Laser-induced thermoelastic effects can evoke tactile sensations

Mid-Air Tactile Sensations Evoked by Laser-Induced Plasma: A Neurophysiological Study

This study demonstrates the feasibility of a mid-air means of haptic stimulation at a long distance using the plasma effect induced by laser. We hypothesize that the stress wave generated by laser-induced plasma in the air can propagate through the air to reach the nearby human skin and evoke tactile sensation. To validate this hypothesis, we investigated somatosensory responses in the human brain to laser plasma stimuli by analyzing electroencephalography (EEG) in 14 participants. Three types of stimuli were provided to the index finger: a plasma stimulus induced from the laser, a mechanical stimulus transferred through Styrofoam stick, and a sham stimulus providing only the sound of the plasma and mechanical stimuli at the same time. The event-related desynchronization/synchronization (ERD/S) of sensorimotor rhythms (SMRs) in EEG was analyzed. Every participant verbally reported that they could feel a soft tap on the finger in response to the laser stimulus, but not to the sham stimulus. The spectrogram of EEG evoked by laser stimulation was similar to that evoked by mechanical stimulation; alpha ERD and beta ERS were present over the sensorimotor area in response to laser as well as mechanical stimuli. A decoding analysis revealed that classification error increased when discriminating ERD/S patterns between laser and mechanical stimuli, compared to the case of discriminating between laser and sham, or mechanical and sham stimuli. Our neurophysiological results confirm that tactile sensation can be evoked by the plasma effect induced by laser in the air, which may provide a mid-air haptic stimulation method.

Spatiotemporal Pinpoint Cooling Sensation Produced by Ultrasound-Driven Mist Vaporization on Skin

In this study, we achieved a noncontact tactile display that presents a pinpoint and instantaneous cooling sensation on the skin surface with no devices directly in contact with the user's body. We employed ultrasound phased arrays to generate a focused ultrasound, which locally and instantaneously expedites the vaporization of room-temperature water mist floating near the surface of the user's skin, offering a sudden pinpoint cooling sensation. In this article, we describe the physical configuration of the proposed method and show the measurement results, demonstrating how the user's skin surface was cooled. During the experiments, we discovered that a part of the skin exposed to a focused ultrasound within the floating mist was selectively cooled with negligible delay. Our prototype system offers a cooling spot of approximately 15 mm in diameter, which causes a temperature decrease of 4.6 K in 1 s and 3.3 K in the first 0.5 s on a hand situated 500 mm away from the device. Additionally, the ultrasound-driven cooling spot can be controlled on the skin surface, which is felt as a cool moving spot. Such a position-free cooling system with a high spatiotemporal resolution will open the door to unprecedented practical tactile applications.

Development of a Tactile Actuator with Non-Contact and Trans-Object Characteristics Using a Time-Varying Magnetic Field

A non-contact tactile stimulation system using a time-varying magnetic field was developed. The system comprises a control unit, power unit, output unit, and actuator. The control unit adjusts stimulation parameters, particularly the signal intensity and frequency. The power unit produces high voltages for generating the magnetic field, whereas the output unit transmits the energy generated according to the signal from the control unit to the actuator. A spiral coil actuator generates the magnetic field. To validate the effectiveness of the system, preliminary experiments on 10 male adults without neurological disorders (23.2 ± 3.05 years) were conducted. Magnetic field stimuli were presented to the right palm of the subjects at three different frequencies (10, 30, and 50 Hz), and corresponding electroencephalogram (EEG) signals were measured simultaneously. Event-related potential (ERP) analysis showed that N100 and P300 components were identified in somatosensory areas. Subjective evaluations revealed that feelings such as “tingling,” “trembling,” “tapping,” and “percussing” were induced. Moreover, as the stimulus frequency changes, differences may occur in induced feeling. The system uses a time-varying magnetic field, which not only induces tactile stimulation without contact but also has trans-object characteristics that can present tactile sensations, even when there is an obstacle between an actuator and skin.

