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Using only a microphone array system, echolocation pulses and three-dimensional flight paths in the frequency-modulated bat, Pipistrellus abramus, during natural foraging, were simultaneously examined. During the search phase, the inter-pulse interval, pulse duration, and moving distance of the bat between successive emissions were relatively constant at around 89.5 ± 18.7 ms, 6.90 ± 1.31 ms, and 0.50 ± 0.20 m, respectively. The bats started to decrease these acoustical parameters within 2-3 m of the prey capture point. For every emission along a flight path, the distance between a bat and its prey capture point was calculated as both direct distance to capture (DDC), which corresponded to the target distance, and flight distance to capture (FDC) along the flight path. The DDC matched the FDC after the start of the approach phase, indicating that foraging bats followed a straight-ahead path to the target. In addition, the duration of the quasi-constant frequency component of emitted pulses was slightly extended just before the convergence of the DDC with the FDC. These findings suggest that the bats confirm the presence of target prey by extending the duration of the pulse and then select a straight-ahead approach by forecasting the movement of the prey.

For the downsizing, the coaxial thermoacoustic system (coaxial-type) has been proposed. The coaxial-type is expected to have high efficiency because the energy conversion with traveling wave phase like looped-tube is realized. Additionally, this system is more compact than the looped-tube. The circular flow path of the coaxial-type is made of an annular flow path between the inner and the outer tube and a cylindric flow path in the inner tube. By propagating in the cylindric flow path after passing through the annular flow path, a traveling-wave sound field is generated. The edge space between the annular flow path and the inner tube was studied due to the reduction of the propagation loss. The influence of the inner tube length and the edge shapes of outer tube on the energy conversion was examined. The two edge shapes were used: the flat one and the spherical one. It was confirmed the sound energy generated in the system with the spherical shape is higher than the one with the flat shape. It is suggested a traveling-wave sound field is easily generated by the spherical shape because of the focus effect. Thus, the edge shape is one of important points for designing the coaxial-type.For the downsizing, the coaxial thermoacoustic system (coaxial-type) has been proposed. The coaxial-type is expected to have high efficiency because the energy conversion with traveling wave phase like looped-tube is realized. Additionally, this system is more compact than the looped-tube. The circular flow path of the coaxial-type is made of an annular flow path between the inner and the outer tube and a cylindric flow path in the inner tube. By propagating in the cylindric flow path after passing through the annular flow path, a traveling-wave sound field is generated. The edge space between the annular flow path and the inner tube was studied due to the reduction of the propagation loss. The influence of the inner tube length and the edge shapes of outer tube on the energy conversion was examined. The two edge shapes were used: the flat one and the spherical one. It was confirmed the sound energy generated in the system with the spherical shape is higher than the one with the flat shape. It is suggeste...

We discuss the stack which is the key device of the thermoacoustic system. We elucidate the stack mechanism to realize further energy conversion efficiency improvement. We propose installing a heater inside the stack. This heater adjusts the internal temperature of the stack and controls the heat flow in the stack. Controlling the heat flow in the stack can also affect the mutual conversion of the heat flow and the work flow. In this report, the effect of the resonance frequency with the standing-wave thermoacoustic-system and the internal temperature of the stack on the heat flow in the stack was experimentally investigated. The resonance frequency was changed with the total length of the system. As a result, the lower the frequency, the larger the amount of the work flow generated in the stack. This can be influenced by the increase and decrease of the dissipation with changing the resonance frequency. Also, at any resonance frequency, the amount of the work flow generation increased with controlling the heat flow in the stack. The heat flow can be controlled by adjusting the internal temperature of the stack at any resonance frequency.We discuss the stack which is the key device of the thermoacoustic system. We elucidate the stack mechanism to realize further energy conversion efficiency improvement. We propose installing a heater inside the stack. This heater adjusts the internal temperature of the stack and controls the heat flow in the stack. Controlling the heat flow in the stack can also affect the mutual conversion of the heat flow and the work flow. In this report, the effect of the resonance frequency with the standing-wave thermoacoustic-system and the internal temperature of the stack on the heat flow in the stack was experimentally investigated. The resonance frequency was changed with the total length of the system. As a result, the lower the frequency, the larger the amount of the work flow generated in the stack. This can be influenced by the increase and decrease of the dissipation with changing the resonance frequency. Also, at any resonance frequency, the amount of the work flow generation increased with controlling th...

