Timo Salpavaara

Capacitive insole sensor for hip surgery rehabilitation

We are developing a capacitive insole sensor in order to measure the force between foot and an insole. The sensor is intended to guide a hip surgery patient to train the operated leg with a suitable force. In this paper, we propose a flexible, laminated structure for a capacitive force sensor matrix. The preliminary measurements indicate that the sensor could be used as a limit detector to sort out too light and too heavy steps. We have also evaluated our method comparing our sensor signal to the signal measured with a commercial force transducer. Finally, we have made long-term measurements in order to evaluate the stability of the capacitive sensor elements.

Novel wireless electroencephalography system with a minimal preparation time for use in emergencies and prehospital care

BackgroundAlthough clinical applications such as emergency medicine and prehospital care could benefit from a fast-mounting electroencephalography (EEG) recording system, the lack of specifically designed equipment restricts the use of EEG in these environments.MethodsThis paper describes the design and testing of a six-channel emergency EEG (emEEG) system with a rapid preparation time intended for use in emergency medicine and prehospital care. The novel system comprises a quick-application cap, a device for recording and transmitting the EEG wirelessly to a computer, and custom software for displaying and streaming the data in real-time to a hospital. Bench testing was conducted, as well as healthy volunteer and patient measurements in three different environments: a hospital EEG laboratory, an intensive care unit, and an ambulance. The EEG data was evaluated by two experienced clinical neurophysiologists and compared with recordings from a commercial system.ResultsThe bench tests demonstrated that the emEEG systems performance is comparable to that of a commercial system while the healthy volunteer and patient measurements confirmed that the system can be applied quickly and that it records quality EEG data in a variety of environments. Furthermore, the recorded data was judged to be of diagnostic quality by two experienced clinical neurophysiologists.ConclusionsIn the future, the emEEG system may be used to record high-quality EEG data in emergency medicine and during ambulance transportation. Its use could lead to a faster diagnostic, a more accurate treatment, and a shorter recovery time for patients with neurological brain disorders.

Embedded capacitive sensor system for hip surgery rehabilitation: Online measurements and long-term stability

We are developing an embedded system that measures the force between foot and insole with a low-cost laminated capacitive sensor matrix. The system is intended to guide a hip surgery patient to train the operated leg with a suitable force. In this paper, we present an embedded measurement system, which is able to estimate the total plantar force in real-time and to give instant feedback to a user. We also present a method for compensating the drift of capacitive sensors. A 5-hour long test measurement was made in order to validate the system. According to the preliminary test, the compensation method effectively prevents the drift of the baseline of the force reading.

Biodegradable encapsulation for inductively measured resonance circuit

The feasibility of biodegradable encapsulation for LC resonance circuits is studied. The used biodegradable polymers are polycaprolactone (PCL) and poly-L-lactide/caprolactone (PLCL). The encapsulated circuits are immersed in a phosphate buffer solution and the phase and magnitude responses are measured by using an inductive link during an 80-day test period. The features derived from the resonance curves are extracted and studied. The features change fast when the encapsulation absorbs water during the first days of immersion. After the initial water intake, there is a drift in the extracted estimates for the resonance frequency. The drift of the frequency of the resonance circuit in PLCL is faster compared with the drift of a circuit in PCL. The resonance curve of the PLCL specimen also diminished to undetectable after 72 days of immersion. The resonance curves of the sample in PCL were easily detectable throughout the test period. The achieved results promote further studies based on this concept in order to monitor biodegradable polymers and their properties.

Development of a Lower Extremity Rehabilitation Aid Utilizing an Insole-Integrated Load Sensor Matrix and a Sole-Embedded Measurement Node

Following an individual exercise program after a hip or a knee operation is crucially important as it enables the muscles of the operated leg to regain their strength and thereby support the recovery of the operated joint. Usually the patients have no assisting devices at home to help determine how much weight they put on the operated leg. Training with a scale helps, but in general, humans can not accurately estimate the amount of weight they put on the leg. To address this problem we have designed a lower extremity rehabilitation aid, which utilizes an insole-integrated capacitive load sensor matrix and a sole-embedded read-out electronics with wireless communication link. In this paper we present in detail the manufacturing process of the insole sensor. The placement of the electrodes, calibration, and user interfaces are also discussed. The system is found to be suitable for detecting too light and too heavy steps.

