Re: squeezing a field

On 25/10/2024 7:37 pm, Liz Tuddenham wrote:

Bill Sloman <bill.sloman@ieee.org> wrote:
 

On 25/10/2024 7:56 am, Liz Tuddenham wrote:

john larkin <jl@glen--canyon.com> wrote:
>

On Thu, 24 Oct 2024 18:45:20 +0200, Lasse Langwadt <llc@fonz.dk>
wrote:

[...]

plugging numbers pulled out of thin air into LTSpice is better that
doing the actual measurement?

>

It is for people who don't actually work with real parts.

>
Actually, it is extremely useful for people who work with real parts and
who want to know exactly what is going on. You can see stuff that is
very hard to measure on real parts.
>

Peter Baxandall (of tone control and QUAD amplifier fame) claimed to use
analogue computing to work out his designs  i.e. He built prototypes and
measured them.

>
But he understood what he was measuring - a least most of the time.
His revolutionary ideas about capacitor microphones and the patent
application he made fell down when he found out about the Philips
capacitative pressure gauges which had been exploiting the same
principle for about a decade before.

 If anything, that enhances his reputation rather than diminishing it,  A
single inventor working on a project in his spare time compared with a
laboratory-full of specialists working full-time on commercial projects
(if I remember rightly) one of which was almost certainly partly
financed by the Ford Motor Company.

The Philip's capacitative pressure gauges were scientific instruments, not mass market products, and if I could find them as graduate student, somebody whose day job was at the Royal Radar Establishment in Malvern should have been able to do that too. My direct boss at George Kent in Luton - Colin Hunter - had done his electronic appenticeship at the RRE under Peter Baxandall. He wasn't any kind of single inventor working on stuff in his spare time, but rather a full time expert exploiting the resources his job gave him to follow his interests outside of his day job.

This played out in the pages of Wireless World, between the first and
second parts of a two part article.

 The articles were in WW Nov/Dec 1963.  At the end he refers to two Dutch
papers:
 Philips Technical Review Vol9 Nr12  1947/48  pp357-363
 Omroep-technische Mededelingen  Feb15 1961
 These are both describing to low-noise condenser microphones but he
points out that they don't have some of the desirable features of his
design.

Very likely. 1947/48 was pre-transistor. The planar process was invented around 1955, and Fairchild started selling cheap planar transistors around 1959. They revolutionised circuit design,and I latched onto that in 1965 as a graduate student in chemistry. By 1963 you could suddenly do a lot with planar transistors which hadn't been practical with earlier parts.

I don't think he mentioned the Philips pressure gauges,

  >but I've got a 1954 reference to them in my

1970 Ph.D. thesis

 That may have been the article on capacitive pressure gauges for car
engines in the Philips Technical Review.

It wasn't. The references in my Ph.D. thesis are to J.J.Opstelten and N. Warmholtz, App.Sci.Res.Hague B4 page 329 (1955)
and J.J.Opstelten, N. Warmholtz and J.J. Zaalberg van Zelst ibid B6 page 129 (1956).
There may have been work on a product for the car market, but they weren't cheap enough for that.

Their main problem was that
the temperatures and pressures they were trying to measure gave a short
diaphragm life if the diaphragm was thin enough to respond to the
required frequency range with sufficient sensitivity.

Etched silicon diaphragms with strain gauge sensors in the diaphragm was the mass market product, and they came a lot later.
--
Bill Sloman, Sydney