An onboard microphone (Telemike) was developed to examine changes in the basic characteristics of echolocation sounds of small frequency-modulated echolocating bats, Pipistrellus abramus. Using a dual high-speed video camera system, spatiotemporal observations of echolocation characteristics were conducted on bats during a landing flight task in the laboratory. The Telemike allowed us to observe emitted pulses and returning echoes to which the flying bats listened during flight, and the acoustic parameters could be precisely measured without traditional problems such as the directional properties of the recording microphone and the emitted pulse, or traveling loss of the sound in the air. Pulse intensity in bats intending to land exhibited a marked decrease by 30 dB within 2 m of the target wall, and the reduction rate was approximately 6.5 dB per halving of distance. The intensity of echoes returning from the target wall indicated a nearly constant intensity (-42.6 +/- 5.5 dB weaker than the pulse emitted in search phase) within a target distance of 2 m. These findings provide direct evidence that bats adjust pulse intensity to compensate for changes in echo intensity to maintain a constant intensity of the echo returned from the approaching target at an optimal range.

To establish safety criteria of ultrasound for blood, we examined hemolysis induced by low-intensity pulsed ultrasound and performed in vitro experiments using bovine blood. Quantitative evaluation by microscopic observations and the relationship between the hemolysis and cavitation microbubbles were discussed. Hemolysis was evaluated by red blood ghost cell. The presence of red blood ghost cells in the plasma component implies that the cell membrane was broken and the internal hemoglobin flowed out to surrounding blood plasma. Pulsed ultrasound at 1 MHz with the maximum sound pressure amplitude of 200 kPa was irradiated for one minute, and the ratio of non-exposure time (0—80%) was changed. After ultrasound exposure, the blood samples were centrifuged and divided into two layers: blood cells and plasma components. 10 μL of the plasma components was sampled and the number of the red blood ghost cells was counted. The number of red blood ghost cells increased gradually with the decrease in the ratio of non...

The thermoacoustic system with coaxial geometry (coaxial-type) is discussed. The coaxial-type has high efficiency because it performs the energy conversion with the traveling wave mode as the same of the looped tube type thermoacoustic system (loop-tube-type). Additionally, the coaxial-type can be realized more downsizing in comparison with the loop-tube-type, and it is also expected to expand the practical use. In this report, the experimental studies of the coaxial-type refrigerator were carried out. A pair of stacks was placed in the experimental setup. Those stacks were employed as a prime mover and a heat pump. In the case of the loop-tube-type, those are usually placed symmetrically. However, it is not practical for the coaxial-type to place stacks symmetrically because of the difficulties for the taking off cold energy; therefore, both of stacks were placed in annular path. As a result, temperature decreases were confirmed, that is, amount of 5 decreases from room temperature were observed at the cooling point of a heat pump. It is thought that the energy conversion with the traveling wave mode is occurring in stacks. These results show that the coaxial-type can be possible to become a new design to take the place of the loop-tube-type.

Echolocating bats use frequency-modulated (FM) and/or constant-frequency (CF) sound for ultrasonic sensing depending on the situation during flight. We investigated discrimination ability of object’s texture for sighted subjects to understand acoustic clues for texture recognition in human echolocation. FM and CF ultrasonic echoes from six objects with different materials and surface structures were acquired by a 1/7-size miniature dummy head for presentation of 1/7-times pitch converted binaural audible sounds to listeners through headphones. In the results, averaged rate of correct answer in the case of extremely different surface condition (i.e., acrylic board versus artificial grass) was more than 90% while one in the slightly different surface condition (i.e., acrylic board versus foamed polystyrene) was under 40%. Furthermore, the rate of correct answers in the CF sound condition was approximately 13% lower than one in the FM sound condition. The correlation diagram among targets by multidimensional...