A Light-Driven Vibrotactile Actuator with a Polymer Bimorph Film for Localized Haptic Rendering

A vibrotactile actuator driven by light energy is developed to produce dynamic stimulations for haptic rendering on a thin-film structure. The actuator is constructed by adopting a thermal bimorph membrane structure of poly(3,4-ethylenedioxythiophene) doped with p-toluenesulfonate (PEDOT-Tos) coated onto a polyethylene terephthalate (PET) film. Upon irradiation of near-infrared (NIR) light, the light energy absorbed at the PEDOT-Tos layer is converted into thermoelastic bending deformation due to the mismatch in coefficient of thermal expansion between PEDOT-Tos and PET. Since the light-induced deformation is reversible, spatially localized, and rapidly controllable with designed light signals, the proposed actuator can produce vibrotactile stimulation over 10 dB at arbitrary areas in the human-sensitive frequency range from 125 to 300 Hz using a low input power of ∼2.6 mW mm^-2, as compared with a complex electrical circuit and high input power needed to achieve such actuation performance. Together with its simple structure based on light-driven actuation, the advent of this actuator could open up new ways to achieve substantial advances in rendering textures at a flexible touch interface.

A Survey of Mid-Air Ultrasound Haptics and Its Applications

Ultrasound haptics is a contactless haptic technology that enables novel mid-air interactions with rich multisensory feedback. This article surveys recent advances in ultrasound haptic technology. We discuss the fundamentals of this haptic technology, how a variety of perceptible sensations are rendered, and how it is currently being used to enable novel interaction techniques. We summarize its strengths, weaknesses, and potential applications across various domains. We conclude with our perspective on key directions for this promising haptic technology.

Dynamics of the perception and EEG signals triggered by tonic warm and cool stimulation

Thermosensation is crucial for humans to probe the environment and detect threats arising from noxious heat or cold. Over the last years, EEG frequency-tagging using long-lasting periodic radiant heat stimulation has been proposed as a means to study the cortical processes underlying tonic heat perception. This approach is based on the notion that periodic modulation of a sustained stimulus can elicit synchronized periodic activity in the neuronal populations responding to the stimulus, known as a steady-state response (SSR). In this paper, we extend this approach using a contact thermode to generate both heat- and cold-evoked SSRs. Furthermore, we characterize the temporal dynamics of the elicited responses, relate these dynamics to perception, and assess the effects of displacing the stimulated skin surface to gain insight on the heat- and cold-sensitive afferents conveying these responses. Two experiments were conducted in healthy volunteers. In both experiments, noxious heat and innocuous cool stimuli were applied during 75 seconds to the forearm using a Peltier-based contact thermode, with intensities varying sinusoidally at 0.2 Hz. Displacement of the thermal stimulation on the skin surface was achieved by independently controlling the Peltier elements of the thermal probe. Continuous intensity ratings to sustained heat and cold stimulation were obtained in the first experiment with 14 subjects, and the EEG was recorded in the second experiment on 15 subjects. Both contact heat and cool stimulation elicited periodic EEG responses and percepts. Compared to heat stimulation, the responses to cool stimulation had a lower magnitude and shorter latency. All responses tended to habituate along time, and this response attenuation was most pronounced for cool compared to warm stimulation, and for stimulation delivered using a fixed surface compared to a variable surface.

Laser-induced elastic wave classification: thermoelastic versus ablative regimes for all-optical elastography applications

SIGNIFICANCE

Shear wave optical coherence elastography is an emerging technique for characterizing tissue biomechanics that relies on the generation of elastic waves to obtain the mechanical contrast. Various techniques, such as contact, acoustic, and pneumatic methods, have been used to induce elastic waves. However, the lack of higher-frequency components within the elastic wave restricts their use in thin samples. The methods also require moving parts and/or tubing, which therefore limits the extent to which they can be miniaturized.

AIM

To overcome these limitations, we propose an all-optical approach using photothermal excitation. Depending on the absorption coefficient of the sample and the laser pulse energy, elastic waves are generated either through a thermoelastic or an ablative process. Our study aimed to experimentally determine the boundary between the thermoelastic and the ablative regimes for safe all-optical elastography applications.

