13 research outputs found
Physically sound model of a non-Foster negative capacitor
In both engineering and physics communities, it is believed that approximation of a realistic non-Foster negative capacitor (within its operating bandwidth) with an ideal dispersionless negative capacitor is acceptable for practical purposes. However, the ideal negative capacitor is not causal and, therefore, not compatible with basic physics. Its use in the design process is misguiding since it often predicts entirely non-physical behaviour. Here, we show that a realistic negative capacitor can always be modelled as a dispersive voltage-controlled source, the internal impedance of which is an ordinary positive capacitor. This equivalent circuit clearly explains the origin of negative conductance that always accompanies negative capacitance, as well as the background physics of previously reported counter-intuitive phenomena in nonFoster metamaterials. Theoretical analysis was verified by simulations and measurements on an experimental low-frequency (100 Hzā25 kHz) negative capacitor demonstrator. Measurement results agreed well with theoretical predictions, showing that the proposed model is indeed physically sound
Utjecaj simetrije transformatora na mjerenja prijenosne karakteristike sustava za prijenos signala ljudskim tijelom prilikom koriÅ”tenja uzemljenih ureÄaja
Transformers with one winding terminal symmetrical with respect to ground (capacitances between their terminals and ground are the same) are referred to as balun transformers, and are often used for decoupling in the measurements of the intrabody communication (IBC) system transmission characteristics. We measured IBC system amplitude and phase transmission characteristics using three types of galvanic decouplers: non-symmetric RF transformers, balun transformers with center tap grounded and balun transformers with center tap floating. Four possible electrode configurations (AA, AB, BA, and BB) and four electrode arrangement (GSGS, GSSG, SGGS, and SGSG), result in a total of 16 measurement scenarios for each of three measurement setups. We showed that the change in the measured amplitude for different signal and ground electrode arrangements while measuring with non-symmetric transformers is influenced by the transformer symmetry to the ground, and not the capacitive intrabody communication transmission characteristics. The change of the amplitude in case symmetric balun transformers are used is negligible for practical purposes.Transformatori kojima su prikljuÄci jednog namota simetriÄni u odnosu na masu (kapaciteti izmeÄu prikljuÄaka i mase su jednaki) se nazivaju balun transformatori i Äesto se koriste za galvansko odvajanje prilikom mjerenja prijenosne karakteristike sustava za prijenos signala ljudskim tijelom (IBC). Mi smo mjerili amplitudnu i faznu prijenosnu karakteristiku IBC sustava koriÅ”tenjem tri naÄina galvanskog odvajanja transformatorima: nesimetriÄnim RF transformatorima, balun transformatorima s uzemljenim srednjim izvodom i balun transformatorima s plivajuÄim srednjim izvodom. Äetiri konfiguracije elektroda (AA, AB, BA i BB) i Äetiri naÄina spajanja signalne i referentne elektrode na tijelo (GSGS, GSSG, SGGS i SGSG), rezultiraju s ukupno 16 scenarija za svaki od tri mjerna postava. Pokazali smo da na promjenu amplitude prijenosne karakteristike uslijed zamjene položaja signalne i referentne elektrode prilikom mjerenja s nesimetriÄnim RF transformatorima utjeÄe simetrija izvoda transformatora prema masi, a ne karakteristika kapacitivnog IBC sustava. Promjena amplitude prilikom mjerenja balun transformatorima je bila zanemariva za praktiÄne namjene
Somatosenzorni evocirani potencijali pobuÄeni vibracijskom stimulacijom: parametri stimulacije
In a clinical application, a method for an examination of a vibratory sense is not very objective and it depends on an active cooperation of a patient, which cannot be achieved in every situation. The aim of this research is to deļ¬ne parameters of an evoked potentials method with a vibratory stimulation technique which would establish reliable and repeatable results applicable in a clinical usage. During the research, different experimental conditions were performed (different methods of stimulation, different stimulation frequencies, different stimulus durations, different areas of stimulation). Presented results conļ¬rm the initial assumption that it is possible to detect reliable
