Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: like butta Date: Sun, 26 Jan 2025 23:54:45 -0000 (UTC) Organization: A noiseless patient Spider Lines: 78 Message-ID: References: <6791c34a$0$2757$882e4bbb@reader.netnews.com> <67932535$1$14$882e4bbb@reader.netnews.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Mon, 27 Jan 2025 00:54:45 +0100 (CET) Injection-Info: dont-email.me; posting-host="009e42b1ea25dd91ec4174700914c699"; logging-data="286212"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX188AaAPBXQz7fx0Ri//3JkD" User-Agent: NewsTap/5.5 (iPhone/iPod Touch) Cancel-Lock: sha1:IJsYzy9uilYTQEv16G1zM6jMWAY= sha1:Oqed0BV4Na5xDPZG0p0yxt/BSJg= Bytes: 4021 bitrex wrote: > On 1/23/2025 8:41 AM, Phil Hobbs wrote: >> bitrex wrote: >>> On 1/22/2025 10:43 PM, Phil Hobbs wrote: >>>> Simon and I are working on a TDR based soil moisture sensor for >>>> agriculture. Like many such things, it uses two parallel tines made of >>>> 18/8 stainless, that form a balanced transmission line. >>>> >>>> Ours has a slide hammer for pounding it into really difficult soil, e.g. >>>> hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 >>>> gees, and over its lifetime it might see around 1E6 blows. Challenging. >>>> >>>> Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. >>>> We’re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm >>>> coax. The resulting 50-Ω differential mode goes into a machined tapered >>>> structure that maintains 50 ohms while spreading out the mode to match the >>>> 25-mm tine spacing. >>>> >>>> For survivability, the whole thing is being potted in very hard epoxy with >>>> a dielectric constant of 3.5ish. This means that it’s hard to iterate—we >>>> get one try per apparatus. >>>> >>>> Sooooo, I tried making a soft material with that epsilon, which turns out >>>> to be nontrivial. My initial thought was to use alumina lapping powder >>>> (9.3) for filler and vaseline (2.0) for the matrix, but it turned into >>>> clumps by the time it got to 3.0. >>>> >>>> Casting about for alternatives, I remembered the butter in the lab fridge, >>>> so I measured that: 3.8, better than good enough. >>>> >>>> We were able to verify the design without doing anything irrevocable, and >>>> there was some left over for the bagels. >>>> >>>> Fun. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>>> >>> >>> Cold you please test ninja turtle ooze and report back. It's some kind >>> of guar gum/vinyl acetate and borate gelatin: >>> >>> >>> >>> >>> >> >> Nah, Western religious art, particularly Italian Renaissance stuff, leaves >> me cold. Cute little cupids representing the glorious cherubim, Madonnas >> modeled after artists’ paramours, corrupt prelates and donors painted into >> biblical scenes, blech. >> >> Cheers >> >> Phil Hobbs >> >> >> > > Right well I don't know if pizza's dielectric properties have been > studied thoroughly but there's been a lot of work done on Jell-O, it > seems pretty customizable. There's always room for Jell-O > > > It’s been used for making edible lasers. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics