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2. Can you share any experiences of overcoming challenges that you have faced in your research?
I have made a breakthrough that could lead to photophones—devices without electrical connections that convert light energy directly into sound. Perhaps this discovery will help commercialize optical telephone networks. It could also allow robots to respond directly to light, again, without the need for wire connectors. This discovery is occasionally used to teach students about entrepreneurship.

Where did I come up with the idea for this light conversion? Not with the sunlight shining through my office window and not outside feeling the warmth of the sun, but I came up with the idea in a dimly lit karaoke bar. I was working on ceramic actuators—a kind of transducer that converts electrical energy to mechanical energy—at the Tokyo Institute of Technology when the trigger for “the light-controlled actuator” was initiated. In 1980, one of my friends, a precision-machine expert, and I were drinking together at a karaoke bar, where many Japanese people go, to enjoy drinks and our own singing. We called this activity our “after-5-o'clock meeting” in the pre-Twitter or Facebook period. At that time, my friend studied micro-mechanisms such as millimeter-sized walking robots. He explained that, as electrically controlled walking mechanisms become very small (on the order of a millimeter), they do not walk smoothly because the frictional force drops drastically, and the weight of the electric lead becomes more significant.

After a few drinks, it becomes easier to play “What if?” games. That is when he asked, “What if you, an expert on actuators, could produce a remote-controlled actuator? One that would bypass the electrical lead?” To many people, “remote control” equals controlled by radio waves, light waves, or sound. Light-controlled actuators require that light energy be transduced twice: First from light energy to electrical energy, and second from electrical energy to mechanical energy. These are “photovoltaic” and “piezoelectric” effects.

A solar cell is a well-known photovoltaic device, but it does not generate sufficient voltage to drive a piezoelectric device. So, my friend’s actuator needed another way to achieve a photovoltaic effect. Along with the drinking and singing, we enjoyed these intellectual challenges. I must have had a bit too much that night since I promised I would make such a machine for him. But I had no idea how to do it! While my work is applied research, I usually come home from scientific meetings about basic research with all kinds of ideas. At one of these meetings, about six months after my promise, a Russian physicist reported that a single crystal of lithium niobate produced a high electromotive force (10 kV/mm) under purple light. His talk got me excited. Could this material make the power supply for the piezoelectric actuator? Could it directly produce a mechanical force under purple light?

I returned to the lab and placed a small lithium niobate plate onto a plate of piezoelectric lead zirconate titanate. Then, I turned on the purple light and watched for the piezoelectric effect (mechanical deformation). But it was too slow, taking an hour for the voltage to get high enough to make a discernable shape change. Then, the idea hit me: what about making a single material that could be used for the sensor and the actuator? Could I place the photovoltaic and piezoelectric effects into a single asymmetric crystal? After lots of trial and error, I came up with a tungstate-doped material made of lead lanthanum zirconate titanate (PLZT) that responded well to purple light. It had a large piezoelectric effect and had properties that would make it relatively easy to fabricate.

To make a device out of this material, I pasted two PLZT plates back-to-back, but placed them in opposite polarization, and then connected the edges. I shined a purple light to one side, which generated a photovoltaic voltage of 7 kV across the length. This caused the PLZT plate on that side to expand by nearly 0.1% of its length, while the plate on the other (unlit) side contracted due to the piezoelectric effect through the photovoltage. The whole device bent away from the light. For this 20 mm long, 0.4 mm thick bi-plate, the displacement at the edge was 150 µm, and the response speed was 1 second. This fast and significant response was pretty exciting.

Remembering the promise to my friend, I fabricated a simple “light-driven micro walking machine,” with two bi-plate legs attached to a plastic board. When the light alternately irradiated each leg, the legs bent one at a time, and the machine moved like an inchworm. It moved without electric leads or circuits! That was in 1987, seven years after my promise.

I got busy with my “toy”, but not too busy to attend the “after-5-o’clock meetings” in Tokyo’s nightclub area. In 1989, at my favorite karaoke bar, I was talking about my device to another friend who worked for a telephone company. He wanted to know if the material could make a photo-acoustic device—perhaps as a solution to a major barrier in fiber-optic communication. The technology to transmit voice data—a phone call—at the speed of light through lasers and fiber optics had been advancing rapidly. But the end of the line—the ear speaker—limited the technology, since optical phone signals must be converted from light energy to mechanical movement via electrical energy.

I thought my material could convert light flashes directly into sound. I chopped two light beams to make a 180-degree phase difference and applied each beam to one side of the bi-plate. The resonance point, monitored by the tip displacement, was 75 Hz, just at the edge of the audible range for people! We’re now working to fabricate real photo-speakers (I call them “photophones”) and have ideas that may increase the vibration frequency several-fold to reproduce human speech correctly. Photophones could provide a breakthrough in optical communication.