and repeatable cortical potentials evoked by the vibratory stimulation. Characteristic shapes and spatiotemporal distributions of evoked responses are established. Optimal stimulation parameters are deļ¬ned as a prelude for a future research.U kliniÄkoj uporabi, metoda ispitivanja dubokog osjeta pomoÄu vibracija nije objektivna i zahtijeva aktivnu suradnju pacijenta Å”to u brojnim situacijama nije moguÄe. Svrha ovog istraživanja je deļ¬nirati parametre metode evociranih po-tencijala pobuÄenih vibracijskom stimulacijom primjenjive u kliniÄkoj uporabi, koja Äe davati pouzdane i ponovljive rezultate. Tijekom ispitivanja, primijenjeni su razliÄiti eksperimentalni uvjeti (razliÄite tehnike stimulacije, razliÄite frekvencije stimulacije, razliÄita trajanja stimulacije, razliÄita podruÄja stimuliranja). Rezultati potvrÄuju poÄetnu pretpostavku da je moguÄe detektirati pouzdane i ponovljive kortikalne potencijale pobuÄene vibracijskom stimulacijom. UtvrÄeni su karakteristiÄni valni oblici evociranih odgovora i njihove prostorno-vremenske karakteristike. Optimalni stimulacijski parametri su deļ¬niriani kao podloga za buduÄa istraživanj
Measurement System for Neurophysiological Functions Monitoring
U radu je opisana realizacija sustava kojim se ubrzava snimanje intraoperacijskih evociranih potencijala. Ubrzavanje snimanja intraoperacijskih evociranih potencijala ima veliku dijagnostiÄko-terapijsku važnost prilikom neurokirurÅ”kih zahvata. KritiÄni parametar kod snimanja evociranih potencijala o kojem ovisi uÄinkovitost nadzora je vrijeme, koje protekne od promjene u izgledu evociranih potencijala do njene detekcije, a temeljni problem kod snimanja je visoka razina smetnji, koje postoje za vrijeme kirurÅ”kog zahvata. Kod danas dostupnih izvedbi ureÄaja, te smetnje dovode pojaÄalo u zasiÄenje, onemoguÄavajuÄi tako snimanje evociranih potencijala. Konstrukcija mjernog sustava je stoga podreÄena skraÄivanju tog vremena. U tom cilju napravljena je analiza mjernog sustava, vrsta smetnji koje se javljaju kod operacijskih zahvata, te prenosnih puteva preko kojih se one prenose u mjerni sustav. Temeljem te analize uoÄeni su kritiÄni parametri sustava (ulazna impedancija, faktor potiskivanja i Å”um) i odreÄene vrijednosti, koje oni moraju dosegnuti kako bi sustav mogao uspjeÅ”no funkcionirati u uvjetima operacijskih zahvata. Prikazana je detaljna razrada konstrukcije pojedinih dijelova sustava te je pokazano na koji naÄin i u kojoj mjeri njihove karakteristike utjeÄu na dostizanje zacrtanih karakteristika cijelog sustava. Temeljem analize svojstava smetnji, koje se pojavljuju u isprekidanim intervalima za vrijeme operacijskog zahvata, te Äinjenice da je konstrukcijskim zahvatima moguÄe skratiti vrijeme trajanja zasiÄenja pojaÄala, predložena je nova metodologija snimanja evociranih potencijala. Nova metodologija omoguÄava iskoriÅ”tavanje pauzi izmeÄu pojavljivanja smetnji na naÄin da se okidanje stimulatora, pa time i poÄetak snimanja sekvence evociranih potencijala, iniciraju tek kada nema smetnji i pojaÄalo nije u zasiÄenju. Mjerenjem u stvarnim uvjetima pokazano je da se predloženim sklopovskim rjeÅ”enjem može postiÄi skraÄenje trajanja snimanja od 2,5 do 5 puta. VeliÄina skraÄenja ovisi o vrsti evociranih potencijala koji se snimaju. Ta ovisnost proizlazi kao posljedica razliÄitog trajanja sekvence evociranih potencijala te prosjeÄnog trajanja pauze u kojoj se ona može snimiti.Realisation of the system for faster recording of intraoperative evoked potentials was described in the thesis. Faster recording of intraoperative evoked potentials has huge diagnostic and therapeutic importance during neurosurgical procedures. Crucial parameter in an evoked potential recording on which efficient monitoring depends is the time interval between evoked potential change and notice of this change. The main problem that lengthened this interval is high level of noise present during surgical procedure. This level of noise will saturate standard equipmentās amplifiers and making recording of evoked potentials impossible. A shortening of time interval between change of an evoked potential and its notice was chosen as the primary design goal. The thorough analysis of various noise types and possible paths of interference into recording system was made. Based on this analysis critical parameters of the system were recognised (input impedance, common mode rejection ratio and amplifier noise). Necessary level of performance for each parameter is established which will assure that complete system performance goals will be reached. Detailed analysis of each system parts was presented along with the description of dependencies between their and system characteristics. Based on the noticed interval occurrence of noise during surgical procedure and the fact that is possible to shortened amplifier saturation by means of additional circuits, new method of recording is proposed. New method of recording enables using of time intervals between noise occurrence by synchronisation between amplifier and stimulator. Trigger impulses are generated only if there are no excessive noise on an amplifierās output and it is not saturated. Measurements in an operating room were revealed that the new method of recording can shorten time interval between evoked potential change and notion of this change between 2,5 and 5 times. Enhancement depends on the type of an evoked potential that is recorded. Difference come from the different length of time window of an evoked potential and the pause between occurrences of noise