The echolocation behavior of Pipistrellus abramus during exposure to artificial jamming sounds during flight was investigated. Echolocation pulses were recorded using a telemetry microphone mounted on the bats' backs, and their adaption based on acoustic characteristics of emitted pulses was assessed in terms of jamming-avoidance responses (JAR). In experiment 1, FM jamming sounds mimicking echolocation pulses of P. abramus were prepared. All bats showed significant increases in the terminal frequency (TF) by an average of 2.1–4.5 kHz when the TF of the jamming sounds was lower than the bats' own pulses. This frequency shift was not observed using jamming frequencies that overlapped with or were higher than the bats' own pulses. These findings suggest that JAR in P. abramusare sensitive to the TF of jamming pulses and that the bats' response pattern was dependent on the slight difference in stimulus frequency. In experiment 2, when bats were repeatedly exposed to a band-limited noise, the bats in flight more frequently emitted pulses during silent periods between jamming sounds. These results demonstrate that bats could rapidly adjust their vocalized frequency and emission timing to avoid frequency and temporal overlap with jamming sound even during flight. [Research supported by JSPS.]

Using a super microphone-array system, 3-D flight paths of echolocating Japanese house bats, Pipistrellus abramus, across whole foraging area were successfully measured in the field, together with the directional aim of their sonar beams. Sonar sounds were sometimes rapidly alternated between its direction and other one or two particular directions during search phase. Especially, when the bats consecutively captured multiple insect preys, their emissions were directed toward not only the current target prey and also the next target. These suggest that the bats process multiple echo streams by time-sharing manner and plan the flight path to efficiently capture multiple target preys. In order to examine whether the bats select the efficient flight path to consecutively capture multiple targets, the bats' 3-D flight behavior while approaching two target preys was then modeled. The modeling analysis suggested that the echolocating bats select their flight paths to easily direct their sonar beams toward both targets. [This research was supported by the Aihara Project, the FIRST program from JSPS, initiated by CSTP, a Grant-in-Aid for Young Scientists (A) of JSPS, and the Murata Science Foundation.]

We classified communication calls of Japanese pipistrelle bats (Pipistrellus abramus) by acoustic characteristics D. The Japanese pipistrelles emitted communication calls that were completely different from FM echolocation calls. Data showed that in general duration of communication calls was longer than that of echolocation calls (e.g., echolocation call, 1 ms; long CF communication call, 50 ms) and that frequency of commu‐nication calls were lower than that of echolocation calls (e.g., echolocation call, 80–40 kHz; long CF communication call, about 14 kHz). Typical classified communication calls were as follows: slightly short CF call (20 ms, 14 kHz), short CF call (5 ms, 14 kHz), slightly long CF call (30 ms, 14 kHz), long CF call (50 ms, 14 kHz), slightly long FM call (15 ms, 30–15 kHz), long FM call (20 ms, 25–15 kHz), complicated FM call (10–50 ms, 25–15 kHz), short intermittent CF call (1 ms, 14 kHz) and noise call (20–100 ms, below 60 kHz). Details will be discussed more specifically. [Research supported by a grant to RCAST at Doshisha Univ. from MEXT and by the Innovative Cluster Creation Project promoted by MEXT.]

Arterial filters are employed in extracorporeal circulations to remove microbubbles and thrombus from the blood flow and prevent the emboli. Filters with mesh structure have a risk to generate the thrombi when the blood flows through it. In this report, a meshless filter using ultrasound is discussed. The filter consists of an aluminum cylinder (length: 130 mm; inner diameter: 30 mm) and two annular ultrasound PZT transducers. The filter has one inlet at the center of the side and two outlets at both ends. By exciting the transducer, the acoustic traveling wave can be generated in the liquid inside the filter. Air bubbles flowing from the inlet can be led toward the outlet by acoustic radiation force. The characteristics of the filter were investigated through a circulation system using distilled water at the driving frequencies of 200 kHz and 1 MHz. Flow and injected air were set as 5.0 l/min and 10 ml/min, respectively. The microbubbles were filtered by using ultrasound and the amount of filtered bubbles was increased with theinput voltage to the transducer: 50.6 and 53.7% of microbubbles were filtered at 200 kHz and 1 MHz, respectively, when the input voltage was 100 Vpp.

One obstacle to practical realization of a loop-tube type thermoacoustic system is insufficient cooling capacity. The system cooling capacity is known to be improved by setting the phase adjuster (PA), which reduces the system cross-section locally. This improvement is considered to occur because setting the PA enables control of the resonance mode and the setting of PA controls to one wavelength. However great dissipation of energy occurs with the PA because of the reduced cross-section. Greater cooling capacity of the system, with less energy dissipation, is expected from control resonance mode. An expanding phase adjuster (EPA), the device proposed herein, can expand the cross-section locally to reduce energy dissipation. The cooling capacity is expected to improve if the EPA can be set to control the resonance mode. After verifying that setting the EPA can control resonance mode, we compare the system set with EPA to that with PA. Results show that the cooling capacity of the system with PA is greater than that with EPA. However, greater cooling capacity is expected by shifting the condition of EPA because the energy used for cooling in the system with EPA is greater than that with PA.

In a thermoacoustic system, as the temperature ratio of both ends of a stack increases gradually and reaches a critical value, sound waves begin to oscillate. This temperature ratio is called the onset temperature ratio. It is necessary to decrease the onset temperature ratio for practical application of a thermoacoustic system using factory exhaust heat or solar heat. A previous study examined a thermoacoustic system with a number of prime movers connected in series. This system can be driven by a lower onset temperature ratio than a thermoacoustic system with a prime mover. However, it is considered that the heat loss increases when the heat is carried to a number of high heat exchangers. Therefore, a parallel loop-tube thermoacoustic system was proposed. This system can drive two prime movers by a heat input part because it is connected in parallel to prime movers. This study compared the onset temperature ratio of this system with that of a normal loop-tube system with a prime mover. Results show that the parallel loop-tube system can be driven by a lower onset temperature ratio than the normal loop-tube system.

As the temperature ratio of the both ends of the stack increases gradually and reaches a critical value, sound waves begin to oscillate. This temperature ratio is called the onset temperature ratio. The thermoacoustic systems can use waste heat effectively, and are applied as electrical generation and cooling systems. However, the required temperature to drive the current thermoacoustic systems is higher than the temperature of waste heat, and energy conversion efficiency of the systems is just only a few percent. In order to use of the systems effectively, these need to be improved. The onset temperature ratio and energy conversion efficiency are dependent on the geometry of the systems and working fluids. In this report, it is focused on the gas in the systems, and the mixture gas of argon and helium was used as working fluids. The influence of the onset temperature ratio and energy conversion efficiency was investigated, when the mixture ratio was changed. These are calculated by using the linear stabi...

Downsizing of thermoacoustic system is discussed in order to be applied to the electronic equipments. In our previous studies for the miniature thermoacoustic system, the stable oscillation is successfully realized on the straight-tube with opened-closed ends type although the inner working fluid cannot be shut in. To realize the working fluid be shut in the tube and keeping the stable oscillation, a new system is combined of two tubes with different cross-sectional area. The large sized system is applied instead of the small sized one because of the measurement difficulty. As the results, it was confirmed that the efficiency of the energy conversion was improved by using the system which combines two kinds of tubes with different cross-section tube. The reason of the efficiency improvement was estimated that the resonance became to be strong by the overlap of two kinds of resonances. This estimation was confirmed by changing the ratio of length of connecting tubes with different cross-section. The efficiency of the energy conversion was improved by controlling of the acoustic field. Those were realized by connecting of two tubes with different cross-sectional area.

Analysis of the bat's reactions to relevant target echoes enables us to directly assess biosonar performance. Here, we recorded the sonar broadcast and its echoes the bat received during flight by using an on-board telemetry microphone (Telemike) mounted on the bat's back. Telemike recordings confirmed that flying bats adjust the amplitude and frequency of their sonar broadcasts to compensate for increases in echo amplitude and for Doppler-shifts. For insect capturing, the bat exhibited Doppler-shift compensation for echoes from the static target ahead, but not for echoes from the target moth even though the flying bat attended to the moth for capture. Positive and negative Doppler shifts (acoustic glints) caused by insect fluttering were observed in the constant-frequency component of observed echoes, which synchronized with wingbeat cycle of the moth. Combined frequency and amplitude compensation for the static target may be advantageous for detection of acoustic glints of target prey. We also construct...