EMFi in wearable audio applications

Flexible microphone and earphone prototypes for wearable applications were developed by using ElectroMechanical Film (EMFiℳ)*. A suitable application for the developed headset can be, for instance, as accessory of rescue services or sport enthusiasts. Due its versatile properties, EMFi can be used both as microphone and earphone material. The sensor operation is based on thickness changes caused by an external force or pressure, generating charge and thus voltage on the electrodes. EMFi also works conversely, converting electrical energy to vibration and hence functioning as an actuator. In addition, measurement electronics for the microphone and earphone were implemented. Preliminary test measurements were carried out: the frequency response of the EMFi microphone was compared with the one of a reference B&K microphone. The EMFi microphone provides rather good response. Also subjective listening tests were done. For these measurements, the EMFi headset was integrated inside a neoprene hood used by the surface rescuers. Both with the microphone and earphone the quality of voice was sufficient. Based on the results, EMFi seems to be a promising material for some wearable audio applications.

Testing and comparing of film-type sensor materials in measurement of plantar pressure distribution

Simple in-shoe sensors based on film-type sensor materials were developed in this study. Three sensor materials were tested: polyvinylidenefluoride (PVDF), cellulose nanofibrils (CNF) and ElectroMechanical Film (EMFi). Plantar pressure distributions of a subject were measured with the developed in-shoe sensors; each consisting of three sensor channels (lateral and medial metatarsal heads and heel). In addition, piezoelectric sensor sensitivities and crosstalk between the sensor channels were determined. Differences between the tested film-type materials and measured plantar pressure distribution signals were studied.Simple in-shoe sensors based on film-type sensor materials were developed in this study. Three sensor materials were tested: polyvinylidenefluoride (PVDF), cellulose nanofibrils (CNF) and ElectroMechanical Film (EMFi). Plantar pressure distributions of a subject were measured with the developed in-shoe sensors; each consisting of three sensor channels (lateral and medial metatarsal heads and heel). In addition, piezoelectric sensor sensitivities and crosstalk between the sensor channels were determined. Differences between the tested film-type materials and measured plantar pressure distribution signals were studied.

EMFi material as wearable heart rate sensor for night time recordings

We propose a method for night time monitoring of heart rate. Our method uses one or more pressure sensitive elements integrated into a wristwatch. The sensing elements are made of film type electret material called EMFi (Electro Mechanical Film). We designed the signal processing algorithms keeping in mind on-line processing and later integration into a micro controller for wearable applications. We have evaluated our method by comparing beat-to-beat heart rate values obtained with EMFi sensors with accurate reference values calculated from reference ECG signal. We suggest based on the 209 s average continuous recognition time and 0.51 bpm mean error that our method provides adequate accuracy for night time heart rate and heart rate variability analysis, which enables the method to be used in various applications.

Unconstrained Night-Time Heart Rate Monitoring with Capacitive Electrodes

An unobtrusive measurement system for night-time heart rate (HR) monitoring is presented. The system uses capacitive electrodes that do not require galvanic skin contact, thus allowing user to wear clothes while being monitored. The electrodes are located transversely on the bed and the electrocardiographic signals are measured between each electrode and a common reference. The signals are then combined in order to remove the common mode move-ment artifacts and the best one is selected for HR detection.

Non-invasive System for Mechanical Arterial Pulse Wave Measurements

A non-invasive multichannel measurement system for arterial pulse wave (PW) recording is presented. The system uses sensors made of EMFi (ElectroMechanical Film) material for measuring mechanical PW signals simultaneously from various arterial sites all over the body. In addition to mechanical PW, also electrocardiographic, respiration and photoplethysmographic signals can be recorded with the system. By extracting parameters from the PW contour, valuable information on the subject’s vascular health can be obtained.