultrasonic longitudinal waves in multi-layer elastic media are studied, revealing an exponential relationship between ultrasonic wave attenuation and the thickness of the cold shrink tube. Finally, by establishing a theoretical model of the radial stress of the cold shrink tube, using the thickness of the cold shrink tube as an intermediate variable, an effective measurement of the stress of the cold shrink tube was achieved.

Implementasi Internet of Things pada Otomasi Pemberian Pakan Ayam Ras Petelur

Adequate nutrition affects the quality and quantity of egg production which has an impact on the profitability of laying hen breeders. Rizqie Farms experienced problems with the management of feeding laying hens, when the rainy season and open cage conditions made feeding irregular. It is important to be disciplined in feeding layer chickens on time at the same time as a research ur-gency, so that the chickens do not become stressed so that discipline in feeding management increases the quality and quantity of egg production. The design thinking method as a meth-od-ology for completing the creation of Android smartphone tools and applications. The com-pletion stages start with empathize, define, ideate, prototype and test. The materials used to make the tool are ESP32 DEVKIT V1 S2, Ultrasonic Sensor, Servo driving droplet feed, Power Source/Supply 12v 1A, Stepper Motor Driver l928n, Stepper Motor Nema 17 20nm, DS3231 RTC Module (timer), Arduino Uno R3, Buzzer / Speaker, LCD 1062 16x2 with I2c port. Sensor data connected to the ESP32 DEVKIT V1 S2, Ultrasonic Sensor, Servo drive is converted to an Android smartphone as a monitoring medium. Monitoring is carried out via a mobile application, with the Internet of Things connected to the device as an internet-based communication medium. Feeding equipment testing had an average delay of 40.2 seconds and MSE 0,0514. Black box testing was carried out to test the functionality of the monitoring application on 5 users with a percentage of 100%.

Radiation Impedance of Rectangular CMUTs.

Recently, capacitive micromachined ultrasound transducers (CMUTs) with long rectangular membranes have demonstrated performance advantages over conventional piezoelectric transducers; however, modeling these CMUT geometries has been limited to computationally burdensome numerical methods. Improved fast modeling methods, such as equivalent circuit models, could help achieve designs with even better performance. The primary obstacle in developing such methods is the lack of tractable methods for computing the radiation impedance of clamped rectangular radiators. This paper presents a method that approximates the velocity profile using a polynomial shape model to rapidly and accurately estimate radiation impedance. The validity of the approximate velocity profile and corresponding radiation impedance calculation was assessed using finite element simulations for a variety of membrane aspect ratios and bias voltages. Our method was evaluated for rectangular radiators with width:length ratios from 1:1 up to 1:25. At all aspect ratios, the radiation resistance was closely modeled. However, when calculating the radiation reactance, our initial approach was only accurate for low aspect ratios. This motivated us to consider an alternative shape model for high aspect ratios, which was more accurate when compared with FEM. To facilitate the development of future rectangular CMUTs, we provide a MATLAB script that quickly calculates radiation impedance using both methods.

Realistic Aspects of Cardiac Ultrasound in Rats: Practical Tips for Improved Examination.

Echocardiography is a reliable and non-invasive method for assessing cardiac structure and function in both clinical and experimental settings, offering valuable insights into disease progression and treatment efficacy. The successful application of echocardiography in murine models of disease has enabled the evaluation of disease severity, drug testing, and continuous monitoring of cardiac function in these animals. However, there is insufficient standardization of echocardiographic measurements for smaller animals. This article aims to address this gap by providing a guide and practical tips for the appropriate acquisition and analysis of echocardiographic parameters in adult rats, which may also be applicable in other small rodents used for scientific purposes, like mice. With advancements in technology, such as ultrahigh-frequency ultrasonic transducers, echocardiography has become a highly sophisticated imaging modality, offering high temporal and spatial resolution imaging, thereby allowing for real-time monitoring of cardiac function throughout the lifespan of small animals. Moreover, it allows the assessment of cardiac complications associated with aging, cancer, diabetes, and obesity, as well as the monitoring of cardiotoxicity induced by therapeutic interventions in preclinical models, providing important information for translational research. Finally, this paper discusses the future directions of cardiac preclinical ultrasound, highlighting the need for continued standardization to advance research and improve clinical outcomes to facilitate early disease detection and the translation of findings into clinical practice.