Changes in frequency range (ΔF) of FM echolocation pulses were recorded with an onboard wireless microphone (Telemike) for Pipistrellus abramus and Miniopterus fuliginosus in a cluttered environment created by dense chain‐row obstacles. The duration of echo streams (ESD) from the chains reached ∼40 ms when the bats were flying toward the chain‐row obstacles. P. abramus emitted pulses in pairs (strobe group) with 20–40 ms interpulse intervals (IPIs), which occasionally created pulse‐echo ambiguity (IPI was shorter than ESD). When successive echo streams did not overlap, ΔF within strobe groups was less than 2–3 kHz. When overlap occurred, Δ F increased to 5–6 kHz (F‐test, P < 0.001). By shifting frequency range of successive FM pulses, P. abramus appeared to assign echoes to the corresponding pulses and avoid pulse‐echo ambiguity. Similar finding was previously reported in Eptesicus fuscus. On the other hand, M. fuliginosus never emitted pulses in a strobe group, and IPIs were always adjusted to be longer than ESDs. Thus, the amount of ΔF was less than 2 kHz, which corresponded to that in P. abramus without pulse‐echo ambiguity. These comparative results suggest that echolocation strategy in the cluttered environment is different between two FM bat species. [Work supported by JSPS and ONR.]

To investigate relationships between flight and echolocation behaviors in one CF‐FM (Rhinolophus ferrumequinum) and two FM (Pipistrellus abramus and Miniopterus fuliginosus) Japanese echolocating bats, relationships between wingbeat and pulse‐emission timings during landing flight were examined. Wingbeat timings were measured by a dual high speed video camera system (500 fps) and pulse‐emission timings were precisely recorded by a wireless telemetry microphone mounted on the bats’ head. The R. ferrumequinum and P. abramus emitted multiple pulses in a burst (pulse trains) per single wingbeat cycle, and pulse‐emission timings were perfectly synchronized with their wingbeat, indicating that pulse‐emission timings were affected by wingbeat. On the other hand, relationships between wingbeat and pulse‐emission timings in M. fuliginosus were different compared with two other bats. The M. fuliginosus never emitted pulse trains, but proportionally increased emission rate of single pulse after approach phase starte...

A new technique to destroy the gas‐filled capsule is proposed, making use of the collapsing bubble near the capsule in the ultrasound field. At the moment of collapses under the ultrasound irradiation, the bubble causes flow and acoustic wave radiation. These phenomena are expected to assist the destruction of the capsule. We observed the effect of the bubble on this destruction, using a high‐speed video camera which enables the real‐time imaging. In this experiment, we use gas‐filled capsule made of polyvinyl chloride. When no bubble was near the capsule at sound pressure of 60kPa, the capsule showed no vibration. However, in the presence of neighboring bubble, the capsule showed the destruction behavior of the deformation and the emission of internal gas. At higher sound pressure such as over 100kPa, the capsule showed above destruction behavior even if the bubble was not located near the capsule. In the presence of the bubble, however, the capsule was destructed in a shorter time. These experimental results give significant knowledge to a technique manipulating the gas‐filled capsule destruction in the drug delivery system.

It was generally considered that energy conversion efficiency of a thermoacoustic cooling system was improved by increasing proportion of a thermal boundary layer in the stack. Thinning down a channel radius of the stack is required to increase the thermal boundary layer per unit area. A ceramic stack is difficult to satisfy this requirement. To satisfy this requirement, we propose to use a lamination mesh which is formed by piled up a stainless mesh. Since the lamination mesh has complex channel, the effect of changing the mesh number on the cooling effect is obscure. The experiments were carried out by changing the mesh number and the insertion position of the stack using the straight acoustic tube to measure the cooling effect. From the experimental results, changing mesh number causes the distribution shift of the phase difference between pressure and particle velocity. The insertion position of the stack for which the maximum temperature decrease come close to center of the acoustic tube. This is corresponded to a result using the ceramic stack. It suggests that a same design method, which is used in case of applying the ceramic stack, can be adapted to the lamination mesh.

Thickness pure‐shear mode film bulk acoustic wave resonators (FBARs) made of (11‐20) textured ZnO films have been fabricated. We have also fabricated FBAR structure consisting of two layers of the (11‐20) textured ZnO film with opposite polarization directions. This FBAR structure operated in second overtone pure‐shear mode, and allowed shear‐mode FBARs at higher frequency. The effective electromechanical coupling coefficients keff2 of pure‐shear mode FBAR and second overtone pure‐shear mode FBAR in this study were found to be 3.3% and 0.8%, respectively. The temperature coefficient of frequency (TCF) of thickness extensional mode FBAR, pure‐shear mode FBAR, and second overtone pure‐shear mode FBAR were measured in the temperature range of 10‐60 °C. TCF values of ‐63.1 ppm/°C, ‐34.7 ppm/°C, and ‐35.6 ppm/°C were found for the thickness extensional mode FBAR, the pure‐shear mode FBAR, and the second overtone pure‐shear mode FBAR, respectively. These results demonstrated that pure‐shear mode ZnO FBARs have ...