Well, what is my message for you, dear reader? To find a noisy karaoke bar? Perhaps that is not necessary, but what is necessary is listening to others outside of your particular research area, for instance, basic researchers or people with specific, applied objectives.

3. What do you believe the hot topics in the field of piezoelectric actuator research will be over the next few years, and why do you think these subjects will become important?
Innovative materials and drive/control developments have not been seen in the past two decades, except for performance improvements. Thus, new application developments should be focused, aiming at million-selling products. The author comments on the paradigm shift from “econo-engineering” to politico-engineering in science and technology development. In the 1980s, i.e., the “Bubble Economy” period, cost/performance technologies were sought that fitted the governmental slogan, “lighter, thinner, shorter, smaller (軽薄短小)”, while, in the 2000s, sustainability and crisis technologies should be mainstream, alongside the slogan “cooperation, protection, reduction, continuation (協守減維)”. These trendy technologies are primarily initiated by political regulations.
The crises include the following:
(1) Natural disasters;
(2) Infectious/contagious diseases;
(3) Enormous accidents;
(4) Intentional terrorist/criminal incident;
(5) External and civil war/territorial invasion.

To the contrary, sustainability technologies were introduced in the following piezoelectric device areas, including medical applications:
(a) Non-toxic Pb-free piezo-materials;
(b) Ultrasonic disposal technology for hazardous materials;
(c) Reduction of contamination gas with piezo-devices;
(d) New energy source creation (i.e., piezoelectric energy harvesting);
(e) Energy-efficient piezoelectric device development;
(f) Medical acoustic probes and micro-disruptors for medical catheters.

I propose a new four-Chinese-character slogan for the era of “politico-engineering”, “協, 守, 減, 維 (cooperation, protection, reduction, and continuation)”. The standardization of internet systems and computer cables requires global “cooperation” and coordination to accelerate mutual communication. The “Paris Agreement” in 2016 is an international agreement on “Greenhouse Gas” regulation linked to the United Nations Framework Convention on Climate Change. “Protection” is mandatory for the territory and environment from the enemy or natural disaster and from pandemic disease spread. A “reduction” in toxic materials and energy consumption should be urged, then society’s “continuation” (or a sustainable society), in parallel with medical technology advancements, will be the ultimate desire. This development strategy is the key for the new generation of researchers.

4. As the conference chair, could you briefly describe what kind of meeting you are looking forward to in particular?
Let me explain the so-called “Google Syndrome”. The search engine Google went online in 1998. After this event, research approaches changed significantly. When I encourage them to research something new, most of my current Ph.D. graduate students take the following research steps: (1) search the recent research papers on the indicated topics on the Google search engine, (2) summarize the results, picking up the unstudied parts by believing that the already-published results are correct, and (3) set a research plan for himself/herself. Most recently, even the research plan/proposal is generated with ChatGPT. This “addiction” was named “Google Syndrome”. The important point is the fact that no completely new idea comes out because Google and ChatGPT can only generate the combined idea of already-published materials. I encourage young researchers to find a very innovative and unique idea, which the present Google does not include. Therefore, I am expecting this sort of unique paper, which does not include other groups’ paper citations.

5. With numerous conferences being organized each year, do you have any suggestions that might make our conference more meaningful for scholars and students?
Most of the current MDPI Actuators papers focus on performance improvement. In the drive/control area, for example, complicated mixed systems (including neuro networks) are reported, which I would say is “Spaghetti Syndrome”. I sincerely hope to collect very innovative and unique ideas for our conference, which present Google searches may not include.

6. Could you share some of your past conference experiences? Did these conferences assist you in promoting your research results, expanding your network, finding potential collaborators, advancing your career, etc.?
The International Conferences on Actuators and Transducers organized by the Penn State International Center for Actuators and Transducers were organized in that direction: (1) Only the eminent worldwide researchers were invited (a small number attendance less than 50), with both academic and industry researchers in a 50-50 ratio. (2) The invitees were selected from various fields, including physics, chemistry, ceramics, electrical, mechanical, computer engineering, etc. (3) By putting a long discussion time between each presentation, we encouraged researchers to find their future collaborators. (4) Students could demonstrate their capabilities to companies that they could join in the future.

7. What are your thoughts on the current trends and development of open access publishing?
Open access publication is good for disclosing a scientific idea quickly. Personally, considering intellectual property, I usually finish the patent and other IP applications first, followed by the report to the Research Contract Agencies. The publication, especially for open access, will be delayed typically by 4–5 years, after finishing all processes for commercialization.