Comparing New Smartphone-Connected Handheld Ultrasound Device vs. Traditional Ultrasound in Vitreo-Retinal Disease Diagnosis.

(1) Background: Ocular emergencies account for 1.5-3% of emergency department (ED) visits and require urgent diagnosis to prevent serious complications. Ultrasonography is a crucial, non-invasive diagnostic tool for these conditions but traditionally lacks portability and integration with modern electronic smart devices. The purpose of this study was to assess the accuracy and performance of a new handheld ultrasound device in comparison to a conventional cart-based sonographic machine in patients attending to the ED for vitreo-retinal diseases. (2) Methods: three specialists in ophthalmology, with at least 4-year experience in vitreo-retinal diseases and eye ultrasound, evaluated images of 50 eyes with both portable and traditional ultrasound probes. Each specialist made the diagnosis based on the images captured with both probes and then rated their overall image quality and confidence of diagnosis with a five-point Likert scale. The concordance of diagnosis between the two probes was evaluated. (3) Results: The sample comprised 42 patients. Twenty (40%) healthy eyes and thirty eyes with the following vitreo-retinal interface conditions were examined: 12 retinal detachment (24%), 8 vitreous hemorrhage (16%), and 10 posterior vitreous detachment (20%). The overall accuracy of the two devices appeared to be comparable (70.7% vs. 69.3%). The Butterfly iQ+ probe showed similar sensitivity in retinal detachment diagnosis (91.7% vs. 94.4% of the Accutome B-scan Pro), while it showed poor performance in diagnosing posterior vitreous detachment (sensitivity = 27.2%); (4) Conclusions: The Butterfly iQ+ device demonstrated high sensitivity in the diagnosis of retinal detachment. Significant adjustments are still needed to improve the resolution of the vitreous body.

Temporoorbital pulse rate can be obtained in ball pythons (Python regius) of any size and age and agrees with heart rate.

Currently, a standardised technique to obtain pulse rate in reptiles is lacking. We evaluated the feasibility of obtaining a temporoorbital pulse rate in ball pythons of various ages and sizes and whether it agreed with the heart rate. Heart rate and pulse rate were recorded in 40 ball pythons (Python regius) weighing between 0.05 and 2.2 kg using a standard veterinary ultrasonic Doppler flow detector. The temporoorbital pulse rate was obtained on the dorsal aspect of the head at the level of the temporoorbital artery. Each measurement was performed in a randomised fashion by two operators, who were blinded to each other's results. Pulse rate and heart rate were successfully obtained for all snakes. The median heart rate was 60beats per minute (bpm)(range 48‒88 bpm), and the median pulse rate was 60bpm (range 48‒88 bpm). The mean difference between the pulse rate and heart rate was 1.2 beats (95% limits of agreement: ‒10.6 to 13.0). When pulse rate and heart rate were measured at the same time, they were synchronous. Only healthy snakes were included. Temporoorbital pulse rates can be easily obtained in ball pythons of any size. This novel method to assess peripheral pulse allows for a more complete cardiovascular evaluation in this species.

Ultrasound Probe Pressure Affects Aortic Wall Stiffness: A Patient-Specific Computational Study in Abdominal Aortic Aneurysms.

Ultrasound imaging is key in the management of patients with an abdominal aortic aneurysm (AAA). It was recently shown that the cyclic diameter variations between diastole and systole, which can be quantified with US imaging, increase significantly with the strength of the applied probe pressure on the patient's abdomen. The goal of this study is to investigate this effect more thoroughly. With finite-element modeling, pulsatile blood pressure and probe pressure are simulated in three patient-specific geometries. Two distinct models for the aortic wall were simulated: a nonlinear hyperelastic and a linear elastic model. In addition, varying stiffness was considered for the surrounding tissues. The effect of light, moderate, and firm probe pressure was quantified on the stresses and strains in the aortic wall, and on two in vivo stiffness measures. In addition, the Elasticity Loss Index was proposed to quantify the change in stiffness due to probe pressure. Firm probe pressure decreased the measured aortic stiffness, and material stiffness was affected only when the wall was modeled as nonlinear, suggesting a shift in the stress-strain curve. In addition, stiffer surrounding tissues and a more elongated aneurysm sac decreased the responsiveness to the probe pressure. The effect of probe pressure on the AAA wall stiffness was clarified. In particular, the AAA wall nonlinear behavior was found to be of primary importance in determining the probe pressure response. Thus, further work will intend to make use of this novel finding in a clinical context.