Bats are supposed to have effective strategies for achieving a good balance between echolocation and flight behaviors while capturing small moving insects in the field. To reveal their strategies for catching insects, we successfully reconstructed 3‐D flight trajectories for the bat to forage in the field by a four‐microphone array system, and conducted both acoustical and behavioral analyses for capturing behavior. Data show that the flying bats changed their flight direction flexibly, and sometime repeated capturing insects every two to three seconds. During the search phase, the bat moved 0.5‐0.8 m during an interval between successive pulses (IPI) and then decreased that the moving distance during an IPI up to 0.1 m just before capturing a prey. Interestingly, we found that the bat tended to descend toward a prey from above when the approach phase started. This suggests that foraging bats may effectively utilize gravity for an easy acceleration toward the prey to concentrate on the complex echolocation for capturing moving insects. [Supported by a grant to RCAST at Doshisha Univ. from MEXT of Japan: Special Research Grants for Development of Characteristic Education from the Promotion and Mutual Aid Corporation for Private Schools Japan, Innovative Cluster Creation Project.]

The interactive force called the secondary Bjerknes force works among multiple bubbles under ultrasound irradiation, which results in the complicated behaviors of bubbles. In this study, we have experimentally examined the direction of the interactive force depending on the distance between two bubbles. When two bubbles vibrate individually, the direction of the interactive force depends on the phase difference between vibrations of these bubbles. In addition to this theory, considering the influence of the radiated acoustic wave from a bubble vibration on the other bubble vibration, Ida has pointed that this influence induces a change in the direction of the interactive force [M. Ida et al., Phys. Rev. E 67, 056617 (2003)]. In order to examine this theoretical prediction, the behaviors of both a free bubble and a bubble adhered to the polymer were observed under ultrasound irradiation, using a high‐speed video camera. From the results, we found the reversal of the direction of the interactive force due to the variation in the distance between two bubbles. These innovative experimental results give an interesting point of view to understand the dynamics of multiple bubbles.

The feasibility of implementation of a sunlight‐based loop‐tube‐type thermoacoustic cooling system is investigated. Sunlight is condensed using a 0.60 m diameter Fresnel lens and irradiated to the high‐temperature heat exchanger. Then, the temperature of heat exchanger is risen. This heat energy from condensed sunlight is applied to the driving hear energy of the loop‐tube‐type thermoacoustic cooling system. The total length of the loop tube is 3300 mm, and a gaseous mixture of He and Ar (50% / 50%) is used as the working fluid. A 50‐mm‐long ceramic honeycomb is used for the stack. The channel radius of the prime mover stack is 0.45 mm; that of the heat pump is 0.35 mm. The cooling point temperature falls from 29°C to ‐4.3°C before sunlight is irradiated to the high‐temperature heat exchanger. Consequently, a temperature drop of 33.3°C is achieved using sunlight. Result obtained in this experiment underscores the feasibility of implementation of a sunlight‐based loop‐tube‐type thermoacoustic cooling system.

The purpose of this study was to examine characteristics of vocalization emitted by an FM bat, Japanese pipistrelle bats (Pipistrellus abramus), during their group flight. We used a wireless microphone system, Telemike, to record vocalization of five bats while they were flying in a chamber with a companion (a paired flight). Echolocation pulses and returning echoes were measured by the Telemike (0.6g; including a battery) placed at the bats head. Simultaneously, a pair of high‐speed video cameras were used to reconstruct their flight trajectories. The Telemike recorded not only their own pulses and echoes but also those of the companion bat. Overlapping of their own echolocation signals with those of the companion bat were analyzed. For one out of two bats, overlapping was always much lower than chance level on average. On the other hand, overlapping was around chance level for the other one. Their strategy appeared that one bat reduced the overlapping while the other did not. Communication calls were also recorded between two individuals during flight, which were never recorded when the bats flew alone. [The research supported by a grant to RCAST at Doshisha Univ. from MEXT and by the Innovative Cluster Creation Project promoted by MEXT]