APPROACH

Tissue-mimicking graphite-doped phantoms and chicken liver samples were used to investigate the boundary between thermoelastic and ablative regimes. A pulsed laser at 532 nm was used to induce elastic waves in the samples. Laser-induced elastic waves were detected using a line field low coherence holography instrument. The shape of the elastic wave amplitude was analyzed and used to determine the transition point between thermoelastic and ablative regimes.

RESULTS

The transition from the thermoelastic to the ablative regime is accompanied by the nonlinear increase in surface wave amplitude as well as the transformation of the wave shape. Correlation between the absorption coefficient and the transition point energy was experimentally determined using graphite-doped phantoms and applied to biological samples ex vivo.

CONCLUSIONS

Our study described a methodology for determining the boundary region between thermoelastic and ablative regimes of elastic wave generation. These can be used for the development of a safe method for completely noncontact, all-optical microscale assessment of tissue biomechanics using laser-induced elastic waves.

A STUDY ON COGNITIVE RESPONSE TENDENCY AND DAMAGE THRESHOLD OF ABSORBING MEDIUM BY LASER-INDUCED INDIRECT STIMULATION

Laser-based research can be used in biology, medicine, engineering and many other industries. The use of pulsed laser can induce thermoelastic effect in a short time and give mechanical stimulation to the human body. When the elastic medium is attached to the human body and the laser is irradiated, the mechanical stimulus induced in the elastic medium can be transferred to the human body, which may cause tactile sensation. In this study, we investigated the effects of laser-induced indirect stimulation on cognitive response and damage to absorbing medium. Through the human body experiment, we studied the laser parameter condition that most subjects feel touch. In addition, thermal analysis simulations were performed to predict the condition of the laser pulse energy, the laser frequency and the temperature at the damage threshold of the absorption medium. The results of this study are expected to be useful for conducting non-contact tactile sensation using laser, and this technique can be widely used in laser biomedical stimulation, haptic technology, and other biological and medical fields.

INTERACTION EFFECT BETWEEN BEAM DIAMETER AND ENERGY DENSITY IN LASER-INDUCED TACTILE PERCEPTION

This study aims to investigate the interaction effect between the beam diameter and energy density, which are perceived as laser-induced tactile perception by humans, by diversely varying the laser parameters, beam diameter, and energy. Eight healthy male college students of 23.5[Formula: see text][Formula: see text][Formula: see text]1.7 years participated in the study. The range of the beam diameter of the displayed laser stimulation was between 0.03[Formula: see text]mm and 8[Formula: see text]mm, and a total of 21 sizes were displayed. The laser energy was sequentially displayed from the minimum energy that can be displayed by one beam diameter to the maximum energy range that does not exceed the maximum permissible exposure (MPE) level since the energy varies according to the beam diameter. The laser energy was controlled by an optical density ([Formula: see text]) filter and was measured by an optical power meter (energy meter). Furthermore, the beam diameter was adjusted by moving the lens, which was confirmed with the beam profiler. The experimental test consists of the control phase (19[Formula: see text]s), stimulus phase (7[Formula: see text]s), and response phase (4[Formula: see text]s); the total duration of the test was 30[Formula: see text]s. The stimulus phase is the period in which stimulation was displayed on the skin through laser irradiation, and the stimulation was displayed by changing the beam diameter and the energy from the laser. The total number of beam diameter and energy pairs displayed to the subjects was 113 and 5 trials of irradiation were conducted for each pair. Stimulation perception response was recorded by pressing the response buttons during the response phase, and the responses were predefined as “no feeling,” “tactile sensation”, and “pain.” Through the extracted response data from the response phase, the beam diameter and energy density pair in which more than 50% of the subjects responded as having perceived tactile sensation were selected from the possible laser energy that could be displayed from one beam diameter. The simulation results showed that increasing the beam diameter increased the penetration depth, indicating an effective energy transfer to the skin. Therefore, increasing the beam diameter results in increased scattering, and hence increased penetration depth, and ultimately a more effective energy transfer. Therefore, increased beam diameter results in higher energy transfer efficiency, indicating that the required energy density by more than 50% of the subjects to perceive tactile sensation decreased.