Measurement System for Neurophysiological Functions Monitoring
U radu je opisana realizacija sustava kojim se ubrzava snimanje intraoperacijskih evociranih potencijala. Ubrzavanje snimanja intraoperacijskih evociranih potencijala ima veliku dijagnostiÄko-terapijsku važnost prilikom neurokirurÅ”kih zahvata. KritiÄni parametar kod snimanja evociranih potencijala o kojem ovisi uÄinkovitost nadzora je vrijeme, koje protekne od promjene u izgledu evociranih potencijala do njene detekcije, a temeljni problem kod snimanja je visoka razina smetnji, koje postoje za vrijeme kirurÅ”kog zahvata. Kod danas dostupnih izvedbi ureÄaja, te smetnje dovode pojaÄalo u zasiÄenje, onemoguÄavajuÄi tako snimanje evociranih potencijala. Konstrukcija mjernog sustava je stoga podreÄena skraÄivanju tog vremena. U tom cilju napravljena je analiza mjernog sustava, vrsta smetnji koje se javljaju kod operacijskih zahvata, te prenosnih puteva preko kojih se one prenose u mjerni sustav. Temeljem te analize uoÄeni su kritiÄni parametri sustava (ulazna impedancija, faktor potiskivanja i Å”um) i odreÄene vrijednosti, koje oni moraju dosegnuti kako bi sustav mogao uspjeÅ”no funkcionirati u uvjetima operacijskih zahvata. Prikazana je detaljna razrada konstrukcije pojedinih dijelova sustava te je pokazano na koji naÄin i u kojoj mjeri njihove karakteristike utjeÄu na dostizanje zacrtanih karakteristika cijelog sustava. Temeljem analize svojstava smetnji, koje se pojavljuju u isprekidanim intervalima za vrijeme operacijskog zahvata, te Äinjenice da je konstrukcijskim zahvatima moguÄe skratiti vrijeme trajanja zasiÄenja pojaÄala, predložena je nova metodologija snimanja evociranih potencijala. Nova metodologija omoguÄava iskoriÅ”tavanje pauzi izmeÄu pojavljivanja smetnji na naÄin da se okidanje stimulatora, pa time i poÄetak snimanja sekvence evociranih potencijala, iniciraju tek kada nema smetnji i pojaÄalo nije u zasiÄenju. Mjerenjem u stvarnim uvjetima pokazano je da se predloženim sklopovskim rjeÅ”enjem može postiÄi skraÄenje trajanja snimanja od 2,5 do 5 puta. VeliÄina skraÄenja ovisi o vrsti evociranih potencijala koji se snimaju. Ta ovisnost proizlazi kao posljedica razliÄitog trajanja sekvence evociranih potencijala te prosjeÄnog trajanja pauze u kojoj se ona može snimiti.Realisation of the system for faster recording of intraoperative evoked potentials was described in the thesis. Faster recording of intraoperative evoked potentials has huge diagnostic and therapeutic importance during neurosurgical procedures. Crucial parameter in an evoked potential recording on which efficient monitoring depends is the time interval between evoked potential change and notice of this change. The main problem that lengthened this interval is high level of noise present during surgical procedure. This level of noise will saturate standard equipmentās amplifiers and making recording of evoked potentials impossible. A shortening of time interval between change of an evoked potential and its notice was chosen as the primary design goal. The thorough analysis of various noise types and possible paths of interference into recording system was made. Based on this analysis critical parameters of the system were recognised (input impedance, common mode rejection ratio and amplifier noise). Necessary level of performance for each parameter is established which will assure that complete system performance goals will be reached. Detailed analysis of each system parts was presented along with the description of dependencies between their and system characteristics. Based on the noticed interval occurrence of noise during surgical procedure and the fact that is possible to shortened amplifier saturation by means of additional circuits, new method of recording is proposed. New method of recording enables using of time intervals between noise occurrence by synchronisation between amplifier and stimulator. Trigger impulses are generated only if there are no excessive noise on an amplifierās output and it is not saturated. Measurements in an operating room were revealed that the new method of recording can shorten time interval between evoked potential change and notion of this change between 2,5 and 5 times. Enhancement depends on the type of an evoked potential that is recorded. Difference come from the different length of time window of an evoked potential and the pause between occurrences of noise