Fast acoustic droplet ejection based on annular array transducer

Acoustic droplet ejection (ADE) has become the preferred method for liquid transfer in a variety of applications including synthetic biology, genotyping and drug discovery.Comparing with traditional pipetting techniques, the accuracy and data reproducibility of ADE based liquid transfer are improved, waste and cost are reduced, and cross-contamination is eliminated. The key component in the ADE system is the ultrasound transducer, which is responsible for generating focused ultrasound beam for droplet ejection. However, current ADE systems commonly utilize a single-element focused transducer with a fixed focal length that require mechanical movement to focus on the liquid surface, resulting in reduced liquid transfer efficiency. In this study, we first present a high-frequency annular array transducer for the ADE technology, which enables rapid and dynamic axial focusing to the liquid surface without mechanically moving the transducer, thereby accelerating liquid transfer. Experimental results show that the proposed 10 MHz, 5-element annular array transducer has good dynamic axial focusing ability, and can achieve accurate and stable droplet ejection of nanoliter volume at the designed focal length of 26–32 mm. Our results highlight the potential of the annular array transducer in advancing ADE system for rapid liquid transfer. This technology is expected to be useful in a variety of applications where precise and high-throughput liquid transfer is crucial.

Ultrasound Diagnosis of Clavicle Fractures in Newborns: A Systematic Review.

Fractures of the clavicle are the most common birth injury among newborns. Aim of this systematic review was to provide a comprehensive analysis of the role of ultrasound (US) in diagnosing clavicular fractures in neonates. A systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) using PubMed and Embase, including studies focusing on US in neonatal clavicle fracture. Age at US, number of cases examined by US and X-ray, US and X-ray diagnoses, US probe used, fracture site were systematically extracted. A total of 231 articles were found. We ultimately selected 7 publications that satisfied the inclusion criteria, involving 136 patients examined between 3 days and 3 weeks of age, with 135 confirmed fractures. US was performed on all patients and correctly diagnosed all fractures (135/135, 100%). X-ray was performed on 94/136 patients (69.1%) and correctly diagnosed 89/93 fractures (95.7%). Fracture site was: medial in 2/79, middle in 37/79, and lateral in 40/79. In the remaining 57 cases, site was not reported. This review indicates that ultrasound is extremely reliable in diagnosing clavicle fractures in newborns and should be considered as the gold standard in this context.

Estimating the viscoelastic anisotropy of human skin through high-frequency ultrasound elastography.

The skin is the largest organ of the human body and serves distinct functions in protecting the body. The viscoelastic properties of the skin play a key role in supporting the skin-healing process, also it may be changed due to some skin diseases. In this study, high-frequency ultrasound (HFUS) elastography based on a Lamb wave model was used to noninvasively assess the viscoelastic anisotropy of human skin. Elastic waves were generated through an external vibrator, and the wave propagation velocity was measured through 40MHz ultrafast HFUS imaging. Through the use of a thin-layer gelatin phantom, HFUS elastography was verified to produce highly accurate estimates of elasticity and viscosity. In a human study involving five volunteers, viscoelastic anisotropy was assessed by rotating an ultrasound transducer 360°. An oval-shaped pattern in the elasticity of human forearm skin was identified, indicating the high elastic anisotropy of skin; the average elastic moduli were 24.90±6.63 and 13.64±2.67kPa along and across the collagen fiber orientation, respectively. The average viscosity of all the recruited volunteers was 3.23±0.93Pa·s. Although the examined skin exhibited elastic anisotropy, no evident viscosity anisotropy was observed.