To realize the generation of self‐sustained sound in lower temperature heat source, a 5‐μm in thickness rubber membrane was applied in the loop‐tube thermoacoustic cooling system. It is known that the existence of dc flow acts as the negative effect for the loop‐tube. The membrane reduces a loss of thermal energy supplied to the prime mover by suppressing the dc flow. So it is considered that lower temperature difference between both the edges of the stack can be realized by using presented system. The locating position of the membrane was moved, and then the temperature differences of the stack were observed. The experiments were carried out on the condition that the thermal energy supplied to the prime mover was constant. It was found that the temperature difference is affected by the position of the membrane. When the membrane was set at the approximate antinode of pressure, the lowest temperature difference was realized. In this condition, the temperature difference with the membrane was 430 K, which was 160 K lower than without the membrane. These results suggest that a lower temperature heat source can be available by setting the membrane on the loop‐tube thermoacoustic cooling system.

For the medical use, it is important to understand the micro‐capsule behavior during collapsing under the ultrasonic sound field. In this report, the behavior of micro‐capsule collapse was observed using the high‐speed video camera system (HPV‐1, SHIMADZU: maximum recording rate; 1 000 000 frames/second). By using this system, the detail phenomena can be observed. The micro‐capsule leaked the internal gases through a small pin hole on the surface of the micro‐capsule while repeating asymmetrical vibration. The internal gases were emitted during the positive period of driving sound pressure and returned again in the micro‐capsule during the negative period. By repeating the outflow and inflow of internal gases, the stress was cumulated on the shell. Therefore, the small pin hole developed into the big one, then, the micro‐capsule emitted a large amount of internal gases and the capsule was collapsed. After the collapsing, only the shell was remained. From the results, it was found for the effect of t...

The mechanical action of a micro‐jet, which arises from the collapse of bubbles, has been widely used for ultrasonic cleaning and sonoporation in medical field. The generation mechanism of a micro‐jet induced by the ultrasound irradiation is focused on. In previous theoretical and experimental researches, the generation mechanism is well known when a single bubble is adhered to a rigid wall. However, its mechanism is not understood in detail when multiple bubbles exist on rigid wall. The optical observation of multi‐bubble collapse greatly contributes to the development of micro‐jet applications. It was observed that the collapses of two bubbles adhered to the quartz wall in an ultrasound field with high speed video camera (HPV‐1, SHIMADZU). Maximum recording rate of this high speed video camera is 1 000 000 frames/second. The emitted ultrasound frequency is 27 kHz. From the observation, one of two bubbles was deformed after these bubbles vibrate. The micro‐jet was generated to the opposite side aga...

A thermoacoustic cooling system to drive a looped‐tube with the fundamental resonance frequency by connecting a triggered tube is proposed. The heat pump is located in the triggered‐tube. The existence of dc flows, which is caused by harmonics in the looped tube, has been pointed out as negative effects. The presented thermoacoustic cooling system, however, connected the triggered‐tube is expected to suppress the harmonics and to improve cooling effect, so that the length of the triggered tube is designed to have the fundamental resonance frequency. It is well known that the phase relation between sound pressure and particle velocity is important, and approximately in‐phase relation is the best position for cooling effect. In the presented system, the sound energy is supplied from the looped tube. It is important to know the best connecting position where the phase relation is approximately in phase. The sound pressures were observed, then the phase relations were calculated by two‐sensor power method. By...

The purpose of the present study was to examine the daily consistency of constant frequency component (CF) of CF‐FM bats and to examine biosonar sound characteristics of leaf‐nosed bats (Hipposiderous terasensis) during flight by a telemetry microphone system (telemike) mounted on the bat’s head. Experiments were done within a steel‐walled chamber. When at rest, the fundamental frequency of the bat was about 35 kHz. The second harmonic (70 kHz) was the most intense. The second harmonic of CF component (CF2) at rest and during flight varied significantly over several months. A systematical change in CF2 frequency during flight was observed through the telemike. Doppler‐shift compensation in CF2 frequency, amplitude compensation, and pulse emission rate just before landing were confirmed. We will discuss time‐sharing dual signal processing found during flight. [Research supported by Special Coordination Funds, and a grant to RCAST at Doshisha University from the Ministry of Education, Culture, Sports, Science and Technology of Japan.]