CHANGE OF INDUCED STRESS WAVE ON COLLAGEN TISSUE FOR BIOSTIMULATION BY FREQUENCY-DOUBLED Nd:YAG LASER

In this research, thermoelastic effect was investigated for biostimulation without damage on the biological medium using laser. Thermoelastic effect was generated and mechanical stress was induced by laser irradiation on the collagen, the main protein in the human body, under various conditions with short pulsed laser. The threshold laser energy to induce stress wave in each medium thickness was examined with a piezo sensor. Based on the test, the stimulation strength can be controlled through the adjustment of medium thickness, laser energy and beam diameter. The result implies that precise stimulation with various strengths of stress waves can be generated at the target depth without direct contact with the biological medium. This research can be used valuably in various fields such as contactless biostimulation, low power laser treatment and laser haptic applications.

Laser parameters for efficient biomedical stimulation: A study to increase cognitive response rate

BACKGROUND:

The laser is able to irradiate the exact amount of stimulation to an area by a non contact method, and has the advantage of being able to stimulate the local target area.

OBJECTIVE:

This study examined an efficient method of laser tactile stimulation using laser parameter combinations.

METHODS:

The laser parameters that could cause an increase in the cognitive response rate of human subjects were examined without increasing the amount of total laser energy.

RESULTS:

As a result, the appropriate matching parameters such as duty ratio, pulse frequency, and exposure time of laser pulses showed a dominant influence in effectively increasing the tactile response rate of subjects with limited amount of total laser energy.

CONCLUSIONS:

This study can be applied to neurophysiology, cognitive research, and clinical laser application.

Mid-Air Tactile Stimulation Using Indirect Laser Radiation

In this paper, we demonstrate that a laser irradiated on a thin light-absorbing elastic medium attached on the skin can elicit a tactile sensation of mechanical tap. First, we present simulation results that show laser irradiation to the elastic medium creates inner elastic waves on the basis of thermoelastic effects and these elastic waves trigger the bending deformation of the medium, which then stimulates the skin. Second, we analyze the physical properties of the associated stimulus by measuring its force profile. Third, we identify the perceptual characteristics of the stimulus in comparison to those of mechanical and electrical stimuli by means of a perceptual experiment employing dissimilarity rating. All the evidence indicates that indirect laser radiation provides a sensation of short mechanical tap. Furthermore, little individual difference was observed in the results of the perceptual experiment. To the best of our knowledge, this study is the first in reporting the feasibility of indirect laser radiation for mid-air tactile rendering.

Evaluation of the possibility and response characteristics of laser-induced tactile sensation

In this study, we examined the possibility and perceptual response characteristics of tactile sense induced by laser stimulation to the finger with different laser energy densities through human response experiments. 15 healthy adult males and 4 healthy adult females with an age of 22.6±2.2 years were tested. A frequency-doubled Q-switched laser was used with a wavelength of 532 nm and a 5 ns pulse width. The experimental trial spanned a total of 30 s and included a rest phase (19 s), a stimulation phase (7 s), and a response phase (4 s). During the rest phase, subjects kept their fingers comfortable. During the stimulation phase, one of three types of laser energy density (13.5, 16.6, 19.8 mJ/cm(2)) or a sham stimulation was used to irradiate the distal phalanx on the right index finger. During the response phase, the cognitive response to the laser stimulation was recorded by a PC by pressing the response button. The confusion matrix was configured to evaluate the possibility that the tactile sense was caused by the laser. In addition, changes in the response characteristics were observed according to three types of laser energy densities. From the analysis of the confusion matrix, the accuracy and sensitivity were not high. In contrast, precision and specificity were found to be high. Furthermore, there was a strong positive correlation between the laser irradiation and tactile perception, indicating that tactile sense can be induced using a laser in a mid-air manner. In addition, it was found that as the laser energy density increased, the tactile perception possibility also increased.