Measurement System for Neurophysiological Functions Monitoring
U radu je opisana realizacija sustava kojim se ubrzava snimanje intraoperacijskih evociranih potencijala. Ubrzavanje snimanja intraoperacijskih evociranih potencijala ima veliku dijagnostiÄko-terapijsku važnost prilikom neurokirurÅ”kih zahvata. KritiÄni parametar kod snimanja evociranih potencijala o kojem ovisi uÄinkovitost nadzora je vrijeme, koje protekne od promjene u izgledu evociranih potencijala do njene detekcije, a temeljni problem kod snimanja je visoka razina smetnji, koje postoje za vrijeme kirurÅ”kog zahvata. Kod danas dostupnih izvedbi ureÄaja, te smetnje dovode pojaÄalo u zasiÄenje, onemoguÄavajuÄi tako snimanje evociranih potencijala. Konstrukcija mjernog sustava je stoga podreÄena skraÄivanju tog vremena. U tom cilju napravljena je analiza mjernog sustava, vrsta smetnji koje se javljaju kod operacijskih zahvata, te prenosnih puteva preko kojih se one prenose u mjerni sustav. Temeljem te analize uoÄeni su kritiÄni parametri sustava (ulazna impedancija, faktor potiskivanja i Å”um) i odreÄene vrijednosti, koje oni moraju dosegnuti kako bi sustav mogao uspjeÅ”no funkcionirati u uvjetima operacijskih zahvata. Prikazana je detaljna razrada konstrukcije pojedinih dijelova sustava te je pokazano na koji naÄin i u kojoj mjeri njihove karakteristike utjeÄu na dostizanje zacrtanih karakteristika cijelog sustava. Temeljem analize svojstava smetnji, koje se pojavljuju u isprekidanim intervalima za vrijeme operacijskog zahvata, te Äinjenice da je konstrukcijskim zahvatima moguÄe skratiti vrijeme trajanja zasiÄenja pojaÄala, predložena je nova metodologija snimanja evociranih potencijala. Nova metodologija omoguÄava iskoriÅ”tavanje pauzi izmeÄu pojavljivanja smetnji na naÄin da se okidanje stimulatora, pa time i poÄetak snimanja sekvence evociranih potencijala, iniciraju tek kada nema smetnji i pojaÄalo nije u zasiÄenju. Mjerenjem u stvarnim uvjetima pokazano je da se predloženim sklopovskim rjeÅ”enjem može postiÄi skraÄenje trajanja snimanja od 2,5 do 5 puta. VeliÄina skraÄenja ovisi o vrsti evociranih potencijala koji se snimaju. Ta ovisnost proizlazi kao posljedica razliÄitog trajanja sekvence evociranih potencijala te prosjeÄnog trajanja pauze u kojoj se ona može snimiti.Realisation of the system for faster recording of intraoperative evoked potentials was described in the thesis. Faster recording of intraoperative evoked potentials has huge diagnostic and therapeutic importance during neurosurgical procedures. Crucial parameter in an evoked potential recording on which efficient monitoring depends is the time interval between evoked potential change and notice of this change. The main problem that lengthened this interval is high level of noise present during surgical procedure. This level of noise will saturate standard equipmentās amplifiers and making recording of evoked potentials impossible. A shortening of time interval between change of an evoked potential and its notice was chosen as the primary design goal. The thorough analysis of various noise types and possible paths of interference into recording system was made. Based on this analysis critical parameters of the system were recognised (input impedance, common mode rejection ratio and amplifier noise). Necessary level of performance for each parameter is established which will assure that complete system performance goals will be reached. Detailed analysis of each system parts was presented along with the description of dependencies between their and system characteristics. Based on the noticed interval occurrence of noise during surgical procedure and the fact that is possible to shortened amplifier saturation by means of additional circuits, new method of recording is proposed. New method of recording enables using of time intervals between noise occurrence by synchronisation between amplifier and stimulator. Trigger impulses are generated only if there are no excessive noise on an amplifierās output and it is not saturated. Measurements in an operating room were revealed that the new method of recording can shorten time interval between evoked potential change and notion of this change between 2,5 and 5 times. Enhancement depends on the type of an evoked potential that is recorded. Difference come from the different length of time window of an evoked potential and the pause between occurrences of noise