The purpose of the present study was to examine the daily consistency of the constant frequency component (CF) of CF‐FM bats and to test the significance of a telemetry microphone system (telemike) mounted on the bat’s head. We examined sonar sound characteristics of leaf‐nosed bats (Hipposiderous terasensis) when bats were at rest and during flight. Experiments were done within a steel‐walled chamber. Their emitted pulses were simultaneously recorded by a fixed microphone at the wall and the telemike. The second harmonic of the CF component (CF2) at rest and during flight varied significantly over several months. When at rest, the fundamental frequency of the bat was about 35 kHz. The second harmonic was the most intense. There was little difference between data taken from two different microphones when at rest. However, during flight we found significant differences between data obtained by the microphone at the wall and the telemike. We could see a systematic change in CF2 frequency during flight through the telemike. Our findings may suggest that the bats compensated for the frequency of the CF component of their pulses by detecting Doppler‐shifted CF of returning echoes from the target. We will discuss the individuality and consistency of the CF component during flight and at rest. [The present research was supported by Special Research Grants for the Development of Characteristic Education from the Promotion and Mutual Aid Corporation for Private Schools Japan, a grant to RCAST at Doshisha University from the Ministry of Education, Japan and Doshisha University’s Research Promotion Fund.]

The effects of the existence of micro bubbles in water for the increasing of acoustic streaming velocity are experimentally discussed. Velocity of acoustic streaming is observed on the sound axis by LDV (laser Doppler velocimeter). Acoustic streaming is generated by continuous ultrasonic sound transmitted by some PZT transducers whose diameter is 15 mm and resonant frequencies are 2.98 or 3.46 MHz. Sound pressures of ultrasonic sound are set to 80, 160, and 240 kPa at the last peak position on the sound axis. Micro bubbles are generated by extracting water with a syringe mechanism, decreasing the pressure of water down to 6.4% below static pressure. Average radius of micro bubbles is approximately 220 μm. The experimental results clearly show the velocity of acoustic streaming increases; the velocity increases from 9 to 13.5 mm/s when the micro bubbles exist. The harmonics are observed when the micro bubbles are generated. The mechanism for the increase of acoustic streaming is discussed from the point of...

Applying ultrasound to hyperthermia treatment, the temperature rise caused by irradiation of focused ultrasound is discussed. A piezoelectric concave‐shaped transducer whose radius of aperture is 100 mm, radius of concativity is 25 mm, and resonant frequency is 1 MHz is used. Glycerin is introduced as the phantom because of its transparency. The heat‐sensitive tape which consists of thermometric ink covered with a Teflon thin film of 100 μm in thickness is used. The tape is spread out on the phantom with an observation area 50 mm long and 8 mm wide. The tape indicates the temperature as the color differences. The spatial distribution of the local heat generation, especially surrounding the focal point, is observed as a function of irradiation time. The experiments are carried out in the same kind of transmission conditions. The theoretical analyses for both the spatial thermal distribution and the time profile of the temperature rise are estimated by using the heat equation. The observed results show good...

A new method of measuring B/A using a parametric receiving array is presented. The coefficient of nonlinearity β is treated exactly and is divided into two physically different terms. The effective value of βe (= cos θ + B/2A) is defined as the function of the crossing angle θ of two waves. The angle‐dependent pattern of βe is applied to the measurements of B/A. The following two practical methods are presented: (1) using the non interacting angle θn [= cos−1(− B/2A)] and (2) using the front‐back ratio of βe. The measurements were carried out using the two above methods for a gaseous medium and using (2) for water. The array lengths of the probing wave used were 90 mm and 40 kHz for gas, and 40 mm and 5 MHz for water, respectively. The phase modulation of the probing wave was observed and the angle dependency of β was detected. It was found that the estimated values of B/A showed good agreement with theoretical values and with the observed results presented by the other researchers.

An analytical approach is presented to derive the intensity of a virtual source from the viewpoint of the distortion in the finite‐amplitude wave. The distortion in the arbitrary waveform over a small distance is discussed in connection with the local sound velocity which depends on the local particle velocity. From the variation in the particle velocity due to the waveform distortion, the intensity of the virtual source is derived. It is dearly shown that the virtual source can be derived using only distortion in the time domain. The present analytical approach will be useful in understanding phenomena of nonlinear acoustics.