Numerical simulation and experimental study on nonlinear ultrasonic characterization of graphite size in nodular cast iron

Graphite morphology has a significant influence on mechanical properties such as tensile strength and hardness in nodular cast iron (NCI). Compared to the detection of graphite nodularity, there is relatively less ultrasonic simulation and detection experiment research on the graphite size. Therefore, it is of great importance to study rapid nondestructive testing methods for the internal graphite size of NCI. This study establishes a simulation model of nonlinear ultrasonic penetration longitudinal wave detection for graphite size. The acoustic nonlinearity parameter (ANP) is used to characterize the graphite size. Nonlinear ultrasonic detection experiments on the internal graphite size are conducted to verify the reliability of the nonlinear ultrasonic simulation model. The simulation and experimental results show that the ANP of penetrating longitudinal waves decreases with the increase of average graphite diameter. The relationship between ANP and internal graphite size is established. Moreover, the experimental results verified the accuracy of the numerical model. The decrease in ANP may be related to the decrease in the number of grain boundaries. Therefore, the nonlinear ultrasonic technique is an effective method for characterizing the internal graphite size. The establishment of a nonlinear ultrasonic simulation model for graphite size in NCI lays the research foundation for nonlinear ultrasonic microstructure characterization experiments.

A discrete CMUT self-biasing circuit towards implanted devices application

Wireless power transfer is an essential feature of biomedical engineering. It reduces the need for energy storage devices in medical implants. To recharge a body implanted battery, a convenient way is to transmit ultrasounds through the skin to a connected ultrasonic transducer. Lead-less, System-on-Chip compatible (SoC) and wideband, Capacitive Micromachined Ultrasonic Transducers (CMUT) are competitive with piezoelectric based technologies. However, their need for a high bias voltage is an obstacle to their use in implanted medical devices (IMDs). The voltage source required must meet precise specifications, such as reliability and volume, which the research community intends to respect. To meet this challenge, this work proposes an electronic circuit that allows a CMUT device to self-bias from a very low initial energy input. After presenting the electronic architecture and its main features, simulation and experimental results validate the solution’s working principle and operating points. With an electronic circuit made up of discrete components, a bias voltage of 60 V is built up from an implanted battery voltage of 2.2 V and an incident pressure of 120 kPa in water.

Near Stochiometric LiNbO3 Crystal: the Piezoelectric Features and the Shear Horizontal Guided Wave Transducer for Structural Health Monitoring up to 650 °C.

The application of shear horizontal (SH) guided wave transducers in high-temperature structural health monitoring (SHM) is a topic of significant interest across various industrial engineering sectors. In this study, we utilized the novelty piezoelectric crystal of near stoichiometric lithium niobate (NSLN), which exhibited a robust piezoelectric response (d15 = 77.6 pC/N@room temperature). Next, the pure thickness shear vibration mode d15' through size optimization was designed. It was demonstrated that the NSLN-based ultrasonic guided wave transducers utilizing the optimum d15' mode were proficient in transmitting and receiving pure fundamental SH wave (SH0 wave) along two orthogonal main directions (0° and 90°) over a wide frequency range (100-350 kHz), exhibiting strong response to the SH0 wave. Under the driving voltage of 100 V, the signal voltages of the NSLN-based transducer were found to be on the order of 200.3 and 11.8 mV at room temperature and high temperature of 650 °C, respectively. Moreover, the NSLN-based SH0 transducer showcased its better defect localization ability, and the signal-to-noise ratio (SNR) sensitivity of NSLN-based transducer was evaluated to be 16.1 dB at high temperature of 650 °C. To sum up, the ultrasonic wave transducer based on NSLN crystal demonstrated higher potential applications for in situ SHM under elevated temperatures.

Active and passive electronic interfaces adapted to a capacitive micromachined ultrasonic transducer (CMUT) used in acoustic energy transfer

Wireless power transfer is a key feature in the field of biomedical engineering. It allows a reduction of the energy storage devices in medical implants. An efficient way to safely transfer energy to medical implants is to convey ultrasounds through the body to a Capacitive Micromachined Ultrasonic Transducer (CMUT). For an application of ultrasonic energy transfer through skin, the present work compares the efficiency of two different electronic architectures to receive energy from an array of CMUT. The well known Synchronous Switch Harvesting on Inductor (SSHI) is compared in simulation to a simple impedance matching. Indeed, for an ultrasonic energy transfer, the high excitation frequency (1–8 MHz) allows the use of an inductor matching the CMUT’s clamped capacitor. The simplicity of an impedance matching circuit, its low volume and its efficiency makes it the best choice for an efficient energy transfer process to the targeted load. The CMUT model used in the simulations is a mason’s model which component values are extracted from the impedance measurement of a real device. In the end, the impedance matching is experimentally tested on this same device and compared to the simulation. A maximum 4,5 mW power is transferred to an optimal load for an input ultrasound pressure of 90 kPa.